* Force of Gravity: The force of attraction between two objects with mass.

* Mass: The amount of matter in an object.

* Distance: The separation between the centers of the two objects.

The Key Relationship: The force of gravity is directly proportional to the product of the masses and inversely proportional to the square of the distance between them. This is described by Newton's Law of Universal Gravitation:

```

F = G * (m1 * m2) / r^2

```

Where:

* F = Force of gravity

* G = Gravitational constant

* m1, m2 = Masses of the objects

* r = Distance between the centers of the objects

Answering Your Question:

If the distance between two objects stays the same, and the force of gravity decreases, the mass of one or both of the objects must have decreased.

Here's why:

* Decreasing Force of Gravity: The only way to reduce the force of gravity while keeping the distance constant is to reduce the product of the masses (m1 * m2).

* Mass Change: This means either one or both of the objects must have lost mass.

Example:

Imagine two planets, A and B, are a fixed distance apart. If the force of gravity between them weakens, it means either planet A lost mass, planet B lost mass, or both planets lost mass.