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Re: [Phys-l] Centrifugal redux



The reason I posted my comment, and the problem I have with using
centrifugal force, is that students tend to use the term without the
necessary mental change in reference frame to a rotating frame of
reference. In an inertial frame, the centrifugal force in actuality does
NOT exist and it is not correct to refer to it. If I am to accept the
students use of the term, I need to be convinced that he/she is using
the correct reference frame to give meaning to the centrifugal force.

My reference to a plane going straight when the central lift component
is said to be equal to the centrifugal force is because the obvious
intent of the explanation is 9 out of 10 times to be from the ground's
point of view. From that view, a centrifugal force does not exist. If it
did, the plane would have to fly in a straight line.

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Philip
Keller
Sent: Wednesday, March 18, 2009 12:53 PM
To: 'Forum for Physics Educators'
Subject: Re: [Phys-l] Centrifugal redux

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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