The force of gravity between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. This relationship is known as Newton's law of universal gravitation.

The equation for Newton's law of universal gravitation is:

```

F = Gm1m2/r^2

```

Where:

* F is the force of gravity between the two objects

* G is the gravitational constant (6.674×10^-11 N·m²/kg²)

* m1 and m2 are the masses of the two objects

* r is the distance between the two objects

From this equation, we can see that the force of gravity between two objects increases as the product of their masses increases and decreases as the square of the distance between them increases.

For example, if the mass of one object is doubled, the force of gravity between the two objects will be doubled. Similarly, if the distance between the two objects is doubled, the force of gravity between them will be reduced to one-fourth of its original value.