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Re: Waves

On Mon, 3 Jul 2000, Mark Sylvester wrote:

A few years ago I was hiking in the Alps. At a refuge where we spent the
night there was a very long steel cable for hauling goods up from the
valley. It was a single span, goodness knows how long. I couldn't resist
whacking it with a piece of firewood from a stack nearby. The pulse came
back from the valley after what seemed like a very long time. The
interesting part is that for a few seconds before the main pulse arrived
the cable sang with high frequency noise.

Cool! Isn't this your p-waves leading your s-waves?

I've heard a rumor that the original gun-blasts in the Star Wars movie was
a recording of somebody whacking a long steel cable.

After playing with sound-tubes in science museums, I know that the high
frequencies outrace the low frequencies whenever the diameter of the
waveguide is less than the operating wavelength. If the steel cable acts
like a hollow tube, then your applied impulse should become spread out,
and should sound like "deeeeeoooooouuuuuu" on its return. Electromagnetic
"whistlers" do the same, as the spike-impulses of lightning strikes are
spread out as they are ducted across long distances through the Earth's
magnetosphere.

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William J. Beaty SCIENCE HOBBYIST website
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