[Phys-L] Re: work and heat

[John Denker <jsd@AV8N.COM>]

Carl Mungan wrote:
> At the risk of opening a can of worms....

The can is already open.  The worms are on the loose.  We urgently
need to send them to obedience school.

> I ask the question why distinguish work from heat in thermodynamic processes?

That's a good question, but perhaps we would be wiser to precede
it with the question of *whether* we should spend class time trying
to define work and heat.

 From the letter at:
   http://usna.edu/Users/physics/mungan/Publications/FEd2.html

> Defining W and Q via abstract equations rather than by two lists categorizing specific
> interactions is not helpful for introductory students.

As the proverb says:  Learning proceeds from the known to the
unknown.

We agree that defining W and Q in terms of E and S is unhelpful
!IF! the students lack a robust prior understanding of E and S.
But ... note the big !IF! in the previous sentence.

Here's where I'm coming from:  The more I learn about E and S,
the more precise my understanding becomes.  The concept of
energy shows up in lots of places, and it always means the
same thing.  Energy is energy.  Similarly, the concept of
entropy shows up in lots of places, and it always means the
same thing .  Entropy is entropy.

I definitely cannot say the same thing about work.  The more
closely I look, the more inequivalent notions of work I find.
At
   http://www.av8n.com/physics/thermo-laws.htm#sec-work
I document one major problem and several minor nuisances.

Heat is even more of a quagmire.  At
  http://www.av8n.com/physics/thermo-laws.htm#sec-def-heat
I document three major inconsistent things that heat might
reasonably mean, plus one completely unreasonable meaning
that is nevertheless common in chemistry-land.

IMHO no matter how you define heat and/or work, you are going
to be inconsistent with one or another segment of the application
space.

Today's textbooks are full of end-of-chapter problems involving
blah-blah-heat and blah-blah-work.  But in the real world, if
you're trying to design something or analyze something, you are
vastly better off keeping track of the energy and the entropy.

Bottom line:  We agree that this topic is important, and we largely
agree as to the nature of the problem.  But my recommended solution
is different from Carl's.

My recommendation:  Spend the least possible class time on heat and
work.  Concentrate on achieving a robust understanding of energy
and entropy.
_______________________________________________
Phys-L mailing list
Phys-L@electron.physics.buffalo.edu
https://www.physics.buffalo.edu/mailman/listinfo/phys-l