noise pollution

...Noise, Noise Pollution and It's Control
What is noise?

Noise is the background disturbance caused by signals that are random and unpredictable. This can be called sound which is the sounds of everyday life. It is generated when a disturbance sets the air moving. We hear sounds when `tiny vibrations in the air called sound waves strike our eardrums. A sound wave consists of air molecules vibrating backwards and forwards. The molecules are crowded together in some areas producing places of high pressure and spaced out in others producing regions of low pressure. These waves move through the air spreading out from the source of the sound. These sound waves carry the sound to your ears. A high pitched sound makes the air vibrate backwards and forwards more times per second than a low pitched sound. The number of vibrations per second is called the frequency and is measured in hertz (cycles per second). Humans can't hear sounds with frequencies above about 20,000 hertz or below about...