Dispersion and Absorption of High Frequency Sound Waves

TLDR

Sound absorption in gases was previously attributed to friction and heat conduction. The study introduces a third factor: the slow energy exchange between translational motion and molecular internal degrees of freedom. Formulas for sound absorption and dispersion that include friction, heat conduction, and the new energy‑exchange effect are derived, and the exchange rate is calculated. Experimental comparison indicates the new energy‑exchange effect has considerable or even predominant influence on sound absorption.

Abstract

The absorption of sound waves in gases had been explained heretofore by friction and heat conduction. A third factor is here introduced, namely, the slow rate of exchange of energy between the translational movement and the internal degrees of freedom of the molecules. The formulas determining the absorption and dispersion of sound waves, due to these three effects, are developed. Comparison with the experimental data available shows that the new effect is either of considerable influence or even predominant. The rate of exchange can be calculated.