Galileo showed a cannonball and a musket ball fall at exactly the same rate
Aristotle had taught for 2,000 years that heavier objects fall faster than light ones. Galileo's inclined-plane experiments, rolling balls down a ramp to slow their motion enough to time with the clocks of his day, showed that all objects accelerate downward at the same rate regardless of weight, once air resistance is removed. The famous Leaning Tower of Pisa drop may be a later legend, but the ramp experiments in his own notebooks are real and well documented.