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**bossk171****Member**- Registered: 2007-07-16
- Posts: 303

A catenary is the curve:

If you roll a parabola along the x-axis, the focus of the rolling parabola traces out a catenary. I read this a number of places, but I've yet been able to find, or create, a proof.

Can anyone help? Please?

*Last edited by bossk171 (2010-07-30 15:08:18)*

There are 10 types of people in the world, those who understand binary, those who don't, and those who can use induction.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,824

Hi bossk171;

I read that too and it is cited in at least 4 spots:

http://www.centralillinoiswoodturners.c … 20Form.pdf

http://www.pballew.net/arithme8.html#catenary

http://www.npr.org/templates/story/stor … Id=6434007

http://www-groups.dcs.st-and.ac.uk/~his … enary.html

I have been unable to find that proof.

According to this page,

http://webcache.googleusercontent.com/s … =firefox-a

Maxwell is the discoverer of the proof you are looking for!

Check this out!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,824

Hi;

http://translate.google.com/translate?h … 26prmd%3Db

This page here gives the differential equation for the all the conic sections, yours is on the bottom. The differential equation can used to derive the curve as the focus of the parabola rides on the x axis, it will be found to be a catenary. This derivation is a proof.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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**namealreadychosen****Member**- Registered: 2011-07-23
- Posts: 16

Is the shape of the streamlines formed by a swimming duck a catenary? Is the shape of a supposedly shatterproof (I have broken them) ruler being bent, each end pressed onto my fingertips, a catenary? I know that the shape of a chain held at both ends is a catenary.

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

hi bosk171

would this help?:http://www.proofwiki.org/wiki/Catenary#Proof

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Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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