On Wednesday, January 13, 2016 at 1:18:06 PM UTC-7, Davoud wrote:
Quadibloc:
it would seem as though one could make tiny electrical power generators that
broadcast power by radio that used a self-winding watch mechanism... to
convert
heat directly into useful work, in violation of the laws of thermodynamics.

That wouldn't be converting heat into useful work, it would be the
conversion of kinetic energy into radio waves. As for heat-to-useful
work, the steam engine and the internal combustion engine do a
reasonable job of that. And none of it violates the principles of
thermodynamics.

Steam engines and other devices that exploit the Carnot cycle don't break the
laws of thermodynamics because they produce useful energy by taking heat from a
hot place and and harnessing its flow to a cold place.

But a direct _net_ conversion of heat energy to useful work - taking something
hot, and cooling it off, without making anything else warmer, and getting
useful work from the heat energy you've consumed, is what violates the laws of
thermodynamics.

Converting the kinetic energy of molecules to useful work _is_ in this category
because *that's what heat is*. Now, this may not truly violate the laws of
physics, because statistical mechanics is the truth, and thermodynamics is only
the approximation... but it would seem that it is at least considered so.

John Savard