Re: multi-step reasoning

[Tim Folkerts <tfolkert@FHSU.EDU>]

Joseph,

> With all do respect, zero pressure does not exist, and zero pressure
> difference is not zero pressure...I can't think of a case in which
> changing the volume doesn't involve work being done.

While zero pressure is not possible in practice, it is possible in a
gedanken experiment.


John's example with a bellows requires a change in the # of particles, but
that is not even necessary.  The standard example is a "free expansion".
A rigid container has a partition in the middle.  Half of the container has
a pressure gas; the other half is vacuum.  A hole is introduced into the
partition.  The gas doubles in volume, but no part of the container moves,
so F*dx = 0.

If you object to the zero pressure, it works just as well with two
different gasses on the two sides at the same pressure.  Each one
independently expands into the other side.  Each changes volume but does no
work.

Tim Folkerts


Department of Physics
Fort Hays State University
Hays, KS  67601
785-628-4501