longitudinal wave

Wave in which the displacement of the medium's particles is in line with or parallel to the direction of travel of the wave motion.

Various methods are used to reproduce waves, such as a ripple tank or a loosely-coiled spring, in order to understand their properties. If a loosely-coiled spring is given a slight ‘pushing’ force, the wave travels in the same direction as the movement of the coils. The waves consist of a series of compressions (where the coils of the spring are pressed together) and rarefactions (where the coils of the spring are more widely spaced). This is known as a longitudinal wave. The moving coils represent waves travelling along the spring. The spring remains as it was after the wave has travelled along the spring; waves carry energy from one place to another but they do not transfer matter. Sound waves are an example of longitudinal waves.