【educational toy】excellent educational science gadget. Not only demonstrates a pendulum, but also shows the laws of conservation of momentum and energy.friction and damping effects are also observed. 【relive stress】when feeling tired of studying and working, you can stir balls to hear the clinking sound to ease. 【stimulate scientific interest】excellent educational & science gadget, own your very own piece of scientific history and explore significant values of physics. 【interesting gameplay】pull back one or more of the balance balls, release them and the same number of balls will swing up on the opposite side. 【desktop decoration】great for home ornament, study or office desk table decor accessories, etc. Also good for birthday gift and kids toy. 4 aa batteries no included