Upcoming Deadlines

Eighth homework Reverse Video Reference of Walking

Due Thursday, Oct. 27 (this week)20 points (10 points if late)

For full schedule, visit course website:ArtPhysics123.pbworks.com

Pick up a clicker, find the right channel, and enter Student ID

Homework #8Reverse video reference of walking Normally, animators shoot video and use it as

reference for their work. In this assignment, you will do the reverse. Specifically, you will watch each of three animation clips and shoot video in which you recreate them as accurately as possible.

Homework #8• Watch each of the three video clips on the

assignment page• Film yourself acting out each scene, each in a

separate clip. Reproduce the motion of the character as accurately as possible - you will be graded on how well you do this. Don’t just quickly act it out. Study each clip carefully to capture all of the motion details. Pay attention to staging, camera angle, camera moves (if any), etc.

• Post all three videos in a blog entry entitled “Reverse Video Reference of Walking”

Homework #8

Assignment is due by 8AM on Thursday, Oct. 27th20 points (10 points if late)

Survey QuestionUp to now, roughly how many

hours per week do you spend this class (outside of attending class):

A) An hour or less per weekB) About two hours per weekC) Four hours, on averageD) Six hours a week, more or

lessE) Well over 6 hours per week

Review QuestionMr. A pushes way from Mr. B while Mr. B just

holds his hand rigidly in place.Which of them has the largest acceleration?

Mr. Apushes

Mr. B holdsA) Mr. AB) Mr. BC) They have

the same acceleration

Review Question

Object A Object BActionReaction

Accelerations

Mr. A has the larger acceleration.If A pushes B then both accelerate by equal forces.By Law of Acceleration, Object A, having less mass, will accelerate more than the heavier Object B.

Wile E. Coyote, PropelledWhich of these devices would actually work to propel Wile E. Coyote?

A) Outboard motor in a tub of water.

B) Big fan blowing a large sail.

C) Both would work.D) Neither would

work.

A)

B)

Internal Propulsion

Air pushes sail

Sail pushes air

Propeller pushes air

Air pushes propeller

Action/Reaction Pairs

Internal propulsion is not possible because the impulse gained from one reaction is lost due to another internal action.

Back of the tub acts

like the sail.

This would work!

Jumps

JumpingJumping is a basic character animation exercise that incorporates many of the basic elements found in drop tests for inanimate objects.

By Danielle Domurat

http://www.youtube.com/watch?v=jwerYsdE9Xs

By Carlos Nunez

http://www.youtube.com/watch?v=XWheRtQkC9o

X = Center of Gravity

X

X

Crouch Take-off

Apex

Jump Height

Jump TimeThe simplest part of a jump is the time in the air and how it is related to the height of the jump.

Timing the Jump

Jump Time & HeightJump Time (seconds)

Frames Jump Height

1/24 1 1/3 inch1/12 2 1 1/3 inches1/8 3 3 inches1/6 4 5 1/3 inches

¼ 6 12 inches1/3 8 21 inches

½ 12 4 feet2/3 16 7 feet

¾ 18 9 feet

1 24 16 feet

The same table we saw for the ball drop gives the jump time (from take-off to apex) and jump height.The formula to compute this table is:(Distance in inches) = (Number of Frames) x (Number of Frames) x (1/3 inch)

Jump Time Example

X = Center of Gravity

X

X

X

Take-off

Apex

Landing

21 inches

8 frames8 framesFor a jump time of 8 frames, the jump height is 21 inches

Hang time = 2x(Jump time)

Crouching Tiger, Hidden Dragon (2000)

Characters stay in the air an unrealistically long time, even considering the impressive height of their jumps.

http://www.youtube.com/watch?v=xxCvv3bDyvw

X

X = Center of Gravity

X

X

Crouch Take-off

Apex

Push Height

Jump Height

Jump TimePush Time

You can time the push (from crouch to take-off) using a simple formula

Timing the Push

Jump Magnification

Jump Magnification = Jump HeightPush Height

Jump Magnification = 2 Jump Magnification = 8

Timing of the push depends on the jump magnification.

Formula for Timing the Push

Can use this formula to check the timing of the push depending on the timing of the jump.

Push Time = Jump Time Jump Magnification

Timing the Push Example

X

X = Center of Gravity

X

X

X

Crouch Take-off

Apex

Landing

10 ½ inches

21 inches

8 frames8 frames4 frames

Jump magnification = 2so push time is half aslong as the jump time.

Planning a Jump

1) Pick the desired jump time or jump height.

2) Use the table to find the jump height given the jump time (or vice versa).

3) Pick the desired push height for the crouch

4) Determine the push time from the jump magnification.

Animators can plan out a realistic jump by these steps:

A Big JumpApex

A character jumps 16 feet into the air. From the table, that’s a jump time of 24 frames (take-off to apex). The push height is 16 inches; what is the push time?

Push Time = Jump Time Jump Magnification

A) Two framesB) Four framesC) Six framesD)Eight framesE) Twelve frames

Jump Height = 16 feetPush Height = 16

inchesJump Time = 24

frames

A Big JumpApex

Push Time = Jump Time Jump Magnification

Jump Height = 16 feetPush Height = 16

inchesJump Time = 24

frames

A)Two framesJump magnification is 12 (=16 feet/16 inches)

Push time is (24 frames)/12 = 2 frames

Push Factor

Jump Magnification = (Push Factor) x (Push Height in Feet)Push Time (in frames)

Push Factor

1 36

2 9

3 4

4 2 1/4

6 1

8 9/16

Push Factor = 36 / (Push Time in Frames)2

Can calculate jump magnification with this:

The Incredible HulkThe Incredible Hulk is big, let’s say 10 feet tall.Say his push height when he jumps is 3 feet.If you animate 2 frames from crouch to take-off, how high does he jump?For a push time of 2 frames the push factor = 9 so the jump multiplier is

(Jump multiplier) = (9) x (3) = 27 (Push Factor) x (Push Height)

He jumps 81 feet into the air since his push height of 3 feet gets magnified by a factor of 27 (the jump multiplier).

Jumps about 8x his height

The Hulk (2003)

http://www.youtube.com/watch?v=5JsDylEPNh0

The enormous jumps by the Hulk look fake because, for such huge jump magnifications, the push time would be less than one frame.

Boundin’ (2003)Big jump magnifications and jump times give a feeling of lightness and happiness in a cartoon.

http://www.youtube.com/watch?v=CDtiZImH0qI

Timing the LandingIf the crouch on landing is similar to the crouch when pushing off then the landing has similar timing to the take-off.

If the crouch on landing is shorter then the timing of the landing is shorter; if the crouch is longer, the timing is longer.

Forces when JumpingThe three main forces on a person jumping

are:• Gravity (Downward)• Support of the floor (Upward)• Frictional force of the floor (Horizontal)Only these forces can accelerate the person.Gravity is constant but the force exerted by the floor can increase in reaction to the action of the person exerting a force on the floor.

Jumping is done by pushing downward on the ground (action) so the ground pushes upward on you (reaction).

How high you jump depends on the force and on the distance over which you apply that force. Can only push while in contact

with the ground so squatting helps by increasing distance.

Jumping Action/Reaction

Action

Reaction

You can determine the average force exerted when jumping as:

(Jump Force) = (Jumper’s Weight)

x (Jump Magnification)

Remember that

Average Push Force

Jump Force(Action)

Jump Magnification = Jump HeightPush Height

The Incredible HulkIf The Hulk has a push height of 3 feet and he makes a huge jump, rising a height of 300 feet, how much force does he push with?Jump magnification is 100 so the push force is 100 times his weight. The Hulk is twice as tall as a normal person so his weight is at least 8 times larger (probably closer to 10-12 times larger). So if The Hulk weighs 2000 lbs, he’s pushing off with 200,000 lbs of force (200 tons).

Action/Reaction Jumping Forward

Action

Reaction

To jump upward and also forward, the action force (pushing downward with your legs) needs to also be pushing towards your back so that reaction force of the floor is upward and forward.Jumping forward at a 45° requires almost 50% more pushing force to reach the same vertical height.

Forces when LandingIf the timing of the landing is similar to the timing of the take-off then the forces on landing are similar to the forces on take off.

If the landing has quicker timing then the forces are proportionally larger on the landing.

If the landing has slower timing than the take-off then the landing forces are smaller. Action

Reaction

Hancock (2008)One of the few things in this movie that’s physically accurate is that the force exerted on the ground is just as extreme on the take-off as it is on the landing.

Take-off Landing

Overlapping ActionOverlapping action is all the secondary motions that occur in addition to the primary motion.

In this example the primary motion is the jump itself.Motion of the arms and head are active secondary motions, created by the character, while the drag of the clothing, hair, etc. are passive secondary motions.

Secondary ActionSecondary actions are a part of acting. They are the extra actions that actors (and animators) use to convey personality or mood.

For example, in this scene Hogarth is playing with the telephone cord to convey that he is bored and knows exactly what his mother is going to tell him to do.

Clickhttp://www.synchrolux.com/?p=273

Timing of Overlapping Actions

Overlapping actions may or may not have timing that matches that of the primary motion.

Passive secondary motion, like follow-through and drag, is more likely to be synchronized with the primary motion but sometimes active secondary motion is also synchronized, in support of the primary motion.

Swinging Arms in a JumpThe natural motion when jumping is to swing the arms upward as fast as possible while the feet are in contact with the ground.Swinging the arms raises the center of gravity and also increases the downward action force pushing off the ground.

Swinging Arms in a JumpThe height of a jump is significantly lower (almost 30% lower) if you don’t swing your arms during the take-off portion of a jump.

However, if you swing your arms after leaving the floor, then the height of the jump is much lower.

Home Demo: Jumping & Arm SwingFirst, jump normally, that is, swing your arms upward while feet are still on the ground.

Now try swinging your arms upward after you leave the ground; you’ll notice a big difference.

Home Demo: SomersaultNow let’s try using the arms in a backwards somersault

Motion of the arms is also useful here for control of the rotation.

Tuck increases rotation speed

Arm Motion while in the AirWhile in the air, moving your arms can shift the center of gravity and change rotation but it cannot change time in the air or the distance.

http://www.youtube.com/watch?v=P5Sg_kACPRM

Long jumpers move their arms to control the rotation of their body so as to land feet first.

Demo: Skater’s Spin

SlowRotation

FASTRotation

Exert a force to pull hand weights toward my body, causing a big increase in rotational speed.

Demo: Spin Up the Wheel

ZeroRotation Clockwise

Rotation

Counter-ClockwiseRotation

By pushing the bike wheel to turn it one way, the recoil causes me to rotate in the opposite direction.

Blades

Body

Helicopter’s TailWhen a helicopter’s blades start turning in one direction, by conservation of angular momentum the body would spin in the opposite direction.

To compensate, the small rotor in the tail exerts a force to keep the body from turning. If small rotor fails, helicopter spins out of control.

Demo: Mid-Air TwistStand up and clear

space around you.When I say “Jump!”,

jump.In mid-air I’ll point

left or right and I want you to try to turn so you land facing that direction.

Jump! Turn Land

How can you rotate in mid-air without pushing off of anything?

Demo: Mid-Air Twist

Jump! Turn

As you turn your legs 90 degrees, your arms and torso rotate in the opposite direction.

Sticking your arms out as you turn helps by increasing the rotational inertia of your upper body.

A large rotation of your legs is exactly cancelled by a small rotation of your outspread arms and torso.

Demo: Mid-Air TwistYour rotation stops as soon as you stop rotating your upper body but by that time you’ve landed with your feet turned to the side.

Once on the ground you can push off on the ground to restore your arms and torso to a normal stance.

Turn Land

Front Side 180

Jump! Turn Land

The same principle is used in skateboarding tricks, such as a front side 180, in which a skater does a half turn in mid-air, turning upper and lower torso in opposite directions.

Demo: Drop the Cat Again

www.abc.net.au/science

Cat lands on its feet by clever use of action/reaction combined with changing rotational inertia by extending or pulling in legs.

Demo: Drop the Cat Again

Demo: Drop the Cat Again

http://www.youtube.com/watch?v=t84a0L76ju4

Next LectureWalks

Reverse Video Reference of Walking due Thursday

Please turn off and return the clickers!