Re: pseudowork

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

I wrote:
> The conventional definition of work is the integral of F dot ds.

And I gave the following example of energy transfer that
was _not_ work:
> Suppose I bring 10 kg of trinitrotoluene into the aforementioned
> Control Volume.  Does that act represent 42 megajoules of work?
> Certainly it has the ability raise a weight sky-high... but most
> people would not call this act "work".  Using the word "work" in
> such idiosyncratic ways would lead to needless misunderstandings.

So that says what it isn't.
The purpose of this note is to make a more positive statement,
to say something about what it _is_.

For an elementary class, my recommendation would be to call it
energy transfer and leave it at that.

If somebody demands more detail, I would tend to classify
this as _advection_ of energy, when a highly energetic
substance is transported across the boundary.  This form
of energy transfer is extremely common and important in
real life.

======================

Tangentially related remark:  I suspect some students suffer from
the notion that energy is _defined_ in terms of work, so that any
energy transfer must (by definition) be a form of work.

We have here a perfect counterexample to this notion.

To my way of thinking, energy is primary and fundamental.  Work
is a secondary concept at best.  In some situations, if/when
work (F dot ds) helps you think about the energy, fine.  Otherwise,
forget about work.  Go with the energy.

*) Sometimes the energy transfer is best described as advection.
*) Sometimes the energy transfer is best described as work.
*) Sometimes neither of the above;  for instance when a block
slides along a table there is no practical way to calculate
the work (F dot ds) because we don't know the microscopic
forces (F) nor the microscopic displacements (ds) in sufficient
detail.  Indeed elementary physics does not suffice to
calculate the energy transfer, so IMHO we don't really need
a fancy name to apply to something that we can't calculate
anyway.