ISTOCK, STARASMathematics may now explain why we hear a “pop” when our knuckles crack. The sound comes from the partial collapse of little gas bubbles in joint fluid, researchers report today (March 29) in Scientific Reports.
“The cavity in between the two knuckles is filled with a fluid that is called the synovial fluid, and when you suddenly change the pressure in that fluid as a result of increasing the spacing between the knuckles, some of the gases in that fluid can nucleate into a bubble,” study coauthor Abdul Barakat of École Polytechnique in France tells The Guardian.
Previous research had suggested that the collapse of the bubbles can generate the cracking noise, but others argued that pressure changes produce the sound, Barakat tells The Guardian. Images of knuckle cracking taken in an MRI scanner and published in 2015 suggested the sound was the result of a quick separation of the joint that occurred while bubbles formed, not collapsed. In fact, ...
