Newton's cradle, Carejoy newton's cradle balance balls with Metal Balance Ball and Black Wooden Base accompany your child's Grown-Up CHILDS DREAM: All kids dream of being scientist, how should we help our child? Let's start from newton's cradle balance balls and give the dream to your child 30-40 SECOND: Balls to move smoothly for up to 40 seconds Can help you explain your child that physical knowledge and Newton's story, Can help your explore The mysteries of the natural sciencesn with your child toghter BLACK WOODEN BASE: the hard wooden base can keep the smooth operation of the newton's cradle balance balls OUR PROMISE: The material of newton's cradle is metal and wooden, Not plastic. We have a full refund for any quality problems