Re: Benjamin Thompson's experiment

[brian whatcott <inet@intellisys.net>]

At 17:31 9/1/97 -0700, you wrote:
> Bottom line, folks: energy is not locally conserved. It is not
> locally conserved precisely because it cannot be localized*.
> Energy is an abstract quantity which depends upon the parameters
> which describe the state of a system. Do not imbue energy with
> a reality of its own. That way lies utter confusion. It would
> be ironic indeed to teach such things in a "conceptual" physics
> course.
>
> Charge is locally conserved; baryons, leptons, etc. are locally
> conserved. Milk is locally conserved in the absence of cows or
> consumers.
>
> Energy is *different*. Charge and milk flow; energy doesn't.
>
> No one has explained Benjamin Thompson's observation in terms
> of a "flow of energy" because it can't be done! Why is it that,
> more than two centuries after his discovery, with the progress
> made since then (especially relativity), and with all the
> exposure his discovery has had in textbooks at all levels (my
> text for next semester even has a racy personal profile of him
> in it) the important lesson hasn't been learned? Energy doesn't
> flow. Caloric flows, but it doesn't explain Nature.
>
> Consider once more Thompson's observation:
>
> We have a motor doing work with power P at one end of a shaft.
> At the other end we have a dull bit in a bath of lubricant in a
> cannon bore. The internal energy of the bath and the cannon is
> increasing at a rate P. For the purposes of this discussion we
> will assume that its temperature remains constant, a condition
> that could be realized, for example, by putting ice cubes in
> the lubricant and running it at 0 degrees C.
>
> It is important to note that the intervening shaft is not
> "transmitting energy". Its energy is constant; no part of it
> exhibits any time evolution whatever....
> Bottom line: energy is not locally conserved.
>
> Leigh
>
> *One cannot uniquely determine the amount of this quantity
> contained within an arbitrarily small volume.
This is a most interesting and illuminating note.
It helps me to recall that when James Watt settled on the
"Horsepower" as his marketing token for the effectiveness
of his condensing steam engines made in the manufactory at
Soho Works, Handsworth, he was if any thing, a little generous
in rating the power provided by the working ( shire or draft )
horses then in use, with which he was set up to compete.

 He could demonstrate that his steam engine could provide enough 
tension on a hempen rope  so that ( after the smallest delay which
represents the speed of sound in that rope material) a force was 
available to lift a particular weight of water at a particular speed.

We easily recognize in the units of force times speed the necessary 
units for measuring the rate of doing work.

They then thought that the energy provided by the engine
was transmitted by the rope to a water bucket, whose potential energy 
was thereby increased.
 Count Rumford (to name but one) discounted the material or 'energy-flow' 
idea for heat in favor of the concept of a mode of motion.

I believe we can all easily say that the engine 
or the horse does work via a force transmitted through a rope.
 And in the case in point, this force provides a weight with increased 
potential energy. 


Regards
brian whatcott <inet@intellisys.net>
Altus OK