But as we increase the muzzle velocity for our imaginary cannon, the projectile
will travel further and further before returning to earth.
Finally, Newton reasoned that if the cannon projected 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.