1) The universal law of gravitation states that every body in the universe attracts other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

2) The direction of the force of attraction is along the line joining the centers of the two bodies.

3) Let two bodies of masses M and M be separated by a distance of ’d’. Then the force of gravitation between them.

4) F_{grav} ∝ GM_{1}M_{2}/d^{2}

5) F_{grav} = GM_{1}M_{2}/d^{2}

6) G is a proportionality constant called universal gravitational constant and found by Henry cavendish to be G = 6.67 × 10_{-11} Nm^{2} Kg^{-2}