<<the most unproductive arguments
are those about definitions -they rank slightly below arguments about
religion.
<< Someone suggested that we teach logic to our students. Great
idea, but let's start with the teachers. >>
At the risk of starting another argument about definitions, I would assert
that this response constitutes "flaming", and has no part in a list like
phys-l. Teachers need to be able to express themselves freely here without
fear of ridicule and sarcasm. There is a note of defensiveness in more than
one response to this thread, not just in Jack's reply. Defensiveness is
usually a good indicator that the writer is feeling a bit uneasy about the
ground they are standing on.
I think the issue being reaised in this thread is a very significant one and
while I know that there are people who have spent a lifetime considering the
matter of the relationship of the force laws to the Pauli exclusion
principle, I have not yet seen an explanation which would be adequate to
give to a student, much less to the average high school physics teacher.
The problem is this: as physics teachers we are teaching a Newtonian (or in
some cases an Einsteinian) system of mechanics in which every interaction
between two bodies involves a force, and every acceleration is evidence of
the action of a net force. We present students with the example of an
object sitting on a table and ask them: "what are the forces on the object?"
The students are usually reluctant to say that the table exerts a force on
the object, and will argue that the table is just "in the way of" the
object's falling." Through some line of reasoning, experiments and
demonstrations then we lead the students to the conclusion that the table
must be pushing up on the object with a force equal in magnitude to its
weight and opposite in direction. At first they call this the "normal
force" or some variant thereof. Eventually they may learn that this force
is derived from the electromagnetic force between pairs of atoms.
But let's look at this answer a bit more closely. The force interaction
between atoms can be explained in terms of Coulomb attraction and repulsion
until they are forced into very close proximity, but there the repulsive
force rises very sharply due to the resistance of the electrons around the
two atoms to occupying the same quantum state. This force is certainly as
worthy of being given a name as is a spring force, a normal force or a
buoyant force. Also like these others it is evidently not a fundamental
force, not at the level of a "canonical force".
The challenge here is to first find an appropriate name for the "exclusion
principle force", for within our Newtonian system such a force most
certainly does exist, and then to develop an argument which a college
sophomore or jusior - or a physics teacher who has had one course in quantum
mechanics and one course in statistical mechanics - could follow that this
is derived from the electromagnetic (or electroweak) force and is not a new
fundamental force.
Some of us at least may out of this inquiry come to a deeper understanding
of atomic physics.
Chris
* * * * * * * * * * * * *
Christopher A. Horton, Ph.D.
4158 RR#3 (Hwy. 204)
Amherst, NS B4H 3Y1
CANADA
ChrisAHorton2@hotmail.com
(902) 447-2109
* * * * * * * * * * * * *
"Many discoveries are reserved for ages still to come, when memory of us
will have been effaced. Our universe is a sorry little affair unless it has
in it something for every age to investigate ... Nature does not reveal her
mysteries once and for all."
- Seneca, "Natural Questions", first century, quoted by Carl Sagan in
"Cosmos", p.xi.