RATTLEBACKS PLASTIC EDUCATIONAL TOY PKG(10)
Rattlebacks are plastic semi-elliptical shapes, 3-7/8" long, that illustrate Newton's laws of motion, while mystifying kids. Set them down (the rattlebacks, not the kids) and their offset center of gravity makes them spin. Spin them in one direction and they stop and reverse themselves. You get a package of (10) in assorted colors, along with a lesson plan and suggested activities.