The Incredibly Stretchy Condom: A Lab Success Story

In my nonmajors biology class, our first lab of the semester is about the process and tools of science. Students get to practice with hypothesis-testing, the elements of an experiment, showing data in graphs, and metric units of measure.

The lab has undergone occasional bursts of evolution. Long ago, we had students measure the weights, volumes, and lengths of random objects and weigh piles of butter, sugar, and gelatin equivalent to the fat, sugar, and protein in a Snickers bar. Then, not quite as long ago, we made a big improvement: we adopted a “paper towel absorbency” activity, in which students had to use rulers, balances, and pipettes to determine which of several brands of paper towels was most absorbent (see, for example, this ABLE mini-workshop by Laine and Heath). They had to figure out their own methods, and each group used a different technique, so it was a good exercise for demonstrating multiple ways to approach the same problem.

However, it is probably fair to say that paper towel absorbency is not the #1 issue on the minds of our students. So I was happy to stumble across an article called “Sex and the Scientific Method: Using Condoms to Engage College Students” (Dorothybelle Poli, August 2011, The American Biology Teacher, p. 348). The basic idea of the lab is very simple: Have students ask and answer their own questions about condom strength, size differences, stretch, expiration dates, country of origin, and so forth. It’s reinforcing the same skills as our paper towel activity, but condoms lend themselves to questions that are a LOT more interesting to students.

A Very Stretchy Condom

Some condoms could be stretched a meter or more.
(Photo courtesy K. Gayler.)

I am happy to report that the lab went really well. Typical experiments included determining how far a condom could stretch (see photo at right) and counting how many marbles or measuring how much water condoms could hold without breaking. Some groups even tried to correlate a condom’s weight with its stretchiness, but most groups simply predicted that some condoms would be stretchier than others.

One of my main concerns was that some students might be too immature to handle condoms in a lab. For example, we had each group use the Explain Everything iPad app to present experimental methods and results; I secretly feared that at least one group would try to stretch a condom over an iPad, but no one did. Nor did anyone sling condoms full of water across the lab, pour water on an iPad, or make lewd condom-related suggestions.

That is not to say that all was perfect. One problem was that some groups gravitated toward the easiest experiments (i.e., measuring the length to which a condom would stretch); they were done much sooner than groups that chose more time-consuming (and more interesting) experiments. Next time, I think I will require groups to incorporate two or more types of measurements (length, mass, or volume) into their experiments so they have to be more creative and can’t get away with just measuring the stretched length.

A second problem was that most groups did not seek patterns beyond just predicting that brands would not perform equally. For example, I hoped they would survey the types of condoms available and seek patterns — they might have asked whether ultrathin condoms are consistently stretchier than “regular” ones, or whether ribbed condoms are the strongest. Next time, we will provide a worksheet that will help students think through and justify their variables and predictions, and perhaps even have them make a graph of their predicted results.

Finally, we need to tweak the materials we have available for students. The marbles were hugely popular, but we didn’t have enough to go around; you would be surprised at how many marbles a condom can hold! Next time, I will provide something heavier, like metal BB’s or ball bearings, which should cause the condoms to break much sooner than the marbles did.

Overall, however, students and TA’s agreed that the new lab was a huge success. Thank you, Dorothybelle Poli, for giving me the nerve to take a risk and try something new!

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12 Responses to The Incredibly Stretchy Condom: A Lab Success Story

  1. Kari Eamma says:

    Marielle, do you post your exercise 1 lab materials and procedures online for students to print and bring to lab? Or how do you work out changing your labs from year to year?

    • Good question. We have a bound, customized lab manual that we update every couple of years. When we have changes like this, we just tell students during lab that we’re going to do “this” instead of “that.” That gives us some experience with the lab before we immortalize it in the lab manual. If it were critical that they read ahead, but the new procedures weren’t in the lab manual, then yes, I think we would post the materials online for students to print.

  2. Sam Smith says:

    I’m both new at instruction and new at “official content attribution”. I’m wondering if you use information gleaned from a journal article like this project was, do you simply make a statement of it being modified from said article? Or is there a more complex system if it is included in a custom lab manual? Thank you in advance and I really love your willingness to share your experiences!

    • I think you’re asking whether in your own lab manual you can just say the activity is modified from Poli 2011 or whether you have to do something more formal. In my opinion, since ABT is giving you the idea but you still have to write your own instructions for the students, all you need is a note at the end of the lab exercise saying that the activity is modified from [complete reference].

      • Sam Smith says:

        This is exactly what I was wondering. We’ve got a copyright librarian here so I’m going to follow up with her. Thanks for your fast reply!

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  4. Sam Smith says:

    My class has 10 sections of 30 students each, so I’d rather not use water for volume or mass a condom can hold before breaking — too much wasted water. However, BBs were a great reusable solution (at least in my tests). We got a few of these: http://goo.gl/2WpgVh from a local store.

    I’m adding the option to use our Vernier labquest 2 units with force sensors (for the stretching tests), and gas pressure sensors to use if they want to inflate the condoms. To make the blow-a-condom-up sanitary I plan on using a rubber stopper that has one hole for the gas pressure sensor and another for a washable breathing tube/bike pump/sphygmomanometer bulb.

    This should be a much more engaging lab than our students had in the past!

  5. This is a great idea! We don’t have gas pressure sensors (as far as I know) but if you used a bike pump with a built in pressure gauge do you think that would work? And if you did use a bike pump, how might you make a leak-proof connection between the “out” nozzle of the pump and the rubber stopper? I love the idea of having another way for students to measure the strength.
    One more question: For the BBs, what proportion of a bottle would go into a condom before it broke? I’m trying to figure out how many to buy. Thanks!

    • Sam Smith says:

      I’m not sure that a built in pressure gauge would be sensitive enough to distinguish differences. The condoms could only handle about 2-3 kPa (about 0.3-0.4 psi). I cut off the whatchamadoohicky from an inner-tube and connected it to some tubing that went to the rubber stopper; this created an adapter to which we connected the pump. Here’s a picture of the setup: http://imgur.com/KrTCQyx

      You can fit around 2 bottles of BBs in the condoms we tried. Be sure to have a shopvac handy for the BBs. We used a large trash can to try and contain the mess, but a few tend to fly around.

      In addition to the regularly stored condoms, I put a selection in an incubator at 55C for a month to simulate them being stored in a glove compartment. I don’t know if it’s going to make a difference, but that’s what hypothesis testing is all about!

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  7. jamesjukosky says:

    Your blog has been extremely helpful for my teaching and finding great teaching resources. I now use a lab similar to this one in my Human Biology course (also a non-majors biology class). Recently, I started teaching an introductory evolution class and I came up with a blog post on my own blog to describe some of the great teaching resources that are available: http://biologyislife.com/4-great-resources-for-teaching-evolution/

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