chapter17.ppt.pptx - Chapter 17 Sound Waves Introduction to...

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Chapter 17 Sound Waves
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Introduction to Sound Waves Waves can move through three-dimensional bulk media. Sound waves are longitudinal waves. They travel through any material medium. Commonly experienced as the mechanical waves traveling through air that result in the human perception of hearing As the sound wave travels through the air, elements of air are disturbed from their equilibrium positions. Accompanying these movements are changes in density and pressure of the air. The mathematical description of sinusoidal sound waves is very similar to sinusoidal waves on a string. Introduction
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Categories of Sound Waves The categories cover different frequency ranges. Audible waves are within the sensitivity of the human ear. Infrasonic waves have frequencies below the audible range. Ultrasonic waves have frequencies above the audible range. Introduction
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Speed of Sound Waves The diagram shows the motion of a one-dimensional longitudinal sound pulse moving through a long tube containing a compressible gas. The piston on the left end can be quickly moved to the right to compress the gas and create the pulse. Before the piston is moved, the gas has uniform density. When the piston is suddenly moved to the right, the gas just in front of it is compressed. Darker region in b The pressure and density in this region are higher than before the piston was pushed. Section 17.1
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Speed of Sound Waves, cont When the piston comes to rest, the compression region of the gas continues to move. This corresponds to a longitudinal pulse traveling through the tube with speed v. Section 17.1
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Producing a Periodic Sound Wave A one-dimensional periodic sound wave can be produced by causing the piston to move in simple harmonic motion. The darker parts of the areas in the figures represent areas where the gas is compressed and the density and pressure are above their equilibrium values. The compressed region is called a compression. Section 17.1
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Producing a Periodic Sound Wave, cont. When the piston is pulled back, the gas in front of it expands and the pressure and density in this region ball below their equilibrium values. The low-pressure regions are called rarefactions. They also propagate along the tube, following the compressions. Both regions move at the speed of sound in the medium. The distance between two successive compressions (or rarefactions) is the wavelength. Section 17.1
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Periodic Sound Waves, Displacement As the regions travel through the tube, any small element of the medium moves with simple harmonic motion parallel to the direction of the wave. The harmonic position function is s (x, t) = s max cos (kx – ω t) s max is the maximum position of the element relative to equilibrium. This is also called the displacement amplitude of the wave.
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  • Spring '12
  • Prof.Mirza

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