Very-Low-frequency evanescent liquid pressure waves


  • Reinhart Frosch Sommerhaldenstrasse 5B, CH-5200 Brugg, Switzerland


Density of liquids, Elastic waves, Waves, Classroom demonstrations, Linear oscillations, Liquid particle, Liquid pressure, Spatial extension, Standing wave, Thermal motion, Very low frequency


Evanescent liquid sound-pressure waves are standing waves of limited spatial extension. These waves involve variable pressure and liquid-particle velocity but negligible liquid-density variation: they are predicted to occur also in strictly ideal liquids. The present note is intended to show that classroom demonstrations of these latter waves can provide a plausible introduction to the subject of spring-driven evanescent liquid sound-pressure waves. That inaccuracy occurs because the small- displacement approximation has been used. In both cases, standing waves with linear oscillations of liquid particles along time-independent streamlines are generated. Since thermal motion and diffusion of the molecules are neglected, in the no-wave state the liquid particle is concluded to keep its initial place and shape.




How to Cite

Frosch R. Very-Low-frequency evanescent liquid pressure waves. Canadian Acoustics [Internet]. 2011 Sep. 1 [cited 2022 Aug. 19];39(3):120-1. Available from:



Proceedings of the Acoustics Week in Canada