Siphons, Water Clocks, Cooling Coffee, and Leaking Capacitors: Classroom Activities and a few Equations to Help Students Understand Radioactive Decay and Other Exponential Processes

Although an understanding of radiometric dating is central to the preparation of every geologist, many students struggle with the concepts and mathematics of radioactive decay. Physical demonstrations and hands-on experiments can be used to good effect in addressing this teaching conundrum. Water, heat, and electrons all move or flow in response to generalized forces (gradients in pressure, temperature, and electrical potential) that may change because of the flow. Changes due to these flows are easy to monitor over time during simple experiments in the classroom. Some of these experiments can be modeled as exponential decay, analogous to the mathematics of radioactive decay, and can be used to help students visualize and understand exponential change. Other, similar experiments produce decay or change that is not exponential. By having classes, in small groups, conduct several experiments involving flows, a learning synergy can be encouraged in which the physical and mathematical similarities of flow processes are emphasized. For the best results, students should be asked to analyze the experimental data, using graphs and algebra or calculus as appropriate to the class, to determine the nature of the decay process and to make predictions, either forward or backward in time as would be done for radiometric dating. Basic quantitative skills are strengthened or developed as part of these activities. Encountering a number of important geologic processes in the same mathematical context provides a good introduction for further study of any one of them.