DIFFUSIVE PROPERTIES OF MOTION ON A BUMPY PLANE

We report on experiments studying the statistical properties of the mo tion of balls on a bumpy surface. This motion is found to be diffusive . In the direction of the mean flow. the coefficient of diffusion is f ound to attain a constant value, independent of the size of the ball a nd the inclination angle. The diffusion transverse to the mean flow is characterized by a coefficient which decreases with the inclination o f the plane, and scales with the size of moving ball.