Synchronous motion in a devil's stick -- variation on a theme by Kapitza

TL;DR

This paper reveals that the rotational motion of a devil's stick and the self-stabilization of a Kapitza pendulum are fundamentally identical phenomena, introducing a new friction-stabilized synchronized state that explains the stick's motion.

Contribution

It demonstrates the equivalence of devil's stick motion and Kapitza pendulum stabilization, and reports a new friction-stabilized synchronized rotation state in the pendulum.

Findings

Identified the equivalence between devil's stick motion and Kapitza pendulum.

Discovered a new friction-stabilized synchronized rotation state.

Explained the rotational motion of the devil's stick through this new state.

Abstract

The counter-intuitive rotational motion of the propeller of a devil's stick when the agitator is rubbed against the pylon has long intrigued performers, audiences and scientists. The apparently unrelated phenomenon of self-stabilization of a Kapitza pendulum at the inverted position, once again an amazing lecture demonstration, has on the other hand been subjected to years of investigation and research. Here we show that the two systems are in fact identical, and obtain a previously unreported, friction-stabilized synchronously rotating state in the Kapitza pendulum, which in fact explains the rotational motion of the Devil's stick.