Theory of Machine
The static balancing is satisfactory for low speed rotors but with increasing speeds, dynamic balancing becomes necessary. This is because, the

Effects of unbalances are directly proportional to the speed
Unbalanced couples are caused only at higher speeds
Effects of unbalances are proportional to the square of the speed
Unbalanced forces are not dangerous at higher speeds

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Theory of Machine
The relation l = (2/3).(j + 2) apply only to kinematic chains in which lower pairs are used. This may be used to kinematic chains in which higher pairs are used, but each higher pair may be taken as equivalent to

One lower pair and two additional links
Two lower pairs and two additional links
Two lower pairs and one additional link
Any one of these

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