ActionFly Newtons Cradle Balance Balls Physics Pendulum Science Desk Office Classic Toy MATERIALOur newton cradle use nylon line of good material instead of cheap fishing line which other sellers used. Wooden base and the unique design idea make an impression. Different size give you more choices. SWING TIME--The balance balls continue in perpetual motion for only 15-25 seconds due to the resistance of the air and friction, but it won't influence the effect of playing although it can not reach the seamless convergence among balls in the vacuum. EDUTAINMENT--Suitable for children to experience the fun of mechanics in the process of playing this fun gadget. APPLICATION--Apply to psychology, teaching tools and furnishings. Frequency swing keeps you in a calm state. AFTER SALE SERVICES--Give you support and help at the first time whether it damage, receive the wrong goods or broken and other problems.