Cracking knuckles has something to do with air bubbles, but would it work in the same way if there is no gravity? If not, how would it be different? Would there still be a popping sound and/or sensation?
closed as off-topic by Frostfyre, bilbo_pingouin, James♦ Mar 15 at 15:14
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The cracking mechanism and the resulting sound is caused by carbon dioxide cavitation bubbles suddenly partially collapsing inside the joints.
The collapsing of the bubbles is due to pressure differential between the inside and the outside of the bubble.
When we consider the pressure in a liquid, we can distinguish two components:
- pressure due to the proper weight of the fluid above the measuring point
- pressure exerted from outside the fluid (i.e. atmosphere)
In microgravity 1 would be 0, but 2 will still be present (else any liquid in microgravity would immediatly evaporate).
Therefore, if the person cracking knuckles is in microgravity but still under some atmospheric pressure, the pressure differential will be of the same order of magnitude. Therefore it is reasonable to expect the same phenomena to happen.