Bounce

1. Hold up a racquetball and have students discuss what it is. 
2. Have students discuss some characteristics of a racquetball (very bouncy)!
3. Ask students what material they think a racquetball is made out of. Where does it come from? Can this material be recycled? Have students share ideas.
4. Racquetballs are made out of rubber, the same material used to make tires. Why would a racquetball or tire be made of latex rubber rather than something hard like wood or metal?
5. Every substance has characteristic properties. The special properties of latex rubber make it ideal for many purposes! Natural rubber (latex) comes from the sap of tropical trees. Humans have figured out ways to make a synthetic rubber. About 21 percent of today’s passenger tires are made from natural rubber (synthetic rubber represents 27 percent and carbon black 28 percent).
6. Can tires be reused or recycled? Each year, Americans generate approximately 100 million scrap tires, with more than 90 percent recycled and reused annually.
7. Show students the image of a Merry-Go-Round that is made of recycled tires. What might be other uses?
8. Explain that students will learn more about the properties of rubber by using the racquetballs in an experiment.

Grab a ball and let’s play scientist! Each material has special traits or properties. The properties make it ideal for making certain items and purposes. In this activity, you’ll examine the elasticity (ee-la-stis-itee) of a racquetball. You will explore how temperature affects how high the ball bounces, and think about the many uses for rubber.

Materials:

• Device with internet access
• Student Data Sheet (printable PDF)
• Three racquet balls
• Three large paper cups
• Ice cube
• Thermometer
• Markers for labeling cups
• Meter stick
• A large graduated cylinder
• Water (warm and room temperature)

Safety Notes:

• When using technology, engage in safe, legal, and ethical behavior; this applies to devices (hardware), application or programs (software), and interactions with others.
• There are no anticipated physical safety risks associated with this Activity.

Part 1: Make Observations

1. Your teacher will give you a piece of a racquetball. Make observations and list at least 5 traits. What materials is the racquetball made of? Divide teams into groups of 3-4 students. Pass out a piece of a racquetball. Have students make observations and list at least 5 traits (have them consider texture, smell, weight or mass, color, size, and what happens when pulled or twisted?)
2. Share observations with the class. What happens when you pull the piece from different ends? When you twist it? Discuss the word elasticity (the ability of an object or material to resume its normal shape after being stretched or compressed; stretchiness). Have students conduct activity.
3. Fill a cup or graduated cylinder about 2/3rds of the way up with room temperature water.
4. Make a hypothesis about what might happen when the piece of racquetball is placed into the water. Will it sink or float and why?
5. Place your piece of racquetball into the water – what happens? What does this tell you about the ball? Depending on grade level and abilities, you may include a more extensive exploration of density, and have students actually calculate it (using displacement method in water to calculate volume, and a scale for mass, where d=m/v). At the most basic level, floating vs. sinking in water is a good way to get a general idea of density (objects more dense than water will sink; objects less dense than water will float). This portion of the activity is a quick and good way of getting kids into “observation mode” and measuring qualities of a material that a scientist might also do if he/she were learning more about its behavior and properties.

Part 2: Warm-up

The warm-up portion of the activity should have students thinking about procedure and methods. This is a good time to challenge them to think about how many times (trials) they should do their test and why. How can they repeat it the same way each time? This is also a good time to discuss with students the importance of dropping balls from a certain height, same height each time. Throwing the balls down will: lead to safety issues (hitting someone or something); be hard to measure (because it will go too high or off at a different angle); and make it difficult to control the force with which they throw the ball down every time which could lead to errors. This gives students a chance to think about experimental design and science practices. Discuss and review as a whole class. Eventually, students will follow the guidelines provided in the lab as one example of how to control the variables and plan a safe experiment. Depending on age and ability, you might also allow students to follow their own procedures as long as they are safe and workable.

1. How high do you think a racquetball can bounce? Can you figure out a way to measure this? With your teammates, discuss how you could find this out. 
2. Discuss your plan with your teacher to get approval. Then test it out! How high did the ball bounce? Record your measurement.
3. How do you think temperature might affect the ball’s bounce height (rebound)? Make a prediction. Discuss how you would test this.
4. Discuss ideas with the class.

Part 3: Test the Bounce!

1. Fill 3 cups halfway with water: warm, room and cold. Make the cold water by putting an ice cube in the last cup.
2. Measure the temperature in each cup and record it.
3. Place one racquetball in each cup. Leave it there for five minutes.
4. One member of your group should hold a meter stick upright. One member will be the observer, and one the recorder.
5. Remove each ball from the water, dry it quickly and drop it from a height of one meter (don’t throw it; just let it fall). Record the height of the ball’s first bounce. Repeat two times.
6. Calculate the average height (how would you do this?) Which ball bounced the highest? The lowest? Provide guidance as needed during the experiment. Review how to calculate an average as necessary. For younger audiences, you may need to skip this.

Reflect and Apply:

• Elasticity is a trait or property of rubber. The more elastic a material is, the more “bounce” it will have. How did the temperature affect the elasticity (bounciness) of rubber?
• Can you think of other things that are made of rubber? Make a list and explain why rubber is good for that use.
• Rubber can be reused and recycled. Look at this photo of a running track at a Michigan middle school. It is made of tiny cubes cut from recycled tires! Discuss the traits or properties that might make rubber a great material to use in a running track! What do you think might happen to the track when the weather changes, and how would it affect the people running on it? Discuss with your class. INSERT IMAGE FROM PAGE 5 of ORIGINAL PDF of RUNNING TRACK SURFACE

Extension:

• Use the internet to find out where rubber trees are grown and where natural latex is obtained. Use the map provided to mark the locations.
• The special properties of rubber make it a valuable material. It can be re-used for many purposes. Think of the properties of good rubber tires and good running tracks. Use the Venn diagram provided to compare and contrast the properties of tires and running tracks. How are they alike? How are they different? How is rubber an ideal material for both?
• Journal Question: Imagine a world without rubber! If you could make a new kind of tire, what would it be made out of and why? Your new tire can be made from other materials that exist or from imaginary materials. Include a drawing if you wish!