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# Re: Standing waves

In a running wave every point along the
string repeats the motion of the point
closer to the source (same amplitude
and same frequency). In a standing
wave the amplitude is different for
different points along the string. The
derivation of the P formula is based
on the assumption that the amplitude is
the same for all points along the string.
Ludwik Kowalski

On Monday, Feb 9, 2004, at 17:33 America/New_York, Wolfgang Rueckner
wrote:

At 1:48 PM -0800 2/9/04, John Denker wrote:
P=0.5*mu*w^2*A^2*v [1]

This is an object lesson in the perils of plug-and-chug,
or to say the same thing in more positive terms, a lesson
in the importance of knowing the domain of applicability
and validity of a formula.

That derivation and the resulting formula [1] make some
sense in the context of a running wave. They make no sense
whatsoever in the context of a standing wave.

But the standing wave is the superposition of the running wave and
it's reflection. Why do you say that it makes no sense whatsoever
(aside from the Q that you mention)? -- Wolfgang