1. Upcoming Deadlines
Have clicker ready
First Term Paper The Laws of Physics in an Animation Universe Due Tuesday, October 9th (Next week) 100 points (50 points if late) Eighth Homework (Reverse Video Reference) Due Tuesday, October 16th (In 2 weeks) 20 points (10 points if late) For full schedule, visit course website:

2. Extra Credit Opportunity
Visit the Cartoon Art Museum in SF to see the Avengers Assemble! or the The Art of ParaNorman! exhibits.
Avengers exhibit runs until Oct. 7th ; ParaNorman! exhibit opens Oct. 6th
Turn in proof of attendance (ticket receipt) for 10 points extra credit.
For info: cartoonart.org

3. Extra Credit Opportunity
Attend a screening or event at the Mill Valley Film Festival
(Oct. 4th -- 14th)
Turn in proof of attendance (ticket receipt) for 10 points extra credit.
For info:

4. Extra Credit Opportunity
Visit the Walt Disney Family Museum in SF to see the Between Frames: The Magic Behind Stop Motion Animation exhibition.
Exhibit runs Sept. 27, to April 28, 2013
Turn in proof of attendance (ticket receipt) for 10 points extra credit.
For info:

5. Extra Credit Opportunity
Visit the Exploratorium in San Francisco.
Turn in your ticket receipt for ten points extra credit.
Hours: Tuesday-Sunday: 10a.m.-5p.m
Admission: $12.00 for students
Location: 3601 Lyon Street, SF 94123
Next to Palace of Fine Arts complex

6. Extra Credit Opportunity
Visit The Tech Museum in downtown San Jose to see the Mythbusters exhibit.
Exhibit runs  October 13th - January 6th  
Turn in proof of attendance (ticket receipt) for 5 points extra credit.

7. First Term Paper Term paper is due by 8am on Tuesday, Oct. 9th
The required length of the term paper is 1500 words. Use a word count to verify that you are not significantly below this required length.
Upload your term paper to your blog in a post entitled "The Laws of Physics in an Animation Universe."
If you find that you significantly deviate from the outline, please add a brief explanation at the end of your term paper (which does not count towards the 1500 words).
Term paper is due by 8am on Tuesday, Oct. 9th
100 points (50 points if late)

8. SPECIAL OPTION
If you score 80 points or higher on your first term paper then you have the option of skipping the second term paper.
If you are eligible and select this option then you receive the same points for the second term paper as you did on the first paper.
If you are eligible but decide to turn in a second term paper anyway then your score will be no less that that of the first term paper.

9. Survey Question
“This course has ___ changed the way that I view animation.”
Very Significantly
Significantly
Somewhat
Been interesting but not really

10. Review Question
In this classic contrapposto pose, the weight of the body is primarily on which leg?
A) Right Leg
B) Left Leg

11. Hips and Shoulders A) Right Leg
Notice the angles of the hips and shoulders and that they converge on the side that bears most of the weight.
Weight shifts from foot to foot are reflected by corresponding shifts in the hips and shoulders.
Donatello's bronze statue of David (circa 1440s)

12. Weight Shift in Animation
Rex Grignon, head of character animation at Dreamworks, says that not having weight shift is one of them most common errors seen in the work of student animators.
Even when the lower body is out of frame, as in this medium shot, a good animator will think about what the lower body is doing because that’s reflected in the whole pose.

13. Review Quiz
In which of these situations does the character gain weight?
#1 and #2
#1 and #3
#2 and #3
#2 and #4
#3 and #4
#1: Falling & Speeding Up
#2: Rising & Speeding Up
#3: Rising & Slowing Down
#4: Falling & Slowing Down

14. Dynamic Weight D) #2 and #4 Falling & Speeding Up: Lose Weight
With gravity
Against gravity
With gravity
Against gravity
Corey Tom
Falling & Speeding Up:
Lose Weight
Rising & Speeding Up: Gain Weight
Rising & Slowing Down: Lose Weight
Falling & Slowing Down:
Gain Weight

15. Review Question
In this scene from Bullitt, the car is making a high speed turn in which direction?
A) Screen Left
B) Screen Right

16. Centrifugal Force A) Screen-Left Turn
Centrifugal force pulls the CG towards the outside of the curve and, combined with the weight, it tilts the car.
Centrifugal
Force X CG
This side goes down.
Weight
Tight Turn

17. Action & Reaction

18. Newton’s Laws of Forces
Newton established three basic laws to explain how motion is caused by forces:
Law of Inertia
Law of Acceleration
Action-Reaction Principle
Today we look at the Action-Reaction Principle, also known as Newton’s Third Law.
Sir Isaac Newton

19. Action-Reaction Principle
For every action force there is an equal reaction force in the opposite direction.
Reaction
Action
Action
Reaction

20. Action and Reaction
Common expression for the principle is,
To every action there’s an equal and opposite reaction.
What’s an “action”?
A force exerted by one object on second object.
What’s a “reaction”?
A force exerted by second object back on the first object that is causing the action.
How can reaction be “equal” and “opposite”?
Equal in magnitude but opposite in direction.

21. Action-Reaction Pairs
Action-reaction always occurs in pairs.
Reaction: Jaw exerts force on fist
Action: Fist exerts force on jaw
Action: Man exerts force on rock
Reaction: Rock exerts force on man
Action: (Thing A) exerts a force on (Thing B). Reaction: (Thing B) exerts a force on (Thing A).

22. Timing of Action and Reaction
The action force and reaction force always act simultaneously.
Action force on jaw occurs simultaneous with reaction force on the fist.
This is not Newton’s 3rd Law Slaps are not simultaneous.

23. Class Demo: Mutual Repulsion
Mr. A pushes on Mr. B, who just holds his arm steady.
The action force accelerates Mr. B towards screen-right.
The reaction force accelerates Mr. A towards screen-left.
Action
Mr. A pushes
Mr. B holds
Reaction
Put them on skateboards to minimize the effect of friction.

24. Equal Forces, Not Accelerations
Action and reaction forces have equal magnitude but the resulting accelerations are not equal.
Small weight, Big recoil speed
Action
Big weight, Small recoil speed
Reaction
Although a pair of action-reaction forces have equal magnitude, they don’t have equal effect. The resulting accelerations depend on the weight of the objects the forces are pushing. In this example, Mr. A (screen left) pushes on Mr. B; to make the resulting effect obvious we’ve put the on skateboards. The characters move apart due to the action-reaction forces but since Mr. A weighs less he will accelerate more, moving away at a high speed while Mr. B will move away more slowly due to his large weight. The difference between their recoil speeds indicates their relative weights.
Small Acceleration
Large Acceleration
Mr. A pushes Mr. B

25. Law of Acceleration (Reminder)
Object A has less weight (lighter) than Object B.
Push each object with the same force.
Object A
Force
Accelerations
Object B
Force
By Law of Acceleration, Object A accelerates more than the (heavier) Object B.

26. Mutual Repulsion Summary
If A pushes B then both accelerate by equal forces. By Law of Acceleration, Object A, having less weight, will accelerate more than the heavier Object B.
Reaction
Action
Object A
Object B
Acceleration
Acceleration

27. Class Demo: Mutual Repulsion (cont.)
If we replace Mr. B with a solid wall then Mr. A pushes on the wall (that’s the action force) but due to the enormous mass of the building, the wall does not move.
Wall exerts a reaction force, pushing Mr. A away from the wall.
Mr. A
Action
Reaction
Acceleration

28. Wile E. Coyote & Action/Reaction
“Beep Beep” (1952)
Action/Reaction is often violated for comic effect.
“Gee Whiz-z-z-z” (1956)

29. Jumping Action/Reaction
Jumping is done by pushing downward on the ground (action) so the ground pushes upward on you (reaction).
Reaction
Action

30. Force, Time, and Impulse
When any force causes a change in velocity, the more time that the force can act, the greater the change in the velocity.
Pushing apart, these guys only exert forces on each other as long as their hands are together.

31. Crouching for a Jump X
Crouch
Take-off
Apex
Crouching is useful when jumping because it extends the time of contact for pushing off the ground.

32. Walking Action/Reaction
In walking a character exerts an action force on the floor, which results in a reaction force on the character.
If the character is unable to exert a side-ways action force (e.g., slippery ice) then the character cannot walk.
Reaction
Action

33. Reaction Force on the Foot
The floor exerts a reaction force that either slows us down (from squash to passing position) or speeds us up (from passing position to stretch).
“Butterfly diagram” of force vectors.
Squash
Stretch
Passing Position
Passing Position
Squash
Stretch
Floor’s Reaction Force
Walking this way

34. Pushing an Object
The man pushes on the rock but he is also pushing on the ground.
Action: Man exerts force on rock
Reaction: Rock exerts force on man
Reaction: Ground exerts force on man
Action: Man exerts force on ground
Man moves forward when reaction from the ground is more than from the rock.

35. Shaolin Soccer (2001)
Extreme kung-fu action appears in Shaolin Soccer.
Think about the forces exert by the woman’s arms (pushing) and feet (holding her in place).

36. Class Demo: Mutual Attraction
If only Mr. A pulls on Mr. B then Mr. B accelerates.
Reaction force of equal magnitude so Mr. A also moves.
Who moves faster? Mr. A, Mr. B, or the same?
Mr. B
Reaction
Action
Mr. A
Mr. A weighs less than Mr. B
Accelerations
Mr. A goes faster (greater acceleration) since his mass is less.

37. Mutual Attraction Summary
If A pulls B then both accelerate by equal forces. By Law of Acceleration, Object A, having less weight, will accelerate more than the heavier Object B.
Object A
Object B
Reaction
Action
Accelerations

38. Class Demo: Mutual Attraction (cont.)
When both persons pull then there are two action forces and two reaction forces.
If both pull with same force, how much greater is the acceleration than when only one pulls?
Mr. B
Reaction A
Action A
Mr. A
Action B
Twice the force, twice the acceleration
Reaction B
Accelerations

39. Class Demo: Mutual Attraction (cont.)
We replace Mr. B with a solid wall and Mr. A pulls on the wall (that’s the action force) .
Due to the enormous mass of the building, the wall does not move.
Wall exerts a reaction force, which pulls Mr. A towards the wall.
Mr. A
Reaction
Action
Acceleration

40. Action / Reaction for Gravity
The reaction force due to the gravitational pull on a character has a negligible effect since Earth is massive.
Action Force: Earth pulls down on Wile
Reaction Force: Wile pulls up on Earth

41. Pulling a Character .

42. Forces on Gia Reaction: Alex exerts force on Gia
Action: Gia exerts force on Alex
Gravity
Action: Gia exerts force on train
Reaction: Train exerts force on Gia
In this shot Gia is pulling Alex into the train car. Because she is exerting an action force on him there’s an equally large reaction force pulling her towards the outside of the car (even if Alex is just passively holding his arm out to her). To stay in the train car, Gia pushes towards screen left with her feet; the resulting reaction force pushes her towards the inside of the car. If the two reaction forces on Gia plus the force of gravity (her weight) are in balance then her center of gravity won’t move, otherwise she’ll either be pulled out of the car or fall backwards into the car.

43. Forces on Alex Reaction: Alex exerts force on Gia
Action: Gia exerts force on Alex
In this shot Gia is pulling Alex into the train car. Because she is exerting an action force on him there’s an equally large reaction force pulling her towards the outside of the car (even if Alex is just passively holding his arm out to her). To stay in the train car, Gia pushes towards screen left with her feet; the resulting reaction force pushes her towards the inside of the car. If the two reaction forces on Gia plus the force of gravity (her weight) are in balance then her center of gravity won’t move, otherwise she’ll either be pulled out of the car or fall backwards into the car.
Gravity
Action: Alex exerts force on ground
Reaction: Ground exerts force on Alex

44. Recoil Action/Reaction principle applies to recoil.
The action force that accelerates the bullet results in a matched reaction force in opposite direction, recoiling the gun.
Heavy gun
Action/Reaction principle also describes recoil. The action force that accelerates the bullet results in a matched reaction force in opposite direction, recoiling the gun. Specifically, when there are no other forces: Recoil Speed = (Bullet/Gun Weight Ratio) x (Bullet Speed).
Fast bullet
Recoil Speed = (Bullet/Gun Weight Ratio) x (Bullet Speed)

45. Recoil
Example: If the cannon weighs 100 times more than the cannon ball then cannon’s recoil speed is 100 times less than cannon ball’s speed.
Heavy cannon
Fast cannonball
Recoil Speed = (Bullet/Gun Weight Ratio) x (Bullet Speed)

46. Recoil from a Gun High recoil speed is cause by either:
* Large Bullet/Gun Weight Ratio
* High Bullet Speed
Shooting an elephant gun

47. Predator (1987)

48. Recoil & Wile E. Coyote
Unexpected recoil is another common gag in animated cartoons.
Guided Muscle (1955)

49. Wall-E Fire, Propelled
Would using a fire-extinguisher for propulsion, as done by Wall-E, would actually work, A) Yes or B) No?

50. Class Demo: Extinguisher Rocket
Using a fire-extinguisher for rocket-like propulsion.

51. Two-stage Rockets
The first stage accelerates the rocket until it runs out of fuel.
The first stage is discarded, reducing the rocket’s mass.
Rocket mass reduced so recoil acceleration is greater.

52. Mythbusters Two-Stage Rocket Sled

53. IMPORTANT!!!
Action force & reaction force NEVER cancel because they act on different objects!
Repeat this to yourself over and over again

54. Balance of Forces?
Miss A pushes the cart (action); cart pushes back on her (reaction). Do these forces cancel?
No, the two forces act on different objects.
Force on Miss A is to the left; how can she move forward (to the right)?
Miss A pushes back on the ground with her feet (action) reaction of ground on her is to the right.
What if ground had zero friction (like ice)?
Then Miss A can’t move forward.
Miss A
Action
Reaction
Action
Reaction
Action-
Reaction
Pairs

55. Balance of Forces?
Mr. B also pushes from the inside of cart but obviously he can’t move the cart alone. In terms of Newton’s laws, why not?
Because the total force exerted by Mr. B on the cart is zero.
What other force does Mr. B exert on the cart besides his hands?
His butt pushes back on the cart and the floor of the cart pushes back on him.
The two action forces balance each other and the two reaction forces balance each other.
Mr. B
Reaction
Action
Action
Reaction
Action-
Reaction
Pairs

56. Wile E., Propelled
From “Ready, Set, Zoom”
Would using an outboard motor in a tub for propulsion, as done by Wile E. Coyote, actually work? A) Yes or B) No

57. Internal Propulsion
B) No. Internal propulsion is not possible because the impulse gained from one reaction is lost due to another internal action.
Water pushes propeller
Propeller pushes water
Tub pushes water
Water pushes Tub
Action/Reaction Pairs

58. Wile E., Propelled II
From “Scrambled Arches”
Would using a strong fan and a big sail for propulsion, as done by Wile E. Coyote, actually work? A) Yes or B) No

59. Internal Propulsion
Doesn’t work!
B) No. Internal propulsion is not possible because the impulse gained from one reaction is lost due to another internal action.
Air pushes propeller
Propeller pushes air
This would work!
Sail pushes air
Air pushes sail
Action/Reaction Pairs

60. Next Assignment: First Term Paper Due Tuesday (Next week)
Next Lecture Jumping
Next Assignment: First Term Paper Due Tuesday (Next week)