Julia Punch (of RPEMS) and I just did an interesting project to try to teach the kids about gravity. We had them make mobiles of the Earth-Moon system, and hung them from the ceiling. This is the handout we made.

Ideally (if the stick was massless) the thing would balance at the center of gravity, but using 1/16" oak dowels from Home Depot, the thing balances in the center. We're looking at using some dried bamboo from Julia's yard the next time. You can model the mass difference by using a roll of pennies ($0.50) for the Earth and a single penny for the Moon-- sting 'em up 30" apart and they balance quite close to the Earth. I kept their attention by holding this over my head and having it "orbit" as I summarized at the end of the class, passing it from hand to hand as necessary.

You could use a similar apparatus to demonstrate reflex motion of a star with an orbiting planet, if you wanted to teach about planets around other stars.

 out of  found this valuable. Do you find this valuable?