Mean Force on a Sphere in a Spherical Sound Field. II. (Experimental)

The theory of the previous paper has been verified by a series of quantitative experiments. Several hollow glass spheres (0.228 to 3.029 cm radius) were suspended in turn by a fine glass fiber in the sound field in air; the deflection of each was measured at known frequencies (300 to 7000 cps) and amplitudes (0 to 1400 d/cm2) of the sound field. Care was taken to protect the sphere from any gas streaming to or from the source and to insure that the field was accurately spherical. All measurements were made under such conditions that the sound field was substantially sinusoidal. Good agreement was obtained between theory and experiment within the range of the variables investigated. In the region where radiation forces of attraction existed, this agreement was always within a few percent, even though the magnitude of the forces changed by a factor of 100 or even 1000 to 1 in a single experiment. In the region of repulsion, measurements could not be made with any great accuracy, but even so the agreement here was within the limits of experimental error.