井盖为何是圆的？
Why is the manhole cover round?
一、不易掉落
1、 Not easy to fall
圆形最大的特点是半径长度相等。因此当把圆形的井盖放到井口时，井盖就不会掉到井底。如果井盖是矩形，井盖的宽度就不是一定的。矩形的对角线长度大于任何一条边，井盖都有可能掉进井底。
The biggest characteristic of a circle is that its radius and length are equal. Therefore, when the round well cover is placed at the wellhead, the well cover will not fall to the bottom of the well. If the manhole cover is rectangular, the width of the manhole cover is not fixed. If the diagonal length of the rectangle is greater than any side, the manhole cover may fall into the bottom of the well.
图片
picture
二、不易受损
2、 Not easily damaged
圆形受力均匀，能承受来自不确定方向的负载。当车轮开过，井盖依然平整。如果是其他有棱角的多边形，不但容易翘起造成安全事故，而且棱角也容易磨损。
It can bear the load from uncertain direction. When the wheels pass, the manhole cover is still flat. If it is other polygon with edges and corners, it is not only easy to cause safety accidents, but also easy to wear.