Vì sao nắp cống hình tròn?: Câu hỏi phỏng vấn của Microsoft từng


Microsoft, one of the largest technology giants in the world, holds the dream of many individuals to become their employees. However, in order to turn this dream into reality, candidates must not only have an impressive track record but also go through a series of interviews. Microsoft is known for asking clever and intriguing questions to their applicants. One of those questions is: “Why are manhole covers round?”

The Puzzle

At first glance, this may seem like a simple question, but it has left even the smartest individuals perplexed. The truth is, not everyone can pass this challenge from the Microsoft recruiters.

Have you ever wondered why manhole covers are always round and not triangular or square?

This seemingly obvious question becomes difficult to answer. In reality, it is not a tricky riddle or a highly sophisticated trap. It is a way to test the quick thinking, creativity, and problem-solving ability of the respondent, especially when they are in a tense interview environment.

The Standard Answer

So, what is the standard answer? The round design of manhole covers must have a logical reason behind it, rather than being a random choice. The simplest and most concise answer is: Because the sewer pipes are cylindrical, the manhole covers need to be round. The manhole covers are always larger than the surface area of the sewer, so they will never fall inside. On the other hand, designs like triangles, squares, or rectangles have the possibility of falling into the sewer when placed in certain positions, regardless of their larger sizes.

A round manhole cover is simply to prevent it from falling into the sewer.

If we want a comprehensive, scientific answer that nobody can argue with, we also need to consider architecture, cost, and transportation. You might be surprised by the series of advantages offered by the round manhole cover design:

Advantages of Round Manhole Covers

1. Easy Installation

From a scientific standpoint, round manhole covers are the easiest to install because they do not require rotation, measurements, or angular adjustments like squares, rectangles, triangles, and other shapes.

2. Easy Transportation

Manhole covers are usually heavy, making the task of moving and installing them laborious. With a round design, workers can easily roll them on the ground, making it more convenient and lightweight. Consequently, it saves labor and equipment rental costs, such as using trolleys.

3. High Durability and Material Efficiency

Due to the round shape, the force applied by the wheels vertically from above is distributed evenly across the surface of the manhole cover, avoiding excessive concentration on a single point, which can cause cracks. In the case of square and other polygonal shapes, the corners will experience less force compared to the remaining areas. Therefore, round manhole covers tend to have higher durability and are more material-efficient than other shapes.

Indeed, there may be triangular or square manhole covers, but they are the minority and only used in special cases.

So, the next time you come across a round manhole cover, you’ll know why it is the ideal choice in every aspect.

Manhole Cover

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