Upcoming Deadlines

1. Pick up a clicker, find the right channel, and enter Student ID Upcoming Deadlines Eighth Homework (Reverse Video Reference) Due Thursday, March 22nd (This week) 20 points (10 points if late) Spring Break - March 26th to March 30th Ninth Homework (Stop-motion Character Animation) Due Tuesday, April 10th (In three weeks) 20 points (10 points if late) For full schedule, visit course website: ArtPhysics123.pbworks.com

2. Homework Assignment #8 Normally animators shoot video and use it as reference for their work. In this assignment, you'll do the reverse. Specifically, for four different animation clips you’ll shoot video of yourself in which you recreate those clips as accurately as possible. Go to Homework Assignment 8 on the course website to find the animation clips you’ll recreate: https://artphysics123.pbworks.com/Homework-8

3. Homework Assignment #8 Upload your four clips to your blog in an entry entitled “Reverse Video Reference of Walking." This assignment is due by 8am on Thursday, March 22nd (this week). 20 points (if late, 10 points). For each of the four animation clips the best video clip will get an extra 20 points of credit.

4. Survey Comments Like: Demos; Videos; Interesting & organized lectures; Clickers; Grading system & extra credit Dislike: Term papers; Tracker; Quizzes Suggest: Change 8am due-time; more clicker questions; more clicker time; clicker points?; fewer term papers; free beer

5. Survey Question The amount of time that you’re given to answer the clicker questions is: • too short; would like more time. • about the right amount of time. • too long; don’t need so much time.

6. Swinging Arms in a Jump • The natural motion when jumping is to swing the arms. To jump as high as possible you should swing them upward: • While your feet are still touching the ground. • Just after your feet leave the ground. • Either way, since the forces on the arms and on the feet are not related.

7. Swinging Arms in a Jump • While your feet are still touching the ground. Swinging the arms raises the center of gravity and also increases the downward action force pushing off the ground.

8. Spin or Tumble? A • Rotation around two of these axes is spinning.In this pose, the axis of rotation that tumbles is: • Twisting axis (Head-to-toe axis; • Turn left-to-right) • B) Somersault axis(Side-to-side axis; • Turn front-to-back) • C) Cartwheel axis(Front-to-back axis; • Turn head-to-feet) B C

9. Spin or Tumble? B) Somersault axis(Side-to-side axis; Turn front-to-back) B Rotating along this axis typically results in irregular tumbling. Spinning is possible but requires more control than along the other two axes.

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

11. WalksPart I

12. Characters in Motion - Walks Walking is a great example for studying character motion because it has all the basic elements of mechanics.

13. Walks with Personality From the basic walk it’s possible to create many variations to express personality through acting.

14. Walking (1968) Ryan Larkin created an Oscar-nominated short of people walking, animated in a variety of styles. http://www.nfb.ca/film/Walking http://www.nfb.ca/film/ryan/ This clip is from Chris Landreth’s Oscar-winning short, Ryan, about the troubled life of Ryan Larkin.

15. Stride & Passing Position Passing Position Stride Feet on the ground One foot in the air Concentrate on these two key poses, the stride and the passing position.

16. Squash & Stretch Squash Stretch Passing position Stride Stride These are the transition poses between the stride and the passing position.

17. Animating a Walk Cycle Is animating a walk cycle just a matter of getting the right sequence of poses? No, it’s more complicated. Let’s see why…

18. Video Analysis To help us analyze a walk, let’s look at some video analysis using the Tracker software.

19. Video Analysis

20. Video Analysis

21. Head Position Passing Height Stride

22. Richard Williams’ Walk Williams puts the “up” position just after the passing position, which happens if the heel rises in a quick walk.

23. Preston Blair’s Walk Preston Blair makes the passing position the tallest point in his basic walk cycle. Stride Passing Stride But in walks with attitude, he mixes it up. Stride Passing Stride Richard Williams also does this in many cases.

24. Rules vs. Tools There is enormous variety in walks and each has unique timing and spacing. As Glenn Vilppu says, “No rules, just tools!” Physics is a tool that helps animators create believable walks.

25. Step, Stride, Gait Stride = 2 Steps Distance Gait is the timing of movement in walking, running, etc. Time

26. Cadence of a Walking Gait A normal walking gait ranges from a third to two-thirds of a second (8 to 16 frames) per step, with a half second (12 frames) per step being about average. A full stride (both right and left steps) is, on average, one second (24 frames) per cycle. Parade march time is 120 beats per minute (one beat per step). One stride (two steps) Strobe photo (5 flashes per second)

27. Contact with the Ground Each foot is on the ground about 60% of the time. About a 20% of the time both feet touch the ground. Right Foot 40% 10% 10% 60% 10% 10% 60% 40% Left Foot On the ground In the air Time of dual contact decreases as walking speed increases.

28. Walking Slower or Faster Going from a slow walk to a fast walk you increase both your stride length and your stride rate to increase your speed. At around 6-7 feet per second (4-5 m.p.h.) the gait pattern transitions into a run.

29. Period of a Simple Pendulum Time required for a full oscillation (one round trip) is called the period of oscillation. Period of a simple pendulum depends only on its length (distance from the pivot to the mass). Greater the length, the slower the oscillation. Period of this pendulum is about one second per oscillation

30. Period of a Cylinder Pendulum X X Period of a cylinder pendulum depends mostly* on its length (distance from the pivot to center of gravity). Leg swing is like this Greater the length, the longer the period for the swing (that is, the slower stride rate). * Also depends on the radius; larger the radius, the slower the oscillation.

31. Period of Walking Gait During the stride, the passing leg swings at its natural period of oscillation. Short legged characters have quicker gait than long legged ones.

32. Running Gait In running, you bend your leg and raise your calf and foot to quicken gait by shortening the distance from the pivot (hip) to the center of gravity of the leg. XCG XCG

33. Drag of Articulated Limbs Drag (inertia) is seen with articulated limbs Fast Fast Swing Slow Slow Swing

34. Drag in Character Effects Drag (inertia) is also seen in character effects, such as hair and clothes Fast Fast Swing Slow Slow Swing

35. Timing of the Walk Slowing Out Slowing In XCG XCG XCG Timing is almost even but there is some slowing in and slowing out as the center of gravity rises and falls.

36. Inverted Pendulum In the passing position the whole body swings up and down, as an inverted pendulum.

37. Rolling Egg Timing Slowing Out Slowing In XCG XCG XCG The timing of the motion due rising and falling center of gravity (CG) is like that of a rolling egg.

38. Home Demo: Carrying Water Slowing Out Slowing In To appreciate the “rolling egg” timing of a walk, carry a shallow tray of water and notice the rhythm of the sloshing. XCG XCG XCG Walking stiff legged, like Frankenstein, exaggerates the slowing in and out.

39. Weight Shift in Walks Up and down motion in a walk causes weight changes for the character. With gravity Falling & Speeding Up: Lose Weight Rising & Slowing Down: Lose Weight Falling & Slowing Down: Gain Weight Rising & Speeding Up: Gain Weight Against gravity

40. Weight on the Ground • Stride • Squash • Passing Position • Stretch • Same weight at all times At which position do you exert the least weight on the ground? Stretch P.P. Stretch P.P. Stride Stride Stride Squash Squash

41. Force Plate Experiments Stride C) Passing Position Can measure weight shift during walk cycle using force plates. Squash Squash Stretch Stretch Body Weight Passing Position Passing Position

42. Weight Shift – Normal Walks

43. Weight Shift – Normal Walks The weight on the back foot is peaks just as the heel of the front foot touches the ground. Moments later, the weight on the front foot is peaked right as the back foot leaves the ground. Andrew Harkins, Dreamworks animator

44. Weight Shift – Normal Walks In the middle of the passing position the weight on the planted leg dips to a minimum. This weight is actually 20%-40% less than the person's weight when standing stationary on one foot.

45. Inverted Pendulum In the passing position the whole body swings up and down, as an inverted pendulum. Falling & Speeding Up: Lose Weight Rising & Slowing Down: Lose Weight

46. Weight Shift – Normal Walks I’m going to kill Garcia for this! The reason that the weight decreases is that the body rises upward then downward during the passing position, swinging like an inverted pendulum. Due to the centripetal force required to move your body in a small arc during the passing position causes your weight to be lower. This effect is seen in overlapping actions, especially if a character has long hair or loose fitting clothes.

47. “Counteraction” Richard Williams calls this effect of varying weight the counteraction. Williams writes, “When the character goes up – the drapery or hair or soft bits go down.” Lose Weight Gain Weight Lose Weight

48. Normal, Slow, and Fast Gaits Notice the differences in the three walks yet the similarities among different persons. Normal walk Slow walk has less variation in the weight shift Fast walk has more variation in the weight shift

49. Force Plate – Slow Walks

50. Force Plate – Fast Walks