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17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Video: How the 'Chain Fountain' Defies Gravity
14 January 2014 7:15 pm
Things fall down: Thanks to gravity, it’s one of the defining features of life—and physics—on Earth. So how to explain the chain fountain above, in which a 50-meter string of metal balls briefly flows up before plunging to the ground? Steve Mould, the BBC science presenter whose YouTube video recently drew attention to the weird phenomenon, has one explanation: The chain, which has to travel over the lip of the beaker before it can make its downward turn, is moving so quickly that it can’t instantly change direction. Instead, it continues traveling up for a bit, “chang[ing] direction slowly, over the course of a loop.” But when two Cambridge physicists tried to write an equation describing the chain fountain’s behavior, they discovered that Mould’s intuitive explanation was wrong. Math tells us that chains have no problem instantly turning even the sharpest corners, the physicists say, so they had to look elsewhere to explain the chain fountain’s surprising vertical leap. By working through the calculus, they discovered that the creation of the flowing loop depends not on inertia, momentum, or gravity, but rather on the upward force coming from the bunched-up end of the chain still in the beaker. In other words, as gravity pulls down, the chain itself pushes up—and it’s these opposing forces that create the fountain effect. Still, the physicists’ model—described online today in the Proceedings of the Royal Society A—doesn’t explain what causes the twists and waves at the top of the chain, leaving room for Mould’s explanation that they are the result of the chain hitting the lip of the beaker during its journey.