Serena raised her hand.

Aristotle believed that the laws governing the motion of the heavens were a different set of laws than those that governed motion on the earth. Galileo's concept of inertia was quite contrary to Aristotle's ideas of motion: in Galileo's dynamics the arrow (with very small frictional forces) continued to fly through the air because of the law of inertia, while a block of wood on a table stopped sliding once the applied force was removed because of frictional forces that Aristotle analyzed incorrectly.

Also, Galileo's extensive telescopic observations of the heavens made it more and more plausible that they were not made from a perfect, unchanging substance. In particular, Galileo's observational confirmation of the Copernican hypothesis suggested that the Earth was just another planet, so maybe it was made from the same material as the other planets.

Galileo laid the groundwork to overthrow the physics of Aristotle, in addition to his astronomy. It fell to Isaac Newton to bring these threads together and to demonstrate that the laws that governed the heavens were the same laws that governed motion on the surface of the Earth.