Longitudinal waves

In longitudinal waves, the vibrations are parallel to the direction of wave travel.

Examples of longitudinal waves include:

  • sound waves
  • ultrasound waves
  • seismic P-waves

One way to remember the movement of particles in longitudinal waves is to use the 'P' sound: longitudinal waves such as seismic P-waves may be thought of as pressure or push waves as the particles move parallel to the wave.

Demonstrating longitudinal waves

Longitudinal waves show areas of compression and rarefaction:

  • compressions are regions of high pressure due to particles being close together
  • rarefactions are regions of low pressure due to particles being spread further apart

Longitudinal waves are often demonstrated by pushing and pulling a stretched slinky spring.

An outstretched slinky spring

In the diagram, the compressions move from left to right and energy is transferred from left to right. However, none of the particles are transported along a longitudinal wave. Instead, they move backwards and forwards between compressions as the wave is transmitted through the medium.

The Surfing GB team help demonstrate the different types of wave