A while back I came across the following question:
"Why do forces always occur in pairs?"
That question comes from a CONCEPT CHECK in Hewitt chapter 7,
but I ask the following questions more generally:
*) Have you ever asked that question on a homework assignment
or quiz? If so:
-- What is the official correct answer?
-- What are the top one or two incorrect answers?
*) Let's assume that "some" students read the book. What
do they do when they come to this question? Have any of
them ever asked you about it?
*) If this question has never come up, why not?
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These are genuine non-rhetorical questions. I am quite sure
I don't know why forces occur in pairs. Probably I don't
understand the question, although all the words seem simple
enough.
I tried googling, but the only answers I could find were
infantile or circular or both. Paraphrasing slightly, the
leading contenders were:
-- Because forces always occur in pairs.
-- Because God said so.
-- Because Newton said so.
-- Because Hewitt said so.
Are we really teaching students to give answers like that?
If this is what "conceptual physics" means, may God bless
it and keep it, far away from me.
As for me, the only way I can imagine responding to the
question would have to be considered a non-answer, and
even so it is more complicated than anything one could
reasonably expect from a high-school student.
So what's the deal? Was Hewitt asking a trick question?
Or is there an actual answer?