In physics, a wave is a disturbance that travels through a medium such as air or water, and moves energy from one place to another. Sound waves, as the name implies, bear a form of energy that our biological sensory equipment -- i.e., our ears and brains -- recognize as noise, be it the pleasant sound of music or the grating cacophony of a jackhammer.
Sound waves have several features in common with other waves. One is that they must have a substrate, or medium, in which to travel; some are more suitable than others. A second is that they must have a source -- say, the plucking of a guitar string or two hands clapping together. A third is that they transmit energy through direct particle-to-particle interaction, which means that they are a type of mechanical wave.
Sound waves can travel through any material, but not in a vacuum, which is why there is no sound in outer space. The speed of sound in air is about 330 m/s, meaning that it covers a mile in about five seconds. Sound actually travels at far quicker speeds in other media; for example, in biological tissues, it moves at 1,540 m/s.
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