Centrifugal force: A gedanken experiment

Abstract

A simple gedanken experiment, the motion of a bead inside a rotating linear pipe, is considered. It is shown that at large enough velocities a centrifugal force acting on the bead changes its usual sign and attracts towards the rotation axis. The motion of the bead is oscillatory, resembling a well-known case of the mathematical pendulum. A possible relevance of this highly idealized problem to the real motion of charged particles in a pulsar magnetosphere is pointed out.