Why is the manhole cover round?

This question was first tested by Microsoft when recruiting employees. Friends don't dare to answer because they are Microsoft's test questions or simply say that I have not learned I don't know.

As long as the children who have learned this knowledge point are not difficult to think of the answer to the question. If you can't solve this problem for a while, let's review the characteristics of the circle. 

By learning the circle we know that a circle has an infinite number of radii and diameters, and that all radii and diameter are equal in length within the same circle, and the length of the radius is half the diameter.

 Do you have any inspiration to understand these? Someone has to ask what is the relationship with the manhole cover? The relationship can be big! Because each diameter of the circle is equal, the manhole cover is rounded so that the lid does not fall into the well no matter how it is placed. Do you think that this design is very reasonable! 

You must know when the design was originally designed, but many designers have tried many times to determine the graphics. From a mathematical point of view:

It uses the same diameter inside the same circle. Only the round manhole cover can't find the diagonal line, so no matter how the manhole cover is moved, the cover will not fall down, so the construction workers below will have safety! 

From a physical point of view: In fact, in addition to safety, the other advantage of the manhole cover is that it is easy to transport. From a geometric point of view:

1. If it is designed to be triangular or square, although the cover is larger than the wellhead, it still has the possibility of falling. If it is round, since the diameter of the circle is equal, the cover will not fall if it is a little larger. 

2. Since the wells sometimes require manual combing or wiring, etc., the area of the well is required to be as large as possible. In these figures, the area of the circle is the largest when their circumferences are equal. At the same time, the round shape is in line with our body shape, which is convenient for the staff to enter and exit. 

3. The triangle or square edge is composed of straight line segments, and the angle formed is sharp. If it is encountered during repair, it is easy to cause injury. The rounded edge is an arc and this problem does not occur. From the perspective of mechanics: 

In order to withstand loads from uncertain directions. Imagine if the lid of the sewer is square or other angular shape, the corners are easily damaged when the impact load of the wheel is applied. The reason why the inspection wells of the sewers are rounded is also due to the force considerations - the arched structure can effectively resist the earth pressure. 

However, since the area of the circle is the largest in the figure with the same circumference, the material used is the most. Therefore, from an economic point of view, manhole covers of other shapes have been designed in some places.

Most of the manhole covers are iron products, and generally require several people to work together to move. The manhole cover is roughly divided into a reclaimed resin composite manhole cover, a FRP composite manhole cover, a quartz sand composite manhole cover, a cement manhole cover, a ductile iron manhole cover, etc. 

The manhole cover has brought tremendous contributions to our lives! After the manhole cover is rounded, the workers can roll the manhole cover, which saves labor! Looking around you, you will find that there are many things in life that are designed using the characteristics of a circle, such as a teacup cover and a lid. 

When you talk about it, everyone is very surprised. A small circle can make such a big knowledge. In fact, many items in life are designed and manufactured using mathematical knowledge. 

As long as you carefully observe and think hard, there will be many unexpected gains!