Talk:Helix

Meaning of "slope"

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)

No explanation why a spring is not a helix

"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)

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)

Vague description of "handedness"

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)

Isn't the picture of the plant labelled incorrectly. It says right handed, but it is a left handed helix? — Preceding unsigned comment added by 86.186.35.35 (talk) 20:23, 12 May 2013 (UTC)

Chirality

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)

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)

Three dimensional object (?!)

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)

Go ahead. This page could do with some clean up. --Salix alba (talk) 22:13, 8 September 2008 (UTC)

Length of a helix

There's a formula for the length, but I can't work out what it is saying. I'm trying to find the length of wire needed to make a helix given I know the diameter, spacing between turns, and the number of turns. Drkirkby (talk) 11:22, 9 June 2012 (UTC)

Consider cutting a cylinder so that it flattens into a rectangle. Each coil of a helix becomes a diagonal of a rectangle whose width is the circumference of the cylinder and whose height is the coil spacing (i.e. the distance between centers of the wire). Remember that the diameter of the cylinder, for this purpose, includes a half-thickness of the wire. —Tamfang (talk) 16:19, 9 June 2012 (UTC)

I agree it has not been written that clearly in the article. The formula for length is $T\cdot {\sqrt {a^{2}+b^{2}}}$ where T is angle you go round the helix, expressed in radians, so one complete rotation would be T=2π. a is the radius of the helix and the pitch is 2πb, ie it goes up 2πb in one rotation.--Salix (talk): 18:31, 9 June 2012 (UTC)

I am confused by this section on the equation for a helix.

1) $t\mapsto (a\cos t,a\sin t,bt),t\in [0,T]$

2) equals $T\cdot {\sqrt {a^{2}+b^{2}}}$

is line 1 equal to line 2? Like so?

$t\mapsto (a\cos t,a\sin t,bt),t\in [0,T]=T\cdot {\sqrt {a^{2}+b^{2}}}$

It seems like nonsense, but this is not my field so I could be wrong. What should it say?155.99.105.209 (talk) 02:25, 29 October 2013 (UTC) ~¥agoth

I think you know how to figure out the length by what you wrote, but if not, I'll assist. Take one complete rotation and unwrap it to form a right triangle. The hypotenuse would be the helix and the bottom side the circumference, the height being the pitch.Thomas_Blankenhorn (talk) 03:25, 21 December 2013 (UTC)

Helix Nebula is a nebula, but not a helix

   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)

Comment on units

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)

Comment on pitch

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)

Counterintuitive definition of "double helix"

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)

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)

Spiral

In December 2023 there was a bit of backing and forthing about including "spiral" in the lead. I believe that spiral, since it also (even principally?) describes a flat curve, more like the mainspring of a clock than an artillery worm or corkscrew, is too equivocal to be useful in defining "helix". Just plain Bill (talk) 16:47, 18 April 2024 (UTC)

Most recent chronology:

• Just plain Bill's "A helix is a shape like a cylindrical coil spring or a screw thread" edit included the superfluous mention of cylindrical, since all coil springs are cylindrical; "screw thread" complicates the issue since not all are helical.
• My "A helix is a shape like a coil spring or cylindrical screw" edit included cylindical screw to specify – for the benefit of readers who don't click the link – the relevant type of screw differs from nine non-cylindrical types of screws as they're defined in an ordinary dictionary.
• Just plain Bill's "A helix is a shape like a coil spring or corkscrew" edit reverts to the original problem, i.e., a corkscrew is a composite tool with three types of business ends: spiral, prong, or bolt. It's equivocal to say a helix is a shape of a corkscrew, but it's fair to say – in some manner of encyclopediac phrasing – it's like the business end of a regular the most common form of a corkscrew. The most recent edit doesn't specifiy the relevant part of corkscrew.

The December 2023 back-and-forth edits about "spiral" was limited to the mention of spiral staircase, which led to an editor's complaint that "the link is misleading, as there is a clear difference between a helix and a spiral".

Yet, it's well established that (1) a helix is something spiral in form, such as an ornamental volute or a coil formed by winding wire around a uniform tube, and that (2) the worm of a common corkscrew is called a spiral.

So, I'm reinserting (but changing the link re) "the spiral of a corkscrew" in deference to whomever it was that first added corkscrew as a visual referent. I'd be happy with just plain "A helix is a shape like a cylindrical coil spring or a screw." Kent Dominic·(talk) 16:08, 21 April 2024 (UTC)

A claim that "all coil springs are cylindrical" is ill informed. Anyone who has ever paid attention while changing the cells in a common flashlight knows otherwise; also see the pictures near the top of Wikipedia's coil spring article.

A cork puller with prongs is not a corkscrew. Not sure what Kent means by a "bolt" in this context, but imagine it would serve well as a cork destroyer.

I have added a picture of a no-frills corkscrew, hoping that helps. Just plain Bill (talk) 19:35, 21 April 2024 (UTC)

A claim that '"all coil springs are cylindrical" is ill informed" is unenlightened and a moot point re the article since the editor who interpolated it (not to mention the one who grudgingly attempted to emend its usage) ultimately deleted it.

NOTE: For edification's sake, however, the -al suffix doesn't connote being a cylinder. A true logophile knows it connotes relating to a cylinder.

Indeed a cork puller with prongs doesn't have a screw, which is another moot point since corkpuller is nowhere mentioned in the article nor otherwise in this thread except as initially interpolated in the manner that prompted this reply.

NOTE: For edification's sake, however, people regularly refer to a cork puller as a corkscrew despite its absence of a screw. Anyone who doesn't like it should consider deleting this section from the corkscrew article. The matter doesn't rise to a level of bother for my interests.

The picture does help. The '"screw" part' verbiage is unencylopediac phrasing. It's a spiral. (And, it's cylindrical, but not a cylinder.) Yet, that point, too, is mooted by the following misgiving...

I resisted changing it back to "spiral of a corkscrew," whose phrasing is an improvement but I'll quickly admit my ongoing reservations about keeping "corkscrew" in the lede. Meticulo added it on 18 January 2020 saying the text should be accessible & to avoid difficult-to-understand terminology. "Corkscrew" accomplishes that aim, but I'm not convinced likening a helix to a corkscrew spiral is entirely accurate.

Also, I'm walking back my being happy with just plain "A helix is a shape like a cylindrical coil spring or a screw" suggestion. Instead, it should be: "A helix is a shape like the cylindrical part of coil spring or a machine screw." (Just plain "screw", including wood screws, is open to the same criticsm that '"the screw part/spiral of a corkscrew" invites.)

(l-r) Tension, compression and torsion coil springs

A machine screw in macro view

Kent Dominic·(talk) 05:20, 22 April 2024 (UTC)