Re: The sign of work

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Tue, 29 Feb 2000, Eugene P. Mosca wrote:

> ... I checked an engineering thermodynamics textbook (Cengel and Boles,
> 1989) and found they use the same convention that the physics community
> now uses -- work done by the system is positive.  It seems likely that
> other engineering thermo texts also follow this convention.
>
> Should we adopt the chemistry convention or stick with the
> physics-engineering convention?  It appears this decision is being made
> by the AP Physics Development Committee.  Any comments?

As a matter of practice I prefer the "make sure you get it right by making
sure it makes sense in each individual circumstance" approach to
determining the signs of *both* heat and work.  But I also approve of
having internally consistent definitions wherever possible and I have
thought for a long time that consistency almost demands the convention
that the AP committee is recommending.  With this change we get 1)
consistency with the mechanical definition of work, 2) consistency with
the convention for heat, and 3) consistency with the definition used by
chemists.  Perhaps we lose 4) consistency with the definition used by
engineers, but 3 outta 4 ain't bad.

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm