Define the "universal law of gravitation".

(N/A) The universal law of gravitation states that every object in the universe attracts every other object with a force that is directly proportional to the product of their masses $(M_1 \times M_2)$ and inversely proportional to the square of the distance $(r^2)$ between their centres.
Mathematically, this is expressed as $F = G \frac{M_1 M_2}{r^2}$, where $F$ is the gravitational force, $G$ is the universal gravitational constant, $M_1$ and $M_2$ are the masses of the two objects, and $r$ is the distance between them.