Sound waves and sound pressure

  • Thread starter Booney
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  • #1
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Homework Statement


Consider a sound wave in air of density 1.2 kg/m3. The displacement wave has the form s(x,t)=smaxcos(kx-[tex]\omega[/tex]t) where k=8.79rad/m, [tex]\omega[/tex]=3021.6 rad/s and smax=2.51 x 10-7m.
Calculate the sound pressure [tex]\Delta[/tex]P(x,t) of this wave at x=0.282m and t=0.00137s. Answer in units of Pa.


Homework Equations


[tex]\Delta[/tex]Pmax=[tex]\rho[/tex]v[tex]\omega[/tex]smax
[tex]\Delta[/tex]P=[tex]\Delta[/tex]Pmaxsin(kx-[tex]\omega[/tex]t)

The Attempt at a Solution



I have a feeling I'm not using the correct equations because the equations I've found include a velocity, which isn't given, and don't include the displacement function. How do I relate the displacement function to the pressure equations?
 

Answers and Replies

  • #2
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The only way I can think to solve this is by using the kinetic theory of an ideal gas to derive pressure based on average velocity. You can review this derivation at http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kinthe.html#c3". The important equation is:

[tex]\frac{1}{3} \frac{N}{V} m \bar{v}^2[/tex]

You can calculate velocity from your displacement equation.
 
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