superposition

[kowalskil@alpha.montclair.edu]

Donald Simanek wrote:
> I may have missed it, but I don't think anyone clearly stated what "The
> superposition principle" is. First, it isn't a *physics* principle or law.
> It is a mathematical relation. Is it any different than *additivity*?

In my opinion the superposition principle is a pre-mathematical relation. 
Math people can define anything they want. As physicists they try to define 
things to reflect relations in the physical world. For example, if a charge 
Q1 at point A produces E1 at a point C while a charge Q2 at B produces E2 
at C then Q1 and Q2 together produce E3 which happens to be the sum of E1 
and E2 at C. Very often this is an experimental fact and mathematians are 
inspired by it. They develop conceptual tools which we use to solve problems.
That is how I understand Dan's generalization:

> If cause A produces result A', and cause B produces result B', then the
> two causes acting together will produce result A' + B'.  ... we say that 
> the cause and result obey a principle of superposition.

The power of mathematics is in its internal consistancies; the starting 
assumptions must come from elsewhere.
                                                   Ludwik Kowalski