Physical processes
Electricity, types of energy forces, space, sound and light are covered in this section.
bbc.co.uk navigation
Site links
BBC links
© 2012
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.