SWIRLING GRANULAR MATTER - FROM ROTATION TO REPTATION

Experiments and numerical simulations of granular material under swirl ing motion of the container are presented. At low packing densities th e material rotates in the same direction as the swirling motion of the container (rotation). At higher densities the cluster of granular mat erial rotates in the opposite direction (reptation). The change of the direction of the motion of the cluster takes place at a critical pack ing density while the diffusion coefficient changes significantly. The measured critical density of the packing is in good agreement with re sults obtained by molecular-dynamics simulation.