1-8 The principle of superposition

Unlike particles, two or more waves can be present at the same position and at the same time.  When a wave meets another wave in the same medium, it does not collide with it, instead, it moves through it as if the other wave were not present in the medium. The motion of each wave is not affected by the other.  The displacement of the medium will be the algebraic sum of the individual displacement of each wave.  This is why we can hear more than one person speaking at same time and we can transmit thousands of calls on the same telephone line.