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)
Please turn off and return the clickers!