What is Video Analysis?
Short videos, often just 20 to 30 frames in length, can be extremely useful in physics teaching. Not still photographs, but too short to be considered movies, these "live photos" can be played on the computer monitor at any speed, backward or forward. Moreover, just as a ruler can be used to make measurements on a photograph, positions in a video frame can be measured by pointing a mouse and clicking. The data that is generated can be graphed, analyzed in spreadsheets, compared to theoretical models, and even used to display vectors or points superimposed on the original video.
This use of the analysis of digital video as a learning tool in physics laboratory courses has become popular in recent years. In practice, a student does this with a computer program such as Logger Pro, Tracker or VideoPoint. For example, the student might analyze the acceleration of a ball undergoing projectile motion inside an accelerating elevator (see Figure 1).
elevatorexample.JPEG

After starting VideoPoint and opening the movie file, the video appears in a window on the computer monitor along with an empty data table. The student calibrates the system by clicking on the ends of an object in the video of known length (the person's forearm in the figure) that lies in the plane of motion, and entering the value of that known length. Then the student points to the ball in the first frame and clicks the mouse. The coordinates of the ball, measured in physical units thanks to the calibration, appear in the first row of the data table corresponding to time t=0. The video advances to frame number two, and the student clicks on the ball again, causing not only the coordinates of the ball but also the elapsed time for one frame of the video to appear in row two of the data table. Continuing in this way, the student generates data of the position of the ball as a function of time. Depending on the assignment, the student might graph the data in VideoPoint or export it to a spreadsheet for modeling. Other points, such as the outside window frame at the left edge of the figure, can be marked as well. By choosing another calibration length in the plane of the window, such as the window height, the student can use the window measurements for measuring the acceleration of the elevator itself.