Isotopic decay of chewing gum
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This page first made public: Jul 11, 2008
Skills and concepts that students must have mastered
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Description of the activity/assignment
Student preparation for this assignment is the same as any other class. They are responsible to complete the reading before class. After I have introduced the concept of isotopic decay I have three student volunteers conduct the 'experiment'. One student is the time keeper while the other two students chew gum and weigh the gum at one minute intervals. The only instructions to the students are to chew consistently and to make sure they try to weigh a 'dry' piece of gum. The time keeper is responsible for making sure the gum chewers weigh the sample after each minute of chewing. I enter the data into a spread sheet as it is collected. That way I can discuss the data, explain the equations and ask questions. The entire experiment takes about 25 minutes to complete. After all of the data are collected, we determine half-lives through an iterative process by minimizing the RMS error. This also allows me to introduce error and one way to quantify it.
This demonstration could be expanded into a component of a laboratory. Multiple students could chew the same gum to increase the sample size, the could chew different types of gum and measure a different decay constant, they could plot their own graphs, calculate their own decay constants and half-lives, and use a type of candy that does not follow the from exponential decay form. In this form students could form their own hypotheses and test them.
There is no additional information that you need to know. I have included a spreadsheet of data from Fall 2007. You can use the same spreadsheet and just adjust for the data from your students. The only thing to keep in mind is that gum will not decay to almost 0 because there is a portion of the gum that will remain. We are only interested in the portion of the gum that does 'decay'. Therefore, I have included a 'mass correction' calculation based on the mass of the gum after the 10 minute mark.
Determining whether students have met the goals
Download teaching materials and tips
- Gum Decay Spreadsheet Example (Excel 26kB Jul16 08)