Tuesday, September 13, 2011

Physics of dogs shaking dry

A team of scientists at Georgia Institute of Technology published a paper in Fluid Dynamics examining the optimum speed and frequency at which dogs should shakes themselves to dry off. For the hair to dry, its tangential acceleration must exceed the surface adhesion between the hair and the water. The hair has to move fast enough to slip out from under the water and allow the water to fly off. Centripetal force varies depending on the radius of the dog. This helps explain why the frequency of oscillation is different for different sized animals.

Dogs were filmed shaking themselves dry with a marker placed on their skin to track its movement. They analyzed videos of many other animals as well. They found that the frequency of oscillation ranged from 27 Hz in mice to 4 Hz in bears. The relationship between frequency and size was not linear, but approached 4 Hz asymptotically. When graphed, the angular position of the skin makes a sinusoidal pattern. - written by Janna Minehart



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