motion and design: an stc kit
DESCRIPTION
Motion and Design: an STC kit. Bruce Palmquist, CWU, [email protected]. M&D-related N ational S tandards. Abilities necessary to do scientific inquiry Plan and conduct investigations Position and motion of objects - PowerPoint PPT PresentationTRANSCRIPT
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Motion and Design: an STC kitBruce Palmquist, CWU, [email protected]
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M&D-related National StandardsAbilities necessary to do scientific inquiry
◦Plan and conduct investigationsPosition and motion of objects
◦Describe changes in positions of objects using the concepts of displacement, velocity, and acceleration
◦Represent motion on a graph Motion and forces
◦Define forces◦Apply the concept of forces to motion and changes
in motionIf you have a question, write it on a post-it
note and stick it to the question wall.
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Workshop outlinePart 1: Describing Motion
◦Constant motion activity◦Speeding up motion activity◦Graph analysis computer simulation (if time)
Part 2: Forces and Motion◦ Introduction to forces◦“Deriving” Newton’s 2nd Law of Motion◦Ramp: Forces and Motion (computer)
Part 3: Energy◦Types of mechanical energy◦Mini-hovercraft activity◦Conservation of mechanical energy
Material at http://cwuphys106.pbworks.com/◦Click ESD 105 folder in the Navigator box on the right
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Learning Objectives◦Describe the motion of a fan cart using words,
graphs, and “oil drop” diagrams. ◦Translate between a verbal description, a
graph, or an “oil drop” diagram of motion.Engage: Page Keeley Assessment ProbeExplore: Describing constant motionExplain: Fan cart lab activityElaborate: Name that motion (if time)Evaluate: Translating motion descriptions
Part 1: Describing Motion
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From Uncovering Student Ideas in Physical Science by Page Keeley and Rand Harrington, page 23-30
Engage: What do you think?
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From Uncovering Student Ideas in Physical Science by Page Keeley and Rand Harrington, page 23-30
Engage: What do you think?• Take 1
minute to answer on your own.
• Compare answers with partners for about 1 minute. Come up with a group answer to the graphing question.
• Share your group’s answer with the class.
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Given whatever tools you have or can find around you, determine the velocity of your car.
Is the velocity constant? How do you know? Devise a method to test if the velocity is constant.
Summarize your method and results in a short paragraph on the provided note card.
We know the velocity is constant if equally sized displacements are travelled in equal time intervals.
The smaller the duration measured, the more accurate our proclamation that the velocity is constant.
Explore: Describing Constant Motion
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Explore: Constant velocity GraphThe car moves equal
intervals in equal amounts of time.
Car is not speeding up or slowing down (or changing direction).
Graph is a straight line. See example.
How do we know the car is not speeding up or slowing down between data points?
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Now you will get a car that speeds up. Please be careful of the propeller. It can pinch your finger.
You will also get a tape timer, a device that puts a mark on a paper every 0.1 s or 0.025 s.
Attach about 2 meters of tape to the back of your cart.
Make a data table with about 10 position and corresponding time values.
Use Excel to make a position vs. time graph for your car. Excel worksheet template at http://goo.gl/1SvRV
When you are done with your spreadsheet and graph, give the file a creative name and email it to me at [email protected].
Explain: Fan Cart Activity
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Explain: Graphing motionTime (s) Position
(cm)Velocity (cm/s)
0 0 00.1 1.5
(compared to the zero point)
15
0.2 3.5(compared to the zero point)
20
0.3 6.0 25
To make a position vs time graph, plot time along the x-axis and position along the y-axis.
Determine the best fit curve using Excel (either linear or polynomial)
Email to [email protected]
Excel template:http://goo.gl/1SvRV
Sample data
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Explain: Increasing velocity
The car moves increasing distances in equal amounts of time.
Graph is a upward curve.
How do we know the car is not constant or slowing down between data points?
Compare different cars.
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Sample Position vs. time graph
What does each parameter represent here?
Here y is position, x is time, 8.1279 is 1/2a, 22.288 is initial velocity and 0.8107 is initial position.
0 0.5 1 1.5 2 2.5 3 3.50
20
40
60
80
100
120
140
160
f(x) = 8.1279072707048 x² + 22.287649155627 x + 0.8106671554252R² = 0.999929612637343
Motion of a Fan Cart
Time (s)
Posi
tion
(cm
)
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The slope of a position vs. time graph is the velocity.
If the velocity is changing, the slope at each point represents the velocity at that point.
The slope of a velocity vs. time graph is the acceleration.
Definition of acceleration:Acceleration = change in velocity/change in time
a=∆v/ ∆tThe more the velocity changes for a set time
interval, the greater the acceleration.Acceleration can be positive or negative
Explain: Acceleration
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Explain: Ticker Tape diagramsDescribe the motion of the object that made each of these tapes. Justify your answer.
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Explain: Ticker Tape diagramsLet’s practice this more.
Constant velocity
High acceleration Low acceleration
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(If time and technology permits)Open the Name that Motion
simulationWork in your groups. Just enter one
name on the screen but fill out your own answer sheet.
View each motion. Type the number of the description on the worksheet that matches the motion.
Elaborate: Describing complex 1-D motion
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From Uncovering Student Ideas in Physical Science by Page Keeley and Rand Harrington, page 31-34
Evaluate: Analyzing a graphTake one minute to
answer on your own.Talk to your partners
for about two minutes and compare answers. On the back of your sheet, write your group answer and explanation.
Share your group’s answer with the class.
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Bill has confused the position vs. time graph with a picture of the path of motion. He needs help understanding what a position vs. time graph tells him.
Patti seems to understand that a steeper line means faster and less steep line means slower. But she does not adequately describe the meaning of the flat line.
Kari has the best answer. She seems to understand that a flat line on a position vs. time graph means no change in position, an object that is not moving.
Mort has confused the position vs. time graph with a picture of the path of motion. He needs help understanding what a position vs. time graph tells him.
Evaluate: What understanding does each answer indicate
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Part 2: Forces and MotionIntroduction to forces“Deriving” Newton’s 2nd Law of
MotionForces in 1-Dimension activity
(computer)
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Learning ObjectivesSketch the main forces acting on an
object.Name the main forces acting on an
object using the official naming rules.Sketch and name the major forces
acting on a rolling ball.Use Newton's second law of motion
to solve for an unknown.
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Naming forcesDevelop a definition of a force.A force is a push or pull that changes
the motion of an object.Bruce’s rule for naming forces: “The
(blank) push/pull of the (blank) on the (blank)”
Typical forces in k-12 science: gravitational, contact, elastic, friction, tension, electric and magnetic
A force is a vector meaning it has magnitude and direction
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ForcesThe contact push of the table on the book.
The gravitational pull of the Earth on the book.
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ForcesNow I’ll give a
book a push. Sketch a diagram of all of the forces acting on the book well after the push but before the book stops.
Go over Net Force Help Sheet
The frictional push of the table on the book
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Rolling ball motionSketch and name the forces for
the ball◦Rolling uphill◦Rolling on a flat surface◦Rolling downhill
In which of these situations are the forces balanced? Unbalanced?
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Rolling ball motionUphill
Flat
Downhill
What do you notice about the uphill and downhill diagrams?
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Newton’s Laws of MotionFrom his study of the work of Galileo
and Kepler, Newton extracted three laws that relate the motion of a body to the forces acting on it.
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Deriving Newton’s 2nd LawMaterials: low friction cart, kitchen
scale, long hall, 1 “pusher”, 3 “riders”The pusher will push each rider
individually down the hall with the same force (same reading on the scale).
The rest of the class will note how the motion of each rider differs.
The rest of the class will also make sure the pusher keeps the same force reading on the scale the entire time.
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Results of Newton’s 2nd Law demoForce Size of rider Rate of speeding
up
•Another word for “rate of speeding up” is acceleration.•Conclusions?•For a constant force, as the size of the rider (m) decreased, the acceleration (a) increased.•m α 1/a (mass is inversely related to acceleration) •A more familiar way to write this is FNet = ma•Practice using newton’s 2nd Law
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Newton’s 2nd law of MotionWork on Forces in 1-Dimension at
http://phet.colorado.edu/en/simulation/forces-1d or http://goo.gl/ijN0Q
What happened as the person pushed harder on the cabinet before it moved?
The friction force grew as the applied force grew.What happened to the friction force once the cabinet
started to move?It got smaller.What happened to the cabinet as the applied force was
continually exerted on the cabinet?It accelerated.Review homework
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1. If the total force acts in the same direction as the crate is sliding, the crate
A. slows downB. speeds up C. remains at same speed D. slows down, changes direction and
then speeds up going the other way
E. remains at same speed, but changes direction
Crate was moving to the right
Then, the guy pushed the crate
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2. If the total force acts in the opposite direction as the cabinet is sliding, the cabinet would A. slow downB. speed up C. remain at same speed D. slow down, change direction and
then speed up going the other way
E. remain at same speed, but change direction
Cabinet was moving to the left
Then, the guy pushed the cabinet
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3. If there is zero total force acting on on the refrigerator, the refrigerator would A. slow downB. speed up C. remain at same speed D. slow down, change direction and
then speed up going the other way E. remain at same speed, but change
direction
Refrigerator was moving to the right
Then, the guy pushed the refrigerator
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FrictionPair up. You’ll need
a pusher and a sitter.
Push the sitter’s chair lightly. What do you notice?
Push harder but not hard enough to move? What do you notice?
Once sitter starts to move, what did you notice about the “feel” of your push?
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Part 3: EnergyTypes of mechanical energyMini-hovercraft activityConservation of mechanical
energy
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Learning objectivesUse the definitions of Work, KE,
PE, and TME to solve for an unknown
Given a scenario, determine whether KE, PE or TME increases, decreases or stays the same.
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Work = F*d*cosqScenario 1: Maximum
positive work done, typically means an increase in kinetic (motion) energy
Scenario 2: Maximum negative work done, typically means an decrease in kinetic (motion) energy
Scenario 3: No work done, no change in kinetic (motion) energy
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WorkWhich path requires the least energy to get
to the top of the hill?A D, the straight steep path (2)B D, the winding path (5)C D, the straight non-steep path (15)All equal (7)Pick an answer and justify using the
concept of workWatch
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Mechanical energyThere are two main types of mechanical energyMotion energy, also called kinetic energyKE = ½ mv2
◦m=mass of the object, v = velocityGravitational potential energyPE = mgh where h = height of the object above
the “ground”
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Work and energyAs the skier goes down the hill, how do
KE, PE, work, and TME (total mechanical energy) change? Is there a relationship?
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Work and energyAs the skier goes downhill, KE + PE = TME.On the packed snow, PE = 0 and KE = TME.TME is a constant when no work is being
done by friction.On the unpacked snow, KE goes down as
friction due to snow does negative work on the skier.
Let’s practice mechanical energy concepts
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Energy and frictionless pucksUse the wooden ramp, plastic puck, rubber stopper
and balloon for the following.Determine the speed of each mass puck at the
bottom of the ramp without using a stop watch. Use formulas for PE and KE. Assume no frictional force.
Determine the relationship between the angle of a ramp and the speed of a frictionless puck near the bottom of the ramp. Before starting the activity, write a hypothesis and share it with the instructor. Sketch a speed vs. angle graph in your notebook. Extra challenge: derive a formula that shows the relationship.
Discuss.
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Challenge solutionPE at top = KE
at bottommgh = ½ mv2
gh = ½ v2
gLsinq = ½ v2
2gLsinq = v2
(2gLsinq)½ = v
hL
q
Sinq = h/Lh=L sinq
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Teacher applicationHow can you use what you learned today
to enhance your own instruction of the Motion and Design unit?◦Pick a specific activity you did or concept you
heard about today◦Decide where it would support your teaching of
the Motion and Design unit or some other topic◦Briefly describe how you will use this activity
or concept.◦Think about this by yourself or with your school
team for about five minutes. Then share with another group.
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Online Resources used todayOnline physics resource including tutorials,
simulations, and worksheets.◦ I took my worksheets and notes from here.◦http://www.physicsclassroom.com/
Detailed simulations for teaching physics and other science concepts◦My force “lab” activity is found here. Many other
simulations for upper elementary through college students.
◦http://phet.colorado.edu/Website for my CWU Physics by Inquiry course
◦My CWU physics course for pre-service elementary and middle school teachers. Today’s notes found here.
◦http://cwuphys106.pbworks.com/