There are four pendulums hanging in a line connected with a lax matter.
Each oscillator has its own natural frequency. When you push the “start” button,
the first pendulum on the left will start its oscillation. After a while,
only the third pendulum which has an equal natural frequency to the left one will begin its oscillation,
while the second and the fourth pendulum will remain stable. The “reset” button is for initialization.
Please wait until they get stable before pushing the “start” button.