quote:Original post by EelcoThat''s very true. Since everything in the solar system orbits in the same direction, it must be orbiting with us.quote:
Actually there''s lots of rarified gas floating around up there. Not enough to breathe certainly, but, unless you''re in deep, deep space, you''re certainly not in a vacuum. So sure there''s resistance. It''s very small, but it''s there.
however much ''air'' there is in space, it orbits along with the planets anyway, otherwise it would have fallen into the sun long since .
Anyway, Geoff''s explanation is excellent.
Just set the centripetal force equal to the gravitational force.
And if you''re still confused about the planets falling into the sun, think about this: When you spin a ball tied to a string around your head, is there some sort of magic "acceleration that is constantly applied at a perpendicular angle to the direction to the sun" (in your own words) being applied here? No - the only thing keeping that ball moving in a circle around your head is the force of you pulling inward on the string. (Although in reality your hand is swirling about, moving the center of rotation around, but don''t worry about that)