Self-rotation of a camphor scraping on water: New insight into the old problem

The translational and rotational motion of a camphor scraping at an air/water interface was investigated. The characteristics of the rotation depended on the temperature, surface tension, and the chemical structure of the camphor derivative. The direction of rotation, either clockwise or counterclockwise, is determined by asymmetry in the shape of the solid camphor scraping, The essential features of the motion of a camphor scraping were reproduced by a computer simulation. The driving force on this motion is believed to be the spatial heterogeneity of the camphor layer at the air-water interface.