Acoustic forces and torques

Abstract

In ordinary daily experience, the forces associated with sound waves are usually negligible. In a resonator, the sound levels can be much greater and hence the Bernoulli forces can create a variety of dramatic effects. This video will illustrate the pressure and velocity fields in a standing wave tube using a microphone and hot‐wire anemometer. This standing wave field will then be used to demonstrate the “Maidenform effect” and acoustic levitation. Radiation pressure will be demonstrated using a Helmholtz resonator and then a pair of Helmholtz resonators will be used to make an acoustic radiometer. The standing wave field will then be extended from one to two dimensions to illustrate the torque on a Rayleigh disk and, finally, the controlled rotation of objects in a standing wave field whose particle motion is determined by the relative phasing of the degenerate modes. [Work supported in part by the Naval Postgraduate School Direct Funded Research Program.]