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Energy



I really don't want to post this, but several list members whom I highly
respect have privately urged me to do so. They have suggested that there
are new list members who might benefit from the following comments. On the
other hand many on the list already know my views. It has been suggested
that some of them might benefit from a review. However, many of them have
shown that they don't respect those views. I beg those list members just
to delete this post, Please! I hope that I will not be drawn into a
"debate" over this issue. I don't have the motivation to do so. I don't
get paid enough.

These views are not mine uniquely; they are/have been shared by others on
his list and my understanding has been aided by their posts.


General Comments

Energy is a _property_ of a system; It is not stuff which can be moved,
transformed, transferred, poured, etc. Blue might be a property of a
system -- One would not conceive of saying that "blue"
moves/flows/transfers/etc. Blue _paint_ can flow -- a substance can
flow. But properties don't move independently. Likewise, it is also
inaccurate to say that for example mass moves -- a massive block can move,
but mass doesn't move independently. Further, it would be incorrect to say
that relativity equates mass and energy, therefore energy is stuff. No. No
No. Neither energy nor mass is stuff. They are both properties of some
system. It is also incorrect to picture energy as "propagating" through a
surface -- or through anything else. These comments are valid for all
other properties of a system as well eg charge, roughness, size, etc etc ad
nauseam.

The energy of a system can be increased or decreased -- but not
transferred, The _only_ way to change the level of the energy of a system
is to do work on the system.


Consider the following example:

Someone in a tall building wants to descend quickly. S/he decides to slide
down a canvas tube of sorts to the ground. (I take it back; a woman would
have better sense.) But the tube is not frictionless (if it were the person
might as well just jump off the roof. ) The Earth does work on a person
who is sliding down the tube and thereby increases his kinetic
energy. And decreases his potential energy. And may later do work to
stop him -- perhaps very suddenly -- and decrease his kinetic
energy. Frictional forces also do work on the sliding person and decrease
his kinetic energy somewhat. But the frictional work also increases his
internal energy -- and fries him to a crisp.

Now does energy move? Well yes. The internal energy of the person moves
as the hapless fellow slides. So does the kinetic and potential energy of
the person. The brown of his hair moves. His mass moves. The charge
of his molecules moves.

But none of these properties is "transferred" from one system to
another. The system moves and the properties move with it. The level of
energy can be changed but only by doing work.

Yes, the person does work on his environment and changes its energy:
canvas, Earth, etc. And the total energy of the Universe remains
constant. But the changes in levels of energy of the various systems can
only be effected by doing work.

......
I agree that sometimes information can be transferred more fluidly with
shorthand language. But only with the great danger that the conversants
forget that it is shorthand -- and in complicated discussions commonly
do. In the classroom it is usually a disaster.

It would be far better to be precise in physics dialogue -- It is just too
easy to make a mistake -- or worse teach faulty concepts.

I might add an analogy -- This also dangerous because analogies are never
accurate and I am not sure that this one is effective:

A person walks into the local branch of his bank with some green
dollars. He deposits these dollars in his account. He flies to another
city and goes to his bank's branch there. He draws out some of his
dollars -- Well no he doesn't. He draws out somebody else's dollars, The
physical dollars don't move from city to city. Just the numbers associated
with his account do.

Alright alright alright I don't like it either.


Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen