Upcoming Deadlines

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Upcoming Deadlines

• First Term Paper
• Wednesday, October 14th (in two days)
• Campus-wide Furlough Day
• Monday, October 19th (a week from today)
• (Art/Phys 123 will meet on Wed., Oct. 21st)
• Seventh Homework (Analysis of Walking)
• Due Wednesday, October 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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Squash and Stretch(Part 1)
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Gertie the Dinosaur (1914)
Although this early short Winsor McCay is not the
first animated film, it is one of the first
cartoons to feature a character with a distinct
personality.
Running time 12 minutes
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The Adventures of Prince Achmed (1926)
The Adventures of Prince Achmed, by the German
animator Lotte Reiniger, is the oldest surviving
feature-length (at 65 minutes) animated film.
In this silent movie, Reiniger used silhouette
animation, which involves manipulating cutouts
(basically two-dimensional stop motion
animation).
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Evolution of Motion Pictures
Movies advanced rapidly in the beginning of the
last century, adding sound and color.
Birth of a Nation (1915)
Gone with the Wind (1939)
As realism in movies increased, the stories and
the acting had to change as well.
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Early Cartoons
Early animations also added sound and color but
remained restricted to short films.
Flowers and Trees (1931), the first cartoon in
full Technicolor.Running Time 8 minutes
Steamboat Willie (1928), the first cartoon with a
complete soundtrack.Running Time 7 minutes
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Realism Barrier
Feature length animated films were not produced
because audiences demanded more realistic,
complete characters in such movies.
Feature-length
Appeal ?
Short
Would you sit through a 90 minute Betty Boop
cartoon?
Realism ?
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Snow White
Disneys Snow White was the first full-length
feature film using traditional (cel) animation.
Snow White and the Seven Dwarfs (1937, 83 min.)
Snow White (1933, 7 min.)
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Disneys Principles of Animation
From life studies, Disney animators discovered
that 1 principle that was key to adding realism
in character animation was Squash Stretch.
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Basic Squash Stretch
Stretch usually indicates speed due to motion
blur.
Actual Shape
As Seen byHuman Eye
Squash indicates force, such as on impact.
Much more
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Character Animation
Squash and stretch are easy to learn from a
bouncing ball but their importance is in how
squash and stretch appear in the motion of
characters.
From Preston Blairs, Cartoon Animation
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Luxo Jr.s Squash Stretch
An object need not deform in order to squash and
stretch. For instance, a hinged object like Luxo
Jr. squashes by folding over on itself, and
stretches by extending out fully. John Lasseter
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Water Balloon Drop
Water balloon is a good animation exercise
because it almost moves like a living creature.
Play
Play
Mai Vu
Ken Calvert
Play
Play
Slow-motion Drops
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Stretching Dimensions
Stretch proportions depend on whether we want to
preserve equal areas or equal volumes.
Stretch in animationpreserves volume
81
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Equal Areas
Equal Volumes
150
150
Sphere (3D)
Circle (2D)
0.67 x 1.50 1
0.81 x 0.81 x 1.50 1
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Stretching Dimensions
Table below lists the proportions for stretching
with equal areas or equal volumes. Values are the
same for all object shapes.
Y
L 50 67 75 80 90 100 110 125 133 150 200
W 200 150 133 125 111 100 91 80 75 67 50
X,Y 140 122 115 112 105 100 95 89 87 82 71
Area and volume proportions similar
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Incompressibility
Most solids and liquids are almost
incompressible it takes enormous force to change
their volume. Elastic materials may stretch
easily but their volume stays constant.
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Youngs Modulus (Stiffness)
Youngs modulus indicates amount of force
required to compress or expand a material.
Material Youngs Modulus (GPa)
Rubber 0.01 to 0.1
Water 8
Wood 9 to 11
Concrete 30
Steel 200
Water is almost as incompressible as wood!
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Class Demo Incompressibility of Water

• Place a brick on top of a syringe filled with
  air.
• Air compresses (a bit).
• Place a brick on top of a syringe filled with
  water.
• Water doesnt compress.

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Stretch in Falling
The force of gravity does not stretch objects as
they fall. Slowing out occurs during falling but
all parts of a body slow out together.
Common gag in animation but its not realistic.
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Freefall Weightlessness
Freefall is the state of weightlessness that
occurs during falling, even though gravity is
present.
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NASAs Vomit Comet

• NASA has a special airplane for training
  astronauts in free-fall weightless conditions.
• The Vomit Comet nickname tells you its quite a
  wild roller-coaster ride.
• Zero G Corp. offers commercial flights (for 4000)

The plane flies between 20,000 and 30,000 feet,
same as commercial flights.
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Flight of the Vomit Comet
Weightless Freefall
Near the apex, the planes path of action is
parabolic arc.
Power Climb
Pull out of Dive
Boeing 707 (modified)
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Class Demo Falling Slinky

• Hold a Slinky and its weight stretches it out.
• Now drop it.
• What happens?
• In freefall its in a state of weightlessness so
  Slinky immediately contracts.

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Pressure in Liquids

• Pressure in a liquid depends on depth.
• As with a stack of bricks, weight of whats above
  determines pressure.

Low
Medium
Low
Medium
High
High
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Water Balloon at Rest

• Water pressure pushes on the rubber, stretching
  it into a flattened shape.

Low
Medium
Water Pressure
High
Tension of the rubber also affects the shape.
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Class Demo Bed of Nails
Pressure depends on weight and on the area
supporting that weight.

• One may safely lay or sit on a bed of nails, as
  long as there are enough nails so that the
  pressure, measured as force per nail, is small.
• Weight of 150 pounds is distributed over 300
  nails. Force per nail is ½ lb. Need 5 lb per nail
  to pierce skin.

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Class Demo Pressure Weight

• A can full of water has holes in the sides
  through which water comes out.
• What happens when you drop the can?
• The can is now in freefall and weightless. Water
  stops flowing as the can falls since the pressure
  was due to the waters weight.

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Falling Water Balloon
Slides off and falls
Because free fall is a weightless state, the
water balloon will be roughly spherical as it
falls.
May have some initial vibrations depending on how
it is released.
Faucet drip
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Ready, Set, Zoom (1955)
This clip has several examples of stretch.
Stretch in falling is not realistic.
Stretch due to the law of inertia (drag) does
occur.
Play
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Stretch Animation
Can accentuate rapid motion blur by using extreme
stretch on single frames.
These are consecutive frames from Ready, Set,
Zoom.
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The Dover Boys (1942)
Play
The Dover Boys is a classic cartoon directed by
Chuck Jones that has great examples of stretch
(also called smear) animation.
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Momentum

• Momentum of an object is,
• (Momentum)
  (Mass) X (Velocity)
• Examples of objects with large momentums are
• Supertanker (large mass)
• Bullet (large velocity)

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Momentum and Force

• To stop an object with a large momentum requires
  either
• Large force (stopping the object quickly).
• Small force applied for a long time.
• Notice that changing objects momentum depends on
  force and time interval.

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Impulse

• Define impulse acting on an object as,
• (Impulse)
• (Force on object) X (Time interval)
• Objects have momentum.
• Impulse acts on an object.

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Impulse Momentum

• Impulse is related to momentum by,
• (Change in momentum) (Impulse)
• or
• (Change in momentum)
• (Force) X (Time interval)

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Demo Egg Throw

• Throw a raw egg as fast as possible at a bed
  sheet thats held loosely.

X
X
X
X
X (Hold here)
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Egg Throw Analyzed

• Throw egg at a bed sheet it stops but doesnt
  break.
• Throw egg at the wall with same speed, it stops
  but breaks.
• In which case is the impulse on the egg the
  greatest?
• Hitting the bed sheet
• Hitting the wall
• Same in the two cases

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Egg Throw Analyzed

• C) The impulse is the same in the two cases.
• The change in velocity is the same in the two
  cases so the change in momentum is the same.
• Since the impulse equals the change in momentum,
  the impulse is the same in the two cases.
• But the forces are not the same!

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Egg Throw Analyzed

• Throw egg at sheet or wall with same speed.
• Impulse is the same in the two cases.
• Which case has
• Largest time of impact?
• Throw at the sheet.
• Largest force on the egg?
• Throw at the wall.

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Automobile Safety

• Maximizing time of impact on the driver minimizes
  the force of impact.
• This principle used in design of

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Demo Vampire Stake

• Place a heavy stake on my chest and strike with a
  hammer.
• Why am I not killed?

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Demo Vampire Stake

• Safest when slow moving stake placed on a soft,
  fleshy spot on the chest.

(force) x (TIME)
Not safe if stake strikes hard skull
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Ironman

• Ironman falls off the roof of a 10 story building
  and lands on the sidewalk.
• Even though he is an ordinary man, hes unhurt as
  long as his metal suit is undamaged and intact.
• This is physically realistic.
• True or False

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Ironman

• False. The suit does not increase the time of
  impact so the force of impact is the same.

Metal cylinder
Putting a metal cylinder (or a coin) on my
forehead is no protection against hammer blows.
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Next LectureSquash Stretch(Part 2)

• First Term Paper due onWednesday, October 14th
• (This week!)

Please return the clickers!