1. Upcoming Deadlines
Pick up a clicker, find the right channel, and enter Student ID
Sixth Homework (Stop-motion Animation) Due Thursday, October 6th (Next week) 20 points (if late, 10 points) Bonus prize of 20 extra points to top three. Seventh Homework (Outline of First Term Paper) Due Thursday, October 13th (In two weeks) 10 points (5 points if late) For full schedule, visit course website: ArtPhysics123.pbworks.com 1

2. Activating your Clicker
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* Type in your student ID; hit Enter/Send.
Clicker is now ready to use; leave it on.
Hit any key to wake the clicker from sleep mode. 2

3. Homework Assignment #6
In this assignment you will create a stop-motion animation of a falling object.
It can be a simple as a ball bounce cycle or (preferably) something more interesting, like a flour sack or a water balloon.
Because you will have to pose your object at different heights, you'll either need to suspend it from a string or have the motion occur on the ground with the camera positioned directly overhead. 3

4. Homework Assignment #6
If you have a webcam, an easy way to film a stop-motion animation is to use SAM Animation ( It's free software that runs on both Macs and PCs; it was developed at Tufts University as part of a National Science Foundation project for teaching using animation. The software is designed so that it can be used by even elementary school children so you shouldn't have much trouble figuring it out. 4

5. Demo of SAM Software 5

6. Homework Assignment #6
While I encourage you to help each other out, for this assignment each person needs to create their own animation. Finally, describe in a brief paragraph how you created your animation. Post your animation clip to your blog in an entry entitled "Stop Motion Animation of Falling.“ Due by 8am on Wednesday, March 3rd. 20 points (if late, 10 points) The top three animation clips in the class will receive a bonus of 20 extra points. 6

7. Total Recall (1990) 7

8. Breathing & Boyle’s Law8

9. Pressure & Air Resistance
Force of air resistance is due to a difference in pressure.
High pressure builds by compression in front of a falling object while low pressure is created in the wake.
LOW PRESSURE L
HIGH PRESSURE H 9

10. Sailing Ships
The wind blowing on a sail also produces a pressure difference, creating the force that moves the ship. H L
Wind 10

11. Buoyancy
The buoyant force pushing submerged objects upward is also due to a pressure difference. L H 11

12. Prairie Dog Vacuum
Prairie dogs captured by giant vacuum truck with a padded bin. 12

13. The Curse of the Were-Rabbit (2005)13

14. Vacuum Cleaner Force
As with any vacuum cleaner, it’s the difference of pressure that creates the net force pushing objects towards the low pressure side. A L
Force
Truck A 14

15. Vector Addition of Forces
Two forces pulling an object are equivalent to a single total force.
Net Force
A + B
Force B
Parallelogram rule
Force A
Object 15

16. Sliding Sideways If leaf/paper is tilted then it slides sideways.
Air Pressure Force
If leaf/paper is tilted then it slides sideways.
Slides this way
Gravity
Picks up speed (slows out) as it slides down, as if it were sliding down an incline. 16

17. Timing and Spacing, Up & Down
When it rises due to lift* it loses speed (slows in).
When the leaf/paper slides downward, it picks up speed (slows out).
Imagine riding a roller coaster.
* With no wind 17

18. Roller Coaster Timing 18

19. Aerodynamic Lift
If airflow is faster over one side than the other then a pressure difference develops, creating aerodynamic lift.
Lift
Lift
Wing
Moving this way 19

20. Aerodynamic Lift
If leaf/paper is tilted relative to its path of action then there is also an aerodynamic lift.
Also get lift if leaf/paper is curled like a wing.
Lift
Air Resistance
Moving this way
Gravity 20

21. Effect of Lift
Lift requires tilt and speed; no lift if paper/ leaf is not moving
Lift
Path of action deflected by lift.
Lift force can also deflect the path of action downward, depending on the tilt angle of the leaf/paper.
No Lift 21

22. Bernoulli’s Principle
Where the speed of a fluid increases the pressure in the fluid decreases.
This phenomenon is due to energy conservation; when fluid’s kinetic energy increases (velocity increases) its internal potential energy (pressure) decreases.
Still Air A
Wind L 22

23. Home Demo: Blow It Up
Hold a sheet of paper in front of your mouth and blow; the paper will rise. L A
Low pressure on top; Average pressure on bottom 23

24. Blow the Roof
If wind blows hard enough the low pressure above can create a large enough force to lift the roof off. L A
New Orlean’s Superdome after hurricane Katrina 24

25. Class Demo: Blow the Funnel
Blow hard through a funnel with a ping pong ball in the funnel’s bowl.
Instead of being blown away, the ball is held tightly in the bowl. L A
Ping
Pong
Ball

26. Home Demo: Keep It Up (cont.)
Bernoulli effect keeps the ball in the middle of the air stream. A L A A L A 26

27. Increments & Acceleration
In the Odd Rule, the spacings get bigger with time and always by the same amount.
That is, the increment from one spacing to the next is always the same (red arrow).
Since the spacings tell you the speed, if the spacings get larger and larger then the moving object is accelerating.
The increment tells you the acceleration. The acceleration due to gravity is constant (since the increment is always the same). 27

28. Demo: Throwing You a Curve
Putting a spin on a thrown baseball causes the airflow to be faster on one side than the other, which creates a pressure difference.
No Spin
Spin L L
Bernoulli
Forward Motion H L
Depending on the axis of rotation this could be a rising fastball, a sinker, or a curve ball. 28

29. Demo: Can Crush Pour small amount of water into an empty soda can.
Heat water to boiling.
Quickly transfer the can, upside-down, into a pan of cold water.
Soda can is quickly crushed. 29

30. Can Crush, Analyzed A A L Steam
Cool the can and steam condenses back into water, leaving almost a vacuum inside. Low pressure inside and atmospheric pressure outside.
Boil the water and inside of the can fills with steam, pushing out the air.
Atmospheric
Pressure A A L
Steam
Low
Pressure 30

31. Crush the Rail Tanker Car
The interior of the tank car was washed out & cleaned with steam. Then all the outlet valves were shut and the tank car was sealed.
All the workers went home for the evening and when they returned, this is what they found.
Apparently as the tank car cooled, it collapsed. The shell on these tank cars is 7/16th inch thick steel. 31

32. Demo: Air Heavier than Water
Fill a glass with water to the brim then place an index card on top. Hold the card while you carefully invert the glass over a sink. If the seal stays tight, atmospheric pressure will support the weight of the water. 32

33. Demo: Lift Water Fill a glass underwater. Lift the glass, upside-down.
Water stays in the glass because atmospheric pressure enough to balance weight of the water.
Pressure of air inside the glass is below atmospheric pressure (about 1% less for a 3 inch tall glass). L A A
Weight 33

34. Demo: Drinking Straw
With lungs, you reduce pressure in your mouth and in the straw.
The higher pressure on the outside pushes the liquid up the straw.
Force due to the pressure difference must match or exceed the weight. L
Weight A A
NO “SUCKING” FORCE 34

35. Odd Rule & Newton’s 2nd Law
The Odd Rule applies anytime the forces are constant, with spacings given by 2nd law.
The forces are constant, with the support force of the ground balancing (canceling) the weight, leaving only friction.
If the friction force is half the weight then spacings are half as long as those of an object falling downward.
Support
Apex
Friction
Gravity (Weight) 35

36. Law of Acceleration Example
In this example the total force equals 1/3 of the weight so the spacings are 1/3 of what they are normally are for falling.
Gravity (Weight)
Total Force
Normally an object that falls for 6 frames goes a distance of 12 inches so this bubble falls only 4 inches after 6 frames
Golf
Ball
Bubble
Bouyancy 36

37. Ground-effect Cushion
Moving this way L L
LOW PRESSURE H H
HIGH PRESSURE
Flat sheet sliding over a smooth surface compresses the air beneath it and forms a low-friction cushion, allowing it to slide.
This ground-effect won’t occur with an irregular leaf or with a rough surface. 37

38. Next Lecture Squash & Stretch
By Thursday of this week: Complete 5th homework (Video analysis of jump)
By Thursday of next week: Complete the 6th homework
(Stop-motion Animation of Falling)
Please turn off and return the clickers! 38