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From: Randy Yates on 31 Dec 2009 00:04 Jerry Avins <jya(a)ieee.org> writes: > [...] > Relying on a large brittle flange extending out from a stress raiser > (abrupt change in section) is an engineering sin you wouldn't commit. So when you asked the question, "Why are manhole covers round?", you expected the answer to be based on such knowledge of materials? -- Randy Yates % "So now it's getting late, Digital Signal Labs % and those who hesitate mailto://yates(a)ieee.org % got no one..." http://www.digitalsignallabs.com % 'Waterfall', *Face The Music*, ELO
From: Muzaffer Kal on 31 Dec 2009 00:23 On Thu, 31 Dec 2009 00:04:22 -0500, Randy Yates <yates(a)ieee.org> wrote: >Jerry Avins <jya(a)ieee.org> writes: >> [...] >> Relying on a large brittle flange extending out from a stress raiser >> (abrupt change in section) is an engineering sin you wouldn't commit. > >So when you asked the question, "Why are manhole covers round?", you >expected the answer to be based on such knowledge of materials? To decide that a piece of metal with twice the area, consequently twice the weight of another is a worse (ney, unacceptable) choice to solve the identical problem doesn't require any extensive knowledge of materials. -- Muzaffer Kal DSPIA INC. ASIC/FPGA Design Services http://www.dspia.com
From: Jerry Avins on 31 Dec 2009 08:48 Randy Yates wrote: > Jerry Avins <jya(a)ieee.org> writes: >> [...] >> Relying on a large brittle flange extending out from a stress raiser >> (abrupt change in section) is an engineering sin you wouldn't commit. > > So when you asked the question, "Why are manhole covers round?", you > expected the answer to be based on such knowledge of materials? The expected answer is "So they don't fall through." Knowledge of materials is needed only to deal with nitpicking. :-) This was dealt with here before. What I intended as an allusion became instead a discussion. Happy New Year! Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: robert bristow-johnson on 31 Dec 2009 12:13 On Dec 31, 8:48 am, Jerry Avins <j...(a)ieee.org> wrote: > .... > What I intended as an allusion became instead a discussion. that's what happened to this whole friggin' thread. note the Subject: header. > Happy New Year! i dunno. instead of seeing an Old Man 2009 going out and the Baby 2010 coming in, i think what i see is the Old Man holding a condom with attached label "2010". such as it is. Happy New Year (i'll be accompanying my kids to "Burlington First Night", also, coincidentally, i turn 54 tomorrow, big fat hairy deal.) r b-j
From: Randy Yates on 31 Dec 2009 12:47
Muzaffer Kal <kal(a)dspia.com> writes: > On Thu, 31 Dec 2009 00:04:22 -0500, Randy Yates <yates(a)ieee.org> > wrote: > >>Jerry Avins <jya(a)ieee.org> writes: >>> [...] >>> Relying on a large brittle flange extending out from a stress raiser >>> (abrupt change in section) is an engineering sin you wouldn't commit. >> >>So when you asked the question, "Why are manhole covers round?", you >>expected the answer to be based on such knowledge of materials? > > To decide that a piece of metal with twice the area, consequently > twice the weight of another is a worse (ney, unacceptable) choice to > solve the identical problem doesn't require any extensive knowledge of > materials. Factually, it is NOT (necessarily) twice the weight. I demonstrated that with a conservative scenario in an earlier post in this thread and got a weight increase of 47 percent. Other scenarios could be reasonably formulated that would result in even less of a difference. Of course I and any other engineer would, all other things being equal, still choose the solution that resulted in the least amount of material/weight/cost/use of resources, whether the alternate solution is 100 percent, 10 percent, or 1 percent more. That is not my point. THE POINT IS _NOT_ THAT THE ROUND HOLE COVER IS NOT THE BEST SOLUTION. The point is WHY round is the best solution. What is the DECIDING FACTOR? It is NOT the best solution because it's the only solution that prevents the cover from falling through the hole. It is the best solution because it's the only solution that prevents the cover from falling through the hole AND that utilizes the least amount of material/weight/cost/use of resources. THE "DECIDING FACTOR" CAN _NOT_ BE A FACTOR THAT IS COMMON TO OTHER SOLUTIONS! For example, if someone asked me why I married my wife, I would NOT say "because she's female." ALL potential marriage partners are female (at least in my neck of the woods they are!), thus this is not the DECIDING factor; it must be some other factor. The same is true for manhole cover geometry. If someone asks, "Why are manhole covers round?" the answer is NOT "Because that keeps it from falling through the hole" because that factor (property) is common with other possible geometries (namely, square). It has been argued that having a reasonable weight is an assumption that would have automatically been made, the implication being that this is not the "deciding factor" for choosing a round cover. This is a fallacy. This is the deciding factor, whether it was assumed or not. -- Randy Yates % "Remember the good old 1980's, when Digital Signal Labs % things were so uncomplicated?" mailto://yates(a)ieee.org % 'Ticket To The Moon' http://www.digitalsignallabs.com % *Time*, Electric Light Orchestra |