Analogy between soap film and gas dynamics. II. Experiments on one-dimensional motion of shock waves in soap films

Abstract

This paper presents an experimental investigation of one-dimensional moving shock waves in vertical soap films. The shock waves were generated by bursting the films with a perforating spark. Images of propagating shock waves and small disturbances were recorded using a fast line scan CCD camera. An aureole and a shock wave preceding the rim of the expanding hole were clearly observed. These images are similar to the x-t diagrams in gas dynamics and give the velocities of shock and sound waves. The moving shock waves cause jumps in thickness. The variations of the induced Mach number, M2 and the ratio of film thickness across the shock wave, δ 2/δ 1, are plotted versus the shock Mach number, M s. Both results suggest that soap films are analogous to compressible gases with a specific heat ratio of γ≅1.0.