Re: Swartz letter in AJP (work-energy theorem)

[ALVIN BACHMAN <bachman2@PRODIGY.NET>]

  The "system" has to be defined explicitly.

Is it the widget only, or the widget+ice ?

If the widget only, then there is an energy transfer
which we attribute to the work done by the force
between the ice and the surface of the widget.



--- Larry Smith <larry.smith@SNOW.EDU> wrote:

> At 10:26 PM -0600 8/31/04, Jim Green wrote:
> > Then he attacks friction.  Let's take a side bar:
> consider a cold widget
> > which is sliding on ice,  the widget slows.
> therefore its level of energy
> > is decreased.  The _only_ way to change the level
> of energy of a system is
> > to do work on the system.  What then does this
> work?  Obviously it is the
> > ice.  But how?  By exerting a frictional force.
> Hence, friction does
> > work.  And again he does not understand the
> work/energy theorem.
>
> Definitions of words such as cavalier are very
> interesting, but the nub of
> the discussion is Jim Green's paragraph above.  Of
> course there is negative
> work, whenever the energy level of an object is
> decreased, and it isn't
> beyond freshman to understand this.
>
> Larry