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Re; centrifugal force, was Banked road



I agree with Joel. But let me ask another question (see below).

Referring to this:
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?

"RAUBER, JOEL" wrote:
I think the word centrifugal is already used, for the case of analysis in a
different frame of reference then your frame (the fixed stars). That is,
use of that word violates your admonition to not use a word already used.
Why not call that reaction force the *normal* force of the wheels of the car
acting on the pipe?

Problem 7.17 in our textbook is about a cylinder (diameter=5 mi) used
as a space colony. The authors ask: "What angular speed must such
a cylinder have so that the centripetal acceleration at its surface equals
Earth's gravity?" The expected answer, w=0.05 rad/s, follows
directly from w^2*r=9.8 (this is about 0.5 rpm).

Will people in this colony feel like on earth? Suppose a frictionless
beam is created along the diameter. A bead on this beam will experience
radial acceleration of 9.8 m/s^2 near the "floor" (and a little less above
the floor). The centrifugal force, fictitious to me but very real in the
rotating frame, would act on the bead (or a person on the beam) as it
slides away from the axis of rotation. It is the only force acting on
the bead, like gravity in free fall. The object is experiencing "artificial
gravity" directed away from the axis of rotation.

But why should the same be true for somebody who is not in contact
with the rigid structure of the rotating pipe? An object half way between
the axis and the wall will not experience any radial pull toward the
nearest wall. Is it correct to say that artificial gravity exists only for
objects which are forced to rotate together with the pipe (like in a
centrifuge), it does not exist for all objects inside a rotating empty pipe?
Ludwik Kowalski