Theory of Machine
Kinematic pairs are those which have

Two elements that permit relative motion
Point or line contact between the two elements when in motion
Surface contact between the two elements when in motion
Elements of pairs not held together mechanically

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Theory of Machine
Crowning on pulleys helps

For automatic adjustment of belt position so that belt runs centrally
In decreasing the slip of the belt
Increase belt and pulley life
In increasing velocity ratio

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