Re: Banked road

[kowalskil <kowalskil@MAIL.MONTCLAIR.EDU>]

"Daniel L. MacIsaac" wrote:
> > Acceleration along an inclined plane does not change N but
> > the circular motion does. In both cases N is a reaction
> > force. In the first case it the reaction to the perpendicular
> > component of mg, in the second case N also has a component
> > which is the reaction to the CENTRIFUGAL force. Is this an
> > acceptable interpretation?
>
> Now you're going to make me into that which I fear most -- the language
> police.  I'd not consider CENTRIFUGAL a worthwhile term to use except
> as an example of less complete reasoning to move away from.  Trying
> to use CENTRIFUGAL forces in FBDs can lead you astray immediately unless
> you develop sophisticated rules for frames of reference, in which case
> you are violating N1.  These rules are also more complex (the phrase
> cognitive overhead comes to mind here) than simply doing the analysis
> in a dynamic (accelerating) frame of reference.
>
> Other than the word CENTRIFUGAL, the rest looks good for instructional
> language to me.


I think it is not only a matter of language; suggest another
name and I will probably have no objection (unless the word
is already used to describe something else).

Let us refer to a cylindrical pipe whose inner surface is used
as a road for a car of mass m traveling along a circle r with a
constant speed, v. Suppose the cylinder is located far away from
all stars and that its mass is M. I am at rest in a frame of
reference which Newton would call "the frame of fixed stars."

To simplify assume tham M>>m so that the pipe is at rest in
my frame of reference. I see only one force acting of the
car; it is the CENTRIPETAL force toward the center Fc=m*v^2/r.
It is the normal force, N, with which the pipe acts on the car.

The car acts on the pipe and the pipe reacts with an equal and
opposite force. If the reaction is real (not fictitious) then
the action is also real in my frame of reference. We need a
name for the force with which the car acts on the cylinder.
What is wrong with CENTRIFUGAL?
Ludwik Kowalski