Universal Law of Gravitation
Every particle of matter in the universe attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
This force of gravitational attraction between the two bodies acts along the line joining their centres. This force is hence mutual.
Consider two bodies of masses m 1 & m 2 with their centers separated by r. let F be the force of gravitational attraction between two bodies. According to newton's law of gravitation,
combining both the factors , we get
Value of G is constant everywhere and hence called as universal constant of gravitation.
Value of G
In si units, G = 6.67 x 10-11 newton m2 kg-2
In cgs , G = 6.67 x 10-8 dyne cm2 g-2 .