You can go “round and round” trying to explain centripetal force to your students, or you can dramatically demonstrate it with this “forceful,” fun device. A cup of colored water is balanced on the 20 cm disc tray. When you swing it from side to side by the attached handle, centripetal force holds the cup on the disc and the water remains parallel to the tray. Not a drop is spilled. This teacher-designed device comes complete with a cup, food coloring, and an excellent instruction booklet with background information. Developed by Walter Pawlowski.