Re: ENERGY BEFORE Q (was Displacement)

["Carl E. Mungan" <mungan@USNA.EDU>]

I only read the digest, so apologies if others have already fully
answered "Ludwik as student".

> We are ready to generalize this observation by
> saying energy is the "ability to do work". IS THIS OK?

In mechanics the answer is yes, because we restrict energy to
mechanical energy and work to pseudowork. As a more general
definition of energy, no way! The second law of thermo has something
to say about this.

> g) I AM NOT SURE IT IS CORRECT TO SAY THAT THE
> CONSERVATION OF ENERGY IS "DERIVED"
> MATHEMATICALLY (IN THE SAME WAY AS THE
> WORK-KINETIC ENERGY WAS DERIVED EARLIER IN
> THE CHAPTER). THE LAW OF CONSERVATION OF
> ENERGY, EVEN IN THIS TRIVIAL CASE, SHOULD BE
> PRESENTED AS AN EXPERIMENTAL FACT. IN OTHER
> WAY, DO NOT TRY TO PROVE THAT KE+PE=CONSTANT.
> WOULD YOU AGREE?

Again, are you doing mechanics or thermodynamics?
You CAN prove that the mechanical energy KE+PE = const PROVIDED that
the net pseudowork done by nonconservative forces is zero.

If you're talking about energy is in its fuller thermodynamical
meaning, then I'm less sure. I tend to say it's experimental. But as
I wrote in my executive summary, I think I can make contact between
mechanics and thermodynamics at the microscopic level. But I'm still
thinking about it.

To put it another way, first define energy better than "ability to do
work" and then I'll tell you if I can prove its conservation. Back to
Feynman's blocks: if we can always invent another block every time
energy is apparently not conserved, then energy is conserved "by
fiat" not by experiment.
--
Carl E. Mungan, Asst. Prof. of Physics  410-293-6680 (O) -3729 (F)
      U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu    http://physics.usna.edu/physics/faculty/mungan/