When and where will the next manhole explosion be? Bonus question: Why are manholes (or is that menhole?) round?
Why is a Black hole emitting a giant gas bubble 1000 light-years wide? Bonus question: How can anything in a vacuum be called a “bubble”?
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Links to books and other items on this page and elsewhere on Greg Ladens' blog may send you to Amazon, where I am a registered affiliate. As an Amazon Associate I earn from qualifying purchases, which helps to fund this site.
Because the circle is the cheapest Reuleaux polygon, both in manufacture and in use.
For the win:
When and where will the next manhole explosion be? “Soon, very soon!”
Bonus question: Why are manholes (or is that menhole?) round? “Don’t be a square, man!”
Why is a Black hole emitting a giant gas bubble 1000 light-years wide? “To get to the other side.”
Bonus question: How can anything in a vacuum be called a “bubble”? “Exactly.”
True, but sometimes there are other considerations for non-circular curves of constant width. It can be argued as a relatively inexpensive way to make something fairly unique and distinctive (which for a city or other municipality, may be enticing), like the British 20p and 50p coins (which take advantage of the standardized diameter to maintain proper function in coin operated devices).
And now I’ll derail the thread.
By coincidence only a couple of hours ago I was wondering about the word manhole.
I was thinking about words and phrases that aren’t gender-neutral and how they are gradually being replaced, and couldn’t remember what the gender-neutral word for manhole was. Access hole? Access cover? Person hole? People Hole? I dunno.
And then I was wondering why sometimes the trend to make terms gender neutral where appropriate (which I support) often comes across as clumsy, at least linguistically or ease-of-talkifyingly… when instead the opportunity is presented to replace what was a crappy and not very descriptive term with a better one.
Example. Man hours. Gender biased, but also not exactly the most obvious expression. It’s not clear WTF is meant by that unless you’re from the culture that uses it all of the time and have heard it many times.
We are replacing it with person hours or people hours. Gender neutral, still clear as fucking mud.
Why are we not replacing it with the more obvious and descriptive “work hours?” Is there a reflexive need to NOT change the course so dramatically, is there some need to make it OBVIOUS that the change has been made so as to openly show a “see! We’re not being biased!” bias?
Or is it just that people just aren’t very imaginative, and even when making a change just have a hard time making a change?
And so this is what I was thinking about, and then I came here, and then I posted this.
Perhaps this is why people find my annoying.
There is a photoblog though somewhere of artistic and interesting utility access covers (manhole covers) from around the world, and if I weren’t tired I would go find it and post a link here because it’s neat and I like foundry stuff.
Manhole covers are round because it is the only shape that has no possibility of falling into the hole on any orientation and it also fits tight on any orientation.
What is very surprising to me is why they haven’t put in devices to mitigate the hazards of explosions.
If a manhole cover gets blown 50 feet in the air, that is a limited and known impulse. It would be a relatively trivial effort to tether the manholes so they don’t go more than 5 feet or so in the air. That would be enough to vent the explosion, but not enough that when the manhole came down it would kill anyone.
The most straight forward way would be to just put multiple heavy chains and not even attach them to anything. If the weight of the chains equaled the weight of the manhole cover, the height would be halved. You could attach chain weights equivalent to the estimated magnitude of the height.
Sorry, Bob, but ’tain’t so. That’s what the whole point was regarding Reuleaux polygons. Look them up.
DC, the Reuleaux polygons (other than circle) do not fit tight in any orientation, only in a limited number of orientations. For example the Reuleaux triangle only fits in 3 orientations, not infinitely many the way a circle does.
Sorry Bob, You answered the wrong question, and you even answered that question incorrectly.
Circular manhole covers are discs for only one reason: To fit circular manholes.
To answer Greg’s question, manholes are cylindrical to better resist the compressive forces against the sides of the shaft. This was especially important when sewers and manholes were made of brick rather than re-enforced concrete.
Which is either good, bad, or unimportant depending on external considerations. On the other hand, they’re cheaper to make, which is always important. (NB: I referred obliquely to the “all orientations” with the “in use” note.)
Re: man hours
I work in an industry where we use this term a lot. I usually had to explain to clients that is referred to the time one person spent on the job.
Person or crewperson hours would be the most gender neutral terms I could think of.
Work hours or crew hours would be more confusing because it could refer to the time the entire crew spent on the project, not individual people.
For manhole, I like utility access hole best. But if I’m putting one on a landscape plan, I’d better use the term manhole or readers may not realize what I’m referring to.
I think the term manhole has lost most gender connection. As a woman, it doesn’t bother me much. Now, “Men Working” signs sure does. The landscape company where I used to work ordered some signs saying that and I vociferously suggested they change it to crew working. I’m not sure they did.
NewEnglandBob has won the thread with the most correct answer. Round is also simpler to mold and machine.
Instead of ‘man hours’ we use ‘FTEs’ or full time equivalencies.
“Circular manhole covers are discs for only one reason: To fit circular manholes.
To answer Greg’s question, manholes are cylindrical to better resist the compressive forces against the sides of the shaft. This was especially important when sewers and manholes were made of brick rather than re-enforced concrete.”
I dunno about your manholes, but our manholes are not the same diameter all the way down, and the access hole (the bit with the cover) is frequently significantly smaller than the rest of the hole.
Katherine @#14,
So what’s your point?
Cylindrical or conic section, the same engineering principal applies.