Re: work done by friction

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Wed, 27 Oct 1999, John Denker wrote:

> In the situation in question, nothing can do work on the table, since it
> was stipulated to be stationary.  The table gains only heat.  The
> frictional heating is not different in principle from shining a heat-lamp
> on it.  According to any reasonable definition, this is heat not work.

I'm sorry John; you can't have it both ways.  Either friction does work on
both the table and the block or it does no work at all.  (I can give you
definitions of work and/or find reference frames that will make it go
either way.)

The only mechanism available to effect any significant short term change
of the block's energy is friction.  I don't care if you want to call that
frictional work or frictional heating, but you've made it very clear that
you want to call it frictional work in the case of the block.  In *any*
event it is that frictional interaction that is responsible for any
significant, short term change of the block's energy and, if the block
loses energy by that frictional mechanism, the table gains it by the
*same* frictional mechanism.

Yes, there will undoubtedly be some purely *thermal conduction* processes
that will operate over the longer term that will also transfer energy from
one system to the other but these can go either wasy depending upon
unknown details of the scenario including whether the block was initially
warmer or colder than the table.

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm