State Newton's universal law of gravitation and represent it in a mathematical expression.

(N/A) Newton's universal law of gravitation states that every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
To obtain the mathematical form,consider two point masses $m_{1}$ and $m_{2}$ separated by a distance $r$. The gravitational force $F$ between them is given by:
$F \propto m_{1} m_{2}$ ... $(1)$
$F \propto \frac{1}{r^{2}}$ ... $(2)$
Combining these two relations,we get:
$F \propto \frac{m_{1} m_{2}}{r^{2}}$
$F = G \frac{m_{1} m_{2}}{r^{2}}$
Here,$G$ is the universal gravitational constant. Its value is $6.67 \times 10^{-11} \text{ N m}^{2} \text{ kg}^{-2}$. It is called a universal constant because its value remains the same everywhere in the universe.