Waves in a pendulum system
Using the lever, which is connected to the metal comb, smoothly move it across the balls 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. Observe their movements.
How does it work
What we have here is a system of sixteen independent pendulum weights the lengths of which are specifically selected. From the original balanced position, the identical swing of the balls (in this case identical phase and amplitude) at the same time, causes movement in the released pendulum weights which reproduce a sequence of traveling and standing waves. Finally, after performing the whole cycle, the balls come back to their initial state. In this cycle we can observe a system of many independent objects that seemingly interfere with each other.
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 one with a longer cord.