Re: work, energy, etc

[Larry Cartwright <exit60@CABLESPEED.COM>]

Bernard Cleyet wrote:
> I would think one should introduce concepts first that are easily apprehended
> (original meaning).  i.e. work first, as it's so kinesthetic, while energy is
> rather nebulous.

 From my classroom experience I would say that, to a beginning student,
work is considerably more nebulous than energy.  Even the "non-academic"
physical science students had a pretty clear intuitive sense that a
heavy object held over their heads had some property or character that
made it substantially different from an identical object at their feet
on the floor.  Moving vehicle vs. parked vehicle.  Electrical circuit
turned on vs. turned off.

Regarding work, I think most beginners have a pretty good sense of what
a force is and what a distance is; but the result of combining the two
to produce this thing *we* call work seems more like an mathematical
artifice than something "real".  The whatever-it-is that makes a can of
gasoline different from a can of water, or a flask of boiling water
different from a flask of lukewarm water, is more "real" to them.

I don't want to get in over my head in an argument over what is the
scientifically "most correct" way of approaching how work and energy
relate to each other, but I do think we're probably better off trying to
take advantage of whatever intuitive sense of "reality" students
possess.

Of course sometimes their intuition sucks and we have to fight it.  I
once had a student who was firmly convinced that freezing water had more
energy than lukewarm water.  His reasoning:  Freezing water can harm you
by giving you frostbite, whereas lukewarm water is harmless.  Anything
that can put you in the hospital must be really loaded with energy,
n'est-ce pas?

Best wishes,

Larry

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright   <exit60@cablespeed.com>
Retired (June 2001) Physics Teacher
Charlotte MI 48813 USA
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