Chandrasekahr developed the theory on the stability of a rotating drop by equating the entire mechanical energy of a drop with its surface energy tensor. In his theory he assumed that the surface energy is symmetrical about the center of a drop, and the symmetry itself prevents the theory from dealing with multi-lobed waves. In this report, an equation for multi-lobed waves induced on a rotating drop by sound waves is shown. The wave equation is first derived on the assumption that the acoustic radiation pressure around a drop is constant. Then the effects of the deformed drop on the radiation pressure surrounding the drop are considered. In addition, the equation for the relationship between the radiation pressure and a drop that becomes oblate due to the radiation pressure is obtained. The two equations are compared with the results of both ground experience and flight experience and it is shown that good agreement exists between the theoretical prediction and the experimental results.