Re: A Little Astronomy Question

["Rauber, Joel Phys" <RAUBERJ@mg.sdstate.edu>]

A couple of comments were:

JR
> Put a higher temperature object in thermal contact with a lower temperature 
object.  >Heat flows from the hot object to the colder object, thereby 
increasing the energy of >the cool object and decreasing the energy of the 
hot object.  One might describe this >as a "energy flow" and yet it occured 
without work being done by one body on >another.  Therefore I disagree with 
what was said above.

Leigh
> Heat is
> the name of any process by means of which energy is transferred from
> one system to another with no resulting change in external coordinates
> of either system. Work is the name we give to any process by which
> energy is transferred from one system to another by means of changing
> the external coordinates when the systems are themally isolated from
> one another. We say "energy flows" from one system to another; we never
> say "work flows", and we *should not* say "heat flows". That is the
> conventional assignment of meaning to those words. If you do not wish
> to use those terms that is your choice, but you do students a great
> disservice by teaching them language that other physicists do not use.

Mark
> Q is work on a microscopic, entropy-related scale. W is macroscopic work.
> Both are measures of energy transfer, and there are good reasons for
> distinguishing between them.

I like all three of these statements, mine was the least carefully written, 
I naturally was referring to macroscopic work.  Which is the only sense in 
which Thermodynamics alone deals with work; microscopic work deals with the 
statistical mechanical underpinnings of Thermodynamics.

In class I usually use the words "heat flows" as a short hand for the 
paragraph that Leigh stated above.  I think this may cause some confusion, 
as it reinforces the idea of "heat" being a substance  rather than a 
process; but stating the above parapgraph is simply too awkward in the 
classroom.  To be sure, I have given the paragraph above and then tell the 
students that I'll use the word "heat flows" simply as a short hand and 
emphasize many times that this usage doesn't mean Q is an attribute of a 
physical system.  I'm not comfortable with this and welcome other ideas of 
terminology; but also realize that part of the job is teach the terminology 
that is used by practitioners.

Another point which I'm uncomfortable with in the classroom.  I too eschew 
the use of Delta Q and W for the obvious reason; but in my calculus level 
class I have to refer to dQ and dW, and I've previously in mechanics 
emphasized that d(anything) is a small change in something.  So I have to do 
some fancy footwork here and say that dQ and dW only mean a small quantity 
and not a change, I mention the words "inexact differential" as well (not 
that I expect them to understand inexact differentials, but simply to 
sensitize them to the use of terminology that they will see later.) 
 Comments or suggestions?

Joel
rauberj@mg.sdstate.edu

PS - I have my own views on the terminology "constructivism"; of which I 
won't unburden myself yet.