Question

What was Newton’s major contribution to overturning Aristotelian cosmology?

Answer 1

Aristotle believed that motion, even constant steady motion, required a force. Galileo agreed that force changes motion, but he knew force wasn’t necessary for motion. The tendency of things to keep moving was what Galileo called “inertia.”

Newton refined Galileo’s idea further and made it his first law. He wrote it in Latin, but here’s the direct translation:

Every object continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

That is, Objects continue doing what they’re doing until there’s an unbalanced force applied to them.