Momentum, radiation pressure, and other second-order quantities in ideal gas (liquid) in some boundary-value problems

Problems related to such properties of sound waves as momentum, radiation p ressure, and sound energy density and flux are investigated on the basis of the solutions of particular problems in the first- and second-order approx imations using the Eulerian representation. Specifically, it is shown that a disturbance propagating in a continuous medium may have a nonzero momentu m when the average density of the medium in the volume occupied by the wave coincides with the density of the undisturbed medium. In this case, the mo mentum and the related mass transfer and radiation pressure are caused by v ariations in the wave profile (envelope). Andreev's expression for the ener gy density that differs from the commonly used one is verified, and some ot her paradoxical consequences of the theory of sound art: considered. The co rrectness of using the quantities averaged over time and space is discussed . (C) 2000 MAIK "Nauka/Interperiodica".