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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.