Re: why pseudowork (NOT)

[Robert A Cohen <bbq@ESU.EDU>]

The recent focus on precisely how one goes about creating a coefficient of
restitution of 0.5 suggests to me that some people cannot calculate the
work done by a force without first knowing what it is that is producing
the force.  I suppose this was also the problem with the "work due to
friction" debate.  Could someone please tell me why we need to really
understand the microscopic "goings-on" that produces friction in order to
identify whether it does work or not?

In a related matter, I agree that part of the reason for the debate here
is that different people are using different definitions of work. However,
there seems to be a difference in philosophy as well.  Some people like to
use F=ma as a basis and move toward everything else (including
thermodynamics).  Other people like to start with conservation of energy
as a basis.  Either way is fine, as far as I can tell.  There are certain
reasons why one might be better or worse for certain situations.  To me,
they just represent different expressions of the underlying physics.
Which expression we use depends on the problem at hand.
   However, when we start to imply that one way or another is indeed
wrong, that rubs me the wrong way.  Even worse is when someone implies
that we cannot link the two at all.  Such an approach reminds of a
discussion I once I had with a teacher.  I had once employed energy ideas
within an analogy to help with understanding why evaporation is associated
with cooling.  The analogy used "students in a room" as analogous to
"molecules in a liquid".  Of course, as with any analogy, this one wasn't
perfect.  However, whereas I would blame the inadequacies on the
less-than-perfect link between students and molecules, this teacher blamed
the problem on my attempt to link "energy" concepts with "state of matter"
concepts, which he asserted were two different concepts.  Turns out that
the curriculum he was following had linked every possible physical science
concept in "groups", two of which were "states of matter" and "energy".
Nowhere was there any concept that was included in both, which proved in
his mind that they were separate and any attempt to link them was doomed
to failure.  Does this bother other people as well?  Or am I the only one
who thinks that *everything* is linked somehow.

----------------------------------------------------------
| Robert Cohen               Department of Physics       |
|                            East Stroudsburg University |
| bbq@esu.edu                East Stroudsburg, PA  18301 |
| http://www.esu.edu/~bbq/   (570) 422-3428              |
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On Fri, 29 Oct 1999, John Mallinckrodt wrote:

> Since you have Interactive Physics you could also simulate the collision.
> Just make the "elasticity" of both objects 0.5.
>
> This morning when I posted this question, I really had no intention of
> getting sidetracked onto the not very interesting topic of momentum
> conservation in one dimensional collisions.  I was far more interested in
> how people viewed the work-energy relationships in this very ordinary
> collision.  I am sorry that that more revealing question has been lost in
> the noise.