Re: wave momentum

[James McLean <jmclean@CHEM.UCSD.EDU>]

brian whatcott wrote:
> Carl Mungan wrote:
> > But what about mechanical waves? ...
> > Intuitively it seems a mechanical wave doesn't carry momentum since there's
> > no mass flow. A cork on the surface of the sea just bobs up and down (okay,
> > the bobbing is slightly circular, but never mind that).
>
> Carl is undoubtedly teasing us.
>  We would undoubtedly be more comfortable with the oscillatory motion of
> individual balls in the Newton's Balls demonstration, I'd think.
>  A liquid may not be able to sustain a transverse body wave, but it most
> certainly propagates a longitudinal wave quite nicely.
True enough, but that doesn't really address Carl's question.  I don't
see that a longitudinal wave carries any momentum either.  The famous
"Maxell tape" poster notwithstanding.

(That's the poster/advertisement with a speaker (presumably at high
volume) producing a wind which blows on a guy in a easy chair, in case
I'm being too obtuse.)

I'm tempted to suggest that a wave carries momentum only when there is
no medium.

--
--James McLean
jmclean@chem.ucsd.edu
post doc
UC San Diego, Chemistry