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**Newton’s universal law of gravitation**:

This law states that every particle of matter in this universe attracts every other particle with force.

The force between the particles is always attractive, and it does not depend on the medium where they are placed.

Let ${m}_{1}$ and ${m}_{2}$ be the masses of two bodies \(A\) and \(B\), placed \(r metre\) apart in space.

*The gravitational force between two masses*This force of attraction is directly proportional to the multiplication of their masses (${m}_{1}$ and ${m}_{2}$) and inversely proportionate to the square of the distance between the centres (${r}^{2}$) of these masses. This force acts in the direction along the line connecting the masses.

$\begin{array}{l}\mathit{Force}(F)\phantom{\rule{0.147em}{0ex}}\propto \phantom{\rule{0.147em}{0ex}}{m}_{1}\times {m}_{2}\\ \\ F\propto \frac{1}{{r}^{2}}\end{array}$

On combining the above two expressions,

$\begin{array}{l}\mathit{Force}(F)\phantom{\rule{0.147em}{0ex}}\propto \phantom{\rule{0.147em}{0ex}}\frac{\phantom{\rule{0.147em}{0ex}}{m}_{1}\times {m}_{2}}{{r}^{2}}\\ \\ \mathit{Force}(F)\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\frac{G\times \phantom{\rule{0.147em}{0ex}}{m}_{1}\times {m}_{2}}{{r}^{2}}\end{array}$

Where,

\(G\) is the universal gravitational constant.

The SI unit of universal gravitational constant is $N{m}^{2}{\mathit{kg}}^{-2}$, and its value is $\mathit{6}.\mathit{674}\phantom{\rule{0.147em}{0ex}}\times \phantom{\rule{0.147em}{0ex}}{10}^{-11}\phantom{\rule{0.147em}{0ex}}N{m}^{2}{\mathit{kg}}^{-2}$.