What is a pendulum primarily characterized by?

A pendulum is primarily characterized by a weight that swings back and forth. This swinging motion occurs due to the force of gravity acting on the weight, also known as the bob, which is attached to a fixed point by a string or rod. When the weight is displaced from its resting position and released, gravity pulls it downward, causing it to swing through an arc and return to its starting point, demonstrating a regular and repeating motion. This characteristic of swinging back and forth makes it a key example of harmonic motion in physics.

While the other options touch on related concepts, they do not define the primary characteristic of a pendulum. The fixed point is essential for the pendulum's function, but it alone does not characterize the pendulum itself. Although pendulums can be used in scientific experiments and time measurement dispositifs, these are applications of the pendulum rather than its defining characteristic.