Upcoming Deadlines Fifth Homework (Video analysis of Path of Action): Due Friday, September 25 th (This Friday); 15 points (10 points if late) Sixth Homework (Outline of First Term Paper) Due Wednesday, September 30 th Campus-wide Furlough Day Monday, October 19th (Art/Phys 123 will meet on Wed., Oct. 21 st ) For full schedule, visit course website: ArtPhysics123.pbworks.com

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.

Homework Assignment #5 Shoot reference of yourself doing a running jump. Use the Tracker software to mark your path of action while in the air (tracking center of torso). Upload image showing track and graphs for one of your jumps to your blog. Record a clip showing the tracked motion. Upload both original reference and the tracked Quicktime clip to your blog. For details, see course website; for an example, see the course blog. This assignment is due by 8am on Friday, September 18 th (This Friday). 15 points

Homework Assignment #6 Write a one-page outline for your first term paper. The general topic for your first term paper is: The Laws of Physics in an Animation Universe Modern science is based on the principles of experimental observation and theoretical analysis; in this assignment you will apply these principles in a critical analysis of animation and special effects.

Homework Assignment #6 For the term paper, you will select an animation film (or a live-action film featuring CGI animation special effects). You will then formulate three distinct scientific hypothesis for the universe portrayed in that film (which may or may not obey the same physical laws as the real world). For example, in your animation’s universe the laws gravity may be different (e.g., heavy objects may fall faster than light objects).

Homework Assignment #6 Your hypotheses should be such that there is relevant observational evidence in the film; you need to describe what that evidence is and how it supports your theories. You will also formulate competing theories and present evidence that the universe portrayed in your film does not follow those alternate hypotheses.

Homework Assignment #6 For this homework assignment you are to choose the film that you'll analyze and write a one-page outline for the term paper. Post this outline on your blog; an example has been posted on the course blog. This assignment is due by 8am on Wednesday, September 30th. (10 points; 5 points if late) Note: The term paper will be due in mid-October.

Arcs in Animation

Disney’s Principles of Animation In their classic book, Disney Animation – The Illusion of Life, Frank Thomas and Olie Johnston list a set of basic principles for animation. 1.Squash & Stretch 2.Timing 3.Anticipation 4.Staging 5.Follow Through & Overlapping Action 6. Straight Ahead & Pose-to-Pose Action 7.Slow In and Slow Out 8.Arcs 9.Exaggeration 10.Secondary Action 11.Appeal

Disney’s Principles of Animation In their classic book, Disney Animation – The Illusion of Life, Frank Thomas and Olie Johnston list a set of basic principles for animation. 1.Squash & Stretch 2.Timing 3.Anticipation 4.Staging 5.Follow Through & Overlapping Action 6. Straight Ahead & Pose-to-Pose Action 7.Slow In and Slow Out 8.Arcs 9.Exaggeration 10.Secondary Action 11.Appeal We have already discussed several of these principles of animation, specifically:

Disney’s Principles of Animation In their classic book, Disney Animation – The Illusion of Life, Frank Thomas and Olie Johnston list a set of basic principles for animation. 1.Squash & Stretch 2.Timing 3.Anticipation 4.Staging 5.Follow Through & Overlapping Action 6. Straight Ahead & Pose-to-Pose Action 7.Slow In and Slow Out 8.Arcs 9.Exaggeration 10.Secondary Action 11.Appeal Today we will discuss arcs and how they relate to animated motion.

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

Speed in Circular Motion Rotational Speed: Revolutions per second Tangential Speed: Total distance per second Same Rotational Speed Different Tangential Speeds

Throwing Arm Tangential Speed 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 arm length quadruples 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 Uniform Slow in

Rolling & Slipping Rolling ball turns one revolution when it travels a distance equal to three times its diameter (actually diameter) ROLLING SLIPPING Slipping and rolling are both uniform in spacing and rotation.

Wagon Wheel Illusion In this illusion, the wheel seems to spin backwards. Often seen in westerns

Nyquist Effect In this illusion is due to persistence of vision. The brain tracks the movement of the spokes by looking for the nearest location on each frame. This effect limits how fast a wheel can spin in an animation and still be seen as turning. Actual Rotation Illusion #1 #2 Wheel on frames #1 and #2

Uniform Rotation in Perspective The timing for uniform rotation has texture when seen in perspective. Half orbit Quarter orbit Rotation from key #1 to #5 in background takes twice as long as from #6 to #8 in foreground.

Non-Uniform Circular Motion Two common types of motion on circular arcs that have non-uniform timing and spacing are: Exponential SpacingPendulum Spacing Example: Tipping over Example: Stride in walking

Tipping Over Tipping over is a common example of motion on a circular arc. Two ways to tip over: X X Center tipped past point of contact Center past an edge

Tipping Rotation A brick rotates about a point as it tips; that point is the center of a circular arc. X X 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 Spacing Constant acceleration (Odd Rule) Release Exponential Spacing

Slowing out from a tipping point is very slow initially, but then accelerates rapidly. Rolling off a Tipping Point Peak

Play 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 Spacing A 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 Swinging A 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. Play

Motion Graph The motion graph (angle vs. frame) confirms that the timing is mostly textured at the apexes. Frame Angle #1 #4 #7

Swinging in Perspective Visually 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 by Richard Williams

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

Bowling Ball Pendulum Play This clip lets you experience what it’s like to do this demo.

Spirals A spiral is just a circular arc with a radius that’s either increasing (spiral out) or decreasing (spiral in). Concept art from Pirates of the Caribbean 3

Rotational Speed in Spirals If 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 Slow Rotation FAST Rotation 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 shorter yet it still spins faster and faster. Coin Vortex

How Does the Brick Fall? Does the brick rotate and then fall down the side of the table? X X No! The brick does not fall this way. X X Play

Forces on the Tipping Brick X X 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 Table The 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 the insect 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? Centrifugal Force 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 Play In reality, it is impossible to travel upside-down, as Wile E. Coyote does in this scene. True or False? “Beep Beep” (1952)

Demo: Loop-the-Loop If 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-Loop Ball 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 Gravity Centrifugal force could be used to simulate gravity in a space station. With the right rate of rotation 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

Simple Spinning Arbitrary 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.

Tumbling Arbitrary There is no simple way to describe tumbling. However, the brick’s center still follows the same path of action. A falling brick may turn by a more complicated tumbling motion.

Tennis Racket Theorem When an object turns about its long or its short axis, it tends to spin. When an object turns about its middle axis, it tends to tumble. SPIN TUMBLE

Irregular Objects SPIN TUMBLE SPIN TUMBLE

Spin or Tumble? Rotation around two of these axes is spinning. The axis of rotation that tumbles is: A)Head-to-toe axis B)Side-to-side axis C)Front-to-back axis A B C

Next Lecture Creating Action By Friday of this week: Complete the 5 th homework (Video analysis of Path of Action) Please return the clickers!