Double pendulum 
On this pendulum, it is possible to watch a very realistic simulation of movement, with a real-time graphic indication of the energies involved (kinetic and potential for each mass and also the sum of the four) and of the trajectory in the configuration space, which, in this case it is a torus.
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In this applet, as in any of the others of this type, it is possible for the user to duplicate any of the frames and enlarge it separately,
to continue to follow the evolution in more detail in real time. It is very interesting to try out different values of the masses and lengths of the rods, to try to obtain the known effects of chaotic type, so characteristic of this type of pendulums. Just as it is possible to observe how the existence of friction has a significant impact on the creation and persistence of such effects.
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