Hydrodynamics

The dispersive nature of water waves is responsible for the complicated wave pattern generated at the free surface of a still liquid by a moving disturbance such as a partially immersed object (e.g. a boat or an insect) or an external surface pressure source. The propagating waves generated by the moving disturbance continuously remove energy to infinity. Consequently, the disturbance will experience a drag called the wave resistance. In the case of ships (for which surface tension is negligible), this drag is known to be a major source of resistance.

We have studied the opposite case of objects that are small compared to the capillary length and showed that objects moving in circles on the surface of water exhibit a striking difference from objects moving in straight lines. These results may be important in the context of insect locomotion on water surfaces, in particular for the whirligig beetle, named for its trademark of walking in circles on the surface of water !

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