Dynamics of a bouncing capsule: An impulse model vs a Hertzian model

Abstract

A capsule-shaped object, unlike a sphere, can rebound to a higher height than it is dropped from if it has an initial spin. In this paper, we compare two quantitative models of this phenomenon: an impulse-based analytic model and a force-based Hertzian model. We experimentally studied the effects of impact angular velocity and contact angle on the capsule's rebounding velocity and angular velocity. Our experimental findings showed successful agreement with our Hertzian model but not with our impulse model. We attribute the comparative success of the Hertzian model to its intricate treatment of the slip–stick behavior of friction during the collision.