SoylentNews

"exec" writes:

It has puzzled scientists for over 100 years but now they appear to have cracked it: what, exactly, is it that causes that wince-inducing sound when you pop your knuckles?

And "popping", it turns out, is exactly what it is, researchers said on Thursday after finding that the distinctive cracking sound was caused by the collapse of microscopic bubbles of joint fluid in the hand.

Using a mathematical model alongside a geometrical representation of the joint, experts from Paris' Ecole Polytechnique and Stanford University in the United States simulated the events leading up to the crack.

"The sound that is generated when one cracks his or her knuckles is due to the partial collapse of a cavitation bubble that's in the fluid in the joint," explained Abdul Barakat, a professor at the Ecole Polytechnique. "It could be multiple bubbles, but we showed that the collapse of a single bubble is sufficient to give you the signature sound you get," he told AFP by phone.

Although experts had initially linked the sound to the collapse of knuckle bubbles back in 1971, their findings were thrown into question after further studies showed there were still bubbles left in the fluid after the knuckles had been cracked.

But the mathematical model appears to resolve this apparent contradiction by showing the sound can be produced by partial collapse, the researchers said.

https://phys.org/news/2018-03-experts-knuckle-popping-puzzle.html

-- submitted from IRC

Original Submission