Re: Oh No! - Another question on heating

[Bob LaMontagne <rlamont@POSTOFFICE.PROVIDENCE.EDU>]

Carl - thanks for the response. It is precisely your comment in example
2 that prompted my question. It seems that using the verb form for heat
will constantly generate the 'collision' of meanings in questions such
as the one I cited. The temperature change and direction of heat flow
are not necessarily correlated. I find it very unnatural to talk about
heating something that is not changing temperature or that might even be
decreasing in temperature (cooling?)

I'm sure all this is in the archives somewhere, but I'm too involved
with finals and meetings to search it out right now.

Thanks

Bob at PC

"Carl E. Mungan" wrote:
> Bob LaMontagne queried:
>
> > I know this subject has been talked to death, but I'd like to ask the
> > 'heat is a verb' crowd what they would consider an acceptable student
> > answer to the following question:
> >
> > 'Work is done on a system without changing its temperature. Is the
> > system heated, cooled or not necessarily either? Justify your answer.'
>
> Not necessarily either.
>
> Example 1: I exert a constant force F horizontally on a rigid block
> on a frictionless surface as it moves a distance d. I did Fd work on
> the block, its temperature didn't change, and no heat flowed into or
> out of the block.
>
> Example 2: I infinitesmally slowly push down a piston in a cylinder
> containing an ideal gas in contact with a heat bath. I did work
> -integral(PdV) = nRT*ln(V_i/V_f) and the temperature of the gas
> stayed constant because heat nRT*ln(V_i/V_f) flowed out of the gas
> and into the heat bath.
>
> In example 2, I would be cautious about saying the gas was "cooled"
> since its temperature didn't change. Nevertheless, heat *did* flow
> out of the gas, so in that sense it was cooled. There's a collision
> between two common meanings of "cool": (1) a drop in temperature and
> (2) a loss in heat.
>
> Carl
>
> ps: There is a general schema for distinguishing examples 1 and 2.
> Pseudowork was done in the first example, but not in the second. The
> reason is that in the second example, a second force is doing an
> exactly canceling amount of pseuodwork on the gas that I did, namely
> the normal force exerted on the gas by the face opposite the piston I
> push on. (This is what keeps the gas from gaining the bulk
> translation KE that the block gained in case 1.) Happy trails!
> --
> Carl E. Mungan, Asst. Prof. of Physics  410-293-6680 (O) -3729 (F)
>        U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5040
> mailto:mungan@usna.edu       http://usna.edu/Users/physics/mungan/