Sound waves are longitudinal waves. Interference and Superposition Unlike solid objects, waves can occupy the same space at the same time. Waves obey the Principle of Superposition . That is, when two or more waves occupy the same space the net displacement of the medium at any given point is simply the sum of the displacements due to the individual waves. This superposition of waves is also referred to as interference .
Waves displace the media through which they travel in both positive and negative directions.
When two interfering waves happen to displace the medium in the same direction at the same position at the same time, the principle of superposition tells us that the medium is displaced more at this position than it would be by the individual waves. This is known as constructive interference , and the waves are said to be in phase with each other at that position and time. Destructive interference takes place at positions and times at which interfering waves are out of phase with each other. That is, they have displacements of opposite sign and tend to cancel each other out. Beats from two tuning forks.