Hello I'm a beginner in physics and came across an explaination for Gravitation, it explains it using the moons orbit around earth as an example, they also say firing a projectile at a certain velocity can put that projectile in orbit, but they confused me with that one, can anyone help? this is the link (its only one page) http://csep10.phys.utk.edu/astr161/lect/history/newtongrav.html What I don't understand is how the moon doesn't get accelerated down to the earth's surface by the earth's gravity, I know that the earth's gravity keeps it in orbit (obviously) but don't understand why. The only reasons I can think of is that for instance you hit a ball in the vaccum of space with no other forces acting on it and that ball will travel at that velocity forever. Is that whats happening to the moon in space? what keeps it orbiting? I know about the universal gravitational constant and that tells me there is attraction between the earth and moon but perhaps not enough to send the moon crashing to the earth and not too little to let the moon escape orbit, is that possible? Its seems like a relationship between velocity and gravity that would explain it.