A double pendulum consists of two bobs, each with a mass of m, that can move in a vertical plane. There is an external time-dependent force f(t) acting on the lower bob in the horizontal direction. The pendulum has two rigid linkage arms with a length of L and negligible mass. Theta1 and theta2 can be used as generalized coordinates. We will ignore any friction and damping effects.
Question: Obtain the equations of motion for the two bobs in the double pendulum using Newton's Second Law, free-body diagrams, and rotational equations of motion.
Figure 1: The double pendulum in a vertical plane.