Angular momentum conservation by video analysis using the flat balls toy

Abstract

The angular momentum of a particle system and its division into an orbital term and a spin term is a subject usually relegated to the background, or even absent, in introductory mechanics courses in undergraduate courses. In addition, the angular momentum conservation of a system, in the absence of external torques, can often be counterintuitive. The present work uses a toy called flat ball, which has a format similar to discs, in the context of a two-dimensional collision. Two identical flat balls are launched spinning in opposite directions and collide on a negligible friction surface. The experiment has great pedagogical potential because it provides a qualitative and quantitative analysis of the magnitude of the linear and angular momenta of the system, as well as its conservation, using the technique of video analysis. The surprising result of the experiment has the potential to arouse students' curiosity, as well as opening the way to address the transition of the system's absolute values of the orbital angular momentum and spin angular momentum, before and after the collision.

Keywords:
video analysis; collisions; angular momentum conservation