Demonstration of Forced Harmonic Motion

Set the spring constant to 5. Click on the Reset button. Observe that the tidal frequency is only 1.25 i.e. the standing-wave cannot move as fast as the tidal surge. Note that the lag value is only just less than 1 i.e. it is low 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 opposite times, confirming that the tides are out-of-phase with the Moon.

Click the Reset button to stop the demonstration.