Upcoming Deadlines
Sixth Homework (Stop-motion Animation)Due this Thursday, October 6th 20 points (if late, 10 points)Bonus prize of 20 extra points to top three.
Seventh Homework (Outline of First Term Paper)Due next Thursday, October 13th 10 points (5 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 Assignment #6Stop-motion animation of a falling
object. * Plan your scene, especially the timing,
spacing, path of action, anticipation, etc.* Photograph your object in a sequence of
images suitable for combining into an animation.
* Create a video clip with at least a dozen unique frames.
* Adjust the timing by adding or removing frames; if needed, re-shoot your animation.
Homework Assignment #6* Post your animation to your blog in an
entry entitled "Stop Motion Animation of Falling".
* In your posting describe in one paragraph how you created your animation.
Due by 8am on Thursday, Oct. 6th
20 points (if late, 10 points)Score based on believability and creativity.The top three animation clips in the class
will receive a bonus of 20 extra points.
Homework Assignment #6
http://www.youtube.com/watch?v=uOTncsocsUE
Here is a good example from last semester. Not only does the falling motion look believable but the action is simple yet entertaining.
Survey QuestionYou have already started
working on your stop-motion animation due this Thursday.
True or False
Review QuestionA spool is pulled by a
string, wrapped around the center, as shown.
The spool will move:
PullB) RightA) Left
Force and DirectionA) LeftObjects always change
their velocity in the direction of the applied force.
PullPullMotion
Motion
Motion
Review QuestionBlow hard through a
funnel with a ping pong ball in the funnel’s bowl.
Instead of being blown away, the ball is held tightly in the bowl.
This is because:
PingPongBall
BLOW
A) Compression produces low pressureB) Moving air produces low pressureC) The ball spins, producing low pressureD)None of the above
Class Demo: Blow the FunnelB) Moving air
produces low pressure.
This demonstrates the Bernoulli effect, which says that the higher the air speed, the lower the pressure.
PingPongBall
BLOW
L
A
L
Squash and Stretch
In the first part of the course we’ve covered some of the basics of animation.
We now move to more advanced topics, specifically those relevant to character animation.
Character Animation
Gertie the Dinosaur (1914)This early short Winsor McCay is not the first animated film, it is one of the first to feature a character with a distinct personality.
Running time: 12 minuteshttp://www.youtube.com/watch?v=UY40DHs9vc4
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).
The Adventures of Prince Achmed (1926)
http://www.youtube.com/watch?v=25SP4ftxklg
Evolution of Motion PicturesMovies 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.
Early CartoonsEarly animations also added sound and color but remained restricted to short films.
Steamboat Willie (1928), the first cartoon with a complete soundtrack.Running Time: 7 minutes
Flowers and Trees (1931), the first cartoon in full Technicolor.Running Time: 8 minutes
Realism BarrierFeature length animated films were not produced because audiences demanded more realistic, complete characters in such movies.
Realism
Appe
al
Short
Feature-length
Would you sit through a 90 minute Betty Boop cartoon?
Snow WhiteDisney’s Snow White was the first full-length feature film using traditional (cel) animation.
Snow White (1933, 7 min.)
Snow White and the Seven Dwarfs (1937, 83 min.)
Snow White (1933)
http://www.youtube.com/watch?v=IUsp2XxgZTY
Snow White (1937)
http://www.youtube.com/watch?v=nN1BegE3QR0
Disney’s Principles of AnimationFrom life studies, Disney animators discovered that #1 principle that was key to adding realism in character animation was “Squash & Stretch.”1. Squash & Stretch2. Timing3. Anticipation4. Staging5. Follow Through
& Overlapping Action
6. Straight Ahead & Pose-to-Pose Action
7. Slow In and Slow Out8. Arcs9. Exaggeration10. Secondary
Action11. Appeal
Basic Squash & StretchStretch shows speed due to motion blur.
Actual Shape
As Seen byHuman Eye
Squash shows force, such as on impact.
Actual Shape Cartoon
Basics of squash and stretch are present in even the simple ball bounce exercise.
Character Animation
From Preston Blair’s, Cartoon Animation
Basic 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.
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
Luxo Jr. (1986)Luxo Jr. was the first CG film nominated for an Academy Award.
http://www.youtube.com/watch?v=PvCWPZfK8pI
Water Balloon DropWater balloon makes a good animation exercise because it moves like an animate character.
By Mai Vu By Ken Calverthttp://www.youtube.com/watch?v=0yWTJpaoJXIhttp://www.youtube.com/watch?v=ajC1oCZl
kQI
Water Balloon Reference
http://www.youtube.com/watch?v=XbGVBV3-F48
http://www.youtube.com/watch?v=FI-Mq6BDtMQ It’s always useful
to animators to study reference, both live and video.
The motion of the water balloon is different with every take, yet has a consistent feel.
Elements of a Water Balloon Drop
Let’s look more carefully at the physics in each element of a water balloon drop. Initial Drop
Squash Settle
Bounce
Part 1: The Initial DropThe initial part of the water balloon drop is similar to other drop tests yet the fluid nature of the balloon adds new elements.
Initial Drop
IncompressibilityMost solids and liquids are almost incompressible; it takes enormous force to change their volume.
Elastic materials may stretch easily but their volume stays constant.
Young’s Modulus (Stiffness)
Material Young’s Modulus (GPa)
Rubber 0.01 to 0.1
Water 7
Wood 9 to 11
Concrete 30
Steel 200
Rubber is compressible but water is almost as incompressible as wood!
Young’s modulus indicates amount of force required to compress or expand a material.
Demo: Incompressibility of WaterPlace 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 doesn’t compress.
Demo: Bed of Nails
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.
Pressure depends on weight and on the area supporting that weight.
Pressure in LiquidsPressure in a liquid depends on
depth.As with a stack of bricks, weight of
what’s above determines pressure.
HighMediumLow
High
Medium
Low
Water Balloon at RestWater pressure pushes on the
rubber, stretching it into a flattened shape.
High
MediumLowWater
Pressure
Tension of the rubber also affects the shape.
Repose Angle and Contact AngleWater balloon has a repose angle and contact angle that depend on the rubber’s stiffness.
StiffFlaccid
Repose
Contact
Beads of liquid have similar shapes, depending on surface tension.
Mercury
Water
Class Demo: Pressure & WeightA 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 water’s weight.
Falling Water Balloon
Because free fall is a weightless state, the water balloon will be roughly spherical as it falls.
Slides off and falls
May have some initial vibrations depending on how it is released.
Faucet drip
Air Resistance?Because the water balloon falls
faster, the air resistance force on a water balloon is greater than on an air-filled balloon!
However, a few ounces of air resistance force is insignificant for a water balloon weighing several pounds.
Water
Air
Gravity
Air Resistance
Part 2: Squash on ImpactThe fluid nature of the balloon makes the squash on impact very pronounced.
Squash
http://www.youtube.com/watch?v=UMeJ4ZfRd3w
Force of Impact for SquashTo understand the force of impact you need to understand momentum and impulse.
http://www.youtube.com/watch?v=-p5zoufjOwc
MomentumMomentum of an object is,(Momentum) =
(Mass) X
(Velocity)
Examples of objects with large momentums are:
• Supertanker (large mass) • Bullet (large velocity)
Momentum and ForceTo 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 object’s momentum depends on force and time interval.
ImpulseDefine impulse acting on an object
as,
(Impulse) = (Force on object) X (Time
interval)
Objects have momentum.Impulse acts on an object.
Impulse & MomentumMomentum is related to impulse by,
(Change in momentum) = (Impulse)
When mass stays constant then,
(Mass) X (Change in velocity) =(Force) X (Time interval)
Demo: Egg ThrowThrow a raw
egg as fast as possible at a bed sheet that’s held loosely.
X X
X
X
X (Hold here)
Egg Throw AnalyzedThrow egg at a bed sheet; it stops but
doesn’t break. Throw egg at the wall with same speed,
it stops but breaks.
In which case is the impulse on the egg the greatest?
A) Hitting the bed sheetB) Hitting the wallC) Same in the two cases
Egg Throw AnalyzedC) 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!
Egg Throw AnalyzedThrow 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.
LONG TIME
short time
small force
LARGE FORCE
Automobile SafetyMaximizing time of impact on the driver
minimizes the force of impact. This principle used in design of:
Seatbelts Air Bags CrumpleZones
Demo: Vampire StakePlace a very heavy stake on my
chest and strike with a hammer. Why am I not killed?
Demo: Vampire StakeSafest when slow moving stake
placed on a soft, fleshy spot on the chest.(force) x (TIME)
X X Ouch!
(FORCE) x (time)
Not safe if stake strikes hard skull
Slugging out the JiggleJiggling is fast so difficult to slug out. Try: Count the number of vibrations in 10 secondsorTime how long it takes balloon to jiggle 10 timesExample: If balloon jiggles 30 times in 10 seconds then each vibration is 1/3 second, or 8 frames per vibration.
Shattered PiecesA brick hits the floor and two shattered pieces simultaneously fly into the air.Which piece hits the ground first?
A) Smaller piece that flies off fast but low.
B) Larger piece that flies off slower but happens to go higher.
C) Could be either one.A
B
Shattered PiecesA) Smaller piece that flies off fast but low will
hit the ground first (also reaches apex first).
The time in the air, both going up and coming back down, only depends on the apex height.A
B