![]() ![]() And that gives rise to this extra kick from the pot which drives the fountain." “The far end of the rod under those two motions actually goes down, and therefore pushes down. The end that is not picked up pushes downwards, and the pot provides a reaction force, he says. It makes the rod lift, but it also causes it to rotate. Picking up a rod from the pot with an upward force on one of its ends causes two things to happen, says Biggins. The size of a rod corresponds to the number of beads it takes to turn a section of chain back on itself by 180 degrees (it takes six). In their model, each rod is made up of three beads and two connectors. Rather than a flexible string of isolated beads, the chain is more like a series of short, rigid 'rods', say the authors, who publish their results today in Proceedings of the Royal Society A. This challenges not only the explanation given by Mould, but the conventional mathematics of chains. ![]() The only way to account for the rise is for the chain to receive a kick from the pot from which it is being pulled, say Biggins and his Cambridge colleague Mark Warner. “If that were true, it would mean the chain would pile up in the top region, which we don’t see,” he adds. If inertia were causing the flowing fountain, the chain would be stationary at the top of the curve, says Biggins, in the same way that a ball tossed into the air is stationary at its highest point. Mould’s explanation was clever, but wrong, says physicist John Biggins of the University of Cambridge, UK. This, in turn, makes them leap before gravity can slowly reverse their momentum. And it is far from intuitive.īritish science presenter Steve Mould, who made the experiment famous with a video that went viral on the Internet, explained the phenomenon as simply one of inertia: the falling chain has downward momentum, causing an upward momentum in beads leaving the pot. Now physicists think they have an explanation. Leaping up out of a jar in an arc before falling to the floor, the fountain-like motion of a chain of beads has puzzled millions around the world with its apparently gravity-defying behavior.
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