The torque due to the weight is where we've used the small angle approximation . The equation relating torque to angular acceleration is . Here the rotational inertia of a single mass, m , a distance from the axis of rotation is . Thus we can write which rearranges to give the equation . Once again we recognize the simple-harmonic oscillator, and the solutions is with identified by examining our equation.
Energy oscillates between kinetic and potential energy due to gravity.