Wednesday, December 28, 2005

Shrimp Cavitate

Those of us who left active duty before the year 2000 probably missed this sonar tidbit. Although the concept sounds goofy, it is supported well enough in scientific communities to assure winning your next beer bet.

From the start of WWII, researchers studied snapping shrimp. As any submariner knows and many heard firsthand, these "biologicals" create loud, underwater noise. Colonies produce such a din that during World War II, the constant crackling from these shrimp sometimes foiled the military's attempts to find enemy subs.

For years, the assumption had been that the cracking sound occured when the moving part of the shrimp's claw struck its stationary opposite, like castanets. Instead, cavitation--the mechanical process which plagues ships' propellers--is to blame. Cavitation occurs when liquid is forced to move above a certain speed and, as a result, experiences a pressure drop (known as Bernoulli's principle). This phenomenon causes tiny air bubbles in the fluid to swell. As the fluid slows and the pressure again rises, the imploding bubbles generate a shock wave with audible sound.

The little ol' shrimp communicate with one another, defend their territory, and stun their prey with this sound.

For doubters: here, here and you more scientific folk will like the link here.


At 9:40 PM, Blogger geezernuke said...

I guess I'm going to be the sole lamenter of this new scientific description of that familiar sound I first knew as "Carpenter Fish". A few years later I was told that it wasn't a fish at all but a Shrimp. I actually felt relieved at this initial enlightenment since I had difficulty envisoning a fish wielding a hammer. But thinking of a hammer held in the claw of a Shrimp was no stretch at all. Now I'm being asked to endure scientific revelation that there is no "hammer". It's like learning that there is no "Santa". What kind of Grinch would reveal this "truth" at this season.

At 10:04 PM, Blogger Greg said...

That's amazing. I wouldn't have thought that something as relatively small as a shrimp could cavitate.

Learn something new everyday. Now if they take advantage of thermal layers to hide their sprints, I'll be really impressed...

At 5:29 PM, Blogger Vigilis said...

Bo, carpener fish is what we called them, which was even more frightening -what were they building?

Greg, that was good. Laughing out loud.


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