Intermittent motion of a camphor float

The periodic motion of a camphor float on water was investigated as a simple example of an autonomous motor. When a camphor disk was placed on a water surface, a periodic change in the surface tension at the camphor solid/water interface was observed which was synchronized with a change in the meniscus. When a camphor disk that was connected to a larger plastic disk was floated on a water surface, intermittent motion (alternating between rest and rapid motion) was observed. The duration of the rest period increased with an increase in the diameter of the plastic disk. When the resting camphor started to move, a camphor layer developed on the side opposite the direction of the motion. The nature of this intermittent motion is discussed in relation to the state of the camphor disk with the surface tension of the camphor layer as the driving force.