Superposition

Here are two waves that have amplitudes of 1.0 travelling in opposite directions:

Superposition is the process by which two waves combine into a single wave form when they overlap.

If we add these waves together the resultant depends on where the peaks of the waves are compared to each other. Here are three examples of what the resultant could be: a wave with an amplitude of 1.5, no resultant wave at all and a wave with an amplitude of 2.0