FORCE-FREE MOTION OF A MERCURY DROP ALTERNATIVELY SUBMITTED TO SHIFTED ASYMMETRIC POTENTIALS

We present a macroscopic experimental realization of force-free motion consisting in a mercury drop experiencing alternatively in time two l ocally asymmetric and periodic potentials which are spatially shifted. A system of electrodes creates the potentials and the force applied t o the drop is of electrocapillary nature. We study the macroscopic vel ocity of the drop as a function of the times during which it experienc es each potential and investigate different regimes of macroscopic vel ocity. Adjusting the different times allows some of the drops to move whereas others of different local velocities have a zero macroscopic v elocity. This system thus acts as a filter. We also study the case of stochastic modulation of the potentials. These results compare well wi th theoretical predictions and experimentally validate a model which h as been proposed for motor protein assemblies.