State the universal law of gravitation.

Explanation

Universal law of gravitation: The law states every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance betwene them. The force is along the line joining the centres of two objects.

Let two objects A and B of masses M and m lie at a distance d from each other as shown in fig. Let the force of attraction betwen two objects be F. According to the univesal law of gravitation the force between two objects is directly proportional to the product of their masses.
That is
`F prop Mxxm`.........1
And the force between two objects is inversely proportional to the square of the distance between them that is
`Fprop1/(d^(2))`........2
Combining equation 1 and 2 we get
`Fprop(Mxxm)/(d^(2))` .....3
or `F=G(Mxxm)/(d^(2))` ..........4
where G is the constant of proportionality and is called is universal gravitation constant. Its value at all places in this universal is `6.673xx10^(-11)Nm^(2)kg^(-2)`.