This Things of Science unit covers center of gravity. While a simple and small topic in physics, as a young boy center of gravity and center of pressure were big and new concepts when I was learning about model rocketry and how to design a rocket that will be stable. I think this is the perfect unit for a young person just into middle school. Follow this unit with some model rocketry and I think you have the basis for an excellent curriculum.
A photo of the things:
Here is the booklet:
More Things of Science scanned here.