Newton's cannonball
Newton's cannonball was a thought experiment Isaac Newton used to hypothesize that the force of gravity was universal, and it was the key force for planetary motion. It appeared in his posthumously published 1728 work De mundi systemate.
Theory
In this experiment described near the start of his De mundi systemate, Newton visualizes a stone being projected from the top of a high mountain, and "that there is no air about the earth, or at least that it is endowed with little or no power of resisting".As a gravitational force acts on the projectile, it will follow a different path depending on its initial velocity.
If the speed is low, it will simply fall back on Earth.
If the speed is the orbital speed at that altitude, it will go on circling around the Earth along a fixed circular orbit "and return to the mountain from which it was projected".
If the speed is higher than the orbital velocity, but not high enough to leave Earth altogether, it will continue revolving around Earth along an elliptical orbit.
If the speed is very high, it will leave Earth in a parabolic or hyperbolic trajectory.