Abstract
Recently, an investigation by Grochowski et al of the transport properties of granular material on a circularly driven, annular conveyor gave the surprising result that reversals of the transport direction can be observed as a function of the driving. We present a comparatively simple model that treats the granular dynamics as a combination of sliding and oblique hopping of a granular block with specific inelastic and frictional properties. This model quantitatively reproduces the experimental findings and indicates the reason for the current reversals. The special case of solely solid friction during the sliding process already agrees qualitatively with the experimental data; in particular, the current reversal effect can be obtained.