What makes your knuckles pop?

When you crack your knuckles you hear a CRACK, your joints produce that sound when the bubbles burst in the fluid surrounding the joint. Joints are the meeting place between two seperate bones,held together and in place by connective tissues and ligaments. All of the joints in our bodies are surrounded by synovial fluid, a thick, clear liquid. When you stretch or bend your finger to pop the knuckle, you're causing the bones of the joint to pull apart. As they do, the connective tissue capsule that surrounds the joint is stretched. By stretching this capsule, you increase its volume. And as we know from chemistry class, with an increase in volume comes a decrease in pressure. So as the pressure of the synovial fluid drops, gases dissolved in the fluid become less soluble, forming bubbles through a process called cavitation. When the joint is stretched far enough, the pressure in the capsule drops so low that these bubbles burst, producing the pop that we associate with knuckle cracking. When you crack your knuckles you may relase pressure, that will take 20-30 min to go back in order to start cracking again.