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Re: conservation of energy

--- John Denker <jsd@AV8N.COM> wrote in part:
SNIP
Here's my take on conservation of energy:
-- As an example of a reasonably general
formulation of
the principle of conservation of energy, consider
this:
The energy in a region cannot change except by
the
flow of energy across the boundary of the
region.
Specifically, the decrease in energy in the
region
is equal to the flow of energy outward across
the
boundary. Since this is a conservative flow,
the
flow outward across the boundary of this region
must simultaneously be accounted as a flow
inward
to an adjacent region.
SNIP

Instead, for an intro-level course, my
recommendation is
to take the law of conservation of energy as
primary and
fundamental. (I wouldn't quite call it
axiomatic, because
it remains subject to experimental test. But it
is an
input to the intro-level understanding of
physics, not an
output.)

-- In particular, I don't know whether to laugh or
cry when
I see statements of the form "the _only_ way to
change the
energy of a system is to do work" [emphasis in
the original].

I agree completely. My intro students have benefitted
greatly from the approach which focuses on the energy
of a system and examining how that energy may be
changed by various processes - workING, radiatING,
heatING, transportING (ie, adding fresh cells, more
fuel etc), all of which are means to the end of
altering the energy of a system.
John Barrere