Question

Why is the restoring force not zero at the equilibrium position of simple harmonic motion?

Answer 1

Look bro,..in case of simple harmonic motion the restoring force provided by the tension of the string and the centrifugal force[during oscillation]...but when the pendulam is at rest or every time a attractive force due to gravity act on the pendulam [if the mass is "m",then the force is "mg"] .so is force provide the tension so as this force remain for all time so the restoring force always remain..  :-)