Trying to understand basic gravitation

1. May 13, 2012

U.Renko

I have a bit of intuition on microscopic structures, so I "easily" understand things such as chemistry, nuclear and particle physics and the such. I'm no expert in these subject or anything but I do have a easier time learning it.

But I REALLY have a hard time understanding some macroscopical/astronomical structures.
But I intend to fix it.

Anyways, what I still don't understand about gravity is the circular/elliptical orbits of planets/satellites/stars/etc. This question might sound silly but...

Why don't the moon just falls on Earth? I understand it is constantly "falling" towards the Earth and all. What I mean is, why does it have a horizontal component of velocity which makes it "not really fall"? Is it because it had a initial velocity different than zero? Does it depends on the initial conditions of the system or something like that?

2. May 13, 2012

tiny-tim

Hi U.Renko!
Yup, that's exactly it!

Anything that's orbiting anything else is doing so only because the initial conditions were right.

(Having said that, the formation of the Moon is actually a bit of a mystery … very likely, it happened when a proto-Moon in the same orbit as Earth "backed into" Earth … I suppose it must have done it with "sidespin", or the debris would just have gone straight up and down again?! )