Upcoming Deadlines

Campus Furlough: No classes on Monday, Feb. 15th

Fourth Homework (Analyzing Video)Due Wednesday, Feb. 17th (Next week)15 points (10 points if late)

For full schedule, visit course website:ArtPhysics123.pbworks.com

Pick up a clicker, find the right channel, and enter Student ID

Uploading VideosPlease use YouTube or Vimeo for videos

posted to your blog on Blogger.Videos uploaded directly into Blogger often fail

to play correctly; when they do play the quality is often poor.

You can still embed a YouTube or Vimeo video directly into your blog posting. Or you can just put the link, if you prefer.

Finally, be sure that your video is not marked “Private” so that I can view it to grade.

Activating your Clicker

* Turn on your clicker.* Enter the channel number or letter for

joining this class. Hit Enter/Send key.* Clicker should read AP123S258* Type in your student ID; hit Enter/Send.Clicker is now ready to use; leave it on.

Hit any key to wake the clicker from sleep mode.

Madagascar 2 (2008)Carefully observe the path of action when the plane is in the air.

http://www.youtube.com/watch?v=Anflb_oWdgo

Review Question

This path of action is a parabolic arc.

Trueor

False

Review Question

False.The arc is shallow when the plane flies off the cliff but very steep after the apex.

Parabolic arc is symmetric about the apex

Homework Assignment #4We will be using a video analysis program called

"Tracker" to study motion. Download a copy of the program from the Tracker website:

http://www.cabrillo.edu/~dbrown/tracker/

Run the Tracker program on your computer, import the video clip of a falling object that you created in the previous homework assignment and analyze the falling motion (will demo in class today).

This assignment is due by 8am on Wednesday, February 17th (next week).

Extra Credit Opportunity

Go to any event at Cinequest Film Festival in downtown San Jose.

Turn in proof of your attendance (receipt, photos, etc.) for 5 points of extra credit.

Extra Credit Opportunity

Student registration is $75 (ouch)

Turn in your receipt for 10 points of extra credit.

For info: www.gdconf.com

Attend the Game Developer’s Conference in San Francisco, on Saturday, March 13th

Paths ofAction(cont.)

Maximum RangeMaximum range is at a launch angle of 45

degrees (when air resistance is negligible).

Range

Heig

ht Same initial speeds

Onager (Catapult)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

Stone ejectedat 45º angle

13

BallistaThe 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.

Rope bundles provide tension

Notice 45º angle of tilt

Trebuchet

Siege of Jerusalem

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. Counterweight lifted by human powered “hamster wheels”

MangonelThe mangonel is a simplified

trebuchet using a fixed counter-weight.

Releasing the ProjectileThe release mechanism is

designed to throw the rock at a 45 degree angle.

45º

Release

Importance of RangeHeavy medieval weapons had to operate outside the range of archers (about 200 yards).

A trebuchet can hurl stones out to 350 yards, with a launch speed of 130 miles per hour.

LotR: Return of the King (2003)

http://www.youtube.com/watch?v=7bFTw95pJp8

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.

Tracking and Motion Graphs

Using Reference

Animator Ken Harris at work, using himself as a model.

Visual artists have always used models and reference in their work.

One of the most useful tools for the modern animator is the digital movie camera.

Video Reference & Madagascar 2

Click

http://www.youtube.com/watch?v=GUBEwUvtssE

Analyzing Video Reference

Reference is not for rotoscoping (tracing images from a film) but to study the motion.

We can also use video analysis tools to help us see the patterns of motion in a scene that we’ve filmed.

Tracker Video Analysis Software

Let me demonstrate how to use the Tracker software for video analysis software.

To download Tracker, visit: http://www.cabrillo.edu/~dbrown/tracker/

Tracker is a free program created by Doug Brown, a physicist at Cabrillo College.

Tracking the Ball Drop

HorizontalMotion

VerticalMotion

Importing Video into Tracker

Run the Tracker program on your computer and import your video clip of a falling object.You may need to convert your clip into a format that Tracker can import (either MOV or AVI), if it's not already in that format. If you have trouble using your clip from Homework 3 then you may shoot new reference.

Tracking an Object in Tracker

In the "Tracks" menu select "New -> Point Mass"; a Track Control window should appear.

Toggle the "Set Trail Length" button (near center of video window) to mark all points. Optional: Right click on the video to zoom in or out. Go to the first frame in your clip that you want to analyze, hold down the shift key to change the cursor into cross-hairs, then click on the center of your object. The program will mark that position and advance one frame.

Tracking an Object (cont.)

Continue holding down the shift and marking the position of the object until it hits the ground (which should be after 15 to 20 frames for 30 fps).  

Due to motion blur the object will "stretch" as it falls and it may be difficult to locate the exact center but just do your best to estimate the center of the blur.

Plotting the Position Data

Click on the "Plots" button in the upper-right corner and select the 2 plot option.

You now have two plots showing the horizontal (x) and vertical (y) positions of the object versus time. Select and drag the bar separating the plots from the data tables and pull the bar down to expand the plots window.  

Posting your Plots

In the "Edit" menu select "Copy Image -> Frame" to copy the whole window to the clipboard.

Open your favorite graphics program, such as Paint or PhotoShop, paste the image, then save it to a file. Finally, upload that image to your blog into a post called "Tracker video analysis of falling".

Graph of Ball Drop Heights

Frames

Heig

ht

Notice the shape of the curve made by the dots. This is a parabolic arc.

Tracking a Jump

HorizontalMotion

VerticalMotion

Motion Graphs

In computer animation the timing and spacing of motion is often viewed using motion graphs, which can be manipulated in a graph editor.

Posi

tion

Frame

Autodesk Maya softwareMaya is one of the leading tools

in computer animation.

You will do two homework assignments near the end of the semester using Autodesk Maya.

Motion Graphs in Maya

The motion graph for a ball drop looks something like this in Maya

Posi

tion

Frame

Maya Demo for Bouncing Ball

Let me demonstrate how to set up a simple bouncing ball in Autodesk Maya.Our animation will be of a ball that is 4 inches in diameter (2 inches in radius)

The ball will fall from a height of 4 feet (48 inches).

It takes ½ second (12 frames) to reach the ground.

Use Fourth Down at Half Time

Motion Graph for Uniform MotionThe motion graph for uniform motion at a constant speed is a straight line.

Posi

tion

Frame

Parabolic Arcs

The motion graphs for a ball on a parabolic path of action.

Posi

tion

Frame

HorizontalVertical

Maya Demo for Bouncing Ball

Can add horizontal motion to the bouncing ball as well as bounces at decreasing height.A simple way to make parabolic arcs with apexes of decreasing height is to use the upper part of the previous arc.

Motion CaptureMotion capture is automated video tracking.

Data from sensor points can be used to create motion graphs in Maya.

Beowulf (2007)

Using Reference Wisely

Artists know that reference is very important but they also recognize that they shouldn’t be slaves to their reference.

Thomas Eakins,The Swimming Hole (c. 1884)

Photo reference shot by Eakins

Physics helps understand motion yet animators shouldn’t be slaves to it.

Using Physics Wisely

The plane’s path of action feels like a roller coaster drop.

Next MondayNo Class (Campus

Furlough)

Next Wednesday

ArcsBy Wednesday of next week:Complete the 4th homework

(Tracker video analysis of Falling)

Please turn off and return the clickers!