The (not so simple!) chain fountain

TL;DR

This paper investigates the mysterious chain fountain phenomenon, exploring the underlying physics and reaction forces involved, and provides new experimental insights that challenge previous explanations.

Contribution

It offers new experimental evidence and a broader explanation for the reaction force causing the chain fountain, surpassing prior hypotheses.

Findings

The chain fountain is caused by an anomalous reaction force.

Experimental results suggest a more complex origin of the force than previously proposed.

The phenomenon involves forces acting at the top of the chain pile, not just simple gravity.

Abstract

Given a sufficiently long bead chain in a cup, if we pull the end of the chain over the rim of the cup, the chain tends to continuously flow out of the cup, under gravity, in a common siphon process. Surprisingly enough, under certain conditions, the chain forms a fountain in the air! This became known as the Mould effect, after Steve Mould who discovered this phenomenon and made this experiment famous on YouTube, in a video that went viral. The reason for the emergence of this fountain remains unclear. This effect was shown to be due to an anomalous reaction force from the top of the pile of beads, a possible origin for this force was proposed in the same paper. Here, we describe some experiments that give a contribution towards the clarification of the origin of this force, and show that the explanation goes far beyond the one proposed before.