This simulation allows you to manipulate two simple waves (represented by sine-wave patterns) that pass each other moving in different directions.  You can control the amplitude (strength—represented by the vertical “width” of the wave) and frequency (the number of wave crests, or troughs, that are contained within a given distance) of each wave. 

To set the waves into motion, click the START button.  One wave will move to the right, the other to the left.  The combined wave formed by the interference of the two waves will be shown in the window below.

Use the "+" and"-" buttons to increase and decrease the amplitude and frequency of the waves.