chapter14 - Chapter 14 Sound Producing a Sound Wave Sound...

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Chapter 14 Sound
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Producing a Sound Wave Sound waves are longitudinal waves traveling through a medium A tuning fork can be used as an example of producing a sound wave This picture is not in the new version, but fits very nicely. Either omit or see if it can stay.
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Using a Tuning Fork to Produce a Sound Wave A tuning fork will produce a pure musical note As the tines vibrate, they disturb the air near them As the tine swings to the right, it forces the air molecules near it closer together This produces a high density area in the air This is an area of compression
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Using a Tuning Fork, cont. As the tine moves toward the left, the air molecules to the right of the tine spread out This produces an area of low density This area is called a rarefaction
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Using a Tuning Fork, final As the tuning fork continues to vibrate, a succession of compressions and rarefactions spread out from the fork A sinusoidal curve can be used to represent the longitudinal wave Crests correspond to compressions and troughs to rarefactions
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Categories of Sound Waves Audible waves Lay within the normal range of hearing of the human ear Normally between 20 Hz to 20,000 Hz Infrasonic waves Frequencies are below the audible range Earthquakes are an example Ultrasonic waves Frequencies are above the audible range Dog whistles are an example
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Applications of Ultrasound Can be used to produce images of small objects Widely used as a diagnostic and treatment tool in medicine Ultrasonic flow meter to measure blood flow May use piezoelectric devices that transform electrical energy into mechanical energy Reversible: mechanical to electrical Ultrasounds to observe babies in the womb Cavitron Ultrasonic Surgical Aspirator (CUSA) used to surgically remove brain tumors Ultrasonic ranging unit for cameras
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Speed of Sound in a Liquid In a liquid, the speed depends on the liquid’s compressibility and inertia B is the Bulk Modulus of the liquid ρ is the density of the liquid Compares with the equation for a transverse wave on a string B v
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Speed of Sound in a Solid Rod The speed depends on the rod’s compressibility and inertial properties Y is the Young’s Modulus of the material ρ is the density of the material Y v
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Speed of Sound, General The speed of sound is higher in solids than in gases The molecules in a solid interact more strongly The speed is slower in liquids than in solids Liquids are more compressible property inertial property elastic v
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Speed of Sound in Air 331 m/s is the speed of sound at 0° C T is the absolute temperature 331 273 m T v s K
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Intensity of Sound Waves The average intensity I of a wave on a given surface is defined as the rate at which the energy flows through the surface divided by the surface area, A The direction of energy flow is perpendicular to the surface at every point The rate of energy transfer is the power Units are W/m 2 1 E I A t A
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