Question

why does our finger pops???

Answer 1

Great question!

I had the pleasure of stumbling across an article describing this phenomena.

Basically, it's an application of Henry's Law: "the solubility of a gas in a liquid is directly proportional to the pressure of the gas."

Within the synovial fluid surrounding our joints is dissolved gas. When you crack your knuckles, you stretch the joint such that it relieves pressure on the fluid. Relieving the pressure allows the gas to momentarily come out of solution as bubbles...which, when popped, give that characteristic sound. Also worth noting is that this doesn't lead to arthritis....there was (a perhaps anecdotal) experiment done by a man who cracked one of his hands for many many years, and left the other untouched.

At the end of it, neither hand was in better shape than the other.

Anyways, I'll search up the source material for this so you can do some more reading. My memory's a bit shaky so I probably left out some details.

Answer 2

http://io9.com/5877454/henrys-law-explains-why-your-knuckles-crack

Here you go - very interesting read.