When an undulatory movement passes from one medium of propagation to another, its speed and direction are usually modified.  This is the phenomenon called refraction. That is why, for example, fish in an aquarium seem bigger when they are inside it than when we take them out.

Although all undulatory movements can be subjected to refraction, we will analyse as an example the case of a wavefront in a pond when the water passes from a shallow part of the pond to a deeper part and vice versa.

In our example you can vary the direction of the front by dragging the end of the direction arrow with your mouse. You can also alter the relation between the velocity in the first medium and the second one. A relative velocity of 1 means that the speed is identical in the two media; if the relative velocity is 2, the speed in the second medium will be double that in the first ...etc.

You can also vary the general speed of the simulation, to adapt it to the characteristics of your computer.