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Bouncing Science

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Overview

Many popular sports, including basketball, are based upon the use of a ball.  Yet each type of ball is easily associated with a specific sport, because each ball is distinctly different. A ball’s performance is directly influenced by its characteristics or properties. For example, the oval shape of a football allows it to travel farther in the air than a ball that is round.

In this activity, students will explore the properties of various balls from different sports, and discuss why the design of each ball is suited to its associated sport.  Students will investigate the bounce ability of different types of balls, and learn that the composition and elasticity of each ball, as well as the amount of air pressure inside the ball, can affect its bounce.

6-8

Suggested Time

1-2 (45 minute) periods

Materials

• Golf balls
• Baseballs
• Tennis balls (or any assortment of sport balls)
• Meter sticks
• Tape

Before The Lesson

Vocabulary

Potential energy: the energy that is stored in an object.

Kinetic energy: the energy of motion.

Elasticity: the ability of a material to return to its original shape after it has been stretched or deformed.

Elastic potential energy: potential energy that is stored due to the deformation of an elastic object, such as a stretched spring.

Air pressure: the force exerted by air pushing on a surface.

Part I: What To Do

1. Begin the lesson by having students watch the Science Friday video Physics of Basketball. Have students name their favorite ball sport, and then describe the type of ball that they would use to play that sport. Why does each ball sport use a specific type of ball?

2. Show students the basketball, golf ball, baseball, and tennis ball. Ask them to explain why they think each ball is the best type of ball to use for that particular sport.  Compare and contrast each of their different properties, such as size, shape, texture, material, and weight.  How do these properties affect the ball’s performance or function?

3. Tell students that they will be testing the bounce of each ball.  Discuss with students possible methods for testing bounciness. Hand out meter sticks and have students tape the meter stick to a wall. The bottom of the meter stick should be touching the floor and numbers should increase from the bottom to the top of the stick.

4. Tell students that they will be measuring how high each of the balls bounce by placing each ball, one at a time, at the top of the meter stick, and then dropping it.  If possible, have students work in pairs so that one student can drop the ball while the other student can observe and record the measurements. In order to ensure accurate results, review the following measuring tips with students:

a. Before dropping the ball, make sure the bottom of the ball is at the very top of the meter stick.

b. To make sure each ball starts out with the same initial speed, gently release the ball and allow it to fall on its own.

c. Measure the highest height reached by the bottom of the ball.

Optional: To increase accuracy, students can drop each ball three times and take the average of those results.

5. Before students begin measuring, create a three-column chart with one column listing the type of sport ball, one column for students’ predictions, and one column for actual results.  Have students  predict which type of ball will bounce the highest and which ball will bounce the lowest.  Record their predictions on the chart on a scale of one to four, with one being the highest bounce and four being the lowest bounce. Ask students to explain why they think the ball they choose will bounce the highest or lowest.

6. After students are finished taking measurements, record their results on the chart in the appropriate column. Compare and contrast their results with their predictions. Ask students why they think some of the balls bounced higher or lower than others.

Part II: What's Happening?

Certain types of sport balls are composed of materials that have elasticity, or the ability to quickly and easily revert back to their original shape after being stretched or deformed. Rubber, for example, is a type of material that is very elastic. When a rubber ball is dropped and hits the ground, the bottom of the rubber ball will become slightly deformed. Since this isn’t the original form of the rubber ball, it will quickly revert back to its original shape, a round sphere. The pressure of the ball snapping back into a round sphere will push against the ground, causing the ball to bounce back up.

Sport balls that require a greater degree of bounce, such as handballs and basketballs, also are aided by air pressure, or the amount of air inside the ball. The air inside the ball puts pressure on the rubber walls, which helps the ball spring back into its original position after it hits the court’s surface and deforms.

Part III: Topics for Science Class Discussion

• What other factors (besides elasticity and air pressure) do you think affect the bounce of a ball?  Why? What would happen if you bounced the ball on a carpeted floor or on a grassy lawn?
• In the video, Dr. Fontanella showed that spinning the ball changed the way it traveled. How do you think this effect might be used to your advantage?
• How are potential energy, kinetic energy, and elastic potential energy related to a bouncing ball?

Part IV: Extended Activities and Links

• Explore how temperature can affect the bounce of each ball by measuring the bounce after placing the balls in a freezer for 30 minutes.  Compare your results before and after freezing.  Why did the cold affect the ball’s ability to bounce? Explain how elasticity and air pressure are affected by temperature.
• Cut a variety of sport balls in half and examine the composition of each ball from the inside.  Is it hollow or composed of different materials or layers?  How does the design of a ball on the inside affect its performance?
• Assign each student to research the history of a specific ball sport.  Have each student present how and why the design of the ball changed over time for each specific sport.