1 atoms and stars ist 2420 class 12, november 24 fall 2008 instructor: david bowen course web site:
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11/24/08 Atoms and Stars, Class 12 11
Atoms and StarsIST 2420
Class 12, November 24Fall 2008
Instructor: David BowenCourse web site: www.is.wayne.edu/drbowen/aasf08
11/24/08 Atoms and Stars, Class 12 2Atoms and Stars, Class 12 2
Agenda
• Assignments, passbacks, initial signin sheet• The semester is ending• Upcoming assignments• Essay 2• Reading: Chemistry• Waves and the Uncertainty Principle• Lab 7: Specific gravity
11/24/08 Atoms and Stars, Class 12 3Atoms and Stars, Class 12 3
Upcoming …
• Don’t put off Essay 1!!! See me instead.• This week (November 24):
o Reader: Chemistryo Manual: Lab 7: Specific Gravityo Turn in Lab 9 as a whole
• Next week (December 1:)o Essay 2 due via Blackboardo Lab 11 – The Orbiting Bottleo SET
11/24/08 Atoms and Stars, Class 12 4Atoms and Stars, Class 12 4
Upcoming …
• December 8 (last regular class)o Review for Final Examo Due: all work to count in regular grade
• Work can be turned in later (up to one year after the end of this semester – this course only) but will count for a Change of Grade after the regular grades are turned in. See the Syllabus for this.
• December 15: nothing that night but the Final Exam
11/24/08 Atoms and Stars, Class 12 5Atoms and Stars, Class 12 5
Grade What-If
• Grade What-If (on course web site – see first slide for this URL)o Reminder: to get current course average, do
NOT put anything in for assignments you haven’t been graded for yet
• If you put anything in, remove it using “delete” keyo To see what happens if you miss assignments,
put in zeroes for those (this is what I will do)
11/24/08 Atoms and Stars, Class 12 6Atoms and Stars, Class 12 6
Semester is Ending!
• If you have been relying on being able to turn work in late, it is time to get goingo Alternatives: D, F, I, drop – see counselor!
• Getting ready for Final:o Read Information Sheet carefully – a lot of
information thereo Look at Final Topics carefullyo Use Review Session!
11/24/08 Atoms and Stars, Class 12 7Atoms and Stars, Class 12 7
Essay 2 (Review)
TOPIC: What has this course been about? You should answer this question with a core concept or idea, perhaps with dependent parts, and illustrated by referring to course experiences, such as labs and discussions, and materials, such as readings, notes, lab materials, and so on. A starting point is the “Course Description” section in the Syllabus. You can agree with, make changes to, or disagree with this description, but if you disagree, include an equivalent description – that is, one that covers the course as a whole.
11/24/08 Atoms and Stars, Class 12 8Atoms and Stars, Class 12 8
Essay 2 (cont’d)
• This topic does NOT ask for a simple listing of all of the topics and activities (“laundry list”), and does not ask for an evaluation of me or the course (that’s for SET).
• The topic asks for “a” core concept and suggests a starting point for your analysis
• Due 12/1. At the end of tonight’s class, we will have covered all of the core topics.
• Review Syllabus for other requirementso All quotes must have references
11/24/08 Atoms and Stars, Class 12 9Atoms and Stars, Class 12 9
Effects of Newton’s Laws
• Changed view completely from planets locked on spheres with earth fixed at center (Aristotle) to bodies mutually acting on each other through known laws, with nothing fixed
• Each (Copernicus to Newton) saw themselves as making marginal changes to improve model supported by religion
11/24/08 Atoms and Stars, Class 12 10Atoms and Stars, Class 12 10
Newton’s Laws (cont’d)
• However, looking back from where we are, Newton made it possible to see a universe without a God (except for setting up universe and starting it off)o Newton: “clockwork universe,” God as
clockmakero Role of God in celestial motion is possible but
not required – maybe “hand of God” as causeo We cannot escape this change (explanation)
11/24/08 Atoms and Stars, Class 12 11Atoms and Stars, Class 12 11
What Can We Trust as a Fact?
• As practical matters, Newton Laws, Special Relativity, General Relativity and Quantum Mechanics (all 20th Century) are extremely accurate, within their range of authority.
• Philosophically, each of the more recent ones undermines the earlier ones, even within their range of authorityo Practical changes are too small to detect
11/24/08 Atoms and Stars, Class 12 12Atoms and Stars, Class 12 12
Fact? (cont’d)
• So science offers practical certainty, but not philosophic certaintyo Also, scientific knowledge changes
• Does religion offer certainty?o Each claims to be certain, but they disagreeo Each claims to be eternal and unchanging, but
they have changed• My conclusion: humans cannot have
universal, eternal truth, but we can do well enough for any practical purpose
The Development of Chemistry
11/24/08 Atoms and Stars, Class 12 14
Readings – Galileo and Later
1450 1500 1550 1600 1650 1700 1750
Copernicus
BraheKepler
GalileoDescartes
NewtonBacon
The Rise of Science(the core of this course)
The Greeks
11/24/08 Atoms and Stars, Class 12 15Atoms and Stars, Class 12 15
Readings – Chemistry (Q10c#2, d)
• Chemistry developed after Newton (who started physics) from:o Alchemy – transmutation of elementso Medicineo Industry – much demand for chemicals 1700so Mechanical approach from Descartes & Newton
• 1700 still the four Aristotelian elementso Earth – fixed volume & shapeo Water – fixed volume only
11/24/08 Atoms and Stars, Class 12 16Atoms and Stars, Class 12 16
Chemistry• 1700 still Aristotelian elements
o Air – volume & shape expanded to containero Fire - passed through container walls
• 1727 – Stephen Hale: released “fixed” air (put out flames) from solids, much interest
• 1749 Jean-Jacques DeMairan evaporated liquids (e.g. ether) in a vacuum, froze watero But liquids supposed to evaporate into airo Fire combined with liquid = air? Many types?
• Water could be solid, liquid, vapor –differ by fire?
11/24/08 Atoms and Stars, Class 12 17Atoms and Stars, Class 12 17
Chemistry• How could “big four” be elements?• 1750s Joseph Black experiments with
“magnesia alba,” gave off “fixed air” that extinguished flame (CO2), denser than “common air,” turned limewater cloudyo Use limewater test to show fixed air came from
fermentation & charcoal combustion, would not support life
• “Fixed air” became specific name for this gas (CO2)
11/24/08 Atoms and Stars, Class 12 18Atoms and Stars, Class 12 18
Chemistry• 1766 Henry Cavendish: “inflammable air” H• 1772 Joseph Priestley obtained “fixed air” in
other ways, demonstrated solubility in water (& taste – birth of carbonated beverage industry)o Many other types of air – “dephlogisticated air” O
• Phlogiston theory of combustion – burning releases phlogiston – from Germany, industrially useful
– Phlogiston theory before Caloric and Kinetic theories of heat• When air is saturated with phlogiston, combustion and
life cease
11/24/08 Atoms and Stars, Class 12 19Atoms and Stars, Class 12 19
Chemistry
• Antoine Lavoisier (1743 – 1794)o Graduated in law but continued science studieso Accurate weighing, also many practical resultso (Calcination – turn a metal to powder (“calx”) by
heating in air below melting point – phlogiston theory explained this as driving off phlogiston)
o But Lavoisier’s weighing showed that weight of calx increased, for all metals – a problem for phlogiston theory of combustion
11/24/08 Atoms and Stars, Class 12 20Atoms and Stars, Class 12 20
Chemistry
• Calx of mercury (oxide of mercury) when heated gave off air (gas) that supported combustion and lifeo Priestley found this air better (5×) for combustion
and life than “common air” (air) – “eminently respirable air”
• Lavoisier had assumed it was common airo Lavoisier confirmed this, but common air was
then a mixture
11/24/08 Atoms and Stars, Class 12 21Atoms and Stars, Class 12 21
Chemistry
• 1778 Lavoisier showed this air also formed acids, named it oxygen (“acid former”) (but we now know that hydrogen makes acid)
• 1783 Cavendish’s assistant told Lavoisier about Cavendish’s experiment of applying spark to inflammable air (H), finding dew which was identified as watero Lavoisier – water was not an element,
combination with oxygen for all combustion
11/24/08 Atoms and Stars, Class 12 22Atoms and Stars, Class 12 22
Chemistry
• Lavoisier named flammable air “hydrogen” for “water former”
• Lavoisier and others formed new chemical terminology – speaking well was like reasoning wello Oxide – combination with oxygeno Names indicated amount of oxygen (ous < ic)
• Sulfurous acid H2SO3
• Sulfuric acid H2SO4
11/24/08 Atoms and Stars, Class 12 23Atoms and Stars, Class 12 23
Chemistry
• Lavoisier terminologyo Gas – any vaporo Air – the atmosphere, a mixture (80% N, 20% O)o Fire was caloric (no correct theory until 19th
century – started by Count Rumford)• John Dalton (1766 – 1844), meteorologist
o Converted to chemistry when he understood air was a mixture – why didn’t different gases separate by gravity?
11/24/08 Atoms and Stars, Class 12 24Atoms and Stars, Class 12 24
Chemistry
• John Dalton (1766 – 1844), meteorologisto Also gases dissolved in water proportional to
pressure – why?o Hypothesized gases composed of atoms, each gas
interacted with itself (see later slide)o “Law of definite proportions” – chemicals
combined by weight in simple ratioso Dalton proposed formulae based on these –
chemical atomism
11/24/08 Atoms and Stars, Class 12 25Atoms and Stars, Class 12 25
Chemistry
• John Dalton (1766 – 1844), meteorologisto Dalton proposed formulae based on theseo Many of his formulae were wrong
• Example: he said water is HO• More were right, enough to straighten out the errors
over timeo (DB) Physicists did not accept chemical atomism
until they accepted Maxwell and Boltzmann at the end of 19th century
o (DB) Direct observations of atoms in 20th century
11/24/08 Atoms and Stars, Class 12 26Atoms and Stars, Class 12 26
Chemistry (DB)• John Dalton (1766 – 1844), meteorologist
o What led Dalton to hypothesize atoms?• Characteristics of matter
– Solids cannot occupy the same space– Some liquids can– All gases can
• Why didn’t lighter gas rise, heavier sink?– Composition of atmosphere the same to 15,000 feet– Fog
• Gases could interpenetrate if it was atoms with lots of empty space in between
• Water could be gas, liquid, solid, these forms must have atoms
• Extended to all liquids and solids
11/24/08 Atoms and Stars, Class 12 27Atoms and Stars, Class 12 27
Experiment IV (not done) (Q11)
• Chemical composition of water
• Electrical current decomposes water: H2O 2H + O
Lab ManualPg 13
11/24/08 Atoms and Stars, Class 12 28Atoms and Stars, Class 12 28
Atomic Nature of Matter (Review)
• First direct evidence 1827 Robert Brown (10c#2)o Noticed spores jiggling under microscopeo “Brownian motion” – bombarded by molecules
• Robert Brown, 1827o See next slides, or
http://www.is.wayne.edu/drbowen/Class-Room_Models/Welcome.htm http://www.colorado.edu/physics/phet/web-pages/simulations-base.html
o Now we have more direct evidence
11/24/08 Atoms and Stars, Class 12 29Atoms and Stars, Class 12 29
Brownian Motion (Review)
Jagged tracks of pollen particles.
Gas molecules mode visible. Jagged tracks explained as due to collisions with gas molecules.
Expanding Circles
Implication #1, Example 3
11/24/08 Atoms and Stars, Class 12 31Atoms and Stars, Class 12 31
Expanding Circles (Q16)
• Review: science started out as isolated areas• Then areas expand – science always
pushing its boundaries• Implication #1: What happens when two
expanding circles meet?• Implication #2: What happens when circles
fill the space?o My answer: science drives technology (see
C8S15-19 for details)
11/24/08 Atoms and Stars, Class 12 32Atoms and Stars, Class 12 32
Expanding Circles
• Implication #1: What happens when two expanding circles meet? I promised three examples (Q15)1. Newton uniting celestial (stars) and terrestrial
(on land) – already done (C12S12)2. James Clerk Maxwell uniting Electricity and
Magnetism (Class 9, November 3)3. Ludwig Boltzmann uniting atoms and
Newton’s Laws (this class)
11/24/08 Atoms and Stars, Class 12 33Atoms and Stars, Class 12 33
Expanding Circles (Q15)Example 3: Statistical Mechanics• Ludwig Boltzmann, end of 19th century
o Physicists had never accepted idea of atomso Boltzmann (Austrian physicist) one of firsto Worked out Newtonian mechanics for a gas of
colliding atoms and molecules - Statistical Mechanics• With J. Willard Gibbs – now has his own stamp
o DB: “Atomic Theory meets Isaac Newton”o Same results as Thermodynamics (accepted, see later)
• Also explained how those results came about (explanatory)
• Other physicists still sharply rejected these ideaso May have contributed to Boltzmann's 1906 suicide
11/24/08 Atoms and Stars, Class 12 34Atoms and Stars, Class 12 34
Expanding Circles• Now Boltzmann honored as pioneer
o Statistical Mechanics very important• Significantly modified by Quantum Mechanics.
• Second Law of Thermodynamicso If a hot object and a cold one are in contact,
energy always goes from hot to cold• Atoms in hot object more energetic (Rumford),
travel more• Slowed down by collisions with slower atoms from
cold object, but these are sped up• Statistical Mechanics explains why this happens• Demonstration – diffusion – atoms of dye
11/24/08 Atoms and Stars, Class 12 35Atoms and Stars, Class 12 35
Expanding CirclesStatistical Mechanics• Theory: molecules in a gas move and
collide randomly, governed by laws of statistics and by Newton’s Lawso Too many particles to follow each, so calculate
the averages• Once particles mix, essentially no chance of
their separating again• Computer simulation of this mixing
11/24/08 Atoms and Stars, Class 12 36Atoms and Stars, Class 12 36
A Taste of Statistical Mechanics• See next slide, but here is the explanation
o “Gas” with spaces for 4 atomso Gas divided into left & right halveso Two green atoms, two blueo In each half, the 4 atoms arrange randomlyo Atoms too small to see, we see the average color in
each halfo One chance for left being green, right blueo Another chance for the oppositeo 4 chances for mixed – turquoise
• Chances get more lopsided with more atoms
11/24/08 Atoms and Stars, Class 12 37Atoms and Stars, Class 12 37
A Taste of Statistical Mechanics• Start with gas (4
slots) and atoms• We see average
of color in each half
• Most common is mixed
• Odds more lopsided with more atoms
Two Different Types of Things
Background for reading for 12/8, “Knowledge or Certainty “
11/24/08 Atoms and Stars, Class 12 39Atoms and Stars, Class 12 39
Two different types of things• Particle (“thing,” “object”)
o Examples: baseball, soup can, projectile, staro One location (or center)o Newton’s three laws govern motion
• Waveo Examples: waves in water, sound waves, radio
waveso Spread out, exists in many placeso “Wave Equations” governed motion (not
Newton)
11/24/08 Atoms and Stars, Class 12 40Atoms and Stars, Class 12 40
Two different types of things
Particle WavePosition: Definite – one
position (center)Spread out, no one place
Try to catch it – result is:
Get all or none Only get part, if that
Collision with another:
Ricochet, bounce, shatter
Pass through each other
Existence: All by itself In something – the “medium” (before Maxwell)
11/24/08 Atoms and Stars, Class 12 41Atoms and Stars, Class 12 41
Demonstrations• PhET (Physics Education Technology)
http://phet.colorado.edu/simulations/sims.php?sim=Gas_Properties
o Particles: Gas Properties – they bounceo Waves: Sound >> Interference by Reflection
• Interference: light peak, dark trougho http://www.colorado.edu/physics/2000/schroedinger/big_interference.html –
some areas gray (unlit)• Light: early 1800s, Thomas Young proved
light is a wave – “double slit experiment”o http://www.colorado.edu/physics/2000/schroedinger/two-slit2.htmlo Confine a wave – it spreads out
11/24/08 Atoms and Stars, Class 12 42Atoms and Stars, Class 12 42
Particles collide…
Particles of gas mix together, collide
11/24/08 Atoms and Stars, Class 12 43Atoms and Stars, Class 12 43
but waves pass through each other
Sound wave and its reflection(type – sound - is unimportant here)
11/24/08 Atoms and Stars, Class 12 44Atoms and Stars, Class 12 44
Waves “interfering”
Confine a wave and it spreads out
11/24/08 Atoms and Stars, Class 12 45Atoms and Stars, Class 12 45
Waves• Wavelength –
distance between peaks (or troughs)
• Fixed speed• Until 20th century,
Wave / Particle – we thought everything was one or the other
Wavelength
11/24/08 Atoms and Stars, Class 12 46Atoms and Stars, Class 12 46
Wave-Particle Duality
• In 20th century, with rise of Quantum Mechanics, we understood that everything was both.o For a wave, x (position) and v (velocity)
connected – see later slideo Led to “Uncertainty Principle”
• Irreducible uncertainty in our knowledge
11/24/08 Atoms and Stars, Class 12 47Atoms and Stars, Class 12 47
Uncertainty Principle
• 1795 Carl Friedrich Gauss (college student)
• Uncertainty called (“sigma”, LC Greek s)• Also Uncertainty Principal 1927 Werner
Heisenberg – cannot locate particle exactly
11/24/08 Atoms and Stars, Class 12 48Atoms and Stars, Class 12 48
Uncertainty Principle
• No practicaleffect atmacroscopic levelo A philosophical problem with The Mechanical
Universe and with “The God’s eye view” or The Clockwork Universe over age of universe
• Important at atomic and molecular levelo Uncertainties are large on atomic scaleo What underlies our reality is strange
11/24/08 Atoms and Stars, Class 12 49Atoms and Stars, Class 12 49
Uncertainty Principle
• Example: A = 20 / C
• Uncertainty small for large masses, large for small masses, atoms have very small masses
C A
2 10 Divide by small number, get big number. Divide by larger number, get smaller number.5 4
Experiment 9
11/24/08 Atoms and Stars, Class 12 51Atoms and Stars, Class 12 51
Experiment 9: overall
• Important conclusions from Part 1 (Circle):o The formula is almost certainly correcto Value of almost certainly correcto The method for measuring C is valid within .1” or .2”
• Method: putting pins along path, looping string along pins, removing string and measuring its length
• Circle part and ellipse part are connected. DO NOT treat them as separate.
• Should measurement errors be the same, or different?
• If they are different, how can this happen?
Experiment 7
Specific Gravity
11/24/08 Atoms and Stars, Class 12 53
Experiment 7
• Checking on Archimedes: saw water rise when he got into bathtub, ran through city shouting “Eureka”
• Displaced water – submerse object in water, water level rises, this is displaced water = volume of object
• Specific Gravity – property of material:SG: (object’s weight)/(displaced water’s weight)
• S.G. is a help in identifying the material• Weighing objects (wood block, dumbbell, displaced
water):o Weight in pounds and ounces using fish scaleo Use string slings for block and dumbbell
11/24/08 Atoms and Stars, Class 12 54
Experiment 7
• Using the fish scales:o Turn ono Wait for numbers to stop flashing
• While numbers are flashing, scale is adjusting the zero• Will show 0 0 when flashing stops
o After numbers have stopped flashing, THEN attach weight and read it
• Reading is pounds and ounces• Convert ounces to decimal pounds by dividing by 16
11/24/08 Atoms and Stars, Class 12 55
Experiment 7 (cont’d)
• Converting pounds and ounces to decimal pounds:1. Divide # ounces by 16 (result between 0 and 1),
call this “X” (round to nearest tenth)2. Check: multiply X by 16, should get about the
original # ounces – SHOW THIS CHECK ON DATA SHEET !!!
3. Add X to # pounds to get decimal pounds
11/24/08 Atoms and Stars, Class 12 56
Experiment 7 (cont’d)
• Converting inches and sixteenths to decimal inches:o Same as for pounds and ounces to decimal
ounces, INCLUDING CHECK !!! (previous Slide)
• For step # 5, ignore rounded edges and grooves in block: V = L × W × H
• Same for #6, volume of watero H = change in height with/without block
11/24/08 Atoms and Stars, Class 12 57
Experiment 7 (cont’d)• For both wood block and dumbbell:
o Find object’s weight and weight of displaced water, divide to find Specific Gravity
• For wood block only:o Find object’s volume and compare to volume of
displaced water. Archimedes: volumes the same• For dumbbell only:
o Find object’s weight “in water,” compare with weight “in air” (normal) and weight of displaced water
11/24/08 Atoms and Stars, Class 12 58
Experiment 7 (cont’d)
• For #7, you will probably have to use different amounts of water in the tub for each object.o Hold object down if necessary (i.e. wood),
cover with water, remove object, then start that part of the lab
11/24/08 Atoms and Stars, Class 12 59
Experiment 7 (cont’d)
• Measuring length starting from 1” can be more accurate, but be carefulo Subtract the 1 from the end readingo What is the distance between two marks below?
• 1½” or 2½”?