Tap the water to make a ripple. It spreads out in a growing circle, just like a stone dropped in a pond.
Turn on the 2nd source and two sets of ripples will cross each other.
Where two crests meet, the wave gets extra big and bright — that is constructive interference.
Where a crest meets a dip, they cancel out and the water goes flat and dark.
The Frequency slider sets how close together the ripples are. The Amplitude slider sets how tall and strong they are.
Turn on the Wall — it has a small gap. Waves squeeze through the slit and bend out in a fan on the far side. That bending is called diffraction.
The readout shows the wave speed — how fast each crest races across the tank.