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First Term Paper
The Laws of Physics in an Animation Universe
Due Tuesday, March 13th (Next week)
100 points (50 points if late)
Eighth Homework (Reverse Video Reference)
Due Thursday, March 22nd (In 2 weeks)
20 points (10 points if late)
For full schedule, visit course website:
ArtPhysics123.pbworks.com
Extra Credit Opportunity
Attend any Cinequest Film Festival
event in downtown San Jose.
Turn in proof of your attendance (e.g., access
pass, ticket receipt) for 5 points extra credit.
For info: www.cinequest.org
See Bloom tonight
@ 9:45pm show
Stop-Motion Animation of Falling
Top three stop motion animation shots
of falling (20 bonus points):
Nicholas Carpenter
Mina Evans
Man Yee Wong
Honorable mentions (10 bonus points):
Kimberly Lambe
Graeme Potts
First Term Paper
The Laws of Physics in an Animation Universe
Modern science is based on the principles of
experimental observation and theoretical analysis; in
this assignment you will apply these principles in a
critical analysis of animation and special effects.
Specifically, you will select an animation film (or a liveaction film featuring CGI animation special effects)
and formulate three distinct scientific hypothesis for
the universe portrayed in that film (which may or may
not obey the same physical laws as the real world).
First Term Paper
For example, in your animation’s universe the laws
gravity may be different (e.g., heavy objects may fall
faster than light objects).
Your hypotheses should be such that there is relevant
observational evidence in the film; you need to
describe what that evidence is and how it supports
your theories.
You will also formulate a competing theories and
present evidence that the universe portrayed in the
film does not follow those alternate hypotheses.
First Term Paper
The paper will be graded according to the rubric posted on
the website on this page:
http://artphysics123.pbworks.com/First-Term-Paper
Upload your term paper to your blog in a post entitled
"The Laws of Physics in an Animation Universe."
Paper is due by 8am on Tuesday, March 13th
100 points (if late, 50 points)
Survey Question
“This course has ___ changed the
way that I view animation.”
A)
B)
C)
D)
Very Significantly
Significantly
Somewhat
Been interesting but not really
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
Ball’s
CG
X
Her CG
XX
Total CG if
ball is light
Total CG if
ball is very
heavy
Weight Shift
(cont.)
Dynamic Balance
A pose that’s out of balance
for a stationary character may
be in dynamic balance if the
character is moving.
Charlene Fleming
Tilting the Line of Gravity
Acceleration tilts the line of gravity.
Stationary or
Steady Train
Accelerating
Train
Charlene Fleming
Stopping and Starting
You lose balance on a sudden stop or start
since acceleration tilts the line of gravity.
Sudden
stop
Sudden
start
Fall towards the new Center of Pressure.
Leaning into a Turn
Centripetal acceleration tilts
the line of gravity to the
inside of the turn.
Centripetal
Acceleration
Charlene Fleming
Faster and/or tighter the
turn, the greater the
angle of the tilt.
Centrifugal Force
Can view roll-over loss of balance in terms of
the centrifugal force pulling the CG outward.
Centrifugal
Force
Centripetal
Acceleration
X
CG
Centrifugal
Force
Weight
“Roll Over” Loss of Balance
Car making a tight turn may lose balance due to tilting of the
line of gravity caused by centripetal acceleration.
Tips
Over
Centripetal
Acceleration
X
CG
Similar to a car
parked on a slope
Bullitt (1968)
Watch the cars as they
take high-speed turns.
Leaning In vs. Tilting Outward
Motorcycle riders
actively lean into
the turn to maintain
dynamic balance.
Car’s suspension
is passive so
centrifugal force
tilts it outward.
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).
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.
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?
Mr. B
Reaction
Action
Mr. A
Mr. A has
less mass
than Mr. B
Accelerations
Mr. A goes faster
(greater acceleration)
since his mass is less.
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
Accelerations
Action
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?
Mr. B
Reaction A
Action A
Mr. A
Action B
Twice the force,
twice the
acceleration
Reaction B
Accelerations
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. B holds
Mr. A
pushes
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
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; how
Miss A
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 to
Reaction
the right.
What if ground had zero friction
Reaction
(like ice)?
ActionThen Miss A can’t move forward.
Action
Reaction
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
Action
Reaction
ActionReaction
Pairs
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
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)
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
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
Next Assignment:
First Term Paper
Due next Tuesday, March 13th
Please turn off and return the clickers!