Why doesn’t the moon come crashing out of the sky onto the earth? Is it because of the Earth’s gravity? Well, it cannot be because gravity pulls everything down but the moon is holding up like it is being acted up by some other kind of force. Also, why is the moon moving in a circle around Earth? From Newton’s first law of motion, things usually like to go in a straight line. But the moon is not actually doing that, is it?
Newton over 20 years to figure this stuff out. And of course, he had to invent calculus along the way, which is no small feat! But thanks to his genius thought experiment, we can wrap our heads around it in little less than 20 years. His thought experiment is called Newton’s cannonball.