Q. Why do the knuckles make a cracking sound?
Ans. The joints in our bodies are surrounded by a thick fluid. When we stretch or bend our fingers to pop the knuckles, we gradually increase the space or volume between the bones. As the joint is surrounded by a certain amount of fluid to fill this increased volume, the pressure in this region decreases which causes the gases dissolved in this fluid to come out forming a bubble or cavity there. As the joint is stretched more, the pressure falls so low that the gas bubble collapses producing a cracking sound.
