Upcoming Deadlines

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Upcoming Deadlines

• Sixth Homework (Outline of First Term Paper)
• Due Wednesday, September 30th
• Seventh Homework Cancelled due to furloughs
• (Automatic 20 points of credit)
• Campus-wide Furlough Day
• Monday, October 19th
• (Art/Phys 123 will meet on Wed., Oct. 21st)
• For full schedule, visit course website
• ArtPhysics123.pbworks.com

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Activating your Clicker

• Turn on your clicker.
• Enter the number or letter that I give you for
  joining this class. Hit Enter/Send key.
• Clicker should read PHY123SCI2
• Type in your student ID hit Enter/Send.
• Clicker is now ready to use.

Hit any key to wake the clicker from sleep mode.
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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 live-action 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).

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First Term Paper

• For example, in your animations 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.

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First Term Paper

• The required length of the paper is 1500 words,
  which is about 6 double-spaced typewritten pages
  (not counting images).
• 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 explaination at
  the end of your term paper (which does not count
  towards the 1500 words).
• This assignment is due by 8am on Wednesday,
  October 14th.
• 125 points (if late, 75 points)

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Extra Credit Opportunity
Visit the Walt Disney Family Museum in San
Francisco (opens Oct. 1st).

• Give me your ticket receipt for ten points extra
  credit.

Hours Wednesday-Monday 10a.m.-6p.m Admission
15.00 for students Location 104 Montgomery
Street Inside The Presidio of San Francisco
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Extra Credit Opportunity
Visit the Exploratorium in San Francisco.

• Give me your ticket receipt for ten points extra
  credit.

Hours Tuesday-Sunday 10a.m.-5p.m Admission
11.00 for students Location 3601 Lyon Street,
SF 94123 Next to Palace of Fine Arts complex
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Collisions, Crashes, and Combat
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Action-Reaction Principle
For every action force there is an equal reaction
force in the opposite direction.
Action
Reaction
Reaction
Action
This is also known as Newtons Third Law of Motion
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Action and Reaction

• Common expression for this principle is,
• To every action theres an equal and opposite
  reaction.
• Whats an action?
• A force exerted by one object on second object.
• Whats 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.

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Action-Reaction Pairs

• Here are examples of action-reaction pairs.
• Think of other examples of an object exerting a
  force on a second object.
• Practice identifying action-reaction pairs.

????
????
????
????
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Demo Equal Magnitudes

• With spring scales, we verify that action and
  reaction forces have equal magnitudes.

Action
Reaction
5
15
Hold
Pull
10
0
0
10
15
5
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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. A
Mr. B
Mr. A has less mass (weighs less) than Mr. B
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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
Accelerations
Mr. A has less mass than Mr. B
Mr. A goes faster (greater acceleration) since
his mass is less.
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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
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Class Demo Mutual Attraction (cont.)

• We replace Mr. B with a solid wall and Mr. A
  pulls on the wall (thats 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
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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. Apushes
Reaction
SmallAcceleration
LargeAcceleration
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Class Demo Mutual Repulsion (cont.)

• If we replace Mr. B with a solid wall then Mr. A
  pushes on the wall (thats 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
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Wile E. Coyote Action/Reaction
Play
Wile E. Coyote demonstrates action/reaction in
Beep Beep (1952)
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Collisions Crashes

• A 2 ton car, going 60 m.p.h. hits a 5 ton truck,
  going 20 m.p.h..
• The force of impact is greatest on which vehicle,
  the car or the truck?
• Forces of impact are equal.
• (Force of car on truck) (Force of truck on
  car)
• The change in velocity (the acceleration) is
  greatest for which vehicle?
• For the car, which has less mass.Law of
  acceleration says thatfor a given force, the
  smallerthe mass, the greater theacceleration.

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Action/Reaction in KFP
Play
End credits of KFP play with the 3rd law, but
consistently
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IMPORTANT!!!

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

Repeat this to yourself over and over again
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Balance of Forces?

• Miss A pushes the car (action) car 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 on the floor with her feet (action)
  towards the left reaction of floor on her is to
  the right.
• What if floor had zero friction?
• Then Miss A cant move forward.

Miss A
Action
Reaction
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Balance of Forces? (cont.)

• Miss B also pushes the car can she move the car
  by herself?
• Obviously not.
• In terms of Newtons laws, why is this not
  possible?
• Because the net force exerted by Miss B on the
  car is zero.
• What other force does Miss B exert on the car
  besides her hands?
• The friction of the car seat on Miss B (action)
  keeps her from moving.
• Reaction (Miss Bs butt pushing on car) balances
  force of her hands.

Miss B
Action
Reaction
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Wile E. Coyote, Propelled
Play
Using an outboard motor in a tub for propulsion,
as doneby Wile E. Coyote, would actually work,
True or False?
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Wall-E Fire, Propelled
Using a fire-extinguisher for propulsion, as used
by Wall-E,would actually work, True or False?
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Class Demo Extinguisher Rocket
Play
Using a fire-extinguisher for rocket-like
propulsion.
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Forces when Jumping

• The three main forces on a person jumping are
• Gravity (Downward)
• Support of the floor (Upward)
• Frictional force of the floor (Horizontal)
• Only these forces can accelerate the person.

Gravity is constant but the force exerted by the
floor can increase in reaction to the action of
the person exerting a force on the floor.
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Jumping Action/Reaction

• Jumping is done by pushing downward on the ground
  (action) so the ground pushes upward on you
  (reaction).
• How high you jump depends on the force and on the
  distance over which you apply that force.

Reaction
Can only push while in contact with the ground so
squatting helps by increasing distance.
Action
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Action/Reaction Jumping Forward
To jump upward and also forward, the action force
(pushing downward with your legs) needs to also
be pushing towards your back so that reaction
force of the floor is upward and forward.
Reaction
Action
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Jump Magnification
Define jump magnification as
Jump Height Push Height
Jump Magnification
Jump Magnification 8
Jump Magnification 2

• Get a large jump magnification when
• Push Height is large
• Push Time is short

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Push Factor
Can calculate jump magnification with this
Jump Magnification (Push Factor) x (Push Height
in Feet)
Push Factor 36 / (Push Time in Frames)2
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Average Push Force

• You can determine the average force exerted when
  jumping as
• (Jump Force) (Jumpers Weight)
• x (Jump Magnification)
• Remember that

Jump Height Push Height
Jump Magnification
Jump Force (Action)
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The Incredible Hulk
The Incredible Hulk is big, lets say 10 feet
tall. Say his push height when he jumps is 3 feet.
If you animate 2 frames from crouch to take-off,
how high does he jump?
For a push time of 2 frames the push factor 9
so the jump multiplier is (Jump multiplier)
(9) x (3) 27 (Push Factor) x (Push
Height) He jumps 81 feet into the air since his
push height of 3 feet gets magnified by a factor
of 27 (the jump multiplier).
Play
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Force Plate Analysis of Jumps
Can measure the force during a jump using a force
plate.
Understanding how this force varies during the
jump helps you animate secondary actions like the
drag of hair and clothes.
Force
Normal Weight
Play
Time
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Force Plate Analysis of Jumps
a) Standing still before starting the jump. Force
on the ground is just our normal weight.
Force
Normal Weight
Time
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Force Plate Analysis of Jumps
b) Start coming down. Force goes below normal
weight as we accelerate downward.
Force
Normal Weight
Time
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Force Plate Analysis of Jumps
c) Midpoint of downward motion. Pushing upward to
decelerate the motion.
Force
Normal Weight
Time
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Force Plate Analysis of Jumps
d) Lowest point in the crouch. Pushing upward
with near maximum force.
Force
Normal Weight
Time
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Force Plate Analysis of Jumps
e) Rising out of the crouch, just before lifting
off. Force decreases as feet are nearly losing
contact.
Force
Normal Weight
Time
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Force Plate Analysis of Jumps
f) Lift-off! Moment you lose contact with the
ground.
Force
Normal Weight
Time
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Force Plate Analysis of Jumps
g) Apex. Motion goes from upward to downward.
Force
Normal Weight
Time
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Force Plate Analysis of Jumps
h) Landing. Moment you regain contact with the
ground.
Force
Normal Weight
Time
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Force Plate Analysis of Jumps
Jump magnification for this jump is roughly equal
to one (jump height push height)
PushTime
Average jump force is roughly equal to my weight.
Force
JumpForce
Normal Weight
Time
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More Incredible Hulk
If The Hulk has a push height of 2 feet and he
makes a huge jump, rising a height of 200 feet,
how much force does he push with?
Since The Hulk is twice as tall as a normal
person, his weight is at least 8 times larger
(probably closer to 10-12 times larger). So the
push force of this jump would be about 1000 times
the weight of a normal person if he jumps
straight up and about 1400 times if he jumps at a
45 degree angle.
Similar force on jumping and landing (if similar
push and crouch height)
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Swinging Arms in a Jump
The natural motion when jumping is to swing the
arms upward as fast as possible while the feet
are in contact with the ground.
Swinging the arms raises the center of gravity
and also increases the downward action force
pushing off the ground.
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Swinging Arms in a Jump
The natural motion when jumping is to swing the
arms upward as fast as possible while the feet
are in contact with the ground.
Swinging the arms raises the CG and also
increases the downward action force pushing off
the ground.
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Swinging Arms in a Jump
The height of a jump is significantly lower
(almost 30 lower) if you dont swing your arms
during the take-off portion of a jump.
However, if you swing your arms after leaving the
floor, then the height of the jump is much lower.
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Home Demo Jumping Arm Swing
First, jump normally, that is, swing your arms
upward while feet are still on the ground.
Now try swinging your arms upward after you leave
the ground youll notice a big difference.
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Home Demo Somersault
Now lets try it with a backwards somersault
Tuck increases rotation speed
Motion of the arms is also useful here for
control of the rotation.
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Arm Motion while in the Air
While in the air, moving your arms can shift the
center of gravity and also cause rotation but it
cannot change time in the air or distance jumped.

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Next LectureBalance

• First Term Paper due onWednesday, October 14th
• (Two weeks from today)

Please return the clickers!