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

[Jack Uretsky <jlu@hep.anl.gov>]

As I understand the question, the "gas" is an irrevancy.  I think 
Dan's question boils down to the following:
	In 1 dimension, consider a spring with one end fixed.  At time
t=0, apply a constant force to the other end (the "running end", to be 
nautical).  Describe the subsequent motion of the running end as a 
function of time.
	Happy New Year and regards,
				Jack




On Mon, 1 Jan 2007, John Denker wrote:

> 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.
>
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