Re: work done by friction

[Brian McInnes <bmcinnes@PNC.COM.AU>]

Jim,
I know you are " over here in my little corner" and I also am aware of
your interest and insight in thermodynamics.  I agree with just about
everything you have written about the field on your web site.

But here you have misread a couple of points I have made.

You write
> To say that somehow "external kinetic energy" is being "transferred" to
> internal energy (mistakenly called "thermal energy" above) leads us right
> back to the terrible idea that energy is a fluid being moved somehow.

I didn't write "transferred" for the very reason you state:the nasty
energy fluid.  I wrote "there is a book-keeping transaction". Nothing
has moved.  Originally there is a calculation that gives us a number
for the joules of kinetic energy; finally there is a calculation that
gives us a number for the joules of thermal energy.

You also point out "I don't see a clear statement of work done on
_what_".
But Jim, the system I am considering for the application of the first
law of thermodynamics is the system of the two blocks.  I wrote "If we
take the system made up by A and B and write the first law as W + Q  =
delta U".
Even if one believes that frictional forces do work that is internal
to the system and isn't (cannot be) part of the W on the LHS of the
equation.
Those frictional forces are the means whereby a transaction between
macroscopic and microscopic  forms of energy occurs.

Finally, Jim, all my references to work being done is written as work
being done by forces.  Like you I deplore lazy references to work
being done by objects (animate or inanimate).  Reread my two
contributions to this thread yesterday and you will see expressions
such as "A pushing force would do work"; "There is no work done by the
individual forces";"frictional forces do not do work".


Brian McInnes