Chemical Education Today edited by Erica K. Jacobsen JCE Secondary School Editor
Classroom Activity Connections
“Having a Ball with Chemistry”: More Things To Try by Thomas S. Kuntzleman, David Sellers, and Rachel Hoffmeyer
From the Editor JCE Classroom Activities—NCW and Beyond A typical piece of the Journal’s October National Chemistry Week (NCW) issue is a JCE Classroom Activity that matches the American Chemical Society’s selected NCW theme. However, generating that Activity can be anything but typical. For the past couple of years, we’ve been lucky enough to identify potential authors and receive Activity submissions for these issues. Although we prefer to bring you an Activity written by teachers currently in the classroom, we don’t always receive submissions to match a particular theme. In order to share a themed Activity the October 2008 issue, it was necessary that the author be “JCE Editorial Staff ” (1). You’ll see from the following Classroom Activity Connections article that we might have been able to publish a great (and similar!) NCW Activity by a teacher and ACS Student Affiliates group—we just didn’t know about it. Kuntzleman, Sellers, and Hoffmeyer developed an activity using racquet balls. They tested rebound heights of balls over a wide range of temperatures. They then linked the tests with a discussion of glass transition temperatures and the elastic properties of muscles, and also used it as a lead-in for a very popular classic demonstration.
Featured Activity ◭ Extension to JCE Classroom Activity: #98. That’s the Way the Ball Bounces (or Is It?) by JCE Editorial Staff, J. Chem. Educ. 2008, 85, 1376A–1376B.
movie special effects and things regarded as “magic”) (2). Chemists Celebrate Earth Day: The general topics are on a repeating four-year cycle (3). Upcoming themes are: air (2009); plants and soil (2010); recycling (2011); 2012 (water).
Literature Cited (sites accessed Aug 2008) 1. JCE Editorial Staff. J. Chem. Educ. 2008, 85, 1376A–1376B. 2. About National Chemistry Week. http://portal.acs.org/portal/ Navigate?nodeid=1041. 3. Chemists Celebrate Earth Day Past Themes. http://portal.acs.org/ portal/Navigate?nodeid=1571.
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2008/Nov/abs1478.html Abstract and keywords
Share Your Ideas Do you have an idea for an Activity or article to submit for an upcoming theme? Here is the lineup: NCW 2009: Chemistry—It’s Elemental (periodic table) NCW 2010: Behind the Scenes with Chemistry (includes
Full text (PDF) Links to cited URLs and JCE articles
Erica K. Jacobsen is Editor, Secondary School Chemistry, JCE;
[email protected].
Bouncing Ball Breakdown Great minds think alike! That’s what our American Chemical Society Student Affiliates group at Spring Arbor University collectively thought when we read JCE Classroom Activity #98 (1) in the October 2008 issue of this Journal. You see, our group designed a very similar activity during the 2007 NCW Chemvention Competition. In the competition, Student Affiliate groups were challenged to design a hands-on activity for elementary school children focusing on the 2008 NCW theme, “Having a Ball with Chemistry”. We wanted to use balls easily purchased at local stores. We initially tried this activity with super balls, but were disappointed in the small difference in the rebound heights of the hot and cold super balls—less than 10 cm, similar to what was reported in the JCE Classroom Activity (1). After testing a wide variety of sports balls (tennis balls, golf balls, etc.), we found excellent variability in temperaturedependent rebound height using Penn-brand racquet balls. Extensions that we found useful while presenting this activity to children are outlined below. 1478
Extension 1 Testing Balls over a Wide Temperature Range To emphasize the dramatic effect of temperature on rebound height, we incubated racquet balls, as well as super, happy, and unhappy balls, at many different temperatures for several minutes and subsequently tested the rebound ability of each ball at each temperature (Table 1). Extension 2 The Glass Transition Temperature While conducting this activity, we noticed that the balls tend to rebound less as they are cooled below 100 °C. However, this loss of rebound ability doesn’t continue indefinitely. After reaching a minimum rebound height at a particular temperature, the balls gain rebounding ability as the temperature is cooled further. For example, the unhappy ball rebounds 63 cm at
Journal of Chemical Education • Vol. 85 No. 11 November 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
Chemical Education Today
photos by Stephanie Ling Students measure rebound heights of racquet balls at a range of temperatures. At left, Anna Comfort incubates a racquet ball at 100 °C to prepare to test its rebounding ability at this higher temperature. Center photo, Steve Lane (left) and David Sellers (right) test the rebound characteristics of a racquet ball dropped from a higher height. At right, Stephanie Ling (left) prepares to test the properties of a racquet ball while Rachel Hoffmeyer (right) takes notes.
100 °C, 2 cm at 20 °C, and 13 cm at 0 °C. This curious behavior of the balls may be explained by the glass transition temperature (Tg) of amorphous polymers. Above Tg, a polymer is said to be in a viscoelastic state (2). In the viscoelastic state, polymers are often referred to as elastomers because they have elastic, rubbery properties. When displaying elastomer-like properties, a polymer ball will bounce like a normal rubber ball. Below Tg, a polymer is said to be in a “glassy” state (2, 3). In this state, a polymer will behave like a hard solid and will bounce pretty well—sort of like a glass marble against a hard surface. However, a polymer will not bounce very well near Tg. This is why the unhappy ball
doesn’t bounce so well at room temperature: it is very close to its glass transition temperature. A previous article in this Journal provides detailed explanations of the behavior of polymers near Tg (2). Values of Tg for a variety of polymers have been tabulated (Table 2); see (4–7) for more extensive lists.1 After completing the exercise with happy, unhappy, super, and racquet balls, students can estimate Tg for each polymer ball by noting the approximate temperature at which the rebound height was a minimum. Students can then suggest possible compositions of the various balls by comparing the experimental estimates of Tg to tabulated values.
Table 1. Effect of Temperature on Rebound Height of Various Balls Temperature/°C
To reach this temperature, the ball was:
Rebound height/cm Rebound height/cm Penn racquet ball super balla
Rebound height/cm happy ball
Rebound height/cm unhappy ball
100
placed in boiling water
80
90
74
63
20
left at room temperature
70
82
63
2
0
placed in an ice/water mixture
50
70
53
13
−20
placed in an ice/ acetone mixture
45
60
20
55
−78.5
covered with dry ice in a small cooler
5
10
5
65
−196
dipped in liquid N2 for a few minutes
ball shattersb
60
67
75c
Estimated Tg
—
−78.5 °C
−78.5 °C
−78.5 °C
20 °C
aBecause super balls differ in composition, variation in results should be expected. bWe have intermittently observed racquet balls cooled in liquid N2 to rebound about 30 cm without shattering. cUse caution when cooling unhappy balls in liquid N2. Occasionally, these balls spontaneously shatter when chilled in liquid N2 for long periods of time or while they warm to room temperature after removal from liquid N2.
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 11 November 2008 • Journal of Chemical Education
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Chemical Education Today
Classroom Activity Connections Table 2. Glass Transition Temperatures of Polymers Used in Balls Polymer Name
Common or Trade Name
Tg/ °C
poly(cis-chloroprene) -20 poly(trans-chloroprene) -40 polychloroprene neoprene (happy ball) -49 polynorbornene Norsorex (unhappy ball) 30 poly(cis-isoprene) natural rubber -60 to -73 poly(trans-isoprene) -53
Extension 3 The Glassy Racquetball Using racquet balls for this activity and a subsequent discussion of Tg provides a nice segue into the classic demonstration of chilling a racquet ball in liquid nitrogen and subsequently throwing it against a hard surface—the ball shatters! Once students understand that all polymers have a particular Tg, they can recognize that the racquet ball shatters because it has been cooled below Tg for the polymer that comprises the ball.2 Details of the molecular processes involved in this unforgettable demonstration have been described previously (3). Extension 4 Elastic Properties of Muscles Because of the sports-related theme for NCW, 2008, we extended this activity to a discussion of athletic performance. After conducting the activity, students look at the effect of temperature on rebound height for each ball in the viscoelastic state (above Tg for each ball). We point out that polymers that display rubbery properties above Tg are called elastomers (8–10), and elastomers become more springy (elastic) as they reach higher temperatures. That’s why the balls bounce higher as they reach higher temperatures above Tg. We then connect this to the idea that muscles are made of molecules that behave very much like elastomers (11–12). Once the students realize these simple facts, they can usually give you at least one reason why it’s a good idea to warm up muscles before exercise!
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Notes 1. Note that unlike a melting point, Tg for a particular polymer can vary widely depending upon several factors, including how fast the polymer is warmed or cooled, the method of measurement, and many other factors. In addition, Tg usually represents a range of temperatures through which a polymer changes from glassy to viscoelastic. 2. An interesting aside is that 1986 U.S. space shuttle Challenger explosion is believed to have been caused by faulty O-rings in rocket boosters on the spacecraft. These O-rings were unfortunately cooled below their Tg on unusually cold mornings before launch.
Literature Cited
1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12.
JCE Editorial Staff. J. Chem. Educ. 2008, 85, 1376A–1376B. Sperling, L. H. J. Chem. Educ. 1982, 59, 942–943. Hawkes, S. J. J. Chem. Educ. 2008, 85, 1377–1380. Thermal Transitions of Homopolymers: Glass Transition & Melting Point. http://www.sigmaaldrich.com/aldrich/brochure/ al_pp_transitions.pdf (accessed Aug 2008). Dashora, P. Physica Scripta 1994, 49, 611–614. Beck, K. R.; Korsmeyer, R.; Kunz, R. J. J. Chem. Educ. 1984, 61, 668–670. Burfield, D. R. J. Chem. Educ. 1987, 64, 875. Kauffman, G .B.; Seymour, R. B. J. Chem. Educ. 1990, 67, 422–425. Kauffman, G. B.; Seymour, R. B. J. Chem. Educ. 1991, 68, 217–220. Seymour, R. B.; Kauffman, G. B. J. Chem. Educ. 1992, 69, 967–970. Cuming, W. G.; Alexander, R. M.; Jayes, A. S. J. Exp. Biol. 1978, 74, 75–81. Hirano, M.; Rome, L. C. J. Exp. Biol. 1984, 108, 429–439.
Thomas S. Kuntzleman is a member of the Department of Chemistry, Spring Arbor University, 106 E. Main Street, Spring Arbor, MI 49283;
[email protected]. David Sellers and Rachel Hoffmeyer are senior chemistry and biochemistry majors, respectively at Spring Arbor University. David plans to go to graduate school; Rachel intends to go to veterinary school.
Journal of Chemical Education • Vol. 85 No. 11 November 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
