1. Upcoming Deadlines
Have clicker ready
Eighth Homework (Reverse Video Reference) Due Tuesday, October 16th (Next week) 20 points (10 points if late) Ninth Homework (Stop-motion Character Animation) Due Tuesday, October 30th (In 3 weeks) For full schedule, visit course website:

2. Extra Credit Opportunities
Cartoon Art Museum
Mill Valley Film Festival
Walt Disney Family Museum
Exploratorium
The Tech Museum
Visit course website for more info.

3. Homework Assignment #8
Normally animators shoot video and use it as reference for their work.
In this assignment, you'll do the reverse.
Specifically, for four different animation clips you’ll shoot video of yourself in which you recreate those clips as accurately as possible.
Go to Homework Assignment 8 on the course website to find the animation clips you’ll recreate.

4. Homework Assignment #8 Clip A

5. Homework Assignment #8 Clip B

6. Homework Assignment #8 Clip C

7. Homework Assignment #8 Clip D

8. Homework Assignment #8
Film yourself acting out the scene in each of these animation clips, recording a separate clip of yourself for each one. Reproduce the motion of the character in the animation as accurately as possible (you'll be graded on how well you do). Don't just quickly act it out but rather study each animation clip carefully to capture all the details in the motion, including staging and camera angle. Be sure that you have enough room to do all the steps in the walk; do not walk in place, it’s not the same!

9. Homework Assignment #8
Upload your four clips to your blog in an entry entitled “Reverse Video Reference of Walking.”
The purpose of this exercise is to have you carefully observe the motion in each clip so that you will learn the complexity of different walks.
This assignment is due by 8am on Tuesday, October 16th (next week).
20 points (if late, 10 points).
For each of the four animation clips the best video clip will get an extra 20 points of credit.

10. Survey Question Writing the term paper was: Rather enjoyable 
Somewhat enjoyable OK
Somewhat painful
Rather painful 

11. Review Question
Mr. A pushes while Mr. B just holds his hand rigidly in place. Mr. A weighs less than Mr. B.
Which of them has the largest acceleration?
Mr. B holds
Mr. A
Mr. B
They have the same acceleration
Mr. A pushes

12. Action/Reaction & Acceleration
Mr. A has the larger acceleration.
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.
Object A
Object B
Action
Reaction
Accelerations

13. Review Question The woman pushing the car exerts more force:
With her hands
With her feet
About the same with her hands as with her feet

14. Pushing an Object C) About the same with her hands as with her feet
When the force exerted by the hands and feet are equal then the character stays in place after pushing the object.
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.

15. Review Question
Which of these devices would actually work to propel Wile E. Coyote?
Outboard motor in a tub of water.
Fan blowing a large sail.
Both could work.
Neither would work. A) B)

16. Internal Propulsion
Back of the tub acts like the sail.
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

17. Action & Reaction (cont.)

18. Fight Scenes
Fight scenes are more realistic when reaction punches and kicks show the reaction force.
Reaction: Jaw exerts force on fist
Action: Fist exerts force on jaw

19. From Russia with Love (1963)
This early James Bond film has a very brutal, realistic fight scene.
A recent Bond film (Casion Royale, 2006) starts with a similarly realistic fight scene in a bathroom.

20. Kung fu Hustle (2004)
In a comedy it’s best to make a fight scene less realistic, which makes it funny.

21. Spiderman 3 (2007)
Most elements of this fight scene do not have realistic reaction forces to match the actions.

22. The Incredible Hulk (2008)
Using motion capture has the disadvantage that some stunts can only be done using wire rigs.
The action will look fake without the right reaction.

23. Kung-Fu Panda
End credits of KFP play with the 3rd law, but consistently. Strong characters have mass; the weak ones are light.
Weak
Strong

24. Action/Reaction in KFP
Watch the reaction for each character as they strike the inanimate punching bag.

25. Manipulating Action-Reaction
Action/Reaction principle is often manipulated to give “weight” to a dramatic character or to make a comedic character “light.”
Finally, the action-reaction principle is often violated in films, both animated and live-action. Heros deliver powerful punches (or shoot big guns) with negligible recoil while the villain goes flying backwards. This may be done intentionally for dramatic effect (to make the hero look powerful) or for comic effect (to defuse the violence) but if it's unintentional and unexpected then there's a chance of shattering the audience's suspension of disbelief.
Image courtesy of Dreamworks Animation

26. Jumps

27. Jumping
Jumping is a basic character animation exercise that has many of the basic elements found in drop tests for inanimate objects.
By Carlos Nunez
By Danielle Domurat

28. Timing the Jump
X = Center of Gravity X
Crouch
Take-off
Apex
Jump Height
Jump Time
The simplest part of a jump is the time in the air and how it is related to the height of the jump.
The timing of the character while in the air is also simple since gravitational acceleration is the same for all objects. That is, from the height of the jump (vertical distance from take-off to apex) we can find the jump time (number of frames from take-off to apex).
Image by Corey Tom

29. Jump Time & Height
The same table we saw for the ball drop gives the jump time (from take-off to apex) and jump height.
Jump Time (seconds)
Frames
Jump Height
1/24 1
1/3 inch
1/12 2
1 1/3 inches
1/8 3
3 inches
1/6 4
5 1/3 inches 6
12 inches
1/3 8
21 inches 12
4 feet
2/3 16
7 feet 18
9 feet 24
16 feet
This table lists the jump heights for various jump times. The values in the table are obtained using the formula:
(Jump height in inches) = (1/3 inch) x (Jump time in frames) x (Jump time in frames)
For example, for a jump time of 6 frames the jump height is (1/3) x (6) x (6) = 12 inches
The formula to compute this table is:
(Distance in inches) =
(Number of Frames) x
(1/3 inch)

30. Jump Time Example
Hang time = 2 x (Jump time)
For a jump time of 6 frames, the jump height is 1 foot
6 frames
6 frames X
1 foot X
For example, everything falls one foot in six frames so jumping one foot in height takes six frames from take take-off to apex and another six frames from apex to landing. This corresponds to a “jump height” of one foot and a “jump time” of six frames. Timing and scale are connected so a four foot jump takes twice as long. Notice that the timing only depends on the (vertical) height of the jump, not on the (horizontal) distance jumped.
Image by Corey Tom
Apex
Take-off
Landing
X = Center of Gravity

31. Crouching Tiger, Hidden Dragon (2000)
Characters stay in the air an unrealistically long time, even considering the impressive height of their jumps.

32. Timing the Push X
X = Center of Gravity
Crouch
Take-off
Apex
Push Height
Jump Height
Jump Time
Push Time
You can time the push (from crouch to take-off) using simple formulas
Now let's consider the start of a jump, when the character is rising out of the crouch, pushing with its legs in order to get into the air. We'll call the distance over which the character pushes off the “push height” and the distance from take-off to apex the “jump height.” Similarly, the time from crouch to take-off we’ll call the “push time” and from take-off to apex we’ll call the “jump time.”
Image by Corey Tom

33. Jump Magnification
Timing of the push depends on the jump magnification.
Apex
Jump Magnification =
Jump Height
Push Height X
Jump Height
The ratio of the jump to push heights is the ``jump magnification'',
Jump Magnification = (Jump height, from take-off to apex) / (Push height, from crouch to take-off)
For example if the character rises from a one foot crouch and jumps four feet into the air then the jump magnification is 4.
Image by Corey Tom X
Push Height X
Jump Magnification = 4
Crouch
Take-off

34. Formula for Timing the Push
Jump Time
Jump Magnification
Push Time =
Can use this formula to check the timing of the push compared with the jump time. X
X = Center of Gravity
Crouch
Take-off
Apex
Push Height
Jump Height
Jump Time
Push Time
The reason that the jump magnification is important is that it determines the timing of the push. The larger the jump magnification, the quicker the push needs to be in order for the jump to look believable. Specifically, if the character pushes with constant force then,
Push time, from crouch to take-off = (Jump time, from take-off to apex) / (Jump Magnification)
Image by Corey Tom

35. Timing the Push Example
8 frames
8 frames
X = Center of Gravity
4 frames
Apex X
20 inches X X
10 inches X
Jump magnification = 2 so jump time is twice as long as the push time.
Crouch
Take-off
Landing

36. Example of Timing the Push.

37. Example of Timing the Push
Jump magnification = 1
3 frames
3 frames X X
In this simple example the jump magnification equals one since the push height (crouch to take-off) equals the jump height (take-off to apex). That means that the push time (number of frames from crouch to take-off) equals the jump time (number of frames from take-off to apex). Notice that the jump time is actually a little short given the height of the jump, nevertheless the jump is believable because the timing is consistent with the jump magnification. X
Crouch
Take-off
Apex

38. Planning a Jump
Animators can plan out a realistic jump by these steps:
Pick the desired jump time or jump height.
Use the table to find the jump height given the jump time (or vice versa).
Pick the desired push height for the crouch
Determine the push time from the jump magnification.

39. A Big Jump Two frames Four frames Six frames Eight frames
A character jumps 16 feet into the air. From the table, that’s a jump time of 24 frames (take-off to apex).
The push height is 16 inches; what is the push time?
Apex
Jump Height = 16 feet
Push Height = 16 inches
Jump Time = 24 frames
Two frames
Four frames
Six frames
Eight frames
Twelve frames
Push Time =
Jump Time
Jump Magnification

40. A Big Jump
Two frames
Apex
Jump magnification is 12 (=16 feet/16 inches) Push time is (24 frames)/12 = 2 frames
Jump Height = 16 feet
Push Height = 16 inches
Jump Time = 24 frames
Push Time =
Jump Time
Jump Magnification

41. Super-hero Jumps X
Apex
Extremely high jumps require the push time to be very small.
Jump Time
36 frames
Jump Height
36 feet
Push Time
1 frame
This is a more complicated example in which the character’s jump height is about 36 feet, which translates to a jump time of 36 frames. Since the jump magnification is x36 the jump time is x36 the push time, which translates to a push time of only one frame.
This calculation is not as important as the concept that it illustrates: The timing when a character is pushing off the ground needs to be quick if the jump is high. When a powerful super-hero jumps exceptionally high the physically accurate push time could be less than one frame. This is why such scenes are sometimes presented as occurring in slow-motion.
Image by Corey Tom
Push Height
1 foot X X
Jump Magnification = 36
Crouch
Take-off

42. Push Factor Can calculate jump magnification with this:
Jump Magnification = (Push Factor) x (Push Height in Feet)
Push Time
(in frames)
Push Factor 1 36 2 9 3 4
2 1/4 6 8
9/16
Push Factor = 36 / (Push Time in Frames)2

43. (Push Factor) x (Push Height in Feet)
Push Factor Example
For a 10 foot tall character, what’s the biggest jump magnification that you could get using a push time (crouch to lift-off) of 3 frames?
The most that the character can crouch is about 5 feet. Using,
Push Time
(in frames)
Push Factor 1 36 2 9 3 4
2 1/4 6 8
9/16
Jump Magnification =
(Push Factor) x (Push Height in Feet)
The jump magnification would be about (4)x(5) = 20 for this deep crouch and very quick push.

44. Hulk (2003)
Watch the timing of the push on the ground compared with the timing of the jump in the air.

45. Unrealistic Timing
Hulk’s jump looks fake since the push timing on the ground isn’t consistent with scale of his jump.
This shallow, forward jump should be about 4-5 stories high.

46. Enhanced Jumping
The force on a jumping character can be increased using elastic, spring platforms.

47. Human Cannonball
The first human cannonball was Zazel (Rosa Richter) in 1877, when she was shot a distance of about 30 feet at Westminster Aquarium in London. Modern performers may fly 200 feet, sometimes over obstacles.
This is possibly the most dangerous of all vaulting acts, with at least 40 confirmed deaths and countless injuries.

48. Stretched Rubber Bands
Cannon Design
Performer is pushed upward on a platform (or on a sled) by stretched rubber bands.
Stretched Rubber Bands
Some designs use compressed
springs or air pressure.
Secondary explosives are only used for show.

49. Apex height in feet = 4 x (Flight time in seconds)2
Human Cannonball
Half the time is spent in the top quarter of the arc
Path of action is a parabolic arc
Apex height in feet = 4 x (Flight time in seconds)2

50. Cannon Range Range of the cannon is roughly equal to:
(Performer’s acceleration in gees) x (Length of the cannon)
A long cannon gives performer a large push height.

51. Jump Magnification and Gees
The jump magnification equals the number of “gees” of acceleration during the push.
Apex X
Acceleration = 4 gees
Jump Height
The ratio of the jump to push heights is the ``jump magnification'',
Jump Magnification = (Jump height, from take-off to apex) / (Push height, from crouch to take-off)
For example if the character rises from a one foot crouch and jumps four feet into the air then the jump magnification is 4.
Image by Corey Tom X
Push Height X
Jump Magnification = 4
Jump Magnification =
Jump Height
Push Height
Crouch
Take-off

52. Human Limits for Launch
Range of the cannon is roughly equal to:
(Performer’s acceleration in gees) x (Length of the cannon)
Above 7 gees a performer will black out due to loss of blood to the brain.
World record is about 200 feet, which is range of 30 foot cannon.

53. Next Lecture Jumps, Part 2
Next Assignment
Reverse Video Reference of Walks
Due Tuesday of next week