Effects of geometry on the characteristics of the motion of a particle rolling down a rough surface

The different dynamic regimes of a sphere rolling on a rough inclined surface have been studied experimentally, with special attention to the effects of energy dissipation and geometry. A controlled roughness of the surface is obtained by gluing glass beads or sand onto a plane. Three different types of rolling spheres (steel, glass and plastic) have been used on two kinds of rough surface (glass beads and sand). The different regimes can be presented in a phase diagram whose control parameters are theta, the inclination angle of the plane, and R, the radius of the rolling sphere (in fact, we use Phi, the surface smoothness, which is the ratio of R and r, the radius of the glued beads). A comparative analysis is done, showing that the behaviour is qualitatively not dependent on the system, and a 'universal' dynamical threshold line is obtained for all the particle-surface systems studied. We also confirm that the motion is characterized by a viscous friction force, strongly dependent on the smoothness.