Shakin’ All Over

Science Men, it must be acknowledged: relentless they are, in their ceaseless quest for knowledge.

Take wet dogs. It is Known that any Normal Person, when confronted with a wet dog, stands clear. Because a wet dog is totally self-absorbed. Interested only in shaking that water free, regardless of who all and sundry might be splattered or drenched.

But a Science Man moves in Closer. Because he’s there to Study. To determine, for example, if the physics by which a dog clears water might be useful in improving the efficiency of washing machines.

From out of the Georgia Institute of Technology comes Abstract: LW.00007: Wet-Dog Shake, summarized as follows:

The drying of wet fur is critical to mammalian heat regulation. We investigate experimentally the ability of hirsute animals to rapidly oscillate their bodies to shed water droplets, nature’s analogy to the spin cycle of a washing machine. High-speed videography and fur-particle tracking is employed to determine the angular position of the animal’s shoulder skin as a function of time. We determine conditions for drop ejection by considering the balance of surface tension and centripetal forces on drops adhering to the animal. Particular attention is paid to rationalizing the relationship between animal size and oscillation frequency required to self-dry.

The Georgia Tech Science Men—Andrew Dickerson, Zack Mills, David Hu—videotaped and X-rayed 40 different animals, from 13 species, to scrutinize how mammals shake themselves dry.

“What would you do on a cold day if you were wet and could not towel off or change clothes?” asks Dickerson. “Every warm-blooded furry creature faces this dilemma often. It turns out that oscillatory shaking exhibited by mammals is a quite efficient way to dry.

“We hope the findings from our research will contribute to technology that can harness these efficient and quick capabilities of drying seen in nature,” he says.

Furred mammals, unlike we naked apes, generally possess loose skin that whips around as the animal changes direction. This, it seems, is crucial to shaking success.

The Georgia Tech Science Men determined that, in their shaking, animals oscillate at frequencies sufficient to lose water droplets. Further, shaking frequency seems to be a function of animal size: the larger the animal, the more slowly it shakes. For example, while a mouse oscillates wildly at 27 shakes per second, a grizzly can manage only four shakes in that same second.

The more minute mammals, while shaking, can experience in excess of 20 g of acceleration. This is far more than any human being long can stomach. A roller-coaster, by contrast, subjects riders to but 3-4 g, while fighter pilots experience but 8 g during the most stressful maneuvers—”[i]f sustained for more than a few seconds, 4 to 6 g is sufficient to induce blackout. To prevent loss of consciousness, fighter pilots wear special pressure suits that squeeze the legs and abdomen, forcing blood to remain in the head.” Even the freaking Space Shuttle is kept at or below 3 g.

Here, it is clear, a mouse truly is, bigger than a man.

Hu and Dickerson, at least, are now hooked on water: they are moving beyond washing machines to illume how animals interact with water in nature. Next up for these Science Men: how creatures such as beavers and otters have adapted to life in the water, and how water droplets interact with hair.

Human beings, of course, also shake, and in a most delightful way. Though that ain’t much about shakin’ off water.


2 Responses to “Shakin’ All Over”

  1. 1 possum January 14, 2011 at 2:04 pm

    Amazing, simply amazing what scientists find to study. Who would have guessed shaking animals would be on the forefront? Thanks for the story and some really fine science reporting.

    • 2 bluenred January 14, 2011 at 2:39 pm

      Thanks. I like how mice, when shaking themselves dry, withstand more g’s than astronauts or fighter pilots. Of course, the same link states that when a person “plops into a chair” 10.1 g’s are involved. I suppose we survive this because said plopping happens instantaneously, and is not stretched out over potentially fatal seconds or minutes.

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