Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!




  1. 1
  2. 2
  1. Next

Sound is produced by vibrating particles that form longitudinal waves. Longitudinal waves have to travel through a medium.

Ultrasound is the name given to sound waves with very high frequencies. It has many practical applications in medicine.


Longitudinal waves

All sound is produced by vibrating particles that form longitudinal waves. In this kind of wave the vibrations of the particles are in the same direction as the wave.

Terms you need to know are:

  • Amplitude the maximum distance the particles move from their normal position. The louder a sound is, the more energy it carries and the bigger its amplitude.
  • Wavelength the length of one wave. It's the distance between one high pressure region (compression) and the next.
  • Frequency the number of waves produced in one second. It's measured in hertz, Hz. A higher pitched sound has a higher frequency than a lower pitched sound.
  • Compression where particles are squashed together.
  • Rarefaction (pronounced rair - ree - fac - shun) where particles are spread out.

Longitudinal waves can only travel through a medium. They cannot travel through a vacuum which is why sounds don't travel through outer space.

Transverse waves - higher tier only

For this type of wave the vibrations are at right angles to the direction of the wave.


  1. 1
  2. 2
  1. Next

Back to Radiation for life index

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.