Re: help conserve ___ energy

["John S. Denker" <jsd@MONMOUTH.COM>]

At 02:57 PM 9/22/01 -0400, Hugh Haskell wrote in part:
> Most of my students, when I ask
> them what "conservation" means, give replies that are along the lines
> of "you need to turn out the lights when you leave a room," or
> "recycle."

Ah yes.

If energy is automatically and rigorously conserved by the laws of nature,
why does the government sponsor energy-conservation programs?

The answer is simple:  In reality, we are being asked to help conserve the
Gibbs free energy (GFE).

It is a terribly sloppy shorthand to say "energy" when one should be saying
"Gibbs free energy".

=========================
Part I: Concepts:

The issue here is thermal energy versus nonthermal energy.  It may be
helpful to visualize the distinction as follows:  Suppose I have
  a) a rapidly-spinning flywheel, and
  b) a warm flywheel.
In one case there is energy in the form of organized kinetic energy, and in
the other case there is energy in the form of disorganized kinetic
energy.  Suppose I have arranged it so that the amount of energy is the
same in both cases.

The important point is that even though the amount of energy is the same,
energy in thermal form is much less valuable.
 -- The nonthermal energy can be converted to other forms (electrical
energy, potential energy, etc.) with very high efficiency.
 -- In contrast, most of the thermal energy is forever trapped.  It's
still there, and it's still energy, but it's not convertible to any
nonthermal form.

So when somebody says "help conserve energy" they are really saying "help
prevent thermalization of our energy".  The Gibbs free energy is a way of
quantifying the distinction between a rapidly-spinning flywheel and a warm
flywheel.

=========================
Part II:  Terminology:

Alas we are really behind the 8-ball on this issue.  The sloppy shorthand
is in very, very wide use.

Pedagogically, this is in some ways a worst-case scenario:
  1) People have to unlearn the definition of energy that they came in
with (the sloppy shorthand).  Unlearning is always hard.
  2) Then they have to learn a new concept of energy, the real
rigorously-conserved honest-to-goodness energy.
  3) Then they have to learn about Gibbs free energy in terms of
honest-to-goodness energy, and they have to remember which is which.
  4) Then they have to go out and function in a world where they are
inundated with the sloppy shorthand.

Urk.  It's a wonder they learn anything.

Another example of near-worst-case terminology problems:
 -- Elastic means one thing on the street, and something very different in
the lab.  Which is more elastic:  foam rubber, or a steel ball bearing
bouncing on a steel anvil?

Not quite so horrific, but still annoying:
 -- A food calorie is 1000 times bigger than a physics calorie.

It might be amusing to collect a list of such things.  Contributions,
anyone?????

=======

Suggestion:  In your classroom, if the light-switch (or some such) has a
sticker that says "please turn me off; help conserve energy" you can cross
out the word "energy" and replace it with "Gibbs free energy".  This won't
help much, but it won't hurt, and it'll produce a smile or two.