Hands Illuminated Reading

Throw a stone into a lake: water waves move outward from the splash. Clap your hands: sound waves carry the noise all around. Switch on a lamp: light waves illuminate the room Water waves, sound waves, and light waves are very different from one another in important respects, but all have in common the basic properties of wave motion. A wave is a periodic disturbance -- a back and fourth change of some kind (of water height in the case of water waves of air pressure in the case of sound waves, of electric and magnetic fields in the case of light waves) that spreads out from a source and carries energy as it goes. Information, too, can be carried by waves; this is how sights and sounds reach us.