🔍 Key Concepts

• Critical speed / resonant speed of rotating shafts • Relationship between natural frequency and forced vibration • How vibration amplitude changes as speed approaches and passes resonance

💭 Think About

• Sketch (even roughly in your mind) a graph of vibration amplitude (vertical axis) versus RPM (horizontal axis). Where is the highest peak likely to occur? • Think about what happens physically when the running speed of the shaft matches its natural frequency. How does the system respond at that exact point compared to slightly below or above it? • Compare the meaning of first order (fundamental) critical speed and second order critical speed. Which one is normally reached first as you increase RPM from zero, and how does that affect the first big resonance peak?

✅ Before You Answer

• Identify which option corresponds to the exact resonant (natural) frequency of the shaft as speed increases from 0 RPM. • Make sure you know that "order" refers to multiples of the running speed (1×, 2×, etc.) in relation to natural frequencies. • Verify which condition (exact resonance, below resonance, above resonance, or between two resonances) typically produces maximum vibration amplitude in basic vibration theory.