The mean torque on an infinite fixed strip due to plane harmonic sound waves is calculated, employing simple acoustical theory as a basis and neglecting viscosity. In the range of wavelength λ small compared to the strip width δ, the torque per unit length is

where α denotes the angle between the incident wave normal and that of the strip and ρο the equilibrium density of the medium. This oscillatory character of the torque in its dependence on δ/λ is not to be found at long wavelengths where, as is well known, the torque acts only in the sense of aligning the strip broadside to the incident wave normal.