Science Buddies: "Ask an Expert"

I am Doing a science project on tennis balls. I don't know how to measure the height of a tennis balls bounce. My teacher said I have to use two different brands like Wilson and Penn. I have to measure it 12 times each. This project is due in Decmember.

Hi ahlott,

A suggestion: use a yardstick. Then you can drop the tennis balls from a known height, say 36 inches, and eyeball where the tennis balls bounce to. Each bounce should be to the same height. Since you're doing the measurements a dozen times, measurement variations should balance out. If don't, however, something is wrong. So post again, and let us know how the experiment is going.

Dave has suggested a good method for you to try. I might add that if you have a partner, this might be easier. A partner could hold the hard stick vertically and hold the ball at a specific height on the stick. You could stand a little bit away from the stick, so you could get a good view of how high the ball bounces. When your partner drops the ball, you will be able to see it easily and record how high it went.

In addition to Dave's suggestions about dropping it several times, and averaging how high it bounces, you should try to drop it from several different heights. Make sure you do several trials from each height.

Another thing you should do is make sure you use several balls from each of the manufacturers you test. Keep careful records of the bounces of all the balls and see if you can see differences between balls of the same make, as well as see differences in the bounce of balls from different manufacturers.

One very interesting thing about tennis balls is that their bounce is affected by their temperature. You might want to test this idea too.

Whatever you do, have fun with science.

Ed Neu
Buffalo, MN

Ed has made some excellent suggestions of different items to plot. If you have access to a camcorder, something else you might try is filming the ball drops. This will make measuring the resulting heights much easier. Depending on the camcorder, you could even put the playback in slow motion or freeze frame.

One of the things you can do is calculate how much energy is lost in the bounce.

I think you just need to take the difference between the initial height and the height of the bounce, and multiply that by the mass of the ball and the acceleration of gravity (9.8m/s/s)

(Since the equation for potential energy is PE = mgh)

I could be completely wrong...Can anyone else confirm that for me?