Upcoming Deadlines

1. Pick up a clicker, find the right channel, and enter Student ID Upcoming Deadlines Sixth Homework (Stop-motion Animation) Due this Thursday, October 6th 20 points (if late, 10 points) Bonus prize of 20 extra points to top three. Seventh Homework (Outline of First Term Paper) Due next Thursday, October 13th 10 points (5 points if late) For full schedule, visit course website: ArtPhysics123.pbworks.com

2. Homework Assignment #6 Stop-motion animation of a falling object. * Plan your scene, especially the timing, spacing, path of action, anticipation, etc. * Photograph your object in a sequence of images suitable for combining into an animation. * Create a video clip with at least a dozen unique frames. * Adjust the timing by adding or removing frames; if needed, re-shoot your animation.

3. Homework Assignment #6 * Post your animation to your blog in an entry entitled "Stop Motion Animation of Falling". * In your posting describe in one paragraph how you created your animation. Due by 8am on Thursday, Oct. 6th 20 points (if late, 10 points) Score based on believability and creativity. The top three animation clips in the class will receive a bonus of 20 extra points.

4. Homework Assignment #6 Here is a good example from last semester. Not only does the falling motion look believable but the action is simple yet entertaining. http://www.youtube.com/watch?v=uOTncsocsUE

5. Survey Question You have already started working on your stop-motion animation due this Thursday. Trueor False

6. Review Question A spool is pulled by a string, wrapped around the center, as shown. The spool will move: A) Left B) Right Pull

7. Force and Direction • Left Objects always change their velocity in the direction of the applied force. Motion Motion Pull Motion Pull

8. Review Question BLOW Blow hard through a funnel with a ping pong ball in the funnel’s bowl. Instead of being blown away, the ball is held tightly in the bowl. This is because: Ping Pong Ball • Compression produces low pressure • Moving air produces low pressure • The ball spins, producing low pressure • None of the above

9. Class Demo: Blow the Funnel BLOW B) Moving air produces low pressure. This demonstrates the Bernoulli effect, which says that the higher the air speed, the lower the pressure. L L Ping Pong Ball A

10. Squash and Stretch

11. Character Animation In the first part of the course we’ve covered some of the basics of animation. We now move to more advanced topics, specifically those relevant to character animation.

12. Gertie the Dinosaur (1914) This early short Winsor McCay is not the first animated film, it is one of the first to feature a character with a distinct personality. Running time: 12 minutes http://www.youtube.com/watch?v=UY40DHs9vc4

13. The Adventures of Prince Achmed (1926) The Adventures of Prince Achmed, by the German animator Lotte Reiniger, is the oldest surviving feature-length (at 65 minutes) animated film. In this silent movie, Reiniger used silhouette animation, which involves manipulating cutouts (basically two-dimensional stop motion animation).

14. The Adventures of Prince Achmed (1926) http://www.youtube.com/watch?v=25SP4ftxklg

15. Evolution of Motion Pictures Movies advanced rapidly in the beginning of the last century, adding sound and color. Gone with the Wind (1939) Birth of a Nation (1915) As realism in movies increased, the stories and the acting had to change as well.

16. Early Cartoons Early animations also added sound and color but remained restricted to short films. Flowers and Trees (1931), the first cartoon in full Technicolor.Running Time: 8 minutes Steamboat Willie (1928), the first cartoon with a complete soundtrack.Running Time: 7 minutes

17. Realism Barrier Feature length animated films were not produced because audiences demanded more realistic, complete characters in such movies. Feature-length Appeal  Short Would you sit through a 90 minute Betty Boop cartoon? Realism 

18. Snow White Disney’s Snow White was the first full-length feature film using traditional (cel) animation. Snow White and the Seven Dwarfs (1937, 83 min.) Snow White (1933, 7 min.)

19. Snow White (1933) http://www.youtube.com/watch?v=IUsp2XxgZTY

20. Snow White (1937) http://www.youtube.com/watch?v=nN1BegE3QR0

21. Disney’s Principles of Animation From life studies, Disney animators discovered that #1 principle that was key to adding realism in character animation was “Squash & Stretch.” • 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

22. Basic Squash & Stretch Basics of squash and stretch are present in even the simple ball bounce exercise. Stretch shows speed due to motion blur. Actual Shape Cartoon Squash shows force, such as on impact. Actual Shape As Seen byHuman Eye

23. Character Animation Basic squash and stretch are easy to learn from a bouncing ball but their importance is in how squash and stretch appear in the motion of characters. From Preston Blair’s, Cartoon Animation

24. Luxo Jr.’s Squash & Stretch “An object need not deform in order to squash and stretch. For instance, a hinged object like Luxo Jr. squashes by folding over on itself, and stretches by extending out fully.” John Lasseter

25. Luxo Jr. (1986) Luxo Jr. was the first CG film nominated for an Academy Award. http://www.youtube.com/watch?v=PvCWPZfK8pI

26. Water Balloon Drop Water balloon makes a good animation exercise because it moves like an animate character. By Mai Vu By Ken Calvert http://www.youtube.com/watch?v=ajC1oCZlkQI http://www.youtube.com/watch?v=0yWTJpaoJXI

27. Water Balloon Reference http://www.youtube.com/watch?v=FI-Mq6BDtMQ It’s always useful to animators to study reference, both live and video. The motion of the water balloon is different with every take, yet has a consistent feel. http://www.youtube.com/watch?v=XbGVBV3-F48

28. Elements of a Water Balloon Drop Let’s look more carefully at the physics in each element of a water balloon drop. Initial Drop Bounce Settle Squash

29. Part 1: The Initial Drop The initial part of the water balloon drop is similar to other drop tests yet the fluid nature of the balloon adds new elements. Initial Drop

30. Incompressibility Most solids and liquids are almost incompressible; it takes enormous force to change their volume. Elastic materials may stretch easily but their volume stays constant.

31. Young’s Modulus (Stiffness) Young’s modulus indicates amount of force required to compress or expand a material. Rubber is compressible but water is almost as incompressible as wood!

32. Demo: Incompressibility of Water Place a brick on top of a syringe filled with air. Air compresses (a bit). Place a brick on top of a syringe filled with water. Water doesn’t compress.

33. Demo: Bed of Nails Pressure depends on weight and on the area supporting that weight. One may safely lay or sit on a bed of nails, as long as there are enough nails so that the pressure, measured as force per nail, is small. Weight of 150 pounds is distributed over 300 nails. Force per nail is ½ lb. Need 5 lb per nail to pierce skin.

34. Pressure in Liquids Pressure in a liquid depends on depth. As with a stack of bricks, weight of what’s above determines pressure. Low Medium Low Medium High High

35. Water Balloon at Rest Water pressure pushes on the rubber, stretching it into a flattened shape. Low Medium Water Pressure High Tension of the rubber also affects the shape.

36. Repose Angle and Contact Angle Water balloon has a repose angle and contact angle that depend on the rubber’s stiffness. Stiff Repose Flaccid Contact Mercury Beads of liquid have similar shapes, depending on surface tension. Water

37. Class Demo: Pressure & Weight A can full of water has holes in the sides through which water comes out. What happens when you drop the can? The can is now in freefall and weightless. Water stops flowing as the can falls since the pressure was due to the water’s weight.

38. Falling Water Balloon Slides off and falls Because free fall is a weightless state, the water balloon will be roughly spherical as it falls. May have some initial vibrations depending on how it is released. Faucet drip

39. Air Resistance? Because the water balloon falls faster, the air resistance force on a water balloon is greater than on an air-filled balloon! Air Resistance However, a few ounces of air resistance force is insignificant for a water balloon weighing several pounds. Water Air Gravity

40. Part 2: Squash on Impact The fluid nature of the balloon makes the squash on impact very pronounced. Squash http://www.youtube.com/watch?v=UMeJ4ZfRd3w

41. Force of Impact for Squash To understand the force of impact you need to understand momentum and impulse. http://www.youtube.com/watch?v=-p5zoufjOwc

42. Momentum Momentum of an object is, (Momentum) = (Mass) X (Velocity) Examples of objects with large momentums are: • Supertanker (large mass) • Bullet (large velocity)

43. Momentum and Force To stop an object with a large momentum requires either: • Large force (stopping the object quickly). • Small force applied for a long time. Notice that changing object’s momentum depends on force and time interval.

44. Impulse Define impulse acting on an object as, (Impulse) = (Force on object) X (Time interval) Objects have momentum. Impulse acts on an object.

45. Impulse & Momentum Momentum is related to impulse by, (Change in momentum) = (Impulse) When mass stays constant then, (Mass) X (Change in velocity) = (Force) X (Time interval)

46. Demo: Egg Throw Throw a raw egg as fast as possible at a bed sheet that’s held loosely. X X X X X (Hold here)

47. Egg Throw Analyzed Throw egg at a bed sheet; it stops but doesn’t break. Throw egg at the wall with same speed, it stops but breaks. In which case is the impulse on the egg the greatest? • Hitting the bed sheet • Hitting the wall • Same in the two cases

48. Egg Throw Analyzed C) The impulse is the same in the two cases. The change in velocity is the same in the two cases so the change in momentum is the same. Since the impulse equals the change in momentum, the impulse is the same in the two cases. But the forces are not the same!

49. LONG TIME small force short time LARGE FORCE Egg Throw Analyzed Throw egg at sheet or wall with same speed. Impulse is the same in the two cases. Which case has: Largest time of impact? Throw at the sheet. Largest force on the egg? Throw at the wall.

50. Crumple Zones Air Bags Seatbelts Automobile Safety Maximizing time of impact on the driver minimizes the force of impact. This principle used in design of: