Re: Energy

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

----- Original Message -----
From: "Robert Cohen" <Robert.Cohen@PO-BOX.ESU.EDU>
> Personally, I think physics is not about what "really" happens but rather
> about what we can measure.  So, whether it really flows or not is
> unimportant compared to the predictions we can make.  I'm still unclear,
> though, which way is pedagogically advantageous.  I'd appreciate some
> guidelines in this regard.

IMO, this depends greatly on the nature of the class.  If you are teaching
thermodynamics to junior physics majors, then 'flow' models may not always
be pedagogically sound.  On the other hand, if you are teaching an
introductory (and terminal) course to liberal arts majors and want to convey
some sense of how the world works to them, you don't have time to change
_all_ of  their vocabulary and intuitive notions.  In this case you might be
better off to use the ideas of flow and 'heat' to help them to a _very_
basic understanding of some physical principles (such as local conservation
laws--without using those words ;-)

I've got to deal with a whole class of Chemistry majors for whom 'heat' is
definitely a noun and for whom heat and energy flow--even in P-Chem-- so it
would NOT be pedagogically sound to try to oppose that model in their two
semester physics course.  It is OK to suggest that there is another approach
and to point out the limitations of their models, but to pronounce them
WRONG when their other courses will ignore that pronouncement is just too
confusing.

I personally like to get down to the microscopic level when talking about
temperature and thermal energy.  However, when placing two metal blocks in
contact, originally at different temperatures, it is seductive to picture
the process as a transfer of kinetic energy from the 'hot' object to the
cold.  I can model this as a 'flow' of increasing random motion into the
'cold' object with a resulting reduction in random motion in the 'hot'
object.  Then again, I can also talk about the collisions at the interface
and the work being done there.   I don't see these as mutually exclusive
models.  Obviously others do.  ;-(

Rick

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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556
rtarara@saintmarys.edu

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