When a long bead chain pours from a tall container, it does not pass straight over the rim but climbs into the air first. can pull downward, not push upward. So what lifts it?
A push from the pile below. An arch forms above the container before the chain drops. The weight of the falling part supplies the pull, and models and experiments show the matters too: the height depends on how the links lie and how they rise. A link that rotates on its way out can press on and receive an upward push from it.
When a long bead chain pours from a tall container it does not pass straight over the rim, but forms an arch that rises above the container before dropping.
The engine is clear: the weight of the falling part pulls the chain and speeds the withdrawal. Except that a downward pull cannot lift a link above the rim, so a further force is required.
The explanation concerns what happens in the pile. A stiff link is not simply drawn out: it rotates, its end presses on the pile beneath it, and the pile presses back upward.
Models and experiments comparing different pile arrangements were built precisely to separate the two contributions. There is no agreement that every chain receives the same force from the pile, and the height of the arch depends on the stiffness of the links, on friction and on the initial arrangement.
wat. A chain fountain comes from the pull of the falling part, and in some arrangements also from a push the links receive from the pile in the container.
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An everyday movement of a chain reveals how a small local structure can change the flow of a long, flexible system.
How do we know?
The researchers compared experiments on chains and on different pile arrangements with a mechanical model and with simulations separating the pull of the chain from a force from the container.
What is still unknown
Physicists do not agree that every chain receives exactly the same force from the pile. The height of the arch depends on the stiffness of the links, on friction and on the initial arrangement.
Learn something?
Where to next
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