University of Virginia
Physics Department

## The Effect of Temperature on a Bouncing Ball

A Physical Science Activity

2003 Virginia SOLs

• PS.1
• PS.2
• PS.6
• PS.10

Objectives

Students will:

• Define the Independent and Dependent Variables in the experiment;
• Control variables in the experiment;
• Discuss the effect of heat on the molecular behavior of objects;
• Define potential and kinetic energy and use those terms in their discussion of the experiment;
• State Newton's Third Law of Motion and explain how it relates to the experiment;
• Understand and apply the Law of Conservation of Energy as it relates to a bouncing ball.

Motivation for Learning

Teacher Demonstration

Materials

• One Happy Ball

The Happy/Sad balls can be found in Sargent-Welch's physics catalog (try www.sargent-welch.com for a free one), or from Science Kit and Boreal Laboratories at sciencekit.com.

Procedure

1. Hold the Happy Ball in one hand and the Sad Ball in the other hand.
2. Tell the students that the two balls are identical in size and shape, but do not behave the same. One ball is happy, but the other ball is sad.
3. Drop both balls simultaneously and ask students if they can decide which ball is happy and which ball is sad.
4. Question students as to why they think that the one ball bounced and the other ball did not.
5. Discuss with students the physics behind a bouncing ball, and the physics behind the ball that does not bounce. (See the Background Information.)
6. Tell students that there are some ways to make the Sad Ball happy and the Happy Ball sad and that you will be conducting an experiment that will accomplish that.

Background Information

Everyone has played with balls that bounce, but few people truly understand the physics behind a bouncing ball. When you hold a ball above a surface, the ball has potential energy. Potential energy is the energy of position, and it depends on the mass of the ball and its height above the surface. The formula for gravitational potential energy is PE = mgh where m is the mass of the ball measured in kg, g is the gravitational acceleration constant of 9.8 m/se c2 , and h is the height of the ball in m. As the ball falls through the air, the potential energy changes to kinetic energy. Kinetic energy is energy of motion. The formula for kinetic energy is KE=1/2 mv 2 , where m is the mass in kg and v is the velocity in m/sec 2 . Both potential and kinetic energy have units of Joules (J).

As the ball falls through the air, the Law of Conservation of Energy is in effect and states that energy is neither gained nor lost, only transferred from one form to another. The total energy of the system remains the same; the potential energy changes to kinetic energy, but no energy is lost. When the ball collides with the floor, the ball becomes deformed. If the ball is elastic in nature, the ball will quickly return to its original form and spring up from the floor. This is Newton's Third Law of Motion- for every action there is an equal and opposite reaction. The ball pushes on the floor and the floor pushes back on the ball, causing it to rebound.

On a molecular level, the rubber is made from long chains of polymers. These polymers are tangled together and stretch upon impact. However, they only stretch for an instant before atomic interaction forces them back into their original, tangled shape and the ball shoots upward.

You may be wondering why the ball does not bounce back to its original height. Does this invalidate the Law of Conservation of Energy? Where did that energy go? The energy that is not being used to cause motion is changed to heat energy or sound energy. After playing a game of tennis or racquetball, you will notice that the ball is warmer at the end of the game than at the beginning because some of the motion energy has been changed to heat energy. Because bouncy balls have tightly linked polymers, most of the energy is transferred back to motion so little is lost to heat or sound energy, and the ball bounces well. This is the way the Happy Ball behaves.

The Sad Ball has different characteristics. When it is dropped from the same height onto the same surface, it does not bounce even though it has been given the same amount of potential energy as the Happy Ball. It does not bounce because it is made up of a different material. Unlike the Happy Ball which is made of Neoprene, or common rubber, the Sad Ball is made of Norbonene. On a molecular level, Norbonene is different from Neoprene because Norbonene's polymers are more loosely arranged and rub together more when the ball deforms. This additional movement results in motion being converted to heat energy; instead of the ball bouncing, it gets warm. There are several ways to make the Sad Ball happy. One way is to change the temperature of the ball. When the Happy Ball is cooled, its molecules are not as flexible, causing the ball to rebound a smaller distance. When the Sad Ball is cooled, the Norbonene polymer does not deform as much, so less energy is converted to heat energy and the ball bounces. If the Sad Ball is heated, the same process occurs and the ball bounces.

Neoprene and Norbonene have many uses besides bouncy balls. Neoprene is commonly used for wire and cable jacketing, automotive gaskets, seals, hoses and tubes, power transmission belts, foamed wet suits, latex gloves and balloons, as waterproof membranes, and for asphalt modification. Neoprene is flexible in its uses because it resists degradation from the sun, ozone, and weather. It performs well when in contact with oil and chemicals and is useful over a wide temperature range. It also resists burning better than exclusive hydrocarbon rubbers and resists damage caused by flexing and twisting. Doping of the Neoprene polymer allows for more versatility and optimal performance. Norbonene rubber has impact absorption uses. It is used as a damping material in shock absorbers and for the protection of conveyor mechanisms. It is used as a padding material in items such as body armor, helmets, sports gloves and mitts, and in the soles of shoes. It is also widely used as an industrial packing material. Stereo speakers make use of Norbonene to minimize resonance and external vibration.

Happy and Sad Balls behave differently in a variety of situations. They roll down a ramp at different speeds, they emit sound waves at different decibels, and they bounce different heights on different surfaces. They can be compressed dissimilar amounts when the same force is applied and they are different densities, so they sink in different solutions at variable rates.

Allow students to play with the balls for a while and experiment with dropping and rolling the balls to allow them some time to compare and contrast the behavior of the balls and for creative ideas to occur. The time frame for completing the lab is approximately 90 minutes, although this can be modified by reducing the temperatures tested to three instead of five, or splitting the class into 5 groups where each group tests only one temperature and then places their results on a class data table. Achieving exact temperatures is unnecessary; near 00C and near 1000C are easy to get through the use of ice and by boiling water. Room temperature is near 200C. Two other temperatures, one lower than room temperature and one higher should be used to more completely explore Happy and Sad Ball trends.

### Student Activity

Materials

• One Happy Ball
• One thermometer
• Four 250 ml beakers
• Ice
• 500 ml of water
• One Hot Plate
• Tongs
• One Hot Hand or comparable mitt for holding a hot beaker
• One meter stick

Procedure:

1. Measure the air temperature of the room. Record in your data chart
2. Tape the meter stick to a wall or a table so that the bottom of the meter stick is touching the floor at zero centimeters.
3. Hold the Happy Ball with the tongs at the 100 cm mark of the meter stick, but a few centimeters away from the meter stick.
4. Drop the ball and observe the height of the first bounce. Record this number in your data chart.
5. Repeat step 4 two more times.
6. Repeat steps 3-5, but use the Sad Ball.
7. Fill a 250 ml beaker halfway to the top with ice. Add 100 ml of water. Submerge the Happy Ball in the ice/water mixture for 5 minutes. Take the temperature of the ice/water mixture and record in your data chart.
8. Remove the ball with the tongs and immediately drop it from the height of 100 cm and observe the height of the first bounce. Record this number in your data chart. Immediately repeat this two more times. (Note: if you believe that the ball has warmed significantly, replace the ball in the water for one minute to re-chill it.) 9. Repeat steps 7-8 using the Sad Ball.
9. Repeat steps 7-8 using water heated or cooled to the temperatures of 100C, 500C, and 1000C.

Data Sheet

 Data Sheet - Effect of Temperature on a Bouncing Ball Height of Bounce in cm. Temperature (C) Trial 1 Trial 2 Trial 3 Average Happy Ball Data Sad Ball Data Use the graph paper provided to graph your data. You should draw a double line graph (graph two lines, one for the Happy and one for the Sad Ball on the same graph paper. Use a key to distinguish the two lines.)

Student Questions

To print out a copy of the Student Questions only, click here.

Answer the following on a separate sheet of paper:

1. What is the independent variable in this experiment?

2. What is the dependent variable?

3. Why is it important to only change the temperature and not any other variable (such as the drop height)?

4. At what temperature did the Happy Ball bounce the highest?

5. At what temperature did the Sad Ball bounce the highest?

6. How did changing the temperature affect the elasticity of each ball?

7. Write a paragraph that explains how a ball bounces. Use the terms kinetic energy, potential energy, Newton's 3rd law of motion, and the law of conservation of energy in your explanation.

Students with Special Needs

Each student should be able to participate in this activity.

Click here for further information on laboratories with students with special needs.

Extensions

To make the lab shorter, reduce the temperatures tested to three instead of five (00C, room temperature, and boiling), or split the class into 5 groups where each group tests only one temperature and then places their results on a class data table.

For remedial students, reduce the temperatures tested to three instead of five (00C, room temperature, and boiling).

Use your calculator based lab and motion detector to more accurately determine the height of the first bounce. Visit the website at http://www.ti.com/calc/docs/act/hsmotion08.html for more information.