From Aristotle to Galileo - The teachings of the great ancient wise Aristotle stating that heavy objects fall faster than light ones were accepted until the XVI Century. We know that if we drop a hammer and a feather or a sheet of paper from the same height, the hammer will reach first the ground. If we crumple the paper giving it a ball shape it is observed that both objects will reach the ground almost at the same time. It was the famous Italian physicist Galileo Galilei who refuted Aristotle's idea stating that, in absence of air resistance all objects fall with the same uniform acceleration. But Galileo didn't have a machine to create vacuum for sucking the air; the first pneumatic machine able to do this was invented afterwards, by the year 1650. He did not have watches exactly enough nor high speed photo cameras either. However, he cleverly proved his hypothesis using inclined planes getting a slower movement which could be measured with the rudimentary watches of that age. The slope of the planes could be increased gradually until reaching almost a vertical position allowing him to predict behavior of objects in free fall.