Is this a reliable way to measure an arc

[camacru]

I have a brass rod with a 90 degree bend. I want to measure the outer and inner radii by placing a piece of string along both of them, and then straightening the string out to determine the linear measurement. Is this an accurate method?

[zgozvrm]

Reliable? Yes (depending on how well you keep the "string" on the line of the outer radius).

Accurate? No. At least not to the tolerances you stated in your previous post, if that's what you're getting at. But feel free to try. I'll bet you get a different measurement each time.

http://www.physicsforums.com/showpost.php?p=2411590&postcount=1

[camacru]

That's what I thought. What would be a more accurate method? I thought about using a graduated flexible curve...

[gmax137]

Why don't you measure the volume of the bent piece (say, by submerging it underwater in a big graduated cylinder). Then calculate the length of an unbent rod with the same volume.

Or, if you know the density, simply calculate the length of unbent rod that has the same weight as your bent piece.