Demonstrate Newton's classic laws of physics! With a flick of the wrist, set the spheres in motion. It really is "all in the wrist!" As the first sphere swings around, it stops and transfers its energy to the second ball, forcing it to swing around. With practice, students can even make the spheres ricochet off one another above and below the handle. Colors may vary. Two sizes. 10 cm (4") handle or 20 cm (8") handle.