Talk:Torsion of a curve

Mathematical error?
Maybe i'm just unable to calculate it correct, but it seems that there is a mistake in the formulas for torsion. The first formula has the denominator $${\left\| {r' \times r} \right\|^2}$$, which is equal to $$\left({r' \times r}, {r' \times r}\right)$$ = $$\left(\left(y'z-z'y, z'x-x'z, x'y-y'x\right), \left(y'z-z'y, z'x-x'z, x'y-y'x\right)\right)$$ = $$\left(y'z-z'y\right)^2+\left(z'x-x'z\right)^2+\left(x'y-y'x\right)^2$$, which is obviously not equal to denominator of the second formula $$(x'^2+y'^2+z'^2)(x^2+y^2+z^2)$$. Penartur (talk) 22:46, 19 June 2011 (UTC)


 * I totally agree with this remark. The formula for the torsiune is wrong. As Penartur noticed, the denominator of the last expression is wrong. — Preceding unsigned comment added by Nico2011 (talk • contribs) 21:10, 2 January 2012 (UTC)

Animation not animated
I cannot see the animation moving. Is there something wrong with it or it is just me? I'm using firefox in a Debian wheezy box. Juliusllb 09:56, 20 November 2013 (UTC) — Preceding unsigned comment added by Juliusllb (talk • contribs)
 * For me it only plays when viewed at full size. — NuclearDuckie (talk) 14:45, 9 April 2014 (UTC)
 * Same for me. —DIV (120.17.85.139 (talk) 04:39, 22 June 2017 (UTC))

"any space curve with constant non-zero curvature and constant torsion is a helix"
Doesn't a helix require non-zero torsion as well, given that constant curvature with zero torsion is a plane curve? — Preceding unsigned comment added by 130.209.117.36 (talk) 16:07, 11 October 2015 (UTC)


 * You are right. I have fixed this. (A curve with constant curvature and zero torsion is a circle.) Arcfrk (talk) 08:09, 13 October 2015 (UTC)

Examples / illustrations
Besides the animation, I think it would be instructive to have static images with very simple curves rendered in colour with respectively their curvature and torsion (i.e. images would have to be paired). A suggestion would be a plane ellipse that is then shown projected/bent onto increasingly curved 'planes'. —DIV (120.17.85.139 (talk) 04:42, 22 June 2017 (UTC))

Are the "Definition" and "Alternative description" intended to be equivalent?
Are this article's "Definition" and "Alternative description" of torsion equivalent?

The article doesn't explicitly say they are, but it might be implied ("Then the torsion can be computed from ..."). I'm led to wonder because the Encyclopedia of Mathematics article "Differential geometry" gives a formula for torsion—



k _ {2} = \frac{( \mathbf r ^  \prime , \mathbf r  ^ {\prime\prime} , \mathbf r ^ {\prime\prime\prime} ) }{| \mathbf r  ^  \prime  \times \mathbf r  ^ {\prime\prime} | ^ {2} } $$

—that, apart from notation, seems the same as this article's "Alternative description"—


 * $$\tau = {{\left( {r' \times r} \right)\cdot r'} \over {\left\| {r' \times r''} \right\|^2}} \text{,}$$

—yet EoM shortly afterward states a version of the Frenet–Serret formulas in which the torsion $$k_2$$ seems to be the negative of the torsion $$\tau$$ known to this article's "Definition" section and to the Wikipedia article on Frenet–Serret formulas.

— 2d37 (talk) 01:25, 15 June 2020 (UTC)