Circle vs. Square edge problem

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Discussion Overview

The discussion revolves around a problem involving the bending of a pipe and the measurements taken to determine the radius of the bend. Participants explore the relationship between the lengths measured from the pipe's ends to the back of the bend and how these relate to the overall length of the pipe after bending. The focus is on deriving a formula to calculate the radius based on these measurements.

Discussion Character

  • Exploratory
  • Mathematical reasoning

Main Points Raised

  • One participant describes a scenario involving a 20-inch long pipe bent at a 90-degree angle, measuring lengths of 9 inches and 13.555 inches from the back of the pipe to the ends of each leg.
  • Another participant suggests a formula to calculate the radius based on the provided lengths, emphasizing the importance of measuring to the middle of the bend rather than the inside or outside edges.
  • A participant expresses confusion about the term "orthogonal" and clarifies their measurement method, indicating difficulty in accurately determining the start of the bend.
  • Further clarification is provided regarding the need to adjust measurements by accounting for the pipe's diameter.
  • One participant attempts to verify their algebraic manipulation of the proposed formula and seeks confirmation of its correctness.
  • Another participant acknowledges the algebra appears correct but notes that the calculated radius pertains to the middle of the pipe rather than the inner corner.

Areas of Agreement / Disagreement

Participants generally agree on the approach to calculating the radius, but there is some uncertainty regarding the measurements and the implications of the formula. No consensus is reached on the clarity of the measurement process or the terminology used.

Contextual Notes

There are limitations regarding the accuracy of the measurements due to the difficulty in determining the exact start of the bend and the need to account for the pipe's diameter in calculations.

ISX
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I got a problem that I need to figure out. I have a piece of pipe 20 inches long and I bend it on a radius at 90 degrees. I measure from the back of the pipe to the end of one side and get 9, I flip it the other way and do the same thing and get 13.555. If you add those you end up with a right angle vs radius' gain of 2.555 inches. Now the 90* bend is only on part of the pipe as the rest is straight. Is there any way to figure the radius based on just what I said? This isn't homework it's just something I have been working on for a few weeks that is puzzling me like crazy. Thanks.
 
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I think I know what you are asking, so, here is something.

First, I am not sure where you are measuring the 9 and 13.555 lengths from/to...it is not clear to me...

But, let's say that you have a 20" long pipe and that when you bend it, the length along the middle of the pipe remains the same.

Then, let's say that you measure the length of the pipe from one end of it to the middle of the 90 degree portion...in other words, you do not measure from one end to the inside of the corner, nor from one end to the outside of the corner...instead, you measure from one end to the middle of the orthogonal 'branch'

Then, I think that having those two lengths, you can calculate the radius to the middle of the corner by:

(x1 - r) + (x2 - r) + 2.pi.r/4 = pipe-length

where x1 and x2 are the two measurements and we take off r to just get the straight portions...then, we add the corner back on (just once)...this should add up to the original length assuming you did not stretch/compress the pipe during bending.
 
I have no idea what orthogonal means. If it means measuring to the start of the bend then that's kinda hard because there is about an inch in a real world scenario where the start of it could be so I can't do that accurately. My measurements were if you bent that pipe at a 90* and had it laying on the ground, but rolled it 90* so that one leg came straight up in the air, you would measure from the ground (back of the pipe) to the end of the leg sticking up. Then you would flip it the other way to measure the other leg.
 
o.k., so you are measuring to the 'back' of the corner...go ahead and take off half the diameter of the pipe from those measurements and apply the equation I have provided.
 
Can you let me know if I did this right.
x1-r+x2-r+(2pir/4)=pl
x1+x2-2r+(6.28r/4)=pl
x1+x2-2r+1.57r=pl
x1+x2-.43r=pl
x1+x2-pl=.43r
(x1+x2-pl)/.43=r

Is that right? I'm not the greatest at algebra.
 
it looks o.k.

just keep in mind that the r calculated this way will also be the radius of the corner but to the middle of the pipe, not to the inside of the corner.
 
Yeah that's really what I needed to find, not the inside or outside radius. Thanks for your help!
 

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