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A wave or not a wave ?



Many Phys-L messages were devoted to inappropriate words
and phrases. I do not recall discussing waves in that context.
A phrase "waving a flag" has as much to do with physics as
the phrase "applying heat", both being used in a social context.
Likewise phrases such as "making waves" or " shaking the
boat", also in a social context, have very little to do with waves
in physics. The same is true for the "waves of heat" one may
experience during a summer. But even in physics we have
some ambiguities.

Sometimes we define a wave as a moving disturbance, such
a "domino wave". But what is a disturbance? On other occasions
we say it is a disturbance (of equilibrium) "exhibiting periodicity
in time and periodicity in space". With that definition domino
pieces falling regularly one after another should not be called a
wave. And what about the ocean waves we observe at a sea
shore? Do consecutive crests really resemble each other? Are
their arrivals strictly periodical? How much departure from
ideal periodicity in space and time is sufficient to say that a
phenomenon is not a wave? And what about a standing wave?
Is it really a propagating disturbance? I have no answers. But
I would like to see comments.

P.S. --> my teaching unit outline, "Introduction to Waves" at

http://alpha.montclair.edu/~kowalskiL

has been modified a little after receiving critical comments
(in private) from one phys-L-er.
Ludwik Kowalski