Levitation of spheres by thin viscous films

Results are presented of an experimental investigation into the levitation of spheres on thin layers of viscous fluid. In one set of experiments the layer is formed on a planar vertical wall and in a second investigation the sphere sits on a fluid layer on the inside of a rotating horizontal cylinder. The motion takes place at a set of fixed locations in the latter case whereas the sphere generally translates up or down the plane wall of the belt. Lubrication layers formed between the surfaces of the spheres and the walls induce slip. Two distinct states are identified, and excellent accord is found between experimental results and those from a recently developed theory for the single-track state which is only observed in the rotating horizontal cylinder. The two-track state exists in both sets of experiments, but theoretical progress with this remains an outstanding challenge.