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Upcoming Deadlines. Fifth Homework (Video Analysis of a Jump) Due Thursday, Sept. 29 th (Next week) 15 points (10 points if late) Sixth Homework (Stop-motion Animation) Due Thursday, Oct. 6 th (In two weeks) 20 points (if late, 10 points) - PowerPoint PPT Presentation

Uniform Motion

Upcoming DeadlinesFifth 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.com1Homework Assignment #5Use 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 tricky2Homework Assignment #5

ParabolicPath of ActionStraight LineParabolic Curve3

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

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Wile E. Coyote & Loop-D-LoopFalse.If his speed is high enough then he stays in contact with the arch, just like the water in the spinning bucket.5Creating Action

6Why Things MoveSo far weve only looked at how things move (slowing in/out, path of action, arcs, etc.).

Now its time to look at why things move, that is, what causes action.

To understand why things move the way they do, you need to consider the forces at play.7Newtons Laws of ForcesNewton 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 Newton8Follow-Through

When a character stops, it doesnt 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 Newtons Law of Inertia.

9Motion, with & without ForcesAn object moves with constant, uniform motion until acted on by a force.No forceAn asteroid floats in space with a constant speed unless gravity deflects its motion.

FORCE

10Balance 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 theres no motion!GravityGravityGravityTensionFloorFloor11Law of InertiaNewtons Law of Inertia says:An object moves with constant, uniform motion until acted on by an unbalanced force.

GravityFloorThe bowling ball moves with constant speed*

*In reality, there is a small unbalanced force, friction, that does slow the balls speed.12Home Demo: Riding the BusWhen a moving bus halts, you continue moving forward.

13Shoot 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.

14Shoot Em Up (2007)

Frame 438Frame 439Frame 440Frame 441Stuntman flies out the window at about 10 m.p.h.This is a bit slow but at a realistic speed the audience wouldnt see the action.15

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

The League of Extraordinary Gentlemen (2003)In this scene, Sean Connery jumps out the side of a speeding car and lands on his feet.

http://www.youtube.com/watch?v=n8SDdkKSqns17Roll 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.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:

18A) Roll forwardYou are moving at the same speed as the car when you jump out so you will roll forward.

Jumping out of a Car

Youll start losing speed after you hit the ground so, relative to the car, youll fall behind as the car continues speeding along.car19

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 youre pulled to the outside bank of the curve.

Centrifugal Force Revisited

Your path20Law of Inertia (cont.)Newtons Law of Inertia also says:An object at rest (not moving) remains at rest until acted on by an unbalanced force.

GravityFloorA stationary bowling ball remains stationary until some unbalanced force comes along.This is nothing more than motion at constant speed but with speed equal to zero.21If the bus starts moving again, you remain stationary, seemingly thrown backwards.Home Demo: Riding the Bus (cont.)

22As seen by observer sitting in the busFrame of Reference

As seen by observer on the streetBus MovesBackground23Space Balls (1987)

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Class Demo: Tablecloth PullYank quicklyDue to the vases inertia it remains at rest since almost no force acts on the vase if one pulls quickly andstraight.26Inertia & DragAn object wont move until a force acts on it so long hair trails behind as head turns. Although this is due to the hairs inertia, in animation its usually called drag.An object at rest remains at rest until acted on by a force.

27Inertia & 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.

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Drag in Arcs and WavesAnimation drag is very noticeable when something like hair or cloth moves in an arc or in a wave-like motion.29Fukkiretahttp://www.youtube.com/watch?v=NFep4vO4TRcClick to play

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Class Demo: Hula SkirtThe 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.31Flour Sack ExercisesThe 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 Sacks32Importance of Follow-through & DragNow 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 Luske33Leaf/Paper Drop TestAnimate a leaf (or piece of paper) drifting slowly to the ground.

That was not a good leaf drop

Lets see some good ones by Gloria Cho and Katie Corna.34Leaf Drop Testhttp://www.youtube.com/watch?v=mbMo4HFJC1Y

36Air ResistanceAir resistance is a force created when an object moves through air.Depends on:

Size (area) of the objectSpeed of the object

Larger the size or speed, larger the resistance.Air ResistanceGravity37Demo: Hand out the WindowExperience the force of air resistance by holding your hand out a car window.Resistance increases as speed increases.Resistance increases as area increases.

38Demo: Falling in a VacuumFeather falls slowly due to air resistance force.If we remove the air (create a vacuum) then feather and coin fall with same acceleration.

39Home Demo: Drop the SheetA 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?AirResistanceWeightBook and sheet fall together40

Falling on the MoonTheres no atmosphere and thus no air resistance on the Moon.http://www.youtube.com/watch?v=5C5_dOEyAfk41Falling with Air Resistance13555Accelerating MotionUniform MotionLight 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.5

42Falling Coffee FilterTracked falling of a coffee filter.

Distance FallenTimeAccelerates in first 1/3 secondConstantSpeedClick

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Terminal SpeedSpeed 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 speed44Wile E Coyote with AnvilThe accident-prone Wile E Coyote walks off a cliff carrying an anvil.

If he lets go of the anvil, hell fall:

SlowerFasterAt the same speed

45Wile E Coyote with Anvil

The answer is:SlowerYou 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).46Estimating Terminal SpeedAir ResistanceGravityTerminal 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.

Thickness, TTTerminal Speed1/100 inch1/105 m.p.h. inch25 m.p.h.1 inch150 m.p.h4 inch2100 m.p.h.9 inch3150 m.p.h

T47Terminal Speed & ThicknessPiece of paper falls much faster when you drop it sideways instead of face-down.Air ResistanceGravityGravityAir ResistanceSmall thickness;Slow terminal speedBig thickness;Fast terminal speed48

Terminal Speed & ShapeTerminal speed of aerodynamic shapes, like a sphere, are about 50%