Which one of the following is an example of the force of gravity of the earth acting on a vibrating pendulum bob?

In a simple pendulum, the force of gravity acts on the center of the pendulum bob. When the bob is displaced from its mean position, it starts an oscillatory motion. The component of the gravitational force (mg sinθ) acts as the restoring force, which is always directed back toward the equilibrium position of the system. This restoring force is responsible for bringing the system back toward equilibrium after it has been perturbed. For small displacements, this force is directly proportional to the displacement, allowing the pendulum to act as a simple harmonic oscillator. While other forces like friction (air resistance) and tension exist, the specific role of gravity in maintaining the oscillation is to provide the restoring force that pulls the bob back to its center.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 8: Measurement of Time and Motion > 8.1.1 A simple pendulum > p. 109