万有引力
Newton used Kepler's laws of planetary motion to derive his law of universal gravitation. Newton's law of universal gravitation was the first law he developed and proposed in his book "Principia". The law states that any two objects exert a gravitational force of attraction on each other. The magnitude of the force is proportional to the product of the gravitational masses of the objects, and inversely proportional to the square of the distance between them. Along with Newton's law of universal gravitation, the "Principia" also presents his three laws of motion. These three laws explain inertia, acceleration, action and reaction when a net force is applied to an object.