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

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

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Theory of Machine
Kinematic pairs are those which have

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

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