2. Equations of motion of the generalized perturbed pendulum
Here we attempt to give a general formulation of the simple pendulum, where different forcing and damping terms
are included in a single expression, with the aim of offering an overview of various situations that a pendulum may have
and portrait all of them in a common framework. From this perspective, several familiar cases including external
perturbations appear in a natural way, as particular cases of this generalized equation.
A simple mathematical pendulum is modelled by a bob of mass m, hanging at the end of a wire of length l and fixed
to a supporting point O (see Fig. 1), swinging to and fro in a vertical plane.
The equations of motion are straightforward to obtain using Lagrangian or Newtonian methods. For its simplicity,
we show here the pendulum equations using Newtonian methods. In this framework it is much more intuitive to visualize
the forces acting on the system, providing a more clearer physical picture of the dynamics of the pendulum, even
though other general formulations are possible. In this context Fig. 1 shows the force diagram of the simple pendulum