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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
Homework Assignment #6
In this assignment you will create a stopmotion 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 stopmotion 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 #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 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.
Turn in proof of your
attendance to this
exhibition (e.g., ticket
receipt) for 10 points
extra credit.
For info: cartoonart.org
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)
http://www.youtube.com/watch?v=n8SDdkKSqns
In this scene, Sean Connery jumps out the side of a
speeding car and lands on his feet.
Review Question
In this scene, Sean Connery jumps out the side of
a speeding car and lands on his feet. In reality, he
would:
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.
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
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.
Review Question
The accident-prone
Wile E Coyote walks
off a cliff carrying an
anvil.
If he lets go of the
anvil, he’ll fall:
A) Slower
B) Faster
C)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 Action
Part 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
Sir Isaac Newton
The Law of Inertia explains motion without forces
(or with only balanced forces).
The Law of Acceleration explains motion with
unbalanced forces.
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?
Spool moves?
Pull
Pull
Force and Direction
Objects always change
their velocity in the
direction of the
applied force.
Pull
Motion
Motion
Pull
Demo: Tricycle
Pull on tricycle pedal with a string.
Which direction does the tricycle move?
Pedal in
bottom
position
Pedal in top
position
Bike moves?
Bike moves?
Pull
Pull
Demo: Tricycle
Notice that the position
of the lower pedal
moves forward as the
wheel is turning.
CLICK
Forces & Slowing In/Out
B
A
L
L
F
A
L
L
I
N
G
When a force pulls in the direction that an object is
already moving, the object slows out (accelerates)
Moving
this way
Force
If a force pushes opposite to the direction of motion
then the object slows in (decelerates)
B
A
L
L
Force
R
I
S
I
N
G
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.
If force is at an arbitrary angle then both
timing and path of action are affected.
Force
(up & left)
Moving
this way
More Force, More Acceleration
The greater the net force on an object, the
greater the acceleration of that object.
Simple Addition of Forces
When two forces pull in parallel directions it’s
simple to add them to get the 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.
Total
Force
Air Resistance
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 Force
100 lbs.
Net Force
20 lbs.
Net Force
Zero
More Mass, Less Acceleration
The greater the mass of an object, the less it
accelerates when acted on by a force.
Distance
Motion Graphs - Speed
Greater the speed, steeper
the slope.
Fast
Slow
Frame
Distance
Motion Graphs - Acceleration
Greater the acceleration,
greater the curvature.
Frame
Big Acceleration
Small
Acceleration
Speed & Acceleration
The spacing between
positions gives the
speed.
The change in the
spacings gives the
acceleration.
Odd Rule & Forces
The Odd Rule applies if forces are constant.
5
Support
3
1
Apex
Friction
Gravity
(Weight)
Forces here are constant; the support force by the ground
balances the weight, leaving only the friction force.
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.
Ice block
Brick
Bigger the frictional force, the quicker the timing (spacings change quickly).
Complex Path of Action
Let’s look further into
why a leaf drop has
such a complex path
of action.
http://www.youtube.com/watch?v=mbMo4HFJC1Y
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
Atmospheric Pressure
We live at the bottom of an ocean of fluid—
the 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.
Demo: Magdeburg Hemispheres
Pair of hemispheres
fit together with airtight seal
Most of the air is
pumped out from
the interior.
Air pressure holds
the two pieces
tightly together.
A
A
L
A
A
A - Atmospheric pressure
L - 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
Buoyant force pushing submerged objects
upward is also due to a pressure difference.
A
AT M O S P H E R I C P R E S S U R E
H
The pressure increases
with depth due to the
weight of the liquid.
H
HIGH PRESSURE
HIGHER PRESSURE
H
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.
Gauge
Syringe
Tank
Compress the gas by
pushing in the syringe.
Dial gauge shows
increase in pressure.
Breathing & Boyle’s Law
A
L
A
H
Demo: Drinking Straw
With lungs, you reduce
pressure in your mouth and
in the straw.
L
The higher pressure on the
outside pushes the liquid up
the straw.
A
Weight
A
Force due to the pressure
difference must match or
exceed the weight.
NO “SUCKING” FORCE
Prairie Dog Vacuum
Prairie dogs captured by giant
vacuum truck with a padded bin.
The Curse of the Were-Rabbit (2005)
Vacuum Cleaner Force
As with any vacuum cleaner, it’s the difference of
pressure that creates the net force pushing
objects towards the low pressure side.
A
L
Force
A
Truc
k
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
Force of air resistance
is due to a difference in
pressure.
LOW PRESSURE
High pressure builds
by compression in
front of a falling object
while low pressure is
created in the wake.
L
HIGH PRESSURE
H
Sailing Ships
The wind blowing on a sail also produces a
pressure difference, creating the force that
moves the ship.
H
Wind
L
Ground-effect Cushion
L
H
LOW PRESSURE
HIGH PRESSURE
Moving
this way
L
H
Flat sheet sliding over a smooth surface
compresses the air beneath it and forms a lowfriction cushion, allowing it to slide.
This ground-effect won’t occur with an irregular
leaf or with a rough surface.
Paper Drop Test
http://www.youtube.com/watch?v=vKf-vIDSIik
Vector Addition of Forces
Two forces pulling an object are
equivalent to a single total force.
Net Force
A+B
Force B
Object
Force A
Parallelogram rule
Sliding Sideways
If leaf/paper is
tilted then it
slides
sideways.
Air Pressure Force
Slides this
way
Gravity
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.
Lift
Lift
Wing
Moving
this way
Aerodynamic Lift
If leaf/paper is tilted relative to its path
of action then there is also an
aerodynamic lift.
Lift
Air Resistance
Also get lift if
leaf/paper is
curled like a
wing.
Moving
this way
Gravity
Effect of Lift
Lift requires tilt and
speed; no lift if
paper/ leaf is not
moving
Lift
Lift force can also deflect
the path of action
downward, depending on
the tilt angle of the
leaf/paper.
Path of action
deflected by lift.
No Lift
Bernoulli’s Principle
Still Air
A
Wind
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.
L
Home Demo: Blow It Up
Hold a sheet of paper in front of your
mouth and blow; the paper will rise.
L
Low pressure on top;
Average pressure on bottom
A
Waves and Bernoulli’s Principle
Wind blowing over the ocean
causes waves to build due to
Bernoulli’s principle.
Where is the pressure lowered?
L
L
A
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.
L
A
New Orlean’s Superdome after hurricane Katrina
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 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.
No Spin
L
Spin
L
Bernoulli
Forward Motion
L
H
Depending on the axis of rotation this could be a
rising fastball, a sinker, or a curve ball.
Curveball Flow Pattern
H
L
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.
BLOW
L
Ping L
Pong
Ball
A
Home Demo: Keep It Up (cont.)
Bernoulli effect keeps the ball in the
middle of the air stream.
A
L
A
A
L
A
Next Lecture
Squash & Stretch
By Tuesday of next week:
Complete the 6th homework
(Stop-motion Animation of Falling)
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