My answer would be because the hole that it cover is round as well. But here is a Microsoft job interview that further elaborates that. (Of course there are other answers of course.). But this one is fun.Round Manhole Covers, or: If Richard Feynman applied for a job at Microsoft
"Why are manhole covers round" is one of the eternal questions in
job interviews, and so it seems to be at Microsoft. The desired and
politically correct answer to the question is: "Manhole covers are
round because round is the only shape that can never fall into the
manhole and hurt someone (with the hole of the same shape, but slightly
smaller size than the cover)". And the answer is wrong.
Let's ask Mr Feynman:
"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."
:)
See Reuleaux Triangles
loaded!!!!! with a a lot of BS but loaded nevertheless hehe galing
ReplyDeleteYeah. I was impressed nga eh. I am sure the interviewer was flummoxed as well. haha.
ReplyDeletewould you believe that this analogy was used in one of our post grad subjects? hahha. ako din nabano dun. hahahha
ReplyDeleteI wouldnt be surprised though. Questions like these makes you come up with the most creative answers, and it is one way of evaluating how one would response and make people to think on their toes. I remember an exam in the uni, the exam was given by one of the legendary professors. He asked them to study from cover to cover and bring at least 2 examination booklets. The question?
ReplyDeleteWhy?
and the right answer was -
Because.
funny BS, yes
ReplyDeletea round object is stronger and has no edges
seriously, round manhole cover cannot fall through its circular opening, whereas a square manhole cover may fall in if it were inserted diagonally in the aperture, a reuleaux triangle or other curve of constant width would also serve this purpose, but round covers are much easier to manufacture.
ReplyDeleteAs for the answer of BDX4, round tubes ( the hole, not the cover ) are the strongest and most material-efficient shape against the compression of the earth around them, and so it is natural that the cover of a round tube / hole assume a circular shape.
But marty, there are manholes in the world that's rectangular. but I heard about the reuleaux triangle, you guys may click on the link after the article. :)
ReplyDeletequestion: Why are there rectangular, square manholes aside from round ones?
I am logging off now but if some one can beat me to that answer... so post it here. ;)
and here is the answer, supposedly from another guy to the question i posed, why there are rectangular or square manholes aside from round ones. it's up to you decide.
ReplyDeleteTuesday, September 28, 2004 10:07 AM by Sushant Bhatia
PS. Did u know that the location of manholes defines the type of manhole cover used. For instance, on a road where cars go over the manhole, the hole is actually indented into the road. And on sidewalks, the holes lay flat with the pavement. Obviusly they are flat on the sidewalk so that people don't trip over the cover and then sue the city. But why the indentation for road manholes covers. I believe this has something to do with the shocks of cars. When one tyre of a car is suddenly allowed to "fall" the shocks will reduce the amount of stress on the manhole. Thus I would say that road manholes are more likely to be round. The stress (weight of the car/vehicle) is a big factor.
Next time you see a manhole on the road, notice whether it has an indent or not? If it does, then the cities road works has done a good job and you should write a thank you note to your local road works. I'm sure everyone appreciates being told they did a good job right :-)
nahilo ako... lol
ReplyDelete<== the issue here was, why is it round? now, your last post was way off, the primary question here was not about how covers are defined, secondly, i never denied the fact that some manholes are rectangular, what i wrote was, " round manhole cover cannot fall through its circular opening, whereas a square manhole cover may fall in if it were inserted diagonally in the aperture " hooyah...
ReplyDeleteOk.. ok... brain fart.. just woke up. ;) cut me some slack marty boy. ;)
ReplyDeleteManhole cover, being usually heavy, would be hard for the men working to lift it up, the round shape allows for the worker to easily roll it aside and back in place.
ReplyDeleteAnd again, the manhole cover being heavy, it would be too difficult for the worker to try to manipulate a square or any other non-round in shape to put it in the right place.
For covers with straight edges and corners, both the corners and edges must be well aligned in order to fit.
The round covers, on the other hand, does not need to be aligned because it has no straight edges or corners, no matter how you place it, it will fit perfectly in place.
Reuleaux Triangle could work too but as Martin said earlier, its much easier to manufacture a Round Cover.
Amazing!!!!!! Impressive.
ReplyDeleteI had already enough idea in regarding with this matter!!
ReplyDeleteGaling no? :)
ReplyDelete