Re: Energy, etc

[William Beaty <billb@ESKIMO.COM>]

On Tue, 3 Aug 1999, Jim Green wrote:

> NO. "Energy" is not "located"  It does not "flow".  It is not like water,
> as Leigh says.  Energy is a property of a system.  You would not say that
> the "blue" of a blue object is "located" anywhere would you?  Not a perfect
> analogy (none are) but close.

If energy is just a property of a system, and is an abstract concept
having no substance-like existence, then I have a problem because energy
is a conserved quantity.  Mass is also a conserved quantity.  I do not
treat mass like "blueness", like an abstract property.  If someone asks me
for the location of an atom's mass, I would immediately state that it is
located mostly in the nucleus.

Can mass have location?  If so, then energy can also have location.  If I
have a charged capacitor in my hand, I will describe the capacitor as
containing electrical energy.  In theory I can even measure the mass of a
charged capacitor and determine that its mass has increased because extra
energy is located within it.  If the capacitor is used to heat a resistor,
I will assert that electromagnetic energy is flowing out of the capacitor
and into the resistor.

In my opinion, conserved quantities are not *just* properties of a system.
As Mr. Denker observes about conserved quantities, they cannot leave the
interior of a closed surface without penetrating a surface.  "Blue" is in
a different catagory.  It is not a conserved quantity, and I can reduce
the net blueness of a system without transporting any "blue" through a
closed surface surrounding that system.  Energy is not like "blue."

If conserved quantities have location, then conserved quantities can move
or flow.  Does everyone here agree that, when matter moves from place to
place, mass is also moving?  How about electric charge?  During an
electric current, does electric charge move?  Electromagnetic energy is
similar:  if a pulse of light is moving, and if electromagnetic energy is
contained within that pulse of light, then electromagnetic energy is
moving.


> Most of our physics language is only to say enough about a system to make
> some sort of calculation and from there some sort of useful
> prediction.  Physics has long since stopped trying to describe reality --
> at least precisely.
>
> The danger I have tried to mention here is that we often come to think of
> our language as some sort of reality --- this because we use phrases
> frequently enough that we forget to think just what it is we are saying --
> like some sort of mantra.  Our misuse of the language may suffice at times,
> but we come to assume that the faulty language is _always_ helpful.
>
> It is not.  And this fact rears is head when we launch into some esoteric
> discussion without clearly thinking through what we are saying,

I have to agree.  It is impossible to describe anything, if our
description must be perfectly accurate, and must include all aspects of
that thing.  Descriptions are inherently inaccurate and misleading.  Our
only option is to communicate information about flaws and limitations at
the same time that we communicate a description.

 From another viewpoint, I could say that all descriptions are wrong
because they are imperfect.  It may be very useful to imagine that energy
can flow out of a capacitor and into a resistor, but if that description
contains any flaws at all, then it is wrong.  (As an engineer, I would
not say this.  Do not destroy usefulness in the pursuit of perfection.)


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