  In this work, we study a mathematical planar pendulum whose support point is
positioned equidistant between two vertical and uniformly electrically charged
wires. Its bob carries an electric charge and, its support point oscillates
vertically, following a harmonic law of motion. We study the dynamics of such
phenomenon and the parametric resonances of the equilibria. Moreover, we obtain
the surface in the parameter space (since such system presents three
parameters) which separates the region of stability from the region of
instability. On the particular case of zero charge, we obtain the boundary
curves of the stability/instability of Matheiu equation.
