Newton along with his three laws of motion, Newton published the law of gravitation in 1687. According to Sir Isaac Newton,
Thus, the magnitude of the gravitational forces F1 and F2 between two particles m1 and m2 placed at a distance r is,
Here, G is a universal constant called gravitational constant whose magnitude is,
[G] = [M-1L3T-2]
The direction of forces ‘F1 and F2‘ are opposite in direction and along the line joining the two particles.
Following three points are important regarding the gravitational force:
- Unlike the electrostatic force, it is independent of the medium between the particles.
- It is conservative in nature.
- It expresses the force between two points masses (of negligible volume). However, for external points of spherical bodies the whole mass can be assumed to be concentrated at its center of mass.
In Newton’s law of gravitation, gravitation is the force of attraction between any two bodies. If one of the bodies is earth, then the gravitation is called ‘gravity’. Hence, gravity is the force by which earth attracts a body towards its centre. It is a special case of gravitation.