Re: What Flows?

[jmclean@chem.ucsd.edu]

Jim Green says:
> ....
>
> Consider two adjacent bodies (A and B) with adiabatic walls except for the
> adjoining wall which is diathermal.  Say the diathermal wall serves only to
> keep A molecules from entering B and vis versa, but nevertheless A heats B.
> Or consider piece of steel A and abutting piece B - where A heats B.  How
> might that happen? 

OK, I'll give it a crack.

Atoms in A are jostling around more than they are in B.  At the interface,
an A atom bumps into a B atom, so that the B atom bumps around more and the
A atom less.  Thus the energy of the A atom decreases and the energy of the
B atom increases.  As this continues among the may atoms of the system, A
heats up B.

Now, since energy is conserved, we can say that the energy is *transfered*
from the A atom to the B atom.  If you step back to see all the atoms and
squint a little, the energy is *flowing* from A to B.  I say this because
I, personally, do not feel that the word "flow" can only apply to coporeal
fluids.  I am quite happy to use the word "flow" for any conserved thing,
be it matter or a characteristic like energy.

Thus the energy moving from A to B shares characteristics with water moving
through a membrane from tank A to tank B.  Sure, there are some very
important differences, but there are important similarities as well.

However, I do regard this entire question as one of *semantics*, which
means that there is no 'correct' answer EXCEPT in the context of the
persons doing the speaking and listening.  Does anyone have any evidence,
anecdotal or otherwise, that using the words 'energy flows' tend to cause
students to think in terms of the caloric model?  Is this true even when
the words are used along with an emphasis that energy is not a substance?
Is there evidednce combining these two ingredients causes confusion?

-- 
--James McLean
jmclean@chem.ucsd.edu
post doc
UCSD