At its highest point, a pendulum is subjected to two main forces: the gravitational force acting downwards and the tension force exerted along the string.

To elaborate, when a pendulum reaches its apex, it encounters two primary forces. The first is the force of gravity, which consistently acts vertically downward. This gravitational force is responsible for the pendulum’s potential energy at this point. It can be expressed mathematically as:

where $m$ represents the mass of the pendulum bob and $g$ denotes the acceleration due to gravity.

The second force present is the tension in the string or rod to which the pendulum bob is attached. This tension force acts along the length of the string or rod, directed toward the pivot point. The tension provides the necessary centripetal force that enables the pendulum bob to maintain its circular motion. At the peak of the swing, the tension force is at its minimum because the pendulum bob is momentarily at rest, and the only force it must counteract is the gravitational force.

It is crucial to understand that the net force acting on the pendulum bob is not zero, even though it is momentarily stationary at the peak of its swing. The pendulum bob is in a state of dynamic equilibrium. Although the forces acting on it are balanced, they are not static. Both the tension force and the gravitational force fluctuate as the pendulum swings back and forth. This dynamic equilibrium is what enables the pendulum to continue its oscillatory motion.

In summary, at the top of its swing, a pendulum is influenced by a downward gravitational force and a tension force along the string. These forces exist in a state of dynamic equilibrium, which facilitates the pendulum’s ongoing movement.