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The speed of sound varies with temperature. Since temperature and sound velocity normally decrease with increasing altitude, sound is refracted upward, away from listeners on the ground, creating an acoustic shadow at some distance from the source. [9]
c is the speed of sound in the medium, which in air varies with the square root of the thermodynamic temperature. By definition, at Mach 1, the local flow velocity u is equal to the speed of sound. At Mach 0.65, u is 65% of the speed of sound (subsonic), and, at Mach 1.35, u is 35% faster than the speed of sound (supersonic).
Particle velocity should not be confused with the speed of the wave as it passes through the medium, i.e. in the case of a sound wave, particle velocity is not the same as the speed of sound. The wave moves relatively fast, while the particles oscillate around their original position with a relatively small particle velocity.
The speed of sound in any chemical element in the fluid phase has one temperature-dependent value. In the solid phase, different types of sound wave may be propagated, each with its own speed: among these types of wave are longitudinal (as in fluids), transversal, and (along a surface or plate) extensional.
A sound speed profile shows the speed of sound in water at different vertical levels. It has two general representations: It has two general representations: tabular form, with pairs of columns corresponding to ocean depth and the speed of sound at that depth, respectively.
where is the Laplace operator, is the acoustic pressure (the local deviation from the ambient pressure), and is the speed of sound. A similar looking wave equation but for the vector field particle velocity is given by
ion speed of sound, the speed of the longitudinal waves resulting from the mass of the ions and the pressure of the electrons: = () , where is the adiabatic index Alfvén velocity , the speed of the waves resulting from the mass of the ions and the restoring force of the magnetic field:
Sound intensity is defined as the time averaged product of sound pressure and acoustic particle velocity. [8] Both quantities can be directly measured by using a sound intensity p-u probe comprising a microphone and a particle velocity sensor , or estimated indirectly by using a p-p probe that approximates the particle velocity by integrating ...