Principle of relativity
In 1600, Italian astronomer Galileo Galilei proved that all objects fall with the same acceleration. Therefore, the longer an object moves with constant acceleration the faster its final velocity is. Also, if different objects each having a different mass are dropped from rest (initial velocity is zero) at the same height in a vacuum, they will all hit the ground at the same velocity regardless of their mass. The experimental discoveries of Galileo and the Laws of Motion developed mathematically by Newton gave birth to modern science.