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.
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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".
Homework Assignment #5
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.
Homework Assignment #5
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
Heig
ht
D)
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
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:
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
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:
Wrong
Right
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!
x2
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
Unifo
rm
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:
XX
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.
XX
Friction tends to keep the brick from sliding until it loses contact with the table.
X
X
As the slope of the incline increases, the acceleration itself accelerates.
Exponential Spacing1
3
7
1
2
3
4
Constant acceleration (Odd Rule)Release
5
1
2
3
4
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
7
8
Peak
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.
Frame
Angl
e#1
#4
#7
FASTFAST
SLOW
SLOW
SLOW,again
SLOW
,ag
ain
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.
Click
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.
Bar
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?
XX
No! The brick does not fall this way.
XX
4
3
2
1
Video Reference of Tipping Brick
http://www.youtube.com/watch?v=otYAYMZ4iGg
Forces on the Tipping Brick
XX
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.
X
X
X
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)
Wile E. Coyote & Loop-D-Loop
In reality, it is impossible to travel upside-down, as Wile E. Coyote does in this scene. True or False?
“Beep Beep” (1952)
Wile E. Coyote & Loop-D-Loop
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
GAP
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
5
7
3
1Arbitrary 2
3
4
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
5
7
3
1Arbitrary 2
3
4
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.
SPIN
SPIN
Irregular Objects
SPIN
SPIN
SPIN
SPIN
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
A
B
C
Spin or Tumble?B) Side-to-side axis
B
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!
