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Re: A work-energy situation




al clark writes:
As I understand it, work is not done by the kinetic energy. Rather the
force of friction, acting in the block, does work, the effect of which
is to reduce the kinetic energy of the block - essentially to 0, if the
plate is massive enough. The work done by the reaction force, acting
on the plate, has the effect of increasing the internal energy of the
system, to the extent that the kinetic energy imparted to the (very
massive)
block is negligible. Under those circumstances, dU = K (almost).

I am somewhat confused by this explanation. If a block is sliding along
a massive plate, the proximity of molecules at the contact surfaces
causes
these molecules to gain energy by interacting and moving faster. This is
true of molecules at the bottom of the block as well as those at the top
of the plate.

The idea of using the terms heat, thermal energy, temperature, and
internal
energy in this instance seems to add more confusion than clarification.

Al Clark goes on the say:

PS. I believe the "internal energy" is normally used to refer only to
the energy of atomic motion with a material, not to the macroscopically
measurable energies. One could use it to refer to the total energy of
a system, if you wished, in which case the discussion would be
different.

Does this mean that internal energy is not measurable?

Herb Gottlieb from New York City
(Where we measure temperature with a thermometer, radiation with a
bolometer or radiometer, and specific heat capacity with calorimeters)