The angular frequency of oscillation for a particle executing angular oscillations  with couple per unit twist of c is

For a body executing simple harmonic motion, Restoring torque acting on it after a  small displacement  θ, about an axis,τ=−cθ  We know that this results in angular oscillations which can be also related by the  equation τ=Iα Equating the above two we get  −cθ=IαWhere for angular oscillations  α=−ω2θHence  −cθ=−Iω2θSimplifying this  c=Iω2Hence  ω=cI