Re: [Phys-L] "the" system versus "the" environment ... or not

[Jeffrey Schnick <JSchnick@Anselm.Edu>]

The engineers use something that they call a control mass and something they call a control volume in thermodynamics.  I think they correspond to what you refer to as a system and a region respectively.  I think they both come in handy and you don't have to unlearn one to learn the other.  I think the system (control mass) view is more convenient when you have moving boundaries with no material flow, such as a collision of two objects where it can be convenient to call the two objects the system, or in the case of a closed cylinder of gas in which the volume occupied by the gas is changing because the position of a piston is changing, where you might call the gas the system; but the region (control volume) point of view is far more convenient if you are analyzing a turbine or the compressor in an air conditioner.

> -----Original Message-----
> From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
> Sent: Wednesday, October 30, 2013 6:28 PM
> To: Phys-L@Phys-L.org
> Subject: [Phys-L] "the" system versus "the" environment ... or not
>
> On 10/30/2013 02:33 PM, Bruce Sherwood wrote:
> > We also make a big investment in the notion of "system" and how the
> > choice of system affects the form of the energy equation. Just last
> > week I reviewed a paper that was quite garbled, specifically due to
> > the author never using the word "system" anywhere in the paper.
>
> That's tricky.  That falls into the catagory one might call pedagogical moral
> hazard.  That is, there is a temptation to do things in the short term that we
> will regret in the longer term.
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