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

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Theory of Machine
When a mass of a critically damped single degree of freedom system is deflected from its equilibrium position and released, then it will

Oscillate with increasing time period
Return to equilibrium position without oscillation
Oscillate with decreasing amplitude
Oscillate with constant amplitude

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