Collisions of Coins

Abstract

This paper addresses a popular topic in science teaching and competitions for primary and secondary school students. Experiments with colliding coins are relatively easy to perform and therefore popular in science lessons. We used the idea in the science competition we organized for pupils aged 6 to 13 years. The science competition is based on a few experiments that the participants have to carry out before the competition. Some years ago, 10- and 11-year-old pupils had to experiment with coins. These were 1-, 10-, 20- and 50-euro cent coins (see Fig. 1), but the experiments can also be carried out with quarters and dimes. The experiments were simple elastic collisions with some obvious but also some profound outcomes, which will be described below. Even if the bodies are moving fast and the collision itself is an instantaneous event, it is possible to reconstruct the trajectories from known initial and final positions of the coins. At the end of this paper, we will present the set of problems that were given in the competition.