Observatoire de Paris
<-   What is a resonance?   ->

An example of resonance is the action made to launch a swing:

To move a swing, we must give it an impulse at each passage, or maybe every two or three passages. In order to maintain the motion, it is important to give the impulses with the swing in the same position : the impulses must be in resonance with the swing.

The impulse period (the time between two impulses) must be equal to the period of the swing (swinging duration), or equal to twice (or triple) the period of the swing.


Around a star, the bodies do not move at the same velocity and they gravitationally interact.

  • If two planets are not in resonance, their successive perturbations get muddled up and yield small displacements of the planets.
  • If the planets are in resonance, their successive perturbations are added to each other and become important.
  • However, a resonant configuration between two bodies can also correspond to an equilibrium position where the two objects "get in each other's way" the least.