Upcoming Deadlines

1. Upcoming Deadlines Fifth Homework (Video Analysis of a Jump) Due Thursday, Sept. 29th (Next week) 15 points (10 points if late) Sixth Homework (Stop-motion Animation) Due Thursday, Oct. 6th (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

2. Homework Assignment #5 Use Tracker to analyze the motion of yourself doing a running jump. Shoot reference with at least 5 takes. Track the center of your body (center of torso at about the beltline) in the air. Upload original video, screen shot with graphs, video with tracking*. This assignment is due by 8am on Thursday, September 29th (next week). 15 points (10 points if late) *May be tricky

3. Homework Assignment #5 Straight Line Parabolic Path of Action Parabolic Curve

4. Review Question In reality, it is impossible to travel upside-down, as Wile E. Coyote does in this scene. True or False? “Beep Beep” (1952)

5. 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.

6. Creating Action

7. Why Things Move So far we’ve only looked at how things move (slowing in/out, path of action, arcs, etc.). Now it’s time to look at why things move, that is, what causes action. The short answer is forces. To understand why things move the way they do, you need to consider the forces at play.

8. Newton’s Laws of Forces • Newton established three basic laws to explain how motion is caused by forces: • Law of Inertia • Law of Acceleration • Action-Reaction Principle • Disney and other early animators rediscovered these laws of forces in their studies of motion. Sir Isaac Newton

9. Follow-Through When a character stops, it doesn’t suddenly freeze. Some parts of the character stop abruptly while others, such as arms, long hair, clothing, etc., continue moving for a few frames. In animation, this is known as follow-through. In physics, we know it as Newton’s Law of Inertia.

10. Motion, with & without Forces An object moves with constant, uniform motion until acted on by a force. No force An asteroid floats in space with a constant speed unless gravity deflects its motion. FORCE

11. Balance of Forces Rarely are there no forces but often forces are balanced so they “cancel” each other out. Important: Balanced forces does not mean that there’s no motion! Floor Tension Gravity Gravity Floor Gravity

12. Law of Inertia Newton’s Law of Inertia says: An object moves with constant, uniform motion until acted on by an unbalanced force. Floor Gravity The bowling ball moves with constant speed* *In reality, there is a small unbalanced force, friction, that does slow the ball’s speed.

13. Home Demo: Riding the Bus When a moving bus halts, you continue moving forward.

14. Shoot ‘Em Up (2007) If the crash occurs at 35 miles per hour then the hero flies off at a speed of about 2 feet per frame.

15. Shoot ‘Em Up (2007) Frame 438 Stuntman flies out the window at about 10 m.p.h. Frame 439 Frame 440 Frame 441 This is a bit slow but at a realistic speed the audience wouldn’t see the action.

16. Shoot ‘Em Up (2007) Frame 459 Stuntman flies into the van at about 5 m.p.h. Frame 460 Frame 461 Frame 462 Noticeably much too slow but the sequence is outrageous anyway, so it works.

17. The League of Extraordinary Gentlemen (2003) http://www.youtube.com/watch?v=n8SDdkKSqns In this scene, Sean Connery jumps out the side of a speeding car and lands on his feet.

18. The League of Extraordinary Gentlemen (2003) In this scene, Sean Connery jumps out the side of a speeding car and lands on his feet. In reality, he would: • Roll forward from where he lands, in the direction of the moving car. • Roll backwards from where he lands. • Land just as he does in the movie; this was actually done by a stuntman.

19. Jumping out of a Car A) Roll forward You are moving at the same speed as the car when you jump out so you will roll forward. Your path car You’ll start losing speed after you hit the ground so, relative to the car, you’ll fall behind as the car continues speeding along.

20. Centrifugal Force Revisited The centrifugal force you experience on taking a sharp curve is nothing more than inertia keeping you moving forward in a straight line. It feels as if you’re pulled to the outside bank of the curve. Your path

21. Law of Inertia (cont.) Newton’s Law of Inertia also says: An object at rest (not moving) remains at rest until acted on by an unbalanced force. A stationary bowling ball remains stationary until some unbalanced force comes along. Floor Gravity This is nothing more than motion at constant speed but with speed equal to zero.

22. Home Demo: Riding the Bus (cont.) If the bus starts moving again, you remain stationary, seemingly thrown backwards.

23. Frame of Reference Bus Moves Background As seen by observer on the street As seen by observer sitting in the bus

24. Space Balls (1987)

25. Jackass (2002) http://www.youtube.com/watch?v=V-dFVdhgSsc

26. Class Demo: Tablecloth Pull Due to the vase’s inertia it remains at rest since almost no force acts on the vase if one pulls quickly and straight. Yank quickly

27. Inertia & Drag An object won’t move until a force acts on it so long hair trails behind as head turns. Although this is due to the hair’s inertia, in animation it’s usually called drag. An object at rest remains at rest until acted on by a force.

28. Inertia & Drag (cont.) Hair remains in motion even after the head stops turning, which is follow-through due to inertia. Object in motion remains in motion until acted on by an unbalanced force.

29. Drag in Arcs and Waves Animation drag is very noticeable when something like hair or cloth moves in an arc or in a wave-like motion.

30. Fukkireta Click to play http://www.youtube.com/watch?v=NFep4vO4TRc

31. Class Demo: Hula Skirt The motion of a hula skirt is an excellent example of animation “drag.” Also notice how the skirt moves outward as it turns due to centrifugal force.

32. Flour Sack Exercises The sack drop and sack pantomime are common animation exercises. A flour sack is a good proxy for learning character animation since it shows follow-through and drag. Dancing withthe Sacks

33. Importance of Follow-through & Drag “Now we could use Follow-through on the fleshy parts to give us the solidity and dimension, we could drag the parts to give the added feeling of weight and reality. It all added up to more life in the scene. The magic was beginning to appear.” From The Illusion of Life - Disney Animation Notice the subtle follow-through in the hands, skirt, and pant legs for the last drawing of the Moving Hold. By Ham Luske

34. Leaf/Paper Drop Test Animate a leaf (or piece of paper) drifting slowly to the ground. That was not a good leaf drop Let’s see some good ones by Gloria Cho and Katie Corna.

35. Leaf Drop Test http://www.youtube.com/watch?v=mbMo4HFJC1Y

36. Paper Drop Test http://www.youtube.com/watch?v=vKf-vIDSIik

37. Air Resistance Air resistance is a force created when an object moves through air. Air Resistance • Depends on: • Size (area) of the object • Speed of the object • Larger the size or speed, larger the resistance. Gravity

38. Demo: Hand out the Window Experience the force of air resistance by holding your hand out a car window. Resistance increases as speed increases. Resistance increases as area increases.

39. Demo: Falling in a Vacuum Feather falls slowly due to air resistance force. If we remove the air (create a vacuum) then feather and coin fall with same acceleration.

40. Home Demo: Drop the Sheet A flat sheet of paper falls slowly because of air resistance. What happens if we place it on top of a book, blocking the air from reaching it? Air Resistance Weight Book and sheet fall together

41. Falling on the Moon There’s no atmosphere and thus no air resistance on the Moon. http://www.youtube.com/watch?v=5C5_dOEyAfk

42. Falling with Air Resistance 1 Light objects, such as a beach ball, initially fall with accelerating motion. Due to air resistance, the motion transitions to uniform motion after falling a certain distance. 3 Accelerating Motion 5 5 Uniform Motion 5 5

43. Falling Coffee Filter Tracked falling of a coffee filter. Accelerates in first 1/3 second Distance Fallen ConstantSpeed Time Click

44. Terminal Speed Speed of falling objects increases until air resistance force balances gravity force. When forces balance, zero acceleration so constant speed. This is the terminal speed, the maximum speed when falling. Heavier parachutist has higher terminal speed

45. Wile E Coyote with Anvil • The accident-prone Wile E Coyote walks off a cliff carrying an anvil. • If he lets go of the anvil, he’ll fall: • Slower • Faster • At the same speed

46. Wile E Coyote with Anvil • The answer is: • Slower You reach terminal speed when the force of air resistance balances your weight. The less you weight, the less air resistance is needed so the terminal speed is also lower (lower speed <-> lower air resistance).

47. Estimating Terminal Speed Air Resistance Terminal speed of a rectangular object (with the density of water) falling flat is approximately: (Speed) = (50 m.p.h.) x T where T is thickness in inches. T Gravity

48. Terminal Speed & Thickness Piece of paper falls much faster when you drop it sideways instead of face-down. Air Resistance Air Resistance Small thickness; Slow terminal speed Big thickness; Fast terminal speed Gravity Gravity

49. Terminal Speed & Shape Terminal speed of aerodynamic shapes, like a sphere, are about 50% faster than for a rectangle. For example, the terminal speed of a raindrop with a radius of 1/8th inch is about 20 m.p.h. Large raindrops are flattened due to air resistance and very large drops are split into smaller drops by the force of air resistance.

50. The Incredibles (2004) http://www.youtube.com/watch?v=j2SmaI6iPxA What is unrealistic about the way objects fall in this scene?