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Re: [Phys-l] The "why" questions

I didn't mean to appeal to authority in the sense that John seems to be
asserting. I agree with John on his first two points, and I didn't mean
to imply any differently. We should not accept arguments based on
appeal to authority, whether the authority be Newton, Galileo, John or
myself.

However, with #3 I'm not sure John disagrees with what I wrote or not.

3) There's no need to be "harsh", but we should not tolerate
nonsense ... and we should not accept arguments based on
appeal to authority.

We agree that we do not need to be harsh. I, for one, understand why
students would say that forces cause motion (see previous message). I
assume John also understands.

John doesn't specifically mention what he considers "nonsense" but I'm
not sure I'd go so far as to say that "force causes motion" is nonsense.
It makes sense in the way I described in my message. [It is precisely
this "sense" that makes "force causes acceleration" more dangerous]

Still, just because we understand why students say something does not
mean we should tolerate that language without question. In this case,
it is sloppy and there are many places that such sloppiness can lead to
confusion. I'm guessing there are situations where I would be more
tolerant than John but that doesn't change our general agreement on this
issue.

----------------------------------------------------------
Robert A. Cohen, Department of Physics, East Stroudsburg University
570.422.3428 rcohen@po-box.esu.edu http://www.esu.edu/~bbq

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf
Of John Denker
Sent: Monday, November 29, 2010 10:54 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] The "why" questions

On 11/29/2010 07:53 PM, Robert Cohen wrote:

This idea that the motion is generated by a force is, in fact, the
same language that Newton used to describe his second law (at least
via the English translation of his Latin) so we shouldn't
be too harsh
on students when they use it.

1) Except that in a later part of the book, Newton
categorically denied that he was making a statement about "causes".

This is one of the notorious problems with appeal to
authority, namely that people tend to mistranslate the
authorities and/or quote them out of context, or otherwise
mutilate the meaning.

2) And even if Newton had gotten this wrong, so what? One
guy making a mistake should not poison the field forever.

That would be almost as childish as saying "The LA Times did
it once, so that makes it OK." I tried a similar line of
reasoning on my mother when I was five: "All the other kids
were doing it." She didn't think that made it OK for me to
do it. I never tried that argument again.

That is another notorious problem with appeal to authority.
Sometimes the authorities are wrong.

3) There's no need to be "harsh", but we should not tolerate
nonsense ... and we should not accept arguments based on
appeal to authority.

======================

The "why" disease is not confined to F=ma. In chapter 7 of
Hewitt's _Conceptual Physics_ it asks the students:
<CONCEPT CHECK: Why do forces always occur in pairs?>

When I read that, I said OK, I'll bite: Why do forces always
occur in pairs?

I cannot imagine how a student (or anyone else) is supposed
to answer such a question.
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