Talk:Helix

message: The article twice uses the phrase "A circular helix of radius a and slope a/b (or pitch 2πb)...". What is "slope" here? It's certainly not the slope angle, which is arctan(b/a), and "slope" is not defined elsewhere in the article.  — Preceding unsigned comment added by 137.22.164.34 (talk) 08:15, 25 April 2024 (UTC)
thread_title:  Meaning of "slope" 

message: "As a mental image of a helix one may take the spring (although the spring is not a curve, and so is technically not a helix, it does give a convenient mental picture)."  The idea that a spring is not a curve and not a helix needs to be clarified, especially in relation to http://en.wikipedia.org/wiki/Helical_spring.  —Preceding unsigned comment added by Blandwa (talk • contribs) 00:54, 5 February 2009 (UTC)
replies: text: I have the same complaint. See also Curve. Furthermore, I dislike the form of the opening paragraph; there is no need for parenthesis. I'll wait a few days and if nothing changes I'm going make a rewrite. --Trakon (talk) 20:36, 23 May 2009 (UTC)
thread_title:  No explanation why a spring is not a helix 

message: The article says "If the curve of the helix moves from the lower left to the upper right, then it is a right-handed helix." This seems to assume an imaginary "box" or a field-of-view, otherwise terms like "lower left" have no meaning. A helix would have to be oriented a certain way in this "box" before describing a lower-left. For example, if I view a right-handed spring from its side, such that its length is vertical, then the description is correct. (I don't want to be hasty in adding this clarification, because I'm not certain if I'm correctly interpreting the description. Someone please give a second opinion.) Viewing the same spring situated horizontally yields movement from upper-left to lower-right. Worse yet, if I view a spring facing the cross-section, then direction of movement can't be described with up/down/left/right. -KKL 16:18, 22 November 2006 (UTC)
thread_title:  Vague description of "handedness" 

message: The article mentions that a helix cannot be rotated or flipped to make it go in the other direction, but if a helix is viewed upside down, just this happens. A clockwise helix, when inverted, is a counterclockwise helix. --♦♦♦Vlmastra♦♦♦ (talk) 14:20, 25 April 2008 (UTC)
replies: text: Yes, that is right: looking on the helix from the -Z direction changes it from clockwise to counterclockwise. But that is not all: if the original helix was rising (that is getting closer to you) the same helix when viewed from -Z direction is descending (getting further away from you). TomyDuby (talk) 16:31, 22 June 2008 (UTC)
thread_title:  Chirality 

message: The article says that a helix is a three dimensional object, and gives a picture of a brick helix. But the helix is not a three dimensional object: it is a space curve. It is a one-dimensional submanifold of three-dimensional space. This discription is, to me, misleading. I intend to rewrite the introduction. If there are any objections and/or comments then please let me know by posting below. I shall wait seven days before making the edit. And please, I don't want any puerile, snotty replies like those that are so common on maths pages. I would like feedback to be polite, in good faith, and to be constructive. Declan Davis (talk) 18:15, 8 September 2008 (UTC)
replies: text: Go ahead. This page could do with some clean up. --Salix alba (talk) 22:13, 8 September 2008 (UTC)
thread_title:  Three dimensional object (?!) 

message: Attentive reading of Helix Nebula shows that the object gives the same impression as a helical structure could, but lacks any helical structure. Including  its image in the article was even more misleading than it would be to put a picture of cross-grained wood in the article cross, and it's now gone.--Jerzy•t 17:03, 16 July 2013 (UTC)
thread_title:  Helix Nebula is a nebula, but not a helix 

message: If you are a mathematician, you will be happy with the proposed notation. If you are a physicist, you will be induced to think that b has units of a velocity,
while a has units of distance. Then they are added as being of teh same type of physical quantity. This is not friendly. 
Perhaps using φ or any greek letter for an angle instead of t would make it better. 
— Preceding unsigned comment added by 137.138.78.118 (talk) 14:58, 25 March 2015 (UTC)
thread_title:  Comment on units 

message: There is a problem with the definition of "pitch". 
If, as said, "The pitch of a helix is the width of one complete helix turn, measured parallel to the axis of the helix." (which is the usual definition), then the pitch of the examples miss a factor 2 pi. 
For example, x(t) = cos(t), y(t) = sin(t), z(t) = t , have a period of 2 pi when projected on the xy-plane, so the distance of a complete turn measured along the z-axis must be 2 pi, rather than 1.
Sjoerd Rienstra, Netherlands  — Preceding unsigned comment added by 81.207.74.189 (talk) 08:57, 19 October 2015 (UTC)
thread_title:  Comment on pitch 

message: The article says this: "A double helix consists of two (typically congruent) helices with the same axis, differing by a translation along the axis."
I'm no mathematician, but I think this is not totally accurate. If you take two congruent helices with the same axis, and you translate one of them along that axis, then they will begin and end in different places—they'll be staggered along their length. But that's not what anyone's chief idea of a double helix looks like.
I think it would be more accurate to say something like, 'A double helix consists of two (typically congruent) helices sharing the same axis, with one helix rotated 180° about the axis.' To me, this would conjure more exactly an image of a typical double helix. 12.109.255.61 (talk) 22:54, 27 January 2023 (UTC)
replies: text: Good point.  A couple of quibbles.  In DNA the offset angle is not 180°. To a mathematician, a helix is endless, so there are no offset ends to worry about.  —Tamfang (talk) 23:42, 27 January 2023 (UTC)
thread_title:  Counterintuitive definition of "double helix"