Could anyone explain this term to me please? Some one said there was some fundamental laws ecplaining this and I cant find out what they are? Thanks Sam

This message has been edited. Last edited by: DorianGreyed,

planetary motion = motion of the planets ;-)
seriously though, planetary motion is determines by two things, momentum (tendency to continue moving at a constant speed in a constant direction) and gravity (a force that affects speed and direction). Planets have momentum propelling them in a straight line, but they are pulled towards the sun. The momentum is at a right angle to the path between them and the sun. Basically, when these two effects combine, the momentum and gravity combine to cause a circle like (usually actually an ellipse) path where the planet is continually falling into the sun through gravity, but moved away from the sun through momentum, to result in little change in the distance between planet and sun. of course, the gravity of the other planets also pulls the planet, so it gets more complicated if you want to calculate exact motions.

I would add to the previous explanation, since you asked for the laws that govern planetary motion, the following website which gives them.Kepler's laws

[This message was edited by frankvan on 02-03-03 at 08:23 PM.]

This is what I needed..thanks guys for explaining this and for the link too! I do appreciate it. Im sure I will have more questions on this soon tho..