Welcome to the store! 1. Excellent educational science gadget. Not only demonstrates the pendulum, but also shows the law of conservation of momentum and energy. 2. Science toys. When you feel tired from studying and working, you can stir the balls and hear the clanging to relieve yourself. 3. Excellent educational and scientific gadget, have your own scientific history, explore the important value of physics. 4. Pull back one or more balance balls, release them, and the same number of balls will swing on the other side. 5. Perfect for home decoration, study or desk decoration, etc. Also suitable for birthday gifts and children's toys. The device demonstrates the law of conservation of momentum and energy through a series of swinging balls. Pull back one or more balance balls, release them, and the same number of balls will swing on the other side. Specifications: Main material: solid wood base + metal bracket and ball Color: Silver Size: 9 x 8 x 9 cm / 3.54 x 3.15 x 3.54 inches (approx.) Package includes: 1 x Balance ball toy Package weight: about 300 grams. Note: 1. Please allow 1-2 cm error due to manual measurement and make sure you don't mind before ordering. 2. Please note that there may be color difference due to different placement of pictures. Your satisfaction is our top priority. We will provide you with the best service. If you find any problems after receiving the product, such as damage, incorrect quantity, etc., please contact us immediately and we will give you the best solution!