In order to avoid resonance, one should operate a machine...

To avoid resonance in a machine, operating it at any speed that is not within 20% of the natural frequency is the most effective approach. Resonance occurs when the frequency of external forces applied to an object coincides with the natural frequency of that object, leading to amplified vibrations and potential failure. By maintaining operational speeds outside this critical range, you significantly reduce the risk of exciting the system's natural frequency, thus avoiding resonance-related issues.

Operating below or above the natural frequency may minimize some risks, but these strategies do not provide the same level of assurance as maintaining a safe distance from the natural frequency. Additionally, operating at or within the natural frequency increases the likelihood of resonance. Thus, specifying a buffer zone of 20% creates a safeguard that is practical and broadly effective in vibration analysis for preventing resonance.