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Planet Earth

How the Wet-Dog Shake Gets Mammals Dry in No Time Flat

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http://youtu.be/AFzWJ6P2iyY There’s a certain expression a wet dog wears as it trots up to you, a kind of gleam in the eye that says, “I’m about to shake so vigorously that in a mere 4 seconds, 70 percent of the water in my fur will fly off of my coat and on to you.” But the wet-dog shake, though it's an annoyance to us, may be a survival technique to dogs. The water that sticks to a mammal’s fur can lower its body temperature, causing hypothermia, so it behooves wild animals to get rid of all that water as quickly and efficiently as possible. To find out just how efficient the wet-dog method is, researchers from the Hu lab at Georgia Tech filmed 33 different wet zoo mammals from rats to kangaroos to lions and tigers and bears (oh yes) with high-speed cameras and analyzed the motion of their bodies, skin, and fur. Their research was first published back in 2010, but their latest study, published in the Journal of the Royal Society Interface, improves their mathematical model of the wet-dog shake and reveals how much force the furballs can generate. (The paper is not yet online; we will provide a link when it becomes available.) Dogs shake with a characteristic oscillation, twisting their bodies from side to side at a set frequency to generate so much centripetal force that water droplets go flying. The shaking animals observed in this study generated forces 10 to 70 times greater than gravity, a feat that was easier for the larger mammals. This was because more massive animals have a bigger body radius: they can shake with a lower frequency and still generate as much centripetal force as the faster-shaking smaller animals. Loose skin helps, too, because it whips around the body and throws off more drops. So if you own a big, jowly dog, you have even more reason to keep your distance after a dip.

Video courtesy of Nature News & Comment

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