Consider a rigid body, for instance a fidget spinner. If an external force is applied on it such that it rotates from θ1 to θ2, about a fixed axis, then the total work done on the body equals the integration of the product of the net torque on it and its angular displacement. Since the net torque on any rigid body is equal to the moment of inertia times angular acceleration, substituting the value of torque in the work expression and using the chain rule, dω/dt can be expressed as dθ/dt multiplied by dω/dθ. Now, dθ/dt is the angular velocity, ω. Therefore, the integrand in the equation equals Iω. Integrating within the limits of initial and final angular velocities, the net work done by the external force to rotate the rigid object about a fixed axis equals the change in the object’s rotational kinetic energy. This is the expression of the work-energy theorem for a rotating rigid body.