Upcoming Deadlines

Ninth Homework (Stop-Motion Animation)Due Wednesday, October 28th (This week)

Tenth Homework (Outline of Second Paper)Due Wednesday, November 4th (Next week)

Second Term PaperWednesday, November 25th (Day before Thanksgiving; no class that day)

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

Extra Credit Opportunity

Survey Questions:1. What do you like most about the course?2. What do you dislike most about the

course?3. What changes would you suggest?4. Do you have any other comments?

Complete anonymous online survey by October 30th; five points extra credit.

Go to course website for link to survey.After completing survey, follow the instructions to receive extra credit.

Extra Credit Opportunity

Survey Questions:1. What do you like most about the course?2. What do you dislike most about the

course?3. What changes would you suggest?4. Do you have any other comments?

Complete anonymous online survey by October 30th; five points extra credit.

Go to course website for link to survey.After completing survey, follow the instructions to receive extra credit.

Opportunity Ends This Friday!

Homework Assignment #9Create a simple stop-motion animation of a moving

character. See course website for software options for creating this

animation.Make the character’s motion look as real and seem as believable

as you possibly can.Due by 8am on Wednesday, October 28th.20 points (if late, 10 points)The top three clips in the class will receive a bonus of 20 extra

points.

Homework Assignment #10

Outline of your Second Term Paper.Topic: Science Fact or Cinematic Fiction?

For this assignment, you will select an animation film (or a live-action film featuring CGI animation special effects) and critique the elements in one scene that are physically unrealistic.

For example, you can describe how the action/reaction principle is violated during a fight sequence, such as when one character recoils but without a matching reaction on the other character.

Homework Assignment #10

Your analysis must describe at least three distinct physical principles that are incorrect in your selected scene.

Alternatively, you may choose a single physics principle, such as conservation of energy, and describe three scenes (possibly from different films) that incorrectly illustrate that principle.

Post your outline in a blog entry entitled, “Outline for the Second Term Paper.”

Outline due by 8am on Wednesday, November 4th.10 points (if late, 5 points)

Activating your Clicker

* Turn on your clicker.* Enter the number or letter that I give

you for joining this class. Hit Enter/Send key.

* Clicker should read PHY123SCI2* Type in your student ID; hit Enter/Send.Clicker is now ready to use.Hit any key to wake the clicker from sleep mode.

WalksPart II

Ray HarryhausenRay Harryhausen, the master of stop-motion animation, created the special effects in many films from the 1940’s to the 1970’s

One of his best scenes in the skeleton battle in Jason and the Argonauts

Energy Budget (Inanimate)Moving objects have an energy budget.For inanimate objects, this budget is:

Kinetic Energy (K) – Energy due to their speedPotential Energy (P) – Energy due to their heightFriction Loss (F) – Energy lost due to friction forces

K = 0P = 100F = 0

K = 20P = 70F = 10

K = 40P = 40F = 20

Total Energy = 100

Demo: Ball RacesMarbles start at equal height and race on

these rail tracks (almost no friction).Track B has a long dip in the center.

Winner? A) Ball A; B) Ball B; C) Near perfect tie.Hint: Kinetic energy + Potential energy stays constant.

Demo: Ball Races

B) Ball B is the winner.

K = 0P = 100F = 0

K = 50P = 50F = 0

K = 50P = 50F = 0

K = 50P = 50F = 0

K = 50P = 50F = 0

K = 100P = 0F = 0

K = 50P = 50F = 0

Ball B has a high speed in the center section.

Energy Budget, Bouncing

K = 45P = 5F = 0

K = 50P = 0F = 0

K = 36P = 4F = 10

Kinetic EnergyPotential EnergyFriction Losses

Total Energy = 50

Energy Budget, Sack DropK = 0P = 200F = 0

K = 0P = 0F = 200

K = ???P = 100F = 5

Kinetic EnergyPotential EnergyFriction Losses

Flour sack sitting on a shelf starts with potential energy.

After it settles, all the energy is lost to friction forces.

What is the kinetic energy when fallen half-way down?

A) ZeroB) 200C) 100D) 95E) 105

(Air resistance)

Energy Budget, Sack DropK = 0P = 200F = 0

K = 0P = 0F = 200

K = 95P = 100F = 5

Kinetic EnergyPotential EnergyFriction Losses

D) 95

The total budget (K+P+F) has to equal 200.

If there was no air resistance then the falling speed would be greater and K=100.

With more air resistance, the friction loss would be greater and kinetic energy less.

(Air resistance)

Energy Budget (Animate)Animate objects can increase their energy budget by doing work.

Work Input (W) – Energy added by doing work.

K = 0P = 0F = 0W = +0

Kinetic EnergyPotential EnergyFriction LossesWork Input

K = 100P = 0F = 10W = +110

K = 300P = 0F = 20W = +320

Energy Budget in Jumping

K = 0P = 50F = 0W = 0

K = 200P = 100F = 50W = +350

K = 145P = 150F = 55W = +350

K = 90P = 200F = 60W = +350Leg muscles

do work as you push off when jumping.

Slow down as you rise to apex so kinetic energy (K) goes down.

Most of the friction loss is during push but a little loss due to air resistance.

Energy Budget in Walking

K = 100P = 100F = 500W = +500

K = 100P = 100F = 0W = +0

Walking takes work due to all the frictional losses.

Muscle Activity, Moving Leg

Muscles in the moving leg accelerate it forward after toe-off and decelerate at the heel strike. Also hold the foot up.

From Dynamics of Human Gait, by Vaughan, Davis, O’Connor Activity: High ; Medium ; Low

Muscle Activity, Planted Leg

For the planted leg there is relatively little muscle activity in the middle of the passing position.

From Dynamics of Human Gait, by Vaughan, Davis, O’Connor Activity: High ; Medium ; Low

Home Demo: Silly WalksTry walking around as John Cleese, the Minister of Silly Walks.

You will find that you use much more energy than normal walking.

Simplified Walking ModelPelvis is a double-forked bar with spherical hip joints. Legs are straight bars without knees, ankles, or feet.

Center of gravity rises and falls as an inverted pendulum.

CG

CG

Passing Position

Passing Position

Stride

Stride

Passing Position

Walking Forward

We have to do work to raise the CG and much of that energy (30-40%) is lost to friction.

Pelvic RotationAs the passing leg swings forward, the hips swing around, rotating about the planted leg.

WithoutRotation

WithRotation

Pelvic Rotation & Center of GravityBy permitting the pelvis to rotate from left-to-right (and right-to-left) the center of gravity does not fall as far during the stride.

CGStride

Passing Position

Passing Position

Passing Position

Stride

CG

Walking is more efficient with pelvic rotation.

Path of Action ofCG with Rotation

Without Rotation

Walki

ng Forw

ard

Pelvic ListIn the passing position the pelvis drops slightly to the non-weight bearing side. This motion is called “pelvic list.”

Note that the knee has to bend to lift the foot, otherwise it would drag the ground.

Pelvic List & Center of Gravity

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

Knee Flexion of Weighted Leg

Knee flexes about 15 degrees immediately after heel strike and remains flexed until the center of gravity passes over the weight bearing leg.

Walki

ng Forw

ard

Knee FlexionKnee flexion keeps the center of gravity from rising as much during the passing position.

Knee flexion also reduces the impact on the body at heel strike.

CG

Stride

Passing Position

Passing Position

Passing Position

Stride

CGPath of Action of CG without Flexion

With Flexion

Walki

ng Forw

ard

Walking is more efficient with knee flexion.

8-Loop & U-Loop

The center of gravity shifts up & down but 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

Stride WidthShifting the center of gravity from left to right requires work so a wide stride is less efficient.

Step Length

When walking, why don’t we take longer (or shorter) steps?We naturally adjust our step length to minimize the energy output required to maintain our desired walking speed.

Step length

Energy is required to:

• Move the leg forward in the stride; longer steps take less energy.

• Raise the body in the passing position; longer steps take more energy.

Move

Raise

XCGXCG

Energy & Step Length

Optimum Step Length

Work

don

e p

er

min

ute

Step Length (meters)

Treadmill data of metabolic rate while walking at 2½ mph

Optimum Step

Length

Longer Steps, Slower

Cadence

Shorter Steps,

Quicker Cadence

The body adjusts the step length to minimize the total energy expended while maintaining desired speed.

Shoulder RotationThe shoulders rotate opposite from the hips, swinging over the planted leg.

Fashion Runway Walk

The walk of a fashion model on a runway exaggerates the pelvic and shoulder rotation as well as the pelvic list.

Arm Swing

The arm swings back and forth, also like a pendulum, roughly 180o out of phase with the leg. The arm and leg are roughly the same length so they swing back and forth with about the same period.

Angular Momentum Balance

It takes less effort if you balance the rotation of the lower body with an opposite rotation of your upper body.

Moving your legs (and hips) as you walk requires a torque (rotational force) to turn them.

Home Demo: The TwistTry dancing The Twist the normal way (moving hips and shoulders in opposite directions). Now try to dance it moving hips and shoulders together, back and forth.

Play

Skeleton Battle Scene

Now that we’ve broken down the mechanical elements of walking, lets it watch again.

Quadruped Animal Walking

Walking for animals is very different than for humans, not so much because they walk on 4 legs but due to bone structure.

AT-AT WalkersIndustrial Light & Magic (ILM) filmed the AT-ATs using stop-motion animation with models from 2 inches to 2 feet in height.

Walking mimics elephants

Star Wars Episode V: The Empire Strikes Back

Shoulder, Elbow, WristFront legs of mammals have the same joints but bones are of various lengths.

From Chuck Amuck: The Life and Times of an Animated Cartoonist By Chuck Jones

Shoulder

Elbow

Wrist

Horse Human Dog Cat ???

Tennis Shoes & Stripped Socks

From Chuck Amuck: The Life and Times of an Animated Cartoonist By Chuck Jones

Chuck Jones presents a good way to remember animal anatomy: Tennis shoes & Stripped socks.

Knee

Ankle

Sole

Sole, Ankle, Knee

From Chuck Amuck: The Life and Times of an Animated Cartoonist By Chuck Jones

Knee

Ankle

Sole

Knee

Knee

Ankle

Ankle

Sole

Sole

HorseHuman Dog

What you think is the “knee” on the hind leg is actually the ankle.

Energy in Four-legged WalksH

eig

ht

x x x x x

Center of Gravity

Four-legged walking gait alternates passing position and stride between fore and hind legs to minimize energy required to lift the center of gravity.

The Journal of Experimental Biology 207, 3545-3558 (2004)

Next LectureEffects Animation

Homework 9 (Stop-motion Animation)Due Wednesday, October 28th

Please return the clickers!