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Re: [Phys-l] Centrifugal redux

What about saying just asking them to identify the agent of the force?

Once one does this, they are not able to generate fictitious forces of any
kind. You can point out that in an accelerating reference frame Newton's
laws do not work, or must be modified. But to get understanding they must
learn to identify forces from the various interactions, and just talking at
them about it will not be very productive. You have to get them to do it,
and tell you what they did so you can ask a question like "describe the
centrifugal that is acting on the object." They need to use agent object
descriptions such as F _N table on book, the table exerts a normal force on
the book. If they insist on the idea then perhaps saying that it is called
a ______________ force and is an idea we make up to keep Newton's laws in an
accelerated frame. You can pick from a variety of words fictitious, pseudo,
virtual, made up... depending on what you think students might accept.

After all forces are a concept we make up to explain things. We then
proceed to "believe" they are real. Medieval scholars looked at motion and
force very differently, and the concept has shifted since Newton.

John M. Clement
Houston, TX



I agree. If a student says that a satellite remains in orbit because the
gravitational force balances the centripetal force, I can't say "No, you
are wrong." If I insist on banishing centrifugal forces from my class,
the more honest response is: "No, I don't want you to think about it that
way." Maybe better to open the door...time spent explaining why these
forces do not really exist could just as easily be spent explaining when
it's OK to use them.

***********

So what is the point of forcing students to go through an intermediate
phase where they are taught centrifugal fields don't exist? For all
of their life before class, after class, and north/south/east/west of
class, centrifugal fields exist.

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