THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

2.2 Sound Generation and Propagation 17p, s. or Ψ10. 50-0.5-1λxVIBRATINGPLANEx = 0ξ10.50-0.5-1xFigure 2.3. Depiction of rarefaction and condensation of air molecules subjected to thevibrational impact of a plane wall located at x = 0. The degree of darkness is proportionalto the density of molecules. Lighter areas are those of rarefactions. Mini-plots of thelocal variations of molecular displacement Ψ, pressure p, condensation s = (ρ − ρ 0 )/ρ 0 ,and particle displacement ξ are given as functions of x for a given instant of the soundpropagation. Note that wavelength λ represents the distance between corresponding pointsof adjacent cycles.101 kPa (14.7 psia or 760 mmHg). Sound velocities are also greater in liquids thanin gases, but remain less in order of magnitude than those for solids. For an idealgas the velocity c of a sound wave may be computed fromc =√ γ pρ = √ γ RT (2.2)where γ is the gas constant equivalent to the thermodynamic ratio of specificheats, c p /c v , p the quiescent gas pressure, and ρ the density of the gas. R is thethermodynamic constant characteristic of the gas and T is the absolute temperature