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Sound Sounds are created when a vibrating source causes waves of acoustic energy to travel through the air. The sound pressure waves move out from the vibrating source and become weaker the further they travel. The waves may be reflected or scattered by objects so that the sound reaching the ear may be different from the sound originally generated. Sounds can be characterised by their frequency (or pitch) and intensity (or loudness). The vibrations producing the sound are cyclical and are measured in hertz (Hz), which gives the number of cycles that occur per second. An adult with good hearing can hear frequencies in the range 20 to 15,000 Hz, while children can hear frequencies above 20,000 Hz. Check that you understand what these words mean in this document Vibrating: moving from side to side. Vibrating source: the point or object which the vibration or sound comes out of. To reflect: to bend or throw back waves of light, sound, or heat . To generate: to produce. For further information visit: Waves The physics of sound