A mass is suspended by two springs, and driven with an oscillator with a user-controlled frequency. Like pushing a child on a swing, you must push at the appropriate times (and not push at inappropriate times). When the natural frequency is achieved, the mass will swing with a large oscillation even though the driver moves a small distance. Energy must be added to keep the object oscillating. In some cases resonance is desired (such as musical instruments) while in other cases it is not desirable to have an object resonate (such as bridges). The driver and the mass are marked with orange ping pong balls to make them easy to see.