Class09

Class09 - Sound Sound waves are longitudinal waves. What's...

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1/27/12 Oregon State University PH 202, Lecture 9 1 Sound Sound waves are longitudinal waves. What’s oscillating? Several attributes, actually: Position, speed, acceleration. And pressure. Like the other properties, the pressure of the air (or whatever solid or fluid the sound is traveling through) varies sinusoidally along the direction of the wave’s travel: P = A cos[(2 π / λ ) x ± 2 π ft ] And of course, as with other waves, the speed of sound, v , can be computed via the equation v = f λ . But we can also predict v from the characteristics of the material. For example, in an ideal gas, v is related to the temperature and the mass of a gas particle: v = ( γ kT/ m particle ) 1/2 In general, sound travels faster in hotter gases. Why? And, sound travels faster in liquids than in gases (and faster in solids than in liquids). Why?

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1/27/12 Oregon State University PH 202, Lecture 9 2 We experience sound (biologically) somewhat differently than we measure it (physically). Measure Experience Pressure variation (Pa) Sound Frequency (Hz.) Pitch Absolute Intensity (W/m 2 ) Relative Intensity (dB) Loudness
1/27/12 Oregon State University PH 202, Lecture 9 3 Sound as a Pressure Variation The wave equation for sound can be expressed as a pressure variation—in units of pressure. For example, a wave equation for a typical level of speech would be something like this:

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This note was uploaded on 03/10/2012 for the course PH 202 taught by Professor Staff during the Winter '08 term at Oregon State.

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Class09 - Sound Sound waves are longitudinal waves. What's...

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