It's a great idea! But...
The thing is that gravity doesn't need air. So if you had a model
of the solar system in a vaccuum jar, all the planets in it would fall
towards the ground.
Now, let's assume that we found a way to keep the Earth's pull out
of it. Still, gravity is a VERY weak force. If you think of it, it take
the entire Earth (and the Earth is pretty darn big) just to create the
little force that you feel as weight. A 1 pound ball would still only
have a tiny fraction of the Earth's pull. (about one billionth of one
billionth of one millionth) So not much would happen with such weak
Now, that being said, it would not be inconceivable to use other
forces than gravity for your model. The electric force is similar to
that of gravity, only it's much stronger. Or perhaps you can think of
some other way to make a good model.
I like your thought, but we'll need some force other than gravity to make it work. Keep the ideas coming!
P.s. If you made a little scale model using balls about the same
density as the Earth and Sun, and managed to put it on a satellite (or
anything in pure free-fall) to keep the Earth's gravity from making
trouble, it would of course still orbit due to the gravity of the
balls. The question is, how quickly would it make one orbit, since, as
Dan points out, the force isn't very strong. The answer turns out to be
that for a real scale model, it would still take one year to make the
orbit! That would be a little slow for viewing, but still should work
in principle. Mike W.
(republished on 07/19/06)