LAUSR

We studied rotational motion of a symmetric self-propelled object on water under periodic halt and release operations with an external force. We propose a novel system in which the direction of rotation inverts after each halt-and-release operation. The considered self-propelled object was composed of a hexagonal plastic plate with a small orifice in the center. Six camphor disks were glued to one side of the plate at the corners. The plate was placed on the water surface and could rotate around a vertical axis located in the center. The initial direction of rotation, either clockwise or counterclockwise, depended on initial conditions. We discovered that, after a temporal halt of the rotor by the external force and next release, the direction of rotation inverted spontaneously. The probability of such inversion was studied as a function of the halt time, release time, area of the plastic plate, and stirring rate of the water phase. The distribution of camphor molecules around a camphor disk was visualize...