Upcoming Deadlines Art/Physics 123 Furlough Day: Monday, September 14th Fourth Homework (Tracker video analysis of Falling): Due Wednesday, September 16 th ; 15 points (10 points if late) Fifth Homework (Video analysis of Path of Action): Due Wednesday, September 23 rd ; 15 points (10 points if late) For full schedule, visit course website: ArtPhysics123.pbworks.com

Homework Assignment #4 We will be using a video analysis program called "Tracker" to study motion. Download a copy of the program from the Tracker website: 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, September 16 th (next week).

Guest Lecture Next Wednesday’s class will be a special guest lecture by Rex Grignon. Rex has been the Head of Character Animation on numerous films, starting with Antz (1998), Shrek (2001), Madagascar 2005) and Madagascar: Escape 2 Africa (2008) and has animated on Sinbad (2000) and Kung Fu Panda (2008). Note: Need volunteer assistant

Extra Credit Opportunity 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 Street San Francisco, California Near Moscone Convention Center Visit the Cartoon Art Museum in San Francisco to see “Once Upon a Dream: The Art of Sleeping Beauty.”

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.

Video Reference

Analyzing Video Reference One of the most useful tools for an animator is a movie camera for shooting 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: Tracker is a free program created by Doug Brown, a physicist at Cabrillo College.

Tracking the Ball Drop Horizontal Motion Vertical Motion

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. Press the second button in the Track Control window and select the "Full Trails" option. 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). 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 Height Notice the shape of the curve made by the dots. This is a parabolic arc.

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.. Position Frame

Autodesk Maya software Maya is one of the leading tools in computer animation.

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

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

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

Speed and Acceleration Speed (or velocity) is defined as how quickly an object’s position is changing. Acceleration is defined as how quickly an object’s velocity is changing. Tracker calculates speed and acceleration from the position data for an object.

Graph of Spacings (by Odd Rule) Frames Spacing By the “Odd Rule”, the spacings go as 1, 3, 5, 7, 9, etc. The graph of speed is also a straight line.

Falling Speed Distance fallen from apex Speed (inches per frame) Speed (miles per hour) 1 foot45 4 feet810 9 feet feet feet feet feet feet feet80100 With this table you can find the speed of an object from the distance it’s fallen. However, this table is accurate only as long as the object’s weight is much larger than the force of air resistance.

Falling Speed Example Distance fallen from apex Speed (inches per frame) Speed (miles per hour) 1 foot45 4 feet810 9 feet feet feet feet feet feet feet80100 About how fast is Alice falling? She is 4 feet tall. We are shooting on twos (2 frames per drawing). A)5 m.p.h. B)15m.p.h. C)25m.p.h. D)35 m.p.h. E)50 m.p.h.

Falling Speed Example Distance fallen from apex Speed (inches per frame) Speed (miles per hour) 1 foot45 4 feet810 9 feet feet feet feet feet feet feet80100 Distance between keys is about two feet; shot on twos that’s 12 inches per frame. Either she’s only fallen from just off-screen (above) or her dress is slowing her fall. About how fast is Alice falling? She is 4 feet tall. We are shooting on twos (2 frames per drawing).

Increments & Acceleration In the Odd Rule, the spacings get bigger with time and always by the same amount. That is, the increment from one spacing to the next is always the same (red arrow). Since the spacings tell you the speed, if the spacings get larger and larger then the moving object is accelerating. The increment tells you the acceleration. The acceleration due to gravity is constant (since the increment is always the same).

Differential Calculus You now know basic differential calculus. The difference between the positions of the ball is the spacing, which gives the speed. The difference between the spacings is the increment, which gives the acceleration.

Next Monday No Class (Course Furlough) Next Wednesday Guest Lecture: Rex Grignon By Wednesday of next week: Complete the 4 th homework (Tracker video analysis of Falling) Please return the clickers!