Bouncing Ball Physics
Talk It Over
What factors affect how high a ball bounces? Do some balls bounce higher than others? If you drop a ball from a high place, will it bounce higher than if you drop it from lower down? How can you find out?
- Yardstick (preferably marked in centimeters) or meterstick
- Small, rubber ball
- A helper
Note: You may need to practice this a few times so you are sure that you are seeing the number at the high point of the ball's bounce.
- Place the board on the floor under the edge of the table.
- Stand the measuring stick vertically from the board to the table. Turn the numbers toward you, so you can see them. Put the 0 end on the board. Tape the stick to the table's edge, like this:
- Lie down on the floor, looking at the measuring stick straight on, so you can see the numbers clearly. Ask your helper to hold the ball with its upper edge at the 20-cm. mark on the measuring stick. When you are ready, ask your helper to drop the ball. Watch carefully and note the high point of the ball's bounce to the nearest centimeter, like this:
- Record the height of the bounce. Repeat four times, so you have five trials. Find the average:
- Repeat steps 3 and 4, dropping the ball from 40 cm, 60 cm, and 80 cm. Conduct fivetrials from each drop height and average your results.
Watch out. Don't let that bouncing ball biff you in the nose!
Follow the "Go" procedure. Get an adult to help you record and average the numbers. If you have trouble seeing the centimeter numbers, you can work in inches. The numbers are bigger and the units farther apart.
Compare different kinds of balls. Try to discover a "rule" that correctly predicts bounce height for all of them.
Show Your Results
Put bounce heights in a data table like this for "Go" and "Go Easy":
|Drop Height||Trial 1||Trial 2||Trail 3||Trial 4||Trial 5||Average|
|60 cm . . . and so on|
For "Go Easy," make a bar graph of the average bounce height from the different drop heights. For "Go," make a line graph with drop height on the horizontal axis and bounce height on the vertical axis. Whichever graph you make, write a sentence that tells how you think drop height affects bounce height.
For "Go Far," make a line graph as for "Go," using different colored lines to compare the different balls you tested. Tell whether the "rule" you discovered applies to all the balls you tried.
Tips and Tricks
- Don't throw the ball. Just release it. Extra force will only push your ball sideways and make your bounce height harder to read.
- If you have a camera that can take stop-action pictures or multiple, continuous images, you may be able to take photographs to show both drop heights and bounce heights. Remember to set your camera on its fastest speed so it "stops" the ball in midair.
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