Question

Critical speed of shaft corresponds to:

• A. Zero angular velocity
• B. Natural frequency of lateral vibration
• C. Highest rpm
• D. No damping

Hint:

Critical speed = Natural frequency of lateral vibration of the shaft. It leads to resonance and high vibrations if not controlled.

Answer 1

The Correct Option is B

Critical speed of a rotating shaft is the speed at which the shaft's rotational frequency matches its natural frequency of lateral (transverse) vibration.
When this happens, resonance occurs, leading to a significant increase in vibration amplitude, which can cause damage or failure.
At this critical speed:
- The system experiences dynamic instability due to resonance.
- The lateral deflection becomes large even if the imbalance is small.
Incorrect options:
- (1) Zero angular velocity means the shaft is not rotating — not relevant to critical speed.
- (3) Highest RPM might be beyond critical speed but doesn’t define it.
- (4) Damping affects the amplitude at resonance but isn’t what defines critical speed.