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Machines Like Us

The physics of the wet dog shake

Saturday, 18 August 2012
by Mano Singham

Anyone who has a dog as a pet knows to avoid getting close to them when they are wet because they have a remarkable ability to shake themselves in such a way that the water flies off and drenches everything nearby. The interesting questions are why they do that and how they do that.

However much we may suspect that they do it because they find it fun to soak those around them, it turns out that it may be a survival necessity, that a lot of water clinging to their fur may cause hypothermia and so they have to get rid of as much as possible and soon as possible. It turns out that the way they shake can get rid of about 70% of the water in as little as four seconds.

Researchers have found that animals tune the frequency of their shakes according to a power law depending of the body size of the animal in order to generate centripetal forces ranging from 10 to 70 times that of gravity.

Here’s a great video from Nature that explains the phenomenon, accompanied by slow motion footage of various animals shaking off water.

You can read more about it here and the abstract of the paper on this work by David Hu and colleagues at the University of Georgia can be read here.