If vibrating force is applied to the spring and weight as shown in the figure, vibration rapidly becomes large when the frequency of the applied force reaches a certain frequency level. This phenomenon is known as “resonance.”
1.Mechanism of the resonance
If vibrating force is applied to the spring and weight by a crank fitted to a motor, the weight begins to move up and down.
(1)The amplitude of the sinker weight movement is relatively small when the frequency (motor revolution) is low.
(2)The amplitude gradually increases as the frequency is increased.
(3)When increasing to a higher frequency, the amplitude reaches the maximum at a specific frequency. This is the state of resonance and the frequency at that state is called the resonance point.
(4)If the frequency is increased further beyond the resonance point, the amplitude starts to decrease gradually.
2.Resonance, noise and vibration of a vehicle
Resonance increases vehicle noise and vibration. An unbalanced tire causes “body vibration” at a certain speed range. An unbalanced propeller shaft causes “booming noise” at a certain speed range. These symptoms are all caused by resonance. Therefore, when handling vehicle noise and vibration, make sure to think about the resonance.
3.Natural frequency