Motion with Memory of a Self-Propelled Object

The concept of self-propelled objects is important for the understanding of biological mobility, as well as for the development of autonomous devices in medicine and engineering. In this study, a simple self-propelled object, driven by a difference in surface tension, was found to exhibit intermittent self-motion (alternately in motion and at rest) in an annular water channel, with resting positions and features of motion in subsequent cycles remaining almost the same as those previously visited; that is, memories of the resting positions and features of motion were observed. The occurrence of the memory phenomenon was found to depend on the relationship between the resting time and the period for one lap of the annular channel. The mechanism of memory is discussed in terms of the distribution of surface-active molecules and local surface tension at the resting positions.