Upcoming Deadlines

Homework #8 - Reverse Video Reference of WalkingDue Wednesday, October 27th (This Wednesday)20 points (10 points if late); 20 point bonus to best for each clip

Homework #9 – Stop-motion character AnimationDue Wednesday, November 3rdth (Next week)20 points (10 points if late); 20 point bonus to top 3

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

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

Homework Assignment #9

In this assignment you will create a simple stop-motion animation of a moving character.

For your character, use a doll or stuffed animal that's easily posed.

You may even use an inanimate object, such as a table lamp, as long as you can animate it so that it looks like a character.

Homework Assignment #9

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

Homework Assignment #9Your animation should be composed of at least a

dozen different images but you can use the same photo in two or more frames to get timing right.

Try to make the motion of the character as realistic as possible so that your audience will momentarily forget that it's not actually alive.

In homework assignment #6 you created a stop-motion animation of an inanimate falling object; if you're not happy with how you produced your earlier animation then re-read that assignment for alternative ways of creating stop-motion.

Homework Assignment #9You may work together with one or more

classmates to create a single animation for the team.

Clearly indicate the work done by each person, for example if different persons animate different characters or different scenes.

More is expected from a team effort; an animation created by a three person team should present three times as much work as a solo effort.

Homework Assignment #9Post your animation clip to your blog in an entry

entitled "Stop-Motion Character Animation.“

Assignment due 8am on Wed., November 3rd

20 points (if late, 10 points)The top three clips in the class, as selected by

another celebrity judge, will receive a bonus of 20 extra points.

Extra Credit Opportunity

November 11–14, 2010Landmark's Embarcadero Center Cinema

http://www.sffs.org/Screenings-and-Events/Fall-Season.aspx

Present proof of your attendance (receipt, photos, etc.) to any festival event or screening for 10 points of extra credit.

Special Campus EventRon Diamond’sAnimation Show of ShowsFriday October 297:30 PM Morris Dailey AuditoriumFree Admission

Activating your Clicker* Turn on your clicker.* Enter the channel number or letter for

joining this class. Hit Enter/Send key.* Clicker should read AP123GF10* Type in your student ID; hit

Enter/Send.Clicker is now ready to use; leave it on.Hit any key to wake the clicker from sleep mode.

Survey QuestionMany videos are shown in this class; would you

say that the number of videos is:A)Too many. Use the class time for other stuff.B)About the right balance.C)Not enough. Add more and leave out other stuff.

Review QuestionIn the passing position the pelvis drops slightly on the non-weight bearing side. This motion is called:A) Pelvic rotationB) Pelvic listC) Knee flexionD)Hip hula-hulaE) The Twist

Pelvic List

Pelvic list keeps the center of gravity from rising as much when the body passes over the weight-bearing leg, keeping the center of gravity on a flatter path of action.

CG

Stride

Passing Position

Passing Position

Passing Position

Stride

CG

Walking is more efficient with pelvic list.

Path of Action ofCG without List

With Pelvic List

Walki

ng Forw

ard

B) Pelvic list

Review Question

In normal walking, the side-to-side and up-down motion shown here is for the:

A)LegB)ArmC)Center of gravityD)Heel of the footE)Hand

Slow Fast

Side-to-Side

Up & Down

Walking

Forward

Figure 8Loop

8-Loop & U-Loop

C) Center of Gravity

The center of gravity shifts up & down and also side-to-side. CG makes a Figure-8 loop when walking slow

Makes a U-shape loop when walking fast.

Slow Fast

Side-to-Side

Up & Down

Walking

Forward

Figure 8Loop

Joints & Levers

Toy Story (1995)

Pixar’s Toy Story, directed by John Lasseter, was the first full-length feature film using computer animation.

Tin Toy (1988, Pixar), also directed by Lasseter, won an Oscar in 1988 for Animated Short Film.

Tin Toy (1988)

http://www.youtube.com/watch?v=vNZtl5SZvbM

The Polar Express (2004)The Polar Express was first full-length feature film made entirely with motion-capture animation.

http://www.youtube.com/watch?v=2g-FRSq7x_o

“Uncanny Valley”Paradoxically, as computer generated characters get more realistic they start to be creepy.

Realism

Ap

peal

Emily Project

PolarExpress

Shrek 1

Beowulf

Toy Story

Tin Toy

http://www.youtube.com/watch?v=GBgURIUQ700

020

4060

80100

020

4060

80100-0.5

0

0.5

1

“Realism Tightrope”

The uncanny valley occurs when some elements are more realistic than others.

Our human instincts warn us something is wrong.

Realistic Image

Ap

peal

Realistic Motion

Completely Natural

Tolerable

Repulsive

Repulsive

RobotZombie

Tolerable

Articulated FiguresIn computer animation characters are articulated figures, like marionette puppets.

The challenge for animators is to move all the elements (arms, legs, hands, etc.) believably from frame to frame.

Joints

Revolute JointPrismatic

Joint (Slider)

Two kinds of joints: Revolute (rotation) and Prismatic (extension/contraction).

Nearly all joints in animals are revolute joints

Axis of RotationRotation occurs around a line called the axis of rotation.

The axel is the axis of rotation for a set of wheels.

Revolute JointsRevolute joints may have a single axis of rotation, like hinge joints and pivot joints, or a variable axis, such as the ball and socket joint.

Elbow

Shoulder

Forearm

Forward KineticsWith forward kinetics (FK) the animator has to specify the axis of rotation and the angle of rotation for each joint on a moving limb.

Lift the arm by a shoulder rotation

Move forearm by an elbow rotation

Forward KineticsForward kinetics (FK) is a tedious process for the animator and it is difficult to maintain certain constraints, such as the planted foot in a walk.

Inverse KineticsWith inverse kinetics (IK) the animator positions the end effector, such as the hand, and the computer calculates the required joint rotations.

Inverse KineticsRotations calculated by the computer using IK are not always natural poses performed by a person. Furthermore, the timing may not be correct.

Ball & Socket

Ball & Socket

Hinge

x

x

Raising hand into “High Five” pose

AwkwardIK Pose

Elbow

Wrist

Shoulder

Understanding Rotation

Just like any other type of motion, rotation is governed by Newton’s laws:

• Law of Inertia• Law of Acceleration• Action-Reaction Principle

Let’s see how inertia, force, reaction, etc. appear in the context of rotational motion.

Sir Isaac Newton

Mass is a measure of inertia for linear motion.

Rotational inertia is similar concept for rotation.

Inertia

M mGold brick Normal brick

Difficult to move Easy to move

x xWood Bat Plastic Pee-wee Bat

Difficult to Rotate Easy to Rotate

Rotational Inertia

Rotational inertia depends on: • Total mass of the object• How the mass is distributed

The farther the object’s mass is from the axis of rotation, the larger the rotational inertia.

Demo: Inertia Sticks

Two metal pipes of the same mass

Rotate

Leadweights

Easyto

Rotate

Hardto

Rotate

Axis ofRotation

Human Rotational InertiaIn which pose does the dancer have a

larger rotational inertia?Axis of Rotation

A B

A) Pose AB) Pose BC) Same for A & B

since mass is unchanged.

Human Rotational Inertia

Axis of Rotation

A B

B) Pose B

Pose B has larger rotational inertia since the leg is extended, putting mass further from the axis of rotation.

Demo: Long Legs

Long legs have greater rotational inertia than short legs so long legged animals have a slow walking stride.

Drag of Articulated Limbs

Fast Swing

Slow Swing

Slow

Fast

The greater rotational inertia of longer limbs results in “drag”, just like with hair and fabrics.

Demo: Drop the Stick

Two meter sticks stand upright against a wall; one has a hunk of clay on the end.

Which stick will swing down and hit the floor first?

The one without the hunk of clay.

Why?Clay increases rotational

inertia, which slows the rotation.

Axis of Rotation

Demo: Drop the Stick

Axis of Rotation

X CG

X CG

Another way to understand why the weighted stick takes longer to fall is that it’s center of gravity is higher.

The higher it is, the longer it takes for an object to fall to the ground.

Longer stick tips over more slowly

Tripping and Falling

Axis of Rotation

X CG

X CG

If small child trips, he hits the ground more quickly than an adult.

Can view this two ways:*Child has small rotational

inertia.*Child’s center of

gravity is initially closer to the ground.

Demo: Hammer Balance

BA

Axis of Rotation

In which case is the hammer easier to balance on your finger?

A)Case AB)Case BC)The same for A & B

Demo: Hammer Balance

B) Case BIn Case B the rotation is

slower and thus easier to balance.

In case B the rotational inertia is greater because most of the mass is far from the axis of rotation (at your fingertip).

BA

X CG

X CG

Tightrope Walkers

The Great Blondin Is First to Walk Across Niagara Falls (June 30, 1859)

Tightrope walkers carry a long pole to increase their rotational inertia, which slows their rotation when they’re off balance.

When a force causes a rotation, we identify this as a torque.

Torque depends on• Magnitude of Force• Lever Arm

(Torque) = (Force) x (Lever Arm)

Torque

Lever ArmLever arm is the perpendicular distance from axis of rotation to the direction of the force.

Opening or Closing a DoorFor a door the hinge is the axis of rotation.

For maximum lever arm (and maximum torque), push perpendicular to the door at the edge opposite from the hinges.

DoorHinge

Pirouettes

A pirouette is typically done en dehors (moving leg starts at the front or the side and moves towards the back).

A ballet turn done on one leg, starting with one or both legs in plié and rising onto demi-pointe (usually for men) or pointe (usually for women).

http://www.youtube.com/watch?v=694S8oNXRZM

Torque for a Pirouette

The farther the distance between the feet, the greater the lever arm so the greater the torque for creating the rotation.

Push onFloor

ReactionForce

LeverArm

Feet apart(Easy)

Feet together(Harder)

Fouetté (Whipped) Turns

Done properly, the dancer returns to the same spot at the end of the turn.

A turn executed with a quick thrust of the moving leg as it passes in front of or behind the supporting leg.

http://www.youtube.com/watch?v=TV-N0QWyeac

Torque for Fouetté Turns

Push onFloor

ReactionForce

LeverArm

Lower heel to the floor

Push off while swinging right leg

Lift heel and return to point

The torque first creates a rotation of the arm & leg, then whole body rotates together

Fantasia (1940)

The Dance of the Hours from Disney’s Fantasia is the most famous ballet scene in animation.

http://www.youtube.com/watch?v=0pbQdtkbCcQ

Tipping and Torques

Slowing out as an object tips over is due to the torque created by the force of gravity.

X

LeverArm

GravityForce

As the tipping angle increases, the lever arm increases so the torque (and acceleration) increase as well.

Slowing In and Slowing Out

X

If brick is not moving…

…then it slows out as it tips over

X

If brick is moving upward…

…then it slows in as

it tips upward

The lever arm changes with angle so the timing of this slowing in or slowing out has a lot of texture.

LeverArm

LeverArm

Horizontal Support

This character’s center of gravity is not over her base of support.

She does not tip over backwards (counter-clockwise rotation) since the wall exerts a torque in the clockwise direction, balancing the torque due to the gravity force.

Wall force

Lever

Arm

Gravity

Lever arm

Line of Gravity

X

Mechanical Lever

Lever converts an effort force into a load force by ratio of distances acting.

Push down with a small effort force over a large distance

Lift a large load weight over a small distance

Axis of rotation goes through the fulcrum point.

Fulcrum

First Class Levers

Fulcrum

Effort ArmLoadArm

Lift a heavy load using small effort by having a long effort arm and/or short load arm.

First Class Lever: Fulcrum is located in between the input force (effort) and output force (load).

Efficiency vs. Speed

EffortLoad

Fulcrum

Effort

Load

Fulcrum

Efficient but slow

Inefficient but fast

Examples of First Class Levers

Crowbar

Scissors

Trebuchet

Effort Load

Fulcrum

Crowbar and scissors are efficient (big load force) but slow (long effort distance).

Trebuchet inefficient (big effort force) but fast (long load distance).

Second Class Levers

Lift a heavy load using small effort by having a long effort arm and/or short load arm.

Second Class Lever: Load is located in between the effort force and the fulcrum.

Effort Arm

LoadArm

Fulcrum

Examples of Second Class Levers

Wheel Barrow

EffortLoad

Fulcrum

Hole Punch

Second class levers are always efficient and slow.

Third Class Levers

Third Class Lever: Effort force is located in between the load and the fulcrum.

Effort Arm

LoadArm

Second class levers are always inefficient but fast (since load arm is longer than effort arm).

Examples of Third Class Levers

Effort

Load

Fulcrum

BroomJaw

Human Arm as a LeverBiceps muscle exerts effort force close to your elbow (fulcrum) to raise your forearm (load).This is what type of lever?

A)First classB)Second classC)Third class

Human Arm as a LeverBiceps is a third class lever so a large effort force acts over a small distance to move a small load over a large distance.

Triceps is also a third class lever, which pulls the arm in the opposite direction.Because muscles can only

contract, they’re almost always found in pairs, like biceps/triceps.

EffortLoad

Human Foot as a Lever

Effort

Load

Fulcrum

To lift the body on the toes, the gastrocnemius (one of the strongest muscles in the body) contracts, lifting the heel upward.

This is an example of a second class lever.

Raising heel, as in walking.

Weight Shift

Effort

Load

Fulcrum

Weight shift forward shortens the load arm, reducing the required effort to lift the heel.

Effort

Load

Fulcrum

Line of Gravity Line of

Gravity

Human Neck as a Lever

Load

Fulcrum

In general, the levers in animals’ bodies sacrifice efficiency for speed and to keep a compact body form.

The neck muscles are the body’s only first class lever This lever is not efficient since the effort arm is shorter than the load arm. Effort

Action/Reaction for TorquesFor every action force there is an equal and

opposite reaction force.

Similarly, the action and reaction torques, caused by these forces, are equal.

Accelerations from these torques dependon objects’ rotational inertia.

If the action torque creates a clockwise rotation, the reaction creates a counter-clockwise rotation (and vice versa).

Action/Reaction for Torques

Weightlifter exerts an action torque on the weights, rotating them counter-clockwise.

The weights exert a clockwise reaction torque, pulling the weightlifter forward.

Action

Reaction

Fouetté Turns, Analyzed

1

2

3

4

5

6

The torque from pushing off gives angular momentum to the right arm and leg, which rotate freely from #1 to #4.

Then the right arm and leg are made to rotate back in the opposite direction.

By action/reaction, the torso recoils and rotates in the original direction.

1

2

3

4

5

6

Anchors Aweigh (1945)The musical Anchors Aweigh has a famous scene in which Gene Kelley dances with Jerry the Mouse. The scene

climaxes with a series of fouetté turns.

http://www.youtube.com/watch?v=xRMGRpDCW6k

Next LectureWaves Part I

Homework 9 (Reverse Video Reference)

Due this WednesdayHomework 10 (Character Animation)

Due Wed., Nov. 3rd (In two weeks)Please turn off and return the clickers!