Kinetic Chaos Toy

Bought from the Exploratorium in San Francisco, this toy demonstrates chaotic motion.

Wikipedia has the following definition of chaotic motion -

' Chaos theory studies the behavior of dynamical systems that are highly sensitive to initial conditions, an effect which is popularly referred to as the butterfly effect. Small differences in initial conditions ... yield widely diverging outcomes for chaotic systems, rendering long-term prediction impossible in general.'

Put another way, even if you always start the pendulum swinging in the same way, you cannot predict where it will be a minute later...