Theory of Machine
A system of masses rotating in different parallel planes is in dynamic balance if the

Resultant force is numerically equal to the resultant couple, but neither of them need necessarily be zero
Resultant couple is equal to zero
Resultant force is equal to zero
Resultant force and resultant couple are both equal to zero

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Theory of Machine
Crowning on pulleys helps

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

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