For years, scientists have been discussing why cracking your finger joints is loud. A new mathematical explanation suggests that the sound is the result of the partial collapse of small gas bubbles in the fluid of the joints.
Most explanations for the crunching sound that the joints produce include bubbles formed at low pressures caused by the movement of the fingers dividing the joint. While some studies point to bubble implants as a source of sound, a 2015 study showed that bubbles do not fully implode. Instead, they are held in the joints for up to 20 minutes after the shooting, suggesting that the collapse of the bubbles is not what creates the noise, but their formation.
But how bubble making can make sounds that are heard so loud was not clear. So once again two scientists from Stanford University and from France’s Polytechnic University tried to solve the mystery.
The sound may come from partially decaying bubbles, the two researchers said on March 29 in Scientific Reports. The mathematical simulation of a partial collapse of the teddy bear explains both the dominant frequency of the sound and its volume. This finding will also explain why the bubbles stick around the liquid.