We present molecular-dynamics simulations of a sphere moving down an inclined plane consisting of similar spheres of smaller size. For a certain range of inclinations, the sphere moves down the plane with a mean velocity ${\overline{v}}_x\ne 0.$ We investigate the properties of the motion in this steady state and the limits for its existence for a certain set of parameters. It is found that the steady-state velocity of the particle is independent of material properties and depends only on the geometry of the system. This means that the particle experiences an effective velocity-dependent friction force, with an effective “viscosity” determined only by the geometry. The fluctuations of the motion, however, can depend on the coefficient of restitution $e_n.$ For example, the diffusion coefficient $D_x$ is influenced by $e_n,$ but hardly depends on the roughness of the plane, while for $D_y$ the reverse is true. The range of the inclination angle and the roughness for which a steady state exists also depends on $e_n.$ We discuss how these results can be understood by considering the details of the motion.

• Received 25 April 1997

DOI:https://doi.org/10.1103/PhysRevE.56.3645