Gravitation – Gravitation is the term given to the natural attraction that takes place between masses. It is the attractive forces that counteract the centrifugal forces that keep the planets rotating round the sun and the moon round the earth. The attractive force (F) between two masses (m₁) and (m₂) a distance (l) apart is given by,  where (G) is a constant known as the gravitational constant. Gravitation is described by the general theory of relativity but Newton’s law of Gravitation is a much simpler and quite a satisfactory approximation for most calculations involving gravitation.