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 #6

Stop-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 Question

You have already started working on your stop-motion animation due this Thursday.

True or False

Review Question

A spool is pulled by a string, wrapped around the center, as shown.

The spool will move:

Pull

B) RightA) Left

Force and Direction

A) LeftObjects always change

their velocity in the direction of the applied force.

Pull

PullMotion

Motion

Motion

Review Question

Blow 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 Funnel

B) 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 minutes

http://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 Cartoons

Early 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

Ap

peal

Short

Feature-length

Would you sit through a 90 minute Betty Boop cartoon?

Snow White

Disney’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 Animation

From 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 Calvert

http://www.youtube.com/watch?v=0yWTJpaoJXIhttp://www.youtube.com/watch?v=ajC1oCZlkQI

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

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.

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.

High

Medium

Low

High

Medium

Low

Water Balloon at RestWater pressure pushes on the

rubber, stretching it into a flattened shape.

High

MediumLow

WaterPressure

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

Momentum

Momentum of an object is,

(Momentum) =

(Mass) X (Velocity)

Examples of objects with large momentums are:

• Supertanker (large mass) • Bullet (large velocity)

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 object’s momentum depends on force and time interval.

Impulse

Define impulse acting on an object as,

(Impulse) = (Force on object) X (Time

interval)

Objects have momentum.Impulse acts on an object.

Impulse & Momentum

Momentum 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 Throw

Throw 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 Stake

Place 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 XOuch!

(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 Pieces

A) 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