According to the traditional account to refute the Aristotelian notion that heavier objects fall faster than light ones Galileo performed an experiment from the top of the leaning tower of Pisa He dropped two spheres of different weight and observed that both hit the ground at the same time Galileo correctly reasoned that when an object falls more slowly it is due to air resistance An object moving solely under the influence of gravity is said to be in free fall; near the surface of the Earth such an object falls at an acceleration of 98