Double pendulum

The double pendulum is an example of a simple dynamical system that exhibits complex behaviour, including chaos. It consists of two point masses at the end of light rods. Each mass plus rod is a regular simple pendulum, and the two pendula are joined together and the system is free to oscillate in a plane.
The second gif illustrates sensitivity to initial conditions: the pendulum is started from two initial configurations differing by 0.001 degrees in the angle of the second mass.