Newtons Cradle Balance Balls, Swinging Balls with Black Base, Fun Science Physics Learning Accessories, Calm Down Fidgets Kit, Desk Toys for Stress Relief, Office Home Decoration (Black)1. High Quality: The Newton's Cradle is composed of a metal ball, a plastic bracket and a plastic base. Use nylon line of good material instead of cheap fishing line. With unique assembly design, the Newton's Cradle is more stable and sturdy. 2. Longer Swing Time: Due to the resistance and friction of the air, the Newton's cradle balance ball will continue to move for 10 20 seconds. You have enough time to observe the physical performance of the