A ratchet is a device designed to convert stochastic energy into directed motion. In 1912, Smoluchovski invented a thought experiment, a miniature ratchet in a molecular gas environment, which he argued to possibly circumvent the second law of the thermodynamics. Feynman showed that this type of device does not produce work at equilibrium condictions.
We construct a granular Smoluchovski-Feynman ratchet (Figure 1) consisting of four vanes that are allowed to rotate freely in a vibrofluidized granular gas. The two crucial ingredients of the ratchet are: (i) the out of equilibrium environment provided by the granular gas, and (ii) the symmetry breaking provided by applying a soft coating to one side of each vane, such that it obtains a lower coefficient of restitution. The onset of the ratchet effect (a non-zero average angular velocity) occurs at a critical shaking strength via a smooth continuous transition.
Figure 1: Smoluchovski-Feynman ratchet