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Re: Heat energy, analogies, lecture demos



This is an analogy for "Heat conduction". The stored energy in the
swinging pendulum is analogous to the "Heat energy" trapped in a single
atom. The moving table is analogous to both the infrared "photon"
component of heat transfer, and also the acoustic/mechanical "phonon"
component. (Perhaps we should mount magnets on the pendulum bobs, that way
the magnets could perform the "photon" transfer, while the wiggling table
would illustrate how "phonons" communicate heat between atoms.

I hate it! This "analogy" is incredibly misconceived. In my opinion
it is exemplary of the misdirection that can be caused by even well
intentioned but ill informed efforts simplify that which does not
require simplification.

(calms down a bit)

This well known physical phenomenon is best known because the two
pendula continue interacting in such a way that the energy of each
oscillates, ideally, periodically. Phonons are a name we give to a
mathematical construct which is manifest in vibrations of the
lattice; phonons *are* the energy; they don't just "transmit it
between atoms". A single phonon necessarily involves almost every
atom in the lattice, save only those which might be located at
nodes of the motion. Phonons, like energy, are not localizable to
a region smaller than the system itself.

Why on Earth would a teacher want to introduce an erroneous concept
using a name already associated with a perfectly respectable
physical entity!? In what way will this help a student to grasp the
workings of Nature?

Leigh