Driven harmonic oscillator

Simple harmonic oscillator

A simple harmonic oscillator is a system that vibrates with a constant amplitude and frequenty. Therefore there are no external forces, such as friction present in this system.

Damped harmonic oscillator

In real life there are always friction forces acting on the system. Because of these forces, the amplitude of the vibration wil decrease. An example is a child on a swing. If the child doesn't do any affort to keep the swing going, the "oscillation" is damped, and wil finally stop.

Driven harmonic oscillator

To get a system that is a harmonic oscillator some kind of force has to be put in. In the example of the child on the swing, that force will be the childs legs going back and forwards. The swing has certain frequency in which it goes back and forwards. This is called the resonating frequency. Every material or mechanism has its own resonating frequency. In order to get a driven harmonic oscillator the driving force must have the same frequency as the resonating frequency of the mechanism. This means that the child pushes its legs forwards every time at the same spot. (the same fase of the oscillation) The driving force puts exactly the same amount of energy in the system then all the friction forces together take away, so the total amount of energy will always stay the same.