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  • The ordinary pendulum that has a weight hanging from a thread is a classic in physics but it is a bit boring. The forces are easy to analyze and even though they lead to an equation L×a´´ = - g×sina that can´t be solved by elementary functions the motion is still so predictable it could put you to sleep. A double pendulum is more than twice as interesting. It moves in complex and mysterious ways and it will take you into a world of chaotic motion and non-linear phenomena.

    The best way to appreciate this is to build your own pendulum. Possible materials are wood or plexiglass. The ball bearings, axes and the counterweight on the inner arm are attached with superglue. To strengthen the suspension of the arms it could be wise to have extra blocks to lengthen the holes for the axes. The outer arm has an adjustable weight. Different positions will result in different behaviour. Below are links to a video clip and a simulation of the pendulum.

    It would be nice if one could monitor the pendulum movements and compare them to the simulation. Inside a non-optical mouse are two devices for measuring rotary motions. If they were removed and placed at the pedulum axes then the (x,y) position of the mouse would be replaced by the angular positions of the arms. Nice, but I doubt it will work.

  • Video clip Simulation