LQ placeholderUnraveling the  chain fountain

Unraveling the chain fountain

John Biggins talks about how he solved the mystery of the chain fountain, in which a chain spontaneously leaps up as it flows out of a jar.

Background BBC science presenter Steve Mould bought a 50m long chain as a prop and stored it in a jar. To his surprise, he found that if he dangled the end of the chain over the rim of the jar, the entire chain would spontaneously flow down to a pile on the floor. More surprisingly, it leapt up in a sustained arc above the jar. Mould made a video of his chain which went viral on YouTube. But despite millions of views and much speculation in illustrious physics departments around the world, no one could explain why the chain rises above the jar.

Talk In this talk, John Biggins explains how he and Mark Warner solved the mystery of the leaping chain. To do so, he first revisits and repairs textbook notions about how chains are picked up from surfaces. He shows that a chain fountain spontaneously forms in the shape of an upside-down catenary, that is, the inversion of the shape of a hanging chain. This is the optimal shape for an arch of perfect compression and has been used by architects and engineers from Hooke and Wren to Gaudi. But the chain fountain is a new structure: an arch of perfect tension stabilized by motion.