Upcoming Deadlines

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

2. 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.

3. 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 18th (This Friday). 15 points

4. 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.

5. 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).

6. 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.

7. 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.

8. Arcs in Animation

9. 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. • Squash & Stretch • Timing • Anticipation • Staging • 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

10. 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. We have already discussed several of these principles of animation, specifically: • Squash & Stretch • Timing • Anticipation • Staging • 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

11. 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. Today we will discuss arcs and how they relate to animated motion. • Squash & Stretch • Timing • Anticipation • Staging • 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

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

13. Importance of Arcs Disney animation legends Frank Thomas and Olie Johnston write: 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.

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

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

16. Throwing Arm The longer the throwing arm, the greater the tangential speed so the farther it can throw. Tangential Speed Sling lengthens the arm at almost no cost in the weight. Doubling the arm lengthquadruples the range!

17. Timing on Circular Arcs A circular arc is a simple path of action but the timing may be complex and textured. • 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 Slow in Uniform Slow out

18. Rolling & Slipping 1 2 3 4 5 6 7 ROLLING Rolling ball turns one revolution when it travels a distance equal to three times its diameter (actually 3.1416 diameter) 1 2 3 4 5 SLIPPING Slipping and rolling are both uniform in spacing and rotation.

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

20. Nyquist Effect In this illusion is due to persistence of vision. Illusion Actual Rotation Wheel on frames#1 and #2 #2 #1 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.

21. Uniform Rotation in Perspective The 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.

22. Non-Uniform Circular Motion Two 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

23. 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

24. Tipping Rotation A brick rotates about a point as it tips;that point is the center of a circular arc. X X X X Friction tends to keep the brick from sliding until it loses contact with the table.

25. Exponential Spacing 1 Constant acceleration (Odd Rule) 1 3 Release 2 5 3 7 1 4 Release 2 3 Exponential Spacing 4 As the slope of the incline increases, the acceleration itself accelerates.

26. Rolling off a Tipping Point 3 2 4 1 5 6 7 Peak 8 Slowing out from a tipping point is very slow initially, but then accelerates rapidly.

27. Anticipation & Exponential Spacing Play Also notice motion blur near top of brick, which has large tangential speed. Texture of the timing as the brick tips over creates anticipation, which you want at the start of a scene

28. 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.

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

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

31. Swinging in Perspective Visually the timing has even more texture when the swing occurs in perspective.

32. 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

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

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

35. Spirals A 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

36. 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. Spacings along the curve stay constant. Spiral In

37. Demo: Interrupted Pendulum An “interrupt” bar changes the radius of the arc for a 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

38. 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. Spacings along the curve get bigger and bigger. Spiral In

39. Demo: Skater’s Spin FAST Rotation Slow Rotation Exert a force to pull hand weights toward my body, causing a big increase in rotational and tangential speeds

40. Rotation in Spirals (cont.) If the tangential speed decreases (say by friction) but inward force constant then the rotational speed still increases. Spacings along the curve get shorter yet itstillspinsfasterand faster. Spiral In Coin Vortex

41. How Does the Brick Fall? 1 Does the brick rotate and then fall down the side of the table? X X 2 X 3 No! The brick does not fall this way. X 4 Play

42. Forces on the Tipping Brick The table pushes on the brick upward and towards the right. Gravity pulls downward X X Center of the brick shifts down and towards the right. If no table…

43. 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.

44. Centrifugal Force 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. What we see What the insect feels

45. Class Demo: Bucket Overhead Centrifugal Force I will put a bucket full of water over my head without getting wet. How? 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

46. 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)

47. 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. Release Velocity

48. Release Velocity 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. GAP

49. Simulated Gravity Rotation 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)

50. Simple Spinning 1 A falling brick may turn by simple spinning around its center. 1 2 Arbitrary 3 3 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. 5 4 7