# Talk:Belt problem

## Cleanup

I tripped over this article while browsing Wikipedia:WikiProject Mathematics/Current activity, so I started cleaning up the formatting, then realised that the worked solution was much too long and the expression for the belt length was not stated in its simplest terms, so I simplified it all, and added the corresponding expression for the "pulley problem" solution. But I can't find any references that show that "belt problem" or "pulley problem" are standard terms, and I am not convinced that Wikipedia needs an article on a couple of straightforward trigonometry exercises. So if someone were to nominate this article for deletion, I wouldn't object. Gandalf61 14:55, 14 May 2007 (UTC)

By the way, Both the image and formulae are wrong. The pulley is tangent to both circles, so you have a parralellogram somewhere. Sorry, i don't know how to edit it out. —Preceding unsigned comment added by 124.178.167.100 (talk) 07:00, 28 April 2008 (UTC)

Where would this parallelogram be? The diagrams are correct in my opinion. -download | sign! 01:48, 17 March 2009 (UTC)

## Deletion is unessecary

This article should not be subjected to deletion. It is not a trigonometry excersise, and it is used in real life. Acince this is an encyclopedia, it should include systems used in real life, and even if there arn't other problems realted to this anywherelse, it is used in real life, so there is no reason it should be deleted. Nate.h.e 23:11, 17 May 2007 (UTC)

## Math use

This article cleverly uses trigonometry and some algebra in an real life situation. Math professors or teachers could use it in their classes. Deleting this article would be unnecessary in my opinion as it would be like throwing away knowledge. —Preceding unsigned comment added by 67.42.81.121 (talk) 02:52, 24 March 2008 (UTC)

## Equation

Why is the font of "CO + DO + EO + FO + arcCD + arcEF" screwed up? MathCool10 Sign here! 04:20, 17 March 2009 (UTC)

I'm pretty sure it's a formatting problem. I'll look into it. -download | sign! 04:47, 17 March 2009 (UTC)
This article has pretty much gone out of my hands now. However, i am impressed in the way that the mathmaticians that have gone over this article have responded and edited. Please leave evreything how it currently is, but if there is a formatting problem try the [itex] prefrences stuff Assasin Joe talk 15:18, 17 March 2009 (UTC)
I've fixed the [itex] stuff. MC10 | Sign here! 20:42, 26 April 2009 (UTC)

## Correction of pulley problem

Hello,

I seem to have found a slightly different formula for pulley problem. The difference comes from, I think, an error when calculating the arc of the smaller circle. I have found that arc to be, in the terms of the article, 2 * phi (not 2* (pi-phi) as happens with the bigger circle. So factoring out the (pi-phi) factor in the last step is not possible, so the length of the belt in the pulley problem, should be:

2*P*sin(phi) + 2 [ (pi-phi)*R1 + phi R2) ]

Please verify, as it is possible that I have made a mistake, so if it is so, please correct me and if possible add a reference to a demonstration.

Thank you,

Marcelo Silva

Mgasilva (talk) 03:30, 22 January 2010 (UTC)

The pulley problem (where the belt does not cross itself) is dealt with in the second half of the article. The formula it gives for the belt length is:
${\displaystyle 2P\sin \left({\frac {\theta }{2}}\right)+r_{1}(2\pi -\theta )+r_{2}{\theta }\,,}$
where θ is the angle between the perpendiulars to the two straight parts of the belt. If we replace θ by 2φ we get
${\displaystyle 2P\sin(\phi )+2r_{1}(\pi -\phi )+2r_{2}\phi \,,}$
which is the formula you give above. So both you and the article are correct. Gandalf61 (talk) 12:13, 24 January 2012 (UTC)

--Gregkap (talk) 21:48, 30 July 2013 (UTC)

Changed the drawing because the tangents on the smaller circle were not perpendicular to the radius.

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