为什么下水道井盖是圆的

通过 格志 再通过 cathayan 看到这个强贴。据说,微软面试的时候总问一些迷题,其中最著名的一个是:为什么下水道井盖是园的?

那个作者假想了,如果费曼去微软面试,被问到这个问题,会怎么样?

后面有我的译文

Interviewer: Now comes the part of the interview where we ask a question to test your creative thinking ability. Don’t think too hard about it, just apply everyday common sense, and describe your reasoning process.

Here’s the question: Why are manhole covers round?

Feynman: They’re not. Some manhole covers are square. It’s true that there are SOME round ones, but I’ve seen square ones, and rectangular ones.

Interviewer: But just considering the round ones, why are they round?

Feynman: If we are just considering the round ones, then they are round by definition. That statement is a tautology.

Interviewer: I mean, why are there round ones at all? Is there some particular value to having round ones?

Feynman: Yes. Round covers are used when the hole they are covering up is also round. It’s simplest to cover a round hole with a round cover.

Interviewer: Can you think of a property of round covers that gives them an advantage over square ones?

Feynman: We have to look at what is under the cover to answer that question. The hole below the cover is round because a cylinder is the strongest shape against the compression of the earth around it. Also, the term “manhole” implies a passage big enough for a man, and a human being climbing down a ladder is roughly circular in cross-section. So a cylindrical pipe is the natural shape for manholes. The covers are simply the shape needed to cover up a cylinder.

Interviewer: Do you believe there is a safety issue? I mean, couldn’t square covers fall into the hole and hurt someone?

Feynman: Not likely. Square covers are sometimes used on prefabricated vaults where the access passage is also square. The cover is larger than the passage, and sits on a ledge that supports it along the entire perimeter. The covers are usually made of solid metal and are very heavy. Let’s assume a two-foot square opening and a ledge width of 1-1/2 inches. In order to get it to fall in, you would have to lift one side of the cover, then rotate it 30 degrees so that the cover would clear the ledge, and then tilt the cover up nearly 45 degrees from horizontal before the center of gravity would shift enough for it to fall in. Yes, it’s possible, but very unlikely. The people authorized to open manhole covers could easily be trained to do it safely. Applying common engineering sense, the shape of a manhole cover is entirely determined by the shape of the opening it is intended to cover.

Interviewer (troubled): Excuse me a moment; I have to discuss something with my management team. (Leaves room.)

(Interviewer returns after 10 minutes)

Interviewer: We are going to recommend you for immediate hiring into the marketing department.

考官:现在我们进行面试中测试你创造力的部分。不要太辛苦的想,应用你日常的普通认识,并且描述你的推理过程。
这是问题:为什么下水道井盖是圆的?

费曼:他们不全是。一些下水道井盖是方的。确实有一些圆的,但是我见过一些正方形的,也见过其他矩形的。

考官:但是让我们仅仅考虑那些圆形的,为什么它们是圆的?

费曼:如果我们“仅仅考虑那些圆形的”,那么它们就被定义成圆的。这个陈述是重复的。

考官:我的意思是,为什么确实有圆形井盖存在?圆形井盖是否有什么特别的好处?

费曼:是的。当被遮盖的洞是圆形时,我们使用圆形的盖子。圆洞配圆盖是最直接的。

考官:你能思考圆形盖子比矩形盖子具有的优势吗?

费曼:为了回答这个问题,我们必须考虑井盖下面的情况。井盖下面的洞是圆的因为圆柱是承受周围泥土压力的最坚固形状。并且,它的名称“manhole(井盖)”暗示了一个足够容纳一个人的通道,一个爬下梯子人类的截面可以粗略看成圆形。所以圆柱体是下水道的自然形状。所以,为了遮盖下水道,井盖是简单的圆形。

考官:你相信其实这是一个安全的方案吗?我的意思是,难道方形井盖不会掉进洞里,以至于会让一些人受伤吗?

费曼:可能性不大。有时下水道是方形的,在预制的出口使用方形井盖。盖子比洞口大,盖子放在支撑它边缘的边框上。它们一般使用固体金属制成,十分沉重。我们来假想一个边长两英尺的洞口和0.5-1英寸宽的边框。为了让井盖掉下去,你必须抬起它的一边,旋转30度以使它脱离边框,然后倾斜45度让重心转换到可以让井盖掉下去的位置。是的,这是可能的,但是非常不容易。被授权打开下水道井盖的人被简单培训后肯定可以的避免这种事故。应用普通工程学的知识,下水道井盖的形状只是被它需要覆盖的洞口的形状决定。

考官(被搞晕的):请给我一点时间;我必须和我所在的考查小组商量一些事情。(离开房间)

(10分钟后考官回来)

考官:我们将会推荐市场部直接聘用你。

9 thoughts on “为什么下水道井盖是圆的

  1. 加菲教徒

    我告诉你啊`

    如果那个#盖子是钢的,那就是圆的

    如果那个#盖子是石灰的,那就是方的,至少我周围是这样的`

    Reply
  2. Walker Obeng

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