Question about gravity and the solar system

Suns gravity holds the planets around it in an orbit. There are great distances between the planets themselves so how is it that the planets that are the furthest away don't fly off into space and the closest ones get pulled into to the sun? It seems that whatever is in the "middle" should remain in a stationary orbit. How is this possible?

Because the planets on the far end of the solar system orbit very slowly around the sun, while the planets closest to the sun orbit the fastest.

It's simple physics.

Edit to add: See the entry for orbit on wikipedia.

[edit on 22-6-2009 by Kaytagg]