Re: Re[2]: wave momentum

[Phil Parker <PPARKER@TWSUVM.UC.TWSU.EDU>]

> Date:    Wed, 17 Mar 1999 10:02:05 -0600
> From:    Philip Zell <Zell@ACT.ORG>
>
> =For a true shock wave, the medium is disturbed.  For instance, with a
> =sonic boom there is a region of compressed air, but no region of
> =rarefied air (as there is in a normal sound wave).  Thus, as the boom
> =passes through the air, each little chunk of air ends up displaced from
> =its initial position.  Although the pressure, average velocity, etc. of
> =the air is the same afterwards as before, the position of each chunk
> =has changed, and hence it's average velocity (during passage of the
> =boom) was non-zero.
> =--
> =--James McLean
>
> Been a long time since I studied shocks, so I can't provide a lot of detail.  As
> I write this, I am referring to "Astrophysical Formulae" by K. R. Lang.
> Pressure, velocity, and temperature do change across a shock front.  I think a
> shock is, by definition, a discontinuity.
I thought it was something which changed so abruptly that a discontinuity was
a reasonable mathematical model.  If so, then the model wouldn't hold up well
if pushed beyond its reasonable range, and I suspect very close to Mach 1 is
not reasonable, based on McLean's computations (not quoted here) from
Rankine-Hugoniot.

---------------------------------------------
Phil Parker        pparker@twsuvm.uc.twsu.edu
Random quote for this second:
  Gerrold's Laws of Infernal Dynamics:
  1. An object in motion will be heading in the wrong direction.
  2. An object at rest will be in the wrong place.