# how to figure circumfrence (sp)

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• posted on August 17, 2004, 1:14 am
knowing that the diameter of a circle is 32 and 1/2 inches, How do I figure the outside length of the disk.
TIA
moyo
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• posted on August 17, 2004, 1:24 am
On Tue, 17 Aug 2004 01:14:50 +0000, moyo wrote:

Pi times the diameter. Two times pi times the radius. Pi is 3.141592654 (Pi has infinite digits beyond the decimal, but your calculator doesn't care.)
102.1 inches.
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• posted on August 17, 2004, 2:43 am
On Mon, 16 Aug 2004 20:24:10 -0500, Australopithecus scobis

102 3/32 for those without decimal rulers.
Bill.
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• posted on August 17, 2004, 9:56 am
My, My....thats an awfully big pi...

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• posted on August 17, 2004, 1:50 pm

Pi are not square. Pi are round. Cake are square.
Is this the world's oldest math joke?
Bob
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• posted on August 17, 2004, 3:55 pm
On Tue, 17 Aug 2004 05:56:37 -0400, "Mark Hopkins"

wi?
102.101761241668280250035909956584
Iiiii Knoooowwwww! My donkey kicked me in the behind just the other day.... ***************************************************** Marriage. Where two people decide to get together so that neither of them can do what they want to because of the other one.
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• posted on August 17, 2004, 1:37 am
moyo wrote:

( п = 3.1415926535897932384626433832795 [approximately])
C = п · D = п · 32.5 = 102.10176124166828025003590995658 [approximately]
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Morris Dovey
DeSoto, Iowa USA
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• posted on August 17, 2004, 2:21 am

Ya, but my ruler is not able to read that close. Why not just round it off to a more realistic number like 102.10176124166828?
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• posted on August 17, 2004, 2:34 am
Edwin Pawlowski wrote:

Can if you want to - but I have standards to maintain!
Just imagine the horrible consequences of an only 0.00000000000000025003590995658" gap in a tinfoil helmet...
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Morris Dovey
DeSoto, Iowa USA
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• posted on August 18, 2004, 12:37 pm
Now if you live in Indiana, you can simplify your Pi calculations.
If you've never heard this story, it's an interesting read:
http://www.agecon.purdue.edu/crd/Localgov/Second%20Level%20pages/Indiana _Pi_Story.htm
Lou
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• posted on August 18, 2004, 1:13 pm
loutent wrote:

Lou...
Interesting read. About that same time there were a number of states who considered similar legislation; and (I've heard but haven't confirmed) at least one state who actually enacted a statute defining pi to be exactly three.
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Morris Dovey
DeSoto, Iowa USA
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• posted on August 18, 2004, 6:19 pm
| | and (I've heard but haven't confirmed) at least one state who | actually enacted a statute defining pi to be exactly three.
Tennessee, and only in Robert Heinlein's "Stranger in a Strange Land." It didn't actually happen. The Indiana story is true enough, but it has spawned numerous spurious copycat stories that are standard April Fool's Day fare. Heinlein's is just the most immediately credible. The state in question is always some state presumed inhabited by rustics. But no state in the U.S. has ever had a law passed legislating the value of pi. Indiana came close.
--Jay
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• posted on August 18, 2004, 10:17 pm
Jay Windley wrote:

Whew! That's definitely reassuring. (-:
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Morris Dovey
DeSoto, Iowa USA
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• posted on August 19, 2004, 6:06 pm

I annoyed my HS geometry teacher by announcing I could trisect an angle.
True, a Carpenter's Square is illegal under the rules of "Geometric Construction", but I could easily prove that it worked.
There are other methods, using other tools, but a carpenter's square is probably the easiest to prove correct.
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• posted on August 19, 2004, 6:31 pm
wrote: | | There are other methods, using other tools, but a carpenter's square is | probably the easiest to prove correct.
Hence the original masons used three tools: the straightedge, the compass, and the square. It's amazing what you can do with those tools and a little "secret" geometretic knowledge.
-- Jay
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• posted on August 23, 2004, 8:47 pm
On Thu, 19 Aug 2004 12:31:22 -0600, "Jay Windley"

I'm still a neophyte, but I'm increasingly reaching the conclusion that a little geometric knowledge is all you *want* to have. Because of a misspent youth, I can do a lot of what people tell me is fairly complex mathematics in my head. So I wind up designing furniture that contains 18.7457 degree angles, or better yet, angles that are arctan(5.75/11) or lengths that are (5+sqrt(7))/2 or something. I actually computed a fifth order polynomial approximation to the chair leg curve I wanted on a table I made for my mother-in-law last year.
Unfortunately, I have learned that I can do the math, but I can not cut these crazy dimensions accurately. From now on, it's 90 degrees or 45 degrees or re-design it because it's wrong.

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• posted on August 23, 2004, 8:46 pm
Ken McIsaac wrote:

I had the same problem. You can solve (most) such problems with a CNC router; but it's a tad spendy if you're not serious about making it pay its own way.
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Morris Dovey
DeSoto, Iowa USA
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• posted on August 23, 2004, 11:29 pm
wrote:

That one I'd like to see.

Then your own designs are fairly simple. I admire people who do their own design. It's not the math, it's art. The math I can do easily, and often apply it in the shop, or on the computer or wherever, but the art? Stick people are beyond me. I need plans with numbers on them mostly. I did figure out how IKEA designed their neat folding table though.
Bill.
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• posted on August 24, 2004, 3:26 pm
wrote:

I knew the shape I wanted, but I can't draw (as you say, stick people are also beyond me), so the only way I could represent it was mathematically. I wanted the leg to be two inches wide at the top, one inch wide at the bottom and one-and-a-half-inch wide halfway down. I also knew I wanted the first derivative to be zero at the top and at the bottom, and I wanted the second derivative to be zero halfway down. That's enough to define a fifth order polynomial. The fun part was going to be to try to do it on two faces of the leg to get the three-dimensional shape I wanted.
So I got out Matlab and plotted the thing, then I tried to draw it on the leg with a pencil. Then I contemplated actually cutting it with my crappy jigsaw. Then I decided my mother in law would be very happy with a tapered leg. :)

It's not quite that my designs are simple. It's just that I have to take my original crazy designs and simplify them until they contain no parts that I can't make. Right now, that means it has to require no skill. I need a fence or guide or something to follow or the results are not pretty. I understand from my reading that people typically cut curves by following a hardboard template. I'm not sure how this solves the problem, since you first have to get the template right.
I have also learned that two or three hours with coarse sandpaper can make anything look good. :)
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• posted on August 24, 2004, 3:18 pm
Ken McIsaac wrote:

Plot your design. You can either superimpose it on a grid and scale it; or you can find a way to plot it full size. If necessary run it out on your printer in pieces, one piece per page, and then tape the printed pieces together...
Now you can transfer the design to the hardboard. Did you know that you can get hardboard with a slick white surface at the lumberyard?) I have a piece tacked to the wall that I sketch on with dry erase markers - lets me re-draw to my heart's content.
Practise makes (more) perfect. (-:
--
Morris Dovey
DeSoto, Iowa USA
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