Upcoming Deadlines

First Term Paper The Laws of Physics in an Animation UniverseDue Today! (at 8AM)100 points (50 points if late)

Eighth homework (Reverse Video Reference)Due Thursday, Oct. 27 (Next week)20 points (10 points if late)

For full schedule, visit course website:ArtPhysics123.pbworks.com

Pick up a clicker, find the right channel, and enter Student ID

Homework #8Reverse video reference of walking Normally, animators shoot video and use it as

reference for their work. In this assignment, you will do the reverse. Specifically, you will watch each of three animation clips and shoot video in which you recreate them as accurately as possible.

Homework #8• Watch each of the three video clips on the

assignment page• Film yourself acting out each scene, each in a

separate clip. Reproduce the motion of the character as accurately as possible - you will be graded on how well you do this. Don’t just quickly act it out. Study each clip carefully to capture all of the motion details. Pay attention to staging, camera angle, camera moves (if any), etc.

• Post all three videos in a blog entry entitled “Reverse Video Reference of Walking”

Homework #8

Assignment is due by 8AM on Thursday, Oct. 27th20 points (10 points if late)

Extra Credit Opportunities* Attend the Animation Show of Shows - Friday (tomorrow),

7:30 at the Morris Daley Aud. There will be 10 films shown and out of 5 of the films, the directors will be there. Pls see Lauren B for attendance credit.

* Attend any event at the NY-SF International Children’s Film Festival (October 21-23) Present proof of your attendance (receipt, photos, etc.) for 10 points of extra credit.

* Attend any event at the San Francisco International

Animation Festival (November 10-13). Present proof of your attendance (receipt, photos, etc.) for 10 points of extra credit.

Review Question

In this classic contrapposto pose, the weight of the body is primarily on which leg?

A) R

ight

Leg

B) L

eft L

eg

Hips and ShouldersA) Right LegNotice 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)

Weight Shift in AnimationRex 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.

Lifting a WeightThis character is of normal human weight.The ball she’s lifting is:

A) Very light, like a beach ball.

B) Extremely heavy (she has super-human strength).

C) Either A) or B) aboveis possible.

Lifting a Heavy Weight

X

A) Very Light.X

XHer CG

Ball’sCG

Total CG if ball is light

No matter how strong thecharacter is, the posecannot be in balance if theball is very heavy because the total center of gravity would not be over the base of support.

Imagine this as a free-standing statue; obviously it would tip over if the ball was very heavy.

XTotal CG if ball is very heavy

Action &Reaction

Newton’s Laws of ForcesNewton 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

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

Reaction

Action

Reaction

Action and ReactionCommon 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.

Action-Reaction PairsAction-reaction always occurs in pairs.

Action: Fist exerts force on jaw

Reaction: Jawexerts forceon fist

Action: (Thing A) exerts a force on (Thing B).Reaction: (Thing B) exerts a force on (Thing A).

Action: Man

exerts force

on rock

Reaction: Rock

exerts force

on man

Law of Acceleration (Reminder)

Object A

Object B

Force

Accelerations

By Law of Acceleration, Object A accelerates more than the (heavier) Object B.

Force

Object A has less mass (lighter) than Object B.Push each object with the same force.

Class Demo: Mutual Attraction

What happens when:• Mr. A pulls, Mr. B holds.• Mr. A holds, Mr. B pulls.• Mr. A & Mr. B

both pull.

Mr. B

Mr. A

Mr. B has more mass (weighs more) than Mr. A

Put them on skateboards to minimize the effect of friction force.

Class Demo: Mutual Attraction (cont.)

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?

ActionReactionMr. A

Mr. B

Mr. A goes faster (greater acceleration) since his mass is less.

AccelerationsMr. A has less mass than Mr. B

Mutual Attraction Summary

Object A Object BActionReaction

Accelerations

If A pulls B then both accelerate in response to equal forces.By Law of Acceleration, Object A, having less mass, will accelerate more than the heavier Object B.

Class Demo: Mutual Attraction (cont.)

Action AReaction AMr. A

Mr. B

Accelerations

Twice the force, twice the

acceleration

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?

Action BReaction B

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.

ActionReactionMr. A

Acceleration

Class Demo: Mutual Repulsion

Similar demonstration is to have Mr. A and Mr. B push away instead of pull together.

Same results; if Mr. A pushes and Mr. B holds then both move apart.

Action

Reaction

Mr. Apushes

Mr. B holds

LargeAcceleration

SmallAcceleration

Mutual Repulsion Summary

Object A Object BActionReaction

Accelerations

If A pushes B then both accelerate by equal forces.By Law of Acceleration, Object A, having less mass, will accelerate more than the heavier Object B.

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.

Action

Reaction

Mr. A

Acceleration

Wile E. Coyote & Action/Reaction

“Beep Beep” (1952)

http://www.youtube.com/watch?v=vobhUvhO8N0

http://www.youtube.com/watch?v=csIIFGFr1wU

“Gee Whiz-z-z-z” (1956)

Action/Reaction is often violated for comic effect.

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

WeakStrong

Action/Reaction in KFP

Watch the reaction for each character as they strike the inanimate punching bag.

http://www.youtube.com/watch?v=YGg6QiNOZ28

Fight Scenes

Action: Fist exerts force on jaw

Reaction: Jawexerts forceon fist

Fight scenes are more realistic when reaction punches and kicks show the reaction force

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

From Russia with Love (1963)This early James Bond film has a very brutal, realistic fight scene.

A recent Bond film (Casino Royale, 2006) starts with a similarly realistic fight scene in a bathroom.

http://www.youtube.com/watch?v=Ea7JxAvzUMg

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

http://www.youtube.com/watch?v=glsUlacDN7Q

Recoil

Recoil Speed = (Bullet/Gun Weight Ratio) x (Bullet Speed)

Action/Reaction also explains recoil, such as from a gun.The action force that accelerates the bullet results in areaction force in opposite direction, recoiling the gun.

Heavy cannon Fast cannonball

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.

Recoil from a Gun

http://www.youtube.com/watch?v=MlFlXMHaSVQ

http://www.youtube.com/watch?v=bpFDHO-tqUY

High recoil speed is cause by either:* Large Bullet/Gun Weight Ratio* High Bullet Speed

Shooting an elephant gun

Predator (1987)

Eraser (1996)

http://www.youtube.com/watch?v=aHoIMBXKSos

Recoil & Wile E. Coyote

Guided Muscle (1955)

http://www.youtube.com/watch?v=Wxm9EdVFxk8

http://www.youtube.com/watch?v=7H6Pwzdw7oQ

Unexpected recoil is another common gag in animated cartoons.

Force, Time, and ImpulseWhen 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.

Crouching for a Jump

X

X

Crouch Take-off

Apex

Push Height

Crouching is useful when jumping because it extends the time of contact for pushing off the ground.

Pushing an Object

Action: Man

exerts force

on rockReaction: Rock

exerts force

on man

Action: Man

exerts force

on ground

Reaction: Ground

exerts force

on man

The man pushes on the rock but he is also pushing on the ground.

Man moves forward when reaction from the ground is more than from the rock.

Shaolin Soccer (2001)

http://www.youtube.com/watch?v=bREfcVPssiE

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).

IMPORTANT!!!

Action force & reaction force NEVER cancel because they act on different objects!

Repeat this to yourself over and over again

Balance of Forces?

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

Miss A pushes the cart (action); cart pushes back on her (reaction). Do these forces cancel?

No, the two forces act on different objects.

Balance of Forces?

Mr. BActionReaction

Action-Reaction

Pairs

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.

ReactionAction

Wile E., Propelled

Using an outboard motor in a tub for propulsion, as doneby Wile E. Coyote, would actually work, True or False?

http://www.youtube.com/watch?v=rv7PWDjjjqk

From “Ready, Set, Zoom”

Internal Propulsion

Water pushes Tub

Tub pushes water

Propeller pushes water

Water pushes propeller

Action/Reaction Pairs

False. Internal propulsion is not possible because the impulse gained from one reaction is lost due to another internal action.

Wile E., Propelled II

Using a strong fan and a big sail for propulsion, as doneby Wile E. Coyote, would actually work, True or False?

http://www.youtube.com/watch?v=wkMOfeXItUU

From “Scrambled Arches”

Internal Propulsion

Air pushes sail

Sail pushes air

Propeller pushes air

Air pushes propeller

Action/Reaction Pairs

False. Internal propulsion is not possible because the impulse gained from one reaction is lost due to another internal action.

This would work!

Wall-E Fire, Propelled

Using a fire-extinguisher for propulsion, as used by Wall-E, would actually work, True or False?

http://www.youtube.com/watch?v=2lkffSsImXc

Class Demo: Extinguisher Rocket

Using a fire-extinguisher for rocket-like propulsion.http://www.youtube.com/watch?v=9F_VjHZATbY

Next LectureJumping

Homework #8 (Reverse Video Reference of Walking)

Due next Thursday

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