Upcoming Deadlines

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Upcoming Deadlines
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• Sixth Homework (Stop-motion Animation)
• Due Wednesday, March 3rd (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 Wednesday, March 10th (In two weeks)
• 10 points (5 points if late)
• For full schedule, visit course website
• ArtPhysics123.pbworks.com

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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.

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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.

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Demo of SAM Software
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Homework Assignment 6

• While 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 Wednesday, March 3rd.
• 20 points (if late, 10 points)
• The top three animation clips in the class will
  receive a bonus of 20 extra points.

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Survey Question
You have some experience with creating
stop-motion animation. True or False?
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The League of Extraordinary Gentlemen (2003)
http//www.youtube.com/watch?vn8SDdkKSqns
In this scene, Sean Connery jumps out the side of
a speeding car and lands on his feet.
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The League of Extraordinary Gentlemen (2003)
In this scene, Sean Connery jumps out the side of
a speeding car and lands on his feet. In reality,
he would

1. Roll forward from where he lands, in the
   direction of the moving car.
2. Roll backwards from where he lands.
3. Land just as he does in the movie this was
   actually done by a stuntman.

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Jumping out of a Car
A) Roll forward You are moving at the same speed
as the car when you jump out so you will roll
forward.
Your path
car
Youll start losing speed after you hit the
ground so, relative to the car, youll fall
behind as the car continues speeding along.
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Review Question
A golf ball and a ping pong ball are about the
same size golf ball is heavier. Drop both from
the roof of a 10 story building. What happens?

1. Balls hit the ground at the same time and hit the
   ground with the same speed.
2. Balls hit the ground at the same time but the
   golf ball has a higher speed.
3. The golf ball hits the ground first but they both
   hit the ground with the same speed.
4. Golf ball hits the ground first and it also has a
   higher speed.

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Review Question
Ping pong Ball
Golf Ball
D) Golf ball hits the ground first and it also
has a higher speed. The terminal speed of the
ping pong ball is much slower that that of a golf
ball so the golf ball falls faster, which also
means it reaches the ground first.
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Creating ActionPart II
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Newtons 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
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Demo Spool

• Pull on string wrapped around a spool.
• Force is to the right-to-left.
• In what direction does the spool move?

Pull
Pull
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Force and Direction

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

Motion
Motion
Pull
Motion
Pull
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Demo Tricycle

• Pull on tricycle pedal with a string.
• Which direction does the tricycle move?

Pedal in bottom position
Pedal in top position
Pull
Pull
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Forces Slowing In/Out
FALLING BALL
When a force pulls in the direction that an
object is already moving, the object slows out
(accelerates)
Moving this way
Force
RISING BALL
If a force pushes opposite to the direction of
motion then the object slows in (decelerates)
Moving this way
Force
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Forces Path of Action
When a force is perpendicular to the path of
action then it deflects the motion into an arc.
If force is at an arbitrary angle then both
timing and path of action are affected.
Force (up left)
Moving this way
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More Force, More Acceleration

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

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Simple Addition of Forces

• When two forces pull in parallel directions its
  simple to add them to get the total force.

Total Force
Gravity (Weight)
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
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Air Resistance on a Falling Object
Gravity force on an object (i.e., weight) is
constant but air resistance depends on an
objects 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)
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More Mass, Less Acceleration

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

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Demo Bowling Ball in a Bag

• Can slowly lift a plastic bag holding a bowling
  ball by exerting only a little more force than
  the weight of the ball.
• If we try to lift the bag quickly, this large
  acceleration requires a very large force.
• If we pull up too quickly then this large force
  will break the handle.

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Motion Graphs - Speed
Greater the speed, steeper the slope.
Fast
Distance
Slow
Frame
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Motion Graphs - Acceleration
Greater the acceleration, greater the curvature.
Big Acceleration
Distance
SmallAcceleration
Frame
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Increments Acceleration
In the Odd Rule, the spacings get bigger with
time and always by the same amount. That is, the
increment from one spacing to the next is always
the same (red arrow). Since the spacings tell
you the speed, if the spacings get larger and
larger then the moving object is
accelerating. The increment tells you the
acceleration. The acceleration due to gravity is
constant (since the increment is always the same).
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Differential Calculus
The difference between the positions of the ball
is the spacing, which gives the speed.
The difference between the spacings is the
increment, which gives the acceleration.
You now know basic differential calculus.
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Law of Acceleration

• If the total force equals the objects 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.

The bigger the friction force, the quicker the
timing (shorter the spacings).
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Atmospheric Pressure
We live at the bottom of an ocean of fluidthe
fluid is air ocean is the atmosphere.

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

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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.

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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)
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Total Recall (1990)
http//www.youtube.com/watch?vILqe_mmtBrE
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Demo Can Crush

• Pour small amount of water into an empty soda
  can.
• Heat water to boiling.
• Quickly transfer the can, upside-down, into a pan
  of cold water.
• Soda can is quickly crushed.

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Can Crush, Analyzed
Cool the can and steam condenses back into water,
leaving almost a vacuum inside. Low pressure
inside and atmospheric pressure outside.
Boil the water and inside of the can fills with
steam, pushing out the air.
Atmospheric Pressure
A
A
L
Steam
Low Pressure
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Crush the Rail Tanker Car
The interior of the tank car was washed out
cleaned with steam. Then all the outlet valves
were shut and the tank car was sealed. All the
workers went home for the evening and when they
returned, this is what they found. Apparently as
the tank car cooled, it collapsed. The shell on
these tank cars is 7/16th inch thick steel.
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Demo Boyles Law

• The pressure in a gas increases when the gas is
  compressed.
• When a gas expands, the pressure decreases.

Gauge
Syringe
Tank
Compress the gas by pushing in the syringe. Dial
gauge shows increase in pressure.
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Breathing Boyles Law
A
A
H
L
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Pressure Air Resistance
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
createdin the wake.
LOW PRESSURE
L
HIGH PRESSURE
H
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Ground-effect Cushion
Moving this way
L
L
LOW PRESSURE
H
H
HIGH PRESSURE
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 wont occur with an irregular leaf
or with a rough surface.
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Sailing Ships
The wind blowing on a sail also produces a
pressure difference, creating the force that
moves the ship.
H
L
Wind
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Buoyancy
The buoyant force pushing submerged objects
upward is also due to a pressure difference.
L
H
43
Prairie Dog Vacuum

• Prairie dogs captured by giant vacuum truck with
  a padded bin.

44
Vacuum Cleaner Force
As with any vacuum cleaner, its the difference
of pressure that creates the net force pushing
objects towards the low pressure side.
A
L
Force
Truck
A
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Vector Addition of Forces

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

Force A
Object
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Sliding Sideways
Air Pressure Force

• If leaf/paper is tilted then it slides sideways.

Slides this way
Gravity
Picks up speed (slows out) as it slides down, as
if it were sliding down an incline.
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Timing and Spacing, Up Down
When it rises due to lift it loses speed (slows
in).
When the leaf/paper slides downward, it picks up
speed (slows out).
Imagine riding a roller coaster.
With no wind
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Roller Coaster Timing
49
Aerodynamic Lift

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

Lift
Lift
Wing
Moving this way
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Bernoullis Principle

• Where the speed of a fluid increases the pressure
  in the fluid decreases.
• This phenomenon is due to energy conservation
  when fluids kinetic energy increases (velocity
  increases) its internal potential energy
  (pressure) decreases.

Still Air
A
Wind
L
51
Home Demo Blow It Up

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

L
A
Low pressure on top Average pressure on bottom
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Class Demo Blow the Funnel
BLOW

• Blow hard through a funnel with a ping pong ball
  in the funnels bowl.
• Instead of being blown away, the ball is held
  tightly in the bowl.

Ping Pong Ball
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Blow the Roof
If wind blows hard enough the low pressure above
can create a large enough force to lift the roof
off.
L
A
New Orleans Superdome after hurricane Katrina
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Aerodynamic Lift

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

Also get lift if leaf/paper is curled like a wing.
Lift
Air Resistance
Moving this way
Gravity
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Effect of Lift
Lift requires tilt and speed no lift if paper/
leaf is not moving
Lift
Path of action deflected by lift.
Lift force can also deflect the path of action
downward, depending on the tilt angle of the
leaf/paper.
No Lift
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Demo Throwing You a Curve

• Putting a spin on a thrown baseball causes the
  airflow to be faster on one side than the other,
  which creates a pressure difference.

L
No Spin
Spin
L
Bernoulli
Forward Motion
H
L
Depending on the axis of rotation this could be a
rising fastball, a sinker, or a curve ball.
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Next LectureSquash Stretch

• By Wednesday of next week
• Complete the 6th homework
• (Stop-motion Animation of Falling)

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