Author: Emily Conover / Source: Science News for Students
“Pop!” goes the knuckle. Why? Scientists disagree over what’s behind the cracking. Now, a new explanation comes from math.
It suggests the sound results from the partial collapse of tiny gas bubbles in the joints’ fluid.A role for bubbles is not new. Most explanations for knuckle cracking involve them. Those bubbles form under the low pressures produced by finger movements that separate the joint. Some studies have proposed that a bubble’s implosion creates the crack. But a paper in 2015 showed that the bubbles don’t fully implode. Instead, they persist in the joints for as much as 20 minutes after cracking. And that has suggested the bubble’s collapse doesn’t make the noise. So maybe its formation does.
But it wasn’t clear how a bubble’s debut could make sounds loud enough to be heard across…
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