We present the results of experiments on the motion of a solid particles which are free to move in a viscous fluid inside horizontal rotating cylinder. At low rotation rates steady motion is observed where spheres adopts stable equilibrium positions rotating adjacent to the rising wall at a speed which is in close agreement with recent theory. We show that novel cavitation effects are required to sustain the motion. The effects of surface roughness are considered and robust behaviour is found.

Surprising counterintuitive motions is observed when the spheres are replaced by a small cylinders and spheroids.