Upcoming Deadlines

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Upcoming Deadlines

Fifth Homework (Video Analysis of a Jump)Due Wednesday, Feb. 24th (Next week)15 points (10 points if late)

Sixth Homework (Stop-motion Animation)Due Wednesday, March 3rd (In two weeks)20 points (if late, 10 points)Bonus prize of 20 extra points to top three.

For full schedule, visit course website:ArtPhysics123.pbworks.com

Pick up a clicker, find the right channel, and enter Student ID

Activating your Clicker* Turn on your clicker.* Enter the channel number or letter for

joining this class. Hit Enter/Send key.* Clicker should read AP123S258* Type in your student ID; hit Enter/Send.Clicker is now ready to use; leave it on.

Hit any key to wake the clicker from sleep mode.

Extra Credit OpportunityGo to any event at Cinequest Film Festival in downtown San Jose.

Turn in proof of attendance (receipt, photos, etc.) for 5 points of extra credit.

Extra Credit Opportunity

Student registration is $75 (ouch)

Turn in your receipt for 10 points of extra credit.

For info: www.gdconf.com

Attend the Game Developer’s Conference in San Francisco, on Saturday, March 13th

Homework Assignment #5In this assignment you’ll again use Tracker

software to analyze the motion of a moving object from video reference.

First, shoot some reference of yourself doing a running jump.

Position your camera so that you're in frame the entire time that you're in the air.

Stage the jump to be in profile. Shoot at least 5 takes, even if they are more or

less the same.

Homework Assignment #5

Original Video Reference

Homework Assignment #5Import your video reference into the Tracker

software (as in previous homework).Track the center of your waistline or beltline,

which is approximately the location of your center of gravity.

Marking your position from the time you leave the ground until you’ve landed.

After tracking your motion, upload the screen image from Tracker to your blog into a post called "Video analysis of path of action".

ParabolicPath of Action

Straight Line

Parabolic Curve

Homework Assignment #5Finally, rewind your video to the first

frame of your jump and from the "File" menu select "Record -> Quicktime Movie".

Hit the play button and allow the clip to play until the end of your jump. Next, in the "Capturing Quicktime MOV" window click "Save As" to save the recording.

Video Reference with Tracking

Homework Assignment #5Check that your saved Quicktime movie has

the track showing the path of action then put both clips (original and with tracking) in your blog post using YouTube or Vimeo.

This assignment is due by 8am on Wednesday, Feb. 24th (week from today).

15 points (10 points if late)

Survey QuestionSo far the pace of the class has been:

A)Too fastB)A little fastC)About rightD)A little slowE)Too slow

Review QuestionThe motion graph for a ball drop, going from the apex until the ball just touches the ground, looks like:

A) B) C) D)

Motion Graph of a Ball Drop

Frames

Arcs in Animation

Disney’s Principles of AnimationIn their classic book, Disney Animation – The Illusion of Life, Frank Thomas and Olie Johnston list a set of basic principles for animation.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

We have already discussed several of these principles of animation, specifically:

Action11. Appeal

Today we will discuss arcs and how they relate to animated motion.

Arcs of MotionMotion usually follows an arc, which may be simple, like a circle, or very complex and irregular.

Importance of Arcs

One of the major problems for the inbetweeners is that it is much more difficult to make a drawing on an arc.Drawings made as straight inbetweens completely kill the essence of the action.

Disney animation legends Frank Thomas and Olie Johnston write:

Circular ArcsCircular arcs are common since motion is often around a fixed pivot point, such as a joint.

Speed in Circular MotionRotational Speed: Revolutions per secondTangential Speed: Total distance per

secondSame Rotational Speed

Different Tangential Speeds

Throwing Arm TangentialSpeed

The longer the throwing arm, the greater the tangential speed so the farther it can throw. Sling lengthens

the arm at almost no cost in the weight.

Doubling the speedquadruples the range!

Timing on Circular Arcs

In this golf swing the motion:• Slows out (accelerates) to hit the ball• Uniform after the hit• Slows in as the swing finishes follow-through

A circular arc is a simple path of action but the timing may be complex and textured.

Slow out

Slow in

Non-Uniform Circular MotionTwo common types of motion on circular arcs that have non-uniform timing and spacing are:

Exponential Spacing Pendulum Spacing

Example:Tipping over

Example:Stride inwalking

Tipping OverTipping over is a common example of motion on a circular arc. Two ways to tip over:

Center tipped past point of contact

Center past an edge

Tipping RotationA brick rotates about a point as it tips;that point is the center of a circular arc.

Friction tends to keep the brick from sliding until it loses contact with the table.

As the slope of the incline increases, the acceleration itself accelerates.

Exponential Spacing1

Constant acceleration (Odd Rule)Release

Release

Exponential Spacing

Slowing out from a tipping point is very slow initially, but then accelerates rapidly.

Rolling off a Tipping Point

1 2 3 4 56

Video Reference of Tipping Brick

http://www.youtube.com/watch?v=otYAYMZ4iGg

Anticipation & Exponential Spacing

Texture of the timing as the brick tips over creates anticipation, which you want at the start of a scene

Also notice motion blur near

top of brick, which has large

tangential speed.

Pendulum SpacingA pendulum’s path of action is also a circular arc but the spacing is very different from the exponential spacing of tipping over.

Spacing & Timing in SwingingA pendulum will slow in and out as it swings back and forth, the same as a ball rolling in a half-pipe.

Most of the texture in the timing is at the endpoints; the timing is even in the center.

Pencil Test Example

http://www.youtube.com/watch?v=xuoJdNGxffU

Motion Graph for PendulumThe motion graph (angle vs. frame) shows that the timing is mostly textured (curves the most) at the apexes.

FASTFAST

SLOW,again

Ball goes fastest around the bottom but the speed is almost constant.

Uniform Rotation in PerspectiveThe timing for uniform rotation has texture when seen in perspective.

Half orbit

Quarterorbit

Rotation from key #1 to #5 in background takes twice as long as from #6 to #8 in foreground.

Swinging in PerspectiveVisually the timing has even more texture when the swing occurs in perspective.

Who Framed Roger Rabbit? (1988)

The opening sequence in Who Framed Roger Rabbit? makes great use of the textured timing of arcs in perspective.

Animation byRichard Williams

Who Framed Roger Rabbit? (1988)

http://www.youtube.com/watch?v=sLNqtU-gYPc

Demo: Don’t FlinchPendulum swings back and forth yet it doesn’t hit your face.

Bowling Ball Pendulum

This video clip lets you experience what it’s like to do this demo.

http://www.youtube.com/watch?v=UNsD15GjWWE

SpiralsA spiral is just a circular arc with a radius that’s either increasing (spiral out) or decreasing (spiral in).

Concept art fromPirates of the Caribbean 3

Rotational Speed in SpiralsIf the radius decreases without pulling the object inward then the rotational speed increases (due to shrinking radius) but the tangential speed stays constant.

Spiral In

Spacings along the curve stay constant.

Demo: Interrupted Pendulum

Tangential speed does not increase due to the pendulum whipping around the interrupt bar.

Energy is not increased by the interrupt bar so ball swings back to the same spot.

An “interrupt” bar changes the radius of the arc for a pendulum.

Rotation in Spirals (cont.)If the radius decreases by pulling the object inward then the rotational speed increases due to shrinking radius and due to an increase in the tangential speed.

Spiral In

Spacings along the curve get

bigger and bigger.

Demo: Skater’s Spin

SlowRotation

FASTRotation

Exert a force to pull hand weights toward my body, causing a big increase in rotational and tangential speeds

Rotation in Spirals (cont.)If the tangential speed decreases (say by friction) but inward force constant then the rotational speed still increases.

Spiral In

Spacings along the curve get

shorteryet it

stillspinsfaster

and faster.Coin Vortex

Rotation in a SpiralsIn summary, typically as an object rotates in a spiral, the rotation speed increases as the radius decreases. So as radius goes down,

the r.p.m.s go up.

However the spacings may get longer, or shorter, or stay constant!

How Does the Brick Fall?Does the brick rotate and then fall down the side of the table?

No! The brick does not fall this way.

Video Reference of Tipping Brick

http://www.youtube.com/watch?v=otYAYMZ4iGg

Forces on the Tipping Brick

The table pushes on the brick upward and towards the right.

Gravity pulls downward

Center of the brick shifts down and towards the right.

If no table…

Pushing Off by the TableThe table pushes away on the brick, which causes the brick to move away from the table as it falls.

Once it loses contact with the table, only the force of gravity accelerates the brick.

Centrifugal Force

What we see

What theinsect feels

Insect inside a can rotating in a circle

When we move on an arc, it seems to us as if there is an outward force, pushing us away from the center of the circle.

Physicists call this apparent force the centrifugal force.

Class Demo: Bucket Overhead

I will put a bucket full of water over my head without getting wet. How?

CentrifugalForce

By rotating it fast enough.The water stays in the

bucked as if pressed into it by a centrifugal force.

You experience centrifugal force on taking a sharp turn

Wile E. Coyote & Loop-D-Loop

Watch carefully as Wile E. Coyote travels in a circle around a natural arch bridge.

http://www.youtube.com/watch?v=p4YxdXw9evc

From “Beep Beep” (1952)

In reality, it is impossible to travel upside-down, as Wile E. Coyote does in this scene. True or False?

“Beep Beep” (1952)

False.If his speed is high enough then he stays in contact with the arch, just like the water in the spinning bucket.

Demo: Loop-the-LoopIf the speed of the ball is large then not only does it stay on the track, the ball even pushes outward and against the rail.

Velocity

Release

Demo: Loop-the-LoopBall could even circle a loop with a gap, if the speed was just right so gravity was equal to the centrifugal force.

Velocity

Release

Simulated GravityCentrifugal force could be

used to simulate gravity in a space station.

With the appropriate rotational speed a person on the outer rim would feel as if they stood on the surface of Earth.

Scientifically accurate in the movie 2001: A Space Odyssey (1968)

Rotation

2001: A Space Odyssey (1968)

Simple Spinning1

1Arbitrary 2

In simple spinning, the angle rotates at a constant rate.

A brick tipped 45º as it loses contact with the table will fall spinning about 30º every two frames.

A falling brick may turn by simple spinning around its center.

Tumbling1

1Arbitrary 2

There is no simple way to describe tumbling. However, the brick’s center still follows the same parabolic path of action.

A falling brick may also turn by a more complicated tumbling motion.

Tennis Racket TheoremWhen an object turns about its long or its short axis, it tends to spin.

When an object turns about its middle axis, it may tumble.

Irregular Objects

Spin or Tumble?

Rotation around two of these axes is spinning.The axis of rotation that tumbles is:A)Head-to-toe axisB)Side-to-side axisC)Front-to-back axis

Spin or Tumble?B) Side-to-side axis

Rotating along this axis typically results in irregular tumbling.

Spinning is possible but requires more control than along the other two axes.

Rolling & Slipping1 2 3 4 5 6 7

Rolling ball turns one revolution when it travels a distance equal to three times its diameter (actually 3.1416 diameter)

ROLLING

1 2 3 4 5

SLIPPING

Slipping and rolling are both uniform in spacing and rotation.

Next LectureCreating Action

By Wednesday of next week:Complete the 5th homework

(Video analysis of Path of Action)

Please return the clickers!

Upcoming Deadlines

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