What is the function of the ball & socket joint?
The function of this kind of joint is to connect two bones, but to do so in such a way that the bones (or at least the bone that is the "ball") will be able to move in any direction whatsoever.
To me, the best example of this sort of a joint is the human shoulder joint. Think about how your arm can move. You can move it in any direction and at any angle. This is because it is the "ball" in this ball and socket joint.
By contrast, your knee cannot do this since it is a different kind of joint.
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