Question

When a pendulum reaches the top of it's swing it stops briefly before starting to fall. What happens when the pendulum starts to fall?

Answer 1

During the swing of the pendulum, when it is release after displacing it's position from the equilibrium, then due to disturbance of the bob, it starts to oscillate about the equilibrium position.

When it reaches to the top of the oscillation, then $mg\sin \theta$ will gets balanced or we can say that kinetic energy got converted into the potential energy, and due to the imbalance of the bob, it starts to move to the central point to regain its original kinetic energy.