Waves can be broadly categorized into two types based on the direction of the particle motion relative to the direction of the wave propagation: transverse waves and longitudinal waves.
In a transverse wave, the particles of the medium move perpendicular to the direction of wave energy transfer. In a longitudinal wave, the particles of the medium move parallel to the direction of wave energy transfer.
In the simulation below, you can observe the movement of the particles along the both types of waves. The particles to focus on are the little red dots. Note that each particle is oscillating about its equilibrium position.
This table compares the various aspects of both wave types.
| Characteristic | Transverse Waves | Longitudinal Waves |
|---|---|---|
| Particle Motion | Perpendicular to the direction of wave propagation | Parallel to the direction of wave propagation |
| Wave Components | Crests and Troughs | Compressions and Rarefactions |
| Wavelength (\(\lambda\)) | Distance between two consecutive crests or two consecutive troughs | Distance between two consecutive compressions or two consecutive rarefactions |
| Examples | Light waves, water waves, waves on a string or rope | Sound waves, seismic P-waves, compression waves in a slinky |
The following videos demonstrate the two types of waves created in a slinky.
In a longitudinal wave, particles of the medium oscillate back and forth along the direction of wave propagation. The displacement of these particles from their equilibrium (rest) positions varies with their position along the medium at any given instant.
Usually we will define the positive direction of displacement as the direction of wave propagation.
In the applet below, use the red slider that moves through one particle to another to observe how the displacement is represented.