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June 7th, 2009, 04:26 AM   #1
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A glassblower joining a math forum...

I am here for help with some problems that are beyond my rather basic skills.
Rest assured, I do have some basics, and I am not completely useless.
http://www.talkglass.com/forum/showthread.php?t=20213

Brian
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June 7th, 2009, 07:35 AM   #2
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Re: A glassblower joining a math forum...

Welcome! I'm always glad to see people with different interests joining. I like to watch glass blowing, but I've never tried it myself. (That takes, you know, stuff. )

But you're going to have to remember to spell things out for us, because we're not going to know your field. Taking the question from your example thread:
Quote:
i can't find the formula for this. can any body help me figure out how much 50x1.8mm tubing would it take to equal 4 inches of 38x4mm?
My best guess is that 38 is the exterior diameter (in mm) and 4 is the thickness of the tubing (also in mm). If that's so, then the volume of the glass in the latter case is
4 inches * (19^2 * pi mm^2 - 15^2 * pi mm^2) = 544pi mm^2 in
I'll leave the units as they are (rather than multiply out the pi and convert to cubic millimeters), since they'll cancel out this way.
The volume in the second case is
x * (25^2 * pi mm^2 - 23.2^2 * pi mm^2) = 86.76pi * x mm^2

Since you want the two to be the same,
544pi mm^2 in = 86.76pi * x mm^2
544 in = 86.76 * x
544 in / 86.76 = x
x = 6.27 inches

But if my assumptions are wrong (maybe 38 is the interior diameter?) then the answer won't be right.
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June 7th, 2009, 07:38 AM   #3
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Re: A glassblower joining a math forum...

Oh, and a quick approximation (good for large, thin tubes) is old length * old diameter * old thickness / new diameter / new thickness ? new length. In this case it would suggest about 6.7 inches. That way you can check your answer -- if the two come out very different, either you made a mistake on one or you're working with very fat tubing.
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