Orders of magnitude explained

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/

found whilst looking at some other interesting Physics videos at

http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/index.htm

which was triggered by listening to a download of the ABC.net.au archive of last week's Science Show:
http://mpegmedia.abc.net.au/rn/podcast/current/audioonly/ssw_20080503.mp3

Natural learning working as it does...