Q: Why do our knuckles crack?
A: The bones in the finger are separated by small pads of
cartilage, and in between these pads and the bones are small
pockets of a thick liquid.
Q: Why do our knuckles crack?
A: The bones in the finger are separated by small pads of cartilage, and in between these pads and the bones are small pockets of a thick liquid. When your fingers are bent, the bones pull away slightly from the pads of cartilage and a vacuum forms between the bone, pad and the surface of the liquid. As the bending continues and the bones are pulled farther apart, the surface tension of the liquid eventually gives way and the vacuum bubble bursts, making the cracking sound you hear.
The process is very similar to what happens when you pull a rubber suction cup off a smooth surface, bursting the vacuum seal of the suction cup to the surface and emitting a noise.
