Re: Old guitar strings--actually Leigh's comments

["Daniel L. MacIsaac" <Dan.MacIsaac@nau.edu>]

> > > One of the marks of an educated person is to know the limits of one's own
> > > knowledge and understanding (and there always are limits). Worse than "not
> > > knowing" is "knowing things that aren't so".
> This is interesting in two aspects:  1) Our students teachers with a
> concentration in physics are required to take 30-32 semester hours of
> physics and 6 semester hours of methods/materials in science education.
> How many more hours of physics do they need to know it "fully"? ; and 2) if
> teachers waited to teach until they understood everything fully, would
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> anyone be teaching?
^^^^^^^^^^^^^^^^^^^^^
> John C. Park

I sure wouldn't be teaching.  I learn every time I teach, and I learn from my
students in my interactions with them because I listen carefully to what
they have to say when I teach them.  Addressing forty alternative approaches
and conceptions of any concept I teach leads me to a deeper understanding and 
more thorough consideration of both physics content and how to teach it --\
I get better at what I do. 

As an example, this semester I conducted a new (to me) in-seat lecture activity
(I call them seat experiments) that had students build and describe/explain
small electric motors in their lecture hall desks, and as a result I learned
what back EMF REALLY MEANS in electric motor design.  I have been able to
solve problems on and state definitions for back EMF for about 15 years and
have been (too) comfortable with my understanding of the subject.  I suspect
this is true of many of my departmental colleagues, including some who 
are outstanding teachers.  i would have never developed the grasp I now have
without teaching the topic, nor has anyone sought such an understanding with
me in the course of my many years of physics study and investigation before\
now.  I literally never would have learned this without teaching it.  I am
not ashamed to say I learn more physics EVERY time I teach it, because I
learn more when I think about it and I think about it differently when I
teach it.

Claiming otherwise seems pretty misguided to me; perhaps this reflects a wide
disparity between my philosophy of teaching and learning and those of others.

Dan M

PS -- I was also dismayed by the tone of the language in the earlier message;
it was not conducive to a callaboratory atmosphere on the listerv.  It is too
easy to get snap emails out and treat them as private conversations.  I am
guilty of having done the same, and i think a little leeway can be given
at times -- understanding does not mean condoning.

PPS -- if you want to build the motor (you should!) see 
http://purcell.phy.nau.edu/SeatExpts 
similar motors can run for months, but burn out a bettery in minutes if
stationary.  Back EMF keeps my fingers from burning with these motors (that's
pretty real to me :^)

PPS -- charge a supercapacitor with a Genecon motor/generator.  Stop cranking
the Genecon, release and watch the handle.  WRITE a description of what is 
happening and why, including a description of current flow, back EMF and 
WHY the handle is turning in the direction it does.