摆线也叫旋轮线，它和二次曲线一样，是一种重要曲线，具有广泛的应用。但是，它在分类、形成方式、方程、形状和特例等方面，都比二次曲线更多样化。摆线有普通、内、外摆线三种，而每一种又有长辐、一般、短辐之分，共九类。就是同属某一类的摆线，形状仍可能是千差万别的。 Cycloids are also called spiral wheels. Like quadratic curves, they are important curves and have a wide range of applications. However, it is more diverse than the quadratic curve in terms of classification, formation methods, equations, shapes, and special cases. There are three types of cycloids: ordinary, internal and external. Each of them has long spokes, general spokes, and short spokes. There are nine categories. It is a cycloid that belongs to a certain class. The shape may still be very different.