圆是与定点的距离等于定长的所有点组成的曲线．车轮就是运用了圆的这个重要性质,车轴总是处于一个相对不变的高度,从而使得车辆平稳运动．假设车轮不是圆形的,如三角形、正方形等做车轮,可想而知坐在这样 A circle is a curve made up of all points whose fixed point distance equals a fixed length. The wheel is the use of the important nature of the circle, the axle is always at a relatively constant height, which makes the vehicle move smoothly. Assuming that the wheels are not circular, such as triangles, squares, etc., as wheels, can be imagined sitting in this way