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Eighth Homework (Reverse Video Reference)
Due Thursday, March 22nd (Next week)
20 points (10 points if late)
Spring Break - March 26th to March 30th
For full schedule, visit course website:
ArtPhysics123.pbworks.com
Term Papers
This morning I checked your blogs to verify that
the term papers were turned in on time.
Only two are missing; the student IDs are:
6421142
and
5214002
Over the next few weeks I will read and grade
your papers. Should be finished by the end of
Spring Break.
Homework Assignment #8
Normally animators shoot video and use it as
reference for their work.
In this assignment, you'll do the reverse.
Specifically, for four different animation clips you’ll shoot
video of yourself in which you recreate those clips as
accurately as possible.
Go to Homework Assignment 8 on the course website
to find the animation clips you’ll recreate:
https://artphysics123.pbworks.com/Homework-8
Homework Assignment #8
Clip A
http://www.youtube.com/watch?v=FRSB7p8HAlU
Homework Assignment #8
Clip B
http://www.youtube.com/watch?v=azvjZdO8cBE
Homework Assignment #8
Clip C
http://www.youtube.com/watch?v=haZYnVwlfAk
Homework Assignment #8
Clip D
http://www.youtube.com/watch?v=Xxp96SKQ2S8
Homework Assignment #8
Film yourself acting out the scene in each of these
animation clips, recording a separate clip of yourself
for each one.
Reproduce the motion of the character in the animation
as accurately as possible (you'll be graded on how
well you do).
Don't just quickly act it out but rather study each
animation clip carefully to capture all the details in the
motion, including staging and camera angle.
Be sure that you have enough room to do all the steps
in the walk; do not walk in place, it’s not the same!
Homework Assignment #8
Upload your three clips to your blog in an entry entitled
“Reverse Video Reference of Walking.“
The purpose of this exercise is to have you carefully
observe the motion in each clip so that you will learn
the complexity of different walks.
This assignment is due by 8am on
Thursday, March 22nd (next week).
20 points (if late, 10 points).
For each of the three animation clips the best video clip
will get an extra 20 points of credit.
Survey Question
Writing the term paper was:
A) Rather enjoyable 
B) Somewhat enjoyable
C) OK
D) Somewhat painful
E) Rather painful 
Review Question
Mr. A pushes way from Mr. B while Mr. B just holds
his hand rigidly in place.
Which of them has the largest acceleration?
Mr. B holds
A) Mr. A
B) Mr. B
C) They have the
same
acceleration
Mr. A
pushes
Review Question
Mr. A has the larger acceleration.
If A pushes B then both accelerate by equal forces.
By Law of Acceleration, Object A, having less mass, will
accelerate more than the heavier Object B.
Action
Reaction
Object A
Accelerations
Object B
Review Question
Which of these devices
would actually work to
propel Wile E. Coyote?
A) Outboard motor in a
tub of water.
B) Big fan blowing a
large sail.
C) Both would work.
D) Neither would work.
A)
B)
Back of the
tub acts like
the sail.
Internal Propulsion
Internal propulsion is not
possible because the
impulse gained from one
reaction is lost due to
another internal action.
Air pushes
propeller
Propeller
pushes air
Action/Reaction Pairs
This
would
work!
Sail
pushes
air
Air
pushes
sail
Action &
Reaction
(cont.)
Recoil
Action/Reaction also explains recoil, such as from a gun.
The action force that accelerates the bullet results in a
reaction force in opposite direction, recoiling the gun.
Heavy cannon
Fast cannonball
Recoil Speed = (Bullet/Gun Weight Ratio) x (Bullet Speed)
Example: If the cannon weighs 100 times more than the cannon ball then
cannon’s recoil speed is 100 times less than cannon ball’s speed.
Recoil from a Gun
High recoil speed is cause by either:
* Large Bullet/Gun Weight Ratio
* High Bullet Speed
Shooting an elephant gun
http://www.youtube.com/watch?v=MlFlXMHaSVQ
http://www.youtube.com/watch?v=bpFDHO-tqUY
Predator (1987)
Recoil & Wile E. Coyote
http://www.youtube.com/watch?v=Wxm9EdVFxk8
Unexpected recoil is
another common gag
in animated cartoons.
Guided Muscle (1955)
http://www.youtube.com/watch?v=7H6Pwzdw7oQ
Wall-E Fire, Propelled
http://www.youtube.com/watch?v=2lkffSsImXc
Using a fire-extinguisher for propulsion, as used by
Wall-E, would actually work, True or False?
Class Demo: Extinguisher Rocket
http://www.youtube.com/watch?v=9F_VjHZATbY
Using a fire-extinguisher for rocket-like propulsion.
Two-stage Rockets
The first stage accelerates the rocket until it runs out of fuel.
The first stage is discarded, reducing the rocket’s mass.
Rocket mass reduced so recoil acceleration is greater.
Mythbusters Two-Stage Rocket Sled
http://www.youtube.com/watch?v=gK7ffrN1zcI
Jumps
Jumping
Jumping is a basic character
animation exercise that has
many of the basic elements
found in drop tests for inanimate
objects.
By Carlos Nunez
By Danielle Domurat
http://www.youtube.com/watch?v=jwerYsdE9Xs
http://www.youtube.com/watch?v=XWheRtQkC9o
Timing the Jump
The simplest part of
a jump is the time
in the air and how it
is related to the
height of the jump.
Jump Time
X
Jump Height
X
Apex
X = Center of Gravity
Crouch
Take-off
Jump Time & Height
The same table we
saw for the ball
drop gives the
jump time (from
take-off to apex)
and jump height.
Jump Time Frames
(seconds)
Jump Height
1/
24
1
1/
1/
12
2
1 1/3 inches
1/
8
3
3 inches
1/
6
4
5 1/3 inches
6
12 inches
8
21 inches
12
4 feet
16
7 feet
¾
18
9 feet
1
24
16 feet
¼
1/
The formula to compute
this table is:
(Distance in inches) =
(Number of Frames) x
(Number of Frames) x
(1/3 inch)
3
½
2/
3
3
inch
Hang time =
2x(Jump time)
Jump Time Example
For a jump time
of 8 frames, the
jump height is 21
inches
8 frames
8 frames
X
21 inches
X
X
Apex
Take-off
X = Center of Gravity
Landing
Crouching Tiger, Hidden Dragon (2000)
http://www.youtube.com/watch?v=xxCvv3bDyvw
Characters stay in the air an unrealistically long time, even
considering the impressive height of their jumps.
Timing the Push
You can time the
push (from crouch
to take-off) using a
simple formula
Jump Time
Push Time
X
Jump Height
X
Push Height
X
Apex
X = Center of Gravity
Crouch
Take-off
Jump Magnification
Timing of the push depends on the
jump magnification.
Jump Magnification =
Jump Height
Push Height
Jump Magnification = 8
Jump Magnification = 2
Formula for Timing the Push
Push Time =
Jump Time
Jump Magnification
Can use this formula to
check the timing of the
push depending on the
timing of the jump.
Timing the Push Example
8 frames
8 frames
X = Center of Gravity
4 frames
Apex
X
21 inches
X
10 ½ inches
X
X
Jump magnification = 2
so push time is half as
long as the jump time.
Crouch
Take-off
Landing
Planning a Jump
Animators can plan out a realistic jump by these steps:
1) Pick the desired jump
time or jump height.
2) Use the table to find the
jump height given the
jump time (or vice versa).
3) Pick the desired push
height for the crouch
4) Determine the push time
from the jump
magnification.
A Big Jump
A character jumps 16 feet into the air.
From the table, that’s a jump time of 24
Apex
frames (take-off to apex).
The push height is 16 inches;
Jump Height = 16 feet
what is the push time?
Push Height = 16 inches
Jump Time = 24 frames
A) Two frames
B) Four frames
C) Six frames
D) Eight frames
E) Twelve frames
Push Time =
Jump Time
Jump Magnification
A Big Jump
A)Two frames
Jump magnification is 12
(=16 feet/16 inches)
Apex
Jump Height = 16 feet
Push Height = 16 inches
Jump Time = 24 frames
Push time is
(24 frames)/12 = 2 frames
Push Time =
Jump Time
Jump Magnification
Push Factor
Can calculate jump magnification with this:
Jump Magnification = (Push Factor) x (Push Height in Feet)
Push Time
(in frames)
Push Factor
1
36
2
9
3
4
4
2 1 /4
6
1
8
9/
16
Push Factor = 36 / (Push Time in Frames)2
Push Factor Example
For a 10 foot tall character, what’s
the biggest jump magnification that
you could get using a push time
(crouch to lift-off) of 3 frames?
The most that the character can
crouch is about 5 feet. Using,
Push Time
(in frames)
Push Factor
1
36
Jump Magnification =
(Push Factor) x (Push Height in Feet)
2
9
3
4
4
2 1 /4
6
1
8
9/
The jump magnification would be
about (4)x(5) = 20 for this deep
crouch and very quick push.
16
Unrealistic Timing
Hulk’s jump looks fake since the
push timing on the ground isn’t
consistent with scale of his jump.
http://www.youtube.com/watch?v=itsAA7huvbY
Jump magnification when pushing off for
one frame is 32. This shallow, forward
jump should be about 4-5 stories high.
Boundin’ (2003)
Big jump magnifications and jump times give a
feeling of lightness and happiness in a cartoon.
http://www.youtube.com/watch?v=CDtiZImH0qI
Timing the Landing
If the crouch on landing is similar to the crouch when pushing off
then the landing has similar timing to the take-off.
Landing
Take-off
If the crouch on landing is shorter then the timing of the landing is
shorter; if the crouch distance is longer, the timing is longer.
Forces when Jumping
The three main forces on a person jumping are:
• Gravity (Downward)
• Support of the floor (Upward)
• Frictional force of the floor (Horizontal)
Only these forces can accelerate the person.
Gravity is constant but the force
exerted by the floor can
increase in reaction to the
action of the person exerting a
force on the floor.
Jumping Action/Reaction
Jumping is done by pushing
downward on the ground
(action) so the ground
pushes upward on you
(reaction).
How high you jump depends
on the force and on the
distance over which you
apply that force.
Reaction
Can only push while in contact with
the ground so squatting helps by
increasing distance.
Action
Average Push Force
You can determine the average
force exerted when jumping as:
(Jump Force) = (Jumper’s Weight)
x (Jump Magnification)
Remember that
Jump Magnification =
Jump Height
Push Height
Jump Force
(Action)
The Incredible Hulk
The Hulk crouches 3 feet and
then makes a huge jump,
rising a height of 300 feet.
If he weighs 1000 pounds,
how much force did he push
off with for this jump?
A)
B)
C)
D)
E)
1000 pounds
3000 pounds
9000 pounds
30,000 pounds
100,000 pounds
The Incredible Hulk
E) 100,000 pounds
His push height is 3 feet and
his jump height is 300 feet so
the jump magnification is 100.
That means that he pushed
with a force equal to 100 times
his weight of 1000 pounds.
The Incredible Hulk (cont.)
The jump time (from lift-off to
apex) of The Hulk’s 300 foot
jump is about 100 frames.
What is his push time (from
crouch to lift-off); recall that he
crouches 3 feet for this jump.
A)
B)
C)
D)
E)
1 frame
2 frames
3 frames
6 frames
12 frames
Push Time =
Jump Time
Jump Magnification
The Incredible Hulk (cont.)
A) 1 frame
His push height is 3 feet and
his jump height is 300 feet so
the jump magnification is 100.
Since his jump time is 100
frames his push time is only
one frame.
Push Time =
Jump Time
Jump Magnification
Physical Strength in Jumping
Physical strength of a character is reflected
in the timing of the push, which sets the
jump magnification.
By the Law of
Acceleration, if the
character pushes with
a large force then the
acceleration is large so
the timing of the push
must be quick.
Action/Reaction Jumping Forward
To jump upward and
also forward, the action
force (pushing
downward with your
legs) needs to also be
pushing towards your
back so that reaction
force of the floor is
upward and forward.
Reaction
Action
Jumping forward at a 45° requires almost 50% more
pushing force to reach the same vertical height.
Forces when Landing
If the timing of the landing is
similar to the timing of the
take-off then the forces on
landing are similar to the
forces on take off.
If the landing has quicker
timing then the forces are
proportionally larger on the
landing.
If the landing has slower
timing than the take-off then
the landing forces are smaller.
Reaction
Action
Hancock (2008)
One of the few things in this movie that’s
physically accurate is that the force exerted
on the ground is just as extreme on the takeoff as it is on the landing.
Take-off
Landing
The Incredible Hulk (2008)
http://www.youtube.com/watch?v=NWWzve8Z90s
Review of Hulk films on NPR
In summer 2008, I did an interview on “All
Things Considered” for National Public
Radio on the physics in the new Hulk movie.
Link
http://www.npr.org/templates/story/story.php?storyId=92189335
The Avengers (2012)
http://www.youtube.com/watch?v=bGt-saFvkNk
Next Lecture
Jumps, Part 2
Next Assignment
Reverse Video Reference of Walks
Due Thursday of next week
Please turn off and return the clickers!