Gravity and Orbits
It was Newton, hundreds of years ago, that predicted and described how one can launch a satellite
into orbit by applying his first law of motion (a body remains stationary or moves in a straight line
unless a force acts on it). Newton used the analogy of shooting a steel ball with a very powerful cannon
atop a large mountain or platform.
As we increase the muzzle velocity for our imaginary cannon, the projectile travels further before returning to earth. If the cannon shot the cannon ball with exactly the right velocity, the projectile would travel completely around the Earth, always falling in the gravitational field but never reaching the Earth, which is curving away at the same rate that the projectile falls. That is, the cannon ball would have been put into orbit around the Earth. Newton concluded that the orbit of the Moon was of exactly the same nature: the Moon continuously "fell" in its path around the Earth because of the acceleration due to gravity, thus producing its orbit.
