Upcoming Deadlines

Sixth Homework (Stop-motion Animation)Due Tuesday, February 28th (Next week)20 points (if late, 10 points)Bonus prize of 20 extra points to top three.

Seventh Homework (Outline of First Term Paper)Due Tuesday, March 6th (In two weeks)10 points (if late, 5 points)

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

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

Homework Assignment #6

In this assignment you will create a stop-motion animation of a falling object.

It can be a simple as a ball bounce cycle or (preferably) something more interesting, like a flour sack or a water balloon.

Because you will have to pose your object at different heights, you'll either need to suspend it from a string or have the motion occur on the ground with the camera positioned directly overhead.

Homework Assignment #6

If you have a webcam, an easy way to film a stop-motion animation is to use SAM Animation (http://www.samanimation.com/).

It's free software that runs on both Macs and PCs; it was developed at Tufts University as part of a National Science Foundation project for teaching using animation.

The software is designed so that it can be used by even elementary school children so you shouldn't have much trouble figuring it out.

Homework Assignment #6

Homework Assignment #6While I encourage you to help each other out, for this

assignment each person needs to create their own animation.

Finally, describe in a brief paragraph how you created your animation. Post your animation clip to your blog in an entry entitled "Stop Motion Animation of Falling.“

Due by 8am on Tuesday, February 28th

20 points (if late, 10 points)

The top three animation clips in the class will receive a bonus of 20 extra points.

Extra Credit Opportunity

Academy Award Nominated Animated Short Films

Camera 3 theater in downtown San Jose

Turn in your ticket stub for 5 points extra credit.

Extra Credit Opportunity

Art of Dreamworks’ Puss in Boots at the Cartoon Art Museum in San Francisco.

For info: cartoonart.org

Turn in proof of your attendance to this exhibition (e.g., ticket receipt) for 10 points extra credit.

Extra Credit Opportunity

See Chico and Rita, now playing at Camera 12 in downtown San Jose.

Turn in your ticket stub for 5 points extra credit.

Survey Question

You have some experience with creating stop-motion animation.

True or False?

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=n8SDdkKSqns

A) Roll forward from where he lands, in the direction of the moving car.

B) Roll backwards from where he lands.

C) Land just as he does in the movie; this was actually done by a stuntman.

Review QuestionIn this scene, Sean Connery jumps out the side of a speeding car and lands on his feet. In reality, he would:

A) 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

Your path

You’ll start losing speed after you hit the ground so, relative to the car, you’ll fall behind as the car continues speeding along.

car

Review QuestionThe accident-prone Wile E Coyote walks off a cliff carrying an anvil.

If he lets go of the anvil, he’ll fall:

A)SlowerB)FasterC)At the same speed

Wile E Coyote with Anvil

The answer is:A)Slower

You 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).

Creating ActionPart II

Newton’s Laws of Forces

Newton established three basic laws to explain how motion is caused by forces:

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

The Law of Inertia explains motion without forces (or with only balanced forces).The Law of Acceleration explains motion with unbalanced forces.

Sir Isaac Newton

Demo: Spool

Pull on string wrapped around a spool.

Force is to the right-to-left.

In what direction does the spool move?

Spool moves?

Pull

Pull

Spool moves?

Force and Direction

Objects always change their velocity in the direction of the applied force.

Pull

PullMotion

Motion

Motion

Demo: Tricycle

Pull on tricycle pedal with a string.

Which direction does the tricycle move?

Bike moves? Bike moves?

PullPull

Pedal in top position

Pedal in bottom position

Demo: Tricycle

Notice that the position of the lower pedal moves forward as the wheel is turning.

CLICK

Forces & Slowing In/Out

When a force pulls in the direction that an object is already moving, the object slows out (accelerates)

If a force pushes opposite to the direction of motion then the object slows in (decelerates)

Force

Moving this way

Force

Moving this way

Forces & Path of Action

When a force is perpendicular to the path of action then it deflects the motion into an arc.

Force(up & left)

Moving this way

If force is at an arbitrary angle then both timing and path of action are affected.

More Force, More Acceleration

The greater the net force on an object, the greater the acceleration of that object.

Simple Addition of ForcesWhen two forces pull in parallel directions it’s

simple to add them to get the total force.

Gravity (Weight)

Air Resistance

Total Force

For example, if a bubble weighs 3 oz and air resistance is a force of 2 oz then the total force is 1 ounce.

Air Resistance on a Falling Object

Gravity force on an object (i.e., weight) is constant but air resistance depends on an object’s speed.

As a falling object gains speed, the resistance force gets larger so the net force decreases.

Net force is sum of:Weight (downward)Resistance (upward)

Net Force100 lbs.

Net Force20 lbs.

Net ForceZero

More Mass, Less Acceleration

The greater the mass of an object, the less it accelerates when acted on by a force.

Motion Graphs - Speed

Fast

Slow

Frame

Dis

tanc

e

Greater the speed, steeper the slope.

Motion Graphs - Acceleration

Big Acceleration

SmallAccelerationFrame

Dis

tanc

e

Greater the acceleration, greater the curvature.

Speed & Acceleration

The change in the spacings gives the acceleration.

The spacing between positions gives the speed.

Odd Rule & Forces

The Odd Rule applies if forces are constant.

Forces here are constant; the support force by the ground balances the weight, leaving only the friction force.

Support

Friction

Gravity (Weight)

Apex

135

Law of Acceleration (F=ma)If the total force equals the object’s weight then

the spacing is the same as when falling.

If the total force is greater than the weight then the spacings and increments are larger.

If the total force is less than the weight then the spacings and increments are shorter.

Bigger the frictional force, the quicker the timing (spacings change quickly).

Ice block

Brick

Complex Path of Action

http://www.youtube.com/watch?v=mbMo4HFJC1Y

Let’s look further into why a leaf drop has such a complex path of action.

Timing and Spacing, Up & Down

When the leaf/paper slides downward, it picks up speed (slows out).

* With no windImagine riding a roller coaster.

When it rises due to lift* it loses speed (slows in).

Atmospheric Pressure

The weight of the air above us creates atmospheric pressure, a force of about 15 pounds per square inch.

We live at the bottom of an ocean of fluid—the fluid is air & “ocean” is the atmosphere.

Demo: Magdeburg Hemispheres

Pair of hemispheres fit together with air-tight seal

Most of the air is pumped out from the interior.

Air pressure holds the two pieces tightly together.

A A

AA

L

A

L

- Atmospheric pressure

- Low pressure

Demo: Peeps in a Vacuum

Before vacuum pump is turned on (normal atmospheric pressure)

After vacuum pump is turned on (very low air pressure in chamber)

After vacuum pump is removed (back to normal atmospheric pressure)

Total Recall (1990)

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

Buoyancy

A

Buoyant force pushing submerged objects upward is also due to a pressure difference.

HHIGH PRESSURE

ATMOSPHERIC PRESSURE

HHIGHER PRESSURE

H

The pressure increases with depth due to the weight of the liquid.

Demo: Neutral Buoyancy Balloon

Tie a helium balloon to a long string and allow it to float upward until it can lift no more string.

Cut the string where it touches the floor.

Weight of balloon and string exactly balance the buoyant force.

Demo: Boyle’s Law

The pressure in a gas increases when the gas is compressed.

When a gas expands, the pressure decreases.

Compress the gas by pushing in the syringe. Dial gauge shows increase in pressure.

SyringeGauge

Tank

Breathing & Boyle’s Law

L

A A

H

Demo: Drinking Straw

L

A A

With lungs, you reduce pressure in your mouth and in the straw.

The higher pressure on the outside pushes the liquid up the straw.

Force due to the pressure difference must match or exceed the weight.

Weight

NO “SUCKING” FORCE

Prairie Dog VacuumPrairie dogs captured by giant

vacuum truck with a padded bin.

The Curse of the Were-Rabbit (2005)

Vacuum Cleaner Force

L

AForce

As with any vacuum cleaner, it’s the difference of pressure that creates the net force pushing objects towards the low pressure side.

Truck

A

Fluid Flow and Pressure

Pressure varies when air is moving and we see this effect in the flapping of a flag and the ocean waves kicked up by a strong wind.

These pressure variations are primarily not due to changes of density or temperature.

In fact, most fluid simulations assume air to be incompressible and at constant temperature.

Pressure & Air Resistance

L

H

Force of air resistance is due to a difference in pressure.

High pressure buildsby compression in front of a falling object while low pressure is created in the wake.

HIGH PRESSURE

LOW PRESSURE

Sailing Ships

L

The wind blowing on a sail also produces a pressure difference, creating the force that moves the ship.

H

Wind

Ground-effect Cushion

Flat sheet sliding over a smooth surface compresses the air beneath it and forms a low-friction cushion, allowing it to slide.

This ground-effect won’t occur with an irregular leaf or with a rough surface.

Moving this way

HIGH PRESSURE

LOW PRESSURE L

HH

L

Paper Drop Test

http://www.youtube.com/watch?v=vKf-vIDSIik

Parallelogram rule

Vector Addition of Forces

Two forces pulling an object are equivalent to a single total force.

Object Force A

Force B

Net ForceA + B

Sliding Sideways

If leaf/paper is tilted then it

slides sideways.

Air Pressure Force

Gravity

Slides this way

Picks up speed (slows out) as it slides down, as if it were sliding down an incline.

Aerodynamic Lift

If airflow is faster over one side than the other then a pressure difference develops, creating aerodynamic lift.

Wing

Moving this way

Lift Lift

Aerodynamic Lift

If leaf/paper is tilted relative to its path of action then there is also an aerodynamic lift.

Air Resistance

Gravity

Moving this way

Lift Also get lift if leaf/paper is curled like a wing.

Effect of Lift

Path of action deflected by lift.

Lift

No Lift

Lift force can also deflect the path of action downward, depending on the tilt angle of the leaf/paper.

Lift requires tilt and speed; no lift if

paper/ leaf is not moving

Bernoulli’s Principle

Where the speed of a fluid increases the pressure in the fluid decreases.

This phenomenon is due to energy conservation; when fluid’s kinetic energy increases (velocity increases) its internal potential energy (pressure) decreases.

A

L

Still Air

Win

d

Home Demo: Blow It Up

Hold a sheet of paper in front of your mouth and blow; the paper will rise.

L

ALow pressure on top; Average pressure on bottom

Waves and Bernoulli’s PrincipleWind blowing over the ocean causes waves to build due

to Bernoulli’s principle.Where is the pressure lowered?

L

A

L

A A

Air moves fastest at the tops of the waves so pressure is lowest there.The lower portion of the wave is blocked from the wind so air above the water is at atmospheric pressure.

Blow the Roof

If wind blows hard enough the low pressure above can create a large enough force to lift the roof off.

New Orlean’s Superdome after hurricane Katrina

L

A

Aerodynamics for Race Cars

Airfoil on a race car is an upside-down wing that increases traction (friction) by increasing downward pressure.

Demo: Throwing You a CurvePutting a spin on a thrown baseball causes the airflow to be faster on one

side than the other, which creates a pressure difference.

No Spin

Forward Motion

L

LL

H

Bernoulli

Spin

Depending on the axis of rotation this could be a rising fastball, a sinker, or a curve ball.

Curveball Flow Pattern

L

H

Class Demo: Blow the Funnel

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.

PingPongBall

BLOW

L

A

L

Home Demo: Keep It Up (cont.)Bernoulli effect keeps the ball in the middle of the air

stream.

LA

L

A

AA

Next LectureSquash & Stretch

By Tuesday of next week:Complete the 6th homework

(Stop-motion Animation of Falling)

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