Tue May 31st 2016
14:00 – 15:00
Seminar Jumping on water
Ho-Young Kim


Water striders can jump on water as high as they can jump on land. Quick jumps allow them to avoid sudden dangers such as predators’ attacks, and therefore understanding how they make such a dramatic motion for survival can shed light on the ultimate level of semi-aquatic motility achievable through evolution. However, the mechanism of their vertical jumping from a water surface has eluded hydrodynamic explanations so far although the principles of water striders floating only on tarsi (tiptoe) and walking on water are well known. By observing movements of water strider legs and theoretically analyzing their dynamic interactions with deforming liquid-air interface, we have found that different species of jumping striders always tune their leg rotation speed with a force just below that required to break the water surface to reach the maximum take-off velocity. Here, we start with discussing the fundamental theories of dynamics of floating and sinking bodies which has been pursued in search for the secret of elegant water jumping. The theories then enable us to analyze forces acting on a water strider while it presses down the water surface to fully exploit the capillary force. We further introduce a 68-milligram at-scale robotic insect capable of jumping on water without splash, strikingly similar to the real strider, by utilizing the water surface as a trampoline (J.-S. Koh et al. “Jumping on water: Surface tension-dominated jumping of water striders and robotic insects,” Science 349, 517 (2015)).

Biographic sketch:
Ho-Young Kim is Professor at Department of Mechanical and Aerospace Engineering, Seoul National University, Korea. He received his B.S. degree from Seoul National University, and M.S. and Ph.D. degrees from MIT. Prior to joining SNU as an Assistant Professor in 2005, he worked with Professor L. Mahadevan at Harvard University as a Postdoctoral Associate. He was a visiting scholar of the Wyss Institute for Biologically Inspired Engineering at Harvard University (2011-2012). His research activities center around classical mechanics of solids and fluids at their interfaces. He is currently interested in the dynamics of wetting, semi-aquatic biolocomotion, botanical hydrodynamics, ultrasonic cavitation, etc.
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The 10th Complex Motion in Fluids 2021
Max Planck Gesellschaft
Centre for Scientific Computing