Resonance and damping
Resonance and damping are essential things to consider when designing most large structures and machines and also in many small ones. Resonance occurs when the vibration or oscillation of one thing is easily passed on to another. Something that is vibrating like a motor or a guitar string, will force anything attached to it, like the body of a car or the guitar to vibrate as well. We get resonance when the engine and the car body or the string and the guitar body have the same natural frequency.
The natural frequency is the frequency that an object or a structure naturally vibrates at. We also get resonance when there is a simple multiple between the natural frequency of the two things, that is when one is two, three or four times the other.
Sometimes resonance is desirable, for example within musical instruments. But often it can be very damaging or even catastrophic, for example in excessive vibration in a vehicle or the wild shaking of a tall building in an earthquake.
In cases when vibration is unwanted we use damping. Damping absorbs the energy of vibration.
The first notes sheet gives more detail and examples of what resonance is. The second explains some of the practical ways in which damping can be achieved. The third sheet of notes illustrates the relationship between frequency and the size of the vibrations (the amplitude) and the effect of damping.