Re: Waves

[Leigh Palmer <palmer@SFU.CA>]

> At 04:28 PM 7/4/00 -0700, Leigh Palmer wrote:
> > > >  The high pitched precursor
> > > > to the main pulse is likely due to the transmission of longitudinal
> > > > modes in the cable at speeds higher than those of the transverse mode.
> > >
> > > Yes, but why is "modes" in the plural for longitudinal? Would one expect
> > > the cable to transmit longitudinal waves with a range of speeds? Why?
> >
> > Please excuse my sloppy terminology; there is only one longitudinal
> > mode, of course. The transmission of compressional waves in solids is
> > dispersive,
>
> Aha. I did not know or had forgotten this.
>
>
> > but I don't think I can give a good answer to your "why"
> > question. The transmission of transverse waves in a stiff string is
> > also dispersive, by the way.
>
> I find it hard to say "why" dispersion occurs even when the mathematics
> seems clear. This is strange because it's usually the other way round for me.

I'm not basing my statement on theory, I'm stating an empirical
observation. Remember my ice example?  This result may be simply
expressed in a theory of sound transmission in solids, but I am
unaware of it. I have never subscribed to the dictum "Never trust
an experimental result until it has been confirmed by theory".

Leigh