Re: [Phys-l] Force on an accelerating piston

[John Denker <jsd@av8n.com>]

On 12/31/2006 02:25 PM, Dan Crowe wrote:
> OK, so to first order, at least, it's the velocity of the piston that's
> important.  But is there a higher order correction that depends on
> acceleration?  

[snip]

The question is still quite underspecified.  The snipped details don't
solve the problem.  As it stands, you can get any answer you want,
depending on as-yet unspecified details.

A) The laws of physics say that
 -- "other things being equal", i.e.
 -- "for any particular state of the gas"
the acceleration of the piston doesn't change the physics, to a verrry
good approximation in practical situations.

B) On the other hand, in the vast majority of real-world applications,
the history of the piston (including acceleration, which tells us
something about the history of the velocity) will have changed the
state of the gas.  There's inertia in the gas, which leads to all sorts
of phenomena including viscous flow, sound waves, shocks, and/or whatever.

C) If you really want to find "higher order corrections" there will always
be some.  Do you want to talk about gravitational radiation emitted by the
accelerating piston?  Or how about the lifetime of atoms from the gas
temporarily adsorbed on the face of the piston?

================

If there is a real-world situation that is motivating these questions,
please describe the situation.  Otherwise we're playing a game with no
rules.