An apple falls from a tree because of gravitational attraction between the earth and apple. If F1 is the magnitude of force exerted by the earth on the apple and F2 is the magnitude of force exerted by apple on earth, then
From Newton’s third law of motion: Every action has equal and opposite reaction.
Thus, F1 =F2
where, F1 is the magnitude of force exerted by the earth on the apple and F2 is the magnitude of force exerted by apple on earth.