Re: ENERGY WITH Q

["RAUBER, JOEL" <JOEL_RAUBER@SDSTATE.EDU>]

> At 09:01 AM 10/30/01 -0600, RAUBER, JOEL wrote:
> > But is it true that F dot ds_cm is Delta KE?  Which I think
> is the claim
> > Carl is making.
>
> Good question.
>
> At 09:35 AM 10/30/01 -0500, Bob Sciamanda wrote:
> > The integral of the net external force over the trajectory
> of the system
> > CM will ALWAYS equal the system KE change.
> > See previous (1999?) list discussions.
>
> 1) Wrong answer.
>
> Consider a flywheel, starting from rest.  I spin the thing up
> by applying
> equal and opposite forces to opposite points on the rim.  The
> net force is
> zero.  The net force on the CM is certainly zero.  The motion
> of the CM is
> zero.  The net external force dotted on the trajectory of the
> CM is zero
> squared.  Yet the kinetic energy increases.

Would it help (or is it true) to say:

But is it true that F_ext dot ds_cm + torque_ext times dtheta is Delta KE?
Where the external torque is measured relative to the cm.

> Look, you can't do thermodynamics without entropy.  You just
> can't.

I didn't get the impression that Carl & Ludwik were trying to do
thermodynamics without entropy; but rather they were indicating a first step
on the journey through introductory thermodynamics & some relationships to
work-energy considerations.  Presumably they will (in principle) have whole
other statements (monographs) where they will talk about the introduction of
entropy concepts into intro thermo. I assume everyone agrees that you can't
tell the whole story of thermodynamics without entropy.

Joel R.