The chain fountainphenomenon, also known as the self-siphoning beads or the Mould effect, is a counterintuitivephysical phenomenon observed with a chain of beads placed inside a jar, when one end of the chain is yanked from the jar and is allowed to fall to the floor beneath. This establishes a self-sustaining flow of the chain of beads which rises up from the jar into an arch ascending into the air over and above the edge of the jar with a noticeable gap, and down to the floor or ground beneath it, as if being sucked out of the jar by an invisible siphon.
Details
The effect is most pronounced when using a long ball chain with rigid links. The higher the jar is placed above the ground, the higher the chain will rise above the jar during the "siphoning" phase. As demonstrated in an experiment, when the jar is placed 30 meters above the ground and the chain is sufficiently long, the arch of the chain fountain can reach a height of about above the jar. The phenomenon was first brought to widespread public attention in a video made by science presenterSteve Mould. Mould's YouTube video, in which he demonstrated the phenomenon of self-siphoning beads and proposed an explanation, brought the problem to the attention of academics John Biggins and Mark Warner of Cambridge University, who published their findings about what has now been called the "chain fountain" in Proceedings of the Royal Society A.
Explanation
A variety of explanations have been proposed as to how the phenomenon can best be explained in terms of kinematic physics concepts such as energy and momentum. The scientific consensus has shown that the chain fountain effect is driven by upward forces which originate inside the jar. The origin of the upward force is related to the stiffness of the chain links, and the bending restrictions of each chain joint. When a link of chain is pulled upward from the jar, it rotates like a stiff rod being picked up from one end. This rotation produces a downward force on the opposite end of the link, which in turn generates an upward reactive force. It is this upward reactive force that has been shown to drive the chain fountain phenomenon. Furthermore, because the beads of the chain can drag laterally within the jar across other stationary links, the moving beads of the chain can bounce or jump vertically when they strike the immobile links. This effect contributes to the effect, but is not the primary driver.
