Biologist
David Hu* and his colleagues at
Georgia Tech have deconstructed the motion dogs make to shake the water off their fur! The scientific explanation - the dry graph above to illustrate the wet action (
video here) - applies across animal species. The shake is a very efficient tactic for animals to dry themselves off, but is dictated by the animal's size and the surface tension and density of the water. The research team used high-speed video and fur particle tracking to
understand the common physical characteristics that unite the wet-shakes
of 33 mammals from 16 species. The animals (dogs of varying sizes, pigs, goats, kangaroos, rats, mice, and others) oscillate their bodies at a frequency that removes as
much water as possible with minimal physical effort. Larger animals require lower frequencies to generate the centrifugal force necessary to
overcome the strength of the surface tension that keeps water attached
to their fur. Small animals, on the other hand, need to oscillate at a high frequency or they will remain just as wet. Allowing the animals to achieve the necessary centrifugal force when whipping around their bodies is
loose skin that allows some to generate forces up to 70 times
that of gravity. The result of their fine-tuning is that a large, soggy dog can shed as much as 70% of the water in
its fur in just 4 seconds!
*Dr. Hu made the
New York Times in June after determining that raindrops do not pose a flight risk to mosquitoes, a finding - also based on observations of
high-speed video - that has implications for development of robotic airborne search-and-rescue vehicles.
__________
Woof!
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