Theory of Machine
The rotating shafts tend to vibrate violently at whirling speeds because

Resonance is caused due to the heavy mass of the rotor
Bearing centre line coincides with the axis
The shafts are rotating at very high speeds
The system is unbalanced

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Theory of Machine
The maximum fluctuation of energy is the

Sum of the maximum and minimum energies
Ratio of the mean resisting torque to the work-done per cycle
Variations of energy above and below the mean resisting torque line
Difference between the maximum and minimum energies

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