Walking and standing on water.. An insect like a wasp or a water strider can rest atop the water, held up by surface tension. This means that the cohesive force of the water molecules sticking to each other is stronger than the force of the bug being pulled down by gravity. This works because it spreads its weight out over a large surface area. That creates a slight indentation in the top of the water, changing the direction that the light coming down is refracted and re-directing it slightly sideways (that’s where the bright halos around the dark areas come from). Larger animals are slappers. Surface tension forces are too weak to support the weight of a larger body. The basilisk lizard, water birds including the Western Grebe, and even some tail-walking dolphins must strike the surface with enough force and speed to keep their heavier bodies from going under. Note: A human would be able to run on water only if he were able to achieve speeds of order 30 m/s, and to produce 15 times the muscle power available to him. Sources: tinyurl/pfg2eeu & tinyurl/mgtshzz Review Paper by John W.M. Bush: tinyurl/nt97pbc
Posted on: Wed, 04 Dec 2013 18:55:06 +0000
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