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Homework #9 – Stop-motion character Animation
Due Thursday, November 10th (Next Thursday)
20 points (10 points if late); 20 point bonus to top 3
For full schedule, visit course website:
ArtPhysics123.pbworks.com
Homework Assignment #9
In this assignment you will create a
simple stop-motion animation of a
moving character.
For your character, use a doll or stuffed
animal that's easily posed.
You may even use an inanimate object, such
as a table lamp, as long as you can animate
it so that it looks like a character.
Homework Assignment #9
http://www.youtube.com/watch?v=EiEVdTQGGTM
Homework Assignment #9
Your animation should be composed of at least a
dozen different images but you can use the same
photo in two or more frames to get timing right.
Try to make the motion of the character as realistic
as possible so that your audience will momentarily
forget that it's not actually alive.
In homework assignment #6 you created a stopmotion animation of an inanimate falling object; if
you're not happy with how you produced your
earlier animation then re-read that assignment for
alternative ways of creating stop-motion.
Homework Assignment #9
You may work together with one or more classmates
to create a single animation for the team.
Clearly indicate the work done by each person, for
example if different persons animate different
characters or different scenes.
More is expected from a team effort; an animation
created by a three person team should present
three times as much work as a solo effort.
Homework Assignment #9
Post your animation clip to your blog in an entry
entitled "Stop-Motion Character Animation.“
Assignment due 8am on Thur., November 10th
20 points (if late, 10 points)
The top three clips in the class, as selected by a
celebrity judge, will receive a bonus
of 20 extra points.
Extra Credit Opportunities
• Attend the Star Party this Saturday. Telescope viewing, talks
and hands-on activities on Tower Lawn and Science 142
• Attend the “Technology of Animation” event, featuring guest
speaker Jeffery Katzenberg, at the computer history museum
in Mountain View. Registration is at the bottom.
http://www.computerhistory.org/events/#technologyanimation
• Attend any event at the San Francisco International
Animation Festival (November 10-13).
Present proof of your attendance to any of these (receipt,
photos, etc.) for 10 points of extra credit.
Survey Question
Writing the term paper was:
A) Rather enjoyable 
B) Somewhat enjoyable
C) OK
D) Somewhat painful
E) Rather painful 
Survey Question
For Dr. Kaufman, do you think
reading the term papers was:
A)Rather enjoyable 
B)Somewhat enjoyable
C)OK
D)Somewhat painful
E)Rather painful 
Review Question
At which position
do you exert the
least weight on
the ground?
Stride
Squash
P.P. Stretch
Stride
A) Stride
B) Squash
C) Passing Position
D) Stretch
E) Same weight at
all times
Squash
P.P. Stretch
Stride
Force Plate Experiments
Upward centrifugal
force due to your
motion lightens
your weight.
Stride
C) Passing Position
Can measure
weight shift during
walk cycle using
force plates.
Squash
Stretch
Squash
Stretch
Body
Weight
Passing
Position
Passing
Position
Review Question
Compared with the walking speed of a 6 foot man,
the walking speed of a 150 foot giant is…
A) 25 times slower
B) 5 times slower
C) About the same
D) 5 time faster
E) 25 times faster
than the man.
Jason and the Argonauts
Stride Time and Stride Length
D) 5 times faster
The giant is x25 taller
so each giant stride is
x25 longer (in distance).
Stride Stride Speed
Time
Length
x2
x4
x2
But the stride time for
the giant is x5 more
than the man’s stride.
x3
x4
x5
x 10
So the giant’s speed is
x5 faster than the man.
x9
x 16
x 25
x 100
x3
x4
x5
x 10
Distance
Speed = -----------Time
Jason and the Argonauts (1963)
Notice how the
timing of the
giant’s walking
gives the sense of
his massive scale.
Although the gait
his lumbering, the
giant easily catches
the running men.
http://www.youtube.com/watch?v=2BaLKYlC07w
Walks
Part II
Ray Harryhausen
Ray 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
Skeleton Battle Scene
http://www.youtube.com/watch?v=0gKD7qy98-E
Notice how the animated skeletons walk
(conveniently, we see their pelvis and leg bones).
Energy and Walking
So far we’ve examined
walking from the point
of view of forces.
An alternative
approach is to
examine the
energy expended
in walking.
We’re inherently lazy so many actions that we perform
unconsciously while walking reduce energy expenditure.
Home Demo: Silly Walks
Try walking around as
John Cleese, who is
the Minister of Silly
Walks.
You will find that you
use much more energy
than normal walking.
http://www.youtube.com/watch?v=IqhlQfXUk7w
Energy Budget (Inanimate)
Moving objects have an energy budget.
For inanimate objects, this budget is:
Kinetic Energy (K) – Energy due to their speed
Potential Energy (P) – Energy due to their height
Friction Loss (F) – Energy lost due to friction forces
K=0
P = 100
F=0
K = 20
P = 70
F = 10
K = 40
P = 40
F = 20
Total Energy = 100
Demo: Ball Races
Marbles 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= 0
P = 100
F= 0
K = 50
P = 50
F= 0
K = 50
P = 50
F= 0
K = 50
P = 50
F= 0
K = 50
P = 50
F= 0
K = 100
P= 0
F= 0
Ball B has a high speed in the center section.
K = 50
P = 50
F= 0
Energy and Wile E. Coyote
http://www.youtube.com/watch?v=h2j_n0sRXeU
From Going, Going, Gosh
The energy budget here is wrong because
the rock, after rolling down hill, flies back up
to a point higher than from where it started!
Energy Budget, Bouncing
K = 45
P= 5
F= 0
K = 50
P= 0
F= 0
Total Energy = 50
Kinetic Energy
Potential Energy
Friction Losses
K = 36
P= 4
F = 10
Energy Budget, Sack Drop
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)
B)
C)
D)
E)
Zero
200
100
95
105
Kinetic Energy
Potential Energy
Friction Losses
K= 0
P = 200
F= 0
K = ???
P = 100
F= 5
(Air resistance)
K= 0
P=
0
F = 200
Energy Budget, Sack Drop
D) 95
K= 0
P = 200
F= 0
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. Kinetic Energy
Potential Energy
Friction Losses
K = 95
P = 100
F= 5
(Air resistance)
K= 0
P=
0
F = 200
Energy Budget (Animate)
Animate objects can increase their
energy budget by doing work.
Work Input (W) –
Energy added by doing work.
K=
0
P=
0
F=
0
W = +0
K = 100
P=
0
F=
10
W = +110
Kinetic Energy
Potential Energy
Friction Losses
Work Input
K = 300
P=
0
F=
20
W = +320
Energy Budget in Jumping
Leg muscles
do work as you
push off when
jumping.
K = 200
P = 100
F = 50
W = +350
K = 120
P = 175
F = 55
W = +350
K = 90
P = 200
F = 60
W = +350
Slow down as you
rise to apex so
kinetic energy (K)
goes down.
K=0
P = 50
F=0
W=0
Most of the friction loss is
during push but a little
loss due to air resistance.
Energy Budget in Walking
K = 100
P = 100
F= 0
W = +0
K = 100
P = 100
F = 60
W = +60
Walking takes work due to all the frictional losses.
Simplified Walking Model
Pelvis is a doubleforked 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
Passing
Position
Stride
CG
Stride
Passing
Position
Passing
Position
We have to do work to raise the CG and much
of that energy (30-40%) is lost to friction.
Simplified Walking Model
Pelvic Rotation
As the passing leg swings
forward, the hips swing around,
rotating about the planted leg.
Without
Rotation
With
Rotation
Pelvic Rotation
Pelvic Rotation & Center of Gravity
Pelvic rotation
keeps the center
of gravity from
dropping as far
during the stride
(keeping step
length the same).
CG
Path of Action of
CG with Rotation
Without Rotation
Passing
Position
Stride
CG
Stride
Passing
Position
Passing
Position
Walking is more efficient with pelvic rotation.
Pelvic List
In the passing position the pelvis drops
slightly on 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
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
Path of Action of
CG without List
With Pelvic List
Passing
Position
Stride
CG
Stride
Passing
Position
Passing
Position
Walking is more efficient with pelvic list.
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.
Knee Flexion of Weighted Leg
Knee Flexion
Knee 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.
Path of Action of CG
without Flexion
CG
With Flexion
Passing
Position
Stride
CG
Stride
Passing
Position
Passing
Position
Walking is more efficient with knee flexion.
Heel and Toe
The heel and toes of the foot combine
with knee flexion to reduce the rising
and falling of the center of gravity.
Flexion
reduces the
leg length
Heel increases
effective length
of the leg
Toes
increase
leg length
Energy in Four-legged Walks
Four-legged walking gait alternates passing position
and stride between fore and hind legs to minimize
energy required to lift the center of gravity.
Height
x
x
x
x
x
Center
of
Gravity
The Journal of Experimental Biology 207, 3545-3558 (2004)
Next Lecture
Limbs and Joints
Homework 9
Stop Motion Animation #2
Due Thursday, November 10
Please turn off and return the clickers!