An oscillator is a physical system characterized by periodic motion, such as a pendulum, tuning fork, or vibrating diatomic molecule. Mathematically speaking, the essential feature of an oscillator is that for some coordinate x of the system, a force whose magnitude depends on x will push x away from extreme values and back toward some central value x 0, causing x to oscillate between extremes. For example, x may represent the displacement of a pendulum from its resting position x =0. As the absolute value of x increases, so does the restoring force acting on the pendulums weight that pushes it back towards its resting position.