  Experiments on the motion of a particle on an inclined rough plane have
yielded some surprising results. For example, it was found that the frictional
force acting on the ball is viscous, {\it i.e.} proportional to the velocity
rather than the expected square of the velocity. It was also found that, for a
given inclination of the plane, the velocity of the ball scales as a power of
its radius. We present here a one dimensional stochastic model based on the
microscopic equations of motion of the ball, which exhibits the same behaviour
as the experiments. This model yields a mechanism for the origins of the
viscous friction force and the scaling of the velocity with the radius. It also
reproduces other aspects of the phase diagram of the motion which we will
discuss.
