Using a Vortx to Teach Kepler’s Laws and Potential Energy

For more than 10 years, I had taught Kepler’s laws and the law of universal gravity without a corresponding experiment. I sometimes remember how these topics were difficult for me in my high school days to understand. At that time, I thought that one of the reasons for my difficulty was that these phenomena cannot be visualized using physical objects. In this paper, I report on a method I developed by which students can actually watch some of the phenomena of Kepler’s laws and the law of universal gravity. In an earlier paper, theoretical and experimental results for a ball that rolls without slipping on a surface of revolution in cones and other funnels have been reported. Here I would like to introduce some experiments using a coin bank named Vortx®. The Vortx is a familiar and inexpensive apparatus (less than $50), and many Japanese physics teachers already have one. The Vortx, when used with the following experiments, can help students visualize a gravitational potential well, where the radius represents the distance to a massive body and the height from the funnel tip represents the potential energy per kg (for a description of a gravitational potential well, please refer to, for example, Ogborn). However, when we use the Vortx, we need to take care of some points as described in the following. One goal of this paper is to inform TPT readers how the Vortx can be used in the classroom.