Demonstration of Forced Harmonic Motion

Set the spring constant to 20. Click on the Reset button. Observe that the tidal frequency is 2.5 i.e. the standing-wave can move faster than the tidal surge. Note that the lag value is only a little more than 0 i.e. it is high tide at Full Moon. Click on the Start button. After a short while, the red and blue traces move up and down at almost exactly the same time, confirming that the tides are in-phase with the Moon.

Click the Reset button to stop the demonstration.