Why
stuff goes into orbit:
Imagine I'm on the
moon, and I have a bunch of
tennis balls. If I throw a ball
parallel to the ground, but
not very quickly, it'll go for a while, but eventually
gravity will pull it to the ground and it'll stop. Now, as I throw the balls with greater and greater
velocity, they'll get farther and farther, but they'll all fall eventually. But then I throw one
really, really fast, and it never hits the ground! How can this be?
Let's examine the curved path of the ball as it travels any horizontal distance-- for simplicity's sake, 1
meter. Within that distance, it will fall away from a perfectly
horizontal path (the path it would take if there were no gravity) by a certain amount; let's call it d
vert, and it increases as horizontal velocity increases, since it can travel farther before it hits the ground. Now, let's look at the planet we're on (in this case, the moon); more specifically, 1 meter of it. Since the planet isn't
flat (
last time I checked), it'll curve away from a perfectly flat distance by a certain amount within this 1-meter length.
Now here's the crazy part: If d
vert (the amount the ball falls away from horizontal as it travels 1 meter) ever equals the amount that the planet curves away from the horizontal,
the ball will never hit the ground! Because the earth is curving away at the same rate that the ball is, it will go into orbit.