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. But the mathematical model appears to resolve this apparent contradiction by showing the sound can be produced by partial collapse, the researchers said. Earlier studies using ultrasound had reached a similar conclusion linking the sound to changes in pressure in the joint fluid. A 2015 paper suggesting it was actually the formation of a bubble rather than its collapse which caused the distinctive crack. “After publishing this paper, my daughter tried it out and now she cracks her knuckles,” said Barakat, himself a knuckle-cracker.

Source: Hindustan Times March 29, 2018 14:48 UTC