13 November 2010

Lapping Pussies ~ Fluid Inertia Defeats Gravity!

Nicholas Wade writes in the NYTimes For Cats, a Big Gulp With a Touch of the Tongue about research by MIT professor Roman Stoker and colleagues on How Cats Lap: Water Uptake by Felis catus...
"...the cat’s lapping method depends on its instinctive ability to calculate the point at which gravitational force would overcome inertia and cause the water to fall. What happens is that the cat darts its tongue, curving the upper side downward so that the tip lightly touches the surface of the water. The tongue is then pulled upward at high speed, drawing a column of water behind it. Just at the moment that gravity finally overcomes the rush of the water and starts to pull the column down -- snap! The cat’s jaws have closed over the jet of water and swallowed it. The cat laps four times a second -- too fast for the human eye to see anything but a blur -- and its tongue moves at a speed of one meter per second. Being engineers, the cat-lapping team next tested its findings with a machine that mimicked a cat’s tongue, using a glass disk at the end of a piston to serve as the tip. After calculating things like the Froude number and the aspect ratio, they were able to figure out how fast a cat should lap to get the greatest amount of water into its mouth. The cats, it turns out, were way ahead of them -- they lap at just that speed."
Clever pussies!

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