Nonlinear acoustics
= Nonlinear acoustics
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<Nonlinear acoustics> retains finite-amplitude effects in <sound waves>, including amplitude-dependent propagation <speed>, distortion and possible <shock waves>. For a one-dimensional <polytropic flow> with $p\propto\rho^\gamma$, a rightgoing simple wave has characteristic <speed> $u+c=c_0+(\gamma+1)u/2$ relative to a quiescent reference. Thus small-amplitude <linear acoustics> need not be uniform when a background <velocity> nearly cancels the <speed of sound>.