Specifications: This set is used for study the changing center of gravity of the roller that rolls from high to low. The roller has 6.5 cm in diameter, 10.5 cm in length. There is 2 acrylic rails placed at angularity and the edged of the rails width is 10.5 cm. The base's size is 50x50x11 cm, back drop's size is 50x40 cm. The structure is made from MDF plywood coated by formica.