What is video analysis?
A short video of a physical experiment, such as a falling ball, can be digitized and shown on a computer. With appropriate software, the position of the ball can be marked in each frame of the movie and the computer records its x and y coordinates as a function of time. Video analysis is the use of this data, along with mathematical analysis and graphing, to study the physical system in the experiment. This site is about the use of video analysis in science teaching.
Isn't video analysis about interviews?
People who do educational research often videotape interviews with students. They may refer to the analysis of those interviews as "video analysis." That is not what this web site is about.
How do I use the videos?
There are several ways to teach science using video analysis. How you do it depends partly on whether you have a computer with analysis software at the instructor's station or at each lab station in the classroom. Lecture Demos: Analyze a video in front of the class to illustrate a topic. Class Activities: Have the students, working in teams of 2-3 per computer, analyze a video as part of a class or lab activity. Projects: Students can analyze videos as part of an outside project. Homework: Assign a video for students to analyze at home.
There are lots of videos on sites like YouTube! Why do we need this site?
Video analysis becomes complicated to do if there was camera motion (shaking, panning, etc.), if the plane of motion is not perpendicular to the camera axis, if the lens zooms, or if the camera keeps changing its focus. Most videos that were made for entertainment have at least one of these problems. One of the goals of the LivePhoto Physics project is to create a collection of videos that are ideal for analysis in an introductory physics course.
What camera should I buy?
Manufacturers keep coming out with new models and discontinuing older ones. We can't keep up with them, so we don't recommend any particular models.
What software do I need?
There is a variety of software that you can use, ranging from free open-source to commercial applications. Tracker, Vernier Video Analysis™ and Coach 7 are examples.
How can a computer measure positions in real units?
Whenever you make a video for analysis, be sure to include an object of known length, such as a meterstick, in the plane of motion. The software will have a way of using this length to calibrate the data in real-world units.
When I set the camera shutter speed to 1/1000 s, why don't I get 1000 frames per second?
Shutter speed and frame rate are independent. Frame rate refers to how many images (frames) are recorded at regular time intervals during each second. Shutter speed determines how long the image sensor in the camera is exposed to light while an image is recorded.
A high shutter speed helps to "freeze" the motion in each frame and is used when high-speed motions are being recorded. (In relatively low cost consumer-grade digital cameras the highest shutter speed, about 1/200th to 1/1000th of a second, is sometimes called "sports timing.") Since a high shutter speed requires good lighting, when the light level is low and the object of interest is moving slowly, a slower shutter speed is better.
For camcorders sold in stores in the United States, the frame rate is fixed at 29.97 frames/second in order to be compatible with ordinary television sets. You need a special-purpose camera to get a different frame rate. Some cellphones include high-speed options for making videos.
When I capture a movie and then open it in a movie player, it looks double-exposed or distorted. What happened?
If you use Logger Pro to capture video, it may look normal because the Logger Pro display automatically corrects for certain interlacing and aspect ratio effects. Ordinary movie players often do not correct for these effects. The saved video will still look normal in Logger Pro.
What else might a science teacher need to know about video analysis?
See the video Rolling Shutter: Why Should Physics Students Care? for an explanation of a systematic error that occurs in many video cameras.
Who created this site?
The site was created by Robert Teese (Rochester Institute of Technology). Other past and present members of the LivePhoto team include Alicia Allbaugh (JPL NASA), Patrick Cooney (Millersville University), Priscilla Laws (Dickinson College), E. F. (Joe) Redish (University of Maryland),
David Sokoloff (University of Oregon), Ronald Thornton (Tufts University) and Maxine Willis (Dickinson College).
Are the videos copyrighted?
Why don't you have a movie of my favorite experiment on the site?
Most of these movies were created because we wanted to write an activity on a particular topic of introductory physics. Our goal was to have a collection of activities that span a wide range, from mechanics to thermodynamics to electricity and magnetism. This means we had to skip many topics, especially in mechanics.
Where are the LivePhoto Physics activities?
Physics with Video Analysis has been published by Vernier Software & Technology.