What if the surface is rough? A study on the influence of the friction force in inelastic collisions through video analysis

This paper presents a study that explains the physics associated to the set of successive inelastic collisions of a spherical solid against the rigid surface of the lab’s floor after being launched from a certain height. The solid’s center of mass is tracked by means of a video analysis through the well-known educational software Tracker, allowing us to obtain its velocity in the whole described path. The solid’s linear momentum is then obtained for the instants immediately before and after the collisions, permitting to evaluate its dissipation as well as the kinetic energy dissipation during these events. The role played by the friction force during the collisions is also evaluated through a not widely known quantity in basic physics literature, named by tangential restitution coefficient. Measurements of this quantity presented values close to unit and, therefore, quantitatively revealed that, to the performed experiment, the frictional force contribution to the impulse during the collisions are tiny if compared to that provided by the normal force applied by the lab’s floor. This result is implicitly considered in the collisions models presented in the basic physics’ textbooks, where, without any justification, the frictional force is ignored.

Keywords
Inelastic collision; video analysis; tangential restitution coefficient