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Re: [Phys-l] workable versus unworkable energy



At 12:56 PM 1/10/2007, Jim, you wrote:

[Brian]

>In the case of current interest: a car tire can expend an auto's
>kinetic energy in heating the tire.....

[Jim]
Brian, let me recast your msg in different terms:

Energy, what ever its definition, is not a substance, a system's
kinetic energy can not be "expended," Nor can energy be "consumed".
///
Jim

Jim,

I am drawn to break horses: quarter horses. Hobby horses do not
respond in quite the same way to rewards, nor do they heed
punishment. So, admitting my inexperience here, I will simply
say that the conserved entity that I have been discussing has a
measurable quantity.

After all, you would say that in science, data which cannot
be quantified are meager.
If I can measure a quantity, then in general I can call a reduction
in that quantity an expenditure. And I do call a reduction in kinetic
energy due to braking an expenditure, a dissipation, even.

Moreover, I am just as apt to expend other conserved quantities.
I can expend the linear momentum of a billiard ball on another ball
so that the original ball becomes still on the table while the second
ball rolls off.

Even sadder, I expend the uncertain mass of bank notes in my
wallet upon such things as a cavalry sword, a saddle or a hoof knife.
(Surely this is a net mass increase, in the local area?)

I expect you would like me to rephrase my "energy transfers" and
mass deficits and momentum losses in a much more circumspect way.

Throw in a "property of" here, and an "internal energy" there in
lieu of kinetic energy, and promise never to verbalize a concrete
model of an important concept of this kind.

But I am old and crabby, and probably will mention conserving
entropy at times, but dissipating heat at others.
So you will need to make allowances for me, and other
old folks of this ilk. :-)



Brian Whatcott Altus OK Eureka!