Official News page 7

REAL LIFE NEWS: THE PHYSICS OF THE WET-DOG SHAKE

by Hazed

Dog-owners will be familiar with the scenario: the dog comes indoors soaked through having been out in the rain, or perhaps because it went for a swim or rolled in a puddle, and once inside, it shakes itself vigorously in order to displace as much of the moisture as possible.

But just how hard does a dog need to shake, in order to end up with dry fur?

If this question has been bothering you, you can breathe a sigh of relief, because now it has been answered by Andrew Dickerson and his colleagues at the Georgia Institute of Technology in Atlanta.

The scientists filmed a number of dogs shaking their fur and used the images to measure the period of oscillation of the dogs' skin. Then they created a mathematical model of what's happening. Their reasoning was that the water is bound to the dog by surface tension between the water the hair. When the dog shakes, centripetal forces pull the water away and send it flying off (onto the carpet, your trousers, your sofa and so on). So the centripetal force has to exceed the surface tension or the water won't budge.

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