Waves in a pendulum system
Using a lever connected to a metal comb move the balls evenly from the balanced position. The cords must not be tangled. Then, quickly move the metal comb back to its lower position, thus releasing the balls. Look at their movements for some time.
How it works
What you have here is a system of sixteen independent pendulum weights whose lengths have been specifically selected. From the original balanced position, an identical swing of the balls (in this case identical phase and amplitude) at the same time results in movement in the released pendulum weights which reproduce a sequence of moving and standing waves. Finally, after performing the whole cycle, the balls come back to their initial state. In this cycle, you can observe a system of many independent objects that seemingly interfere with one another.
The oscillation period of a simple pendulum depends only on the length of the cord. The shorter the cord is, the shorter the oscillation period. That is why a pendulum with a shorter cord overtakes the one with a longer cord.