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# Re: [Phys-l] teaching energy

• From: Jack Uretsky <jlu@hep.anl.gov>
• Date: Fri, 29 Sep 2006 13:27:55 -0500 (CDT)

The objection to "fluid models" is of the nature of a "wrong religion"
objection. If a "fluid model" helps you calculate the results of
experiments, as the diffusion equation helps us to calculate certain
thermal phenomena (e.g., "heat conduction"), then the model is a success
and should be taught, IMO.
regards,
Jack

On Fri, 29 Sep 2006, Rauber, Joel wrote:

John C. wrote in part:

| I certainly can not defend one point of view over the other
| as being more correct. But I think that they are trying to
| get students to build a consistent model of energy, so one
| point of view may be more productive than the other.
|

Granted, but the document referenced, is actually saying that the other
viewpoint is *wrong*, implying incorrect physics?

Later they claim:

"If we claim that energy is stored in the gravitational field, and if a
change in energy content is
indicated by some change in the thing that stores it, then what changes
in the field when it gains
or loses energy?

R. McDermott wrote in part:
| The central theme is that the energy must reside somewhere.
| Taken in that
| context, the only "place" for it to be is in the field itself.
|

I don't understand the *must*; why not say it resides in the
configuration of the system. The change in the thing is . . . The
"thing" would be the two body system, the change in the thing would be
its configuration. For point-like objects that would be its separation
distance. Much like a mass-spring system.

They appear to me to be coming dangerously close to re-enforcing a fluid
& container model of energy; i.e. reifying the idea to a possibly
dangerous degree. Though I must admit to only a cursory glance at the
document.

So while I found the document to be interesting and of value (I've
actually bothered to print it off) I worry about the reliance on the
field concept at this level. Both on grounds of practicality and
principle. In terms of principle, didn't Feynman and Wheeler write a
paper in the 40's showing that you could dispense with the field concept
in Electromagnetism. In terms of practicality, the field concept is
more abstract than the configuration of a system . . ., hence my worry.

Just some rambling thoughts for discussion.

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