Re: shock wave as pressure builds in a vacuum?

[Roger Haar <haar@PHYSICS.ARIZONA.EDU>]

Hi,

        I am not sure why you do not like the
water-rushing-in analogy.  The inrushing air has a
linear momentum that must be "absorbed" by the
membrane.  To the zeroth approximation it is
similar to water hammer.  The first order
approximation needs to consider the
compressibility of air compared to water.  An then
there is turbulence.


        One could image an experimental setup like:


   Vacuum  Membrane                 High speed
valve
  _______________________________________  ____
 |           }                           \/    the

|___________}___________________________/\____room

             | y = variable pipe length  |

        I think if the pipe length y was very short (
several centimeters) the membrane survival rate
would be much higher than if if y was long ( a
meter.)  I think there are valve that can close on
a time scale of 10 milliseconds, but I am not sure
of opening times. But 10 ms is still a long time
to do this with a short pipe.

        My other comment is that the term "shock wave"
may have different meanings.  In some fields the
mean is very exact and may mean supersonic shock
wave.  Other uses of the term are probably more
general and more vague.

Thanks
Roger Haar

**********************************************************************
Stefan Jeglinski wrote:
>
SNIP

          It is tempting to make
> an analogy to water rushing into an empty vessel and the force it
> creates when it crashes against the inside walls, but I'm not sure
> the analogy is appropriate here.


SNIP