Talk:Torque

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Contents 1 Symbols vs. Words 2 Introductory text 3 Torque and automobiles 4 Units 5 old units 6 A question about redirects 7 Sin/Cos 8 Sine/Cosine 9 To Sine or not Cosine, that is the question... 10 Confused with relationship bet. torque n speed. 11 Cross product vs. scalar multiplication 12 Proposed Phrase 13 Torque defined about a point not axis 14 Unit Repitition 15 No comments? 16 Proposed merge of torque & moment (physics) 17 Removed text

[edit] Symbols vs. Words

Wouldn't it be easier to use with other articles in physics it symbols (for power, torque and angular velocity) were used instead of their english language equivalents? I'm willing to change them -- but just want to make sure no one else has problems with this. Wilson Harron 02:26, 6 March 2006 (UTC)

Where at in particular? Tom Harrison ^Talk 02:30, 6 March 2006 (UTC)

In the section 'relationships between torque and power' Wilson Harron 00:08, 28 March 2006 (UTC)

[edit] Introductory text

Yo, how about putting the first paragraph in plain English, for us laymen? I took 2 years of physics, and I couldn't follow all that. Take a breath, man.

Better now? -- Tim Starling

Is torque normally written with the letter τ, by the way? I thought it was the letter N. -- []Cyp[]

Never seen that before. In most of physics, N is used for the total number of particles. Also, it's usually a bold τ, which unfortunately is not rendered correctly by our version of TeX. -- Tim Starling

You can use \boldsymbol{} to do bold greek letters for vectors. I've changed the article (please check for correctness), and I'll add the command to the Tex-markup help for reference. -- DrBob 16:01 Jan 28, 2003 (UTC)

I've written some opening remarks in what I hope will pass for English. Michael Hardy 18:52 Jan 28, 2003 (UTC)

Sorry, Michael H, it's not even close. You begin to go awry with "rotational motion," which could've used, say, a bit of parenthetical assistance, e.g. "rotational motion (one object's motion around another object)." But I don't see how you think you can get away with "This force is defined by linear force multiplied by a radius"...you really might as well toss the whole entry once you've gone over that cliff. 194.88.4.146 13:12, 12 January 2007 (UTC)Barry McPhee

[edit] Torque and automobiles

I looked up torque here to see what it means when discussing cars. There's only the briefest mention of cars here, right at the end - could someone who knows about it elaborate, perhaps? -- Joe Bryant 09:30 May 27, 2004 (UTC)

x2 It made my head hurt trying to understand that blob of science. Try this out : http://vettenet.org/torquehp.html -- GS, June 2006

[edit] Units

There is a lot about 'horsepower'. How about watts? It also describes converting power into torque. How can that be? Bobblewik  (talk) 22:06, 17 Apr 2005 (UTC)

Clarified the explanation in the article. Samw 22:11, 19 Apr 2005 (UTC)

Thank you. That is much clearer to me. Would a simple change of constant permit similar arithmetic to be used for a generic scientific conversion (i.e. with metric units)? Bobblewik  (talk) 10:38, 20 Apr 2005 (UTC)

Can you please clarify the question? Yes, simple change in constants typically will convert between different systems (e.g. metric and imperial). In this case, TorquexRPM happens to give power. However, different concepts in physics have different relationships. Samw 00:06, 21 Apr 2005 (UTC)

About half the article is non-metric only. If it is attempting to explain:

• generic points about physics, then I think such points should be made in metric units.
• calculations that work only in non-metric units, then perhaps there are logical flaws.

I don't understand it and can't convert it. Can you help me? Bobblewik  (talk) 11:00, 21 Apr 2005 (UTC)

In any units, power is proportional to torque times angular speed. In SI units, power equals torque times angular speed. Is that what you are asking? What are those SI units which can make the constant equal to one? Watts for power, of course, and newton-meters for torque. Now, how do you need to change those revolutions per second in the formula on the article page to make the 2π disappear?

These aren't "generic points"—the original reason for inclusion here was to explain particular system-dependent calculations. Gene Nygaard 15:22, 21 Apr 2005 (UTC)

The reader's always right . . . so I took another stab at clarifying. We may need a professional tech writer here. :-) Samw 21:44, 21 Apr 2005 (UTC)

Can anyone explain to me why a tutorial on unit conversion is meaningful in the context of the article? I dont see it as being contextually siginificant to this specific article. My suggestion is that a Unit Conversion article be linked here, and either the specific tutorial moved there or deleted. Chobi 19:15, 24 December 2005 (UTC)

Torque and power are related physical quantities. Power = torque times angular speed (tau times omega)...In SI torque is in N*m, ang. speed is in rad (not unit)/s so its in 1/seconds. Therefore, torque is in N*m/s, which reduces to (N*m)/(s). Since newtons time meters can be taken as a dot product and produce the scalar quantity work (in J), we get power in J/s. Work per unit time is the definition of power, so a W (SI unit for power) is just a joule/second, which is metrically equivalent to torque times angular speed.

Unit conversion is one of the ways new concepts are introduced, as framing a "new" unit in terms of existing ones often help learners see the manipulations that the old concepts have undergone. In this case, it shows the relationship of torque to force (linear analogy) and the relationship to power, work and other scalar quantities.

In my opinion, we should do it in ALL METRIC units. SI = easy to understand, especially for a science article.

Ed-it 23:59, 16 November 2006 (UTC)

[edit] old units

Sam said that torque is lbf·ft, not ft·lbf The sequence force·distance is used almost without exception in metric units, so that is a parallel. I am aware not aware of any reason for the sequence. The BIPM seems to have a consistent sequence for units but I am not sure what the guideline is. Do we have any statistics on how often the foot unit is first or second? Google comes up with many for either sequence. Perhaps it doesn't really matter. I don't mind either way. Bobblewik  (talk) 17:22, 27 Apr 2005 (UTC)

The sequence distance-force was common in the old metric "meter-kilograms" and "centimeter-kilograms", more common than "kilogram-meters", the order common for energy. (I have a torque wrench in "meter kilograms", for example.) Google can find several of them as well.

Both "pound-feet" (lbf·ft) and "foot-pounds" (ft·lbf) are in common use, as you discovered. Some experts and style guides recommend the former to distinguish the units of torque from the units of energy/work, a different quantity. See this, for example. But there is much less of a sense of generally accepted rules for the English units (or for the old metric units, for that matter) than there is with SI. Gene Nygaard 17:44, 27 Apr 2005 (UTC)

I've written this up under units. Thanks for the good questions! Samw 21:59, 27 Apr 2005 (UTC)

Your link was bogus. Neither it nor anything else on the BIPM site says anything about the units of torque.

Futhermore, there are sources recommending pound-feet rather than foot-pounds going back to before SI ever existed. So your chronology was wrong there, too. Gene Nygaard 22:30, 27 Apr 2005 (UTC)

Sorry, I didn't notice the second table on that page. Of course, they call it moment of force there, ratrher than torque—do you take that as prescriptive as well?

Here's what they say:

"A derived unit can often be expressed in different ways by combining the names of base units with special names for derived units. This, however, is an algebraic freedom to be governed by common-sense physical considerations. Joule, for example, may formally be written newton metre, or even kilogram metre squared per second squared, but in a given situation some forms may be more helpful than others.

"In practice, with certain quantities preference is given to the use of certain special unit names, or combinations of unit names, in order to facilitate the distinction between different quantities having the same dimension. For example, the SI unit of frequency is designated the hertz, rather than the reciprocal second, and the SI unit of angular velocity is designated the radian per second rather than the reciprocal second (in this case retaining the word radian emphasizes that angular velocity is equal to 2pi times the rotational frequency). Similarly the SI unit of moment of force is designated the newton metre rather than the joule."

So we can probably add something along those lines in the first paragraph of that subsection.

Now let's deal with the silly notion that the order of terms in English units should be determined by the order of terms in SI units. That's nonsense.

As I pointed out above, and as you can determine for yourself by searching the internet with your favorite search engine, when kilograms-force are used, the "meter-kilogams" order is more common than the "kilogram-meters" order (perhaps in part due to he tendency of people to be sloppy in the separation of their units of measure, as can be seen on all the Wikipedia pages still using "Nm" as a symbol for newton-meters, and due to the fact that before SI, "gm" was an acceptable symbol for grams, there would be ambiguity that would need to be resolved if kilogram-meters were used. Is "kgm" the symbol for kilograms, or for kilograms multiplied by meters&that's the question people would have to ask.

As I claimed above, the idea that we should distinguish the English units of torque from the English units of energy and work far predates the International System of Units, which was only introduced in 1960. I have found a clear example:

A.M. Worthington, Dynamics of Rotation: An Elementary Introduction of Rigid Dynamics, London, New York, Bombay, Calcutta, and Madras: Longmans, Green, and Co., 1920., p. 9.

"British Absolute Unit of Torque.–Since in the British absolute system, in which the lb. is chosen as the unit of mass, the foot as unit of length, and the second as unit of time, the unit of force is the poundal, it is reasonable and is agreed that the British absolute unit of torque shall be that of a poundal acting at a distance of 1 foot, or (what is the same thing, as regards turning) a couple of which the force is one poundal and the arm one foot. This we shall call a poundal-foot, thereby distinguishing it from the foot-poundal, which is the British absolute unit of work.

"Gravitation or Engineer’s British Unit of Torque.–In the Gravitation or Engineer’s system in this country, which starts with the foot and second as units of length and time, and the pound pull (i.e. the earth’s pull on the standard lb.) as unit of force, the unit of torque is that of a couple of which each force is 1 pound and the arm 1 foot. This may be called the ‘pound-foot.’"

Nonetheless, there is no clear standard for English units today.

BTW, Worthington, who named the "slug" as a unit of mass in an earlier (1904) edition of this book (which may well have contained much of the same information about torque), also had another bright idea:

"In the interests of clear teaching, the convention (which I am glad to see has been adopted in America) has been adhered to throughout, of using the word ‘pound’ when a force is meant, and ‘lb.’ when a mass is meant, and I have ventured to give the name of a ‘slug’ to the British Engineer’s Unit of Mass, i.e. to the mass in which an acceleration of one foot-per-sec.-per-sec. is produced by a force of one pound.'

It's easy enough to see why that idea didn't catch on. The people who use the mass units would like to have both a spelled out word and a symbol for them, as would the people who use the force units (and, of course, those are often the same people). Gene Nygaard 23:05, 27 Apr 2005 (UTC)

Thanks for the great examples. Of course it was silly of me to assume imperial conventions come from SI. However, I stand by my assertion that lbf-ft predominates over ft-lbf for whatever reason and I suspect that's why SI adopted N-m. See googlefight: http://www.googlefight.com/index.php?lang=en_GB&word1=%22lbf-ft%22+torque&word2=%22ft-lbf%22+torque How can we writeup this factoid? Samw 00:01, 28 Apr 2005 (UTC)

I think that if you looked into it carefully, you would find significant differences in usage in different fields of activities, geography, etc. More a matter of degree than of uniform usage in any particular domain.

It is my impression that when it comes to automobile engine torque, the foot first versions predominate, pretty much everywhere (even as ft-libras and the like). But you will find variations among different manufacturers, variations among different magazine editors, etc., and in large groups little consistency at all. On Wikipedia, ft·lbf clearly predominates over lbf·ft in this context, but that is probably still true but not so overwhelming outside Wikipedia.

I think the feet first is even more predominant when it comes to torque wrenches, and specificantions in shop manuals and installation instrucions and the like, for how much torque to apply to bolts. Gene Nygaard 01:25, 28 Apr 2005 (UTC)

[edit] A question about redirects

I noticed the following question at User talk:Sfoskett.

• When I copied the information from the LT4 page, I assumed "ft.lbf" was a typo, but I see now that it's actually a pretty common way of abbreviating "foot-pounds". It would be somewhat difficult for someone who knew little of US units to figure this out, since no search on Wikipedia ("ft·lbf", "ft.lbf", "ft lbf", and so on) will actually get you to the foot-pound page. Do you think it would make sense to put a redirect in from ft·lbf to Foot-pound and possibly link it (sparsely or at least initially) in articles? I'm somewhat new here and not sure that it's a valid use for redirects, but I think it would be useful. —HorsePunchKid→龜 23:13, 2005 Jun 16 (UTC)

I thought that people here might have something to say about it. Bobblewik  (talk) 12:42, 20 Jun 2005 (UTC)

I added Wikilinks for ft·lbf and ft.lbf going to Foot-pound. We ought to linkify the first instance of this unit anyway, since it's unfamiliar to many. --SFoskett 13:00, Jun 20, 2005 (UTC)

[edit] Sin/Cos

Can someone please verify that this is the correct formula for the magnitude of torque: An anon keeps changing it to sin instead of cos... --SFoskett 17:05, July 18, 2005 (UTC)

I had been wondering about that, but I hadn't really cared enough to work it out until you mentioned it, mainly because I figured it would depend on exactly how the problem is phrased. The cosine version is correct as the problem is stated. Give me a few minutes here, and I'll have a better diagram. —HorsePunchKid→龜 19:46, July 18, 2005 (UTC)

Well, there's a diagram. Not my best work, but if you think it might help clarify the formula, we can find a place in the article for it. —HorsePunchKid→龜 20:08, July 18, 2005 (UTC)

[edit] Sine/Cosine

Here's a little blurb to lay the sine/cosine issue to rest:

First of all, the cosine term in the definition of torque listed on this page is NOT correct. Torque is a result of a vector cross product, that is:

T = r x F

The definition of a cross product in scalar form is the following:

T = (r)(F)[sin(theta)]

Theta is the angle between 'r' and 'F'; while the diagram on the page is correct in stating that the side in question is (F)[cos(theta)], that is not the correct quantity to use when determining torque. The REAL definition is above, and a proof is located in Analytical Mechanics: Sixth Edition by Grant Fowles and George Cassiday, on pages 15-16. In order to use the angle theta as defined in the picture, the correct equation would have to be:

T = (r) (F) {[1-((cos^2)(90-theta))]^(1/2)}

This is true for all cross products. The angle in question is ALWAYS the angle between the two vectors. The presence of a cosine term in the multiplication of two vectors implies a dot product, rather than a cross product.

FYI, the 'Anon' making the edits has a BA in Physics from the University of Maine, and I'm not too far behind; I'm currently finishing up my senior year in Physics at UMaine.

SirMink, 25 July 2005, 09:00 EST.

[edit] To Sine or not Cosine, that is the question...

After being the 'Anon' following this page, I have decided to make myself known.

Torque can be confusing and complicated. The definition is given as a foreign thing called a "cross product", which can easily be confused with simple multiplication because of the symbols invovled. The basic equation of a cross product is:

C = A B = ABsinθ

For a more in-depth discussion on cross products, see cross product

While it is correct to say that the side labeled as '(F)cosθ ' is of that magnitude with the angle defined as it is, the angle cannont be defined as it is because that is not the definition of a cross product. Rather, the angle is defined for us as the angle made by the two vectors (in general, the angle between vectors A and B).

The only reason that I have for putting up this fight over something that seems so trivial is that, as a physicist, I like to see physics things done correctly, to avoid confusion on the part of all people reading the article, from high school students reading this for a refresher before a test, to non-science people searching to expand their knowledge base.

k of slinky
B.A. physics
UMaine- Class of 2005
25 July 2005

Sorry, I'm at work at the moment and don't have time to go over your post in detail, though I certainly will when I've got a moment. Here's my reasoning for using the cosine.

1. The magnitude of the torque (no vector quantities here) is simply the magnitude of the force (at a perpendicular to the lever arm) times the length of the lever arm.
2. The magnitude of the force, that is, the component of the force in the direction perpendicular to the lever arm, is (in this particular problem), the cosine of |F|.
3. Put it all together, and you get Tq=(|F|⋅cos θ)⋅|r|. (Argh... I really do need to learn how to use those <math> tags sometime.)

Does that make sense? —HorsePunchKid→龜 18:08, July 25, 2005 (UTC)

I understand your reasoning for using the cosine now that you have explained it better. However, you are still misleading the reader with the way it is stated right now. If you are going to use this arguement, you should include this in your section, and remove the statement "from the definition of cross product", as you are not using the definition of cross products, but the definition of torque. Otherwise, the sine arguement is the correct one, and the phrase "from the definition of cross product" can remain. Also, if you use the cosine arguement, you need to state that the term Fcosθ is true only for this situation, as situations occur where sine is the appropriate term.

It may be more appropriate, also, to call the angle another name rather than θ, such as α. θ is used to denote the angle between r and F, and is generally the angle given in problems, rather than the angle from the perpendicular.

Does this make sense?

k of slinky
25 July 2005

I agree with "k of slinky", it makes much more sense to use the angle subtended between the force and the radius vectors. -- Tim Starling 01:16, July 27, 2005 (UTC)

For those having trouble with these sorts of trig issues, try defining your axis system so that the X-axis lies along the moment arm. This elimiates one of the components of the moment vector (since the component of the foce along the new x-axis produces no moment), and makes evaluation of the cross product simpler. —The preceding unsigned comment was added by 131.202.212.37 (talk) 03:25, 20 March 2007 (UTC).

[edit] Confused with relationship bet. torque n speed.

Well, this may sound lik a foolish question for some of u, but please clarify my doubt.

If torque is da driving force, then increasin it shld(according to me) increase the speed. But how come the charactersitics of many motors exhibit a inverse relation to that, i.e how come torque is inversely proportional to speed.....

[edit] Cross product vs. scalar multiplication

I find it very confusing that the same symbol is used for both cross product and multiplication of two scalars, as in . I've never seen this symbol used for multiplication (except maybe in elementary school). Usually, the product of two scalars and is written as or simply .

The problem could be that the symbol is called \times in TeX, and someone took this too literally?

You get confused too easily. Why is it okay to use the dot for scalar multiplication but not the cross? Wouldn't you instead get confused with the dot product?

[edit] Proposed Phrase

"Do as I torque, not as I talk!"

"Do as I do, not as I say!".

[edit] Torque defined about a point not axis

The definition of angular momentum and torque on their respective pages must be consistent. Angular momentum is defined about a point with r x p and r being the distance from the point; torque is defined about an axis with r x F and r being the distance from the axis. Someone please change the torque definition. I've only just come across defining angular quantities about a point for the first time so I wouldn't feel happy making the changes myself.

[edit] Unit Repitition

In the intro paragraph, the article says "The SI units for Torque are newton metres," and then in the "Units" section, it says "Torque has dimensions of force times distance and the SI units of torque are stated as "newton-metres"."

That just seemed very repititious to me, especially so close together. Thoughts?Steevven1 14:41, 19 November 2006 (UTC)

[edit] No comments?

Why does the infobox at the top of this talk page say "This article has been rated but has no comments" when there are clearly many comments?Steevven1 14:41, 19 November 2006 (UTC)

[edit] Proposed merge of torque & moment (physics)

• support - they're the same thing. --Matthew 22:01, 7 January 2007 (UTC)
• Oppose merger, unless it is in opposite direction, with the merger to the Torque article. According to Wikipedia:Naming conventions, it should be at the most common name in English. Furthermore, they are not the same. If the articles are not merged, Moment (physics) should be moved to Moment of force for disambiguation purposes. And, why in the hell is Moment of force a redlink now anyway? There are other "moments" such as moment of inertia. Gene Nygaard 10:01, 28 January 2007 (UTC)
• Oppose - there's still some historical differences that could be explored in different articles. James.Spudeman 23:35, 6 February 2007 (UTC)
• Oppose. The context in which torque and moment are used is quite different. Torque is used when calculating the mechanics of a shaft. Moment is used in statics, e.g. there is a moment in the cantilever beam due to a force on the end of the beam. I think the difference relates to long axis vs. short axis-- or obvious rotational axis vs. non-obvious axis. A few other opinions are here-- they also dispute that they are the same. Nephron  T|C 19:11, 16 February 2007 (UTC)
• Oppose - There are some differences between torque and moment (physics).Tekin  T|C 10:50, 28 February 2007 (UTC)
• Oppose. Moment and Torque are not the same. Verkhovensky 21:44, 12 March 2007 (UTC)
• Oppose. Moment is used in several other physics categories, not just torque. For instance, nuclear or dipole moments in spectroscopy. Even though these are entries on their own, I would vote for a disambiguation of "moment" before a merger with torque.--Theoriste 00:18, 28 March 2007 (UTC)

[edit] Removed text

I removed the following recently added text:

In the motor sports community it is a widely held misconception that the torque rating of a motor is an indication of how rapidly it will be able to accelerate a vehicle. Acceleration is work, and as such requires the application of force over distance (the definition of power). Horsepower or watts provide the indication of the power-producing capability of a motor.

First, acceleration is not work and force over distance is not the definition of power (it is the definition of work) and second, while horsepower is important for top speed, it is torque that determines acceleration. Consider the case of an electric powered vehicle at rest. At the moment that the vehicle begins to accelerate, the horsepower generated by the motor (no matter how powerful it is) is exactly zero. Alfred Centauri 02:41, 2 March 2007 (UTC)