When two waves overlap in the same medium at the same time, it is referred to as interference. It is easiest to understand the interference process by observing interfering wave pulses. Use the simulation below to explore the interference of wave pulses. Experiment with waves of various width and various heights, including negative height pulses interfering with positive height pulses.
Notice that the wave pulses do not bounce off of each other, instead, they pass right through each other only showing any effect when they are overlapping. When the two pulses overlap, the resulting wave is the algebraic sum of the two pulses. This is known as the principle of superposition. The principle of superposition can be stated as: the displacement of the medium from the equilibrium position when multiple waves interfere is equal to the algebraic sum of the displacements of the individual waves.
Inteference of Multiple Pulses
When multiple pulses interfere, the principle of superposition can still be applied. The color dotted lines in the animation show the original shape of the pulses, the solid black line shows the actual string position, which is the sum of the original pulses.