Upcoming Deadlines

1
Upcoming Deadlines

• Fifth Homework (Video analysis of Path of
  Action)
• Due Friday, September 25th (New Deadline)
• 15 points (10 points if late)
• Sixth Homework (Outline of First Term Paper)
• Due Wednesday, September 30th
• Campus-wide Furlough Day
• Monday, October 19th
• (Art/Phys 123 will meet on Wed., Oct. 21st)
• For full schedule, visit course website
• ArtPhysics123.pbworks.com

2
Homework Assignment 5

• In this assignment youll again use Tracker
  software to analyze the motion of a moving object
  from video reference.
• First, shoot some reference of yourself doing a
  running jump.
• Position your camera so that you're in frame the
  entire time that you're in the air.
• Stage the jump to be in profile.
• Shoot at least 5 takes, even if they are more or
  less the same.

3
Homework Assignment 5

• Import your video reference into the Tracker
  software (as in previous homework).
• Track the center of your waistline or beltline,
  which is approximately the location of your
  center of gravity.
• Marking your position from the time you leave the
  ground until youve landed.
• After tracking your motion, upload the screen
  image from Tracker to your blog into a post
  called "Video analysis of path of action".

4
Homework Assignment 5
Straight Line
Parabolic Path of Action
Parabolic Curve
5
Homework Assignment 5

• Finally, rewind your video to the first frame of
  your jump and from the "File" menu select "Record
  -gt Quicktime Movie".
• Hit the play button and allow the clip to play
  until the end of your jump. Next, in the
  "Capturing Quicktime MOV" window click "Save As"
  to save the recording.
• Check that your saved Quicktime movie has the
  track showing the path of action then upload both
  clips (original and with tracking) to the blog
  post.

6
Homework Assignment 5
Original Reference
Tracked Reference
Play
Play
This assignment is due by 8am on Friday,
September 25th (This Friday). 15 points
7
Extra Credit Opportunity
Visit the Cartoon Art Museum in San Francisco to
see Once Upon a Dream The Art of Sleeping
Beauty.

• Exhibition runs through Jan. 10.
• Give me your ticket receipt for ten points extra
  credit.

Hours Tuesday Sunday, 11am - 5pm Admission
4.00 for students Location 655 Mission
StreetSan Francisco, California 94105 Near
Moscone Convention Center
8
Activating your Clicker

• Turn on your clicker.
• Enter the number or letter that I give you for
  joining this class. Hit Enter/Send key.
• Clicker should read PHY123SCI2
• Type in your student ID hit Enter/Send.
• Clicker is now ready to use.

Hit any key to wake the clicker from sleep mode.
9
Paths ofAction
10
Path of Action
The path of action is the trajectory or track of
a moving object.
Path of Action
Brick drop exercise illustrates the path of
action for falling.
Play
By Danielle Domurat
11
Line of Action vs. Path of Action
Individual drawings have a line of action, which
indicates the visual flow of action in that
single drawing.
The path of action indicates the trajectory for a
sequence of drawings in an animation.
12
Secondary Paths of Action
The path of action is usually associated with the
primary action but we can also consider paths of
action for secondary actions, such as the motion
of a characters hand, arm, foot, etc.
Primary (Jump)
Secondary (Arm swing)
13
Parabolic Arcs
When gravity is the only force, the path of
action is a parabolic arc.
Paths of action of the falling brick and of a
bouncing ball are parabolic arcs
Water stream
14
Characters in Motion
Living beings obey the laws of physics, were
just a little more complex than a bouncing ball.
Play
By Danielle Domurat
15
Moving Falling
Ball rolling off of a table combines horizontal
and vertical motion. Falling starts with key 4,
with vertical distances increasing as
1357 Horizontal distances equally spaced as
with uniform motion. Arc is the combination of
uniform horizontal motion and accelerating
vertical motion.
16
Rolling off a Table, Tracked
Video reference confirms that the horizontal
motion stays uniform as the vertical motion slows
out.
Play
17
Class Demo Fall and Fire
FALL
1
FIRE
1
1
2
2
One ball is released and falls straight
down. Other ball is fired horizontally. At all
times the balls are at the same height. Hit the
ground at the same time.
3
3
3
5
4
4
18
Shoot the Monkey
Rifle is aimed at monkeys nose.
Monkey lets go of the branch the moment he hears
the gun fire.

• Bullet hits the monkey
• Above the nose
• On the nose
• Below the nose

B) The bullet and monkey are always at the same
height.
Play
19
Falling Brick
1

• The path of action for the falling brick is
• Uniform motion in the horizontal (constant
  velocity).
• Accelerating motion in the vertical (slowing out
  as in the ball drop).

3
5
The center of the brick has a smooth and
consistent parabolic path of action
Play
20
Full Parabolic Arcs
Horizontal spacings are uniform.
Vertical spacings slow in and out following the
Odd Rule.
The rising and falling motion are the same.
21
Common Errors in Arcs
Most common error in arcs is making them straight.
Wrong
Right
This example is exaggerated to make the error
obvious.
22
Nacho Libre
A scene in Nacho Libre has one of the worst paths
of action in cinematic history.
Play
23
Common Errors in Arcs (cont.)
WhatsWrong?
WhatsWrong?
The arc is skewed apex is closer to the left
than right. This error also tends to make both
legs of the arc too straight.
Vertical spacings are uniform. Horizontal
spacings are not.
24
Wile E. Coyotes Path of Action
In this scene Wile E. Coyote (on rocket skates)
is launched straight up the side of a vertical
cliff.
Play
Beep Beep (1952)
In reality, Wile E Coyote would fall straight
back down instead of curving in an arc. True or
False?
25
Wile E. Coyotes Path of Action (2)
Wile E. Coyote travels in a roughly parabolic arc
up to the apex, then stops and falls straight
downward.
Play
Beep Beep (1952)
In reality, he would fall in a downward arc
similar to his upward path of action. True or
False?
26
Staging
Play
(by Ken Calvert)
Staging is one of the principles of
animation. Motion that is usually more
interesting when staged to occur in perspective.
Spend half your time planning your scene and
the other half animating. Ollie Johnston
27
Arcs in Perspective
Parabolic arcs look different in perspective but
the spacings follow all the same rules as for
arcs in profile.
28
Half Arc in Perspective
Falling towards foreground
1
VP
HL
Perspective tends to straighten this arc
3
Use the Fourth Down at Half Time rule to help
locate points
29
Half Arc in Perspective
Falling towards background
1
VP
HL
Perspective tends to increase curvature for this
arc
3
Use the Fourth Down at Half Time rule to help
locate points
30
Parabolic Arc in Perspective
Maximum height (ball at midpoint)
VP
HL
Ball starts and ends on the ground.
31
Parabolic Arc in Perspective (cont.)
1
VP
HL
3
Add points to the curve by using Fourth Down at
Half Time rule.
32
Apex in Perspective
Apex needs to be above the half-way point between
take-off and landing, which is harder to judge
with perspective.
33
Apex of a Jump
Apex
Correct
Play
34
Hancock
Parabolic arcs seen in perspective are
interesting because the timing has texture as the
object goes from the foreground to the
background.
Play
But the timing in this scene from Hancock is
wrong. Can you tell why?
35
Timing a Scene
Its easy to time a scene with a fall or a jump
since we know how to time a straight drop.
36
Time in the Air
Time (seconds) Frames Distance fallen from apex
1/24 1 1/3 inch
1/12 2 1 1/3 inches
1/8 3 3 inches
1/6 4 5 1/3 inches
¼ 6 1 foot
1/3 8 1 ¾ feet
½ 12 4 feet
2/3 16 7 feet
¾ 18 9 feet
1 24 16 feet
2 48 64 feet
When air resistance is negligible (which it is
for a falling brick or jumping human), the rate
at which an object falls due to gravity is given
by this table.
The distances listed here are the vertical
distance fallen horizontal distance is arbitrary.
37
Timing Example
This jump looks to be about one foot in the air,
which takes a total of 12 frames (6 from take-off
to apex and 6 from apex to landing).
3
2
Frame Key
1 1
2 /
3 /
4 2
5 /
6 /
7 3
8 /
4
1
5
X
X
X
X
X
X Center of Gravity
38
Timing the Jump
Frame 78
How high is this jump? About 12 inches high?
More? Less?
Play
This jump has about 4 frames from take-off to
apex and about 5 frames from apex to landing.
Frame 82
This means that the height of the jump, given the
time in the air, should be 6-8 inches.
Frame 87
Given what the height looks to be, would you say
the timing is OK?
39
Throwing at an Angle
With no gravity, a thrown object would follow a
straight line. Due to gravity, the object falls
beneath this line, just as if released from
rest.
No Gravity
36 feet
16 feet
With Gravity
4 feet
12Frames
24Frames
36Frames
40
Speed (1994)
In Speed, a city bus jumps across an unfinished
freeway bridge in Los Angeles.
Play
Is this jump unrealistic?
41
Speed (1994)
Missing section is about two bus lengths, which
is 80-90 feet. At 65 m.p.h. you travel about 95
feet per second.
The bus should be in the air for about one second
(although in the movie its over seven seconds).
42
Speed (1994)
Since the bus is in the air for about a second it
drops 16 feet so the angle of the bridge would
have to be about 10 degrees for the bus to land
correctly on the other side.
16 feet
90 feet
Popping a wheelie does not help!
43
Speed (1994)
The film makers did not jump a bus over a gap in
a bridge. In fact the gap in this bridge is fake
it was painted in digitally.
However they forgot to paint out the shadow on
the ground.
44
Maximum Range

• Maximum range is at a launch angle of 45 degrees
  (when air resistance is negligible).

Height
Range
45
Ballista

• The ballista is a stone throwing war machine used
  in ancient Greece and Rome.
• The ballista resembles a giant crossbow but each
  arm is actually a separate torsion spring made of
  ropes.
• Typical range in battle was a few hundred yards,
  just out of range of enemy archers.

Rope bundles provide tension
Notice 45º angle of tilt
46
Onager (Catapult)
Stone ejectedat 45º angle

• The onager (wild donkey), was a torsion engine
  similar to the ballista but only one arm.
• Stone thrown from spoon or sling.
• This catapult was the largest weapon used by the
  Romans

Rope bundles provide tension
47
Trebuchet
The trebuchet was the ultimate mechanical siege
engine. Developed in the Far East and brought
west in the 10th century by the Mongol and Muslim
armies. European armies adopted the trebuchet
during the Crusades of the 12th century.
Siege of Jerusalem
Counterweight lifted by human powered hamster
wheels
48
Mangonel

• The mangonel is a simplified trebuchet using a
  fixed counter-weight.

49
Releasing the Projectile

• The release mechanism is designed to throw the
  rock at a 45 degree angle.

45º
Release
50
Kingdom of Heaven (2005)
Several full-size trebuchets were built for the
film Kingdom of Heaven. Many more were inserted
into the movie by digital effects.
Play
51
Next LectureArcs in Animation

• By Friday of this week
• Complete the 5th homework
• (Video analysis of Path of Action)

Please return the clickers!
52
Coefficient of Restitution
Roughly, each bounce is lower by the same
fractional amount.
25 Lower
25 Lower
53
Bouncing Range
Decreasing distance covered with each bounce
since time in the air decreases.
9 frames in the air
8 frames in the air
7 frames in the air
54
Motion Graphs (cont.)
The motion graph for uniform motion at a constant
speed is a straight line.
Position
Frame
55
Projectile Motion Air Resistance

• Range can be reduced by air resistance and the
  path of action changes shape.