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Seventh Homework (Outline of First Term Paper)
Due Wednesday, October 13th (This week)
10 points (5 points if late)
First Term Paper
The Laws of Physics in an Animation Universe
Due Wednesday, October 20th (Next week)
100 points (50 points if late)
For full schedule, visit course website:
ArtPhysics123.pbworks.com
Homework #7
One-page outline for your first term paper,
The Laws of Physics in an Animation Universe
* Select an animated feature film or a live-action film
with CGI special effects.
* Identify three simple scientific hypotheses on how
things work in the film's "universe."
* For each hypothesis, identify two or more scenes in
the film that confirm it.
* Point out any scene that possibly contradicts one of
the hypotheses.
Homework #7
* Present at least one competing hypothesis and
identify one or more scenes that contradict it.
* Organize the points above into a concise one-page
outline to be used for your first term paper.
* Post the outline on your blog in a posting entitled
“Outline for the First Term Paper.”
Outline is due by 8am on Wed., October 13th
10 points (5 points if late)
Term paper is due by 8am on Wed., Oct. 20th
100 points (50 points if late)
Extra Credit Opportunities
* Visit the "PIXAR: 25 Years in Animation" exhibition at the
Oakland Museum of California . Present proof of you
attendance (receipt, photos, etc.) for 10 points of extra
credit.
* Attend the Stop & Go Rides Again Animation Festival at the
San Francisco Exploratorium (McBean Theater) on Saturday,
October 16, 2010, 2pm. Present proof of you attendance
(receipt, photos, etc.) for 10 points of extra credit.
* Attend any event at the San Francisco International Animation
Festival (November 11-14). Present proof of you attendance
(receipt, photos, etc.) for 10 points of extra credit.
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Survey Question
The film that you have picked out
for your first term paper is…
A) Animated feature film
B) Live action feature film with SFX
C) Mixed live-action and animation
D) Something other than a film
(TV series, video game, etc.)
E) Yet to be decided
B) Left Leg
In this classic
contrapposto pose,
the weight of the
body is primarily
on which leg?
A) Right Leg
Review Question
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)
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.
Lifting a Weight
This 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) above
is possible.
Lifting a Heavy Weight
A) Very Light.
No matter how strong the
character is, the pose
cannot be in balance if the
ball 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.
X
X
Her CG
XX
Total CG if
ball is light
Ball’s
CG
Total CG if
ball is very
heavy
Action &
Reaction
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
Sir Isaac Newton
Today we look at the Action-Reaction Principle,
also known as Newton’s Third Law.
Action-Reaction Principle
For every action force there
is an equal reaction force in
the opposite direction.
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.
Action-Reaction Pairs
Action-reaction always occurs in pairs.
Action: (Thing A) exerts a force on (Thing B).
Reaction: (Thing B) exerts a force on (Thing A).
Law of Acceleration (Reminder)
Object A has less mass (lighter) than Object B.
Push each object with the same force.
Force
Object A
Accelerations
Force
Object B
By Law of Acceleration, Object A accelerates
more than the (heavier) Object B.
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 has
more mass
(weighs more)
than Mr. A
Mr. A
Put them on
skateboards
to minimize
the effect of
friction force.
Mr. B
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?
Reaction
Action
Mr. A
Mr. A has
less mass
than Mr. B
Accelerations
Mr. A goes faster
(greater acceleration)
since his mass is less.
Mr. B
Mutual Attraction Summary
If A pulls B then both accelerate by equal forces.
By Law of Acceleration, Object A, having less mass,
will accelerate more than the heavier Object B.
Object A
Reaction
Action
Accelerations
Object B
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?
Reaction A
Action A
Mr. A
Twice the force,
twice the
acceleration
Action B
Reaction B
Accelerations
Mr. 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.
Mr. A
Reaction Action
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
Mr. A
pushes
Mr. B holds
Reaction
Large
Acceleration
Small
Acceleration
Mutual Repulsion Summary
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.
Action
Reaction
Object A
Accelerations
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.
Mr. A
Action
Reaction
Acceleration
Wile E. Coyote & Action/Reaction
“Beep Beep” (1952)
Action/Reaction is
often violated for
comic effect.
http://www.youtube.com/watch?v=csIIFGFr1wU
http://www.youtube.com/watch?v=vobhUvhO8N0
“Gee Whiz-z-z-z” (1956)
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
Action/Reaction in KFP
http://www.youtube.com/watch?v=YGg6QiNOZ28
Watch the reaction for each character as they
strike the inanimate punching bag.
Fight Scenes
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.
http://www.youtube.com/watch?v=Ea7JxAvzUMg
A recent Bond film (Casion Royale, 2006) starts with
a similarly realistic fight scene in a bathroom.
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
Action/Reaction also explains recoil, such as from a gun.
The action force that accelerates the bullet results in a
reaction force in opposite direction, recoiling the gun.
Heavy cannon
Fast cannonball
Recoil Speed = (Bullet/Gun Weight Ratio) x (Bullet Speed)
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
High recoil speed is cause by either:
* Large Bullet/Gun Weight Ratio
* High Bullet Speed
Shooting an elephant gun
http://www.youtube.com/watch?v=MlFlXMHaSVQ
http://www.youtube.com/watch?v=bpFDHO-tqUY
Predator (1987)
Eraser (1996)
http://www.youtube.com/watch?v=aHoIMBXKSos
Recoil & Wile E. Coyote
http://www.youtube.com/watch?v=Wxm9EdVFxk8
Unexpected recoil is
another common gag
in animated cartoons.
Guided Muscle (1955)
http://www.youtube.com/watch?v=7H6Pwzdw7oQ
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.
Crouching for a Jump
Crouching is useful when
jumping because it extends
the time of contact for
pushing off the ground.
Push Height
X
X
Apex
Crouch
Take-off
Pushing an Object
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)
Extreme kung-fu
action appears in
Shaolin Soccer.
http://www.youtube.com/watch?v=bREfcVPssiE
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?
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;
Miss A
how can she move forward
(to the right)?
Miss A pushes back on the
Action
ground with her feet (action)
reaction of ground on her is
Reaction
to the right.
What if ground had zero
Reaction
friction (like ice)?
ActionThen Miss A can’t move
Action
Reaction
forward.
Pairs
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
ActionReaction
Pairs
Action
Reaction
Wile E., Propelled
http://www.youtube.com/watch?v=rv7PWDjjjqk
From “Ready, Set, Zoom”
Using an outboard motor in a tub for propulsion, as done
by Wile E. Coyote, would actually work, True or False?
Internal Propulsion
False. 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
Action/Reaction Pairs
Tub
pushes
water
Water
pushes
Tub
Wile E., Propelled II
http://www.youtube.com/watch?v=wkMOfeXItUU
From “Scrambled Arches”
Using a strong fan and a big sail for propulsion, as done
by Wile E. Coyote, would actually work, True or False?
Internal Propulsion
False. 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
Action/Reaction Pairs
This
would
work!
Sail
pushes
air
Air
pushes
sail
Wall-E Fire, Propelled
http://www.youtube.com/watch?v=2lkffSsImXc
Using a fire-extinguisher for propulsion, as used by
Wall-E, would actually work, True or False?
Class Demo: Extinguisher Rocket
http://www.youtube.com/watch?v=9F_VjHZATbY
Using a fire-extinguisher for rocket-like propulsion.
Next Lecture
Jumping
Homework #7
(Outline of the First Term Paper)
Due this Wednesday
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