Wet Dog Teaching Scientists New Tricks
Flam, Faye, Winnipeg Free Press
When a wet dog shakes itself dry, it does something amazing. It hits just the right rhythm to maximize the drying effect with minimal effort.
The seemingly casual jiggle imparts enough centrifugal force to expel 70 per cent of the water in its coat in a fraction of a second.
This fact comes courtesy of experiments by David Hu, a professor of mechanical engineering and biology at Georgia Tech. He and his students found 30 other furry mammals share the highly tuned drying ability.
Hu thinks engineers can learn from some of the remarkable features evolution has built into living things. He envisions harnessing this ability for devices that can dry or clean themselves -- something such as a Mars rover programmed to jiggle the dust off its solar panels.
He was initially inspired to study wet mammals by a toy poodle named Jerry, who was a gift to his current fiancee from her former boyfriend. Jerry ended up in Hu's lab, where high-speed cameras recorded and measured the rhythm by which he shook his coat dry.
Before Jerry, Hu had been interested in the way animals interact with water, but his focus had been on the insect world. Thanks to the surface tension of water, many insects can easily get stuck in a puddle or pond once they get wet. Predatory bugs called water striders -- the subject of Hu's doctoral thesis -- get around this with hairy feet that barely touch the water's surface.
The adaptation allows striders to make dinner out of less water-adapted insects.
Hu realized that surface tension also trapped water on mammals, and shaking was a common adaptation that helped them deal with it. The project expanded from Jerry to guinea pigs, lab mice and a house cat.
In search of more mammals, Hu sent one of his graduate students to the Atlanta Zoo to spritz water on lions, tigers and bears, and record their drying techniques.
Fur, said Hu, is great for keeping animals insulated in cold air. It's not so good when it rains or when a furry animal falls into a frigid lake. Then, the fur can hold in cold water next to an animal's skin. A thoroughly wet 60-pound Labrador retriever, for example, holds about a pound of water.
Letting it dry by evaporation would sap energy equal to 20 per cent of the dog's daily calories. …