Wednesday, August 15, 2012

The physics of how animals shake themselves dry - Washington Post (blog)

Normally we stick with standard-issue cute animal videos for lunch break posts, but today we’re adding in a little science. David Hu and colleagues at the Georgia Institute of Technology in Atlanta filmed 33 wet mammals as they shook themselves dry:

The research is actually pretty interesting:

With the help of an accommodating zoo, David Hu and his colleagues at the Georgia Institute of Technology in Atlanta studied 16 soggy species, including mice, dogs, tigers and bears, and found that each creature tunes its shaking speed to get as dry as possible without wasting too much energy. Some achieve the feat in seconds, which is essential to conserving heat on a cold day.

Small animals shake the fastest in order to generate the force required to overcome the surface tension that holds water to fur, whereas large animals â€" whose size makes it easier to generate sufficient force â€" move slower to reach a comparable degree of dryness.

Some furry animals are aided by loose skin, which “whips the fluid around much faster than if the skin was tight”, says Hu. This generates forces of between 10 and 70 times that of gravity â€" high enough that the animals have to close their eyes to prevent damage from the extreme centrifugal forces. In addition to observing live animals, the scientists studied in detail how drops were ejected using a ‘robotic wet-dog-shake simulator’ that they built in the lab. Their results are published in the Journal of the Royal Society Interface.

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