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Rogers, Melissa J. B.; Vogt, Gregory L.; Wargo, Michael J.Microgravity: A Teacher's Guide with Activities in Science,Mathematics, and Technology. Grades 5-12.National Aeronautics and Space Administration, Washington,DC.

EG-1997-008-110-HQ1997-08-00177p.

Web site: http://spacelink.nasa.gov.Guides Classroom - Teacher (052)MF01/PC08 Plus Postage.Elementary Secondary Education; Gravity (Physics);Mathematics; *Physical Sciences; *Science Activities;Science Education; *Space Sciences; Technology*Microgravity

This teacher's guide explains microgravity, providesinformation on the history of microgravity, the domains of microgravityresearch and introduces classroom activities. Among the contents are thefollowing: (1) "First, What Is Gravity?"; (2) "What Is Microgravity?"; (3)

"Creating Microgravity"; (4) "The Microgravity Environment of OrbitingSpacecraft"; (5) "Biotechnology"; (6) "Combustion Science"; (7) "FluidPhysics"; (8) "Fundamental Physics"; (9) "Materials Science"; (10)

"Microgravity Research and Exploration"; (11) "Microgravity Science SpaceFlight"; (12) "Future Directions"; (13) "Glossary"; (14) "Activities"; (15)

"NASA Resources for Educators"; and (16) "NASA Educational Materials." (YDS)

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Teachers Grades 5-12

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U S DEPARTMENT OF EDUCATIONOffice of Educational Research and Improvement

EDUCATIONAL RESOURCES INFORMATIONCENTER (ERIC)

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Points of view or opinions stated in thisdocument do not necessarily representofficial OERI position or policy

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MicrogravityA Teacher's Guide With Activitiesin Science, Mathematics, and Technology isavailable in electronic format through NASASpace linkone of the Agency's electronicresources specifically developed for use by theeducational community.

The system may be accessed at the followingaddress: http:/ / spacelink. nasa . g o v

3

MicrogravityA Teacher's Guide With Activities

in Science, Mathematics, and Technology

National Aeronautics and Space Administration

Office of Life and Microgravity Sciences and ApplicationsMicrogravity Research Division

Office of Human Resources and EducationEducation Division

This publication is in the Public Domain and is not protected by copyright.Permission is not required for duplication.

EG-1997-08-110-HQ

Acknowledgements This publication was developed for the NationalAeronautics and Space Administration with theassistance of the many educators of theAerospace Education Services Program,Oklahoma State University.

Writers:

Melissa J. B. Rogers, MSTAL-CUT CompanyNASA Lewis Research CenterCleveland, OH

Gregory L. Vogt, Ed.D.Teaching From Space ProgramNASA Johnson Space CenterHouston, TX

Michael J. Wargo, Sc.D.Microgravity Research DivisionNASA HeadquartersWashington, DC

Activity Contributors

Microgravity In The ClassroomAccelerometersAround The WorldInertial BalanceCandle DropCrystallization ModelGregory L. Vogt, Ed.D.Teaching From Space ProgramNASA Johnson Space Center

Gravity-Driven Fluid FlowCharles E. Bugg, Ph.D.Professor EmeritusUniversity of Alabama, BirminghamandChairman and Chief Executive OfficerBiocrypt Pharmaceuticals, Inc.

Craig D. Smith, Ph.D.ManagerX-Ray Crystallography LaboratoryCenter for MacromolecularCrystallographyUniversity of Alabama at Birmingham

Surface Tension-Driven FlowsGregory L. Vogt, Ed.D.Teaching From Space ProgramNASA Johnson Space Center

R. Glynn Holt, Ph.D.Research Assistant ProfessorBoston UniversityAeronautics and Mechanical EngineeringDepartment

Temperature Effects on SurfaceTensionMichael F. SchatzSchool of PhysicsGeorgia Institute of Technology

Stephen J. Van HookCenter for Nonlinear DynamicsDepartment of PhysicsUniversity of Texas at Austin

Candle FlamesHoward D. Ross, Ph.D.ChiefMicrogravity Combustion BranchNASA Lewis Research Center

Crystal Growth and Buoyancy-DrivenConvection CurrentsRoger L. Kroes, Ph.D.ResearcherMicrogravity Science DivisionNASA Marshall Space Flight Center

Donald A. Reiss, Ph.D.ResearcherMicrogravity Science DivisionNASA Marshall Space Flight Center

Rapid CrystallizationMicroscopic Observation of CrystalsDavid Mathiesen, Ph.D.Assistant ProfessorCase Western Reserve UniversityandAlternate Payload SpecialistUSML-2 Mission

Zeolite Crystal GrowthAlbert Sacco, Jr.HeadDepartment of Chemical EngineeringWorchester Polytechnical InstituteandPayload SpecialistUSML-2 Mission

How To Use This Guide

As opportunities for extended space flighthave become available, microgravityresearch in physical and biological sci-ences has grown in importance. Using theSpace Shuttle and soomthe InternationalSpace Station, scientists are able to addlong term control of gravity's effects to theshort list of variables they are to manipu-late in their experiments. Although mostpeople are aware of the floating effects ofastronauts and things in orbiting space-craft, few understand what causes micro-gravity much less how it can be utilized forresearch.

The purpose of this curriculum supplementguide is to define and explain microgravityand show how microgravity can help uslearn about the phenomena of our world.The front section of the guide is designedto provide teachers of science, mathemat-ics, and technology at many levels with afoundation in microgravity science andapplications. It begins with backgroundinformation for the teacher on whatmicrogravity is and how it is created. This isfollowed with information on the domains ofmicrogravity science research; biotechnolo-gy, combustion science, fluid physics, fun-damental physics, materials science, andmicrogravity research geared toward explo-ration. The background section concludeswith a history of microgravity research andthe expectations microgravity scientistshave for research on the InternationalSpace Station.

Following the background information areclassroom activities that enable students toexperiment with the forces and processesmicrogravity scientists are investigatingtoday. The activities employ simple andinexpensive materials and apparatus thatare widely available in schools. The activi-ties emphasize hands-on involvement, pre-diction, data collection and interpretation,teamwork, and problem solving. Activityfeatures include objectives, materials andtools lists, management suggestions,assessment ideas, extensions, instructionsand illustrations, student work sheets, andstudent readers. Because many of theactivities and demonstrations apply to morethan one subject area, a matrix chartrelates activities to national standards inscience and mathematics and to scienceprocess skills.

Finally, the guide concludes with a sug-gested reading list, NASA educationalresources including electronic resources,and an evaluation questionnaire. We wouldappreciate your assistance in improvingthis guide in future editions by completingthe questionnaire and making suggestionsfor changes and additions. The evaluationcan be sent to us by mail or electronicallysubmitted through the Internet site listed onthe form.

7Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,

EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 ()

Note on Measurement andFormat

In developing this guide, metric units ofmeasurement were employed. In a fewexceptions, notably within the "Materialsand Tools" lists, British units have been list-ed. In the United States, metric-sized partssuch as screws and wood stock are not asaccessible as their British equivalents.Therefore, British units have been used tofacilitate obtaining required materials.

The main text of this guide uses large printlocated in a wide column. Subjects relatingto mathematics, physical science, and tech-nology are highlighted in bold. Definitions,questions for discussion, and examples areprovided in smaller print in the narrow col-umn of each page. Each area highlighted inthe text has a corresponding section in thenarrow column. This corresponding sectionfirst lists applicable Mathematics andScience Content Standards, indicated bygrade level: A Grades 5-8, [:1 Grades 9-12.We have attempted to position the appro-priate discussion as close as possible tothe relevant highlighted text. A key word orphrase in each margin discussion is alsohighlighted for ease in identifying relatedtext.

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (a, ), 9-12 (a)

Table of Contents

Introduction 1

First, What is Gravity9 1

What is Microgravity? 3

Creating Microgravity 7

Drop Facilities 8

Aircraft 9

Rockets 10

Orbiting Spacecraft 10

Microgravity Science Primer 13

The Microgravity Environment of Orbiting Spacecraft 15

Biotechnology 16

Protein Crystal Growth 18

Mammalian Cell and Tissue Culture 19

Fundamental Biotechnology 21

Combustion Science 21

Premixed Gas Flames 25Gaseous Diffusion Flames 25Liquid Fuel Droplets and Sprays 25Fuel Particles and Dust Clouds 26Flame Spread Along Surfaces 26

Smoldering Combustion 27

Combustion Synthesis 27

Fluid Physics 28

Complex Fluids 29

Multiphase Flow and Heat Transfer 31

Interfacial Phenomena 32Dynamics and Stability 33

Fundamental Physics 34

Materials Science 37

Electronic Materials 39

Glasses and Ceramics 40

Metals and Alloys 41

Polymers 43

Microgravity Research and Exploration 44

9

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HC), Education Standards Grades 5-8 (A), 9-12 (C) III

Microgravity Science Space Flights 46International Microgravity Laboratory-1, January 1992 49United States Microgravity Laboratory-1, June 1992 49Spacelab-J, September 1992 51United States Microgravity Payload-1, October 1992 52United States Microgravity Payload-2, March 1994 53International Microgravity Laboratory-2, July 1994 55United States Microgravity Laboratory-2, October 1995 57United States Microgravity Payload-3, February 1996 59Life and Microgravity Spacelab, June 1996 62Shuttle/Mir Science Program, March 1995 to May 1998 64

Future Directions68

Glossary71

Activities75

NASA Resources for Educators 167

NASA Educational Materials168

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 po

IntroductionSpace flight is important for many reasons. Spaceflight carries scientific instruments and humanresearchers high above the ground, permitting usto see Earth as a planet and to study the complexinteractions of atmosphere, oceans, land, energy,and living things. Space flight lifts scientific instru-ments above the filtering effects of the atmosphere,making the entire electromagnetic spectrumavailable and allowing us to see more clearly thedistant planets, stars, and galaxies. Space flightpermits us to travel directly to other worlds to seethem close up and sample their compositions.Finally, space flight allows scientists to investigatethe fundamental states of mattersolids, liquids,and gasesand the forces that affect them in amicrogravity environment.

The study of the states of matter and their inter-actions in microgravity is an exciting opportunityto expand the frontiers of science. Areas of inves-tigation include biotechnology, combustion sci-ence, fluid physics, fundamental physics, materi-als science, and ways in which these areas ofresearch can be used to advance efforts toexplore the Moon and Mars.

Microgravity is the subject of this teacher's guide.This publication identifies the underlying math-ematics, physics, and technology principles thatapply to microgravity. Supplementary informationis included in other NASA educational products.

First, What is Gravity?

Gravitational attraction is a fundamental propertyof matter that exists throughout the known uni-verse. Physicists identify gravity as one of the fourtypes of forces in the universe. The others are thestrong and weak nuclear forces and the electro-magnetic force.

11

Mathematics Standards

1:1 Mathematical ConnectionsCI Mathematics as Communication

A Number and Number RelationshipsA Number Systems and Number Theory

Science Standards

A Physical ScienceA 01 Unifying Concepts and Processes

The electromagnetic spectrum is generally separat-ed into different radiation categories defined byfrequency (units of Hertz) or wavelength (units ofmeters). Wavelength is commonly represented by thesymbol X.

Example:

NameApproximateWavelength (m)

Xrays = 10-15 to 10-9

Ultraviolet = 10-8 to 10-7

Visible Light = 10-7 to 10-6

Infrared = 10-6 to 10-3

Microwave = 10-3 to 10-1

Television = 10-1 to 1

AM Radio = 102 to 103


AlgebraConceptual Underpinnings of CalculusGeometryGeometry from an Algebraic PerspectiveMathematical ConnectionsMathematics as ReasoningTrigonometry

Science Standards

A 0 Physical ScienceA 0 Unifying Concepts and Processes

An impressed force is an action exerted upon a body.in order to change its state, either of rest, or of uni-

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (la)

form motion in a straight line. A body force acts onthe entire mass as a result of an external effect notdue to direct contact; gravity is a body force. A sur-face force is a contact force that acts across an inter-nal or external surface of a body.


A D

A

A

A 13

AlgebraConceptual Underpinnings of CalculusGeometryGeometry from an Algebraic PerspectiveMathematical ConnectionsMathematics as ReasoningTrigonometry

Science Standards

A U Physical ScienceA LI Unifying Concepts and Processes

Velocity is the rate at which the position of an objectchanges with time; it is a vector quantity. Speed isthe magnitude of velocity.


A U Mathematical ConnectionsA 0 Mathematics as Reasoning

Science Standards

A U History and Nature of ScienceA Li Science as InquiryA 0 Unifying Concepts and Processes

Newton's discovery of the universal nature of theforce of gravity was remarkable. To take the famil-iar force that makes an apple fall to Earth and be ableto recognize it as the same force that keeps the plan-ets on their quiet and predictable paths represents oneof the major achievements of human intellectualendeavor. This ability to see beyond the obvious andfamiliar is the mark of a true visionary. Sir IssacNewton's pioneering work epitomizes this quality.


A UA

A 0A

A

AlgebraComputation and EstimationFunctionsMathematics as CommunicationNumber and Number RelationshipsPatterns and Functions

Science Standards

A 0 Unifying Concepts and Processes

2

More than 300 years ago the great English scien-tist Sir Isaac Newton published the importantgeneralization that mathematically describes thisuniversal force of gravity. Newton was the first torealize that gravity extends well beyond thedomain of Earth. The basis of this realizationstems from the first of three laws he formulated todescribe the motion of objects. Part of Newton'sfirst law, the law of inertia, states that objects inmotion travel in a straight line at a constantvelocity unless acted upon by a net force.According to this law, the planets in space shouldtravel in straight lines. However, as early as thetime of Aristotle, scholars knew that the planetstravelled on curved paths. Newton reasoned thatthe closed orbits of the planets are the result of anet force acting upon each of them. That force, heconcluded, is the same force that causes anapple to fall to the groundgravity.

Newton's experimental research into the force ofgravity resulted in his elegant mathematical state-ment that is known today as the Law of UniversalGravitation. According to Newton, every mass inthe universe attracts every other mass. The attrac-tive force between any two objects is directlyproportional to the product of the two massesbeing considered and inversely proportional to thesquare of the distance separating them. If we letF represent this force, r represent the distancebetween the centers of the masses, and m1 andm2 represent the magnitudes of the masses, therelationship stated can be written symbolically as:

F oc m' m2r2

From this relationship, we can see that thegreater the masses of the attracting objects, thegreater the force of attraction between them. Wecan also see that the farther apart the objects arefrom each other, the less the attraction. If the dis-tance between the objects doubles, the attractionbetween them diminishes by a factor of four, andif the distance triples, the attraction is only one-ninth as much.

12Microgravity A Teacher's Guide wiih Activities in Science, Mathematics, and Technology,

EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (U)

The eighteenth-century English physicist HenryCavendish later quantified Newton's Law ofUniversal Gravitation. He actually measured thegravitational force between two one kilogrammasses separated by a distance of one meter.This attraction was an extremely weak force, butits determination permitted the proportional rela-tionship of Newton's law to be converted into anequality. This measurement yielded the universalgravitational constant, G. Cavendish determinedthat the value of G is 6.67 x 10-11 N m2/kg2. WithG added to make the equation, the Law ofUniversal Gravitation becomes:

1131 1132F = G r2

What is Microgravity?

The presence of Earth creates a gravitational fieldthat acts to attract objects with a force inverselyproportional to the square of the distancebetween the center of the object and the center ofEarth. When we measure the acceleration of anobject acted upon only by Earth's gravity at theEarth's surface, we commonly refer to it as one gor one Earth gravity. This acceleration is approxi-mately 9.8 meters per second squared (m/s2). Themass of an object describes how much the objectaccelerates under a given force. The weight of anobject is the gravitational force exerted on it byEarth. In British units (commonly used in theUnited States), force is given in units of pounds.The British unit of mass corresponding to onepound force is the slug.

While the mass of an object is constant and theweight of an object is constant (ignoring differ-ences in g at different locations on the Earth'ssurface), the environment of an object may bechanged in such a way that its apparent weightchanges. Imagine standing on a scale in a sta-tionary elevator car. Any vertical accelerations of

110the elevator are considered to be positive

1111 in2F cc r2

F = G 1112

r2

11111112u r2

F = G In2r2

indicates proportionality

indicates equality

is an expression

is an equation


A CI AlgebraA CI Mathematical ConnectionsA 0 Mathematics as CommunicationA Measurement

Science Standards

A CI Science and TechnologyA ID Science as InquiryA 0 Unifying Concepts and Processes

The internationally recognized Systeme International(SI) is a system of measurement units. The SI unitsfor length (meter) and mass (kg) are taken from themetric system. Many dictionaries and mathematicsand science textbooks provide conversion tablesbetween the metric system and other systems ofmeasurement. Units conversion is very important inall areas of life, for example in currency exchange,airplane navigation, and scientific research.

Units Conversion Examples1 kg -=- 2.2 lb 1 in = 2.54 cm1 liter 1 qt 1 yd ---== 0.9 m

Questions for DiscussionWhat common objects have a mass of about1 kg?What are the dimensions of this sheet of paper incm and inches?How many liters are there in a gallon?


A 0

A

1 3

Computation and EstimationMathematics as CommunicationNumber and Number RelationshipsNumber Systems and Number Theory

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)

3

Science Standards

A 0 Science as InquiryA LI Science in Personal and Social PerspectivesA LI Unifying Concepts and Processes

Scientific notation makes it easier to read, write, andmanipulate numbers with many digits. This is espe-cially useful for making quick estimates and for indi-cating the number of significant figures.

Examples:0.001 =

10 = 101

1000 = 103

Which is bigger, 6 x 10-3 or 8 x 10-4? 6 x 103 or8 x 104? How much bigger?


A L Mathematical ConnectionsA 0 Mathematics as Reasoning

Science Standards

A 0 Science and TechnologyA Li Science as InquiryA U Unifying Concepts and Processes

Questions for DiscussionHow does a scale work?What does a scale measure?How many different kinds of scales can you list?Do they need gravity for them to work?Would you get different results on the Moon orMars?How can you measure the mass of an object inmicrogravity?

4

upwards. Your weight, W, is determined by yourmass and the acceleration due to gravity at yourlocation.

If you begin a ride to the top floor of a building, anadditional force comes into play due to the accel-eration of the elevator. The force that the floorexerts on you is your apparent weight, P, themagnitude of which the scale will register. Thetotal force acting on you is F=W+P=mae, where ae

is the acceleration of you and the elevator andW=mg. Two example calculations of apparentweight are given in the margin of the next page.Note that if the elevator is not accelerating thenthe magnitudes W and P are equal but the direc-tion in which those forces act are opposite (W=-P).Remember that the sign (positive or negative)associated with a vector quantity, such as force, isan indication of the direction in which the vectoracts or points, with respect to a defined frame ofreference. For the reference frame defined above,your weight in the example in the margin is nega-tive because it is the result of an acceleration(gravity) directed downwards (towards Earth).

Imagine now riding in the elevator to the top floorof a very tall building. At the top, the cables sup-porting the car break, causing the car and you tofall towards the ground. In this example, we dis-count the effects of air friction and elevator safetymechanisms on the falling car. Your apparentweight P=m(ae-g).(60 kg)(-9.8 m/s2+9.8 m/s2)) =0 kg rn/s2; you are weightless. The elevator car,the scale, and you would all be acceleratingdownward at the same rate, which is due to gravi-ty alone. If you lifted your feet off the elevatorfloor, you would float inside the car. This is thesame experiment that Galileo is purported to haveperformed at Pisa, Italy, when he dropped a can-nonball and a musketball of different mass at thesame time from the same height. Both balls hitthe ground at the same time, just as the elevatorcar, the scale, and you would reach the ground atthe same time.

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (U)

Normalweight

Lighterthan normal

Heavierthan normal

Acceleration and weight

No apparentweight

7he person in the stationary elevator car experiences normal weight.In the car immediately to the right, apparent weight increases slight-ly because of the upward acceleration. Apparent weight decreasesslightly in the next car because of the downward acceleration. Noweight is measured in the last car on the right because of free fall.

For reasons that are discussed later, there aremany advantages to performing scientific experi-

O ments under conditions where the apparentweight of the experiment system is reduced. Thename given to such a research environment ismicrogravity. The prefix micro- (p) derives fromthe original Greek mikros, meaning small. By thisdefinition, a microgravity environment is one inwhich the apparent weight of a system issmall compared to its actual weight due togravity. As we describe how microgravity envi-ronments can be produced, bear in mind thatmany factors contribute to the experienced accel-erations and that the quality of the microgravityenvironment depends on the mechanism used tocreate it. In practice, the microgravity environ-ments used by scientific researchers range fromabout one percent of Earth's gravitational acceler-ation (aboard aircraft in parabolic flight) to betterthan one part in a million (for example, onboardEarth-orbiting research satellites).

Quantitative systems of measurement, such asthe metric system, commonly use micro- to meanone part in a million. Using that definition, the


AlgebraComputation and EstimationConceptual Underpinnings of CalculusMathematical ConnectionsMathematics as Problem SolvingMeasurement

Science Standards

A Physical ScienceA 0 Science and TechnologyA 0 Science as InquiryA 0 Unifying Concepts and Processes

F=W+P=maeRewriting yields P=macmg=m(ae- g).If your mass is 60 kg and the elevator is acceleratingupwards at 1 m/s2, your apparent weight isP=60 kg (+1 m/s2+9.8 m/s2))=+648 kg m/s2while your weight remainsW=mg=(60 kg)(-9.8 m/s2)=-588 kg m/s2.If the elevator accelerates downwards at 0.5 m/s2,your apparent weight isP=60 kg (-0.5 m/s2+9.8 m/s2))=+558 kg m/s2.


A D Mathematics as CommunicationA 0 Mathematics as Reasoning

Sdence Standards

A 0 Science as InquiryA D Science in Personal and Social PerspectivesA la Unifying Concepts and Process6

1 micro-g or 1 ps = 1 x 10-6 g

Questions for DiscussionWhat other common prefixes or abbreviations forpowers of ten do you know or can you find?In what everyday places do you see these used?Grocery stores, farms, laboratories, sporting facili-ties, pharmacies, machine shops.

Common prefixes for powers of ten:I 0-9 nano- n

10-3 milli- m

10-2 centi- c

103 kilo- k

106 mega- M

109 giga- G

1 5Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,

EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)5


AlgebraComputation and EstimationConceptual Underpinnings of CalculusDiscrete MathematicsMathematical ConnectionsMathematics as Problem SolvingMathematics as ReasoningNumber and Number Relationships

Science Standards

A UI Unifying Concepts and Processes

Calculate the times in these examples. Teachers canuse these examples at several different scholasticlevels.

Provide the equation as:

t = 2da

(a 2d)112

Provide the equation as d=(112) at2, and have thestudents re-order the equation.

Making measurements and calculating results involvethe concepts of accuracy and precision, significantfigures, and orders of magnitude. With theseconcepts in mind, are the drop times given in thetext "correct"?


AlgebraComputation and EstimationMathematical ConnectionsMathematics as Problem SolvingMathematics as ReasoningMeasurement

Science Standards

A 1:11

A

A 1:11

Science and TechnologyScience as InquiryUnifying Concepts andProcesses

Questions for DiscussionHow far away is the Moon?How far away is the center of Earth from the cen-ter of the Moon?Why did we ask the previous question?How far away is the surface of Earth from the sur-face of the Moon?What are the elevations of different features ofEarth and the Moon?How are elevations measured?

acceleration experienced by an object in a micro-gravity environment would be one-millionth (10-6)of that experienced at Earth's surface. The use ofthe term microgravity in this guide will correspondto the first definition. For illustrative purposes only,we provide the following simple example using thequantitative definition. This example attempts toprovide insight into what might be expected if thelocal acceleration environment would be reducedby six orders of magnitude from 1 g to 10-6 g.

If you dropped a rock from a roof that was fivemeters high, it would take just one second toreach the ground. In a reduced gravity environ-ment with one percent of Earth's gravitationalpull, the same drop would take 10 seconds. In amicrogravity environment equal to one-millionthof Earth's gravitational pull, the same drop wouldtake 1,000 seconds or about 17 minutes!

Researchers can create microgravity conditions intwo ways. Because gravitational pull diminisheswith distance, one way to create a microgravityenvironment (following the quantitative definition)is to travel away from Earth. To reach a pointwhere Earth's gravitational pull is reduced to one-millionth of that at the surface, you would have totravel into space a distance of 6.37 million kilo-meters from Earth (almost 17 times fartheraway than the Moon, 1400 times the highwaydistance between New York City and Los Angeles,or about 70 million football fields). This approachis impractical, except for automated spacecraft,because humans have yet to travel farther awayfrom Earth than the distance to the Moon.However, freefall can be used to create a micro-gravity environment consistent with our primarydefinition of microgravity. We discuss this in thenext section.

6

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (a)

Creating Microgravity

As illustrated in the elevator examples in the previ-ous section, the effects of gravity (apparent weight)can be removed quite easily by puffing anything (aperson, an object, an experiment) into a state offreefall. This possibility of using Earth's gravity toremove the effects of gravity within a system werenot always evident. Albert Einstein once said, "Iwas sitting in a chair in the patent office at Bernwhen all of a sudden a thought occurred to me: 'Ifa person falls freely, he will not feel his own weight.'I was startled. This simple thought made a deepimpression on me. It impelled me toward a theoryof gravitation." Working with this knowledge, scien-tists involved in early space flights rapidly conclud-ed that microgravity experiments could be per-formed by crew members while in orbit.

Gravity and Distance

The inverse square relationship between gravitational force anddistance can be used to determine the acceleration due to gravi-ty at any distance from the center of Earth, r.

F = Gmem/re2 force of gravity due to Earth on a mass,m, at Earth's surface

F = rng > g = Gme/re2F = Gmem/r2 force of gravity due to Earth on a mass,

m, at a distance, r, from Earth's centerF = ma > a = Gme/r2

gre2 = ar2a = gre2/r2 acceleration due to Earth's gravity at dis-

tance, r, from Earth's center

A typical altitude for a Space Shuttle Orbiter orbit is 296 km.The Earth's mean radius is 6.37x106 m. The acceleration due togravity at the Orbiter's altitude is

a = 9.8 m/s2 (6.37x106 rii)2 / (6.67x106 rn)2 = 8.9 m/s2

This is about 90% of the acceleration due to gravity at Earth'ssurface. Using the same equations, you can see that to achieve amicrogravity environment of 10-6 g by moving away from Earth,a research laboratory would have to be located 6.37x109 m fromthe center of Earth.


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 Go7


AlgebraComputation and EstimationConceptual Underpinnings of CalculusDiscrete MathematicsFunctionsMathematical ConnectionsMathematics as Problem SolvingMathematics as ReasoningPatterns and FunctionsStatistics

Science Standards

Physical ScienceScience and TechnologyScience as InquiryScience in Personal and Social PerspectivesUnifying Concepts and Processes

Questions for DiscussionWhat is the functional relationship between accel-eration, distance, and time?

Use the four sets of drop facility data pointsgiven in the text and the additional data set(0 meters, 0 seconds). What does the (0 meters,0 seconds) data set represent? Why is it a validdata set to use?

Suggested solution methods: Use different types ofgraph paper Use a computer curve fitting program.Do a dimensional analysis.

Knowing that g=9.8 m/s2, what equation can youwrite to incorporate acceleration, distance, andtime?

Assume it costs $5,000 per meter of height to builda drop tower.

8

How much does it cost to build a drop tower toallow drops of 1 second, 2 seconds, 4 seconds,10 seconds?

Why does it cost so much more for the longertimes?

What would be an inexpensive way to double low-gravity time in a drop tower?

Shoot the experiment package up from the bottom.

The use of orbiting spacecraft is one methodused by NASA to create microgravity conditions.In addition, four other methods of creating suchconditions are introduced here and we give exam-ples of situations where the student can experi-ence microgravity.

Drop FacilitiesResearchers use high-tech facilities based on theelevator analogy to create microgravity conditions.The NASA Lewis Research Center has two dropfacilities. One provides a 132 meter drop into ahole in the ground similar to a mine shaft. Thisdrop creates a -reduced gravity environment for5.2 seconds. A tower at Lewis allows for 2.2 sec-ond drops down a 24 meter structure. The NASAMarshall Space Flight Center has a different typeof reduced gravity facility. This 100 meter tubeallows for drops of 4.5 second duration. OtherNASA Field Centers and other countries haveadditional drop facilities of varying sizes to servedifferent purposes. The longest drop time current-ly available (about 10 seconds) is at a 490 meterdeep vertical mine shaft in Japan that has beenconverted to a drop facility. Sensations similar tothose resulting from a drop in these reduced grav-ity facilities can be experienced on freefall rides inamusement parks or when stepping off of divingplatforms.

Schematic of the NASA Lewis Research Center 2.2 SecondDrop Tower


EG-1997-08-110-HO, Education Standards Grades 5-8 (A), 9-12 (a)

AircraftAirplanes are used to achieve reduced gravityconditions for periods of about 15 seconds. Thisenvironment is created as the plane flies on aparabolic path. A typical flight lasts two to threehours allowing experiments and crew members totake advantage of about forty periods of micro-gravity. To accomplish this, the plane climbs rapid-ly at a 45 degree angle (this phase is called pullup), traces a parabola (pushover), and thendescends at a 45 degree angle (pull out). Duringthe pull up and pull out segments, crew and exper-iments experience accelerations of about 2 g.During the parabola, net accelerations drop aslow as 1.5x10-2 g for about 15 seconds. Due tothe experiences of many who have flown on para-bolic aircraft, the planes are often referred to as"Vomit Comets." Reduced gravity conditions cre-ated by the same type of parabolic motiondescribed above can be experienced on theseries of "floater" hills that are usually located atthe end of roller coaster rides and when drivingover swells in the road.

"!)1x10-3g (5-15 sec) 14--

Parabolic Flight Characteristics


0 Conceptual Underpinnings of Calculus01 Functions

A 01 Mathematical ConnectionsA Patterns and Functions

Science Standards

A 0 Earth and Space ScienceA CI Physical ScienceA 01 Unifying Concepts and Processes

Microgravity carriers and other spacecraft followpaths best described by conic sections. The aircraftand sub-orbital rockets trace out parabolas. Orbitingspacecraft are free falling on elliptical paths. When ameteoroid is on a path that is influenced by Earth orany other planetary body but does not get captured bythe gravitational field of the body, its motion, as itapproaches then moves away from the body, tracesout a hyperbolic path.

Plane

Right Circular Cone

Plane

Right Circular Cone

RightCircular Cone

RightCircular

Cone

Plane

Hyperbola

jMicrogravity A Teacher's Guide with ActivitieiAcience, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (Cli)

9

Rocket Parabolic Flight Profile


AlgebraComputation and EstimationConceptual Underpinnings of CalculusDiscrete MathematicsMathematical ConnectionsMathematics as Problem SolvingMathematics as ReasoningNumber and Number Relationships

Science Standards

O Physical ScienceA 0 Science and Technology

Science as InquiryO Unifying Concepts and Processes

Questions for DiscussionHow does the Shuttle stay in orbit? Use the fol-lowing two equations that describe the force actingon an object. The first equation represents the forceof gravity acting on the Shuttle.

G mems

Where:

F1 =

G=me =ms =r =

10

Force of gravity acting on the Shuttle

Universal gravitational constant

Mass of Earth

Mass of the Shuttle

Distance from center of Earth to the Shuttle

RocketsSounding rockets are used to create reducedgravity conditions for several minutes; they followsuborbital, parabolic paths. Freefall exists duringthe rocket's coast: after burn out and before enter-ing the atmosphere. Acceleration levels are usual-ly around 10-5 g. While most people do not get theopportunity to experience the accelerations of arocket launch and subsequent freefall, springboarddivers basically launch themselves into the airwhen performing dives and they experience micro-gravity conditions until they enter the water.

Orbiting SpacecraftAlthough drop facilities, airplanes, and rocketscan establish a reduced gravity environment, allthese facilities share a common problem. After afew seconds or minutes, Earth gets in the wayand freefall stops. To conduct longer scientificinvestigations, another type of freefall is needed.

To see how it is possible to establish microgravityconditions for long periods of time, one must firstunderstand what keeps a spacecraft in orbit. Askany group of students or adults what keepssatellites and Space Shuttles in orbit and youwill probably get a variety of answers. Two com-mon answers are "The rocket engines keep firingto hold it up," and "There is no gravity in space."

Although the first answer is theoretically possible,the path followed by the spacecraft would techni-cally not be an orbit. Other than the altitudeinvolved and the specific means of exerting anupward force, little difference exists between aspacecraft with its engines constantly firing andan airplane flying around the world. A satellitecould not carry enough fuel to maintain its altitudefor more than a few minutes. The second answeris also wrong. At the altitude that the SpaceShuttle typically orbits Earth, the gravitational pullon the Shuttle by Earth is about 90% of what it isat Earth's surface.


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (c)

In a previous section, we indicated that IssacNewton reasoned that the closed orbits of the

planets through space were due to gravity's pres-ence. Newton expanded on his conclusions aboutgravity and hypothesized how an artificial satellitecould be made to orbit Earth. He envisioned avery tall mountain extending above Earth's atmos-phere so that friction with the air would not be afactor. He then imagined a cannon at the top ofthat mountain firing cannonballs parallel to theground. Two forces acted upon each cannonballas it was fired. One force, due to the explosion ofthe black powder, propelled the cannonballstraight outward. If no other force were to act onthe cannonball, the shot would travel in a straightline and at a constant velocity. But Newton knewthat a second force would act on the cannonball:gravity would cause the path of the cannonball tobend into an arc ending at Earth's surface.

Illustration from Isaac Newton, Principia, VII, Book III, p. 551.

21

The second equation represents the force acting on theShuttle that causes a centripetal acceleration,

v2

This is an expression of Newton's second law, F=ma.

V2F2 = nas

rF2 = Force acting on the Shuttle that causes uni-

form circular motion (with centripetalacceleration)Velocity of the Shuttle

These two forces are equal: F1=F2

GIn"r2

my2

Gme

In order to stay in a circular orbit at a given distancefrom the center of Earth, r, the Shuttle must travel ata precise velocity, v.

How does the Shuttle change its altitude? From adetailed equation relating the Shuttle velocity withthe Shuttle altitude, one can obtain the followingsimple relationship for a circular orbit. Certainsimplifying assumptions are made in developingthis equation: 1) the radius of the Shuttle orbit isnearly the same as the radius of Earth, and 2) thetotal energy of the Shuttle in orbit is due to itskinetic energy, 1/2 mv2; the change in potentialenergy associated with the launch is neglected.

At* =

= orbital period, the time it takes the Shuttleto complete one revolution around Earth

2 Ir r3/2

(GrIldI

LV = the change in Shuttle velocityAt* = the change in Shuttle altitude

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (CI)

11

For example:

Consider a Shuttle in a circular orbit at 160 nauticalmiles (296.3 kin) altitude. Determine the new altitudecaused by the Shuttle firing a thruster that increasesits velocity by 1 m/s.

First, calculate the orbital period, T, from the aboveequation.

27c(r +2.96x105 M)3/2e(Gme)1/2

2TE(6.37x106 m+2.96x105 rn)312

(6.67x10-11 m3 x5.98x1024 kg)U2s2kg

= 5.41 x 103 s

Next, use the period and the applied velocity changeto calculate the altitude change.

Ar=t AvIt

5.41x103 smis)It

= 1.72x103 m

This altitude change is actually seen on the oppositeside of the orbit. In order to make the orbit circular atthe new altitude, the Shuttle needs to apply the sameAv at the other side of the orbit.

In the discussion and example just given, we statethat the equations given are simple approximations ofmore complex relationships between Shuttle velocityand altitude. The more complex equations are usedby the Shuttle guidance and navigation teams whotrack the Shuttles' flights. But the equations givenhere can be used for quick approximations of thetypes of thruster firings needed to achieve certain alti-tude changes. This is helpful when an experimentteam may want to request an altitude change.Engineers supporting the experiment teams can deter-mine approximately how much propellant would berequired for such an altitude change and whetherenough would be left for the required de-orbit bums.In this way, the engineers and experiment teams cansee if their request is realistic and if it has any possi-bility of being implemented.

12

Newton considered how additional cannonballswould travel farther from the mountain each timethe cannon fired using more black powder. Witheach shot, the path would lengthen and soon thecannonballs would disappear over the horizon.Eventually, if one fired a cannon with enoughenergy, the cannonball would fall entirely aroundEarth and come back to its starting point. Thecannonball would be in orbit around Earth.Provided no force other than gravity interferedwith the cannonball's motion, it would continuecircling Earth in that orbit.

This is how the Space Shuttle stays in orbit. Itlaunches on a path that arcs above Earth so thatthe Orbiter travels at the right speed to keep itfalling while maintaining a constant altitude abovethe surface. For example, if the Shuttle climbs to a320 kilometer high orbit, it must travel at a speedof about 27,740 kilometers per hour to achieve astable orbit. At that speed and altitude, theShuttle executes a falling path parallel to the cur-vature of Earth. Because the Space Shuttle is in astate of freefall around Earth and due to theextremely low friction of the upper atmosphere,the Shuttle and its contents are in a high-qualitymicrogravity environment.

22

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 po

MicrogravityScience PrimerWe experience many manifestations of gravity ona day to day basis. If we drop something, it fallstoward Earth. If we release a rock in a containerof water, the rock settles to the bottom of the con-tainer. We experience other effects of gravity reg-ularly, although we may not think of gravity asplaying a role.

Consider what happens when a container of wateris heated from below. As the water on the bottomis heated by conduction through the container, itbecomes less dense than the un-heated, coolerwater. Because of gravity, the cooler, more densewater sinks to the bottom of the container and theheated water rises to the top due to buoyancy. Acirculation pattern is produced that mixes the hotwater with the colder water. This is an example ofbuoyancy driven (or gravity driven) convection. Theconvection causes the water to be heated morequickly and uniformly than'if it were heated byconduction alone. This is the same density drivenconvection process to which we refer when westate matter-of-factly that "hot air rises."

In addition to mixing, density differences can alsocause things to differentially settle through aprocess called sedimentation. In this process, themore dense components of mixtures of immisci-ble fluids or solid particles in fluids settle to thebottom of a container due to gravity. If you fill abucket with very wet mud, and then leave thebucket sitting on the ground, over time the moredense soil particles will sink to the bottom of thebucket due to gravity, leaving a layer of water ontop. When you pick up a bottle of Italian saladdressing from the grocery store shelf, you seeseveral different layers in the bottle. The densesolids have settled to the bottom, the vinegar formsa middle layer, and the least dense oil is on top.

Science Standards

A Physical ScienceA 0 Unifying Concepts and Processes

Heat transfer occurs through one of three processesor a combination of the three. Conduction is the flowof heat through a body from an area of higher tem-perature to an area of lower temperature. Moleculesin the hot region increase their vibrational energy asthey are heated. As they collide with molecules withlower vibrational energy (cooler ones), some of thevibrational energy is passed to the cooler ones, theirenergy is increased, and heat is passed on.

Heat transfer by convection is the movement of heatby motion of a fluid. This motion can be the result ofsome force, such as a pump circulating heated water.and is referred to as forced convection. If the motionis the result of differences in density (thermal or com-positional), the convection is referred to as buoyancy-driven, density-driven, or natural convection.

Radiation is the emission of energy from the surfaceof a body. Energy is emitted in the form of electro-magnetic waves or photons (packets of light). Thecharacter (wavelength, energy of photons, etc.)'of theradiation depends on the temperature, surface area,and characteristics of the body emitting the energy.Electromagnetic waves travel with the speed of lightthrough empty space and are absorbed (and/orreflected) by objects they fall on. thus transferringheat. An excellent example of radiative heating is thesun's heat that we experience on Earth.


A 0 Mathematical Connections

Science Standards

A CI Earth and Space ScienceA 0 Physical ScienceA 1=1 Unifying Concepts and Processes

The mass of a body divided by its volume is its aver-age density.

Science Standards

A 1:1 Physical ScienceA 0 Unifying Concepts and Processes

When two or more liquids are immiscible they do notmix chemically.



Density Table

Interstellar spaceAtmosphere at normal altitude

of Space Shuttle in orbitAir at 0°C and 1 atmCarbon DioxideBalsaBoneCorkThe LarchLithiumApplewoodPeat BlocksIce

Olive OilSodiumWater at 0°C and 1 atmRock SaltGraphiteAluminumBasaltTalc

DolomiteDiamond

Average density of EarthIronLeadIridiumOsmiumUranium nucleusNeutron star (center)

Units (kg/m3)

10-21 _ 10-18

1-4x10-11

1.3

1.9

110-140170-200220-260500-560530660-840840920920970100021802300-270027002400-31002700-280028303010-3520552078601134022400225003x1017

1017-1018


AlgebraFunctionsGeometryGeometry from a Synthetic PerspectiveMathematical ConnectionsMathematics as CommunicationMathematics as Problem SolvingMeasummentTrigonometry

Science Standards

A CI Physical ScienceA 0 Science and TechnologyA CI Science in Personal and Social PerspectivesA CI Unifying Concepts and Processes

14

Gravity can also mask some phenomena that sci-entists wish to study. An example is the processof diffusion. Diffusion is the intermingling of solids,liquids, and gases due to differences in composi-tion. Such intermingling occurs in many situations,but diffusion effects can be easily hidden bystronger convective mixing. As an example, imag-ine a large room in which all air circulation sys-tems are turned off and in which a group ofwomen are spaced ten feet apart standing in aline. If an open container of ammonia were placedin front of the first woman in line and each womanraised her hand when she smelled the ammonia,it would take a considerable amount of timebefore everyone raised her hand. Also, the handraising would occur sequentially along the linefrom closest to the ammonia to furthest from theammonia. If the same experiment were performedwith a fan circulating air in the room, the handswould be raised more quickly, and not necessarilyin the same order. In the latter case, mixing of theammonia gas with the air in the room is due toboth diffusion and convection (forced convectiondue to the fan) and the effects of the two process-es cannot be easily separated. In a similar manner,buoyancy driven convection can mask diffusivemixing of components in scientific experiments.

Some behavior of liquids can also be masked bygravity. If you pour a liquid into a container onEarth, the liquid conforms to the bottom of thecontainer due to gravity. Depending on the shapeof the container and on the properties of the con-tainer and the liquid, some of the liquid may creepup the walls or become depressed along the wallsdue to the interrelated phenomena of surfacetension, adhesion, cohesion, and capillarity.

The resulting curved surface may be familiar toanyone who has measured water in a small diam-eter glass container (the water cups upward) orhas looked at the level of mercury in a glass ther-mometer (the mercury cups downward). Thedistance the contact line between the liquid andthe container moves up or down the containerwall is affected by gravity.


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)

Experiments performed on Earth often takeadvantage of the effects of gravity discussed. Formany experiments, however, these effects tend tomake the execution of experiments or the analysisof experimental results difficult and sometimeseven impossible. Therefore, many researchersdesign experiments to be performed under micro-gravity conditions. The different scientific researchareas that are studied in microgravity includebiotechnology, combustion science, fluid physics,fundamental physics, and materials science. Eachof these areas, or disciplines, is discussed below.The discipline is defined, some of the specificeffects of gravity that illustrate the benefits ofmicrogravity research are discussed, and someexamples of current resOarch are presented. Inaddition, a brief discussion of the microgravityenvironment of orbiting spacecraft is provided asis an introduction to the application of microgravityresearch to the exploration and development ofspace.

di The Microgravity Environmentw of Orbiting Spacecraft

While freefall reduces the effects of gravity, beingin an orbiting laboratory introduces other accelera-tions that cause effects that are indistinguishablefrom those due to gravity. When a spacecraft is inorbit around Earth, the orbit is actually defined bythe path of the center of mass of the spacecraftaround the center of Earth. Any object in a loca-tion other than on the line traversed by the centerof mass of the spacecraft is actually in a differentorbit around Earth. Because of this, all objects notattached to the spacecraft move relative to theorbiter center of mass. Other relative motions ofunattached objects are related to aerodynamicdrag on the vehicle and spacecraft rotations. Aspacecraft in low-Earth orbit experiences someamount of drag due to interactions with the atmos-phere. An object within the vehicle, however, isprotected from the atmosphere by the spacecraftitself and does not experience the same decelera-

25

Capillarity can be defined as the attraction a fluidhas for itself versus the attraction it has for a solidsurface (usually the fluid's container). The surfacetension a in a liquid-liquid or liquid-gas system isthe fluids' tendency to resist an increase in surfacearea. Surface tension is temperature dependent.Surface tension, capillarity, adhesion, and cohesionwork together to drive the contact angle 8 between asolid-liquid interface and liquid-liquid interface whena small diameter tube is dipped into a liquid. Whenthe contact angle 0=0, the liquid "wets" the tubecompletely. When 0<90° (an acute angle), the liquidrises in the tube; when 0>90° (an obtuse angle), theliquid is depressed in the tube and does not wet thewalls. The distance between the liquid surface in thecontainer and in the tube is h=2acos0/rpg where r isthe radius of the tube (D/2), p is the density of theliquid, and g is the acceleration due to gravity.


CI FunctionsA Geometry

0 Geometry from a Synthetic Perspective

Science Standards

A 0 Science and TechnologyA Cl Science in Personal and Social PerspectivesA 0 Unifying Concepts and Processes

Something that is concave is curved inward like theinner surface of a sphere. Something that is convexis curved like the outer surface of a sphere. A varietyof concave and convex lenses and mirrors are used inthe design of eyeglasses, magnifying glasses, cam-eras, microscopes, and telescopes. In the example inthe text, water cupping upward produces a concavesurface; mercury cupping downward produces a con-vex surface.

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (la)

15


A

A 0A 0A

Computation and EstimationMathematical ConnectionsMathematics as CommunicationMeasurement

Science StandardsGrades 5-8 (A); Grades 9-12 (0)

A 0 Physical ScienceA 0 Science and TechnologyA 0 Unifying Concepts and Processes

Quasi-steady accelerations in spacecraft are relatedto the position in the spacecraft, aerodynamic drag,and vehicle rotation. For the Space Shuttle Orbiters,these accelerations are on the order of lx10-6 g andvary with the orbital frequency.


A Computation and EstimationA 0 Mathematical ConnectionsA 0 Mathematics as CommunicationA Measurement

Science Standards

A LI Physical ScienceA Cl Science and TechnologyA 0 Unifying Concepts and Processes

g-jitter indicates the vibrations experienced bymicrogravity experiments (for example on parabolicaircraft and the Space Shuttle) that cause effects simi-lar to those that would be caused by a time-varyinggravitational field.

;0.5

g

.g

2

2.5

1.5Time (hrs)

The quasi-steady microgravity environment on theOrbiter Columbia shows the effects of variations inEarth's atmospheric density. The primary contri-bution to the variation is the daylnight difference inatmospheric density. The plot shows that the dragon the Orbiter varies over a ninety minute orbit.

2:5 3

16

tion that the vehicle does. The floating object andspacecraft therefore are moving relative to eachother. Similarly, rotation of the spacecraft due toorbital motion causes a force to act on objectsfixed to the vehicle but not on objects freely float-ing within it. On average for the Space Shuttles,the quasi-steady accelerations resulting from thesources discussed above (position in the space-craft, aerodynamic drag, and vehicle rotation) areon the order of 1 xl 0-6 g, but vary with time due tovariations in the atmospheric density around Earthand due to changes in Shuttle orientation.

In addition to these quasi-steady accelerations,many operations on spacecraft cause vibrationsof the vehicle and the payloads (experiment appa-ratus). These vibrations are often referred to asg-jitter because their effects are similar to thosethat would be caused by a time-varying gravita-tional field. Typical sources for vibrations areexperiment and spacecraft fans and pumps,motion of centrifuges, and thruster firings. With acrew onboard to conduct experiments, additionalvibrations can result from crew activities.

The combined acceleration levels that result fromthe quasi-steady and vibratory contributions aregenerally referred to as the microgravity environ-ment of the spacecraft. On the Space Shuttles,the types of vibration-causing operations dis-cussed above tend to create a cumulative back-ground microgravity environment of aboutxl 0-4 g, considering contributions for all frequen-

cies below 250 Hz.

Biotechnology.

Biotechnology is an applied biological sciencethat involves the research, manipulation, andmanufacturing of biological molecules, tissues,and living organisms. With a critical and expand-ing role in health, agriculture, and environmentalprotection, biotechnology is expected to have a


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (CI)

significant impact on our economy and our lives inthe next century. Microgravity research focuses onthree principal areasprotein crystal growth,mammalian cell and tissue culture, and funda-mental biotechnology.

Gravity significantly influences attempts to growprotein crystals and mammalian cell tissue onEarth. Initial research indicates that protein crys-tals grown in microgravity can yield substantiallybetter structural information than can be obtainedfrom crystals grown on Earth. Proteins consist ofthousandsor in the case of viruses, millionsofatoms, which are weakly bound together, forminglarge molecules. On Earth, buoyancy-inducedconvection and sedimentation may inhibit crystalgrowth. In microgravity, convection and sedimen-tation are significantly reduced, allowing for thecreation of structurally better and larger crystals.

The absence of sedimentation means that proteincrystals do not sink to the bottom of their growthcontainer as they do on Earth. Consequently, theyare not as likely to be affected by other crystalsgrowing in the solution. Because convective flowsare also greatly reduced in microgravity, crystalsgrow in a much more quiescent environment,which may be responsible for the improved struc-tural order of space-grown crystals. Knowledgegained from studying the process of protein crys-tal growth under microgravity conditions will haveimplications for protein crystal growth experimentson Earth.

Research also shows that mammalian cellsparticularly normal cellsare sensitive to condi-tions found in ground-based facilities used to cul-ture (grow) them. Fluid flows caused by gravitycan separate the cells from each other, severelylimiting the number of cells that will aggregate(come and stay together). But tissue samplesgrown in microgravity are much larger and morerepresentative of the way in which tissues areactually produced inside the human body. This

2 7

Protein crystals grown in microgravity can haveregular, simple shapes and a more highlyordered internal structure than those grownon Earth.

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (c)

17

Crystallized protein lysozyme after dialysis toremove small molecule contaminants.

18

suggests that better control of the stresses exert-ed on cells and tissues can play an important rolein their culture. These stresses are greatly reducedin microgravity.

Protein Crystal GrowthThe human body contains over 100,000 differentproteins. These proteins play important roles inthe everyday functions of the body, such as thetransport of oxygen and chemicals in the blood,the formation of the major components of muscleand skin, and the fighting of disease. Researchersin this area seek to determine the structures ofthese proteins, to understand how a protein'sstructure affects its function, and ultimately todesign drugs that intercede in protein activities(penicillin is a well-known example of a drug thatworks by blocking a protein's function). Determin-ing protein structure is the key to the design anddevelopment of effective drugs.

The main purpose in growing protein crystals is toadvance our knowledge of biological molecularstructures. Researchers can use microgravity tohelp overcome a significant stumbling block in thedetermination of molecular structures: the difficul-ty of growing crystals suitable for structural analy-sis. Scientists use X-ray diffraction to determinethe three-dimensional molecular structure of aprotein. They can calculate the location of theatoms that make up the protein based on theintensity and position of the spots formed by thediffracted X-rays. From high resolution diffractiondata, scientists can describe a protein's structureon a molecular scale and determine the parts ofthe protein that are important to its functions.Using computer analysis, scientists can createand manipulate three-dimensional models of theprotein and examine the intricacies of its structureto create a drug that "fits" into a protein's activesite, like inserting a key into a lock to "turn off" theprotein's function. But X-ray diffraction requires

28


large, homogeneous crystals (about the size of agrain of table salt) for analysis. Unfortunately,crystals grown in Earth's gravity often have inter-nal defects that make analysis by X-ray diffractiondifficult or impossible. Space Shuttle missionshave shown that crystals of some proteins (andother complex biological molecules such as virus-es) grown on orbit are larger and have fewerdefects than those grown on Earth. The improveddata from the space-grown crystals significantlyenhance scientists' understanding of the protein'sstructure and this information can be used to sup-port structure-based drug design.

Scientists strive for a better understanding of thefundamental mechanisms by which proteins formcrystals. A central goal of microgravity proteincrystal growth experiments is to determine thebasic science that controls how proteins interactand order themselves during the process of crys-tallization. To accomplish this goal, NASA hasbrought together scientists from the protein crys-tallography community, traditional crystal growers,and other physical scientists to form a multidisci-plinary team in order to address the problems in acomprehensive manner.

Mammalian Cell and Tissue CultureMammalian cell tissue culturing is a major area ofresearch for the biotechnology community. Tissueculturing is one of the basic tools of medicalresearch and is key to developing future medicaltechnologies such as ex vivo (outside of the body)therapy design and tissue transplantation. To date,medical science has been unable to fully culturehuman tissue to the mature states of differentia-tion found in the body.

The study of normal and cancerous mammaliantissue growth trolds enormous promise for appli-cations in medicine. However, conventional statictissue culture methods form flat sheets of growingcells (due to their settling on the bottom of thecontainer) that differ in appearance and function

Science Standards

A ID Physical ScienceA UI Unifying Concepts and Processes

A substance that is homogeneous is uniform in struc-ture and/or composition.

Three different types of protein crystals grownon the Space Shuttle Columbia in 1995:satellite tobacco mosaic virus, lysozyine,and thaumatin.

Microgravity A Teacher's Guide with Activitiearacience, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)

19

Science Standards

A 0 Life ScienceA CI Unifying Concepts and Processes

Differentiation is the process (or the result of thatprocess) by which cells and/or tissues undergo a pro-gressive.specialization of form or function.


O AlgebraO Conceptual Underpinnings of CalculusO Geometry from an Algebraic Perspective

A CD Mathematical ConnectionsA I Mathematics as Problem Solving

Science Standards

A CIA 0A 0

Physical ScienceScience and TechnologyUnifying Concepts and Processes

The forces acting on a surface can be separated intocomponents perpendicular (normal) to and tangentialto the surface. The normal force causes a normalstress and the tangential force is responsible for a tan-gential, or shear, stress acting on the surface. Shearforces cause contiguous parts of a structure or liquidto slide relative to each other.

A bioreactor vessel that flew on the SpaceShuttle Discovery in July 1995.

20

from their three-dimensional counterparts growingin a living body. In an effort to enhance three-dimensional tissue formation, scientists havedeveloped a ground-based facility for cell and tis-sue culture called a bioreactor. This instrumentcultures cells in a slowly rotating horizontal cylin-der, which produces lower stress levels on thegrowing cells than previous Earth-based experi-mental environments. The continuous rotation ofthe cylinder allows the sample to escape much ofthe influence of gravity, but because the bioreac-tor environment tends to be rather passive, it issometimes difficult for the growing tissue to findthe fresh media (food supply) it needs to survive.

Another reason normal mammalian cells are sen-sitive to growth conditions found in standardbioreactors is that fluid flow causes shear forcesthat discourage cell aggregation. This limits boththe development of the tissue and the degree towhich it possesses structures and functionssimilar to those found in the human body. Tissuecultures of the size that can be grown in thesebioreactors allow tests of new treatments oncultures grown from cells from the patient ratherthan on patients themselves. In the future, thistechnology will enable quicker, more thoroughtesting of larger numbers of drugs and treat-ments. Ultimately, the bioreactor is expected toproduce even better results when used in amicrogravity environment.

In cooperation with the medical community, thebioreactor design is being used to prepare bettermodels of human colon, prostate, breast, andovarian tumors. Cells grown in conventional cul-ture systems may not differentiate to form a tumortypical of cancer. In the bioreactor, however, thesetumors grow into specimens that resemble theoriginal tumor. Similar results have been observedWith normal human tissues as well. Cartilage,bone marrow, heart muscle, skeletal muscle, pan-creatic islet cells, liver cells, and kidney cells areexamples of the normal tissues currently being

3 0


grown in rotating bioreactors by investigators. Inaddition, laboratory models of heart and kidneydiseases, as well as viral infections (includingNorwalk virus and Human ImmunodeficiencyVirus (HIV)) are currently being developed using amodified NASA bioreactor experiment design withslight variations in experimental technique andsome adjustments to hardware. Continued use ofthe bioreactor can improve our knowledge of nor-mal and cancerous tissue development. NASA isbeginning to explore the possibility of culturing tis-sues in microgravity, where even greater reduc-tion in stresses on growing tissue samples mayallow much larger tissue masses to develop. Abioreactor is in use on the Russian Space StationMir in preparation for the International SpaceStation.

Fundamental BiotechnologyElectrophoresis has been studied on a dozenSpace Shuttle flights and has led to additionalresearch in fluid physics in the area of electrohy-drodynamics. Phase partitioning experiments,which use interfacial energy (the energy changeassociated with the contact between two differentmaterials) as the means of separation, have flownon six missions.

Combustion Science

Combustion, or burning, is a rapid, self-sustainingchemical reaction that releases a significantamount of heat. Examples of common combustionprocesses are burning candles, forest fires, logfires, the burning of natural gas in home furnaces,and the burning of gasoline in internal combustionengines. For combustion to occur, three thingsmust normally be present: a fuel, an oxidizer,and an ignition stimulus. Fuels can be solid, liq-uid, or gas. Examples of solid fuels include filterpaper, wood, and coal. Liquid fuels include gaso-line and kerosene. Propane and hydrogen areexamples of gaseous fuels. Oxidizers can be solid(such as ammonium perchlorate, which is used in

Science Standards

A CI Physical ScienceA CI Science and TechnologyA La Sciences in Personal and Social PerspectivesA CI Unifying Concepts and Processes

Electrophoresis is the separation of a substancebased on the electrical charge of the molecule and itsmotion in an applied electric field.

Science Standards

A 1=1 Physical ScienceA LI Science and TechnologyA 1:1 Science in Personal and Social PerspectivesA CI Unifying Concepts and Processes

An exception to the standard combustion processis hypergolic combustion. In this situation, a fuel andan oxidizer spontaneously react on contact withoutthe need for an ignition stimulus. The jets used tomaintain and change the Shuttle's orientation when inorbit are powered by hypergolic reactions..

3 tMicrogravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,

EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (D)21

The familiar shape of a candle flame on Earthis caused by buoyancy-driven convection. Inmicrogravity, a candle flame assumes a spheri-cal shape as fresh oxidizer reaches it by diffu-sion processes.

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Space Shuttle booster rockets), liquid (like hydro-gen peroxide), or gaseous (like oxygen). Air,which contains oxygen, is a particularly commonoxidizer. An electrical spark is an example of anignition stimulus.

Combustion is a key element in many of modernsociety's critical technologies. Electric power pro-duction, home heating, ground transportation,spacecraft and aircraft propulsion, and materialsprocessing are all examples in which combustionis used to convert chemical energy to thermalenergy. Although combustion, which accounts forapproximately 85 percent of the world's energyusage, is vital to our current way of life, it posesgreat challenges to maintaining a healthy environ-ment. Improved understanding of combustion willhelp us deal better with the problems of pollu-tants, atmospheric change and global warming,unwanted fires and explosions, and the incinera-tion of hazardous wastes. Despite vigorous scien-tific examination for over a century, researchersstill lack full understanding of many fundamentalcombustion processes.

Some objectives of microgravity combustion sci-ence research are to enhance our understandingof the fundamental combustion phenomena thatare affected by gravity, to use research results toadvance combustion science and technology onEarth, and to address issues of fire safety inspace. NASA microgravity combustion scienceresearch combines the results of experimentsconducted in ground-based microgravity facilitiesand orbiting laboratories and studies how flamesignite, spread, and extinguish (go out) undermicrogravity conditions.

Research in microgravity permits a new range ofcombustion experiments in which buoyancy-induced flows and sedimentation are virtuallyeliminated. The effects of gravitational forces oftenimpede combustion studies performed on Earth.For example, combustion generally produces hotgas (due to the energy released in the reaction),



which is less dense than the cooler gases aroundit. In Earth's gravity, the hot gas is pushed up bythe denser surrounding gases. As the hot gasrises, it creates buoyancy-induced flow that pro-motes the mixing of the unburned fuel, oxidizer,and combustion products.

The ability to significantly reduce gravity-drivenflows in microgravity helps scientists in severalways. One advantage is that the "quieter" andmore symmetric microgravity environment makesthe experiments easier to model (describemathematically), thus providing a better arenafor testing theories. In addition, eliminating buoy-ancy-induced flows allows scientists to studyphenomena that are obscured by the effects ofgravity, such as the underlying mechanisms offuel and heat transport during combustionprocesses. Because buoyancy effects are nearlyeliminated in microgravity, experiments of longerduration and larger scale are possible, and moredetailed observation and examination of importantcombustion processes can occur.

Scientists often desire an even mixture of thecomponent parts of fuels so that models devel-oped for their experiments can use simplified setsof equations to represent the processes thatoccur. Sedimentation affects combustion experi-ments involving particles or droplets because, asthe components of greater density sink in a gasor liquid, their movement relative to the other par-ticles creates an asymmetrical flow around thedropping particles. This can complicate the inter-pretation of experimental results. On Earth, scien-tists must resort to mechanical supports, levita-tors, and stirring devices to keep fuels mixed,while fluids in microgravity stay more evenlymixed without sticking together, colliding, ordispersing unevenly.


Computation and EstimationDiscrete MathematicsMathematical ConnectionsMathematics as CommunicationMathematics as Problem SolvingMathematics as Reasoning

Science Standards

A 0 Physical ScienceA Science as InquiryA 0 Science and TechnologyA 0 Unifying Concepts and Processes

The creation and use of mathematical models is akey element of science, engineering, and technology.Modeling begins with identifying the physical andchemical phenomena involved in an experiment.Associated mathematical equations such as equationsof motion are then identified. These governing equa-tions are solved in order to predict important aspectsof the experiment behavior, using appropriate valuesof experiment parameters such as density, composi-tion, temperature, and pressure. Simple mathematicalmodels can be solved by hand, while more complexexperiments are generally modeled using sophisticat-ed algorithms on high speed computers.

In microgravity research, scientists use modeling inpreparation for flight experiments and in analysis ofthe results. Models and experiment procedures arefine-tuned based on comparisons between model pre-dictions and the results of ground-based microgravityexperiments (for example, drop facilities and parabol-ic aircraft flights). This preliminary work allowsresearchers to best take advantage of space flightopportunities.

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (o)

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Transmission Electron Microscope image oflaser-heated soot.

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To date, combustion science researchers havedemonstrated major differences in the structuresof various types of flames burning under micro-gravity conditions and under 1 g conditions. Inaddition to the practical implications of theseresults in combustion efficiency, pollutant control,and flammability, these studies establish that bet-ter understanding of the individual processesinvolved in the overall combustion process can beobtained by comparing results from microgravityand Earth gravity tests. One clear example of theadvantage of these comparison tests is in thearea of fire safety. Most smoke detectors havebeen designed to detect soot particles in the air,but the sizes of soot particles produced in 1 g aredifferent from those produced in microgravity envi-ronments. This means that smoke-detectingequipment must be redesigned for use on space-craft to ensure the safety of equipment and crew.

Comparisons of research in microgravity and in1 g have also led to improvements in combustiontechnology on Earth that may reduce pollutantsand improve fuel efficiency. Technologicaladvances include a system that measures thecomposition of gas emissions from factory smokestacks so that they can be monitored. In addition,a monitor for ammonia, which is one gas thatposes dangers to air quality, is already being pro-duced and is available for industrial use.Engineers have also designed a device thatallows natural gas appliances to operate moreefficiently while simultaneously reducing air pollu-tion. This may be used in home furnaces, industri-al processing furnaces, and water heaters in thefuture. Another new technology is the use ofadvanced optical diagnostics and lasers to betterdefine the processes of soot formation so thatsoot-control strategies can be developed. Deviceshave also been developed to measure percent-ages of soot in exhausts from all types of enginesand combustors, including those in automobilesand airplanes.

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0i)

The combustion science program supports exper-iments in the following research areas:

Premixed Gas FlamesIn premixed gas flame research, the fuel and oxi-dizer gases are completely mixed prior to ignition.Scientists are interested in flame speed (the rateat which the flame zone travels away from theignition source and into the unreacted mixture) asa function of both the type of fuel and oxidizerused and the oxidizer-to-fuel ratio. With sufficientlyhigh or low ratios, the flame does not move intothe unreacted mixture; these critical ratios arereferred to as lower and upper flammability limitsand are of considerable interest in terms of bothsafety and fundamental science. Gravity canstrongly affect both flame speed and flammabilitylimits, chiefly through buoyancy effects. Scientistsin this area are also researching gravity's effectson the stability, extinction, structure, and shape ofpremixed gas flames.

Gaseous Diffusion FlamesIn this area of research, the fuel and oxidizergases are initially separate. They tend to diffuseinto each other and will react at their interfaceupon ignition. The structure of these flames undermicrogravity conditions is quite different than onEarth because of buoyancy-induced flows causedby Earth's gravity. Scientists study flammabilitylimits, burning rates, and how diffusion flamestructure affects soot formation. Within this area,results of studies of the behavior of gas-jet flamesin a microgravity environment, both in transitionand in turbulent flows, are being used to developmodels with potential applications in creatingeffective strategies to control soot formation inmany practical applications.

Liquid Fuel Droplets and SpraysIn this research area, scientists study the com-bustion of individual liquid fuel droplets suspend-ed in an oxidizing gas (air, for example). For theseexperiments, investigators commonly use fuels

Candle flame energy flow. Adapted from "TheScience of Flames" poster, National EnergyFoundation, Salt Lake City, Utah.


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Ultraviolet images of OH radiation taken athalf-second intervals during a drop tower test ofthe Droplet Combustion Experiment. The diame-ter of the flame produced by burning a heptanedroplet decreases in freefall.

26

such as heptane, kerosene, and methanol.Gravity hinders fundamental studies of dropletcombustion on Earth due to flows induced byhigh-density droplets that sink and buoyancy-induced upward acceleration of hot combustionproducts relative to the surrounding gas. Theseflows cause drops to burn unevenly, making it dif-ficult for scientists to draw meaningful conclusionsfrom their experiments.

This area of study also includes the investigationof the combustion of sprays and ordered arrays offuel droplets in a microgravity environment for animproved understanding of interactions betweenindividual burning droplets in sprays. Knowledgeof spray combustion processes resulting fromthese studies should lead to major improvementsin the design of combustors using liquid fuels.

Fuel Particles and Dust CloudsThis area is particularly important in terms of firesafety because clouds of coal dust have thepotential to cause mine explosions and grain-dustclouds can cause silos and grain elevators toexplode. It is particularly difficult to study the fun-damental combustion characteristics of fuel-dustclouds under normal gravity because initially well-dispersed dust clouds quickly settle due to densi-ty differences between the particles and thesurrounding gas. Because particles stick togetherand collide during the sedimentation process,they form nonuniform fuel-air ratios throughoutthe cloud. In microgravity, fuel-dust clouds remainevenly mixed, allowing scientists to study themwith much greater experimental control with agoal of mitigating coal mine and grain elevatorhazards.

Flame Spread Along SurfacesAn important factor in fire safety is inhibiting thespread of flames along both solid and liquid sur-faces. Flame spread involves the reactionbetween an oxidizer gas and a condensed-phasefuel or the vapor produced by the "cooking" of


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (I:1)

such a fuel. Research has revealed major differ-ences in ignition and flame-spreading characteris-tics of liquid and solid fuels under microgravityand normal gravity conditions. Material flammabili-ty tests in 1 g, which are.strongly affected bybuoyancy-induced flows, do not match resultsobtained in microgravity. It is therefore useful tostudy both flame spread and material flammabilitycharacterie.tics in microgravity to ensure fire safetyin environments with various levels of gravity. Theknowledge gained from these studies may alsolead to better understanding of dangerous com-bustion reactions on Earth. Microgravity experi-ments eliminate complexities associated withbuoyancy effects, providing a more fundamentalscenario for the development of flame-spreadingtheories.

Smoldering CombustionSmoldering combustion is a relatively slow, non-flaming combustion process involving an oxidizergas and a porous solid fuel. Well-known examplesof smoldering combustion are "burning" cigarettesand cigars. Smoldering combustion can alsooccur on much larger scales with fuels such aspolyurethane foam. When a porous fuel smoldersfor a long period of time, it can create a large vol-ume of gasified fuels, which are ready to reactsuddenly if a breeze or some other oxidizer flowoccurs. This incites the fuel to make the transitionto full-fledged combustion, often leading to disas-trous fires (like those involving mattresses or sofacushions). Since heat is generated slowly in thisprocess, the rate of combustion is quite sensitiveto heat exchange; therefore, buoyancy effects areparticularly important. Accordingly, smolderingcombustion is expected to behave quite differentlyin the absence of gravity.

Combustion SynthesisCombustion synthesis, a relatively new area ofresearch, involves creating new materials througha combustion process and is closely tied to workin materials science. One area of particular inter-est is referred to as self-deflagrating high-temper-

View looking down at a piece of ashless filterpaper with a 1 centimeter grid on it. On theUSMP-3 Shuttle mission, a radiant heater (twoconcentric rings exposed at the center of theimage) was used to ignite samples to studyflame spread and smoldering in weak air flowsunder microgravity conditions. In this image,areas where the grid is not seen have beenburned, with the cracking and curling edges ofthe burning paper leaving a cusped appearance.The flame started at the heater site and propa-gated toward the right where a fan provided asource of fresh air Charred paper around theburnt area is a darker grey than the unaffectedpaper White areas to the right of the heaterrings are soot zones.

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (u)

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Science Standards

A 01 Physical ScienceA C21 Unifying Concepts and Processes

A fluid is something that flows. Highly compressiblefluids are usually considered gases; essentiallyincompressible fluids are usually considered liquids.Fluids tend to conform to the shape of a container.On Earth's surface, liquids tend to fill the bottom ofan open or closed container and gases tend to fillclosed containers.

28

ature synthesis. This occurs when two materialsusually two solidsare mixed together, are reac-tive with one another, and create a reaction thatgives off a large amount of heat. Once the reac-tion is started, the flame will propagate through apressed mixture of these particles, resulting in anew material. Much of the initial research in thisgroundbreaking area involves changing variablessuch as composition, pressure, and preheat tem-perature. Manipulating these factors leads tointeresting variations in the properties of materialscreated through the synthesis process.

Flame processes are also being used to createfullerenes and nanoparticles. Fullerenes, a newform of carbon, are expensive to produce at thistime and cannot be produced in large quantities,but scientists predict more uses for them will bedeveloped as they become more readily available.Nanoparticles (super-small particles) are also ofgreat interest to materials scientists due to thechanges in the microstructure of compactedmaterials that can be produced by sintering,which results in improved properties of the finalproducts. These nanoparticles can thus be usedto form better pressed composite materials.

Fluid Physics

A fluid is any material that flows in response toan applied force; thus, both liquids and gases arefluids. Some arrangements of solids can alsoexhibit fluid-like behaviors; granular systems (suchas soil) can respond to forces, like those inducedby earthquakes or floods, with a flow-like shift inthe arrangement of solid particles and the air orliquids that fill the spaces between them. Fluidphysicists seek to better understand the physicalprinciples governing fluids, including how fluidsflow under the influence of energy, such as heator electricity; how particles and gas bubbles sus-pended in a fluid interact with and change theproperties of the fluid; how fluids interact withsolid boundaries; and how fluids change phase,


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either from fluid to solid or from one fluid phase toanother. Fluid phenomena studied range in scalefrom microscopic to atmospheric and includeeverything from the transport of cells in thehuman body to changes in the composition of theatmosphere.

The universal nature of fluid phenomena makestheir study fundamental to science and engineer-ing. Understanding the fluid-like behavior of soilsunder stress will help civil engineers design safebuildings in earthquake-prone areas. Materialsengineers can benefit from a better grasp of howthe structure and properties of a solid metal aredetermined by fluid behavior during its formation.And knowledge of the flow characteristics ofvapor-liquid mixtures is useful in designing powerplants to ensure maximum stability and perfor-mance. The work of fluid physics researchersoften applies to the work of other microgravity sci-entists.

Complex FluidsThis research area focuses on the unique proper-ties of complex fluids, which include colloids, gels,magneto-rheological fluids, foams, and granularsystems.

Colloids are suspensions of finely divided solidsor liquids in fluids. Some examples of colloidaldispersions are aerosols (liquid droplets in gas),smoke (solid particles in gas), and paint (solid inliquid). Gels are colloidal mixtures of liquids andsolids in which the solids have linked together toform a continuous network, becoming very vis-cous (resistant to flow). Magneto-rheological fluidsconsist of suspensions of colloidal particles. Eachparticle contains many tiny, randomly orientedmagnetic grains and an externally applied mag-netic field can orient the magnetic grains intochains. These chains may further coalesce intolarger-scale structures in the suspension, therebydramatically increasing the viscosity of the sus-pension. This increase, however, is totallyreversed when the magnetic field is turned off.

L ga,*

Side views of water and air flowing through aclear pipe. At I g, the air stays on top. In micro-gravity, the air can form a core down the centerof the pipe.


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Science Standards

A 01 Physical ScienceA 1:11 Unifying Concepts and Processes

Rheology is the scientific study of the deformationand flow of matter.

USML-2 Payload Commander Kathryn C.Thornton works at the Drop Physics Module,used to investigate liquid drop behavior inmicrogravity.

30

A foam is a nonuniform dispersion of gas bubblesin a relatively small volume of liquid that containssurface-active macromolecules, or surfactants(agents that reduce the surface tension of liquids).Foams have striking properties in that they areneither solid, liquid, nor vapor, yet they exhibit fea-tures of all three. Important uses for custom-designed foams include detergents, cosmetics,foods, fire extinguishing, oil recovery, and manyphysical and chemical separation techniques.Unintentional generation of foam, on the otherhand, is a common problem affecting the efficien-cy and speed of a vast number of industrialprocesses involving the mixing or agitation ofmulticomponent liquids. It also occurs in pollutednatural waters and in the treatment of wastewater.In all cases, control of foam rheology andstability is required.

Examples of granular systems include soil andpolystyrene beads, which are often used as pack-ing material. Granular systems are made up of aseries of similar objects that can be as small as agrain of sand or as large as a boulder. Althoughgranular systems are primarily composed of solidparticles, their behavior can be fluid-like. Thestrength of a granular system is based upon thefriction between and geometric interlocking ofindividual particles, but under certain forces orstresses, such as those induced by earthquakes,these systems exhibit fluidic behavior.

Studying complex fluids in microgravity allows forthe analysis of fluid phenomena often masked bythe effects of gravity. For example, researchersare particularly interested in the phase transitionsof colloids, such as when a liquid changes to asolid. These transitions are easier to observe inmicrogravity. Foams, which are particularly sensi-tive to gravity, are more stable (and can thereforebe more closely studied for longer periods oftime) in microgravity. In magneto-rheological flu-ids, controlling rheology induced by a magneticfield has many potential applications, from Shockabsorbers and clutch controls for cars to robotic

4 oMicrogravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,

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joint controls. Under the force of Earth's gravity,the magnetic particles in these fluids often fall outof suspension due to sedimentation, but in micro-gravity this problem is eliminated. Investigations ofthe behavior of granular systems, which have pre-viously been hampered by Earth's gravity, aremore feasible in microgravity because they do notsettle as they do on Earth.

Multiphase Flow and Heat TransferThis research area, which has applications in theengineering of heat transfer systems and gaspurification systems, focuses on complex prob-lems of fluid flow in varying conditions. Scientistsare seeking to add to their currently limited knowl-edge of how gravity-dependent processes, suchas boiling and steam condensation, occur in

microgravity. Boiling is known to be an efficientway to transfer large amounts of heat, and assuch, it is often used for cooling and for energyconversion systems. In space applications, boilingis preferable to other types of energy conversionsystems because it is efficient and the apparatusneeded to generate power is smaller.

Another of the mechanisms by which energy andmatter move through liquids and gases is diffusivetransport. The way atoms and molecules diffuse,or move slowly, through a liquid or gas is dueprimarily to differences in concentration or tem-perature. Researchers use microgravity to studydiffusion in complex systems, a process thatwould normally be eclipsed by the force of gravity.

Understanding the physics of multiphase flow andheat transfer will enable scientists to extend therange of human capabilities in space and willenhance the ability of engineers to solve prob-lems on Earth as well. Applications of thisresearch may include more effective air condition-ing and refrigeration systems and improvementsin power plants that could reduce the cost of gen-erating electricity.


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Comparison of thermocapillary flows on Earth(top) and in microgravity (bottom). The flowpattern (indicated by the white areas) in theEarth-based experiment is only evident on thefluid's surface, while the flow pattern in micro-gravity encompasses the entire fluid.

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Interfacial PhenomenaResearch in this area focuses on how an inter-face, like the boundary between a solid and a liq-uid, acquires and maintains its shape. Interfacedynamics relate to the interaction of surfaces inresponse to heating, cooling, and chemical influ-ences. A better understanding of this topic willcontribute to improved materials processing andother applications.

Interfacial phenomena, such as the wetting andspreading of two immiscible liquids or the spread-ing of fluid across a solid surface, are ubiquitousin nature and technology. Duck feathers andwaterproof tents repel water because the wettingproperties of the surfaces of their fibers preventwater from displacing the air in the gaps betweenthe fibers. In contrast, water spontaneously dis-places air in the gaps of a sponge or filter paper.Technologies that rely on dousing surfaces withfluids like agricultural insecticides, lubricants, orpaints depend on the wetting behavior of liquidsand solids. Wetting is also a dominant factor inmaterials processing techniques, including filmand spray coating, liquid injection from an orifice,and crystal growth. Interfaces dominate the prop-erties and behavior of advanced composite mate-rials, where wetting of the constituent materialsdictates the processing of such materials.Understanding and controlling wetting andspreading pose both scientific and technologicalchallenges.

In reduced gravity, wetting determines the config-uration and location of fluid interfaces, thus great-ly influencing, if not dominating, the behavior ofmultiphase fluid systems. This environment pro-vides scientists with an excellent opportunity tostudy wetting and surface tension forces that arenormally masked by the force of Earth's gravity.This research also provides information that canhelp improve the design of space engineeringsystems strongly affected by wetting, including

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 ()

liquid-fuel supply tanks, two-phase heat transferand/or storage loops, and fluids managementdevices for life support purposes.

Dynamics and StabilityThis broad area of research includes drop dynam-ics, capillarity, and magneto/electrohydrodynamics.

Drop dynamics research deals with the behaviorof liquid drops and gas bubbles under the influ-ence of external forces and chemical effects.Research in drop dynamics ranges from the studyof rain in the atmosphere to the investigation ofchemical processes. A potential application ofthese studies is in the realm of materials process-ing. In forming solid materials from liquids inspace, it is usually important to create pureand/or uniform solidsgas bubbles and drops offoreign liquids are undesirable. Yet due to themicrogravity environment, these bubbles anddrops of substances of lower densities would not"rise to the top" the way they would if they wereon the ground, which makes extraction of thebubbles difficult. Researchers are attempting toresolve this problem in order to facilitate bettermaterials processing in space.

Scientists are also interested in studying singlebubbles and drops as models for other natural sys-tems. The perfect spheres formed by bubbles anddrops in microgravity (due to the dominance of sur-face tension forces) are an easy fit to theoreticalmodels of behaviorfewer adjustments need to bemade for the shape of the model. Investigators canmanipulate the spherical drops using sound andother impulses, creating an interactive model forprocesses such as atom fissioning.

Capillarity refers to a class of effects that dependon surface tension. The shape a liquid assumes in

a liquid-liquid or liquid-gas system is controlled bysurface tension forces at the interface. Small dis-turbances in the balance of molecular energies atthese boundaries or within the bulk of the liquid

C*2

This sequential photo shows a liquid bridgeundergoing a series of shape changes. Liquidbridge investigations on the Shuttle have testedtheories of electrohydrodynamics.

In materials science research, float zone sam-ples are sometimes used for crystal growth. Fora float-zone sample, the swface tension of themelt keeps the sample suspended between twosample rods in a furnace. A thorough under-standing of the capillarity and swface tensioneffects in a molten sample allows better experi-ment control and results prediction.


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Science Standards

A 0 Physical ScienceA 0 Science and TechnologyA U Unifying Concepts and Processes

Joule heating occurs when electric current flowsthrough a material. This is how an electric toasterworks.

Researchers observe the float package and datarack of a superfluid helium experiment on aparabolic aircraft flight.

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can cause shifts in the liquid's position and shapewithin a container (such as a fuel tank) or in acontaining material (such as soil). These changes,or capillary effects, often occur in liquids on Earth,but are to some degree masked or minimized bythe stronger force of gravity. In microgravity, how-ever, capillary effects become prominent. Thestudy of capillary phenomena in microgravity willenable researchers to better understand and pre-dict fluid configurational changes both on Earthand in low-gravity environments.

Microgravity fluid physics researchers also studythe effects of magnetic and electric fields on fluidflows, or magneto/electrohydrodynamics.Promising microgravity research subjects in thisarea include weak fluid flows, such as thosefound in poorly conducting fluids in a magneticfield, and Joule heating. In Earth's gravity, Jouleheating causes buoyancy-driven flows which, inturn, obscure its effects. In microgravity, however,buoyancy-driven flows are nearly eliminated, soresearchers are not only able to study the effectsof Joule heating, but they can also observe otherprocesses involving applied electric fields, suchas electrophoresis.

Fundamental Physics

Physics is a major part of fundamental sciencewhere the ultimate goal is to establish a unifieddescription of the basic laws that govern ourworld. At present fundamental physics includeslow temperature physics, condensed matterphysics (the study of solids and liquids), lasercooling and atomic physics, and gravitational andrelativistic physics. A unifying characteristic ofthese research areas is that they address funda-mental issues which transcend the boundaries ofa particular field of science.

The majority of experiments in fundamentalphysics are extensions of investigations in Earth-based laboratories. The microgravity experimentin these cases presents an opportunity to extend


EG-1997-08-110-HO, Education Standards Grades 5-8 (A), 9-12 (0)

a set of measurements beyond what can be doneon Earth, often by several orders of magnitude.This extension can lead either to a more preciseconfirmation of our previous understanding of aproblem, or it can yield fundamentally new insightor discovery. The remainder of fundamentalphysics research involves tests of the fundamen-tal laws which govern our universe. Investigationsaim at enhancing our understanding of the mostbasic aspects of physical laws, and as such maywell have the most profound and lasting long-range impact on mankind's existence on Earthand in space.

There are many examples of how fundamentalscience has had an impact on the average per-son. Basic research in condensed matter physicsto explain the behavior of semiconductors led tothe development of transistors which are nowused in communication devices, and which pro-duce ever more prevalent and capable computertechnology. Research in low temperature physicsto explore the properties of fluids at very low tem-peratures led to advanced magnetic resonancetechniques that have brought extremely detailedmagnetic resonance imaging to the medical doc-tor, so today much exploratory surgery can beavoided. A less widely appreciated part played byfundamental science in today's world has beenthe need to communicate large quantities of datafrom physics experiments to collaborators atmany locations around the world. Satisfying thisneed was instrumental in the development of theInternet and the World Wide Web.

Fundamental physics research benefits from boththe reduction in gravity's effects in Earth-orbit andfrom the use of gravity as a variable parameter. Incondensed matter physics, the physics of criticalpoints has been studied under microgravity con-ditions. This field needs microgravity because theability to approach a critical point in the Earth-bound laboratory is limited by the uniformity of thesample which is spoiled by hydrostatic pressurevariations.

Science Standards

A CI Physical ScienceA 01 Science and TechnologyA Unifying Concepts and Processes

The critical point is the temperature at which the dif-ferences between liquids and gases disappear. Abovethat temperature, the liquid smoothly transforms to thegaseous state; boiling disappears.


A ZI Mathematical ConnectionsA Mathematics as CommunicationA CI Mathematics as Problem Solving

Science Standards

A CI Physical ScienceA 0 Science and TechnologyA 01 Unifying Concepts and Processes

Hydrostatic pressure is the result of the weight of amaterial above the point of measurement.


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A 0 Mathematical ConnectionsA 0 Mathematics as CommunicationA 0 Mathematics as Problem SolvingA Measurement

Science Standards

A 0 History and Nature of ScienceA Physical ScienceA 0 Science and TechnologyA 0 Science as InquiryA 0 Unifying Concepts and Processes

There are three temperature scales commonly usedin the world. The Kelvin scale, the Celsius tempera-ture scale, and the Fahrenheit scale. The SI unit fortemperature is the kelvin. In most scientific laborato-ries. temperatures are measured and recorded inkelvins or degrees Celsius. The Celsius scale is usedfor weather reporting in most of the world. TheUnited States and some other countries use theFahrenheit scale for weather reporting.

The Kelvin scale is defined around the triple point ofwater (solid ice, liquid water, and water vapor coexistin thermal equilibrium) which is assigned the temper-ature 273.16 K. This is equal to 0.01°C and 32.02°F.Absolute zero, the coldest anything can get, is 0 K,273.15°C, and -459.67°F.

Questions for DiscussionHow do you convert between these different tem-perature scales?What are the boiling and freezing points of wateron all these scales, at I atm pressure?

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One of the important issues in condensed matterphysics,is the nature of the interface betweensolids and fluids. The boundary conditions at thisinterface have an influence on macroscopic phe-nomena, including wetting. The microscopicaspects of the system near the boundary are diffi-cult to study. However, when the fluid is near acritical point, the boundary layer adjacent to thesolid surface acquires a macroscopic thickness.Research under microgravity conditions permitsthe study of not only the influence of the bound-aries on thermodynamic properties, but also trans-port properties such as heat and mass transport.One of the most dramatic advancements in atom-ic physics over the last decade has been thedemonstration that laser light can be used to coola dilute atomic sample to within micro- or evennano-degrees of absolute zero. At these low tem-peratures, the mean velocity of the atoms dropsfrom several hundred rn/s to cm/s or mm/s, areduction by four to five orders of magnitude.When atoms are moving this slowly, measurementsof atomic properties can be made more preciselybecause the atoms stay in a given point in spacefor a longer time. In this regime, the effects ofgravity dominate atomic motion so experimentsperformed in a microgravity environment wouldallow even more precise measurements.

Among the most important goals of such researchis the improvement of ultra-high precision clocks.These clocks not only provide the standard bywhich we tell time, but are crucial to the way wecommunicate and navigate on Earth, in the air,and in space. Laser cooled atoms have signifi-cantly improved the accuracy and precision ofclocks because these atoms move very slowlyand they remain in a given observation volume forvery long times. However, observation times inthese clocks are still affected by gravity. Becauseof the effects of gravity, the atoms used in theseclocks ultimately fall out of the observation regiondue to their own weight. Increased observationtimes are possible in microgravity and can result

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in further improvements in precision of at leastone or two orders of magnitude.

Indeed, clocks are central to the study of generalrelativity and in questions concerning the verynature of gravity itself. The motivation for spacebased clocks is not only tied to the improved per-formance expected in a microgravity environmentbut also these clocks will have access to differentpositions in space than are available on Earth. Animportant example of this physics is revealed inthe comparison of an Earth-based clock with aspace-based clock. This comparison provides adirect measurement of the gravitational redshift.Tests of Einstein's theories of relativity and ofother theories of gravitation serve as a foundationfor understanding how matter and space-timeitself behave at large length scales and underextreme conditions. The freefall environment oforbit, the use of low temperature techniques, andthe use of high precision frequency standardsoffer opportunities to perform improved tests ofthese theories. Direct tests of gravitation theoriesand other fundamental theories, including the Lawof Universal Gravitation, can be performed in amicrogravity environment.

Materials Science

Materials science is an extremely broad field thatencompasses the study of all materials. Materialsscientists seek to understand the formation, struc-ture, and properties of materials on variousscales, ranging from the atomic to microscopic tomacroscopic (large enough to be visible).Establishing quantitative and predictive relation-ships between the way a material is produced(processing), its structure (how the atoms arearranged), and its properties is fundamental to thestudy of materials.

Materials exist in two forms: solids and fluids.Solids can be subdivided into two categoriescrystalline and noncrystalline (amorphous)

Properties

Structure Processing

Many materials scientists use a triangle such asthis to describe the relationship between struc-ture, processing, and properties. Microgravitycan play an important role in establishing therelationships in a quantitative and predictivemanner



Science Standards

A CIA CIA CI

Physical ScienceScience and TechnologyUnifying Concepts and Processes

A semiconductor is a substance, such as germaniumand silicon, that is a poor electrical conductor at roomtemperature but is improved by minute additions ofcertain substances (dopants) or by the application ofheat, light, or voltage; a material with a forbiddenenergy gap less than 3 eV.

VideoCamera /

Pyrometer

process Chamber

SuspendedSample

TO POMrCe

Heating Cods Positioning Coils

Schematic of the Electromagnetic ContainerlessProcessing Facility (TEMPUS) used on Shuttlemissions STS-65 and STS-83.

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based on the internal arrangement of their atomsor molecules. Metals (such as copper, steel, andlead), ceramics (such as aluminum oxide andmagnesium oxide), and semiconductors (suchas silicon and gallium arsenide) are all crystallinesolids because their atoms form an ordered inter-nal structure. Most polymers (such as plastics)and glasses are amorphous solids, which meansthat they have no long range specifically orderedatomic or molecular arrangement.

.0ne principal objective of microgravity materialsscience research is to gain a better understandingof how gravity-driven phenomena affect the solidi-fication and crystal growth of materials.Buoyancy-driven convection, sedimentation, andhydrostatic pressure can create defects (irregular-ities) in the internal structure of materials, whichin turn alter their properties.

The virtual absence of gravity-dependent phenom-ena in microgravity allows researchers to studyunderlying events that are normally obscured bythe effects of gravity and which are therefore diffi-cult or impossible to study quantitatively on Earth.For example, in microgravity, where buoyancy-driven convection is greatly reduced, scientists cancarefully and quantitatively study segregation, aphenomenon that influences the distribution of asolid's components as it forms from a liquid or gas.

Microgravity also supports an alternativeapproach to studying materials called container-less processing. Containerless processing has anadvantage over normal processing in that contain-ers can contaminate the materials beingprocessed inside them. In addition, there aresome cases in which there are no containers thatwill withstand the very high temperatures and cor-rosive environments needed to work with certainmaterials. Containerless processing, in whichacoustic, electromagnetic, or electrostatic forcesare used to position and manipulate a sample,thereby eliminating the need for a container, is anattractive solution to these problems.


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Furthermore, microgravity requires much smallerforces to control the position of containerlesssamples, so the materials being studied are notdisturbed as much as they would be if they werelevitated on Earth.

Materials science research in microgravity leads toa better understanding of how materials areformed and how the properties of materials areinfluenced by their formation. Researchers areparticularly interested in increasing their funda-mental knowledge of the physics and chemistry ofphase changes (when a material changes fromliquid to solid, gas to solid, etc.). This knowledge isapplied to designing better process-control strate-gies and production facilities in laboratories onEarth. In addition, microgravity experimentation willeventually enable the production of limited quanti-ties of high-quality materials and of materials thatexhibit unique properties for use as benchmarks.

Microgravity researchers are interested in study-ing various methods of crystallization, includingsolidification (like freezing water to make icecubes), crystallization from solution (the way rockcandy is made from a solution of sugar andwater), and crystal growth from the vapor (likefrost forming in a freezer). These processes allinvolve fluids, which are the materials that aremost influenced by gravitational effects.Examining these methods of transforming liquidsor gases into a solid in microgravity givesresearchers insight into other influential process-es at work in the crystallization process.

Electronic MaterialsElectronic materials play an important role in theoperation of computers, medical instruments,power systems, and communications systems.Semiconductors.are well-known examples of elec-tronic materials and are a main target of micro-gravity materials science research. Applicationsinclude creating crystals for use in X-ray, gamma-ray, and infrared detectors, lasers, computerchips, and solar cells. Each of these devices

Temperature Gradient

Sample

Cold zonesolid portion of sample

Hot zonemeltedportionof sample

melt ertracting growthestablished to grow complete

crystal

Schematic diagram of a multizone furnace usedto grow semiconductor materials on the Shuttle.A mechanism moves an existing crystal throughthe temperature zones, melting the sample thencooling it so that it solidifies. In other furnacedesigns, the heating mechanism moves and thesample is stationary What are the advantagesand disadvantages of each approach?

Microgravity A Teacher's Guide with Activitiesi science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0) 39


A 0A

A

Mathematical ConnectionsPatterns and FunctionsGeometryGeometry from a Synthetic Perspective

Science Standards

A 0 Earth and Space ScienceA CI Physical ScienceA Science and TechnologyA 0 Unifying Concepts and Processes

Schematic of silicon dioxide tetrahedra. The topview is of a crystalline ordered structure. Thebottom view is of a disordered glassy solid.

Questions for DiscussionWhat is an ordinary drinking glass made from?What different things are added to glass to changeits properties?What natural processes produce glasses?What are the differences between how glasses andcrystalline solids fracture?

40

depends on the ability to manipulate the crys-talline and chemical structure (perfection) of thematerial, which can be strongly influenced bygravity as crystals are formed.

The properties of electronic materials are directlyrelated to the degree of chemical and crystallineperfection present in the materials. However, per-fect crystals are not normally the ultimate goal.For example, the presence of just a few impuritiesin some electronic materials can change their abil-ity to conduct electricity by over a million times. Bycarefully controlling crystalline defects and theintroduction of desirable impurities to the crystals,scientists and engineers can design better elec-tronic devices with a wide range of applications.

Glasses and CeramicsA glass is any material that is formed without along range ordered arrangement of atoms. Somematerials that usually take crystalline forms, likemetals, can also be forced to form as glasses byrapidly cooling molten materials to a temperaturefar below their normal solidification point. Whenthe material solidifies, it freezes so quickly that itsatoms or molecules do not have time to arrangethemselves systematically.

Ceramics are inorganic nonmetallic materials thatcan be extraordinarily strong at very high temper-atures, performing far better than metallic sys-tems under certain circumstances. They will havemany more applications when important funda-mental problems can be solved. If a ceramic tur-bine blade, for example, could operate at hightemperatures while maintaining its strength, itwould provide overall thermodynamic efficienciesand fuel efficiencies that would revolutionizetransportation. The problem with ceramics is thatwhen they fail, they fail catastrophically, breakingin an irreparable manner.

Glasses and ceramics are generally unable toabsorb the impacts that metals can; instead, theycrack under great force or stress (whereas metals


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (Li)

generally bend before they break). An importantpart of ceramics and glass research in microgravi-ty involves controlling the minute flaws that gov-ern how these materials fail. From informationobtained through microgravity research, scientistshope to be able to control the processing ofceramics so that they can, during processing,prevent the formation of imperfections that lead tocatastrophic failure.

Applications for knowledge obtained throughresearch in these areas include improving glassfibers used in telecommunications and creatinghigh-strength, abrasion-resistant crystallineceramics used for gas turbines, fuel-efficient inter-nal combustion engines, and bioceramic artificialbones, joints, and teeth.

Metals and AlloysMetals and alloys constitute an important catego-ry of engineered materials. These materialsinclude structural materials, many types of com-posites, electrical conductors, and magneticmaterials. Research in this area is primarily con-cerned with advancing the understanding of met-als and alloys processing so that structure and,ultimately, properties, can be controlled as thematerials are originally formed. By removing theinfluence of gravity, scientists can more closelyobserve influential processes in structure forma-tion that occurs during solidification. The proper-ties of metals and alloys are linked to theircrystalline and chemical structure; for example,the mechanical strength and corrosion resistanceof an alloy are determined by its internal arrange-ment of atoms, which develops as the metal oralloy solidifies from its molten state.

One aspect of the solidification of metals andalloys that influences their microstructures is theshape of the boundary, or interface, that existsbetween a liquid and a solid in a solidifying mater-ial. During the solidification process, as the rate ofsolidification increases under the same thermalconditions, the shape of the solidifying interface

Science Standards

A CI Physical ScienceA 3 Science and TechnologyA ZI Unifying Concepts and Processes

An alloy is a combination of two or more metals.

Magnification of a sample of an aluminum-indium alloy. When the sample is melted thencontrollably solidifies in the AGHE the indiumforms in cylindrical fibers within a solid alu-minum matrix.




GeometryGeometry from an Algebraic PerspectiveGeometry from a Synthetic PerspectiveMathematical ConnectionsMathematics as Communication

Science Standards

A Ll Physical ScienceA 01 Unifying Concepts and Processes

One of the important characteristics of a solid is itsshape. On a visible scale, the function of somesolids may depend on the ability to sit in a stablemanner on a surface or to fit tightly into some config-uration. On a smaller scale, the structures of crys-talline solids are defined by the ordered placement ofatoms. The basis of understanding crystalline struc-ture and the shapes of solids is a knowledge of thedefinitions of two-dimensional shapes (polygons) andthree-dimensional solids (polyhedra).

A simple k-sided polygon is defined by connectingk points in a plane with line segments such that noedges intersect except at the defining points (vertices).The sum of the angles in any polygon equals2x(k-2)x90°. Specific names given to some simplepolygons are given below.

Name # of Sides (k)triangle 3

quadrilateral 4pentagon 5

hexagon 6heptagon 7octagon 8

nonagon 9decagon 10undecagon 11

dodecagon 12

Regular polygons are those for which all the sides arethe same length and all the angles are the same. Theangles of a regular polygon are defined by13=(k-2)x180°/k.

Questions for DiscussionDiscuss special cases of triangles and quadrilateralssuch as isosceles triangles, parallelograms,trapezoids.What is the common name for a regular triangle?For a regular quadrilateral?Is there a general equation for the area of anypolygon?

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has been shown to go through a series of transi-tions. At low rates of growth, the interface is pla-nar (flat or smoothly curved on a macroscopicscale). As the rate of growth increases, the inter-face develops a corrugated texture until threedimensional cells (similar in shape to the cells ina beehive but much smaller) form in the solid. Afurther increase in the rate of growth causes theformation of dendrites. The development of thesedifferent interface shapes and the transition fromone shape to another is controlled by the morpho-logical stability (shape stability) of the interface.This stability is influenced by many factors.Gravity plays an important role in a number ofthem. In particular, buoyancy-driven convectioncan influence the stability and, thus, the shape ofthe solidifying interface. Data obtained about theconditions under which certain types of solidifica-tion boundaries appear can help to explain theformation of the crystalline structure of a material.

Another area of interest in metals and alloysresearch in microgravity is multiphase solidifica-tion. Certain materials, which are known as eutec-tics and monotectics, transform from a singlephase liquid to substances of more than onephase when they are solidified. When these mate-rials are processed on Earth, the resultant sub-stances have a structure that was influenced bygravity either due to buoyancy-driven convectionor sedimentation. But when processed in micro-gravity, theory predicts that the end productshould consist of an evenly dispersed, multiphasestructure.

Eutectic solidification is when one liquid, of uni-form composition, forms with two distinct solidphases. An example of such a material is thealloy manganese-bismuth. Solidifying liquid Mn-Biresults in two different solids, each of which has achemical composition that differs from the liquid.One solid (the minor phase) is distributed as rods,particles, or layers throughout the other solid (acontinuous matrix, or major phase).


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (D)

Monotectics are similar to eutectics, except that amonotectic liquid solidifies to form a solid and a liq-uid (both of which are different in composition fromthe original liquid). Al-In is a monotectic that startsout as indium dissolved completely in aluminum,but when the alloy is solidified under the appropri-ate conditions, it forms a solid aluminum matrixwith long thin "rods" of liquid indium inside it. Asthe system cools, the rods of liquid indium freezeinto solid rods. The indium rods are dispersed with-in the structure of the solidified material.

PolymersPolymers are macromolecules (very large mole-cules) made up of numerous small repeatingmolecular units called monomers. They appearnaturally in wool, silk, and rubber and are manu-factured as acrylic, nylon, polyester, and plastic.Polymers are typically composed of long chains ofmonomers, appearing on the molecular scale as ifthey had a spine of particular elements such ascarbon and nitrogen. The bonding between indi-vidual polymer molecules affects the material'sphysical properties such as surface tension, mis-cibility, and solubility. Manipulation of these bondsunder microgravity conditions may lead to thedevelopment of processes to produce polymerswith more uniform and controlled specific proper-ties. Important optoelectronic and photonic appli-cations are emerging for polymers, and many ofthe properties needed are affected by the poly-mers' crystallinity. This crystallinity, which is theextent to which chains of molecules line up witheach other when the polymer is formed, may bemore easily understood and controlled whenremoved from the influence of gravity.

Growing polymer crystals is more difficult thangrowing inorganic crystals (such as metals andalloys) because the individual polymer moleculesweigh more and are more struCturally complex,which hinders their ability to attach to a growingcrystal in the correct position. Yet in microgravity,the process of polymer crystal growth can be

Regular polyhedra (or the Platonic Solids) are listedand shown below.

Nametetrahedroncubeoctahedrondodecahedronicosahedron

Formed By4 triangles6 squares8 triangles12 pentagons20 triangles

The Five Regular Polyhedra or Platonic SolidsTop-Tetrahedron; second row left-Cube; second rowright- Octahedron; third row left-Dodecahedron;third row right-lcosahedron.

Questions for DiscussionWhat do you think of as a cylinder and cone?What are the general definitions of cylinderand cone?What shapes are some mineral samples you have inyour classroom?Investigate the crystalline structure of halite (rocksalt), fluorine, quartz, diamond, iron.


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NASA's Enterprise for the HumanExploration and Development of Space

The goals of this Enterprise are toIncrease human knowledge of nature'sprocesses using the space environment,Explore and settle the Solar System,Achieve routine space travel,Enrich life on Earth through people livingand working in space.

Microgravity research will contribute to theareas of cryogenic fuel management, space-craft systems, in-situ resource utilization,power generation and storage, life support,fire safety, space structures, and scienceexploration.

Elemental Percent Weight on Earthand Moon

Earth's Crust Lunar HighlandSoils

0 47 45Fe 5 5Si 28 21Mg 2 4Ca 4 11Al 8 13

Na 3 03 0

44

studied in a fundamental way, with special atten-tion to the effects of such variables as tempera-ture, compositional gradients, and the size ofindividual polymer units on crystal growth. Inaddition, just as microgravity enables the growthof larger protein crystals, it may allow researchersto grow single, large polymer crystals for use instudying properties of polymers and determiningthe effects of crystal defects on those properties.

Microgravity Research andExploration

There is one endeavor for which microgravityresearch is essential. That is the goal of exploringnew frontiers of space and using the Moon andMars as stepping stones on our journey. Toachieve these goals, we must design effective lifesupport systems, habitation structures, and trans-portation vehicles. To come up with workabledesigns, we must have a thorough understandingof how the liquids and gases that we need to sus-tain human, plant, and animal life can beobtained, transported, and maintained; of howstructural materials can be formed in-situ (onsite); and of what types of fuels and fuel deliverysystems would allow us to get around most effi-ciently. Microgravity research can provide theinsight needed to get us on our way.

The ability to use extraterrestrial resources is akey element in the exploration of the solar sys-tem. We believe that we can use the Moon as aresearch base to develop and improve processesfor obtaining gases and water for human lifesupport and plant growth; for creating buildingmaterials; and for producing propellants and otherproducts for transportation and power generation.Oxygen extracted from lunar rocks and soils willbe used for life support and liquid oxygen fuel. Abyproduct of the extraction of oxygen from lunarminerals may be metals and semiconductors suchas magnesium, iron, and silicon. Metals producedon the Moon and material mined from the surface


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (ID)

will then be used for construction of habitats, suc-cessive processing plants, and solar cells.

Current research in the areas of microgravity sci-ence will guide our path as we develop the meansto use the Moon as a stepping stone to Mars.Research into how granular materials behaveunder reduced gravity conditions will be importantwhen we design equipment to mine and movelarge amounts of lunar material. The ability toextract gases and metals from minerals requiresan understanding of how gases, liquids, andsolids of different densities interact in lunar gravi-ty. Building blocks for habitats and other struc-tures can be made from the lunar regolith.Research into sedimentation and sintering underreduced gravity conditions will lead to appropriatemanufacturing procedures. Experiments havealready been performed on the Space Shuttle todetermine how concrete and mortar mixes andcures in microgravity. An understanding of fluidflow and combustion processes is vital for all thematerials and gas production facilities that will beused on the Moon and beyond.

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Science Standards

A 0 Earth and Space ScienceA 0 Physical Science

Regolith is a layer of powder-like dust and looserock that rests on bedrock. In the case of the moon,fragmentation of surface rocks by meteorite bom-bardment created much of the regolith material.

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Skylab, America's first space station.

46

MicrogravityScience SpaceFlightsUntil the mid-20th century, gravity was anunavoidable aspect of research and technology.During the latter half of the century, the use ofdrop towers to reduce the effects of gravitybecame more prevalent, although the extremelyshort periods of time they provided (<6 seconds)severely restricted the type of research that couldbe performed.

Initial microgravity research centered around solv-ing space flight problems created by the reductionin gravity's effects experienced on orbit. How doyou get the proper amount of fuel to a rocketengine in space or water to an astronaut on aspacewalk? The brief periods of microgravity avail-able in drop towers at the Lewis Research Centerand the Marshall Space Flight Center were suffi-cient to answer these basic questions and todevelop the pressurized systems and other newtechnologies needed to cope with this new envi-ronment. But, they still were not sufficient to inves-tigate the host of other questions that were raisedby having gravity as an experimental variable.

The first long-term opportunities to explore micro-gravity and conduct research relatively free of theeffects of gravity came during the latter stages ofNASA's first great era of discovery. The Apolloprogram presented scientists with the chance totest ideas for using the space environment forresearch in materials, fluid, and life sciences. Thecurrent NASA microgravity program had its begin-ning in experiments conducted in the later flightsof Apollo, the Apollo-Soyuz Test Project, andonboard Skylab, America's first space station.

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"It 'I"Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (cI)

Preliminary microgravity experiments conductedduring the 1970's were severely constrained,either by the relatively low power levels and spaceavailable on the Apollo spacecraft, or by the lownumber of flight opportunities provided to Skylab.These experiments, as simple as they were, pro-vided new insights into the roles of fluid and heatflows in materials processing. Much of our under-standing of the physics underlying semiconductorcrystal growth, for example, can be traced back toresearch initiated on Skylab.

Since the early 1980's, NASA has sent crews andpayloads into orbit on board the Space Shuttle.The Space Shuttle has given microgravity scien-tists an opportunity to bring their experiments tolow-Earth orbit on a more regular basis. TheShuttle introduced significant new capabilities formicrogravity research: larger, scientifically trainedcrews; a major increase in payload volume andmass and available power; and the return to Earthof all instruments, samples, and data. TheSpacelab module, developed for the Shuttle bythe European Space Agency, gives researchers alaboratory with enough power and volume to con-duct a limited range of sophisticated microgravityexperiments in space.

Use of the Shuttle for microgravity researchbegan in 1982, on its third flight, and continuestoday on many missions. In fact, most Shuttlemissions that aren't dedicated to microgravityresearch do carry microgravity experiments assecondary payloads.

The Spacelab-1 mission was launched inNovember 1983. The primary purpose of the mis-sion was to test the operations of the complexSpacelab and its subsystems. The 71 microgravityexperiments, conducted using instruments fromthe European Space Agency, produced manyinteresting and provocative results. One investiga-tor used the travelling heater method to grow acrystal of gallium antimonide doped with tellurium(a compound useful for making electronic The Spacelab module in the Orbiter Cargo Bay.



The first Spacelab mission dedicated to UnitedStates microgravity science on USML-1. Thecoast of Florida appears in the background.

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devices). Due to the absence of gravity-drivenconvection, the space-grown crystal had a farmore uniform distribution of tellurium than couldbe achieved on Earth. A second investigator usedmolten tin to study diffusion in low gravityresearch that can improve our understanding ofthe solidification of molten metals.

Another Shuttle mission using the Spacelab mod-ule was Spacelab-3, which flew in April 1985.SL-3 was the first mission to include U.S.-developed microgravity research instruments inthe Spacelab. One of these instruments support-ed an experiment to study the growth of crystalsof mercury iodidea material of significant inter-est for use as a sensitive detector of X-rays andgamma rays. Grown at a high rate for a relativelyshort time, the resulting crystal was as good asthe best crystal grown in the Earth-based labora-tory. Another U.S. experiment consisted of aseries of tests on fluid behavior using a sphericaltest cell. The microgravity environment allowedthe researcher to use the test cell to mimic thebehavior of the atmosphere over a large part ofEarth's surface. Results from this experimentwere used to improve mathematical models of ouratmosphere.

In October 1985, NASA launched a Spacelabmission sponsored by the Federal Republic ofGermany, designated Spacelab-D1. American andGerman scientists conducted experiments to syn-thesize high quality semiconductor crystals usefulin infrared detectors and lasers. These crystalshad improved properties and were more uniformin composition than their Earth-grown counter-parts. Researchers also successfully measuredcritical properties of molten alloys.

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International Microgravity Laboratory-1,January 1992More than 220 scientists from the United Statesand 14 other countries contributed to the experi-ments flown on the first International MicrogravityLaboratory (IML-1) in January 1992. Severalbiotechnology experiments concerned with pro-tein crystal growth enabled NASA scientists tosuccessfully test and compare two different crys-tal-growing devices.

A German device called the Cryostat producedsuperior-quality crystals of proteins from severalmicroorganisms including the satellite tobaccomosaic virus (STMV), which has roles in diseasesaffecting more than 150 crop plants. As a result ofthis experiment, scientists now have a much clear-er understanding of the overall structure of STMV.This information is useful in efforts to developstrategies for combating viral damage to crops.

IML-1 also carried experiments designed to probehow microgravity affects the internal structure ofmetal alloys as they solidify. The growth charac-teristics, determined from one of the experiments,matched the predictions of existing models, pro-viding experimental evidence that currenthypotheses about alloy formation are correct.

United States Microgravity Laboratory-1,June 1992In June 1992 the first United States MicrogravityLaboratory (USML-1) flew aboard a 14-day shut-tle mission, the longest up to that time. ThisSpacelab-based mission was an important step ina long-term commitment to build a microgravityprogram involving government, academic, andindustrial researchers.

The payload included 31 microgravity experi-ments using some facilities and instruments fromprevious flights, including the Protein CrystalGrowth facility, a Space AccelerationMeasurement System, and the Solid Surface

Payload Commander Bonnie J. Dunbar andPayload Specialist Lawrence J. De Lucas work-ing in the Spacelab module on USML-1.


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Science Standards

Earth and Space ScienceHistory and Nature of SciencePhysical ScienceUnifying Concepts and Processes

Questions for DiscussionWhat are Cd, Hg, Te, Zn?What do these elements have in common?

Hint: Look at their position on the periodic table ofthe elements.

Fission sequence of a rotating levitated drop.

50

Combustion Experiment. New experiment facili-ties, all designed to be reusable on future mis-sions, included the Crystal Growth Furnace(CGF), a Glovebox provided by the EuropeanSpace Agency, the Surface Tension DrivenConvection Experiment apparatus (STDCE), andthe Drop Physics Module.

Investigators used the CGF to grow crystals offour different semiconductor materials at tempera-tures as high as 1260°C. One space-grownCdZnTe crystal developed far fewer imperfectionsthan even the best Earth-grown crystals, resultsthat far exceeded pre-flight expectations. Thincrystals of HgCdTe grown from the vapor phasehad mirror-smooth surfaces even at high magnifi-cations. This type of surface was not observed onEarth-grown crystals.

Researchers used the STDCE apparatus toexplore how internal movements of a liquid arecreated when there are spatial differences in tem-perature on the liquid's surface. The results are inclose agreement with advanced theories and mod-els that the experiment researchers developed.

In the Drop Physics Module, sound waves wereused to position and manipulate liquid droplets.Surface tension controlled the shape of thedroplets in ways that confirmed theoretical predic-tions. The dynamics of rotating drops of siliconeoil also conformed to theoretical predictions.Experimental and theoretical results of this kindare significant because they illustrate an impor-tant part of the scientific method: hypotheses areformed and carefully planned experiments areconducted to test them.

Sixteen different investigations run by NASAresearchers used the Glovebox, which provided asafe enclosed working area; it also was equippedwith photographic equipment to provide a visualrecord of investigation operations. The Gloveboxallowed crew members to perform protein crystal-lization studies as they would on Earth, including

6 oMicrogravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,

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procedures that require hands-on manipulation.Among other results, use of the Glovebox provid-ed the best-ever crystals of malic enzyme thatmay be useful in developing anti-parasitic drugs.

The burning of small candles in the Glovebox pro-vided new insights into how flames can exist in anenvironment in which there is no air flow. Theresults were similar (though much longer lived) towhat can be seen by conducting similar experi-ments in freefall here on Earth. (See CandleFlames in Microgravity, in the Activities section ofthis guide.) The candles burned for about 45 to 60seconds in the Glovebox experiments.

Another Glovebox investigation tested how wireinsulation burns under different conditions, includ-ing in perfectly still air (no air flow) and in air flow-ing through the chamber from different directions.This research has yielded extremely importantfundamental information and also has practicalapplications, including methods for furtherincreasing fire safety aboard spacecraft.

The crew of scientist astronauts in the Spacelabplayed an important role in maximizing the sci-ence return from this mission. For instance, theyattached a flexible type of glovebox, which provid-ed an extra level of safety, to the Crystal GrowthFurnace. The furnace was then opened, previous-ly processed samples were removed and an addi-tional sample was inserted. This enabled anotherthree experiments to be conducted. Two otherunprocessed samples were already in the furnace.

Spacelab-J,September 1992The Spacelab-J (SL-J) mission flew in September1992. SL-J was the first Space Shuttle missionshared by NASA and Japan's National SpaceDevelopment Agency (NASDA). NASA microgravi-ty experiments focused on protein crystal growthand collecting acceleration data in support of themicrogravity experiments.

Zeolite crystals can be grown in the GloveboxFacility. Shown here are photos (at the samescale) of zeolite crystals grown on USML-1(top) and on Earth (bottom).

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USMP experiments are mounted on MissionPeculiar Equipment Support Structures in theShuttle Cargo Bay.

52

NASDA's science payload consisted of 22 experi-ments focused on materials science and thebehavior of fluids, and 12 human biology experi-ments. NASDA also contributed two experimentfacilities. One of these, the Large IsothermalFurnace, was used to explore how variousaspects of processing affect the structure andproperties of materials. The second apparatuswas a Free-Flow Electrophoresis Unit used toseparate different types of molecules in a fluid.

United States Microgravity Payload-1,October 1992The first United States Microgravity Payload(USMP-1) flew on a 10-day Space Shuttle mis-sion launched on October 22, 1992. The missionwas the first in an ongoing effort that employstelescience to conduct experiments on a carrier inthe Space Shuttle Cargo Bay. Telescience refersto how microgravity experiments can be conduct-ed by scientists on the ground using remotecontrol.

The carrier in the Cargo Bay consisted of twoMission Peculiar Equipment Support Structures.On-board, the two Space AccelerationMeasurement Systems measured how crewmovements, equipment operation, and thruster fir-ings affected the microgravity environment duringthe experiments. This information was relayed toscientists on the ground, who then correlated itwith incoming experiment data.

A high point of USMP-1 was the first flight ofMEPHISTO, a multi-mission collaborationbetween NASA-supported scientists and Frenchresearchers. MEPHISTO (designed and built bythe French Space Agency, Centre Nationald'Etudes Spatiales or CNES) is designed to studythe solidification process of molten metals andother substances. Three identical samples of onealloy (a combination of tin and bismuth) weresolidified, melted, and resolidified more than 40times, under slightly different conditions each

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (6), 9-12 (0)

time. As each cycle ended, data were transmittedfrom the Space Shuttle to Marshall Space FlightCenter. There, researchers analyzed the informa-tion in combination with data from the SpaceAcceleration Measurement System and sent backcommands for adjustments. In all, the investiga-tors relayed more than 5000 commands directlyto their instruments on orbit. Researchers com-pared experiment data with the predictions of the-oretical models and showed that mathematicalmodels can predict important aspects of theexperiment behavior. This first MEPHISTO effortproved that telescience projects can be carriedout efficiently, with successful results.

The lambda point for liquid helium is the combina-tion of temperature and pressure at which normalliquid helium changes to a superfluid. On Earth,effects of gravity make it virtually impossible tomeasure properties of substances very close tothis point. On USMP-1, the Lambda PointExperiment cooled liquid helium to an extremelylow temperaturea little more than 2 K aboveabsolute zero. Investigators measured changes inits properties immediately before it changed froma normal fluid to a superfluid. Performing the testin microgravity yielded temperature measure-ments accurate to within a fraction of one billionthof a degreeseveral hundred times more accu-rate than would have been possible in normalgravity. Overall the new data were five times moreaccurate than in any previous experiment.

United States Microgravity Payload-2,March 1994The second United States Microgravity Payload(USMP-2) flew aboard the Space ShuttleColumbia for 14 days from March 4 to March 18,1994. Building on the success of telescience inUSMP-1, the Shuttle Cargo Bay carried four pri-mary experiments which were controlled byapproximately 10,000 commands relayed by sci-entists at Marshall Space Flight Center. USMP-2also included two Space AccelerationMeasurement Systems, which provided scientists

Science and mission management teams monitorand control experiments from operations centersworldwide.

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A dendrite grown in the Isothermal DendriticGrowth Experiment aboard the USMP-2.This is an example of how most metals solidify

Science Standards

A 0 Physical ScienceA 1 Unifying Concepts and Processes

Dendrites are branching structures that develop as amolten metal solidifies under certainconditions. The root of this word is the Greek den-dron, meaning tree. Branching structures in biology(nerve cells) and geology (drainagesystems) are also referred to as being dendritic.

54

on the ground with nearly instant feedback onhow various kinds of motionincluding crew exer-cise and vibrations from thruster enginesaffect-ed mission experiments. The Orbital AccelerationResearch Experiment in the Cargo Bay collectedsupplemental data on acceleration, providing anindication of the quasi-steady acceleration levelsexperienced by the experiments.

Throughout the mission, the Critical Fluid LightScattering Experimentnicknamed Zenoanalyzed the behavior of the element xenon as itfluctuated between two different states, liquid andgas. First, a chamber containing liquid xenon washeated. Then, laser beams were passed throughthe chamber as the xenon reached temperaturesnear this transition point. A series of measure-ments were taken of how the laser beams werescattered (deflected) as the xenon shifted fromone state to another. Researchers expected thatperforming the experiment on orbit would providemore detailed information about how a substancechanges phase than could be obtained on Earth.In fact, the results produced observations morethan 100 times more precise than the best mea-surement on the ground.

The Isothermal Dendritic Growth Experiment(IDGE) examined the solidification of a materialthat is a well-established model for metals. Thismaterial is especially useful as a model becauseit is transparent, so a camera can actually recordwhat happens inside a sample as it freezes. In 59experiments conducted during 9 days, over 100television images of growing dendrites were sentto the ground and examined by the researchteam. Dendritic growth velocities and tip radii ofcurvature were measured. Results obtained undercertain experiment conditions were not consistentwith current theory. This inconsistency was thesubject of subsequent research on USMP-3. Inanother successful demonstration of telescience,the team relayed more than 200 commands to theIDGE, fine-tuning its operations.



USMP-2 also included a MEPHISTO experiment.On this mission, the MEPHISTO apparatus wasused for U.S. experiments to test how gravityaffects the formation of crystals from an alloy ofbismuth and tin that behaves much like a semi-conductor during crystal growth. Metallurgicalanalysis of the samples has shown that interac-tions between the molten and solid alloy duringcrystallization play a key role in controlling thefinal morphological stability of the alloy.

Another USMP-2 materials science experimentused the Advanced Automated DirectionalSolidification Furnace (AADSF). An eleven dayexperiment using the AADSF yielded a large,well-controlled sample of the alloy semiconductor,HgCdTe. The results of various analysis tech-niques performed on the crystal indicate that vari-ations in the acceleration environment had amarked effect (due to changing residual fluid flow)on the final distribution of the alloy's componentsin the crystal.

40 International Microgravity Laboratory-2,July 1994The second International Microgravity Laboratory(IML-2), with a payload of 82 major experiments,flew in July 1994 on the longest Space Shuttleflight to that time. IML-2 truly was a world classventure, representing the work of scientists fromthe U.S. and 12 other countries.

Materials science experiments focused on varioustypes of metals processing. One was sintering, aprocess that can combine different metals byapplying heat and pressure to them. A series ofthree sintering experiments expanded the use inspace of the Japanese built Large IsothermalFurnace, first flown on SL-J. It successfully sin-tered alloys of nickel, iron, and tungsten.

Other experiments explored the capabilities of aGerman-built facility called TEMPUS. It wasdesigned to position molten metal experiment

Representations of different shapes of the liquid-solid inteiface in a solidifying material: a) pla-nar, b) cellular, and c) dendritic. More informa-tion about intetface morphology is provided inthe Metals and Alloys discussion in theMaterials Science section of this publication.

6 5,Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,

EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (1:1)55


lD Conceptual Underpinnings of Calculus101 Functions

A 01 Mathematical ConnectionsA Patterns and Functions

Science Standards

A 01 Earth and Space ScienceA 01 Physical ScienceA 01 Science and TechnologyA 01 Science in Personal and Social PerspectivesA CI Unifying Concepts and Processes

A gradient is the variation of a quantity such as tem-perature, pressure, or concentration with respect to agiven parameter, typically distance. A temperaturegradient can have dimensions of temperature perlength, for example, °C/cm.

56

samples (molten drops) away from the surfaces ofa container in order to eliminate processing sideeffects of containers. Experiments of four U.S. sci-entists were successfully completed, and theresearch team developed improved proceduresfor managing multi-user facilities.

One of the experiments used a clever approach tomeasure two important thermophysical propertiesof molten metals. While a spherical drop of moltenmetal was positioned in a containerless mannerit was momentarily distorted by using electromag-netic forces to squeeze it. When the squeezingwas released, the droplet began to oscillate. Thesurface tension of the molten metal was deter-mined from the frequency of the oscillation. Theoscillation gradually decayed. The rate at whichthe decay occurred was used to determine theviscosity of the molten material.

Biotechnology experiments were performed usingthe Advanced Protein Crystallization Facility,developed by the European Space Agency. Thefacility's 48 growth chambers operated unattend-ed throughout the flight, producing high-qualitycrystals of nine proteins. High-resolution videocameras monitored critical crystal growth experi-ments, providing the research team with a visualrecord of the processes. U.S. investigators usedthe Bubble, Drop, and Particle Unit to study howtemperature gradients in the liquids influence themovement and shape of gas bubbles and liquiddrops. The Critical Point Facility enabledresearchers to study how a fluid behaves at itscritical point. Research using the Critical PointFacility is applicable to a broad range ofscientific questions, including how variouscharacteristics of solids change under differentexperimental conditions.

6 6


United States Microgravity Laboratory-2,October 1995The second United States MicrogravityLaboratory (USML-2) launched on October 20,1995 for a mission with more than 16 days onorbit. During that time microgravity research wasconducted around-the-clock in the areas of biotech-nology, combustion science, fluid physics, andmaterials science. It was a perfect example of inter-active science in a unique laboratory environment.

Along with investigations that previously flew onUSML-1, several additional experiment facilitiesflew on USML-2. Fourteen protein crystal growthexperiments in the Advanced ProteinCrystallization Facility had varied results that pro-vided more insight into the structures of some ofthe proteins and into optimal experiment condi-tions. The goal of the Geophysical Fluid Flow Cellexperiment was to study how fluids move inmicrogravity as a means of understanding fluidflow in oceans, atmospheres, planets, and stars.The results of the studies of fluid movement andvelocity are still being analyzed.

Four separate studies were performed in theCrystal Growth Furnace (CGF). The goals of theexperiments were to investigate quantitatively thegravitational influences on the growth and qualityof the compound semiconductor, CdZnTe, usingthe seeded, modified Bridgman-Stockbarger crys-tal growth technique; to investigate techniques foruniformly distributing a dopant, selenium, duringthe growth of GaAs crystals; to understand theinitial phase of the process of vapor crystalgrowth of complex, alloy-type semiconductors(HgCdTe); and to test the integration of a currentinduced interface demarcation capability into theCGF system and to assess the influences of achange in Shuttle attitude on a steady-stategrowth system using the demonstrated capabili-ties of the interface demarcation technique.

Earth Environment

Force off ! rMg.1_5N:rental

; ---))

Microgravity Environment

Force of

Gravrtyr Radial

E amental

Gravitational force acting on spherical planetarymodels on Earth and in a microgravity environment

In the Geophysical Fluid Flow Cell, electriccharges, electrostatic force, and heaters areused to simulate buoyancy forces, radial gravity,and heating patterns in planetary atmospheres.As shown in the diagram, attempts to use spher-ical models on Earth are hampered by the forceof Earth's gravity acting perpendicular to thesphere's rotation (indicated by the large curvingarrow around the sphere's equator). In micro-gravity, this problem is removed.

Science Standards

Physical ScienceScience and TechnologyScience in Personal and Social PerspectivesUnifying Concepts and Processes

A dopant is an impurity intentionally added toa pure semiconductor to alter its electronic oroptical properties.

6 7


57

Science Standards

Physical ScienceScience and TechnologyScience in Personal and Social PerspectivesUnifying Concepts and Processes

A surfactant is a substance added to a liquid tochange its surface tension. Surfactants are used inexperiments where a liquid must wet its container ina particular way. A common use of surfactants isdishwashing detergent. The surfactant properties ofthe detergent is what causes food grease and oil toseparate from most household dishware.

58

Two investigators had experiments conducted inthe Drop Physics Module. The Science andTechnology of Surface-Controlled PhenomenaExperiments had three major goals: to determinethe surface properties of liquids in the presenceof surfactants; to investigate the dynamic behav-ior and the coalescence of droplets coated withsurfactant materials; and to study the interactionsbetween droplets and acoustic waves. Theshapes of oscillating drops recorded on videotapewere analyzed frame by frame, revealing the vari-ations of the oscillation amplitude with time. Thefrequency and damping constant of the dropletshape oscillations were calculated. Analysis of theresults is ongoing.

The goals of the Drop Dynamics Experiment wereto gather high-quality data on the dynamics ofliquid drops in microgravity for comparison withtheoretical predictions and to provide scientificand technical information needed for the develop-ment of new fields, such as containerless pro-cessing of materials and polymer encapsulationof living cells. The experiments on the USML-2mission included breaking one drop into twodrops (bifurcation) and positioning a drop of oneliquid at the center of a drop of a different liquid.Preliminary results show that the acoustic levita-tion technique has a strong influence on the dropbifurcation process.

Seven investigations were performed in theGlovebox on USML-2. These studies examinedvarious aspects of fluid behavior, combustion, andcrystal growth. Two separate devices were usedfor protein crystal growth experiments.

The Surface Tension Driven ConvectionExperiment investigated the basic fluid mechanicsand heat transfer of thermocapillary flows gener-ated by temperature variations along free sur-faces of liquids in microgravity. It determinedwhen and how oscillating flows were created._Preliminary analysis indicates that current theo-retical models used to predict the onset of oscilla-tions are consistent with the experiment results.



The USML-2 Zeolite Crystal Growth experimentattempted to establish a quantitative understand-ing of zeolite crystallization to allow control ofboth crystal defect concentration and crystallitesize. The preliminary conclusions indicate that,with few exceptions, the crystals from USML-2are larger in size than their Earth-grown counter-parts and are twice as large as those grown onprevious Shuttle flights. Analysis will continue todetermine the effect of space processing on crys-tal defect concentration.

The projects that measured the microgravity envi-ronment added to the success of the mission byproviding a complete picture of the Shuttle's envi-ronment and its disturbances. The OrbitalAcceleration Research Experiment (OARE) pro-vided real-time quasi-steady acceleration data tothe science teams. The Microgravity AnalysisWorkstation (MAWS) operated closely with theOARE instrument, comparing the environmentmodels produced by the MAWS with the actualdata gathered by the OARE. Two other instru-ments, the Space Acceleration MeasurementSystem and the Three Dimensional MicrogravityAccelerometer, took g-jitter measurementsthroughout the mission. The Suppression ofTransient Events by Levitation demonstrated avibration isolation technology that may be suitablefor experiments that are sensitive to variations inthe microgravity environment.

United States Microgravity Payload-3,February 1996The third United States Microgravity Payloadmission launched on February 22 for 16 days ofresearch on orbit. During that time, microgravityresearch was conducted in the areas of combus-tion science, fluid physics, and materials science.The ultimate benefit of USMP-3 research will beimprovements in products manufactured on Earth.During the eight and one-half days dedicated tomicrogravity science, researchers used tele-science to control materials processing and ther-modynamic experiments in the Cargo Bay and

Science Standards

A CI Physical ScienceA CI Science and TechnologyA 0 Science in Personal and Social PerspectivesA CI Unifying Concepts and Processes

Zeolites are hydrous aluminum silicate mineralswhich also contain cations of sodium, potassium, cal-cium, strontium, barium, or a synthetic compound.They are commonly used as molecular filters. Forexample, they are used to make every drop of gaso-line sold in the United States.

.g

-Et

.r.

0.5 -

0.5

1.0Time (sec)

20

The change in acceleration character seen inthe middle of this plot is due to a crew memberswinging an experiment container around to mixits contents. Examination of the plot indicatesthat the crew member swung his arm aroundseven to eight times in ten seconds.

6 9


59

Vibration Frequencies Commonly Seen inOrbiter Accelerometer Data

Freq. (Hz) Disturbance Source

0.43 cargo bay doors3.5 Orbiter fuselage torsion

3.66 structural frequency of Orbiter4.64 structural frequency of Orbiter

5.2 Orbiter fuselage normal bending7.4 Orbiter fuselage lateral bending17 Ku band antenna dither20 experiment air circulation fan22 refrigerator freezer compressor38 experiment air circulation fan

39.8 experiment centrifuge rotationspeed

43 experiment air circulation fan48 experiment air circulation fan53 experiment air circulation fan60 refrigerator piston compressor80 experiment water pump

166.7 Orbiter hydraulic circulationpump

60

astronauts performed combustion studies in theMiddeck Glovebox.

The MEPHISTO science team used flight-provenequipment to learn how the chemical compositionof solidifying Sn-Bi alloys changes, and can becontrolled, during solidification. Such knowledgeapplies to ground-based materials processing. Forthe first time, the changes in the microgravityenvironment caused by carefully planned Shuttlethruster firings were correlated with the effects offluid flows in a growing crystal. With the help ofdata from the Space Acceleration MeasurementSystem, the experiment data showed that withthruster accelerations parallel to the crystal-meltinterface a large effect was noted, whereas whenthruster accelerations were perpendicular to theinterface there was little impact. Also, theMEPHISTO team successfully monitored the pointat which their sample's crystal interface under-went a key changefrom flat to cellular (like threedimensional ripples)as it solidified.Measurements from the MEPHISTO facility willnow be analyzed, along with the final metallicsamples, in order to increase our understandingof subtle changes that occurred during the sam-ples' solidification and subsequent cooling.

In the Advanced Automated DirectionalSolidification Furnace, three lead tin telluride(PbSnTe) crystals were grown while Columbiaorbited in three different attitudes, to determinehow these orientations affect crystal growth. Thisknowledge is expected to help researchers devel-op processes, and semiconductor materials thatperform better and cost less to produce.

The Isothermal Dendritic Growth Experiment(IDGE) on USMP-3 achieved its mission objec-tives. After collecting data to answer some of thequestions opened by the USMP-2 results,research has shown that the small variations indendritic growth rates (how fast the tree-like solidpattern in a molten metal forms) measured inmicrogravity on the Space Shuttle are not due to


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 Go

variations in the microgravity environment onorbit. The investigators are currently completingmeasurements on the three-dimensional shape ofthese dendritic tips, which will further advance theempirical basis from which more accurate solidifi-cation models are being developed and tested.This is an early step in what will ultimately besolidification models that could be used to makeless expensive and more reliable cast or weldedmetal and alloy products.

The IDGE team also participated in an importanttechnology demonstration by commanding amicrogravity space instrument from a remote sitelocated at the Rensselaer Polytechnic Institute.This first-ever remote commanding to the Shuttlefrom a U.S. university campus foreshadows oper-ations aboard the International Space Station.

Investigators for the Critical Fluid Light ScatteringExperiment were successful in observing, withunprecedented clarity, xenon's critical pointbehaviorthe precise temperature and pressureat which it exists as both a gas and a liquid. Thetransparent xenon sample displayed the unusualcritical point condition, with maximum light scat-tering followed by a sudden increase in cloudi-ness. This effect was much more distinctive thanobserved during the USMP-2 mission and hap-pened at a lower temperature than expected.Knowledge gained from this experiment will provevaluable for applications from liquid crystals tosuperconductors.

This mission was the first flight of a Gloveboxfacility in the Middeck section of the Shuttle. Threecombustion science investigations were conduct-ed by the crew. The Forced Flow FlamespreadingTest burned 16 paper samples, both flat and cylin-drical. Video of the cylindrical samples showedsignificant differences in flame size, growth rate,and color with variations in air flow speed and fueltemperature. The Comparative Soot Diagnosticsinvestigation completed 25 combustion experi-ment runs. The team obtained excellent results,

As we move toward the era of the InternationalSpace Station, more experiment monitoring andcontrol is being petformed from NASA centersand university laboratories "remote" fromMarshall Space Flight Center and JohnsonSpace Center

Glovebox Investigation Module hardware.

Microgravity A Teacher's Guide with Activi7eslin Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)

The Space Shuttle Columbia, carrying the Lifeand Microgravity Spacelab, launched fromKennedy Space Center June 20, 1996.

62

testing the effectiveness of two different smoke-sensing techniques, for detecting fires aboard theShuttle and the International Space Station. TheRadiative Ignition and Transition to SpreadInvestigation team observed new combustionphenomena, such as tunneling flames whichmove along a narrow path instead of fanning outfrom the burn site. Also, for the first time, theseinvestigators studied the effects of sample edgesand corners on fire spreading in microgravity.

Life and Microgravity Spacelab,June 1996The Life and Microgravity Spacelab mission suc-cessfully completed a 17 day flight on July 6,1996. For this mission there was an unprecedent-ed distribution of teams monitoring their experi-ments around the world, with experiment com-manding performed from three sites.

A number of researchers conducted experimentsusing the Advanced Gradient Heating Facility(AGHF) from the European Space Agency. Threealuminum-indium alloys were directionally solidi-fied to study the physics of solidification process-es in immiscible alloys called monotectics. Thethree samples, which differed only in indium con-tent, were processed at the same growth rate topermit a comparison of microstructures, how theindium was distributed in the aluminum matrix.Two of these samples were of compositions whichcannot be processed under steady state condi-tions on Earth due to gravitationally-driven con-vective instabilities and subsequent sedimentationof the liquid indium.

Another AGHF experiment used commercial Al-based samples to obtain insight into the mecha-nism of particle redistribution during solidification.Additional studies were geared toward enhance-ment of the fundamental understanding of thedynamics of insoluble particles at solid/liquidinterfaces. The physics of the problem is of directrelevance to such areas as solidification of metal


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (c)

matrix composites, management of defects suchas inclusions and porosity in metal castings,development of high temperature superconductorcrystals with superior current carrying capacity,and the solidification of monotectics.

A series of experiments was performed in theAdvanced Protein Crystallization Facility. Theexperiments were generally successful in terms ofyielding crystals. Those crystals which showed .

particular promise, based on early microscopicexamination, were ferritin, satellite tobacco mosa-ic virus, satellite panicum mosaic virus, lysozyme,and canavalin.

Several experiments were conducted using theBubble, Drop and Particle Unit (BDPU) from theEuropean Space Agency. In one experiment, thetransition to periodic and chaotic convection wasdetected. The results of this experiment will trig-ger ground based research on the nonlineardynamics of convecto-diffusive systems. In anoth-er experiment, thermocapillary flows in two andthree layer systems were observed for five tem-perature gradients. The results of this experimentwill improve our understanding of heat and masstransfer in other fluid physics research.

An additional experiment studied the interactionbetween pre-formed gas bubbles inside-a solidand a moving solid/liquid interface, obtained byheating an initially solid sample. Early results con-cerning the release of bubbles from the meltingfront indicate that once a hole has been made andthe gas inside the bubble contacts the liquid thenthe liquid enters the cavity (by wetting the solidwalls) and pushes out the gas inside the bubble.

The scientific results of one set of BDPU experi-ments provide us with new insights into bubbledynamics and into evaporation. This will lead to abetter understanding and modeling of steam gen-eration and boiling. Initial findings of anotherexp-eiiment showed that, under microgravity condi-tions, boiling heat transfer is still as efficient as

Magnification of a sample of an aluminum-indium alloy. When the sample is melted thencontrollably solidifies in the AGHF, the indiumforms in cylindrical fibers within a solidaluminum matrix.

7 3


63

Schematic diagram of Space Shuttle Orbiterdocked to Mir.

64

under normal Earth gravity. In contrast to the exist-ing theory the findings show that the influence ofEarth gravity is less than predicted. The heattransfer in a microgravity environment is still asefficient, sometimes even more efficient than, atnormal gravity.

Real-time Orbital Acceleration ResearchExperiment data were used by the science teamsto monitor the microgravity environment duringtheir experiment operations. The effects of mis-sion activities, such as venting of unneeded waterand Orbiter orientation changes, were presentedto help the science teams understand the envi-ronment in which their experiments operated. TheMicrogravity Measurement Assembly (MMA) usedthis mission to verify a new system, augmentedby a newly developed accelerometer for measur-ing the quasi-steady range. MMA provided real-time quasi-steady and g-jitter data to the scienceteams during the mission.

Shuttle/Mir Science Program,March 1995 to May 1998Although competition in the space program hasexisted between the United States and Russia forsome time, there has also been a rich history ofcooperation that has grown into the highly suc-cessful joint science program that it is today. Onepart of that program is geared towards microgravi-ty research.

Many of the investigations from that program areconfigured to run in a Glovebox facility that hasbeen installed in the Priroda research module ofthe Mir Space Station. The Microgravity IsolationMount (MIM) is also located in Priroda. The MIMwas developed by the Canadian Space Agency toisolate experiments attached to it from ongoingg-jitter. The MIM is also able to induce definedvibrations so that the effects of specific distur-bances on experiments can be studied. Additionalexperiments are being performed in individualexperiment facilities that have been placed in thePriroda and other Mir modules.


EG-1997-08-110-HQ, Education Standards Grades 5-8 (6), 9-12 (c)

Various protein crystal growth experiments usethe Gaseous Nitrogen Dewar (GN2 Dewar).Samples are placed in the GN2 Dewar and it ischarged with liquid nitrogen, freezing them. Thesystem is designed so that the life of the nitrogencharge lasts long enough to get the payloadlaunched and into orbit. As the system absorbsheat, the nitrogen boils away and the chamberapproaches ambient temperature. As the samplesthaw, crystals start growing in the Dewar. Thecrystals are allowed to form throughout the longduration mission and are returned to Earth foranalysis. Initial investigations using the Dewarserved as a proof of concept for the experimentfacility. Successive experiment runs using differentsamples will continue to improve our knowledgeof protein crystal structures.

The Diffusion-Controled Crystallization Apparatusfor Microgravity experiment is designed primarilyfor the growth of protein crystals in a microgravityenvironment. It uses the liquid/liquid and dialysismethods in which a precipitant solution diffusesinto a bulk solution. In the experiment, a smallprotein sample is covered by a semipermeablemembrane that allows the precipitant solution topass into the protein solution to initiate the crys-tallization process. Diffusion starts on Earth assoon as the chambers are filled. However, therate is so slow that no appreciable change occursbefore the samples reach orbit one or two dayslater. Such an apparatus is ideally suited for thelong duration Mir missions.

The Cartilage in SpaceBiotechnology Systemexperiment began with cell cultures being trans-ported to Mir by the Shuttle in September 1996on mission STS-79. The investigation is a test bedfor the growth, maintenance, and study of long-term on-orbit cell growth in microgravity. Theexperiment investigates cell attachment patternsand interactions among cell cultures as well ascellular growth and the cellular role in formingfunctional tissue.

75

Thaumatin Alpha Amylase

Creatine Kinase

Ribonuclease

STMV

,

RhombohedralCanavalin

Myoglobin Hemoglobin

Protein and virus crystals grown in theGN2 Dewar on Mir


65

The Biotechnology System-Cartilage in SpaceExperiment in orbit. Top: Astronauts Carl Walz(left) and Jay Apt prepare the experiment fortransfer from the middeck of the Space ShuttleAtlantis to the Priroda module of Mir Bottom:Walz and Apt test the bioreactor media for pH,carbon dioxide, and oxygen levels.

66

The Candle Flames in Microgravity investigationconducted 79 candle tests in the Glovebox in July1996. The experiments explored whether wickflames (candles) can be sustained in a purely dif-fusive environment or in the presence of a veryslow, sub-buoyant convective flow. An associatedgoal was to determine the effect of wick size andcandle size on burning rate, flame shape andcolor, and to study interactions between twoclosely spaced diffusion flames. Preliminary dataindicate long-term survivability with evidence ofspontaneous and prolonged flame oscillationsnear extinction (when the candle goes out).

The Forced Flow Flame Spreading Tests ran inthe Glovebox in early August 1996. The investiga-tions studied flames spreading over solid fuels inlow-speed air flows in microgravity. The effects ofvarying fuel thickness and flow velocity of flamesspreading in a miniature low-speed wind tunnelwere observed. The data are currently being ana-lyzed and compared to theoretical predictions offlame spreading. The numerical model predictedthat the flame would spread at a steady rate andwould not experience changes in speed, shape,size, or temperature.

The Interface Configuration Experiment Gloveboxinvestigation studied how a liquid with a free sur-face in contact with a container behaves in micro-gravity. This provides a basis for predicting thelocations and configurations of fluids with the useof mathematical models. The data are currentlybeing analyzed.

The Technological Evaluation of the MIM (TEM)was a technology demonstration to determine thecapabilities of the MIM. Through observations ofliquid surface oscillations, TEM evaluated the abil-ity of the MIM to impart controlled motions. Thedata are still being analyzed. A follow-on technol-ogy demonstration (TEM-2) was transferred to Mirin September 1996.

7 6


The Binary Colloidal Alloy Test Glovebox investi-gation was also launched to Mir on STS-79 inSeptember 1996. The objective is to conduct fun-damental studies of the formation of gels andcrystals from binary colloid mixtures.

The Angular Liquid Bridge and Opposed FlowFlame Spread Glovebox investigations were car-ried to Mir by the Shuttle on mission STS-81 inearly 1997. The former is an extension of previousfluid physics investigations conducted on theShuttle and Mir and studies the behavior andshape of liquid bridges, liquid that spans the dis-tance between two solid surfaces. The objectiveof the latter is to extend the understanding of themechanisms by which flames spread, or fail tospread, over solid fuel surfaces in the presence ofan opposing oxidizer flow.

A Space Acceleration Measurement System(SAMS) unit was launched to Mir on a Progressrocket in August 1994. Starting in October 1994,the SAMS was used to measure and characterizethe microgravity environment of various 1M mod-ules in support of microgravity experiments.Between October 1994 and September 1996,SAMS collected about sixty gigabytes of accelera-tion data. The data have been used to identifycommon vibration sources, as has been donewith the Shuttles. This information has helpedexperimenters plan the timing and location of theirexperiments. The Passive Accelerometer Systemis a simple tool that is being used to estimate thequasi-steady microgravity environment of Mir dur-ing the increment between STS-79 and STS-81.The motion of a steel ball in a water-filled glasstube is tracked and the distance travelled overtime is used to estimate accelerations caused byatmospheric drag and the location of the tubewith respect to Mir's center of gravity.

77

Vibration Frequencies Commonly Seen inMir Accelerometer Data

Freq. (Hz) Disturbance Source

0.6 Kristall structural mode1.0 Kristall structural mode1.1 structural mode1.2 structural mode1.3 Kristall structural mode1.9 Kristall structural mode

2.75 structural mode3.75 structural mode

15 air quality system24.1 humidifier/dehumidifier

30 air quality system harmonic41 fan

43.5 fan45 air quality system harmonic90 air quality system harmonic

166.6 gyrodyne (system used tomaintain Mir orientation)


67

This illustration depicts the International SpaceStation in its completed and fully operationalstate with elements from the United States,Europe, Canada, Japan, and Russia.

68

Future DirectionsMicrogravity science has come a long way sincethe early days of space flight when researchersrealized that they might be able to take advantageof the reduced gravity environment of orbitingspacecraft to study different phenomena. Shuttleand Mir based experiments that study biotechnol-ogy, combustion science, fluid physics, fundamen-tal physics, and materials science have openedthe doors to a better understanding of many ofthe basic scientific principles that drive much ofwhat we do on Earth and in space.

To reach the next level of understanding aboutphenomena in a microgravity environment, weneed to perform experiments for longer periods oftime, to be able to conduct a series of experi-ments as is done on Earth, and to have improvedenvironmental conditions. The International SpaceStation is being developed as a microgravityresearch platform. Considerable attention hasbeen given to the design of the station and exper-iment facility components so that experiments canbe performed under high-quality microgravity con-ditions. The International Space Station will pro-vide researchers with continuous, controlledmicrogravity conditions for up to thirty days at atime. (The time in between these thirty day incre-ments is used for vibration-intensive activitiessuch as Shuttle dockings, station reconfiguration,and upkeep.) This is almost twice as long as themicrogravity periods available on the SpaceShuttle and there will be a better environmentthan that provided by Mir. This increase in experi-ment time and improvement in conditions will beconducive to improved understanding of micro-gravity phenomena.

Continued microgravity research on the Shuttles,Mir, and on the International Space Station willlead to, among other things, the design of

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improved drugs, fire protection and detection sys-tems, spacecraft systems, high-precision clocks,and semiconductor materials. In addition, thisresearch will allow us to create outposts on theMoon where we can build habitats and researchfacilities. The end result of research in microgravi-ty and on the Moon will be the increased knowl-edge base necessary for our trips to andexploration of Mars.

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (Ia)

69

GlossaryAccelerationThe rate at which an object'svelocity changes with time.

AltitudeHeight above Earth's mean sealevel.

Apparent WeightThe net sum of allforces acting on a body is its apparentweight.

BiotechnologyAny technique thatinvolves the research, manipulation, andmanufacturing of biological molecules, tis-sues, and living organisms to improve orobtain products, or perform specific func-tions.

Buoyancy-Driven ConvectionConvection created by the difference indensity between two or more fluids in agravitational field.

CapillarityThe attraction a liquid has foritself versus the attraction it has for a solidsurface, such as the liquid's container.

Combustion ScienceThe study of theprocess of burning.

ConcaveCurved inward like the inner sur-face of a sphere.

ConvectionEnergy and/or mass transferin a fluid by means of bulk motion of thefluid.

ConvexCurved like the outer surface of asphere.

Critical PointThe temperature at whichthe differences between liquids and gases

disappear. Above that temperature, the liq-uid smoothly transforms to the gaseousstate; boiling disappears.

DendritesBranching structures that devel-op as a molten metal solidifies under cer-tain conditions.

DensityThe mass of a body divided by itsvolume (average density).

DifferentiationThe process by which cellsand/or tissues undergo a progressive spe-cialization of form or function.

DiffusionIntermixing of atoms and/or mol-ecules in solids, liquids, and gases due toa difference in composition.

DopantAn impurity intentionally added toa pure semiconductor to alter its electronicor optical properties.

Drop FacilityResearch facility that cre-ates a microgravity environment by permit-ting experiments to freefall through anenclosed vertical tube.

FluidAnything that flows (liquid or gas).

Fluid PhysicsThe study of the propertiesand motions of liquids, gases, and fluid-likesolids.

ForceAn action exerted,upon a body inorder to change its state, either of rest, orof uniform motion in a straight line.

FreefallFalling in a gravitational fieldwhere the acceleration is the same as thatdue to gravity alone.



Fundamental PhysicsThe study of sev-eral physics subfields, including studieswhere interaction forces are weak, whereextremely uniform samples are required,where objects must be freely suspendedand their acceleration must be minimized,and where mechanical disturbances thatare unavoidably present in Earth-boundlaboratories must be eliminated.

GUniversal Gravitational Constant(6.67x10-1i N rn2/kg2).

gThe acceleration Earth's gravitationalfield exerts on objects at Earth's surface(approximately 9.8 meters per secondsquared).

g-jitterThe vibrations experienced bymicrogravity experiments (for example onparabolic aircraft and the Space Shuttle)that cause effects similar to those thatwould be caused by a time-varyinggravitational field.

GradientThe variation of a quantity suchas temperature with respect to a givenparameter, typically distance, °C/cm.

GravitationThe attraction of objects dueto their masses.

HomogeneousUniform in structureand/or composition.

ImmiscibleThe situation where two ormore liquids do not mix chemically.

InertiaA property of matter that causes itto resist changes in velocity.

72

Joule HeatingHeating a material by flow-ing an electric current through it.

Law of Universal GravitationA law stat-ing that every mass in the universe attractsevery other mass with a force proportionalto the product of their masses and inverse-ly proportional to the square of the dis-tances between their centers.

Materials ScienceThe study of develop-ing quantitative and predictive relationshipsbetween the processing, structure, andproperties of materials.

Microgravity (pg)An environment inwhich the apparent weight of a system issmall compared to its actual weight (due togravity).

MorphologyThe form and structure of anobject.

NucleusA source upon which something,such as a crystal, grows or develops.

Quasi-steady AccelerationAccelerationsin spacecraft related to the position in thespacecraft, aerodynamic drag,_and vehiclerotation.

RegolithA layer of powder-like dust andloose rock that rests on bedrock. In thecase of the moon, fragmentation of surfacerocks by meteorite bombardment createdmuch of the regolith material.

RheologyThe scientific study of the defor-mation and flow of matter.

81

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HO, Education Standards Grades 5-8 (A), 9-12 CD)

SatelliteA natural or man-made objectthat orbits a celestial body.

SemiconductorA substance, such asgermanium and silicon, that is a poor elec-trical conductor at room temperature but isimproved by minute additions of certainsubstances (dopants) or by the applicationof heat, light, or voltage; a material with aforbidden energy gap less than 3 eV.

SkylabNASA's first orbital laboratory thatwas operated in 1973 and 1974.

SpacelabA scientific laboratory developedby the European Space Agency that is car-ried into Earth orbit in the Space Shuttle'spayload bay.

SpeedThe magnitude of velocity.

SurfactantA substance added to a liquidto change its surface tension.

VelocityThe rate at which the position ofan object changes with time; it is a vectorquantity.

WeightThe weight of an object is thegravitational force exerted on it by Earth.

,8 2


73

ActivitiesActivity Matrix 76

Microgravity In The Classroom 79

Accelerometers 88

Around The World 95

Inertial Balance 101

Gravity-Driven Fluid Flow 109

Surface Tension-Driven Flows 114

Temperature Effects on Surface Tension 119

Candle Flames 124

Candle Flames in Microgravity 129

Crystallization Model 135

Crystal Growth and Buoyancy-Driven Convection Currents 141

Rapid Crystallization 148

Microscopic Observation of Crystal Growth 152

Zeolite Crystal Growth 159

83


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Accelerometers

Around The World

Inertial Balance

Gravity-Driven Fluid Flow

Surface Tension-Driven Flows

Temp. Effects on Surface

Candle Flames

Candle Flames in Microgravity

Crystallization Model

Crystal Growth and Buoy

Rapid Crystallization

Microscopic Observation of

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Microgravity A Teacher's Guide with Actia5 in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)

77

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Microgravity In The ClassroomObjective:

To demonstrate how microgravity iscreated by freefall.

Science Standards:Science as InquiryPhysical Scienceposition and motion of objects

Change, Constancy, & Measurement- evidence, models, & exploration

Science Process Skills:ObservingCommunicatingMaking ModelsDefining OperationallyInvestigatingPredicting

Mathematics Standards:Computation & EstimationMeasurement

Activity Management:This activity consists of threedemonstrations that create microgravityconditions by freefall. Although the firstdemonstration is best done by theteacher, the other demonstrations can bedone as activities by students working ingroups of three or four.

Each demonstration requires a clearspace where drop tests can beconducted. Two of the demonstrationsrequire water and you should have a mop,sponges, or paper towels available toclean up any mistakes.

Begin with the Falling Weight apparatusteacher demonstration. Before droppingthe device, conduct a discussion with thestudents to consider possible outcomes.Ask students to predict what they think

Various objects demonstrate microgravity asthey are dropped.

COJ00i-0ZittCDJ4CCIliF<2

Falling weight apparatus(see special instructions)

Plastic cupSmall cookie sheet or

plastic cutting boardEmpty soft drink canNail or some other punchCatch basin - plastic dish

pan, bucket, large wastebarrel

Mop, paper towels, orsponges for cleanup

will happen when the device isdropped. Students will focus on theproximity of the balloon and theneedle. Will the balloon break whenthe device is dropped? If the balloon

8 goes break, will it break immediately or

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HO, Education Standards Grades 5-8 (A), 9-12 (0)

79

when the device hits the floor? Try to getstudents with different predictions to debateeach other. After the debate, drop thedevice. Be sure to hold the wooden frameby the middle of the top cross piece. Hold itout at arm's length in case the weight andneedle bounce your way.

Discuss the demonstration to make sure thestudents understand why the balloonpopped when it did. Before trying any of theother demonstrations, student groupsshould read the student reader entitledMicrogravity.

The second and third demonstrations canalso be done by the teacher or by smallgroups of students. One student drops ortosses the test item and the other studentsobserve what happens. Students shouldtake turns observing.

Assessment:Have students write a paragraph or two thatdefine microgravity and explain how freefallcreates it.

80

Extensions:1. Videotape the demonstrations and play

back the tape a frame at a time. Sinceeach second of videotape consists of 30frames, the tape can be used as a simpletiming device. Count each frame as one-thirtieth of a second.

2. Replace the rubber bands in the fallingweight apparatus with heavy string anddrop the apparatus again to see whetherthe balloon will break. Compare theresults of the two drops.

3. Conduct a microgravity science field tripto an amusement park that has rollercoasters and other rides that involvequick drops. Get permission for thestudents to carry accelerometers on therides to study the gravity environmentsthey experience. On a typical roller-coaster ride, passengers experiencenormal g (gravity), microgravity, high g,and negative g.

8 7


Student Reader 1

Gravity is an attractive force that all objectshave for one another. It doesn't matterwhether the object is a planet, a cannonball,a feather, or a person. Each exerts agravitational force on all other objectsaround it.

The amount of force between two objectsdepends upon how much mass eachcontains and the distance between theircenters of mass. For example, an applehanging from a tree branch will have lessgravitational force acting on it than when ithas fallen to the ground. The reason for thisis because the center of mass of an apple,when it is hanging from a tree branch, isfarther from the center of mass of Earth thanwhen lying on the ground.

Although gravity is a force that is alwayswith us, its effects can be greatly reduced bythe simple act of falling. NASA calls thecondition produced by falling microgravity.

You can get an idea of how microgravity iscreated by looking at the diagram below.Imagine riding in an elevator to the top floorof a very tall building. At the top, the cablessupporting the car break, causing the carand you to fall to the ground. (In thisexample, we discount the effects of airfriction on the falling car.) Since you and theelevator car are falling together, you feel likeyou are floating inside the car. In otherwords, you and the elevator car areaccelerating downward at the same rate dueto gravity alone. If a scale were present,your weight would not register because the

scale would be falling too.The ride is lots of fun untilyou get to the bottom.

Normalweight

Heavierthan normal

Lighterthan normal

No apparentweight

The person in the stationary elevator car experiences normalweight. In the car immediately to the right, weight increases slightlybecause of the upward acceleration. Weight decreases slightly inthe next car because of the downward acceleration. No weight ismeasured in the last car on the right because of freefall.

NASA uses several differentstrategies for conductingmicrogravity research. Eachstrategy serves a differentpurpose and produces amicrogravity environmentwith different qualities. Oneof the simplest strategies isthe use of drop towers. Adrop tower is like a high-techelevator shaft. A smallexperiment package issuspended from a latch atthe top. The packagecontains the experiment,television or movie cameras,and a radio or wire totransmit data during the test.For some drop towers, whenthe test is ready, air from the

Microgravity A Teacher's Guide with Activities in Akice, Mathematics, and Technology,EG-1997-08-110-HO, Education Standards Grades 5-8 (A), 9-12 (0)

81

Student Reader - 2

shaft is pumped out so the package will fallmore smoothly. The cameras; recordingequipment, and data transmitter are turnedon as a short countdown commences.When T minus zero is reached, the packageis dropped.

NASA has several drop tower facilitiesincluding the 145 meter drop tower at the,NASA Lewis Research Center in Cleveland,Ohio. The shaft is 6.1 meters in diameterand packages fall 132 meters down to acatch basin near the shaft's bottom. For

10.51x10-3g (5-15 sec)14--

For the first few seconds of the pull up, theexperiments and experimenters onboard theairplane feel a gravity force of about two timesnormal. During the upper portion of the parabola,microgravity is produced that ranges from one one-hundredth to one one-thousandth of a g. Duringthe pull out, the gravity force again reaches abouttwo times normal.

5.2 seconds, the experiment experiences amicrogravity environment that is about equalto one one-hundred-thousandth (1x10-5) ofthe force of gravity experienced when thepackage is at rest.

If a longer period of microgravity is needed,NASA uses a specially equipped jet airplanefor the job. Most of the plane's seats have

82

been removed and the wall, floor, andceiling are covered with thick paddingsimilar to tumbling mats.

One of the advantages of using an airplaneto do microgravity research is thatexperimenters can ride along with theirexperiments. A typical flight lasts 2 to 3hours and carries experiments and crewmembers to a beginning altitude about 7kilometers above sea level. The planeclimbs rapidly at a 45-degree angle (pull up)and follows a path called a parabola. Atabout 10 kilometers high, the plane startsdescending at a 45-degree angle backdown to 7 kilometers where it levels out (pullout). During the pull up and pull outsegments, crew and experimentsexperience a force of between 2 g and2.5 g. The microgravity experienced on theflight ranges between one one-hundredthand one one-thousandth of a g. On a typicalflight, 40 parabolic trajectories are flown.The gut-wrenching sensations produced onthe flight have earned the plane thenickname of "Vomit Comet."

A parabola is the mathematical shape you getif you slice a cone in the way shownnin thepicture



Student Reader 3

Small rockets provide a thirdtechnology for creating microgravity.A sounding rocket follows a parabolicpath that reaches an altitudehundreds of kilometers above Earthbefore falling back. The experimentsonboard experience several minutesof freefall. The microgravityenvironment produced is about equalto that produced onboard fallingpackages in drop towers.

Although airplanes, drop facilities,and small rockets can be used toestablish a microgravity environment,all of these laboratories share acommon problem. After a fewseconds or minutes of low-g, Earthgets in the way and the freefallstops. When longer termexperiments (days, weeks, months,and years) are needed, it is necessary

Payload separation

J,f#9

High-g acceleration

Launch

Parabolic Trajectory

Microgravity

Deceleration

Telemetry

Recovery

Microgravity begins when the rocket arrives above Earth'satmosphere and the payload section is released.Microgravity ends when the payload falls back into theatmosphere and begins feeling atmospheric drag.

to travel into space and orbit Earth. We willlearn more about this later.

Experiment

MeasurementModule

Experiment

Experiment

Telemetry

:TOIL! g

Ogive RecoverySystem

ExperimentServiceModule

Umbilical AdapterRing

Experiment

Experiment

Rate Control System

flRocket MotorSolid Propellant

Typical design of a sounding rocket used formicrogravity research.

In a few years, it will be possible to conductsensitive microgravity experiments, lasting manymonths, on the International Space Station.



Falling WeightApparatus

-4 Screws

Construction:1. Assemble the rectangular supporting

frame as shown in the diagram. Be sureto drill pilot holes for the screws and gluethe frame pieces before screwing themtogether. Brace the front and back ofeach corner with small triangles of ply-wood. Glue and nail them in place.

2. Drill a 1/2 inch-diameter hole through thecenter of the top of the frame. Be surethe hole is free of splinters.

3. Twist the two screw eyes into the under-side of the top of the frame as shown inthe diagram. (Before doing so, check tosee that the metal gap at the eye is wideenough to slip a rubber band over it. Ifnot, use pliers to spread the gap slightly.)

84

MATERIALS NEEDED:2 pieces of wood 16x2x1 in.2 pieces of wood 10x2x1 in.4 wood screws (#8 or #10 by 2 in.)8 corner brace triangles from 1/4 in.

plywoodGlue2 screw eyes4-6 rubber bands1 6-oz fishing sinker or several

lighter sinkers taped togetherLong sewing needleSmall round balloons (4 in.)StringDrill, 1/2 in. bit, and bit for piloting

holes for wood screwsScrewdriverPillow or chair cushion(Optional - Make a second frame

with string supporting the sinker.)

4. Join three rubber bands together and thenloop one end through the metal loop of thefishing sinker.

5. Follow the same procedure with the otherthree rubber bands. The fishing weightshould hang downward like a swing, nearthe bottom of the frame as shown in theillustration. If the weight hangs near thetop, the rubber bands are too strong.Replace them with thinner rubber bands.If the weight touches the bottom, removesome of the rubber bands.

6. Attach the needle to the weight, with thepoint upward. There are several ways ofdoing this depending upon the design ofthe weight. If the weight has a loop forattaching it to fishing line, hold the needlenext to the loop with tape or low-tempera-ture hot glue. Another way of attachingthe needle is to drill a small hole on top ofthe weight to hold the needle.



Use:Inflate the balloon and tie off the nozzle with ashort length of string. Thread the stringthrough the hole and pull the balloon nozzlethrough. Pull the string snugly and tape it tothe top of the frame.

Demonstration:1. Place a pillow or cushion on the floor.

Hold the frame above the pillow orcushion at shoulder level.

2. Ask the students to predict what willhappen when the entire frame is dropped.

3. Drop the entire unit onto the cushion.The balloon will pop almost immediatelyafter release.

9 2

Explanation:When stationary, the lead fishing weightstretches the rubber bands so the weighthangs near the bottom of the frame. Whenthe frame is dropped, the whole apparatusgoes into freefall. The microgravity producedby the fall removes the force the fishingweight is exerting on the rubber bands. Sincethe stretched rubber bands have no force tocounteract their tension, they pull theweightwith the needleup toward theballoon, causing it to pop. (In fact, thesinker's acceleration toward the balloon willinitially be zero due to the energy released asthe rubber bands relax to their normal,unstretched length.) If a second frame, withstring instead of rubber bands supporting theweight, is used for comparison, the needlewill not puncture the balloon as the devicefalls because the strings will not rebound likethe rubber bands did.

In tests of this device using a televisioncamera and videotape machine as a timer(see extensions), the balloon was found topop in about 4 frames which is equal to four-thirtieths of a second or 0.13 seconds. Usingthe formula for a falling body (see below), itwas determined that the frame dropped onlyabout 8 centimeters before the balloonpopped. This was the same as the distancebetween the balloon and the needle beforethe drop.

d =1

at22

d = Lix 9.8 m/s2 x ( 0.13s )2 = 0 .08m2

d is the distance of the fall in metersa is the acceleration of gravity in meters persecond squaredt is the time in seconds

Microgravity A Teachei's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (o)

85

Falling Water

Procedure:1. Place the catch basin in the center of an

open area in the classroom.2. Fill the cup with water.3. Place the cookie sheet over the opening

of the cup. Press the cup tight to thesheet while inverting the sheet and cup.

4. Hold the cookie sheet and cup highabove the catch basin. You may wish tostand on a sturdy table or climb on astepladder to raise the cup higher.

5. While holding the cookie sheet level,slowly slide the cup off the edge of thecookie sheet and observe what happens.

6. Refill the cup with water and invert it onthe cookie sheet.

7. Quickly pull the cookie sheet straight outfrom under the cup and observe the fallof the cup and water.

8. (Optional) Videotape the cup drop andplay back the tape frame-to-frame toobserve what happens to the water.

86

Plastic drinking cupCookie sheet (with at least one

edge without a rim)Catch basin (large pail, waste

basket)WaterChair or stepladder (optional)TowelsTelevision camera, videotape

recorder, and monitor (optional)

Explanation:Air pressure and surface tension keep thewater from seeping around the cup's edgeswhile it is inverted on the cookie sheet. If

the cup were slowly pushed over the edgeof the sheet, the water would pour out.However, when the sheet is quickly pulledout from under the filled cup, the cup andwater both fall at the same time. Since theyare both accelerated downward by gravityan equal amount, the cup and water falltogether. The water remains in the cup butthe lower surface of the water bulges.Surface tension tends to draw liquids intospherical shapes. When liquids are at rest,gravity overcomes surface tension, causingdrops to spread out. In freefall, gravity'seffects are greatly reduced and surfacetension begins to draw the water in the cupinto a sphere.



Can Throw

Procedure:1. Punch a small hole with a nail near the

bottom of an empty soft drink can.2. Close the hole with your thumb and fill the

can with water.3. While holding the can over a catch basin,

remove your thumb to show that thewater falls out of the can.

4. Close the hole again and stand backabout 2 meters from the basin. Toss thecan through the air to the basin, beingcareful not to rotate the can in flight.

5. Observe the can as it falls through the air.6. (Optional) Videotape the can toss and

play back the toss frame-to-frame toobserve the hole of the can.

Explanation:When the can is stationary, water easilypours out of the small hole and falls to thecatch basin. However, when the can istossed, gravity's effects on the can and itscontents are greatly reduced. The waterremains in the can through the entire fallincluding the upward portion. This is thesame effect that occurs on aircraft flying inparabolic arcs.

Empty aluminum soft drink canSharp nailCatch basinWaterTowelsTelevision camera, videotape

recorder, and monitor (optional)

9 4


87

88

AccelerometersObjective:

To measure the accelerationenvironments created by differentmotions.

Science Standards:Physical Science

position and motion of objectsUnifying Concepts and ProcessesChange, Constancy, & MeasurementScience and Technology- abilities of technological design

Science Process Skills:CommunicatingMeasuringCollecting Data

Mathematics Standards:CommunicationNumber & Number RelationshipsMeasurementComputation & Estimation

Activity Management:This activity provides students withthe plans for making a one-axisaccelerometer that can be used tomeasure acceleration in differentenvironments ranging from +3 g to-3 g. The device consists of atriangular shaped poster board boxthey construct with a lead fishingsinker suspended in its middle witha single strand of a rubber band.Before using the device, studentsmust calibrate it for the range ofaccelerations it can measure.

The pattern for making theaccelerometer box is included inthis guide. It must be doubled insize. It is recommended that

Students construct a device that can measureacceleration environments from +3 to -3 g.

Lightweight poster board(any color)

3 "drilled egg" lead fishingsinkers, 1 ounce size

Masking tapeRubber band, #19 size4 small paper clipsScissorsStraightedgeBallpoint penPatternHot glue (low temperature)

several patterns be available for thestudents to share. To save on materials,students can work in teams to make a singleaccelerometer. Old file folders can besubstituted for the poster board. Thestudent reader can be used at any timeduring the activity.



The instructions call for three egg (shaped)sinkers. Actually, only one is needed for theaccelerometer. The other two are used forcalibrating the accelerometer and can beshared between teams.

When the boxes are being assembled, thethree sides are brought together to form aprism shape and held securely with maskingtape. The ends should not be folded downyet. A rubber band is cut and one end isinserted into a hole punched into one of thebox ends. Tie the rubber band to a smallpaper clip. This will prevent the end of therubber band from sliding through the hole.The other end of the rubber band is slippedthrough the sinker first and then tied off atthe other end of the box with another paperclip. As each rubber band end is tied, thebox ends are closed and held with moretape. The two flaps on each end overlapthe prism part of the box on the outside. It islikely that the rubber band will need someadjustment so it is at the right tension. Thiscan be easily done by rolling one paper clipover so the rubber band winds up on it.When the rubber band is lightly stretched,tape the clip down.

After gluing the sinker in place on the rubberband, the accelerometer must be calibrated.The position of the sinker when the box isstanding on one end indicates theacceleration of 1 gravity (1 g). By making apaper clip hook, a second sinker is hungfrom the first and the new position of the firstsinker indicates an acceleration of 2 g. Athird sinker indicates 3 g. Inverting the boxand repeating the procedure yields positionsfor negative 1, 2, and 3 g. Be sure thestudents understand that a negative gacceleration is an acceleration in a directionopposite gravitys pull. Finally, the half wayposition of the sinker when the box is laid onits side is 0 g.

Students are then challenged to use theiraccelerometers to measure variousaccelerations. They will discover thattossing the device or letting it fall will causethe sinker to move, but it will be difficult toread the scale. It is easier to read if thestudents jump with the meter. In this case,they must keep the meter in front of theirfaces through the entire jump. Better stillwould be to take the accelerometer on a fastelevator, on a trampoline, or a roller coasterat an amusement park.

Assessment:Test each accelerometer to see that it isconstructed and calibrated properly. Collectand review the student sheets.

Extensions:1. Take the accelerometer to an amuse-

ment park and measure the accelerations

Magnetic AccelerometerThree ring magnets with like poles facing eachother.

you experience riding a roller coaster andother fast rides.

2. Construct a magnetic accelerometer.3. Design and construct an accelerometer

for measuring very slight accelerationssuch as those that might be encountered

9 6 on the Space Shuttle.

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (1=1)

89

Accelerometer Box Pattern

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Tephnology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)

Student Reader - 1

Accelert iAcceleration is the rate at which an object's velocity is changing. The changecan be in how fast the object is moving, a direction change, or both. If you aredriving an automobile and press down on the gas pedal (called the accelerator),your velocity changes. Let's say you go from 0 kilometers to 50 kilometers perhour in 10 seconds. Your acceleration is said to be 5 kilometers per hour persecond. In other words, each second you are going 5 kilometers per hour fasterthan the second before. In 10 seconds, you reach 50 kilometers per hour.

You feel this acceleration by being pressed into the back of your car seat. Actu-ally, it is the car seat pressing against you. Because of the property of inertia,your body resists acceleration. You also experience acceleration when there is achange in direction. Let's say you are driving again but this time at a constantspeed in a straight line. Then, the road curves sharply to the right. Withoutchanging speed, you make the turn and feel your body pushed into the left wallof the car. Again, it is actually the car pushing on you. This time, your accelera-tion was a change in direction. Can you think of situations in which accelerationis both a change in speed and direction?

The reason for this discussion on acceleration is that it is important to under-stand that the force of gravity produces an acceleration on objects. Imagine youare standing at the edge of a cliff and you drop a baseball over the edge. Gravityaccelerates the ball as it falls. The acceleration is 9.8 meters per second persecond. After 5 seconds, the ball is traveling at a rate of nearly 50 meters persecond. To create a microgravity environment where the effects of gravity on anexperiment are reduced to zero, NASA would have to accelerate that experiment(make it fall) at exactly the same rate gravity does. In practice, this is hard to do.When you jump into the air, the microgravity environment you experience isabout 1/100th the acceleration of Earth's gravity. The best microgravity environ-ment that NASA's parabolic aircraft can create is about 1/1000th g. On theSpace Shuttle in Earth orbit, microgravity is about one-millionth g. In practicalterms, if you dropped a ball there, the ball would take about 17 minutes just tofall 5 meters!

98


91

Student Work Sheet - 1

Accelerometer Constructionand Calibration

The instructions below are for making a measuring device called an accelerometer.Accelerometers are used to measure how fast an object changes its speed in one or moredirections. This accelerometer uses a lead weight suspended by a rubber band to sensechanges in an object's motion.

Building the Accelerometer:1. Trace the pattern for the accelerometer

on a piece of poster board. Cut out thepattern.

2. Use a ruler and a ballpoint pen to drawthe fold lines on the poster board in thesame place they are shown on thepattern. As you draw the lines, applypressure to the poster board. This willmake the poster board easier to fold.

3. Fold the two long sides up as shown inthe first illustration. The left side withthe tabs is folded over first. The rightside is folded second. This makes along triangle shape. Use tape to holdthe sides together.

4. Punch a small hole in one of the endtriangles. Cut the rubber band to makeone long elastic band. Tie one end of theband to a small paper clip. Thread theother end through the hole.

5. Slip the lead weight on the band. Puncha hole in the other end triangle. Whilestretching the band, slip the free endthrough the second hole and tie it to asecond paper clip.

6. Set the triangular box on its side so thewindow is up. Slide the weight so it is inthe middle of the elastic band. Put a dabof hot glue on each end of the weightwhere the elastic band enters the holes.

7. If the elastic band sags inside the box,roll the elastic around one of the paperclips until it is snug. Then tape the paperclip in place. Tape the other triangularend in place.

92

Fold this side first.The two flaps are onthe inside.

99

to hold.second and tapeFold this side

\VI



Fold ends after rubber band andweight are attached. The two flapson each end are folded to the outside.

Calibrating the Accelerometer:1. Stand the accelerometer on one end.

Using a pencil, mark one side of theaccelerometer next to the middle of theweight. Identify this mark as 1 g.

2. Using a small paper clip as a hook, hanga second weight on the first. Again, markthe middle of the first weight on theaccelerometer. Identify this mark as 2 g.Repeat this step with a third weight andidentify the mark as 3 g.

3. Remove the two extra weights and standthe accelerometer on its other end.Repeat the marking procedure andidentify the marks as -1 g, -2 g, and -3 g.

4. The final step is to mark the midwayposition between 1 and -1 g. Identify thisplace as 0 g. The accelerometer iscompleted.

-3

-2

-1

0

1

2

3

Finished Accelerometer



Student Work Sheet 3

Accelerometer TestsInstrument Construction Team:

Test your accelerometer by jumping in theair with it a few times. What happens to theposition of the sinker?

What g forces did you encounter in yourjumps?

Where else might you encounter g forceslike these?

Explain how your accelerometer measuresdifferent accelerations.

Design Activity:How can this accelerometer be redesigned so it is more sensitive to slight accelerations?Make a sketch of your idea below and write out a short explanation.

1 01



Around The WorldObjective:

To create a model of how satellitesorbit Earth.

Science Standards:Science as InquiryPhysical Science- position and motion of objectChange, Constancy, & Measurement

evidence, models, & exploration

Science Process Skills:ObservingCommunicatingMaking ModelsDefining OperationallyInvestigating

Mathematics Standards:CommunicationGeometry

Activity Management:This activity can be conducted as ademonstration or a small group activity ata learning station where student groupstake turns.

Pick a small ball to which it is easy toattach a string. A small slit can be cut intoa tennis ball or racquetball with a sharpknife. Then, a knotted string can beshoved through the slit. The slit will closearound the string. A screw eye can bescrewed into a solid rubber or wood balland a string attached to it.

If using this as an activity, have studentswork in groups of two. The large ball andflowerpot should be placed on the floor in

102

A ball on a string circles a ball to simulatethe orbits of satellites around Earth.

Large ball*Small ball2 meters of stringFlower pot*

* A world globe cansubstitute for the largeball and flower pot

an open area. Tell students toimagine the ball is Earth with its northpole straight up. One student willstand near the ball and pot and holdthe end of the string the small ball isattached to. This student's handshould be held directly over the largeball's north pole, and enough stringshould be played out so that the small


95

ball comes to rest where the large ball'sequator should be. While the first studentholds the string steadily the second studentstarts the small ball moving. The objective isto move the small ball in a direction and at aspeed that will permit it to orbit the big ball.

Save the student reader for use afterstudents have tried the activity.

Additionarinformation:This model of a satellite orbiting aroundEarth is effective for teaching somefundamentals of orbital dynamics. Studentswill discover that the way to orbit the smallball is to pull it outward a short distancefrom the large ball and then start it movingparallel to the large ball's surface. Thespeed they move it will determine where theball ends up. If the small ball moves tooslowly, it will arc "down" to Earth's surface.NASA launches orbital spacecraft in thesame way. They are carried above most ofEarth's atmosphere and aimed parallel toEarth's surface at a particular speed. Thespeed is determined by the desired altitudefor the satellite. Satellites in low orbits musttravel faster than satellites in higher orbits.

In the model, the small ball and stringbecome a pendulum. If suspended properly,the at-rest position for the pendulum is atthe center of the large ball. When the smallball is pulled out and released, it swingsback to the large ball. Although the realdirection of gravity's pull is down, the ballseems to move only in a horizontal direction.Actually, it is moving downward as well. Aclose examination of the pendulum revealsthat as it is being pulled outward, the smallball is also being raised higher off the floor.

96

The validity of the model breaks down whenstudents try orbiting at different distancesfrom the large ball without adjusting thelength of the string. To make the small ballorbit at a higher altitude without lengtheningthe string, the ball has to orbit faster than aball in a lower orbit. This is the opposite ofwhat happens with real satellites.

Assessment:Use the student pages for assessment.

Extensions:1. Investigate the mathematical equations.

that govern satellite orbits such as therelationship between orbital velocity andorbital radius.

2. Learn about different kinds of satelliteorbits (e.g., polar, geostationary,geosynchronous) and what they are usedfor.

3. Look up the gravitational pull for differentplanets. Would there be any differencesin orbits for a planet with a much greatergravitational pull than Earth's? Less thanEarth's?

4. Use the following equation to determinethe velocity a satellite must travel toremain in orbit at a particular altitude:

v = GM

v = velocity of the satellite in metersGM = gravitational constant times

Earth's mass (3.99x1014meters 3/sec 2 )

= Earth's radius (6.37x106 meters)plus the altitude of the satellite

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Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (6), 9-12 (Ia)

Student Reader - 1

6 Theo4*s

A microgravity environment is created byletting things fall freely. NASA usesairplanes, drop towers, and small rockets tocreate a microgravity environment lasting afew seconds to several minutes. Eventually,freefall has to come to an end becauseEarth gets in the way. When scientists wantto conduct experiments lasting days, weeks,months, or even years, it is necessary totravel into space and orbit Earth. Havingmore time available for experiments meansthat slower processes and more subtleeffects can be investigated.

To see how it is possible to establishmicrogravity conditions for long periods oftime, it is first necessary to understand whatkeeps a spacecraft in orbit. Ask just aboutanybody what keeps satellites and SpaceShuttles in orbit and you will probably hear,"There is no gravity in space." This is simplynot true. Gravity is what keeps a satellite orSpace Shuttle from drifting into space. Itdoes this by bending an orbiting object'spath into a circular shape. To explain howthis works, we can use an examplepresented by English scientist Sir IsaacNewton. In a book he wrote in 1673,Philosophiae Naturalis PrincipiaMathematica (Mathematical Principles ofNatural Philosophy), Newton explained howa satellite could orbit Earth.

.Iftal Direction

ResultingPath

Newton's cannon fires the first cannonball. Thecombination of the cannonball's initial velocity andthe pull of Earth's gravity causes the cannonball toarc to the ground near the ountain.

GreaterForce

A second cannonball is fired using a larger charge ofblack powder. The force exerted on ihe cannonballcauses it to travel faster than the first cannonball.Gravity bends its path into an arc but because of thegreater speed, the cannonball travels farther before itlands on Earth.

Newton envisioned a very tall mountain onEarth whose peak extended above Earth'satmosphere. This was to eliminate frictionwith Earth's atmosphere. Newton thenimagined a cannon at the top of that



Student Reader 2

mountain firing cannonballs parallel to theground. As each cannonball was fired, itwas acted upon by two forces. One force,due to the explosion of the black powder,propelled the cannonball straight outward. Ifno other force were to act on the cannonball,the shot would travel in a straight line and ata constant velocity. But Newton knew that asecond force would also act on thecannonball: Earth's gravity would cause thepath of the cannonball to bend into an arcending at Earth's surface.

Newton demonstrated how additionalcannonballs would travel farther from themountain if the cannon were loaded withmore black powder each time it was fired.With each shot, the path would lengthen andsoon the cannonballs would disappear overthe horizon. Eventually, if a cannonball werefired with enough energy it would fall entirelyaround Earth and come back to its startingpoint. This would be one complete orbit ofEarth. Provided no force other than gravityinterfered with the cannonball's motion, itwould continue circling Earth in that orbit.

In essence, this is how the Space Shuttlestays in orbit. The Shuttle is launched on apath that arcs above Earth so that theOrbiter is traveling parallel to the ground atthe right speed. For example, if the Shuttleclimbs to a 160-kilometer-high orbit, it musttravel at a speed of about 28,300 kilometersper hour to achieve an orbit. At that speedand altitude, the Shuttle's falling path will beparallel to the curvature of Earth. Becausethe Space Shuttle is freefalling aroundEarth, a microgravity environment is createdthat will last as long as the Shuttle remainsin orbit.

98

Greater------ Force

This cannonball travels halfway around Earthbecause of the greater charge of black powder used.The cannonball's falling path nearly matches theshape of Earth.

Greater

The black powder charge in this final cannon shotpropels the ball at exactly the right speed to cause itto fall entirely around Earth. If the cannon is movedout of the way, the cannonball will continue orbitingEarth.

105



Around TheWorld

Procedure:1. Set up your equipment as shown in

the picture. One team memberstands above the large ball andholds the end of the string. Thesecond team member's job is tomove the small ball in differentways to answer the followingquestions. Write down youranswers where indicated and drawpictures to show what happened.Draw the pictures looking straightdown on the two balls.

Orbital DeploymentTeam Members:

1.

2.

1. What path does the satellite (smallball) follow when it is launchedstraight out from Earth?

Show what happened.

EARTH



Student Work Sheet- 2

2. What path does the satellite followwhen it is launched at differentangles from Earth's surface?

3. What effect is there from launchingthe satellite at different speeds?

4. What must you do to launch thesatellite so it completely orbitsEarth?

100

5. Using the results of yourinvestigation and the informationcontained in the student reader,write a paragraph that explains howsatellites remain in orbit.

6. Why will the International SpaceStation be an excellent place toconduct microgravity research?


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 ()

Inertial Balance

Objective:

To demonstrate how mass can bemeasured in microgravity.

Science Standards:Science as InquiryPhysical Science- position and motion of objectsUnifying Concepts and ProcessesChange, Constancy, & Measurement

Science Process Skills:ObservingCommunicatingMeasuringCollecting DataMaking GraphsInterpreting DataControlling Variables

Mathematics Standards:CommunicationNumber & Number RelationshipsComputation & EstimationMeasurement

Activity Management:Before doing this activity, you will needto construct enough inertial balancesfor the entire class. Plan on having onebalance for every three or four students.Except for the empty film canisters,which are free from photo processors,materials and tools for making all thebalances can be obtained at ahardware store where lumber is alsosold. To reduce your cost, buy hacksawblades in multipacks. The dimensionsfor the wood.blocks are not critical andyou may be able to find a piece of scraplumber to meet your needs. The onlytools needed to construct the balances

Objects of unknown mass are measured with abalance that works in microgravity.

Hacksaw blade (12 inch)Coping saw (optional)1 C-clamp (optional)Plastic 35mm film canisterTissue paperMasking tapeWood block (1x2.5x4 inch)Wood sawsGlueObjects to be measuredGraph paper, ruler, and pencilPennies and nickelsStopwatch

are a crosscut or backsaw to cut thewood into blocks and a coping saw tocut the notch for insertion of the blade. Ifyou have access to power tools, use atable scroll saw to cut the notches. Thenotches should be just wide enough forthe hacksaw blade to be slid in. If the


108101

notches are too wide, select a thinner bladefor the coping or scroll saw.

Cut the blocks, one for each balance, about10 centimeters long. Cut a 2 centimeterdeep notch in one end of each block. Slipone end of the hacksaw blade into the notchto check the fit. It should be snug. Removethe blade and apply a small amount of glueto both sides of the end and slip the bladeback in place. Make sure the blade isslightly above and parallel to the bottom flatside of the block. Set the balance aside todry.

102

Cut small notch inwood. Insert andglue end of blade.

Use tape to attach a film canister to theopposite end of each balance. Squirt hotglue into the bottom of the canister and dropin a large metal washer. Repeat two moretimes. The reason for doing this is toprovide extra mass to the canister end of theinertial balance. Students will be countinghow long it takes the device to oscillate fromside to side 25 times. A very light canisterwill swing faster than the students can count.Extra mass will slow the device so thatcounting is possible.

To use the inertial balance, students willplace the wood block on the edge of a table

Use tape to cover saw teeth.

Insert blade with glue.

Side View

Top ViewTape 35mm film canisterto end of blade.

6.5 X 2.5 X 10 cmwood block

12 inch hacksaw blade

1 9

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (s), 9-12 (0)

so the hacksaw and canister stick overthe edge. The balance can beanchored with a clamp or just pressedto the tabletop by one student in theteam. An object of unknown mass isplaced in the canister and the studentsdetermine its mass by.deflecting theblade so it swings from side to side.Unknown masses can be such thingsas nuts and bolts, washers, andpebbles. The tissue paper called for inthe instructions anchors the unknownobject in the canister so it will notslosh around and throw off theaccuracy.

The first step for students is tocalibrate the balance. This is donewith a standard mass such as a penny.The length of time the balance takesto oscillate 25 times is measured forzero through 10 pennies. The resultsare plotted on a graph When an unknownmass is placed in the canister, its time willbe measured. By referring to the graph,students will be able to determine theunknown object's mass by seeing where itfalls on the graph. The mass will be given inunits of pennies. If desired, the balance canbe calibrated in grams by measuring thepennies on a metric beam balance.

Save the student reader for use after theactivity.

Assessment:Collect calibration graphs and data sheets.

Extensions:1. Construct and demonstrate inertia rods.

The instructions follow. The materials listis found on the next page.

A. Using a saW,.cut the PVC tube in half.Smooth out the ends, and check to seethat the caps fit the ends.

2 01 91 81 71 61 51 41 31 21 1

1 0

0

110

Sample Graph

*PennyA Nickel

1 2 3 4 5 6 7 8 9 1 0Number of Pennies

B. Squeeze a generous amount ofsilicone rubber sealant into the end ofone of the tubes. Slide the pipe intothe tube.Using thedowel rod,push thepipe to themiddle ofthe tube.Addsealant tothe otherend of thetube and insert the second pipe.Position both pipes so they aretouching each other and straddling thecenter of the tube. Set the tube asideto dry.

C. Squeeze sealant into the ends of thesecond tube. Push the remainingpipes into the ends of the tubes untilthe ends of the pipes are flush with thetube ends. Be sure there is enough


103

Weight>.

Weight

compound to cement the pipes inplace. Set the tube aside to dry.

D. When the sealant of both tubes is dry,check to see that the pipes are firmlycemented in place. If not, addadditional sealant to complete thecementing. Weigh both rods. If onerod is lighter than the other, add smallamounts of sealant to both ends of thelighter rod. Reweigh. Add moresealant if necessary.

E Spread some sealant on the inside ofthe PVC caps. Slide them onto theends of the tubes to cement them ihplace.

F. Use fine sandpaper to clean the rods.

104

Demonstrate the rods by having astudent pick up both of the rods fromtheir upper ends and tell the classwhether the rods feel the same. Then,the student grasps each rod by itsmiddle, extends arms, and twists the

PVC 3/4 in. water tube(about 1.5 to 2 m long)

4 iron pipe nipples (4-6 in. longsized to fit inside PVC pipe)

4 PVC caps to fit water pipeSilicone rubber sealantScale or beam balanceSawVery fine sandpaper1/2 in. dowel rod

rods side to side as rapidly as possible.One rod will be easy to twist and theother difficult. The effect is caused bythe distribution of the mass in each rod.Because the ends of the rods movemore rapidly than the middle duringtwisting, the student feels more inertiain the rods with the masses at the endsthan the rod with the masses in themiddle. Relate this experience to theway the inertial balances operate.

2. Ask students to design an inertial balancethat automatically counts oscillations.

3. Have students enter their calibration datainto a graphing calculator and use thecalculator to determine unknown masseswhen new measurement results areentered.

lii


Student Reader - 1

a and Micro ra1 1 1 1

The microgravity environment of an orbitingSpace Shuttle or space station presentsmany research problems for scientists. Oneof these problems is measurement of mass.On Earth, mass measurement is simple.Samples, such as a crystal, or subjects,such as a laboratory animal, are measuredon a scale or beam balance. In a scale,springs are compressed by the object beingmeasured. The amount of compression tellswhat the object's weight is. (On Earth,weight is related to mass. Heavier objectshave greater mass.) Beam balances, like aseesaw, measure an unknown mass bycomparison to known masses. With boththese devices, the force produced by Earth'sgravitational attraction enables them tofunction.

In microgravity, scales and beam balancesdon't work. Setting a sample on the pan ofa scale will not cause the scale springs tocompress. Placing a subject on one side ofa beam balance will not affect the otherside. This causes problemsfor researchers. For example,a life science study on thenutrition of astronauts in orbitmay require daily monitoring ofan astronaut's mass. In mate-rials science research, it maybe necessary to determinehow the mass of a growingcrystal changes daily. Howcan mass be measured with-out gravity's effects?

Mass can be measured inmicrogravity by employinginertia. Inertia is the propertyof matter that causes it to

resist acceleration. If you

)01

,

have ever tried to push anything that isheavy, you know about inertia. Imaginetrying to push a truck. You will quicklyrealize that the amount of inertia or resis-tance to acceleration an object has is di-rectly proportional to the object's mass. Themore mass, the more inertia. By directlymeasuring an object's inertia in microgravity,you are indirectly measuring its mass.

The device employed to measure inertiaand, thereby, mass is the inertial balance. Itis a spring device that vibrates the subject orsample being measured. The object to bemeasured is placed in the sample tray orseat and anchored. The frequency of thevibration will vary with the mass of the objectand the stiffness of the spring (in this activ-ity, the hacksaw blade). An object withgreater mass will vibrate more slowly thanan object with less mass. The time neededto complete a given number of cycles ismeasured, and the mass of the object iscalculated.

,4r

Payload Commander Dr. Rhea Seddon is shown using theBody Mass Measurement Device during the Spacelab LifeSciences 2 mission. The device uses the property of inertia todetermine mass.

Nlotr


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (a)105


Measuring MassWith InertiaCalibrating the Inertial Balance:1. Clamp the inertial balance to the table so

the spring (saw blade) and sample bucketextends over the edge of the table.

2. Pick one member of your team to be thetimekeeper, another to record data, andanother to count cycles. Refer to the boxto the right for details on how to performeach task.

3. Begin calibration by inserting a wad oftissue paper in the bucket and deflectingthe spring. Release the bucket and startcounting cycles. When the time for 25cycles is completed, enter the number inthe data chart and plot the point on thegraph for zero pennies. To improveaccuracy, repeat the measurementsseveral times and average the results.

4. Insert 1 penny into the bucket next to thetissue paper wad and measure the time ittakes for 25 cycles. Record the data as 1penny.

5. Repeat the procedure for 2 through 10pennies and record the data.

106

Counter: Pull the sample bucket a fewcentimeters to one side and release it. Atthe moment of release, say "Now" andbegin counting cycles. A cycle iscompleted when the sample bucket startson one side, swings across to the otherand then returns to its starting point. When25 cycles are complete, say "Stop."

Timer: Time the number of cycles beingcounted to the nearest tenth of a second.Start timing when the counter says "Now"and stop when the counter says "Stop."

Recorder: Record the time for 25 cyclesas provided to you by the timer. There willbe 11 measurements. Plot themeasurements on the graph and draw aline connecting the points.

6. Draw a line that goes through or closeall points on the graph. Your inertialbalance is calibrated.

to

Using the Inertial Balance:1. Place an unknown object in the inertial

balance bucket. Remember to use thesame tissue paper for stuffing. Measurethe time for 25 cycles. And record youranswer.

2. Starting on the left side of the graph, findthe number of seconds you measured instep 1. Slide straight over to the rightuntil you reach the graph line you drew inthe previous activity. From thisintersection point, go straight down to thepenny line. This will tell you the mass ofthe unknown object in penny weights.

113



Measuring MassWith Inertia

2 01 91 81 71 61 51 41 31 21 1

1 0

0

Unknown Object 1

Mass:

Unknown Object 2

Mass:

Measurement Team:

Calibration Graph

Pw

Pw

1 2 3 4 5 6 7 8 9 1 0Number of Pennies

Unknown Object 3

Mass:

Unknown Object 4

Mass: Pw

Pw


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 ()107


Questions:

1. Will this technique for measuring mass work in microgravity? Yes NoExplain your answer:

2. Why was it necessary to use tissue paper for stuffing?

3. How could you convert the penny weight measurements into grams?

4. Would the length of the hacksaw blade make a difference in the results?

5. What are some of the possible sources of error in measuring the cycles?

6. What does a straight line in the calibration graph imply?



Gravity-Driven Fluid FlowObjective:

To study gravity-driven fluid flow thatis caused by differences in solutiondensity.

Science Standards:Science as InquiryPhysical Science- position and motion of objects

properties of Objects and MaterialsUnifyinj Concepts and ProcessesChange, Constancy, & MeasurementScience and Technology- abilities of technological design

Science Process Skills:ObservingCommunicatingCollecting DataInferringHypothesizingInterpreting DataControlling VariablesInvestigating

Activity Management:In this activity, students combineliquids of different densities to observethe fluid flow caused by gravity-drivenbuoyancy and settling. The activity isbest done in student groups of two orthree. It can also be done as ademonstration for the entire class. Inthis case, obtain an overhead projectorand place beakers on the lightedstage. The light from below willilluminate the contents of the jars tomake them easily visible from acrossthe room. To reduce distraction, coverthe projector lens to prevent blurryimages from falling on the wall orscreen behind. Caution: Be careful notto spill liquid on the projector.

1 6


,

Water of different densities is mixed toproduce gravity-driven fluid flow.

00

ex

CAJccict2

2 large (500 ml) glassbeakers or tall drinkingglasses

2 small (5 to 10 ml) glassvials

ThreadFood coloringSalt-Spoon or stirring rodMeasuring cup (1/4 cup)WaterPaper towels

If using this as an activity, provide eachstudent group with a set of materials.Salt canisters, food coloring dispensers,and measuring cups can be sharedamong groups. The materials list callsfor glass beakers or tall drinkingglasses. Other containers can besubstituted such as mason jars orplastic jars like those in which peanut

109

butter is sold. The vials are available fromschool science supply catalogs for a fewdollars per dozen. Choose glass vials withscrew tops and a capacity of 3 to 4 ml.Small cologne sample bottles can besubstituted for the vials. It is important thatthe vials or bottles are not too large becausethe process of lowering large containers intothe beakers can stir up the water too much.It is recommended you tie the string aroundthe neck of the vial yourself to make surethere is no slippage.

The student instructions ask the students toconduct three different experiments. In thefirst, the effects of saltwater and freshwaterare investigated. In the second, the effectsof warm and cold water are investigated.The third experiment is an opportunity forstudents to select their own materials. Theymight try mixing oil and vinegar, sugar andsaltwater, or oil and water. It may benecessary for the third experiment to beconducted on another day while the newmaterials are collected.

Give each student group at least one set ofinstructions and two data sheets. Save thestudent reader for use after the experiment.

Assessment :Discuss the experiment results to determinewhether the students understand theconcepts of buoyancy and sedimentation.Collect the student pages for assessment ofthe activity.

110

Extensions:1. How could this experiment be conducted

if it were not possible to use food coloringfor a marker? (In experiments where thedensity of the two fluids is very close, theaddition of food coloring to one fluid couldalter the results.)

2. Design an apparatus that can be used tocombine different fluids for experimentson the future International Space Station.

3. Design an experiment apparatus thatwould permit the user to control thebuoyancy and sedimentation rates in thebeakers.

4. Design an experiment to.measure thegravity-driven effects on different fluids inwhich the fluids are actually gases.

11 7


Student Reader 1

Gravity is an important force at work in themovement of fluids. Fluids can be liquidsor gases. The important thing about fluidsis they can flow from place to place and cantake the shape of the container they are in.

When you pour a liquidfrom one container intoanother, gravity is thedriving force thataccomplishes the transfer.Gravity also affects fluids"at rest" in a container.Add a small amount ofheat to the bottom of thecontainer and the fluid atthe bottom begins to rise.The heated fluid expandsslightly and becomes lessdense. In other words,the fluid becomesbuoyant. Cooler fluid near the top of thecontainer is more dense and falls or sinksto the bottom.

it was. This, in turn, causes a fluid flow inthe solution. The slightly less salty solutionis buoyant and rises to the top of thecontainer while saltier, or more dense,solution moves in to take its place.

I

Dyed freshwater in saltwater beaker

Many crystals grow in solutions of differentcompounds. For example, crystals of saltgrow in concentrated solutions of saltdissolved in water. In the crystal growthprocess, the ions that make up the saltcome out of solution and are deposited onthe crystal to make it larger. When thishappens, the solution that held themolecule becomes a little less salty than itwas a moment ago. Consequently, thedensity of the solution is a little bit less than

118

Scientists are interested ingravity-driven fluid flowsbecause they have learnedthat these flows, whenoccurring during the growthof crystals, can create subtlechanges in the finishedcrystals. Flaws, calleddefects, are produced thatcan alter the way thosecrystals perform in variousapplications. Crystals areused in many electronicapplications, such as incomputers and lasers.

To learn how to grow improved crystals onEarth, scientists have been growing crystalsin the microgravity environment of Earthorbit. Microgravity virtually eliminatesgravity-driven fluid flows and often producescrystals of superior quality to those grownon Earth. One of the major areas ofmaterials science research on theInternational Space Station will involvecrystal growth.


111


Gravity-Driven Fluid Flow

Procedure1. Fill the first beaker with freshwater and

set it on the lab surface. Also fill thesecond beaker with freshwater. Into thesecond beaker add approximately 50 to100 grams of salt. Stir the water until thesalt is dissolved.

2. Dip the first small glass vial into thebeaker with freshwater. Fill it nearly tothe top. Add a couple of drops of foodcoloring to the water in the vial. Close thetop of the vial with your thumb and shakethe water until the food coloring is mixedthroughout. Place this vial next to thesaltwater beaker.

3. Partially fill a second vial with salty waterand food coloring. After mixing, place it infront of the beaker filled with freshwater.

4. Wait a few minutes until the water in thetwo beakers is still. Gently lift one of thevials by the string and slowly lower it intothe beakernext to it. Letthe vial rest onits side on thebottom of thebeaker anddrape thestring over theside as shownin the pictures.Answer thequestions onthe data sheets and sketch what youobserved in the diagrams.

5. Place the second vialin the other beaker as

112

before. Make your observations, sketchwhat you observed, and answer thequestions about the data.

Second Experiment Procedure:1. Empty the two beakers and rinse them

thoroughly.2. Fill one beaker with cold water and the

other with warm water.3. Repeat steps 2 through 5 in the previous

experiments.

Original Experiment:1. On a blank sheet of paper, write a

proposal for an experiment of your owndesign that uses different materials in thebeakers. Include in your proposal anexperiment hypothesis, a materials list,and the steps you will follow to conductyour experiment and collect data. Submityour experiment to your teacher forreview.

2. If your experiment is accepted for testing,gather your materialsconduct the experimentsubmit a report summarizing yourobservations and conclusions

11 9



Gravity-Driven Fluid FlowData Sheet

Research Team Members:

Beaker and Vial:1. Water in beaker (check one)

FreshSalty

2. Water in vial (check one)FreshSalty

3. Describe and explain what happened

Sketch what happened.

Beaker and Vial:1. Water in beaker (check one)

FreshSalty

2. Water in vial (check one)FreshSalty

3. Describe and explain what happened

120 Sketch what happened.


113

114

Surface Tension-Driven FlowsObjective:

To study surface tension andthe fluid flows caused bydifferences in surfacetension.

Science Standards:Science as InquiryPhysical Science- position and motion of objects- properties of objects and

materialsUnifying concepts and processesChange, Constancy, &

Measurementevidence, models, & exploration

Science Process Skills:ObservingCommunicatingMeasuringCollecting DataInferringPredictingInterpreting DataInvestigating

A clay maze is constructed on a cafeteria tray. Water isadded. A drop of liquid soap disrupts the surface tensionof the water and creates currents that are made visible withfood coloring.

Activity Management:The purpose of this activity is todemonstrate how surface tensionchanges can cause fluids to flow. Itrequires shallow trays with raisededges such as cafeteria trays. LargeStyrofoam food trays from asupermarket can also be used, butthey should be the kind with a smoothsurface and not a waffle texture.Light-colored trays make a betterbackground for seeing the surfacetension effects. Encourage studentsto try different mazes and investigatethe effects of wide versus narrowmazes.

1 4111

Cafeteria tray (withraised edge)

Plasticine modeling clayWaterLiquid soapFood coloringToothpickPaper towelsBucket or basin for waste

water

Water handling will be a bit of aproblem. After a drop of liquid soap isapplied to the water, the water must bediscarded and replaced before tryingthe activity again. Carrying shallowwater-filled trays to a sink could bemessy. Instead, it is recommended thata bucket or large waste basket be

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HO, Education Standards Grades 5-8 (A), 9-12 (o)

brought to the trays so the trays can beemptied right at the workstation.

When soap is applied to the water, foodcoloring at the water's surface will be drivenalong the maze by the disruption of thewater's surface tension. Make sure studentsobserve what happens to the water at thebottom of the tray as well. A reverse currentflows along the bottom to fill in for the waterthat was driven along the surface.

Save the student reader for use after theactivity.

Assessment:Conduct a class discussion to ensure thestudents understand that variations insurface tension in a fluid cause fluid flow.Collect the student pages.

Extensions:1. Demonstrate additional surface tension

effects by shaking black pepper into aglass of water. Because of surfacetension, the pepper will float. When adrop of soap is added to the water, thepepper will sink. This same effect can beseen in a broader view by placing waterinto a petri dish and adding pepper andthen soap. The pepper will be driven tothe sides of the dish where particles willstart sinking. The petri dish experimentcan be done as a demonstration with anoverhead projector.

2. Make a surface tension-propelled paperboat by cutting a small piece of paper inthe shape shown to the right and floatingit on clean water. Touch a small amountof detergent to the water in the hole at theback of the boat.

3. Design an experiment to test whether thetemperature of a liquid has any effect onsurface tension.

122

4. Try floating needles on water and observewhat happens when detergent is added.To float the needle, gently lower it to thewater's surface with a pair of tweezers.

Surface Tension Paper Boat(actual size)

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HO, Education Standards Grades 5-8 (A), 9-12 ()

115

Student Reader 1

If you have ever looked closely at drops ofwater, you will know that drops try to formspherical shapes. Because of gravity'sattraction, drops that cling to an eye dropper,for example, are stretched out. However,when the drops fall they become spherical.

The shape of a water drop is a result ofsurface tension. Water is composed ofmolecules consisting of two hydrogen atomsand one atom of oxygen. These moleculesattract each other. In the middle of a drop ofwater, molecules attract each other in alldirections so no direction is preferred. Onthe surface, however, molecules areattracted across the surface and inward.This causes the water to try to pull itself intoa shape that has the least surface areapossiblethe sphere. Because of gravity,

116

drops resting on a surface, like water dropson a well-waxed car, flatten out somewhatlike the figure above.

The molecules on the surface of a liquidbehave like an elastic membrane.You caneasily see the elastic membrane effect byfloating a needle on the surface of a glass ofwater. Gently lower the needle to the watersurface with a pair of tweezers. Examinethe water near the needle and you willobserve that it is depressed slightly asthough it were a thin sheet of rubber.

The addition of a surfactant, such as liquidsoap, to water reduces its surface tension.Water molecules do not bond as stronglywith soap molecules as they do withthemselves. Therefore, the bonding forcethat enables the molecules to behave like anelastic membrane is weaker. If you put adrop of liquid soap in the glass with theneedle, the surface tension is greatlyreduced and the needle quickly sinks. Whenyou added liquid soap to the water in theexperiment, the surface tension wasweakened in one place. The water on thesurface immediately began spreading awayfrom the site of the soap. The clay wallschanneled the flow in one direction. Tomake up for the water moving away from thesite where the soap was added, a secondwater current formed in the oppositedirection along the bottom of the tray.


Student Reader - 2

Air

Car Surface

Molecules inside a water drop are attracted in all directions. Drops onthe surface are attracted to the sides and inward.

Because a microgravity environment greatlyreduces buoyancy-driven fluid flows andsedimentation, surface tension flowsbecome very important. Microgravityactually makes it easier to study surfacetension-driven flows. On Earth, studyingsurface tension in the midst of gravity-drivenflows is like trying to listen to a whisperduring a rock concert. The importance ofsurface tension research in microgravity isthat surface tension-driven flows caninterfere with experiments involving fluids.For example, crystals growing on the

International Space Station could beaffected by surface tension-driven flows,leading to defects in the crystal structureproduced. Understanding surface tensionbetter could lead to new materialsprocessing techniques that either reducesurface tension's influence or takeadvantage of it. One example of a positiveapplication of surface tension is the use ofsprayers to paint a surface. Surface tensioncauses paint to form very small droplets thatcover a surface uniformly without formingdrips and runs.

24


117


Surface Tension-Driven Flows

Team Members:

Setup Instructions:1. Roll clay into long "worms" 1 to 2

centimeters in diameter. Lay the wormsout on the tray to produce a narrow valleyabout 3 to 4 centimeters wide that isclosed on one end. Squeeze the wormsso they stick to the tray and form thinwalls.

2. Add water to the tray until it almostreaches the tops of the maze walls. Letthe water settle before the next step.

3. Add a drop of food coloring to the mazenear its end. Drop the coloring from aheight of about 5 centimeters so thatsome of the food coloring spreads outslightly on the surface while the rest sinksto the bottom.

Make a sketch of the claymaze you constructed.Use arrows to show thedirection of surface watermovement atter you addedthe soap. Use dashed linearrows to indicate thedirection of any subsurfacecurrents.

118

4. Dip the toothpick in the liquid soap andtouch the end of the toothpick to thewater at the end of the maze beyond thedye. Observe what happens.

5. Try a different maze to see how far youcan get the dye to travel.

Questions:1. Why did the surface water move?

2. Did water near the bottom move as well?If it moved, why ?

125


Temperature Effects onSurface TensionObjective:

To investigate the effects of tem-perature on the surface tension of athin liquid.

Science Standards:Science as InquiryPhysical Science- position and motion of objects- properties of objects and materialsUnifying Concepts and ProcessesChange, Constancy, & Measurement

Science Process Skills:ObservingCommunicatingMeasuringCollecting DataInferringPredictingInterpreting DataControlling VariablesInvestigating

Activity Management:This experiment can be done as astudent activity or a classroomdemonstration for small groups ofstudents. If done as a demonstration,it can be set up while students areconducting the Surface Tension-Driven Flows activity. Rotate smallgroups through the demonstration.

Be sure to use Pyrex® petri dishes forthe demonstration. Also provide eyeprotection for yourself and thestudents. It is important that theheating surface of the hot plate belevel. Otherwise, it will be necessaryto add more oil to cover the bottom ofthe petri dish. A thin layer of oil is 1 2 6

A thin pool of liquid heated from belowexhibits polygonal cell structure due tosurface tension-driven flows.

Cooking oilPowdered cinnamonTwo Pyrex® petri dishes and

coversLaboratory hot plateHeat-resistant gloves,

hotpad, or tongsIce cubesEye protection

essential to the success of theexperiment. Thin layers, on the orderof 1 or 2 millimeter, do not exhibitsignificant convection currents as dolayers that are much thicker. Theresimply is not enough room forconvection currents to develop in thinlayers. Heat is conducted through thethin layer to the surface very quickly.Since the lower and upper parts of the

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119

liquid are at nearly the same temperature,no convection currents develop.

The demonstration is conducted with twopetri dishes. Use the lids of both dishes forholding the oil and spice. To see the surfacetension effects, sprinkle the cinnamon froma height of 20 or 30 centimeters to help itspread out evenly on the surface of the oil.

Place the first dish on the hot plate andobserve that patterns are produced by thecinnamon. Before placing the second dishlid on the hot plate, invert and insert thebottom of the second dish into the lid. Thiswill effectively place all the oil in contact withglass so there is not any exposed oilsurface. The reason for the two differentruns of the demonstration is to verifywhether or not buoyancy-driven convectioncurrents are involved in moving thecinnamon markers. If these currents are atwork, the cinnamon will spread out and swirlthrough the oil. In other words, the secondpart of the demonstration is a control for thefirst part.

Assessment:Conduct a class discussion on why it isimportant for microgravity scientists tounderstand about surface tension. Collectthe student pages.

120

Extensions:1. Experiment with other fluid and marker

combinations. Several microgravityexperiments in space have used 10centistoke silicone oil (dimethylpoly-siloxane) with powdered aluminum as amarker. Both chemicals are availablefrom chemical supply catalogs. Thedemonstration works best if the aluminumis more flaky than powder. Aluminumflakes will provide reflective surfaces thatintensify the optical effect. You can makeyour own aluminum flakes by obtainingflat enamel hobby paint and allowing thealuminum flakes to settle to the bottom ofthe bottle. Pour off the fluid and wash thesediment several times with nail polishremover and let dry.

2. Videotape the convective flow patternsand play them back at different speeds tosee more details on how surface tension-driven flows develop.

3. Look for patterns in nature, such as mudcracks, that are similar to the patternsseen in this activity. Are nature's patternsproduced in the same way or by somedifferent mechanism?

12 7


Student Reader - 1

Around the turn of this century, physicistHenri Bénard discovered that liquid in thinpools heated from below quickly forms flowpatterns consisting of polygonal cells. Hemade this discovery by placing tiny markersin the fluid that showed how the fluid moved.The cells resembled those that form due toconvection currents when a pot of soup isheated. The interesting thing aboutBénard's discovery is that buoyancy-drivenconvection currents were not responsible forthe flow that was produced.

When a thick pool of liquid is heated frombelow, liquid at the bottom expands andbecomes less dense. Because of buoyancy,the less dense liquid rises to the top of thepool where it spreads out. Coolersurrounding liquid moves in to take the placeof the warmer fluid that rose to the top. Thisliquid heats up, becomes less dense, andalso rises to the top to create a cycle thatcontinues as long as heat is applied. Thiscycling is called a buoyancy-drivenconvection current.

The problem with studying fluid flows in aheating pot of soup is that convectioncurrents appear to be the only force at work.Actually, surface tension flows are alsopresent but, because they are of lowerintensity, they are masked by the moreviolent buoyancy-driven convection currents.By creating a very thin liquid pool (about 1

mm or thinner), Bénard was able to

eliminate buoyancy-driven convection. Invery thin liquids there just is not enoughvertical distance for significant buoyancy-driven convection currents to get started.The fluid flow Bénard observed wasproduced by changes in surface tension.

In the cooking oil experiment, you observedtwo petri dishes with a thin layer of oil andpowdered cinnamon markers. Theuncovered dish, when heated from below,began forming circular cells that eventuallygrew into each other to produce polygonalcells. Heat from hot spots in the hot platewas quickly conducted to the surface of theoil. The increase in temperature of the oilreduced the surface tension in thoselocations. This reduction was apparentbecause the oil flowed from the center of thehot spots in all directions to the outside.Compare this action to what happenedwhen a drop of liquid soap was touched tothe surface of a tray of water in the previousactivity. In the second petri dish, a layer ofglass was placed over the thin oil layer sothe oil did not have an exposed surface. Inthis manner, surface tension effects wereeliminated. No fluid flows were observed,

4

Polygonal cells produced in a thin pool of liquidheated from below.

28Microgravity A Teacher's Guide with Activities hi Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)

121

Student Reader - 2

meaning that buoyancy-driven convectionwas not at work. This demonstration servedas a scientific control for the first experiment.

In fluid physics experiments aboard theSpace Shuttle and the International SpaceStation, buoyancy is practically eliminatedbecause of microgravity. Surface tension,however, becomes an important force

Cooler Surface.4111-- Flow -10.

122

Thick Liquid Pool

because it is not a gravity dependentphenomenon. In crystal growing and otherfluid physics experiments, surface tension-driven flows can affect the outcome. For thisreason, scientists are trying to understandthe mechanics of surface tension-drivenflows in microgravity.

In these two diagrams, the difference betweenbuoyancy-driven convection currents (left) andsurface tension-driven convection currents (right) isshown. Flow in the left diagram is produced bychanges in fluid density brought about by heating thebottom. Flow in the right diagram is brought about byreducing surface tension above a heated plate.

Cooler Surface

C001 .10. Warn 0 C001

Heated Plate

Thin Liquid Pool

Magnified view of the polygonal cells that are produced by surface tension-driven convection.

1 2 9Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,

EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (CI)


Temperature Effects on Surface Tension

Name:

1. Sketch the fluid flow patterns thatappeared in the thin pool of cooking oilwhen heat was applied to the bottom ofthe first petri dish. Indicate with arrowswhich direction(s) the fluid flowed.

What effect did an increase intemperature have on the surface tensionof the oil?

Why?

2. Sketch the fluid flow patterns thatappeared when heat was applied to thebottom of the second petri dish. Indicatewith arrows the direction(s) of any fluidflows observed.

Explain what you observed.

What effect on surface tension do youpredict lowering the temperature of theoil would have? How could this beobserved?

130


123

0,

,

124

Candle FlamesObjective:

To investigate the effect of gravityon the burning rate of candles.

Science Standards:Science as InquiryPhysical Science

properties of objects & materialsUnifying Concepts & ProcessesChange, Constancy, & Measurement

Science Process Skills:ObservingCommunicatingMeasuringCollecting DataInferringHypothesizingPredictingInvestigating

Mathematics Standards:Measurement

Activity Management:This activity serves as an introduction tothe candle drop activity that follows. Inboth activities, students are organized intocooperative learning groups of three. Itmay be useful to keep the same groupstogether for both activities.

The objective of this activity is to observecandle flame properties and preparestudents to make observations of candleflames in microgravity where observingconditions are more difficult. Beforeletting students start the activity, conducta discussion on the different observationsthey can make. Make a list of terms thatcan be used to describe flame shape,size, color, and brightness.

The burning rate and other properties ofcandle flames are investigated.

Birthday candles (2 pergroup)

MatchesBalance beam scale (0.1 gm

or greater sensitivity)Clock with second hand or

stopwatchWire cutter/pliersWire (florist or craft)20 cm square of aluminum

foilEye protection

At the end of the experiment, studentgroups are asked to write a hypothesisto explain the differences observed inthe burning of the two candles. It maybe helpful to discuss hypothesis writingbefore they get to that part. The


hypotheses should relate to gravity-inducedeffects. In the case of candle 2, the wax ofthe candle is above the flame. Convectioncurrents (a gravity-driven phenomenon)deliver lots of heat to the candle whichcauses more rapid melting than occurs withcandle 1. Much of that wax quickly drips offthe candle (gravity pulls the wax off) somore wick is exposed and the candle burnsfaster.

The wire used in this activity is a lightweightwire of the kind used by florists and in craftwork. You can find this wire in craft andhardware stores. Do not use wire withplastic insulation. The flame of the candletipped at an angle of 70 degrees may reachthe wire and begin burning the insulation.Each group will need two wires about 20centimeters long. Precut the aluminum foilinto 20 centimeter squares. One square isneeded for each group.

Provide each group with one set of studentsheets. Save the student reader for useafter the activity has been completed.

Assessment:Discuss student observations of the candleburning and their hypotheses. Collect thestudent work sheets for assessment.

Extensions:1. Burn a horizontally held candle for one

minute. Weigh the candle before lightingit. As it burns, record the colors, size, andshape of the candle flame. Weigh thecandle again and calculate how muchmass was lost.

2. Repeat the above experiments with thecandles inside a large sealed jar. Let thecandles burn to completion. Record thetime it takes each candle to burn. Deter-mine how and why the burning ratechanged.

3. Burn two candles which are close to-gether. Record the burning rate andweigh the candles. Is the burning ratefaster or slower than each candle alone?Why?

4. Investigate convection currents with aconvection current demonstration appara-tus that is obtained from science supplycatalogs, or construct the apparatus asshown below.

5. Obtain a copy of Michael Faraday's book,The Chemical History of a Candle, and dothe experiments described. (See refer-ence list.)

Light the end ofpaper wad and thenblow out. Smokewill be drawn intochamber.

Wooden box with glassor plastic front. Holdwith tape hinges.

132

Chimneymade fromglass, foodcans, or pipe.

+


125

Student Reader - 1

Candles are useful for illustrating thecomplicated physical and chemicalprocesses that take place duringcombustion. The candle flame surface itselfis the place where fuel (wax vapor) andoxygen mix and burn at high temperatures,radiating heat and light. Heat from the flameis conducted down the wick and melts thewax at the wick base. The liquid wax risesup the wick because of capillary action. Asthe liquid wax nears the flame, the flame'sheat causes it to vaporize. The vapors aredrawn into the flame where they ignite. Theheat produced melts more wax, and so on.

126

Fresh oxygen from the surrounding air isdrawn into the flame primarily because ofconvection currents that are created by thereleased heat. Hot gases produced duringburning are less dense than the coolersurrounding air. They rise upward and, indoing so, draw the surrounding air,containing fresh oxygen, into the flame.Solid particles of soot, that form in theregion between the wick and flame, are alsocarried upward by the convection currents.They ignite and form the bright yellow tip ofthe flame. The upward flow of hot gasescauses the flame to stretch out in a teardropshape.

Light Yellow1,200°C

Dark RedBrown1,000°C

White,1,400'C

H20, CO2(Unburnedcarbon)

LuminousZone(Carbonluminescesand burns)

Oraoge800"C

MainReactionZone

H20CO2OHC2

Primary(Initial)ReactionZone(Carbon particles)

Dead Space600°C

Candle Flame Reaction Zones,Emissions, and Temperature

Candle flame diagrams adapted from "The Science of Flames" poster,National Energy Foundation, Salt Lake City, n



Candle Flames

Candle Flame ResearchTeam Members:

Procedure:

1. Make a wire stand for each candleso that it looks like the picturebelow.

2. Weigh each candle by standing iton a balance beam scale andrecording its weight in grams on thechart on the next page.

3. Put on eye protection.

Candle 2

4. Place candle 1 on the aluminumsquare. Light the candle and let itburn for 1 minute. While it isburning, observe what is happeningand write your observations below.

Draw a life-size picture of thecandle flame.

Weigh candle 1 again and recordits mass in the chart.

134


127


5. Place candle 2 on the aluminumsquare. Light the candle and let itburn for 1 minute. While it isburning, observe what ishappening and write yourobservations below.

Draw a life-size picture of thecandle flame.

Weigh candle 2 again and recordits mass in the table.

Calculate the difference in mass foreach candle and enter youranswers in the table.

128

Candle Mass Table

Beforeburningmass

Afterburningmass

Difference

1 2

Summarize your observations below.

Write a hypothesis for how you thinka candle will burn in microgravity.


Candle Flame in MicrogravityObjective:

To observe candle flame properties infreefall.

Science Standards:Science as InquiryPhysical Science- position and motion of objectsUnifying Concepts & ProcessesChange, Constancy, & MeasurementScience &Technology- abilities of technological design

Science Process Skills:ObservingCommunicatingCollecting DataInferringPredictingInterpreting DataHypothesizingControlling VariablesInvestigating

Activity Management:Before attempting this activity, be sure toconduct the Candle Flames activity.Doing so will sharpen the observationskills of the students. This is importantbecause, in this activity, students will beobserving the size, shape, and color of acandle flame as it is falling.

Investigating candle flames inmicrogravity can be done as either ademonstration or an activity. If used as ademonstration, only one candle drop jar isnecessary. If used as an activity, onecandle drop jar is needed for each studentgroup. Clear plastic food storage jars areavailable at variety stores, but plasticpeanut butter jars will work as well. Thejars should be 1 quart or half g'allbn size

A burning candle is encased by a clearplastic jar and dropped for a study of flamesin microgravity.

Clear plastic jar and lid (2 litervolume)*

Wood blockScrewsBirthday candlesMatchesDrill and bitVideo camera and monitor

(optional)Eye protection* Empty 3-lb plastic peanut

butter jar can be used.

(3 pound size if peanut butter jars areused). The oxygen supply in smallerjars runs out too quickly for properobservations.

The wood block and screws called forin the materials and tools list can bereplaced with a lump of clay. Press thelump to the inside of the jar lid and

Microgravity A Teacher's Guide with Activities in Sciinvb,Utilathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (0)

129

push the end of the candle into the clay. Itwill probably be necessary to reform and/orreposition the clay after a couple of drops.The wood block and screws make a long-lasting candle drop jar.

If you are using wood blocks and screws,prepare the candle drop jars by drilling ahole in the center of the block to hold theend of the candle. Drill two pilot holes intothe wood for the screws. Finally, drill holesthrough the plastic jar lid. With the block inplace, insert screws through the lid holesand screw them into the wood block whereyou drilled the pilot holes. The candle dropjar is ready.

If you are using this as an activity, dividestudents into groups of three. Save thestudent reader for use after the experimenthas been conducted. Students will drop thecandle at least three times during theirinvestigation. During the drops, there arethree jobs that must be performed. Onestudent will drop the candle, another willcatch it, and the third will observe theproperties of the candle flame as it falls.The jobs should be rotated through thegroup so each student performs each jobonce.

Since fire is used, be sure everyone workingwith the activity wears eye protection.The activity works best in a room that canbe darkened. Coordinate the observationsof the student groups so all are ready todrop the candle when the lights are dimmed.

130

Students will observe that the first time abirthday candle is lit, the flame is larger thanwhen it is lit again. This happens becausethe wick sticks out farther from the wax on anew candle than it does on a used candle.The excess is burned quickly and the flamesize diminishes slightly.

Assessment:Use the student pages for assessment. Foradditional work, have students actually builda model of the microgravity experiment theyare instructed to design in the last step onthe student pages. The students canpresent their ideas to the rest of the classand exhibit their device.

Extensions:1. If videotape equipment is available,

videotape the candle flame during thedrop. Use the pause control during theplayback to examine the flame shape.

2. If a balcony is available, drop the jar froma greater distance than is possible in aclassroom. Does the candle continue toburn through the entire drop? For longerdrops, it is recommended that a catchbasin be used to catch the jar. Fill up alarge box or plastic trash can withStyrofoam packing material or looselycrumpled plastic bags or newspaper.

13 7


Student Reader - 1

FelsMicrogravity experiments using drop

towers and Space Shuttle Orbiters haveprovided scientists valuable insights on howthings burn. In the typical experiment, aflammable material, such as a candle, isignited by a hot wire. The ignition andcombustion process is recorded by moviecameras and other data collection devices.Using these devices, scientists have learnedthere are significant differences betweenfires on Earth in normal gravity and those inmicrogravity.

The sequence of pictures, at thebottom of this page, illustrates a combustionexperiment conducted at the NASA LewisResearch Center 132 Meter Drop Tower.These pictures of a candle flame were

1114,in M.cogavityrecorded during a 5-second drop tower test.An electrically heated wire was used toignite the candle and then withdrawn 1second into the drop. As the picturesillustrate, the flame stabilizes quickly, and itsshape appears to be constant throughoutthe remainder of the drop. Instead of thetypical teardrop shape seen on Earth, themicrogravity flame becomes spherical. OnEarth, the flame is drawn into a tip by therising hot gases. However, convectioncurrents are greatly reduced in microgravity.Fresh oxygen is not being delivered to thecandle by these currents. Instead, oxygenworks it way slowly to the flame by theprocess of diffusion. Soon, the flametemperature begins to drop because the

4

(a) (b) (c)

(9) (I)

(d) (f)

Candle flame test in the 132 Meter Drop Tower at the NASA Lewis Research Center



Student Reader - 2

combustion is less vigorous. The lowertemperature slows down the melting andvaporization of the candle wax. Candlesonboard the first United States MicrogravityLaboratory, launched in June 1992, burnedfrom 45 seconds to about 1 minute beforebeing extinguished because of the droppingtemperature and reduction of wax vapor.

Combustion studies in microgravityare important to spacecraft safety. Unlikehouse fires on Earth, you can not runoutside of a space station and wait for thefire department to arrive. Fires have to beextinguished quickly and safely. To do thisit is essential to understand how fires areignited in microgravity and how they spread.The goal is to make sure that a fire nevergets started.

132

In the absence of buoyancy-driven convec-tion, as in microgravity, the supply of oxygenand fuel vapor to the flame is controlled bythe much slower process of moleculardiffusion. Where there is no "up" or "down,"the flame tends toward sphericity. Heat lostto the top of the candle causes the base ofthe flame to be quenched, and only a por-tion of the sphere is seen. The diminishedsupply of oxygen and fuel causes the flametemperature to be lowered to the point thatlittle or no soot forms. It also causes theflame to anchor far from the wick, so that theburning rate (the amount of wax consumedper unit time) is reduced.

139

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Student Sheet - 1

Candle Drop

Candle Drop Team Members:

Procedure:1. Put on eye protection.

2. Light the candle and screw the jaron to the lid. Observe the candleuntil it goes out.

3. Draw a picture of the shape of thecandle flame below.

What is the color of the flame?

Predict what you think will happento the candle flame when thecandle is dropped.

4. Open the jar to release the bad air.Relight the candle and screw thejar back on to the lid. Have oneteam member hold the jar as highoff the floor as possible. On thecount of three, the jar is dropped tothe floor where a second teammember is waiting to catch it. Thethird member acts as the observer.Data are recorded by the observerin the table on the next page.

5. Repeat step 4 twice more but rotatethe jobs so each team membergets the chance to drop the jar,catch the jar, and write downobservations.



Student Sheet 2

Team Member:

Candle flameshape

Candle flamebrightness

Candle flamecolor

Otherobservations

Candle Drop Data Table21 3

What changes took place when the candle flame experienced microgravity?

Compare these changes to the candle flame that was not dropped.

Why do you think these changes took place?

Design a candle flame experiment that could be used on the International Space Station.Write out, on another piece of paper, the experiment hypothesis and sketch the apparatusthat will be needed. Write a short paragraph describing the device, how it will work, andwhat safety procedures you would use.

134



Crystallization ModelObjective:

To demonstrate how atoms in asolid arrange themselves.

Science Standards:Science as InquiryPhysical Science- position and motion of objectsUnifying Concepts & ProcessesChange, Constancy, & MeasurementScience & Technology- abilities of technological design

Science Process Skills:ObservingCommunicatingCollecting DataInferringPredictingInterpreting DataHypothesizingControlling VariablesInvestigating

Activity Management:The crystal model device describedhere is best suited for use as aclassroom demonstration. It is avibrating platform that illustrates intwo dimensions the development ofcrystal structure and defect forma-tion. BBs, representing atoms ofone kind, are placed into a shallowpan which is vibrated at differentspeeds. The amount of vibration atany one time represents the heatenergy contained in the atoms.Increasing the vibration rate simu-lates heating of a solid material.Eventually, the atoms begin toseparate and move chaotically.This simulates melting. Reducingthe amount of vibration brings the

BBs on a vibrating platform arrange themselves inpatterns similar to the atoms in solids.

Cn-J0

4CCI<2

Wood base and supportsShallow pan3 Small bungee cordsSmall turnbuckleSurplus 110 volt AC electric

motorMotor shaft collarVariable power transformerSeveral hundred BBsHook and loop tape

atoms back together where they "bond" witheach other. In this demonstration, gravitypulls the BBs together to simulate chemicalbonds. By observing the movement of BBs,a number of crystal defects can be studiedas they form and transform. Because ofmovements in the pan, defects can combine(annihilation) in such a way that the ideal



hexagonal structure is achieved and newdefects form.

The model is viewed best with small groupsof students standing around the device.After the solid "melts," diminish the motorspeed gradually to see the ways the atomsorganize themselves. It is important that theplatform be adjusted so it is slightly out oflevel. That way, as the motor speed dimin-ishes the BBs will move to the low side ofthe pan and begin organizing themselves. Ifthis does not happen, apply light fingerpressure to one side of the pan to lower itslightly. This will not affect the vibrationmovements significantly. While doing thedemonstration, also stop the vibration sud-denly. This will simulate what happenswhen molten material is quenched (cooledrapidly).

The motor collar required in the materials listis available from a hardware store. Thepurpose of the collar is to provide an off-center weight to the shaft of the motor. Theset screw in the collar may have to be re-placed with a longer one so that it reachesthe motor shaft for proper tightening.

Constructing The Vibrating PlatformNote: Specific sizes and part descriptionshave not been provided in the materials listbecause they will depend upon the dimen-sions of the surplus electric motor obtained.The motor should be capable of severalhundred revolutions per minute.

1. Mount three vertical supports on to thewooden base. They can be attached withcorner braces or by some other means.

2. Mount the surplus motor to the bottom ofthe vibrating platform. The specificmounting technique will depend upon themotor. Some motors will feature mountingscrews. Otherwise, the motor may haveto be mounted with some sort of strap.When mounting, the shaft of the motor

136*

should be aligned parallel to the bottom ofthe platform.

3. Slip the collar over the shaft of the motorand tighten the mounting screw to theshaft. See the diagram below for how theshaft and collar should look when thecollar is attached properly.

4.

5.

6.

7.

Microgravity A Teacher's Guide with ActivitiesEG-1997-08-110-HQ, Education Stan

CollarVALtv

Motor

Motor Shaft

Set Screw

Suspend the platform from the threevertical supports with elastic shock(bungee) cords or springs. Add aturnbuckle to one of the cords for lengthadjustment. Shorten that cord an amountequal to the length of the turnbuckle sothe platform hangs approximately level.Using hook and loop tape, mount the panon the upper side of the vibratingplatform.Place several hundred BBs in the pan. Ifthe BBs spread out evenly over the pan,lengthen the turnbuckle slightly so theBBs tend to accumulate along one side ofthe pan.Turn on the motor by raising the voltageon the variable transformer. If the deviceis adjusted properly, the BBs will startdancing in the pan in a representation ofmelting. Lower the voltage slowly. TheBBs will slow down and begin to arrangethemselves in a tight hexagonal pattern.If you do not observe this effect, adjustthe leveling of the platform slightly untilyou do. It may also be helpful to adjustthe position of the motor slightly.

143in Science, Mathematics, and Technology,

dards Grades 5-8 (A), 9-12 (0)

Conducting The Experiment1. Turn up the voltage on the variable

transformer until the BBs are dancingabout in the pan. This represents meltingof a solid.

2. Shut the variable transformer off. Thisrepresents rapid cooling of the liquid to aglassy (amorphous) state. Observe andsketch the pattern of the BBs and of thedefects.

3. Turn up the voltage again and graduallyreduce the vibration until the BBs aremoving slowly. Observe how the BBsmove and pack together.

Assessment:Collect the student work sheets.

Extensions:1. Obtain some mineral crystal samples and

examine them for defects. Most crystalswill have some visible defects. Thedefects will be at a much larger scale thanthose illustrated in the student reader.One defect that is easy to find in themineral quartz is color variations due tothe presence of impurities.

2. Investigate the topic of impuritiesdeliberately, incorporated in crystals usedto manufacture computer chips. What dothese defects do?

3. Design a crystal-growing experiment thatcould be used on the International SpaceStation. Conduct a ground-based versionof that experiment. How would theexperiment apparatus have to bechanged to work on the space station?


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 ()137

Student Reader - 1

Crystalline solids are substanceswhose atoms or molecules are arrangedinto a fixed pattern that repeats in threedimensions. Crystalline materials gener-ally begin as a fluid of atoms or moleculesin either the liquid or gaseous state. Asthey change to the solid state, the atoms ormolecules join together in repeating pat-terns. Materials that do not form thesepatterns are called amorphous. Glass is agood example of an amorphous material.

The usefulness of a crystal dependson its structure. All crystalline materialshave varying degrees of defects. Defectscan take many forms. Gem-quality dia-monds sometimes have small inclusions ofcarbon (carbon spots) that diminish theirlight refraction and thereby reduce theirvalue. In other crystalline materials, de-fects may actually enhance value. Crystalsused for solid state electronics have impuri-ties deliberately introduced into their struc-ture that are used to control their electricalproperties. Impurity atoms may substitutefor the normal atoms in a crystal's structureor may fit in the spaces within the structure.Other defects include vacancies, whereatoms are simply missing from the struc-ture, and dislocations, in which a half planeof atoms is missing. The important thingabout crystal defects is to be able to controltheir number and distribution. Uncontrolleddefects can result in unreliable electronicproperties or weaknesses in structuralmetals.

138

Sample Crystal DefectsThe following diagrams show a mag-

nified view of an ideal two-dimensionalcrystalline structure (hexagonal geometry)and a variety of defects that the structuremight have.

000......os....405...s',141**4Ideal crystalline structure

0. .:4:e O' .. -**44* .: * ..04. 4.4.4)17 00*_ *Alp_ 744.4.11. 14.:Alr49011//1110 04.ip*.

1:SV *. :Amorphous or glassy structure (when stationary)or a liquid structure (when in motion)

145Crystalline structure with surface (grain boundary)defect


Student Reader - 2

Many forces can affect the structureof a crystal. One of the most importantforces that can influence the structure of agrowing crystal is gravity. Growing crystalsin microgravity can reduce gravity effects toproduce crystals with better defined proper-ties. The information gained by microgravityexperiments can lead to improved crystalprocessing on Earth.

The connection between the force ofgravity and the formation of defects variesfrom very simple and straightforward tocomplicated and nonintuitive. For example,mercury iodide crystals can form from thevapor phase. However, at the growth tem-perature (approximately 125°C) the crystalstructure is so weak that defects can formjust due to the weight of the crystal. On theother hand, the relationship between re-sidual fluid flows caused by gravity and anyresulting crystalline defects is not well un-derstood and may be very complex.

Crystalline structure with point defects (vacanciesand substitution impurities)

0000000000*04000000000000 0001.0000000000000000000100000000000000.00000000*000000410000000.00000000000.0 0 004.0 0 0 0 WO*4000," 000.00000000000000000000000000000000000000.00000000.0000/0000.000000000000000000000.00000000000000000000.000000000'

Crystalline structure (further magnified) withinterstitial defect and edge dislocations

OVIIHEIKOV4110001b:41111AITIO'OYOTOWO

Interstitial

Edge

146

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (s), 9-12 (0)

139

Student Work Page - 1

CrystallizationName:

Based on your observations, describe andsketch each crystallization stage shown withthe model.

Melting:

Fast Cooling:

Slow Cooling:

140

147


Crystal Growth and Buoyancy-Driven Convection CurrentsObjective:

To observe buoyancy-driven covectioncurrents that are created as crystalsgrow in a crystal growing solution.

Science Standards:Science as InquiryPhysical Science- position and motion of objects- properties of objects and materialsUnifying Concepts and ProcessesChange, Constancy, & Measurement

Science Process Skills:ObservingCommunicatingMeasuringCollecting DataInferringPredictingHypothesizing


Activity Management:This activity is best done as ademonstration. While it is easy forstudents to grow crystals by following thedirections, the success of observing thedensity-driven convection currentsdepends upon a very still environment.The crystal-growing chamber should beplaced on a firmly mounted counterwhere it will not be disturbed. Theconvection currents are very sensitive tovibrations. Place a slide projector on oneside of the chamber and direct the lightfrom the projector through the growthchamber so it casts a shadow on the wallbehind. If the wall behind the chamber is

Gravity-driven convection currents are createdin a crystal growth chamber by the interactionof the growing crystal and the solution.

Aluminum potassium sulfateAIK(SO4)2.12H20* (alum)

Square acrylic box**Distilled waterStirring rodMonofilament fishing lineSilicone cementBeakerSlide projectorProjection screenEye protectionHot plateThermometerBalance*Refer to the chart for the

amount of alum needed forthe capacity of the growthchamber (bottle) you use.

**Clear acrylic boxes, about10x1 Ox13 cm, are availablefrom craft stores. Select abox that has no opticaldistortions.

14 8Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,

EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 ozo141

textured or a dark color, tape a piece ofwhite paper there to act as a screen.Viewing may be improved by adding darkpaper shields around the screen to reduceoutside light falling on the screen. Theprojector can be replaced by a clearlightbulb of about 100 to 150 watts that hasa straight filament. Place the bulb in a cliplamp light socket and aim the bulb so thefilament is pointing directly at the growthchamber. This will make the bulb serve as apoint source of light so the shadows will beclear. Do not use a reflective lamp shadewith the light.

When preparing the crystal growing solution,be sure to follow routine safety precautionssuch as wearing eye protection. You canobtain this chemical from school sciencesupply companies or even in food stores inthe spice section. Alum is used in pickling.

To produce large alum crystals, it is neces-sary to obtain seed crystals first. This isaccomplished by dissolving some alum in asmall amount of water and setting it asidefor a few days. Plan to do this step severalweeks before you will use the demonstrationwith your students. To save time, dissolveas much alum as you can in warm water.This will produce a supersaturated solutionwhen the liquid cools and crystallization willstart shortly. After the seed crystals form(about 3-5 mm in size) pour the solutionthrough some filter paper or a paper towel tocapture the seeds. Let them dry beforeattaching the fishing line. In attaching the

142

line, simply place a dab of silicone Cementon a piece of paper and then touch the endof a short length of monofilament fishing lineto the cement. Then, touch the same end ofthe line to the crystal. Prepare several seedcrystals in this manner. When the cementdries, you will be ready for the steps below.

You may discover mysterious variations inthe growth of the crystal over several days.Remember, the amount of alum that can bedissolved in a given quantity of water willvary with the water's temperature. Warmwater can hold more alum than cold water.If the air-conditioning in a building is shut offfor the weekend, the temperature of thealum solution will climb with the room'stemperature and some or all of the crystalmay dissolve back into the water.

Procedure:1. Prepare the crystal growth solution by

dissolving powdered or crystalline alum ina beaker of warm water. The 'amount ofalum that can be dissolved in the waterdepends upon the amount of water usedand its temperature. Refer to the plot(Alum Solubility in Water) for the quantityrequired.

2. When no more alum can be dissolved inthe water, transfer the solution to the.growth chamber acrylic box.

3. Punch or drill a small hole through thecenter of the lid of the box. Thread theseed crystal line through the hole andsecure it in place with a small amount oftape. Place the seed crystal in the boxand place the lid on the box at a 45degree angle. This will expose thesurface of the solution to the outside air topromote evaporation. It may benecessary to adjust the length of the lineso the seed crystal is several centimetersabove the bottom of the box.

4. Set the box aside in a place where it canbe observed for several days withoutbeing disturbed. If the crystal should

Microgravity A Teacher's Guide with Adiv4e9i,n Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (o)

disappear, dissolve more alum into thesolution and suspend a new seed crystal.Eventually, growth will begin.

5. Record the growth rate of the crystal bymeasuring it with a metric ruler. Thecrystal may also be removed and its massmeasured on a balance.

6. Periodically observe the fluid flowassociated with the crystal's growth bydirecting the light beam of a slideprojector through the box to a projectionscreen. Observe plumes around theshadow of the crystal. Convectioncurrents in the growth solution distort thelight passing through the growth solution.Refer to the diagram at the beginning ofthis activity for information on how theobservation is set up.

"g00

2534

20

.<1

46 15c.)

10

35

30


Extensions:1. Try growing other crystals. Recipes for

crystals can be found in reference bookson crystal growing.

2. Collect natural crystals and observe theirsurfaces and interiors (if transparent).Look for uniformity of the crystals and fordefects. Make a list of different kinds ofdefects (fractures, bubbles, inclusions,color variations, etc.). Discuss whatconditions must have existed in nature atthe time of the crystal's formation or afterits formation to cause the defects.

3. Review scientific literature for results frommicrogravity crystal-growing experiments.

Alum Solubility in WaterAIK(SO4 )2.121320

+/

20 25 . 30 35 40 45 50

Temperature Degrees Celsius

150

55

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (D)

143

Student Reader - 1

Crystal Growth and Buoyancy-DrivenConvection Currents

Crystals can be grown using a variety ofmethods. One of the simplest methodsinvolves dissolving a solid into a liquid. Asthe liquid evaporates, the solid comes outof solution and forms a crystal (or manycrystals). This can be done with sugar orsalt or a variety of other compounds suchas alum (aluminum potassium sulfate), LAP(L-arginine phosphate), or TGS (triglycinesulfate).

The usual procedure for growing crystalsfrom a solution is to create the solution first.In this activity, a quantity of alum isdissolved into warm water. Warm waterwas used to increase the amount of alumthat could be dissolved. You may haveobserved this effect by stirring sugar into acup of hot coffee or tea. Hot liquids candissolve more sugar than cold liquids. Afterthe alum was dissolved, the solution wasallowed to cool back down to roomtemperature. As a result, the water heldmore alum than it normally could at thattemperature. The solution wassupersaturated. A seed crystal wassuspended in the solution and it began togrow. The excess alum dissolved in thewater migrated to the crystal and wasdeposited on its surface. Because thecrystal growth chamber was open to thesurrounding air, the solution beganevaporating. This continued the crystalgrowth process because the alum left overfrom the evaporated water was depositedon the crystal.

At first glance, the growth process of thealum crystal looks very quiet and still.However, examination of the solution andgrowing crystal with light to produce

144

00

0OOS0 0

00 000 0

0

0 0000

o0

o

e0

o

Water molecules in this diagram are represented byblack dots and the alum dissolved represented by thelighter dots. Throughout most of the solution, thedots are randomly mixed but, next to the crystal, thedots are mostly black. This happens because thealum nearest the growing crystal attaches to thecrystal structure, leaving behind the water. Theremaining water is buoyant and rises while denserwater with more dissolved alum moves next to thecrystal to take its place.

shadows shows that currents exist in thesolution. These currents become visiblewhen light is projected through thembecause the convection currents distort thelight rays, making them appear as darkplumes on the screen. This image on thescreen is called a shadowgraph.

Where do these convection currents comefrom? The answer has to do with thedifference in the amount of alum in solution

Microgravity A Teacher's Guide with Activities i1185ietce, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 ()

Student Reader - 2

near the growing crystal compared with thesolution near the wall of the growthchamber. Except for near the crystal, thesolution is homogeneous. This means it hasthe same composition and density. Thesolution near the crystal is another matter.As each molecule of alum leaves thesolution to become deposited on thecrystal's surface, the solution left behindbecomes slightly less dense than it was.The less dense solution is buoyant andbegins to rise in the chamber. More densesolution moves closer to the crystal to takeits place. The alum in the replacementsolution also deposits on the crystal,causing this solution to become less denseas well. This keeps the convection currentmoving.

Microgravity scientists are interested in theconvection currents that form around acrystal growing in solution. The currentsmay be responsible for the formation ofdefects such as liquid inclusions. These aresmall pockets of liquid that are trappedinside the crystal. These defects candegrade the performance of devices madefrom these materials. The virtual absence ofbuoyancy-driven convection in amicrogravity environment may result in farfewer inclusions than in crystals grown onEarth. For this reason, solution crystalgrowth has been an active area ofmicrogravity research.

Shadowgraph image of a growth plumerising from a growing crystal.

152


145


Crystal Growth and Buoyancy-DrivenConvection Currents

Name:

1. In the box to the right, make a sketch of what you observed in the shadowgraph of acrystal growing from solution.

2. Explain below what is happening.

Shadowgraph for growing alum crystal

3. In the box to the right, sketch what a shadowgraph should look like for a crystal that isdissolving back into solution.

4. Explain your diagram below.

146

1 5 3Shadowgraph for dissolving alum crystal

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HO, Education Standards Grades 5-8 (A), 9-12 (o)


5. Draw a picture in the space to the right ofwhat you think the shadowgraph shouldlook like for a crystal grown from solutionin a microgravity environment.

6. Explain your picture below.

Shadowgraph for alum crystal grown inmicrogravity

54


147

148

Rapid CrystallizationObjective:

To investigate the growth of crystalsunder different temperatureconditions.

Science Standards:Science as InquiryPhysical Science- properties of objects and materialsUnifying Concepts and ProcessesChange, Constancy, & Measurement

Science Process Skills:ObservingCommunicatingMeasuringCollecting DataInferringPredictingInterpreting DataControlling VariablesInvestigating

Mathematics Standards:CommunicationMeasurement

Activity Management:This activity is best done withcooperative learning groups of two orthree students. This will minimize thenumber of heat packs that have to beobtained. Heat packs are sold atcamping supply stores. It is importantto get the right kind of pack. Thepack, sold under different names,consists of a plastic pouch (approxi-mately 9 by 12 centimeters in size)containing a solution of sodiumacetate and water and a small metaldisk. When the disk is clicked orsnapped, crystals begin to form andheat is released. The pack can be

The rapid growth of crystals in a heat pack isobserved under different heating conditions.

coJ0

CCJ

uJ

Heat pack hand warmers(1 or more per group)

Water boiler (an electrickitchen hot pot can beused)

Styrofoam food tray(1 per group)

Metric thermometer(1 or more per group)

Observation and data table(1 per student group)

CoolerClock or other timer

reused by reheating until all thecrystals are dissolved.

Assemble all the materials needed forthe activity in sets for the number ofstudent groups you have. Prepare theheat packs by heating any that aresolidified until all the crystals dissolve.

A. ,)Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,


Allow one half of the packs to cool to roomtemperature. Maintain the other packs at atemperature of about 45°C. This can bedone by placing the packs in an insulatedcooler with some hot water until the packsare needed.

Before starting the experiment, discuss thedata collection procedure. To reduce heatconductivity problems, heat packs areplaced on the Styrofoam food tray with thebulb of a thermometer slipped between thepack and the tray. Discuss with the studentswhy the tray is necessary and ask themwhere the best placement of the bulb shouldbe. Remind students that the thermometershould be placed the same way for eachtest. Give each student group one studentdata sheet for each test to be performed.

Begin with observation of the roomtemperature pack first. The students shouldbe prepared to make observationsimmediately after the disk is clicked.Complete crystallization should take lessthan a minute. Since the crystallizationprocess is dramatic, demonstrate theclicking process with another heat pack andpass it around for students to feel. If youhave some sort of video display system,show crystallization on the television as it ishappening. This may help students focus onthe investigation when they start their ownpacks crystallizing. Distribute the secondpack after observations of the first pack arecomplete. Crystallization of the second packwill take several minutes to complete.

Students will discover that heat packs withhigher initial temperatures will take longer tocrystallize. Crystals will be more definedthan those forming in packs with coolerinitial starting temperatures. Dependingupon the initial temperature, crystals may

resemble needles or blades. Gravity willinfluence their development. Crystals willsettle to the bottom of the pack andintermingle, causing distortions. Crystalsforming in an initially cool heat packs will beneedlelike but, because so many form atonce, the growth pattern will be fan-shaped.

Use the questions below as a guide todiscuss the results of the investigation.

1. Is there any relationship between theinitial temperature of the pouch and thetemperature of the pouch duringcrystallization?

2. Is there a relationship between the initialtemperature of the pouch and the time ittakes for the pouch to completelysolidify?

3. Do other materials, such as water,release heat when they freeze?


Extensions:1. Discuss what might happen if the heat

pack were crystallized in microgravity.What effect does gravity have? Hold thepack vertically with the steel disk at thebottom and trigger the solidification.Repeat with the disk at the top.

2. Try chilling a heat pack pouch in a freezerand then triggering the solidification.



Student Reader 1

liP4.4ii and CrystatsCrystals are solids composed of atoms,ions, or molecules arranged in orderlypatterns that repeat in three dimensions.The geometric form of a crystal visible to thenaked eye can provide clues to thearrangement inside. Many of the uniqueproperties of materials, such as strength andductility, are a consequence of crystallinestrudture.

It is easy to get confused about thenature of crystals because the word crystalis frequently misused. For example, acrystal chandelier is not crystal at all.Crystal chandeliers are made of glass whichis a solid material but does not have aregular interior arrangement. Glass is calledan amorphous material because it does nothave a regular interior arrangement ofatoms.

Scientists are very interested ingrowing crystals in microgravity becausegravity often interferes with the crystal-growing process, leading to defects formingin the crystal structure. The goal of growingcrystals in microgravity is not to developcrystal factories in space but to betterunderstand the crystal-growing process andthe effects that gravity can have on it.

In this activity, you will beinvestigating crystal growth with a handwarmer. The hand warmer consists of aplastic pouch filled with a food-gradesolution of sodium acetate andwater. Also in the pouch is asmall disk of stainless steel.

041mW/mAorur

,,,a-igt.i1=Afr2Amp.o...Aisaair nmmprAlorarave

&rirzwr AroRWPowrao%War

Snapping the disk triggers the crystallizationprocess. (The exact cause for thisphenomena is not well understood.)

The pouch is designed so that at roomtemperature the water contains many moremolecules of sodium acetate than wouldnormally dissolve at that temperature. This iscalled a supersaturated solution. Thesolution remains that way until it comes incontact with a seed crystal or some way ofrapidly introducing energy into the solutionwhich acts as a trigger for the start ofcrystallization. Snapping the metal diskinside the pouch delivers a sharp mechanicalenergy input to the solution that triggers thecrystallization process. Crystallization takesplace so rapidly that the growth of crystalscan easily be observed.

Heat is released during theprecipitation that maintains the pouch

temperature at about 54°C for about30 minutes. This makes the pouchideal for a hand warmer. Furthermore,the pouch can be reused by reheatingand dissolving the solid contentsagain.

150

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EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 ozo


Team Member Names:

O Heat Pack ExperimentData Sheet

Test number:

Initial temperature of pouch:

Temperature and time atbeginning of crystallization:

Temperature and time atend of crystallization:

Length of time forcomplete crystallization:

Describe the crystals(shape, growth rate, size, etc.)

Sketch of Crystals

Test number:

Initial temperature of pouch:

Temperature and time atbeginning of crystallization:

Temperature and time atend of crystallization:

Length of time forcomplete crystallization:

Describe the crystals(shape, growth rate, size, etc.)

Sketch of Crystals

158


151

152

Microscopic Observation ofCrystal GrowthObjective:

To observe crystal nucleation andgrowth rate during directionalsolidification.

Science Standards:Science as InquiryPhysical Science- position and motion of objects

properties of objects and materialsUnifying Concepts and ProcessesChange, Constancy, & Measurement

Science Process Skills:ObservingCommunicatingInvest i g at i ng

Activity ManagementThe mannite part of this activityshould be done as a demonstration,using a microprojector or microscopewith a television system. It is neces-sary to heat a small quantity ofcrystalline mannite on a glass slide to168°C and observe itsrecrystallization under magnification.The instructions call for melting themannite twice and causing it to coolat different rates. It is better toprepare separate samples so theycan be compared to each other. Theslide that is cooled slowly can easilybe observed under magnification as itcrystallizes. You may not have time toobserve the rapidly chilled sampleproperly before crystallization iscomplete. The end result, however,will be quite apparent undermagnification. If students will beconducting the second part of the


EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (a)

A microprojector is used to observe crystalgrowth.

Bismarck brown YMannite (d-mannitol)HOCH2(CHOH)4CH2OHSalol (Phenyl salicylate)

C131-1,00,

MicroprojectorStudent microscopes (instead

of a microprojector)Glass microscope slides with

cover glassCeramic bread-and-butter

plateRefrigeratorHot plate or desktop coffee

cup warmerForcepsDissecting needleSpatulaEye protection

activity, it is suggested that you prepareseveral sets of mannite slides so theymay be distributed for individualobservations.

The salol observations are suitable for ademonstration, but because of the lowermelting temperature (48°C), it is much saferfor students to work with than the mannite.A desktop coffee cup warmer is sufficient formelting the salol on a glass slide. Becauseof the recess of the warmer's plate, it is bestto set several large metal washers on theplate to raise its surface. The washers willconduct the heat to the slide and make iteasier to pick up the heated slide withforceps. Point out to the students that theyshould be careful when heating the salolbecause overheating will cause excessiveevaporation and chemical odors, and willincrease the time it takes for the material tocool enough for crystallization to occur. Theslide should be removed from the hot platejust as it starts melting. The glass slide willretain enough heat to complete the meltingprocess.

Only a very small amount of bismarck brownis needed for the last part of the activity withsalol. Only a few dozen grains are needed.Usually just touching the spatula to thechemical causes enough particles to cling toit. Gently tap the spatula held over themelted salol to transfer the particles. It willbe easier to do this if the salol slide isplaced over a sheet of white paper. This willmake it easier to see that the particles havelanded in the salol.

If students are permitted to do individualstudies, go over the procedures whiledemonstrating crystallization with thed-mannitol. Have students practicesketching the crystallized mannitol samplesbefore they try sketching the salol.

Refer to the chemical notes below for safetyprecautions required for this activity.

6

Notes On Chemicals Used:Bismarck Brown Y

Bismarck brown is a stain used to dyebone specimens for microscope slides.Because bismarck brown is a stain,avoid getting it on your fingers.Bismarck brown is water soluble.

Mannite (d-mannitol)HOCH,(CHOH),CH,OHMannite has a melting point ofapproximately 168°C. It may beharmful if inhaled or swallowed.Wear eye protection and gloves whenhandling this chemical. Conduct theexperiment in a well-ventilated area.

Salo! (phenyl salicylate)C,,H1003

It has a melting point of 43° C. It mayirritate eyes. Wear eye protection.

Procedure: Observations ofMannite1. Place a small amount of mannite on a

microscope slide and place the slide on ahot plate. Raise the temperature of thehot plate until the mannite melts.Be careful not to touch the hot plate orheated slide. Handle the slide withforceps.

2. After melting, cover the mannite with acover glass and place the slide on aceramic bread-and-butter plate that hasbeen chilled in a refrigerator. Permit theliquid mannite to crystallize.

3. Observe the sample with amicroprojector. Note the size, shape,number, and boundaries of the crystals.

4. Prepare a second slide, but place itimmediately on the microprojector stage.Permit the mannite to cool slowly. Againobserve the size, shape, and boundariesof the crystals. Mark and save the twoslides for comparison using studentmicroscopes. Forty power is sufficient forcomparison. Have the students makesketches of the crystals on the two slides

0 and label them by cooling rate.


153

Observations of Salo!5. Repeat the procedure for mannite (steps

1-4) with the salol, but do not use glasscover slips. Use a desktop coffee cupwarmer to melt the salol. It may benecessary to add a seed crystal to theliquid on each slide to start thecrystallization. Use a spatula to carry theseed to the salol. If the seed melts, waita moment and try again when the liquid isa bit cooler. (If the microprojector youuse does not have heat filters, the heatfrom the lamp may remelt the salol beforecrystallization is completed.)

6. Prepare a new salol slide and place it onthe microprojector stage. Drop a tinyseed crystal into the melt and observethe solid-liquid interface.

7. Remelt the salol on the slide and sprinklea tiny amount of bismarck brown on themelt. Drop a seed crystal into the meltand observe the motion of the bismarckbrown granules. The granules will makethe movements of the liquid visible. Payclose attention to the granules near thegrowing edges and points of the salolcrystals.

154

Assessment:Collect the student data sheets.

Extensions:1. Design a crystal-growing experiment that

could be flown in space. The experimentshould be self-contained and the onlyastronaut involvement that of turning aswitch on and off.

2. Design a crystal-growing experiment forspaceflight that requires astronautobservations and interpretations.

3. Research previous crystal-growingexperiments in space and some of thepotential benefits researchers expect fromspace-grown crystals.

61


Student Reader - 1

Crystal Growth

Directional solidification refers to a processby which a liquid is transformed (by freez-ing) into a solid through the application of atemperature gradient (a temperature differ-ence over a specified distance such as100 C/cm) in which heat is removed in onedirection. The heat travels down the tem-perature gradient from hot to cold. A con-tainer of liquid will turn to a solid in thedirection the temperature is lowered. If thisliquid has a solute (something dissolved inthe liquid) present, typically some of thesolute will be rejected into the liquid aheadof the liquid/solid interface. However, notall of the solute can be contained in thesolid as it forms; the remaining solute ispushed back into the liquid near the inter-face. This phenomenon has many impor-

tant consequences for the solid including howmuch of the solute eventually ends up in thesolid. The concentration of solute in the solidcan control the electrical properties of semi-conductors and the mechanical and corrosionproperties of metals. As a result, soluterejection is studied extensively in solidificationexperiments.

The rejected material tends to build upat the interface (in the liquid) to form a layerrich in solute. This experiment demonstrateswhat happens when the growth rate is too fastand solute in the enriched layer is trapped.

Fluid flow in the melt can also affect thebuildup of this enriched layer. On Earth, fluidsthat expand become less dense. This causesa vertical flow of liquid which will interfere withthe enriched layer next to the growing solid. Inspace, by avoiding this fluid flow, a moreuniform enriched layer will be achieved. This,in turn, can improve the uniformity with whichthe solute is incorporated into the growingcrystal.

Sample Microscope SketchesMannite Crystallization

Slow Cooling Fast Cooling


155


Microscopic Observation of Crystals

Name:

1. Study the mannite crystallization slides. Sketch what you observe in the two circlesbelow. Identify the cooling rate for each slide and the magnification you used for yourobservations.

Mannite (d-Mannitol)

Cooling Rate:

Magnification:

Cooling Rate:

Magnification:

Describe below the difference between the two mannite samples.

How can you explain these differences?

156

163



2. Prepare the salol samples according to instructions provided by your teacher.Remember to wear eye protection as you handle the chemical. Study the salolcrystallization slides. Sketch what you observe in the two circles below. Identify thecooling rate for each slide and the magnification you used for your observations.

Salol (Phenyl Salicylate)

Cooling Rate:

Magnification:

Cooling Rate:

Magnification:

Describe below the difference between the two salol samples.

How can you explain these differences?

6 4


157


3. Prepare a third salol sample according to instructions provided by your teacher.Remember to wear eye protection as you handle the chemical. Adjust the sample on themicroscope stage so you can observe the interface between the growing crystals and themelted chemicals. In particular, look at what happens to the bismarck brown particles asthe growing crystals contact them. Sketch what you observe in the circle below.

Cooling Rate:

Magnification:

Slow

What happens to the resulting crystals when impurities (bismarck brown) exist in the melt?

What caused the circulation patterns of the liquid around,the growing crystal faces? Doyou think these circulation patterns affect the atomic arrangements of the crystals? How?

How do you think the growth of the crystals would be affected by growing them inmicrogravity?

158

I 6 o


Zeolite Crystal GrowthObjective:

To grow zeolite crystals and investi-gate how gravity affects theirgrowth.

Science Standards:Science as InquiryPhysical ScienceUnifying Concepts and ProcessesChange, Constancy, & MeasurementScience in Personal and Social

Perspectives

Science Process Skills:ObservingCommunicatingMeasuringCollecting DataControlling VariablesInvestigating


Activity Management:The preparation of zeolite crystals,although not difficult, is an involvedprocess. A number of differentchemicals must be carefully weighedand mixed. You may wish to preparethe chemicals yourself or assignsome of your more advancedstudents to the task. Refer to thematerials and tools list on the nextpage for a detailed list of what isrequired.

This activity involves maintaining ahot water bath continuously for up to8 days. If you do not have thefacilities to do this, you can conductthe experiment for just the 0 and 1TEA (triethanolamine) samples

166

Zeolite crystals are being grown in a hotwater bath.

described below. Crystals may also beformed if the hot water bath is turned offat the end of the school day and turnedon the succeeding day. Crystallizationtimes will vary under this circumstance,and close monitoring of the formation ofthe crystalline precipitate will benecessary.

Following the growth of zeolite crystals,small samples can be distributed tostudent groups for microscopic study.

Procedure:1. While wearing hand and eye

protection, weigh 0.15 grams of.sodium hydroxide and place it in a 60ml, high-density polyethylene bottle.Add 60 ml of distilled water to thebottle and cap it. Shake the bottlevigorously until the solids arecompletely dissolved. Prepare asecond bottle identical to the first.

2. Add 3.50 grams of sodium


159

Sodium aluminate NaA102FW=81.97Sodium metasilicate

anhydrous, purum,Na203Si, FW =122.06

Sodium hydroxide pellets,97+%, average compositionNaOH, FW=40

Triethanolamine (TEA), 98%(HOHCH2)3N, FW=149.19

Distilled water1000 ml Pyrex® glass beakerAluminum foilMetric thermometer with range

up to 100°CLaboratory hot plate2-60 ml high-density

polyethylene bottles withcaps

4-30 ml high-densitypolyethyene bottles withcaps

Plastic glovesGogglesGlass microscope slidesPermanent marker pen for

marking on bottlesWaterproof tapeLead fishing sinkersTongsEyedropperOptical microscope, 400X

metasilicate to one of the bottles andagain cap it and shake it until all thesolids are dissolved. Mark this bottle"silica solution." To the second bottle,add 5.6 grams of sodium aluminate andcap it and shake it until all the solids aredissolved. Mark this bottle "aluminasolution."

3. Using a permanent marker pen, mark thefour, 30 ml high-density polyethylenebottles with the following identifications:0 TEA, 1 TEA, 5 TEA, and 10 TEA.

160

4. Place 0.85 grams of TEA into the bottlemarked "1 TEA." Place 4.27 grams ofTEA into the bottle marked "5 TEA."Place 8.55 grams of TEA into the bottlemarked "10 TEA." Do not place any TEAinto the bottle marked "0 TEA."

5. Add 10 ml of the alumina solution to eachof the bottles. Also add 10 ml of the silicasolution to each bottle.

6. Cap each bottle tightly and shakevigorously. Secure each cap withwaterproof tape and tape a lead sinker tothe bottom of each bottle. The sinkershould weigh down the bottle so it will befully immersed in the hot water.

7. Prepare a hot water bath by placingapproximately 800 ml of water in a1000 ml Pyrex® beaker. Place the fourweighted bottles into the beaker. Thebottles should be covered by the water.Cover the beaker with aluminum foil andpunch a small hole in the foil to permit ametric thermometer to be inserted. Fixthe thermometer in such a way as toprevent it from touching the bottom of thebeaker. Place the beaker on a hot plateand heat it to between 85 and 95°C. Itwill be necessary to maintain thistemperature throughout the experiment.Although the aluminum foil will reduceevaporation, it will be necessary toperiodically add hot (85 to 90°C) water tothe beaker to keep the bottles covered.

8. After 1 day of heating, remove the bottlemarked 0 TEA from the bath with a pair oftongs. Using an eyedropper, take a smallsample of the white precipitate found onthe bottom of the bottle. Place the sampleon a glass microscope slide and examinefor the presence of crystals under variousmagnifications. Make sketches orphotograph any crystals found. Be sureto identify magnification of the sketches orphotographs and estimate the actual sizesof the crystals. Determine the geometric

6 7

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (ID)

form of the crystals. Look for crystals thathave grown together.

9. Repeat procedure 8 for the 1 TEA bottleafter 2 days of heating. Repeat theprocedure again for the 5 TEA bottle after5 days and for the 10 TEA bottles after8 days. Compare the size, shape, andintergrowth of the crystals formed in eachof the bottles.

Assessment:Collect student sketches and writtendescriptions of the zeolite crystals.

Extension:1. Obtain zeolite filter granules from a pet

shop. The granules are used for filteringammonia from aquarium water. Set up afunnel with filter paper and fill it with thegranules. Slowly pour a solution of waterand household ammonia (ammoniawithout lemon or other masking scents)into the granules. Collect the liquid belowand compare the odor of the filteredsolution and the unfiltered solution. Tryrunning the filtered solution through asecond time and again compare theodors. Be sure to wear eye protection.

168

Al/


161

Student Reader 1

Zeolites

Zeolites are crystals made up of the ele-ments silicon, aluminum, and oxygen. Thecrystals consist of alternating arrays of silica(beach sand, Si02) and alumina (aluminumoxide, A1203) and can take on many geomet-ric forms such as cubes and tetrahedra.Internally, zeolites arerigid sponge-like struc-tures with uniform butvery small openings(e.g., 0.1 to 1.2 nanom-eters or 0.1 to 1.2 X 1 COmeters). Because of thisproperty, these inor-ganic crystals are some-times called "molecularsieves." For this rea-son, zeolites are em-ployed in a variety ofchemical processes.They allow only mol-ecules of certain sizesto enter their poreswhile keeping moleculesof larger sizes out. In asense, zeolite crystalsact like a spaghettistrainer that permits hotwater to pass throughwhile holding back thespaghetti. As a resultof this filtering action, zeolites enable chem-ists to manipulate molecules and processthem individually.

or consumed by the reaction.) Scientistsuse zeolite crystals to produce all theworld's gasoline though a chemical processcalled catalytic cracking. Zeolite crystals areoften used in filtration systems for largemunicipal aquariums to remove ammonia

from the water.Because they areenvironmentallysafe, zeolites havebeen used inlaundry detergentsto removemagnesium andcalcium ions. Thisgreatly improvesdetergent sudsingin mineral-rich"hard" water.Zeolites can alsofunction as filtersfor removing lowconcentrations ofheavy metal ions,such as Hg, Cd,and Pb, orradioactivematerials fromwaste waters.Photomicrograph

The many chemical applications for zeolitecrystals make them some of the most usefulinorganic materials in the world. They areused as catalysts in a large number ofchemical reactions. (A catalyst is a materialthat has a pronounced effect on the speedof a chemical reaction without being affected

162

20 Am

of Zeolite A Crystals

Although scientistshave found many beneficial uses forzeolites, they have only an incompleteunderstanding of how these crystalsnucleate (first form from solution) and grow(become larger). When zeolites nucleatefrom a water solution, their density (twicethat of water) causes them to sink to thebottom of the special container (called anautoclave) they are growing in. This is aprocess called sedimentation, and it causesthe crystals to fall on top of each other. As


EG-1997-08-110-HQ, Education Standards Grades 5-8 (6,), 9-12 (CI)

Student Reader - 2

these crystals continue to grow after theyhave settled, some merge to produce alarge number of small, intergrown zeolitecrystals instead of larger, separate crystals.

Zeolite crystal growth research in themicrogravity environment of Earth orbit isexpected to yield important information forscientists that may enable them to producebetter zeolite crystals on Earth. In

microgravity, sedimentation is significantlyreduced and so is gravity-driven convection.

170

Zeolite crystals grown in microgravity areoften of better quality and larger in size thansimilar crystals grown in control experimentson Earth. Exactly how and why thishappens is not fully understood byscientists. Zeolite crystal growthexperiments on the Space Shuttle and onthe future International Space Station shouldprovide invaluable data on the nucleationand growth process of zeolites. Such anunderstanding may lead to new and moreefficient uses of zeolite crystals.


163


Microscopic Observation ofZeolite Crystals

Name:

Instructions:Observe through a microscope each zeolite crystal sample provided to you by your teacher.Sketch the samples in the circles provided and write a brief description of what you see.

Sample 1

TEA

Sample age day(s)

Description:

Sample 2

TEA

Sample age day(s)

Description:

164

1 71

Magnification: X

Magnification: X



Sample 3

TEA

Sample age day(s)

Description:

Sample 4

Sample age

Description:

TEA

QUESTIONS:

day(s)

Magnification: X

Magnification: X

1. What geometric form (crystal habit) did the zeolite crystals assume as they grew? Wasthere more than one form present? How did the zeolite crystals appear when they grewinto each other?

2. Can you detect any relationship between the length of time crystals were permitted toform, their size and their geometric perfection?

3. Would additional growing time yield larger crystals? Why or why not?

172


165

NASA Resources for Educators

NASA's Central Operation of Resources for Educa-tors (CORE) was established for the national and interna-tional distribution of NASA-produced educational materials inaudiovisual format. Educators can obtain a catalogue and anorder form by one of the following methods:

NASA CORELorain County Joint Vocational School15181 Route 58 SouthOberlin, OH 44074Phone (440) 774-1051, Ext. 249 or 293Fax (440) 774-2144E-mail nasaco@ leeca.esu.k12.oh.usHome Page: http://spacelink.nasa.gov/CORE

Educator Resource Center NetworkTo make additional information available to the education com-munity, the NASA Education Division has created the NASAEducator Resource Center (ERC) network. ERCs contain awealth of information for educators: publications, referencebooks, slide sets, audio cassettes, videotapes, telelecture pro-grams, computer programs, lesson plans, and teacher guideswith activities. Educators may preview, copy, or receive NASAmaterials at these sites. Because each NASA Field Centerhas its own areas of expertise, no two ERCs are exactly alike.Phone calls are welcome if you are unable to visit the ERCthat serves your geographic area. A list of the centers and theregions they serve includes:

AK, AZ, CA, HI, ID, MT NV, OR,UT WA, WYNASA Educator Resource CenterMail Stop 253-2NASA Ames Research CenterMoffett Field, CA 94035-1000Phone: (650) 604-3574

CT DE, DC, ME, MD, MA, NH,NJ, NY, PA, RI, VTNASA Educator Resource LaboratoryMail Code 130.3NASA Goddard Space Flight CenterGreenbelt, MD 20771-0001Phone: (301) 286-8570

CO, KS, NE, NM, ND, OK, SD, TXJSC Educator Resource CenterSpace Center HoustonNASA Johnson Space Center1601 NASA Road OneHouston, TX 77058Phone: (281) 483-8696

FL, GA, PR, VINASA Educator Resource LaboratoryMail Code ERLNASA Kennedy Space CenterKennedy Space Center, FL 32899-0001Phone: (407) 867-4090

KY NC, SC, VA, WVVirginia Air and Space MuseumNASA Educator Resource Center forNASA Langley Research Center600 Settler's Landing RoadHampton, VA 23669-4033Phone: (757) 727-0900 x 757

IL, IN, MI, MN, OH, WINASA Educator Resource CenterMail Stop 8-1NASA Lewis Research Center21000 Brookpark RoadCleveland, OH 44135-3191Phone: (216) 433-2017

AL, AR, IA, LA, MO,TNU.S. Space and Rocket CenterNASA Educator Resource Center forNASA Marshall Space Flight CenterPO. Box 070015Huntsville, AL 35807-7015Phone: (205) 544-5812

MSNASA Educator Resource CenterBuilding 1200NASA John C. Stennis Space CenterStennis Space Center, MS 39529-6000Phone: (228) 688-3338

NASA Educator Resource CenterJPL Educational OutreachMail Stop CS-530NASA Jet Propulsion Laboratory4800 Oak Grove DrivePasadena, CA 91109-8099Phone: (818) 354-6916

CA cities near the centerNASA Educator Resource Center forNASA Dryden Flight Research Center45108 N. 3rd Street EastLancaster, CA 93535Phone: (805) 948-7347

VA and MD's Eastern ShoresNASA Educator Resource LabEducation Complex - Visitor CenterBuilding J-1NASA Wallops Flight FacilityWallops Island, VA 23337-5099Phone: (757) 824-2297/2298

Regional Educator Resource Centers (RERCs) offermore educators access to NASA educational materials. NASAhas formed partnerships with universities, museums, and othereducational institutions to serve as RERCs in many states. Acomplete list of RERCs is available through CORE, or electroni-cally via NASA Spacelink at http://spacelink.nasa.gov

NASA On-line Resources for Educators provide currenteducational information and instructional resource materials toteachers, faculty, and students. A wide range of information isavailable, including science, mathematics, engineering, and tech-nology education lesson plans, historical information related tothe aeronautics and space program, current status reports onNASA projects, news releases, information on NASA educa-tional programs, useful software and graphics files. Educatorsand students can also use NASA resources as learning tools toexplore the Internet, accessing information about educationalgrants, interacting with other schools which are alreadyon-line, and participating in on-line interactive projects, commu-nicating with NASA scientists, engineers, and other team mem-bers to experience the excitement of real NASA projects.

Access these resources through the NASA Education HomePage: http://wwwhq.nasa.gov/education

NASA Television (NTV) is the Agency's distribution system forlive and taped programs. It offers the public a front-row seat forlaunches and missions, as well as informational and educationalprogramming, historical documentaries, and updates on the latestdevelopments in aeronautics and space science. NTV istransmitted on the GE-2 satellite, Transponder 90 at 85 degreesWest longitude, vertical polarization, with a frequency of 3880megahertz, and audio of 6.8 megahertz.

Apart from live mission coverage, regular NASA Televisionprogramming includes a Video File from noon to 1:00 pm, a NASAGallery File from 1:00 to 2:00 pm, and an Education File from2:00 to 3:00 pm (all times Eastern). This sequence is repeated at3:00 pm, 6:00 pm, and 9:00 pm, Monday through Friday TheNTV Education File features programming for teachers andstudents on science, mathematics, and technology. NASATelevision programming may be videotaped for later use.

For more information on NASA Television, contact:NASA Headquarters, Code P-2, NASA TV, Washington, DC20546-0001 Phone: (202) 358-3572NTV Home Page: http://www.hq.nasa.gov/ntv.html

How to Access NASA's Education Materials and Services,EP-1996-11-345-HO This brochure serves as a guide to ac-cessing a variety of NASA materials and services for educators.Copies are aVailable through the ERC network, or electronicallyvia NASA Spacelink. NASA Spacelink can be accessed at thefollowing address: http://spacelink.nasa.gov

Microgravity A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (6,), 9-12 Go

167

NASA Educational Materials

Educational VideotapeEducational Videotapes and slide sets are available throughthe Educator Resource Center Network and CORE (seelisting on page 167).

Microgravity - Length 23:24

This video describes the restrictions that gravity imposes onscientific experimentation and how they can be greatlyreduced in the exciting research environment of the SpaceShuttle and the International Space Station.

NASA publishes a variety of educational resources suitablefor classroom use. The following resources specifically relateto microgravity and living, working, and science research inthe microgravity environment. Resources are available fromdifferent sources as noted.

SlidesMicrogravity Science - Grades: 8-12This set of 24 slides illustrates the basic concepts ofmicrogravity and describes four areas of microgravityresearch, including.: biotechnology, combustion science, fluidphysics, and materials science. 1994

NASA PublicationsNASA (1980), Materials Processing In Space: Early Experi-ments, Scientific and Technical Information Branch, NASAHeadquarters, Washington, DC.

NASA (1982), Soacelab, EP-165, NASA Headquarters,Washington, DC.

NASA (1976-Present), Spinoff, NASA Headquarters,Washington, DC (annual publication).

NASA (1994), "Microgravity News," Microgravity ScienceOutreach, Mail Stop 359, NASA Langley Research Center,Hampton, VA (quarterly newsletter)

NASA (1988), Science in Orbit The Shuttle and SpacelabExperience: 1981-1986, NASA Marshall Space Flight Center,Huntsville, AL.

168

Suggested Reading

BooksFaraday, M., (1988), The Chemical History of a Candle,Chicago Review Press, Chicago, IL.

Halliday, D. & Resnick, R., (1988), Fundamentals of Physics,John Wiley & Sons, Inc., New York, NY.

Holden, A. & Morrison, P., (1982), Crystals and CrystafGrowing, The MIT Press, Cambridge, MA.

Lyons, J., (1985), Fire Scientific American, Inc.,New York, NY.

American Institute of Aeronautics and Astronautics (1981),Combustion Experiments in a Zero-gravity Laboratory,New York, NY

PeriodicalsChandler, D., (1991), "Weightlessness and Microgravity,"Physics Teacher, v29n5, pp. 312-313.

Cornia, R., (1991), "The Science of Flames," The ScienceTeacher v58n8, pp. 43-45.

figFrazer, L., (1991), "Can People Survive in Space?," Ad Astra,v3n8, pp. 14-18

Howard, B., (1991), "The Light Stuff," Omni, v14n2, pp. 50-54.

Noland, D., (1990), "Zero-G Blues," Qiscover, vl1n5, pp. 74-80.

Pool, R., (1989), "Zero Gravity Produces Weighty Improve-ments," Science, v246n4930, p. 580.

Space World, (1988), "Mastering Microgravity," v7n295, p. 4.

Science News, (1989), "Chemistry: Making Bigger, BetterCrystals," v136n22, p. 349.

Science News, (1989), "Making Plastics in Galileo's Shadow,"v136n18, p. 286.

USRA Quarterly, (1992), "Can You Carry Your Coffee IntoOrbit?," Winter-Spring.

7/1

Microgravity - A Teacher's Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5-8 (A), 9-12 (o)

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