Hands-On-Physics

The Great Bungee Jump
Extensions
Measuring with Video

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Extension 4: 2-D with Video

Will the jumper crash into the building before reaching ground? To answer this, we need to look at the two-dimensional motion of the bungee jump. Our experiment was one-dimensional, looking just at the up-and-down motion of the jumper. What about the horizontal motion?

Analyzing both kinds of motion requires a new king of measurment. Our wires were good for one-dimensional motion, but cannot measure two dimensions at the same time. Analyzing a video record is the best way to do this.

The idea is to make a video recording of the bungee jump. Click here to download a sample video students made. This recording can be digitized and analyzed by a computer using special software.

Video frames are 1/30 of a second apart. Using the computer, you can look at each frame and locate the jumper. With the right software, you can click on the jumper in each frame and automatically generate a table of time and height. This is just the table generated by doing a different drop for each line. Click here for a table made from the sample video.

This technique is challenging because it is difficult to digitize video. But if you can solve this problem, you will find that this is a powerful and exciting way to do experiments. There are many other fast-moving events you can analyze the same way, such as a diver, Magic Johnson, collisions, or a rocket launch.

To collect data from video, you need:

• A video camera. You can record the motion with almost any video camera. A tripod is handy to keep the camera steady.
• A digital video editing system. This is a computer equipped with a special board for capturing video and turning it into a digital form that can be saved on disk.
• Digital analysis software. This is special software that allows you to pick out where the jumper is in each frame and convert your mouse click to coordinates. We recommend two different packages: VIEW, a free package from TERC and VideoPoint from Pasco.

Decide on your experiment and what equipment you will need. Before you begin experimenting, tell your instructor what you plan.