In “Galileo’s Great Discovery: How Things Fall” (D.W. MacDougal, Newton’s Gravity: An Introductory Guide 17 to the Mechanics of the Universe, Undergraduate Lecture Notes in Physics, DOI 10.1007/978-1-4614-5444-1_2, # Springer Science+Business Media New York 2012) they write
Galileo Galilei (1564–1642), the famous Italian mathematician at the leading edge of the scientific revolution that was to sweep Europe, was curious about motion. He was an experimentalist who for the first time had the insight and talent to link theory with experiment. He rolled balls down an inclined plane in order to see how things fell toward the Earth. He discovered in this way that objects of any weight fell toward the Earth at the same rate – that they had a uniform acceleration. He surmised that if they fell in a vacuum, where there was no air resistance to slow some objects more than others, even a feather and a cannon ball would descend at the same rate and reach the ground at the same time. He also explored the motion of pendulums and other phenomena. He is perhaps most famous for his 1610 telescopic discoveries of the moving moons of Jupiter, the phases of Venus, and the craters of the moon, all of which convinced him, against the ages-old wisdom of Aristotle and of the Catholic Church, of the rightness of the Copernican heliocentric view of the solar system.
In his investigations of motion, Galileo was the first clearly to understand that the forces acting upon objects could be broken into independent components; that a thrown stone had a force pulling it down as well as the force throwing it horizon- tally outward. These insights would be of great use to Isaac Newton, born the year Galileo died, in devising the calculus and his universal laws of gravity and motion.
Worth a read for some insight into how thinking and physics works.