Rotation and reptation of swirling spheres as slope relaxation and avalanche

Abstract

We re­-explain the phenomenon of swirling granular material. We propose a different picture for reptation, the rotation of a cluster of particles opposite its driving motion. Unlike the rotating pancake model of the original study, we consider reptation as avalanche dominating over slope relaxation. The "centrifugal" force due to swirling motion, which is analogous to gravity, drives avalanche while the swirling motion itself drives slope relaxation. Which of these two dynamics occurs faster determines the direction of rotation of the granular material. We believe that this new perspective is able to account for the granular material's behavior for a long range of packing densities, including the transition from rotation to reptation, in one coherent picture.