<Dd> F → = m g → (\ displaystyle (\ vec (F)) = m (\ vec (g))) </Dd> <P> For an object in free - fall, this force is unopposed and the net force on the object is its weight . For objects not in free - fall, the force of gravity is opposed by the reaction forces applied by their supports . For example, a person standing on the ground experiences zero net force, since a normal force (a reaction force) is exerted by the ground upward on the person that counterbalances his weight that is directed downward . </P> <P> Newton's contribution to gravitational theory was to unify the motions of heavenly bodies, which Aristotle had assumed were in a natural state of constant motion, with falling motion observed on the Earth . He proposed a law of gravity that could account for the celestial motions that had been described earlier using Kepler's laws of planetary motion . </P> <P> Newton came to realize that the effects of gravity might be observed in different ways at larger distances . In particular, Newton determined that the acceleration of the Moon around the Earth could be ascribed to the same force of gravity if the acceleration due to gravity decreased as an inverse square law . Further, Newton realized that the acceleration of a body due to gravity is proportional to the mass of the other attracting body . Combining these ideas gives a formula that relates the mass (m ⊕ (\ displaystyle \ scriptstyle m_ (\ oplus))) and the radius (R ⊕ (\ displaystyle \ scriptstyle R_ (\ oplus))) of the Earth to the gravitational acceleration: </P>

What is meant by force at a distance