Believed that the laws of motion of the heavens were different that those governing the earth.
Nothing moves unless is pushed.
Galileo's Concept
Galileo developed several concepts of motion such as velocity, force and inertia with experiments.
Newton’s Laws
Expanded Galileo’s work and created what we know today as Newton Laws of Motion which were used to understand the physics of motion prior Einstein .
Discovered that the laws of motion were the same on the heavens and on the earth and that the force that kept the earth moving around the sun was the same that pulled an apple form the tree (Dept. Physics & Astronomy University of Tennessee).
General Relativity is published
Einstein general theory of relativity