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Sound Waves Physics 1

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Nature of Sound Sound is a longitudinal mechanical wave that travels through an elastic medium.

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Speed of Sound Longitudinal mechanical waves (sound) have a speed dependent on elasticity factors and density factors.

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Speed of Sound

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For the speed of sound in air, where t c is in degrees Celsius

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Intensity of Sound The sound intensity is the sound power that passes perpendicular through a surface per unit of surface area.

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Intensity of Sound If a source emits sound uniformly in all directions, one can imagine the energy spreading out in a spherical pattern.

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Intensity of Sound The smallest sound intensity audible to the human hearing is 1 x 10 -12 W/m 2. This intensity is called the threshold of hearing (I 0 ). Since human hearing has a wide range, the intensity of audible sounds is compared to the intensity at the threshold of hearing.

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Intensity of Sound The sound intensity of a vacuum cleaner is around 1 x 10 -5 W/m 2. Comparing this intensity to the threshold of hearing,

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Intensity of Sound Due to the large comparison, it is more appropriate to express this relative intensity ( ) in a logarithmic scale.

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Intensity of Sound

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Frequency of Sound The perceived frequency of an observer or pitch (f o ) of an emitted frequency of a sound source (f s ) depends on whether the observer or the source are in motion.

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Frequency of Sound Source and Observer at rest

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Frequency of Sound Moving Source

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Frequency of Sound Moving Observer

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Standing Waves L Fundamental, n = 1 1st Overtone, n = 2 2nd Overtone, n = 3 3rd Overtone, n = 4 All harmonics are possible for open pipes:

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Standing Waves L Fundamental, n = 1 1st Overtone, n = 2 2nd Overtone, n = 3 3rd Overtone, n = 4 All harmonics are possible for open pipes:

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Standing Waves Only the odd harmonics are allowed: Fundamental, n = 1 1st Overtone, n = 3 2nd Overtone, n = 5 3rd Overtone, n = 7 L

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Standing Waves Only the odd harmonics are allowed: Fundamental, n = 1 1st Overtone, n = 3 2nd Overtone, n = 5 3rd Overtone, n = 7 L

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