pseudowork and effective displ.

[LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>]

Replying to John's message posted on Sat, 26 Jul 1997 23:46:58 -0800 (PST)

Hi:
Both of your messages arrived; I am saving the second one. It is always
frustating of not knowing what happens "in the aether". Thanks for your
effort to clarify things again. I think I am not the only one who will
benefit from what you wrote.  

> In the case of the cube, the pseudowork (force of friction x sliding 
> distance) is negative and identically equal (as it must *always* be) 
> to the change in the cube's bulk kinetic energy. However, since the 
> points of contact repeatedly break free and reestablish contact, their 
> effective displacements are *less* than the sliding distance. As a result, 
> the external work is *less* negative than the pseudowork and, therefore, 
> the *total* energy of the cube does not decrease by as large an amount as 
> does the bulk kinetic energy.  

It takes time to get used to pseudowork; most textbooks call it work and
my brain has a lot of mental inertia. I though that my 'eureka' message
will be the last before I go away next Tuesday. But you just remined me
that I had questions about "effective displacements". Perhaps I will ask
them at some later time.
                                           Regards, Ludwik Kowalski