FLIPPING IN A CLASSROOM: USING COINS TO SIMULATE RADIOACTIVE DECAY IN INTRO-LEVEL COURSES

Students in intro-level courses often have trouble with the concepts around radioactive decay and dating concepts. The random nature of coin flipping is a useful way to demonstrate how radioactive atoms behave, at small- and large-scale, and to show basic ideas of radiometric dating, too. Groups of up to four students are given a box with 31 pennies and 1 nickel. Starting with the coins face-up, they shake the covered box and remove all the flipped coins, recording the number of heads remaining on a graph. They continue until either all the coins have flipped or six sets of shakes have passed, taking care to identify when the nickel flipped. Then, they do the procedure a second time. Once they are done, they answer questions which are later discussed as a class: Do both trials look exactly the same? Did the nickel flip at the same time and did you expect it to? On average, what fraction of the coins flipped for every shake? Doing the activities themselves and answering these questions lead the students to the ideas that even though this is a random process (they can’t tell when the nickel will flip), they can expect about half of their sample to flip (or “decay”) each time. I collect everyone’s data and plot it to compare all of their trials, showing how each one is similar, but unique. I also combine it all into a larger sample, so instead of individual 32-coin samples, we have a (up to) 384-coin sample, which looks a little better. Then I show them all the data I’ve collected from from all my classes since 2012, comprising ~7000 coins to-date, which shows them that the larger the sample size, the more ideally it behaves. Finally, we look at radiometric dating by showing you can get a numerical age by assigning a regular time to the period of each shake (thus, a half-life) and knowing how many shakes took place by what percentage of heads are left. I have also adapted this into a larger-scale lab activity for my intro-level conceptual physics class.