Which factor primarily affects the strength of gravitational force?

The strength of the gravitational force is primarily influenced by the distance between the masses. According to Newton's law of universal gravitation, the gravitational force between two objects is inversely proportional to the square of the distance separating their centers. This means that as the distance increases, the gravitational force decreases significantly. Conversely, when the objects are closer together, the gravitational attraction increases. This fundamental principle highlights that while the amount of mass also plays a role in gravitational force, it is the distance between the masses that has a more immediate and dramatic effect on the strength of the force they exert on each other.