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Re: Energy, etc (fwd)

On Tue, 10 Aug 1999, Leigh Palmer wrote:

If kids haven't progressed beyond concret operational they
are not yet ready for a concept like energy. Bill Nye is
not doing them any good at all (and I doubt he will do the
brighter ones any good, either).


Probably most of us here have encountered Feynman's thoughts on this:

"Judging Books By Their Covers" (From SURELY YOU'RE JOKING...)
http://fy.chalmers.se/~f3aamp/teaching/wakalix.html



At *some* advanced grade level the usefulness of the "energy-substance"
concept must outweigh the misconceptions, no? When teaching engineering
students, probably it would be a bad idea to teach that capacitors DON'T
store joules of energy, or that transmission lines DON'T guide EM energy
from place to place at a joules/second rate. If I crank an electric
generator and inject a certain joules/second into the system, and then it
heats an electric heater at an almost identical joules/second rate, then
"joules" moved from my arm to the distant heater. If "joules" in this
situation are conserved and cannot simply vanish spontaneously, then
"joules" are similar to a substance which can flow. (Or instead of
"flow", call it "propagate", since those "joules" move along with the EM
wavefront.)


When radio waves travel in space, must we forever avoid saying that
"energy" travels with them? A laser beam can be measured in terms of
joules per second. Should we deny that "joules" are flowing along the
laser beam at a certain "per second" rate? (By "rate" I mean Watts, not
velocity.) The laser loses "joules", and a distant absorber gains the
same "joules" when the beam strikes it... but we must never say that
"joules" were emitted by the laser and absorbed by the distant target?


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