Re: borrowing from tomorrow

[PHRP@FHSUVM.FHSU.EDU (Roger A. Pruitt)]

> >                             Ludwik Kowalski wrote...
> > How can we introduce
> > the coulomb unit without violating the rule of ideal teaching? The rule calls
> > for logical continuity; it does not allow us to explain something today in
> > terms of what is going to be explained tomorrow. In practice the rule is often
> > violated but this is not desirable. What should we do?
>
> I'm wondering exactly whose logic and whose continuity is entailed in this
> logical continuity.  I know that I and many others for many years (decades?
> centuries even?) have attempted to use this principle, but it does not seem
> to be all that effectve at least in terms of changes in student
> understanding.  I wonder if our logic and our continuity is not what's
> called for here.
>
> Dewey
In one way the expression "logical continuity" used above seems to imply a
sequential development. However, when I read the first posting I assumed,
Ludwig, you were talking about a deductive approach. Now I don't think this
is what you meant and now believe that you were talking about a sequential
approach. However, I don't know that logical continuity necessarily implies
a sequential development. 

Ludwig, you say that logical continuity "does not allow us to explain
something today in terms of what is going to be explained tomorrow." That is
probably true but does physics necessarily fit this? As our understanding is
developed don't several lines of research often converge? Since one recent
discussion has been on electrostatics and current electricity, we might
reflect that research on magnetism and electricity were once widely separate
areas of investigations. They were seen to be related only in the 19th
century. When I started to study physics in the 50's esu's, emu's,
statcoulombs, abcoulombs, rationalized units, unrationalized units, etc.
were still part of the lingo. I'm thankful for SI units. However, the
multitude of different units was historical and related to the separate
areas of research in electrostatics and magnetostatics.

I have personally used in the past the deductive approach in my teaching as
much as possible, but it seems to me that there are times when a new line of
reasoning must be pulled into the process in order to continue.

Do either you or Dewey care to comment?

Roger Pruitt