Further explication:

  1. In physics, chaos is a super-sensitivity to initial conditions combined with complex dynamical evolution.

  2. Many physical systems exhibit chaos, but it's NOT so obvious in everyday life.

    Why? Well, we do NOT usually build our devices and other artificial physical systems to exhibit chaos. You wouldn't want your car engine to be chaotic, now would you?

  3. Now in the image, you can see the motion (AKA dynamical evolution) is very complex.

    If the initial conditions were changed just a tiny amount, you would also see a complex dynamical evolution that was qualitatively the same, but very different in detial, than appears in the image.

    So the double pendulum exhibits chaos.

  4. In the double pendulum system of the image, friction, air drag, and any other forces (like friction inside materials) that dissipate macroscopic mechanical energy (the sum of kinetic energy and gravitational potential energy) to waste heat energy.

    If you could turn off dissipation to waste heat, the double pendulum motion would perpetual motion. This is impossible in reality in the macroscopic world since one can NEVER absolutely turn off all dissipation. One can make it very small in some cases. So the ideal limit of perpetual motion can be perceived, but not reached in the macroscopic world.

    The microscopic world? That takes a bit of a discussion will NOT give here.