When a bat strikes a baseball, both objects change. At the moment of the collision, the energy of the impact gets stored as the physical deformation of both the bat and the ball. If the ball strikes a wooden bat, the ball undergoes most of the "squishing." If an aluminum bat is used, the deformation of the bat becomes the main reservoir for storing this potential energy. As the ball and bat return to their original shape, the stored energy is transformed back into the energy of the ball's movement. This difference in shape deformation accounts for the variance in the action of wooden and aluminum bats. But you don't have to go out on a ball field to explore the relationship between potential energy and its conversion to kinetic energy. A similar energy transfer occurs when a ball rebounds off a surface such as a floor or wall. In this activity, you will explore how the height from which a ball is dropped affects its rebound. Is there an optimal height for observing the greatest rebound? How does temperature affect the ball's rebound?

OBJECTIVE
This activity page will offer:

• Insight into the storage of potential energy within a disfigured rubber ball.
• A hands-on experience in energy transformation.
• An opportunity to manipulate variables and observe effects.
• An exploration of the physics of rebounds.

MATERIALS

• Hollow ball*
• Solid ball *
• Measuring stick
• Tape

*Composed of rubber or other elastic material.

PROCEDURE
Part 1- Obtaining a Baseline

1. Work with a partner to tape a length of paper along a wall so that it extends upwards from the floor to a height of around 6 feet.
2. Use a measuring stick to create a scale along the length of the paper.
3. One team member holds a solid ball at a height of 6 inches. The other member marks this point as the release height.
4. The team member holding the ball releases it. The other team member observes and marks the rebound height on the chart. The person observing the ball should note any change in the ball's appearance as it hits the ground and rebounds.
5. The ball is then released from a height of one foot. Again, its release and rebound heights are recorded and marked on the chart.
6. Keep elevating the release point until you are dropping the ball from the top of the chart.
7. Repeat steps 1-6. This time substitute a hollow ball for the solid one. The same person should continue to drop the ball, and the same person should continue to observe and record it.

QUESTIONS

1. How did the release height affect the rebound height?
2. Did you observe a difference in the ball's shape as it struck the ground? If so, what happened?
3. Was the relationship between release height and rebound height constant? In other words, did the ball bounce highest when released from the highest point?
4. CRITICAL ANALYSIS: At a certain point, further increases in height do not produce a higher rebound height. Explain.

Part 2- Cooling Off

• Golf ball
• Baseball

PROCEDURE

1. Determine the average rebound height for a golf ball kept at room temperature and dropped from a height of about 3 feet.
2. Refrigerate the golf ball for several hours.
3. Again, determine the average rebound height from a 3-foot drop.
4. Repeat steps 1-4, substituting a baseball for the golf ball.

QUESTIONS

1. Did the rebound height change when the golf ball and baseball were refrigerated?
2. Which ball's rebound was affected most by the change in temperature?
3. How would you find the percentage of the bounce lost due to refrigeration?
4. What percentage of the bounce is lost when a baseball is refrigerated?
5. What percentage of the bounce is lost when a golf ball is refrigerated?
6. Why does the change in temperature affect the bounce?

EXTENSIONS

Transfer of Energy
Beginning with the sun, identify all of the energy changes responsible for a basketball's rebound. To simplify matters, assume that the basketball is already manufactured.

Flipping Fun
Have you ever made an animated flipbook? Here's your chance to create one that shows the deformation of a ball as it bounces against the ground. Using scraps of square or rectangular paper and a large fastening clip, assemble a blank flipbook. Draw a sequence of image frames that shows a bouncing ball that deforms as it strikes the ground and rebounds. Don't forget to show the ball's return to its spherical form and the associated rebound.

Hot Stuff
Suppose a golf ball was heated instead of chilled. How might additional thermal energy affect the rebound height? Make a prediction. Then, develop a method for inquiry that would uncover this relationship. Share your experimental design with your instructor. With his or her permission, perform your experiment, gather the data, analyze your results, and draw conclusions based on your data.

Web Connection

Bouncing Balls
A comprehensive reference on the physics of ball bouncing.

Rebound Differences During Play
An article describing the effects of temperature on the bounce of squash balls.

The Energy of a Bouncing Ball
A University of Virginia activity on investigating the energy of a bouncing ball.

The activities in this guide were contributed by Michael DiSpezio, a Massachusetts-based science writer and author of "Critical Thinking Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing Co., NY).