I posted this one on the family blog as well, but I wanted to stick it here as well, since it's an art project. This one has provided lot's of entertainment over here. We put together the catapult and colored and numbered some paper plates for point keeping. Only we didn't end up keeping points, we just thought it was cool to see how many papers would make it into a plate.
Click here, it's the family fun website, where we got the idea.