JCE Classroom Activities are edited by Erica K. Jacobsen
Instructor Information
JCE Classroom Activity: #98
That’s the Way the Ball Bounces (or Is It?) In this Activity, students investigate the physical properties of different balls that may look similar, but have very different rebound properties. Students also investigate how the rebound properties change when the balls are subjected to near freezing and near boiling temperatures. Several science supply companies sell pairs of small, solid balls that appear Maximum bounce height/cm identical, yet behave quite differently when dropped onto a hard floor. At room temperature, one ball has a very high resilience factor and bounces Ball type Cold Room temp. Hot fairly high, while the other has a very low resilience factor and has little to no Happy 51 63 71 bounce. Based on these properties, the balls are marketed as “happy/unhappy Super 61 63 70 balls” and “happy/sad balls”. The balls used to test this Activity were purchased 13 2 60 from Science Kit & Boreal Laboratories (1a); their properties and materials are Unhappy described below, but they may vary from balls purchased from other companies. The “happy” ball is made of polychloroprene (neoprene) rubber, while the “unhappy” ball is made of polynorbornene (trade name, Norsorex). Neoprene has excellent energy conservation properties, while Norsorex is able to absorb energy. If a neoprene ball is dropped and bounces, most of the energy is conserved and contributes to a high bounce; little energy is dissipated through heat. A Norsorex ball absorbs the majority of the energy and bounces hardly at all, dissipating the energy through heat. More information about the chemistry of the polymers is available (2, 3), including suggested explanations for why the bounce properties change at different temperatures.
Integrating the Activity into Your Curriculum This Activity is based on a past JCE article (2) and corresponds with the 2008 National Chemistry Week sports-related theme “Having a Ball with Chemistry”. Similar experiments are available and could be performed with actual sports balls, such as tennis, golf, and baseballs (3, 4). The Activity could be used at the beginning of the school year as an exercise in making observations. It could relate to units on physical properties and polymers.
About the Activity Each student group needs a set of three balls: a pair of happy/unhappy balls and a super ball (found at discount stores). It is ideal if the instructor can locate super balls that are the same color as the happy/unhappy balls, however, this can be difficult. Happy/unhappy balls are available from various companies (1). The goal of the Activity is not to determine the materials that make up each ball, but for students to make observations and compare the available balls. The instructor should distinguish each ball with a mark, such as with small dots of different colored fingernail polish. In this way balls with an identical appearance can be distinguished from each other, especially since their behavior changes at the different temperatures tested. When students determine ball volume for density calculations, it can be a tight fit for the balls in a 100 mL graduated cylinder. The balls can sometimes be eased out by tipping the cylinder downward and gently tapping on the side of the cylinder. The instructor should check the fit beforehand. Alternatively, students can use larger cylinders or measure the circumference of the balls and calculate the volume mathematically (circumference = 2 r π; volume = 4/3 π r3). perforated
Answers to Questions 1. Densities will vary depending on the balls purchased. Ball volumes should be very similar, while the masses differ. In testing, happy: 0.88 g/mL, super: 0.96 g/mL, sad: 1.00 g/mL, although all appeared to sink in tap water. 2. Most people expect the balls to bounce the same way. One of the balls hardly bounces at all; the other two do bounce.
This Classroom Activity may be reproduced for use in the subscriber’s classroom.
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Background
3. See table. The rebound height for the “unhappy” ball changes dramatically when heated. 4. At room temperature, one ball has little to no bounce, making it “unhappy”. The other two balls both bounce, making them “happy” and “super”. At a high temperature, the “unhappy” ball behaves more like a “happy” ball. 5. Answers will vary. Two possible answers are: The “unhappy” material could be used in running shoes. The “happy” and “super” materials could be used in sports where an elastic ball is needed, such as in handball.
References and Additional Related Activities (all URLs accessed Jul 2008) 1. (a) Science Kit & Boreal Laboratories. Happy/Unhappy Balls ($6.40, WW6974500); 800/828–7777. http://sciencekit. com/. (b) Arbor Scientific. Happy/Unhappy Balls ($3.95, P6-1000); 800/367–6695. http://www.arborsci.com. (c) Educational Innovations. Choositz Decision Balls ($6.95, SS-3); 888/912–7474. http://www.teachersource.com. 2. Kauffman, George B.; Mason, Stewart W.; Seymour, Raymond B. Happy and Unhappy Balls: Neoprene and Polynorbornene. J. Chem. Educ. 1990, 67, 198–199. 3. Effect of Temperature on a Bouncing Ball. http://galileo.phys.virginia.edu/outreach/8thGradeSOL/EffectofTemperature.htm 4. Sport! Science: That’s the Way the Ball Bounces. http://www.exploratorium.edu/sports/ball_bounces/ballbounces3.html Supporting JCE Online Material at http://www.jce.divched.org/Journal/Issues/2008/Oct/abs1376A.html
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 10 October 2008 • Journal of Chemical Education
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JCE Classroom Activity: #98
Student Activity
That’s the Way the Ball Bounces (or Is It?) Balls used in different sports are made up of various materials, or even combinations of materials, depending on what the ball is designed to do. For example, golfers might desire a ball that travels as far as possible on an opening drive. Golf balls were originally constructed with materials such as wood and even goose feathers wrapped in leather. These balls did not travel very far. Improvements in distance traveled have been achieved over the years by incorporating different materials, such as types of rubber. These days, balls have been even further improved through the addition of modern materials such as titanium. When you see and use a golf ball made of these particular materials, you tend to know how it will act. What if you encountered a ball that looked ordinary, but acted in a totally unexpected way? What if you could even change the ball’s behavior? In this Activity, you will investigate how several balls bounce at different temperatures. They may look similar, but you might be surprised at how they act.
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photos by Jesse M. Jacobsen
Be Safe! Take care You will need: set of three marked balls from your instructor, water, small bowl, balance (±0.01g), not to burn yourself 100 mL or larger graduated cylinder, meter stick, tape, ice, paper towels, timer, tongs, small pot, and access to a stove or hot plate. or others with boiling water. __1. Observe and record the physical properties of the three balls from your instructor. Some properties you could investigate are: color, feel, surface appearance (shiny, dull?), “squishiness”, etc. How are the balls alike? How are they different? __2. Stand on a hard, smooth, level floor. Hold all three balls at about waist height and drop them simultaneously onto the floor. Record your observations. Does each ball act the same when dropped onto the floor? Did they act as you expected they would? __3. Fill a small bowl about 1/2 full of water. Place all three balls in the bowl. Record whether each ball sinks or floats. Save the bowl of water for step 7. __4. Collect and record data to calculate the density of each ball. Based on your observations from step 2, do you expect the densities to be different or the same? Weigh each ball on a balance. Fill a 100 mL or larger graduated cylinder about half full of water. Observe and record the initial volume of the water. Place one of the balls in the cylinder. Observe and record the final Each ball is dropped volume of the water. If the diameter of your graduated cylinder is too small, what measurefrom a measured height ment could you take to determine a ball’s volume mathematically? onto a hard surface to determine its maximum __5. Stand on a hard, smooth, level floor next to a wall. Using a meter stick and a piece of tape, bounce height. mark a height of 1 m on the wall. You will drop each ball from this height in the remaining tests. Hold or tape the meter stick against the wall so that you can estimate and record the maximum height to which each ball bounces. __6. Drop one of the balls onto the floor from the marked height. Either you or a partner should estimate and record the maximum height to which the ball bounces. Perform at least three trials. Repeat for the remaining balls. __7. Add several ice cubes to the bowl of water from step 3. Place all three balls in the bowl and allow to chill for ten min. __8. Repeat step 6 with each of the chilled balls to measure the maximum bounce height. You may wish to use a particular ball for one trial, then return it to the ice water to ensure it is chilled before using it for another trial. __9. Fill a small pot about 1/2 full of water. Place all three balls in the pot. Heat the pot on a stove or hot plate until the water boils. Boil the balls for 3–5 min. __10. Using tongs to pick up the balls, repeat step 6 with each of the heated balls to measure the maximum bounce height. You may wish to use a particular ball for one trial, then return it to the hot water to ensure it is heated before using it for another trial. Wipe up any water on the floor with paper towels. __11. Allow the balls to return to room temperature. Repeat step 6. Did chilling and heating the balls permanently change their original bounce properties?
Questions 1. Using the data collected in step 4, calculate the density of each ball. Are they the same or different? 2. Some of the balls appear very similar. Did you expect that they would react the same way when bounced? How did they actually react? 3. Create a table of the maximum bounce heights at each of the different temperatures. How do they compare? 4. The three balls are sometimes referred to as “happy”, “unhappy”, and “super”. Which is which? Why? How does this change at different temperatures? 5. Describe ways that the ball materials could be used in a sports environment or elsewhere.
Information from the World Wide Web (accessed Jul 2008) Bill Nye: Spitballs. http://encarta.msn.com/encnet/features/columns/?article=bnspitballs Wired Science: Ball Busters. http://www.pbs.org/kcet/wiredscience/story/45-ball_busters.html This Classroom Activity may be reproduced for use in the subscriber’s classroom.
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Journal of Chemical Education • Vol. 85 No. 10 October 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
