Enclose the diameter in track: ＞ 140 mm

One grows in the main rail: ＞ 400 mm

Complement the rail and grow in the way: ＞ 250 mm

It makes demonstration object laboratory apparatus of circular motion in vertical level; it is simple, ocular to demonstrate centrifugal function and law. When dropped from the top of the track, the ball will make a complete circle in the track without falling out, defying gravity.