Dual-purpose, heavy-duty zinc ball can double as a pendulum bob or as the key element in a dramatic inertia demonstration. Use one of the provided eyelets, attach a string, suspend the bob, and you have a large demonstration pendulum. Attach another string to the bottom eyebolt and let it hang down from the bob. Grasp the lower string and jerk it downward quickly. Which string breaks? Which string breaks if you pull on the lower string in a slow, even fashion? A very dramatic demonstration of the Law of Inertia. Your students will remember the concept for a long time. The solid zinc ball weighs 454 grams, comes complete with eyehooks, background, and instructions. String not provided.