Re: [Phys-l] battery redux and again (part deux)

[John Denker <jsd@av8n.com>]

On 03/01/2007 01:19 PM, Larry Smith wrote:

> I think this is promoted in the article by Sherwood and Chabay that Justin
> cited
> http://www4.ncsu.edu/~rwchabay/mi/circuit.pdf

Yes ... but it can be found elsewhere, too.  I don't know who
has been "borrowing" from whom.

> And their argument seems (to me) to be precisely to proceed from the known
> to the unknown.  This seems entirely reasonable for an intro class, given
> your claim that "the microscopic mechanisms inside batteries are insanely
> complicated."

OK, I'll bite.......

Tell me what is "known" about the "non-Coulomb force Fnc" that S&C
invoke to "explain" the inner workings of the battery.

I've run down the list of non-Coulomb forces that I know about and
drawn a blank:
 -- Gravitational force.
 -- Magnetic force.
 -- Weak nuclear force.
 -- Strong nuclear force.
 -- ??????

Now a philosophical and pedagogical point:  If the argument is going
to depend on a force unknown to physics -- certainly unknown to me and
probably unknown to the students -- where do we draw the line?  Where
is the line between caricature and travesty?

In particular, wouldn't it be pedagogically better to go with all-out
farce, so that the students /know/ it's a farce, rather than foisting
on them something that looks like physics but isn't?  For example, I
would be tempted to "explain" that the Fairy Godmother comes down and
puts some charge in her Easter basket, carries it to the other terminal,
and dumps it out.

The previous paragraph may sound sarcastic, but it's not.  My "explanation"
is facetious, but I'm sincere about preferring the facetious "explanation"
to the pseudo-scientific explanation.

I think it is important for students to know what is science and what
is not.

Please don't tell me that "all models are imperfect".  I know that already.
My point is that in a good model, everybody can tell which parts are apt
and which parts are not.

It makes sense to go into details about the apt parts of the model.  It
makes no sense to go into details about the inapt parts of the model.
IMHO S&C go into vastly too much detail about inapt parts of their battery
model.