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<br />t. <br /> <br />Introduction <br /> <br />Noise is a pollutant. While its physical and emotional effects are difficult to defme <br />quantitatively, the noise level itself can be measured. <br /> <br />Sound. An alteration of pressure that propagates through an elastic medium such as air <br />which produces an auditory sensation. <br /> <br />Noise. Any undesired sound. <br /> <br />Wave Motion <br /> <br />Sound travels in a wave motion through the air to our ears. An effective tool to demonstrate <br />wave motion is a weight hanging from a spring. Picture the following diagram as a single weight <br />and spring combination varying as time progresses along the horizontal axis. <br /> <br />Periodic Motion - Weight on a Spring <br /> <br />+ <br /> <br />/ Spring <br /> <br />o <br />i <br />5 <br />P <br />I <br />a <br />c <br />e <br />m <br />e <br />n <br />t <br /> <br /> <br />. <br /> <br />Period <br /> <br />. <br /> <br />Figure 1.1 <br /> <br />In Figure 1.1, the first position of the weight on the spring is at rest with no forces exerted upon <br />the system. If the weight is raised above its point of rest and the progression of the weight <br />moving down and up again is observed over a period of time, a sinusoidal wave form is <br /> <br />I <br />I <br />I <br />I <br /> <br />L_________ <br /> <br />3 <br />