Sound

Look at This:  
Watch the development of shockwave from an F-14 jet.


Previously Asked Questions

Q:    In some movies scenes involving explosives actors are asked to keep their mouth open and warned that if they don't their eardrums could implode.  Why would a blast from explosives require the actors to keep their mouths open?

A:    When the explosion goes off there is a pressure wave caused by the rapid burring of materials and thus the rapid change in volume of the explosive.  If the actor's mouth is closed, air at the pre-explosion pressure is trapped in the actor's sinus area.  The shock wave causes an area of high pressure to form around the actor.  When the actor's mouth is closed, the difference of pressure between the sinus area and the outside air can cause the ear drums to burst inward.  However, if the actor's mouth is open, the pressure wave will be the same both inside and outside the actor's mouth and the actor should be safe.  This same effect happens (although with less severity) when you go diving or when you go from high to low altitudes.

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References

Equations

Speed Waves
Speed of Sound 18-3.gif (210 bytes)
Longitudinal Displacement of a mass s = sm cos (kx - omega2.gif (834 bytes)t)
Pressure change delta.gif (839 bytes)p = delta.gif (839 bytes)pm sin (kx - omega2.gif (834 bytes)t)
Pressure amplitude delta.gif (839 bytes)pm =(v rho2.gif (832 bytes) omega2.gif (834 bytes)) sm
Interference phi2.gif (845 bytes) = 2pi2.gif (831 bytes) (delta.gif (839 bytes)L / lambda2.gif (834 bytes))
  Condition Corresponds to
Constructive interference phi2.gif (845 bytes) = m 2pi2.gif (831 bytes)     m = 0, 1, 2, ... delta.gif (839 bytes)L = m lambda2.gif (834 bytes)     m = 0, 1, 2, ...
Destructive Interference phi2.gif (845 bytes) = (m + onehalf.gif (67 bytes) ) 2pi2.gif (831 bytes)    m = 0, 1, 2, ... delta.gif (839 bytes)L = (m + onehalf.gif (67 bytes)) lambda2.gif (834 bytes)    m = 0, 1, 2, ...
Sound Intensity
Insensate I = P/A
Intensity related to displacement amplitude (sm) 18-27.gif (204 bytes)
Intensity at a distance r from a sound emitting point source 18-28.gif (177 bytes)
Sound Level in Decibels

beta2.gif (840 bytes) = (10 dB) log ( I / I0 ) where I0 = 10-12 W/m2

Standing Wave Pattern in Pipes
Pipe, two open ends 18-37.gif (352 bytes)
Pipe, one open end 18-39.gif (343 bytes)
Beats

f beat = f1 - f2

The Doppler Effect

18-53.gif (226 bytes)

Shock Wave
Mach cone angle

sin theta2.gif (833 bytes) = v / vs

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Mechanics List of Topics

Measurements Newton's Laws Potential Energy and Conservation of Energy Rotation of
Rigid Bodies
Elasticity
Vectors Forces and Fields Linear Momentum Angular Momentum Mechanical
Oscillations
Motion of Point-Mass Objects in One Dimension The Gravitational Field Collisions Torque Mechanical Waves
Motion of Point-Mass Objects in Two and Three Dimensions Kinetic Energy
and Work
Circular Motion of Point-Mass Objects Equilibrium Sound

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