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From: Randy Yates on 29 Dec 2009 20:07 Jerry Avins <jya(a)ieee.org> writes: > Muzaffer Kal wrote: >> On Tue, 29 Dec 2009 15:39:33 -0500, Jerry Avins <jya(a)ieee.org> wrote: >> >>> Muzaffer Kal wrote: >>>> On Tue, 29 Dec 2009 14:37:29 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>>> >>>>> (I repeat: why are manhole covers round?) >>>> Doesn't that question assume all manhole covers are round? There are >>>> plenty of mhc which are square or rectangle (and some are hexagonal, >>>> star shaped etc.) >>> Yes. What disadvantage do those have? Are they often found in >>> street accesses? Why [not]? >> >> I think your main reason would be that they can't fall in their own >> hole no matter how hard one tries. Another reason is that they're much >> easier to roll than the pointy ones which usually need to be lifted to >> be carried. > > Right on both counts. There is a minor manufacturability advantage, > especially for the receiving surface. Doesn't a manhole cover have to have a lip? You can make a square cover that can't fall into its own hole: set L > ((sqrt(2) - 1) / 2) * d where d is the inside distance and L is the lip size. -- Randy Yates % "Watching all the days go by... Digital Signal Labs % Who are you and who am I?" mailto://yates(a)ieee.org % 'Mission (A World Record)', http://www.digitalsignallabs.com % *A New World Record*, ELO
From: Jerry Avins on 29 Dec 2009 20:19 Randy Yates wrote: > Jerry Avins <jya(a)ieee.org> writes: > >> Muzaffer Kal wrote: >>> On Tue, 29 Dec 2009 15:39:33 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>> >>>> Muzaffer Kal wrote: >>>>> On Tue, 29 Dec 2009 14:37:29 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>>>> >>>>>> (I repeat: why are manhole covers round?) >>>>> Doesn't that question assume all manhole covers are round? There are >>>>> plenty of mhc which are square or rectangle (and some are hexagonal, >>>>> star shaped etc.) >>>> Yes. What disadvantage do those have? Are they often found in >>>> street accesses? Why [not]? >>> I think your main reason would be that they can't fall in their own >>> hole no matter how hard one tries. Another reason is that they're much >>> easier to roll than the pointy ones which usually need to be lifted to >>> be carried. >> Right on both counts. There is a minor manufacturability advantage, >> especially for the receiving surface. > > Doesn't a manhole cover have to have a lip? You can make a square cover > that can't fall into its own hole: set > > L > ((sqrt(2) - 1) / 2) * d > > where d is the inside distance and L is the lip size. Cast iron is too brittle to allow large lips with reasonable thickness. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: Jerry Avins on 29 Dec 2009 20:19 Randy Yates wrote: > Tim Wescott <tim(a)seemywebsite.com> writes: > >> On Tue, 29 Dec 2009 19:37:52 -0500, Randy Yates wrote: >> >>> Jerry Avins <jya(a)ieee.org> writes: >>> >>>> Tim Wescott wrote: >>>>> On Tue, 29 Dec 2009 14:37:29 -0500, Jerry Avins wrote: >>>>> >>>>>> Randy Yates wrote: >>>>>>> Jerry Avins <jya(a)ieee.org> writes: >>>>>>> >>>>>>>> Randy Yates wrote: >>>>>>>>> Rune Allnor <allnor(a)tele.ntnu.no> writes: >>>>>>>>>> [...] "He who thinks his education has finished is not educated. >>>>>>>>>> He is finished." >>>>>>>>> I have found that education exposes one's own ignorance. >>>>>>>> Isn't that its most important purpose? >>>>>>> Good question. I think most people hope it prepares them for a >>>>>>> career. What I was trying to say is that you don't know how ignorant >>>>>>> you are until you get illuminated. >>>>>> Exactly. What we wrongly believe we know hurts a lot. When we >>>>>> perceive our ignorance, we can be careful or use the library. >>>>>> >>>>>>> I know I still want to continue to study (e.g., some more math) but >>>>>>> it comes down to time and money. If I won the lottery I'd probably >>>>>>> become a permanent student! >>>>>> If you don't study your surroundings as you walk, you are in danger >>>>>> of stepping into an open manhole. (I repeat: why are manhole covers >>>>>> round?) >>>>> Because they're easier to turn out on a lathe, of course! >>>> An important secondary reason. >>> To save material? A round cover is the least amount of material for a >>> given minimum radius. >> Try this mental experiment. >> >> Sneak out of your parents house, and find the nearest square manhole. >> Now pick it up (bring a hoodlum friend), and put it into the hole it came >> out of. >> >> Got that all visualized? >> >> OK. Now do the same thing with a round one. > > Jerry had already disqualified that answer as being "the one." That leaves me puzzled. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: Randy Yates on 29 Dec 2009 20:33 Jerry Avins <jya(a)ieee.org> writes: > Randy Yates wrote: >> Jerry had already disqualified that answer as being "the one." > > That leaves me puzzled. I think I got thread overload! Sorry for putting words in your mouth, Jerry. -- Randy Yates % "The dreamer, the unwoken fool - Digital Signal Labs % in dreams, no pain will kiss the brow..." mailto://yates(a)ieee.org % http://www.digitalsignallabs.com % 'Eldorado Overture', *Eldorado*, ELO
From: Randy Yates on 29 Dec 2009 20:36
Jerry Avins <jya(a)ieee.org> writes: > Randy Yates wrote: >> Jerry Avins <jya(a)ieee.org> writes: >> >>> Muzaffer Kal wrote: >>>> On Tue, 29 Dec 2009 15:39:33 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>>> >>>>> Muzaffer Kal wrote: >>>>>> On Tue, 29 Dec 2009 14:37:29 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>>>>> >>>>>>> (I repeat: why are manhole covers round?) >>>>>> Doesn't that question assume all manhole covers are round? There are >>>>>> plenty of mhc which are square or rectangle (and some are hexagonal, >>>>>> star shaped etc.) >>>>> Yes. What disadvantage do those have? Are they often found in >>>>> street accesses? Why [not]? >>>> I think your main reason would be that they can't fall in their own >>>> hole no matter how hard one tries. Another reason is that they're much >>>> easier to roll than the pointy ones which usually need to be lifted to >>>> be carried. >>> Right on both counts. There is a minor manufacturability advantage, >>> especially for the receiving surface. >> >> Doesn't a manhole cover have to have a lip? You can make a square cover >> that can't fall into its own hole: set >> >> L > ((sqrt(2) - 1) / 2) * d >> >> where d is the inside distance and L is the lip size. > > Cast iron is too brittle to allow large lips with reasonable > thickness. Well what about unreasonable thicknesses? The point is, it's not really the "can't fall through" argument, is it? The constraint is something else, like "too heavy" or "too expensive." -- Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven. Digital Signal Labs % She love the way Puccini lays down a tune, and mailto://yates(a)ieee.org % Verdi's always creepin' from her room." http://www.digitalsignallabs.com % "Rockaria", *A New World Record*, ELO |