As two objects move farther apart, the force of gravity between them weakens. The force of gravity is described by Newton's law of universal gravitation, which states that the force of gravity \( F \) between two objects is inversely proportional to the square of the distance \( r \) between them:
\[ F = \frac{G \cdot m_1 \cdot m_2}{r^2} \]
where \( G \) is the gravitational constant, and \( m_1 \) and \( m_2 \) are the masses of the two objects. As the distance \( r \) increases, the force \( F \) decreases.
So, the correct answer is:
The force of gravity between them weakens.