Re: multi-step reasoning

["John S. Denker" <jsd@MONMOUTH.COM>]

Joseph Bellina wrote:
> zero pressure does not exist, and zero pressure
> difference is not zero pressure

That's true as stated, but irrelevant, because work
is F dot dx, where F is the total force, so net
pressure is precisely what is relevant to the
calculation of work, as I previously pointed out.

> ...I can't think of a case in which
> changing the volume doesn't involve work being done.

I have pointed out, twice, that the piston in a bellows
can move, changing the volume within the bellows, with
arbitrarily small F dot dx work being done.  If you disagree,
please provide a reasonable (non-infintesimal, distinctly
positive) lower bound on the work that must be done.

In particular, if the bellows is working at atmospheric
pressure P=1Atm, and the piston has area A and moves a
distance X, are you claiming that the work is equal to,
or a sizeable fraction of, X*A*P?  I claim I can make
the F dot dx work a negligible fraction of X*A*P, easily
less than 1% and probably less than 1 part in a million,
possibly even less than that if really necessary.