Question 1

What is natural frequency?

Accepted Answer

Natural frequency is the frequency at which a system oscillates freely after being displaced from its equilibrium position and released. For a mass-spring system, it depends only on the mass and the spring stiffness. Every mechanical structure has one or more natural frequencies, and they are fundamental properties used in vibration analysis, structural design, and machine diagnostics.

Question 2

Why is natural frequency important for machines?

Accepted Answer

Knowing the natural frequency of a machine or its components is critical because if the operating speed (excitation frequency) coincides with the natural frequency, resonance occurs. Resonance causes dramatically amplified vibrations that can lead to excessive wear, fatigue failure, bearing damage, and even catastrophic structural collapse. Engineers design machines so that operating speeds are well separated from natural frequencies.

Question 3

How to measure spring stiffness?

Accepted Answer

Spring stiffness (rate) can be measured by applying a known force to the spring and measuring the resulting deflection. Stiffness k = Force / Deflection. For example, if a 100 N force compresses a spring by 2 mm, the stiffness is 100/2 = 50 N/mm. You can also use a compression testing machine for accurate results, or consult the manufacturer's datasheet for the spring rate specification.

Question 4

What if the operating speed equals the natural frequency?

Accepted Answer

When the operating speed (excitation frequency) matches the natural frequency of the system, resonance occurs. At resonance, vibration amplitudes increase dramatically — theoretically to infinity in an undamped system, and to very high levels in real (lightly damped) systems. This can cause rapid fatigue failure, excessive noise, bearing damage, and structural collapse. This is why vibration analysis always checks for proximity to resonance.

Question 5

How to avoid resonance in mechanical systems?

Accepted Answer

There are several strategies to avoid resonance: (1) Change the operating speed so it is at least 20–30% away from any natural frequency. (2) Modify the stiffness by adding braces, stiffeners, or changing spring rates. (3) Change the mass of the vibrating component. (4) Add damping using vibration dampers, rubber isolators, or tuned mass dampers. (5) Use variable-speed drives to avoid dwelling at critical speeds during startup or shutdown.

Calculadora de Frequência Natural

Resultados

Frequência Natural de um Sistema Massa-Mola

Frequência Angular

Período e Deflexão Estática

Exemplo Prático