English: Illustration of Orbits using Cannonballs

I created this drawing myself - FrankH 06:31, 12 Jan 2005 (UTC)

If the cannon fires its ball with a low initial velocity, the trajectory of the ball will curve downwards and hit the ground (A). As the firing velocity is increased, the cannonball will hit the ground further (B) and further (C) away from the cannon, because while the ball is still falling towards the ground, the ground is curving away from it. If the cannonball is fired with sufficient velocity, the ground will curve away from the ball at the same rate as the ball falls — it is now in orbit (D). The orbit may be circular like (D) or if the firing velocity is increased even more, the orbit may become more (E) and more (F) elliptical. At a certain even faster velocity (called the escape velocity) the motion changes from an elliptical orbit to a parabola, and will go off indefinitely and never return. At faster velocities, the orbit shape will become a hyperbola.