According to the law of universal gravitation, the force of gravity \( F \) between two objects is given by the equation:
\[ F = G \frac{m_1 m_2}{r^2} \]
where:
- \( G \) is the gravitational constant,
- \( m_1 \) and \( m_2 \) are the masses of the two objects,
- \( r \) is the distance between the centers of the two objects.
From this equation, we can conclude that the force of gravity is inversely proportional to the square of the distance between them. Thus, the correct answer is:
Inversely proportional to the square of the distance between them.