National Geographic : 2011 Sep
ONE OSCILLATION 1 sec 0 Mouse Washing machine Rat Guinea pig Domestic cat Poodle Labrador retriever Sumatran tiger Giant panda Brown bear 4 4 4 5 6 9 14 18 29 17* NOW Furry mammals like dogs dry o with split-second oscillations. e looser the animals' skin, the more water they shed with each shake. Animals not drawn to scale *Oscillation averages have been rounded to the nearest whole number. Shake It O It all begins with a twist of the head---one so powerful it leads to full-body, high-speed oscillations that whip water in all directions. Although hazard- ous to nearby humans, the wet-dog shake is an elegant, effective drying mechanism, says Andrew Dickerson, an engineering student at Georgia Tech who analyzed the mechan- ics of this everyday canine act. In taking less than a second to disperse half the water in a hound's fur, the motion is "more efficient than a washing machine's spin cycle," he says. Using slow-motion video, Dickerson measured rates of oscillation in other animals too and found that the smaller they are, the faster they shake. Being wet adds weight, notes veterinarian Nicholas Dodman, and that makes it harder to run---perhaps one reason speed drying evolved. ---Hannah Bloch PHOTO: TIM FLACH. GRAPHIC: LAWSON PARKER, NGM STAFF SOURCE: ANDREW DICKERSON AND DAVID HU, GEORGIA TECH HOW FAST DOES IT SHAKE? Smaller animals must shake faster than large ones in order to throw off a comparable amount of water. As animal size increases, shaking frequency levels off.