Gravitation is defined as the non-contact force of attraction between any two bodies in the universe (no matter how far the bodies are). The earth attracts (or pulls) all the bodies towards its center. The force with which the earth pulls the bodies towards it is called the gravitational force of the earth or gravity of the earth.

## Characteristics of Gravitational Force

1. Gravitational force is action at a distance force i.e., it does not need any contact between the two bodies.
2. It is a force between two bodies form action-reaction pair i.e., the force exerted by two bodies on each other are equal in magnitude and opposite in direction.
3. Gravitational force is the weakest force in nature.
4. It is 1036 small than electrostatic force and 1038 times smaller than nuclear force.
5. Gravitational force is a constant as well as conservative force.
6. The Gravitational force between two small bodies is very small. On the other hand, the gravitational force between two large bodies (say, the sun and the earth) is large.

Gravitational force is an inverse square force because it is inversely proportional to the square of the distance between the two bodies.

### Universal law of Gravitation (Newton’s Law)

The universal law of gravitation was given by Newton. According to this law, the attractive force between any two objects in the universe is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Consider two bodies A and B having masses m1 and m2, whose centers are at a distance r from each other.

Gravitational Force, F ∝ m1m2/r²

F=Gm1m2/r²

where G is universal gravitational constant. The value of G is 6.67 x 10-11 Nm2kg-2 and dimensional formula of G is [M-1L3T-2].

The law of gravitation is applicable for all bodies, irrespective of their size, shape, and position.

Importance of Universal Law of Gravitation

Universal law of gravitation successfully explained several phenomena like

i) The force that binds us to the earth

ii) Motion of the moon around the earth

iii) Presence of atmosphere around a planet