Waves (both transverse and longitudinal) are typically represented as a graph where:
- The x-axis represents the position of the oscillation along the wave's direction of motion (or along the length of the wave) at a specific point in time (the shape of the graph varies with time).
- The y-axis represents the oscillating physical quantity (e.g. oscillatory displacement of particles, magnetic field, electric field).
A mechanical wave can be represented as a graph of displacement (i.e. oscillatory displacement) vs position.
It is important not to confuse the terms "position" and "displacement" in the context of waves.
- "Displacement" refers to the oscillatory movement of a particle from its equilibrium position and not the displacement of an entire wave from its point of origin.
- "Position" refers to the location of a particle along the direction of motion of a wave (i.e. along a particular axis) and not its position in the oscillatory motion.
Longitudinal waves are sometimes represented as a series of lines corresponding to the positions of the particles of the wave along a single axis (typically the x-axis).
This representation is a more accurate description of a longitudinal wave (as both oscillatory and overall wave movement occurs in a single direction).
A simple longitudinal wave is a series of compressions (contractions) and rarefactions (expansions) of a physical medium.
This series corresponds to the crests (maximum points) and troughs (minimum points) of a sinusoidal transverse wave.
The lines which are close together represent a compression, while lines spaced far apart represent a rarefaction.