Wave Superposition
The green and blue waves add up to the red wave. So if the blue and green waves were simultaneously present, all you would see is the red wave.
You can adjust the amplitude, wavelength and wave speed. The wave speed of both waves is the same, since that would be determined by the medium, but the waves travel in opposite directions.
You can create standing waves by having the same amplitude and wavelength. Other combinations create other wave forms.
It can be useful to hide the blue and green waves by clicking on their dots on the far left.
Nodes
When each of the wavelengths are set to 3 (which should happen when you click the 'Reset' button), how many nodes are there between -5 and 5 on the horizontal axis for the red standing wave?
Anti-nodes
And for the same conditions (each wavelength=3), how many anti-nodes are there between -5 and 5 on the horizontal axis for the red standing wave?
Velocity
What does changing the sign of the velocity do to the red, green, and blue waves? (Change it from 0.5 to -0.5 and see what is different.)