**UNIVERSAL LAW OF GRAVITATION**

Every object in the universe attracts every other object with a force . Attraction force is directly proportional to the product of their masses.

** F ∝ m _{1} × m_{2}** Equation 1

The force between two objects is inversely proportional to the square of the distance between them, that is,

** F ∝ 1/ r ^{2}** Equation 2

Combining Eqs. (1) and (2), we get

F ∝ m_{1} m_{2 }/ r^{2} Equation 3

F = G m_{1} m_{2 }/ r^{2} Equation 4

where G is the constant of proportionality and is called the** universal gravitation constant.**

m_{1} = Mass of one body

m_{2} = Mass of other body

r = Distance between two body

By multiplying crosswise, Eq. (4) gives

F × r^{ 2} = G m_{1 }× m_{2}

G = F × r^{ 2} / m_{1 }× m_{2} Equation 5

**IMPORTANCE OF THE UNIVERSAL LAW OF GRAVITATION**

The universal law of gravitation successfully explained several phenomena which were believed to be unconnected:

(i) the force that binds us to the earth;

(ii) the motion of the moon around the earth;

(iii) the motion of planets around the Sun; and

(iv) the tides due to the moon and the Sun.