How can popped knuckles be so exceptionally loud?
Mark Thompson
Tewkesbury, Gloucestershire, UK
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The loud noise produced when you crack your knuckles is due to the rapid formation of a gas-filled cavity within the synovial fluid that lubricates your joints.
When you pull or stretch your fingers, it lowers the pressure inside the joint, causing dissolved gases like carbon dioxide to form bubbles. So cracking knuckles, with the sudden formation of these bubbles, creates a popping or cracking sound, similar to opening a bottle of pop, or soda.
However, excessive or forceful knuckle cracking may occasionally lead to minor swelling, ligament laxity or discomfort in surrounding tissues. If you keep doing this, it can lead to complications.
Pat French
Telford, Shropshire, UK
They aren’t exceptionally loud.
The pop is caused by a bubble bursting in the finger joint as pressure is reduced when the joint is stretched. The sound of running water, from a domestic tap to a huge waterfall, is all brought about by bubbles. The pop also has a high frequency, meaning it is high pitched, which causes it to sound intense to the human ear.
The lesser water boatman, a 1.5-centimetre aquatic bug, can generate 99 decibels of sound. A shoal of tiny snapping shrimps can make enough noise to mask the sound of a ship. An individual shrimp can stun its prey with sound. The pop of a knuckle sounds loud, but it isn’t exceptional.
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