Re: stationary waves

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Sat Feb 24 2001 - 15:51:06 PST 

Message-Id: <l0311070eb6bdf842b228@[192.174.2.173]>
Date: Sat, 24 Feb 2001 15:51:06 -0800
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: stationary waves

Hi David

If we define a wave as something that satisfies the "wave equation" then it
must move relative to the material in which the wave equation holds.

Although when we see a standinmg wave it looks like a wave going up and
down in place. That is an illusion produced by two waves going through each
other in opposite directions.

However:
Since a wave travels at constant velocity (usually) it is possible to move
into a galilean (constant velocity) frame of reference moving at the same
speed and in the same direction as the wave so that in the frame of the
observer the wave appears at rest. (The wave is still moving relative to
the medium.)

A wave can propagate upstream at the same speed that water is flowing
downstream and thus stay stationary with respect to an observer yet still
travel with respect to the medium.

Just a few thoughts, but remember my sig file.

Paul D

Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld

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