The principle that explains why heavy objects fall at the same rate as light objects is known as Galileo's principle of falling bodies. This principle states that the acceleration due to gravity is constant for all objects, irrespective of their mass. In the absence of air resistance, both heavy and light objects will fall at the same rate, accelerating towards the ground at approximately 9.81 m/s². This principle was significant in the development of classical mechanics and challenged previous notions that heavier objects fall faster than lighter ones.