Why do we hear a sound when we crack our knuckles?
Added by Luz V.
Step 1
This creates a negative pressure in the joint, which causes gases, such as nitrogen and carbon dioxide, to be released from the synovial fluid that lubricates the joint. Show more…
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When you "crack" a knuckle, you cause the knuckle cavity to widen rapidly. This, in turn, allows the synovial fluid to expand into a larger volume. If this expansion is sufficiently rapid, it causes a gas bubble to form in the fluid in a process known as cavitation. This is the mechanism responsible for the cracking sound. (Cavitation can also cause pits in rapidly rotating ship's propellers.) If a "crack" produces a sound with an intensity level of 58 at your ear, which is 20 cm from the knuckle, how far from your knuckle can the "crack" be heard? Assume the sound propagates uniformly in all directions, with no reflections or absorption.
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