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Re: [Phys-l] PV question

It's always good to see that Physics emeriti are confused on some point
raised in an interest list: welcome to MY club! :-)

In this particular case, the note starting "Themo Question..." and continuing with "ASCII art below" seems to originate with an unattributed quote of a note from some other list from Carl M. rather than a continuation of the examination of reversible processes which preceded it. Carl then makes the same points as Leigh.

So the essence turns out to be:
if gas is compressed, is that work done on it, or negative work done by [or on] it?
To which there is general agreement on the appropriate response.

Perhaps there was an intention to trap some hapless engineer into taking the position that expansion provided by a gas is positive work? As Leigh notes, that was an older convention.... :-)

Leigh Palmer wrote:

3.The convention that work done by a gas is defined as positive comes from engineering, where the desired work is that done by an engine. I am old enough to have learned that convention first. The convention that is now in popular use among physicists is the opposite; we define the work done on a system as positive, and the increment of mechanical work is - PdV.
Just as the conventional polarity of work done by expanding gas came from engineering, I suppose it is the case that the topic of thermodynamics itself came from engineering. But conventions change.....

Brian W