Talk:Torque/Archive 1

Archive 1

Archive 2

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)

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)

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 $\times$ B = ABsin$\theta$

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

While it is correct to say that the side labeled as '(F)cos$\theta$ ' 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 Fcos$\theta$ 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 $\theta$, such as $\alpha$. $\theta$ 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).

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.....

I'm not too familiar with that... here's my bet though. ENGINE speed should increase with torque, but not necessarily the vehicle speed. In a common 5-speed transmission, at higher speeds you use upper gears, which necessarily have less torque. —The preceding unsigned comment was added by 204.220.135.214 (talk) 14:59, 5 April 2007 (UTC).

Torque .GIF

Is that .gif accurate? Taking a close look, it seems as if certain frames are incorrect.--74.120.72.234 00:34, 26 June 2007 (UTC)

You mean the animated gif? What is wrong with it? —Yawe 21:15, 3 July 2007 (UTC)

picture with wrench

I removed the picture with the wrench. It had the torque incorrectly labeled. We don't want to give people the idea that the torque is some weird curvy vector in the plane of the force. —Preceding unsigned comment added by 128.103.54.122 (talk) 15:15, 2 November 2007 (UTC)

I don't think very many people would come up with "some weird curvy vector in the plane of the force". How else would you show torque? The curve shows the torque's tendency to rotate the object. 99.240.243.25 (talk) 00:16, 22 November 2007 (UTC)

Translation

Check the translations in other languages. I think there is at least a mistake in the french one. --151.21.85.177 18:55, 12 September 2007 (UTC) Torque seems to have a lot of very diverse meanings in many applications. Some of these applications invite [countertorque] as the inversion of this property. Does torque have a mathematically opposite half?--Lbeben (talk) 05:02, 6 December 2007 (UTC)

Change in the "Relationship between torque, power and energy" section.

i've changed the section "Relationship between torque, power and energy" Power is just not the product of torque and angular velocity as was mentioned a little bluntly. it is the product of the torque and the change in the angular velocity produced due to its application. a rotor may have been rotating at about 1000 rpm before being applied with a torque of 50N-m. the resultant rpm (say 1200 and the corresponding angular velocity 1200*2pi/60) CANNOT be used to find the power transmitted to that rotor. —Preceding unsigned comment added by Sganesh 88 (talk • contribs) 13:51, 1 February 2008 (UTC)

Power is just the product of torque and angular velocity (or of force and linear velocity). The torque is doing work even if the angular velocity does not change (e.g. if something is applying an equal torque in the opposite direction), and the work per unit time (power) depends only on the distance traveled per unit time (velocity) - not on whether the velocity is increasing or decreasing across that distance. I took the liberty of undoing the above change, and adding a different clarification. --Yawe (talk) 23:00, 19 February 2008 (UTC)

Helicopters

Several aviation related articles link to this article in the context of the torque acting on the main body of a helicopter caused by the rotation of the engine driven main rotor(s). It seems to me that someone reading about helicopters might be confused by being directed to a highly technical physics page. Perhaps a page should be started about torque as it aplies to aviation. Thoughts? —Preceding unsigned comment added by 24.22.24.208 (talk) 05:05, 17 February 2008 (UTC)

People also speak of torque as one of the causes of the left turning tendency of prop planes. But really I don't think a special page is necessary.24.21.101.33 (talk) 07:48, 25 March 2008 (UTC)

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)

The argument is in general pointless; you can successfully argue that either torque or horsepower determine acceleration. The fact is that with a rotational system providing energy that is translated into linear motion, torque and power are functions of the other; increase one, and you increase the other by the same amount on a percentage basis.

Then you get the arguments about where you want to be on the powerband for maximum acceleration. For a given gear ratio, maximum acceleration is at peak torque, which also maximizes P/v. For a given speed, choose the gear ratio that places you at maximum power. This also maximizes torque at the wheel.

That being said, any sort of power vs. torque discussion probably doesn't belong on Wikipedia. It's a physics system of equations problem that just confuses those who don't have a fairly decent grasp on physics. Marimvibe 20:21, 22 April 2007 (UTC)

Given a constant torque, the angular acceleration is constant (assuming the moment of inertia is constant). Yet, the power can be negative, positive or even (instantaneously) zero. Thus, I dispute that one can successfully argue that power determines acceleration. Alfred Centauri 21:27, 22 April 2007 (UTC)

Power=Torque X Angular Speed for a rotating system. It's a fact. See: Torque#Relationship_between_torque.2C_power_and_energy for reference. The two are inseperable. In fact, it's easier to calculate acceleration from power than from torque at a given speed, as Force=Power/Velocity, whereas going from torque you need to go through two gear ratios and the moment arm on the tire to obtain the force on the vehicle. Marimvibe 23:34, 22 April 2007 (UTC)

That $P=\tau *\omega$ is well known and further, irrelevant to what I've said above. Don't you understand this? Ask yourself the following question: If all I know is torque and moment of inertia, can I find the angular acceleration? Answer: yes. Follow-up question: If all you know is the power and moment of inertia, can you find the angular acceleration? Answer: no. One must also know the angular speed. But, what is angular speed? That's right, it's the time integral of angular acceleration. But wait, if power is proportional to the time integral of acceleration, then power cannot be used to determine acceleration without the history of the acceleration being known. Don't you see this? Alfred Centauri 00:00, 23 April 2007 (UTC)

If you know torque and rotational speed, you know power, and vice versa. They define each other. Good luck trying to do anything involving conservation of energy with only torque. In any case, your argument doesn't even speak to the section that was removed. As far as whether a car with high horsepower or high torque will be quicker, the car with high horsepower will be quicker, assuming independant gearing for each car. It just won't be as driveable, seeing as how the engine will need to be operated at a higher speed. For example, compare the RX-8 to a '99-'02 Cougar (own one, don't need to look up stats for it.) Both weigh about 3050 lbs. The Cougar produces 165 ft-lb, the RX-8 160. But the RX-8 has 230hp, the Cougar 170hp, about 35% more. And the Cougar takes ~8 seconds to get to 60, the RX-8 ~6, ~33% quicker. Same weight, slightly less torque, ~30% more power, ~30% quicker. So what's more important? Marimvibe 02:29, 23 April 2007 (UTC)

My friend, your statement that "[power and torque] define each other" is nonsense. The rotational speed is not a proportionality constant. If there is a torque, then there is an angular acceleration and if there is an angular acceleration, the angular speed is changing with time. What you have here is a differential equation, not a definition. To see this, consider what I said above in the language of the calculus instead of words:

$\alpha (t)={\frac {\tau (t)}{I}}$

$P(t)=\tau (t)\omega (t)=I\alpha (t)\left(\int _{0}^{t}\alpha (r)\,dr+\omega (0)\right)=\tau (t)\left(\int _{0}^{t}{\frac {\tau (r)}{I}}\,dr+\omega (0)\right)$

Any person reasonably familiar with calculus based physics will agree with the above equations which together say:

(1) At any instant, angular acceleration is proportional to torque and

(2) At any instant, angular acceleration is not proportional to power.

Finally, your statement "Good luck trying to do anything involving conservation of energy with only torque" seems strangely out of context and, more importantly, seems to contradict the very point you keep insisting on. For if, as you claim, power and torque define each other, why would a conservation of energy problem be more difficult with just torque? Please think about that ... Alfred Centauri 04:03, 23 April 2007 (UTC)

Take a look at this picture and decide whether acceleration depends on power or torque. I don't know how it could be any clearer. 74.101.94.34 05:00, 23 April 2007 (UTC)

To anonymous: I agree. The picture clearly shows that the the combination on the right gives the largest torque (861 vs. 651) and thus the largest acceleration. It couldn't be any clearer! Alfred Centauri 12:47, 23 April 2007 (UTC)

The picture might have changed since it's over a year old, but it clearly shows the right engine producing less torque, not more.Totsugeki (talk) 17:18, 13 August 2008 (UTC)

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)

It looks like basically everyone opposes the idea, and there hasn't been any votes for nearly a month. Sounds like "case closed" for me. 74.101.94.34 19:21, 20 April 2007 (UTC)

• Oppose Term torque stands for a moment of a force. In addition, moment is a much wider term than Torque. --Wallach2008 (talk) 20:57, 18 January 2009 (UTC)
• Duplication Is this discussion a partial duplication of that one Talk:Torque#Merge articles of Moment and Couple? --Wallach2008 (talk) 20:57, 18 January 2009 (UTC)

This discussion is out of date. I changed the moment (physics) article entirely last November. If anyone still thinks this is an issue, please start a new discussion at the bottom of the page. --Steve (talk) 23:22, 18 January 2009 (UTC)

• This discussion should be archived according to Merging and moving pages policy and removed from the talk page to avoid ambiguity, see comment of Steve above. --Wallach2008 (talk) 00:07, 19 January 2009 (UTC)

External Links

I removed a couple of pages because they appeared to be Links normally to be avoided, #(2)having unsourced material, and #(11)"Links to blogs and personal web pages, except those written by a recognized authority." I have no other interest whether they stay or go but I am wondering how they meet WP:EL criteria. Ward20 (talk) 20:01, 16 July 2008 (UTC)

I honestly have not bothered to become too familiar with WP:EL. I replaced the links because they seemed quite good. It's not good to have huge lists of external links, but that is not the case here, and I think some people might find those links useful. Rracecarr (talk) 21:25, 16 July 2008 (UTC)

I think the links seem good and potentially useful too, but it seems to me the problem is essentially quality control. The websites have no apparent editorial checks, and an editor looking through the material for accuracy seems to be original research. The links do not appear to meet the inclusion criteria of WP:ELYES either. So I am still unsure if. "the links seem good and potentially useful" is sufficient criteria for inclusion. I am just trying to see if they fit within the guidelines. Ward20 (talk) 23:01, 16 July 2008 (UTC)

I guess I'm ignoring all rules. If the link might be helpful to a user (and if the list of links is not too long), why not include it? (I'm not so thrilled with the unit converter site, btw) Rracecarr (talk) 14:05, 17 July 2008 (UTC)

The information stored at http://www.hbm.com/en/menu/applications/torque-measurement/terms-expressions/ could be quite helpfull for users who need information on torque expressions - maybe it should be added to the article, what do you think? —Preceding unsigned comment added by 62.159.134.140 (talk) 14:08, 5 February 2009 (UTC)

why the left-hand-rule isn´t used for explanation of torque and angular momentum

It´s obvious that this rule is more general and can be used at any scale in any area (which isn´t?) of physics.

79.210.142.19 (talk) 00:59, 23 March 2009 (UTC)

uses of torque on different metals?

we are using torque wrenches to torquen the bolts in assembly of two or more parts of machinery to maintain uniform level of force exert on the joining point.Here we usualy using standard chart; for torquen the bolts;H according to the sizes of bolts.; The chart we are using is very old. It never diffrenciate the different metals. But practically we work with different different metals and assemble different components made out of different metals having different metal strength.Here my request is if any body having the chart with different metal strength please publish through this Wikipedia would be highly helpful to our technical society. thanks Subbiahchandrasekaran (talk) 14:36, 28 March 2009 (UTC)

Article

-- PUSH AND PULL --

"Just as a force is a push or a pull, a torque can be thought of as a twist."

This is not necessary: either you build a theory with just the term "push" or you build it with the term "pull", not both in one. And why should torque be a twist? It´s simply a push or a pull in one direction caused (and the other way around, too)by pushs or pulls in two directions which are square to each other and also to the torque.

79.210.178.118 (talk) 23:30, 30 April 2009 (UTC)

explain torque to a ten year old

the first line should explain torque to a ten year old with force arm wrench . the article reads like a physics course.
Wdl1961 (talk) 18:59, 2 February 2009 (UTC)

re: explain torque to a ten year old

a description for ten year olds should come before high power stuff that most people do not care about and dont understand.

see pevious request

be nice pls put it back

Wdl1961 (talk) 17:16, 3 July 2009 (UTC)

the first line should explain torque to a ten year old with force arm wrench . the article reads like a physics course.
Wdl1961 (talk) 19:00, 2 February 2009 (UTC)

Wdl1961 (talk) 17:16, 3 July 2009 (UTC)

Is it better now? There are only two sentences before the part you wrote, and they're not technical. --Steve (talk) 22:07, 3 July 2009 (UTC)

i did not write anything exept made the original request in the talk page 2 february but thanks anyway .

i think the first sentence should carry teh most information

Wdl1961 (talk) 00:24, 4 July 2009 (UTC)

Merge articles of Moment and Couple

The article Moment (physics) and Couple (mechanics) should be merged into this article. All three both articles are about the same concept. - Sanpaz (talk) 20:24, 25 September 2008 (UTC) Sanpaz (talk) 23:30, 18 January 2009 (UTC)

I would support the merge of Moment (physics) into Torque, but I do not believe that a couple is the same thing as a torque - torque is the moment resulting from the application of a couple. A torque can result from a single force or a combination of different forces. A couple can only result from two equal and opposite forces. Thus a couple is a free vector which can be placed anywhere on the object in consideration. This makes it useful in a number of specific applications where torque, as a more generic concept, is not helpful. –Sarregouset (talk) 01:20, 2 November 2008 (UTC)

I already did the merger from moment (physics) in the past couple days. The page is remaining as a disambig of sorts. --Steve (talk) 03:16, 2 November 2008 (UTC)

Agree on merging Couple (mechanics) into Torque: while, roughly speaking, couple is a special case of two torques. I.e. I would expect Couple (mechanics) to be a subsection in Torque. --Wallach2008 (talk) 20:48, 18 January 2009 (UTC)

Disagree on merging Moment (physics) into Torque: moment is being computed for various physical concepts, while Torque is a specific quantity in mechanics. --Wallach2008 (talk) 20:48, 18 January 2009 (UTC)

FYI, as I wrote right above, the moment (physics) page has changed entirely since this proposal. --Steve (talk) 23:24, 18 January 2009 (UTC)

OK --Wallach2008 (talk) 23:53, 18 January 2009 (UTC)

Duplication Is this discussion a partial duplication of that one Talk:Torque#Proposed_merge_of_torque_.26_moment_.28physics.29 ? --Wallach2008 (talk) 20:48, 18 January 2009 (UTC)

TORQUE OF INERTIA . MOMENT OF AN ENGINE. COUPLE ON A BEAM SOUNDS GOOD.Wdl1961 (talk) 01:06, 22 January 2009 (UTC)

Out of date: I've recently done a lot of editing of both this article and couple (mechanics). I believe that it's now clear what the difference is, and what is the scope of each article. So I've removed the merge tags. If anyone wants to re-propose a merger, they should put the tags back up and start a fresh new discussion. --Steve (talk) 02:49, 8 July 2009 (UTC)

Am I the only one to find the language a bit shallow?

title.. —Preceding unsigned comment added by 93.172.231.32 (talk) 18:08, 4 December 2009 (UTC)

What does that mean? Can you give examples? You are also welcome to edit the page and make any changes you see fit. Strad (talk) 18:13, 4 December 2009 (UTC)

Simple description

I removed the following from the introduction:

Basically torque measures the difficulty to rotate something . For example, imagine a wrench or spanner trying to twist a nut or bolt. The amount of "twist" (torque) depends on how long the wrench is, how hard you push on it, and how well you are pushing it in the correct direction.

I don't believe one would say something like "Basically force measures the difficulty to move something" but that is the linear analog of the above which indeed sounds more like a description of friction. Consider that, in the absence of friction, there is no difficulty to rotate something, only to change it's rate of rotation due to its moment of inertia.

try handcranking a diesel engine .the above was put in for people who do not know excactly what torque is .for some of your problems try fourier analysis. further nothing was perfect in engineering when i worked in it.Wdl1961 (talk) 03:21, 8 February 2010 (UTC)

I'm afraid that after reading the removed material, they still will not know exactly what torque is but they may think they do and that's much worse. Alfred Centauri (talk) 03:44, 8 February 2010 (UTC)

It was recently changed from "In more basic terms, torque measures how hard something is rotated. For example, imagine a wrench or spanner trying to twist a nut or bolt. The amount of "twist" (torque) depends on how long the wrench is, how hard you push on it, and how well you are pushing it in the correct direction." Any problems with that version? I agree the more recent version above is bad. --Steve (talk) 04:48, 8 February 2010 (UTC)

I've taken a stab at rewording it but I'm not particularly satisfied with it. I'm still thinking about it. What I'm cogitating over is the use of the word torque in a static setting, i.e., torque on a bolt, a stationary setting, i.e., torque of an engine just canceling torque of friction so angular speed is constant, and a dynamic setting, i.e., a net torque as causing angular acceleration. I'm going to take a look at the "Force" article to see how it's handled there, if at all. Alfred Centauri (talk) 14:04, 8 February 2010 (UTC)

some handcranked diesels also have a 1:20 compression and piston rod plus crank throw.that aint inertia.Wdl1961 (talk) 15:34, 8 February 2010 (UTC)

Indeed it isn't but it ain't the essence of torque either. To turn the engine over requires applying enough torque to not only exceed the torque generated by the compressed air on the pistons (depends on the position of the piston in the cylinder), and the torque due to the friction of the moving parts (a torque depending on the rpm), but also some more to accelerate the rotation of the engine from zero rpm to starting rpm. This is the point of my previous comment; torque is not basically how hard something is to turn; it's much more.

In the example, I gave above, there are three torques - the applied torque (by hand or by electric motor), the torque due to compression, and the torque due to friction. The net torque is the vector sum of these three torques and it is the net torque that accelerates the rotation of the engine from zero to starting rpm.

Consider that if your are turning over the engine at a constant rpm (assume the fuel is shut off so the engine doesn't start), the net torque is precisely zero (otherwise the rpm would be changing). So which torque is it that measures how hard something is to rotate? It's not the net torque obviously. Is it the torque due to compression and friction? Is it the applied torque? Alfred Centauri (talk) 21:35, 8 February 2010 (UTC)

consider; Wikipedia:Make technical articles accessible.Wdl1961 (talk) 16:10, 9 February 2010 (UTC)

indeed, that's precisely my consideration. How to make the notion of torque accessible while not misleading. Alfred Centauri (talk) 18:06, 9 February 2010 (UTC)

see above . the description becomes so excact that people have little clue what it is all about.details can come later.Wdl1961 (talk) 01:41, 10 February 2010 (UTC)

see what above? Which description? There's no description above, only considerations of the difficulties of describing torque. Alfred Centauri (talk) 02:46, 10 February 2010 (UTC)

Terminology

""" In mechanical engineering (unlike physics), the terms "torque" and "moment" are not interchangeable. "Moment" is the general term for the tendency of one or more applied forces to rotate an object about an axis (the concept which in physics is called torque).[3] "Torque" is a special case of this: If the applied force vectors add to zero (i.e., their "resultant" is zero), then the forces are called a "couple" and their moment is called a "torque".[3] """

""" A moment under torque may mean something as simple as a single coupled heartbeat driven from the atria down into the ventricles. Systole represents a force that drives blood around an axis anchored north and south. Computational study of a single Heartbeat has been studied for many years. """

Well, that's not true. The absense of a resultant force doesn't automatically give a couple. Also, one can deduce from this explanation that a system of applied forces are only considered to induce a torque when the object on which these forces are applied is not accelerating in any other way than through rotation (which would mean that an engine in an accelerating car for example couldn't have any torque). That is, if it is given rotation at all (since this explanation doesn't imply that this is in fact the case). Torque without tendency for rotation just doesn't make any sense. This needs to be clarified or removed.

""" For example, a rotational force down a shaft, such as a turning screw-driver, forms a couple, so the resulting moment is called a "torque". By contrast, a lateral force on a beam produces a moment (called a bending moment), but since the net force is nonzero, this bending moment is not called a "torque".

This article follows physics terminology by calling all moments by the term "torque", whether or not they are associated with a couple. """

Why lateral force? Since there is clearly no picture or anything to describe the position of the beam, this just doesn't help the reader at all. Also, the author of this comment implies that the beam is accelerating ("the net force is nonzero"), and uses that as an argument to why the "bending moment is not called a "torque".". So in order for the moment to be a torque, the system to which the forces are applied can't accelerate? Just as in the first part of this section, this is an equally false statement.

A couple can be rewritten as a moment and v.v., so the example doesn't really explain anything. Either that, or it is very poorly explained. —Preceding unsigned comment added by 193.11.207.155 (talk) 15:01, 11 April 2010 (UTC)

If "the absence of a resultant force doesn't automatically give a couple", then what does? Can you please a suggest a better (more accurate or clearer) definition? (You can also refer to the separate article couple (mechanics) -- is there a better phrasing in that article?)

Would it be an improvement to say "their 'resultant' is zero but their moment is nonzero"?

Would it be an improvement to say "vertical beam"?

What do you mean when you say "a couple can be rewritten as a moment and vice versa"?

An engine does provide torque, I agree. Yet the car accelerates. How do you explain that? What's your definition of torque? My explanation consistent with that section would be: "The engine provides torque that turns the wheel. The friction with the road provides force that accelerates the car." But I'm not 100% sure.

Although I wrote that section, I'm a physicist by training, not a mechanical engineer. I read the sections from a couple mechanical engineering textbooks, and also got a couple mechanical engineers to explain this terminology to me, and to double-check the current description. Certainly it's possible that I nevertheless misunderstood something. I hope you can help improve it. :-) --Steve (talk) 16:31, 11 April 2010 (UTC)

Advertising material

There's a section at the bottom there on torque multipliers, implying that only gearboxes that use epicyclic gearing can multiply torque, and worse, that only those gearboxes supplied by prestigious PowerMaster company can multiply torque. I'd say that the behaviour of torque through gearboxes would be an interesting section to elaborate: what is conserved through a gearbox, what is converted etc. 210.55.20.219 (talk) 20:53, 16 February 2011 (UTC)Eric

I've removed the non-reliable source from this section and cleaned up the grammar. It certainly does still need some more detailed explanation than what's there, but I don't have the expertise to provide it. -- Fyrefly (talk) 21:06, 16 February 2011 (UTC)

Propose to rename article to Moment of force

The following discussion is an archived discussion of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

No consensus to move. Vegaswikian (talk) 21:11, 19 April 2011 (UTC)

Torque → Moment of force —

See Torque#Terminology for background. This article discusses the concept that is called "torque" in many(?) introductory (high school or college) physics courses, but called "moment of force" (or "momont" for short) in engineering. But "torque" means something different in engineering. The problem arises when, say, a mechanical engineer wants to learn about moment on wikipedia. They might miss this article, just looking at the title and thinking to themselves, "This is the article on torque...I know what torque means, and that's not what I'm looking for!"

Basically, "torque" is an ambiguous term, whereas "moment of force" is unambiguous. Therefore "moment of force" is a better article title. I did a quick google and google books search but couldn't figure out that way which term is used more often for this concept. My suspicion is that "moment" is more common, or perhaps "moment" and "torque" are similar. I doubt that "torque" is much more common. --Steve (talk) 04:17, 8 April 2011 (UTC)

• (Just to set my knowledge background from the get go, I'm an ME from the US.) From the standpoint of using the technically correct name, you are absolutely right, it should be moment of force. However, from the WP:COMMONNAMES standpoint, "torque" is far more common and understood. So I can see this going either way. The engineer in me wants to see it at moment of force though, so I'd advocate for that. Wizard191 (talk) 14:44, 8 April 2011 (UTC)

  When I took introductory physics, the terms were used almost interchangeably (unfortunately). The distinction for me was really first made in my intro course on mechanics of materials, where a torque more or less specifically referred to a moment which twisted an object, whereas a moment (of force) bends an object (that's a fairly simplistic look at it). I would also argue for this article to be renamed were there to be any action taken (see below also). That said, I'm not sure I see a problem with how the article is currently structured which would require us to split the information. The mathematics are the same (which are the important part); you're just taking the moment around a different point in the case of a torque as opposed to a moment (in engineering). --Izno (talk) 05:28, 9 April 2011 (UTC)

• Oppose: As you said, "torque" is the term used in high school and college physics classes and is therefore going to be what most people are familiar with. I would guess that a very low percentage of people have taken engineering courses. Personally, I've taken physics classes in high school and three different universities and I had never heard of moment of force before reading this article. A possible concern though is where the information about the engineering version of torque can currently be found. Do we have a spot for it? -- Fyrefly (talk) 14:51, 8 April 2011 (UTC)
  • Comment -- "Torque" is used in some high school and college physics classes (including mine), but not all: At least one person (apparently in the UK) edited the article to say that he/she learned it as "moment". It's hard to figure out the fraction of each. Keep in mind, the common terminology could be different now than 30 years ago, and it could be different in the US than the UK, etc. For the last question, the engineering version of torque is discussed only at Couple (mechanics) as far as I know. :-) --Steve (talk) 20:12, 9 April 2011 (UTC)
• Oppose I have never before even heard the expression "moment of force". JRSpriggs (talk) 10:08, 9 April 2011 (UTC)
  • It exists, and I know I could find reference of it in textbooks (I saw a chapter heading the other day in a PDF online with exactly "moment of force" in the title of the heading). I even had to add "-wiki" because it's listed in both this article and Moment (physics). Speaking of that article, it should probably be merged… --Izno (talk) 15:44, 12 April 2011 (UTC)

I believe Spriggs is simply saying that they don't believe the term is very common, since they've never heard of it, rather than saying it isn't a real term.

• Oppose A lay person is not going to know what a moment is, they will be looking for 'torque', and not find it. A mechanical engineer looking for info on moments should know that moments might be discussed under a torque article. OTOH, the lay person will quit reading at the first sign of higher mathmatics. Bcworkz (talk) 09:39, 12 April 2011 (UTC)
  • Unsubstantiated claims do not often work well in argument. --Izno (talk) 15:44, 12 April 2011 (UTC)
• A comment and a conclusion in support of changing the article name: "force moment" seems to generate 5x more results than even "torque", which suggests that WP:COMMON be applicable. YMMV when looking at the number of Google results, but I suspect a moment of force is the more common term in most applications.

  Checking Google Books, there were far fewer references to "moment of force", but the entirety on the first page were to the primary usage here. The entirety of "torque"'s first page results were related to one of the last definitions on this page, the "machine torque". The first reference that was indicative of a physics usage was in a mechanical engineering book…

  Checking Google Scholar, "moment of force" fairs poorly at 6k results, "moment force" (without quotation marks) does not at 2.4M results, and "torque" follows with 2.0M results, which indicates that the more common usage for this subject matter is "moment", at the very least. These multiple sets of results suggest that, indeed, "moment of forcee" would be a better name, but I think I would settle for moving the information here to Moment (physics), if anywhere (this would require a physical page move rather than a cut and paste, for preservation of article history). This would free up the page name for "torque" in the engineering or in the car senses; the latter seems more common (since I seem to be arguing that way). --Izno (talk) 15:55, 12 April 2011 (UTC)

  Tailored data gathered by questionable methods don't work well in an argument either. Using my own, very similar google searches, I've discovered that "torque" yields about 500 times as many results as "moment of force." While it would be convenient to have some larger scale data than just the thoughts of a few editors, I'd have to say that google search findings aren't going to be very valid. Also, those google books and scholar searches seem to be adding more evidence for "torque" being the more common term. -- Fyrefly (talk) 16:35, 12 April 2011 (UTC)

  GBooks and GScholars are adding more evidence that "torque" is the more common term when used in the machine torque context (naturally, given the number of people infatuated with cars…). This lends weight that "torque" the article should really be about torque in the context of cars; as that is more closely tied to the act of torsion than as a (bending) moment, that suggests that the article called "torque" should be about the moment developed to twist something, rather than about the more general moment, which supports the move request (not exactly; I think the information in this article would be better suited for an article titled moment (physics) than moment of force).

  As for that Google Search: Quotation marks > me? As for that jab at my argument: It's better to have something rather than nothing. Bcworkz's statement was completely rhetoric and could have been completely made up on the spot. --Izno (talk) 16:50, 12 April 2011 (UTC)

• Comments (by proposer) -- "Moment of force" is usually shortened to "Moment", which explains why a "Moment of force" search would discover relatively little. The article moment (physics) is in flux -- until a few days ago it was basically a disambiguation page, then someone expanded it, I discussed why with her, and that led eventually to this proposal here. I don't like the title "moment (physics)" for this article, because there is not just one "moment" in physics, there's also dipole moment etc. I prefer Moment (mechanics). Actually I like "moment (mechanics)" even better than my original proposal, moment of force. So my ideal would be: (1) Put this article (plus the new content in moment (physics)) into moment (mechanics); (2) Redirect moment (physics) there too (or else to the main disambiguation page, moment); (3) The torque page could either redirect to moment (mechanics), or be rewritten as a new article that emphasizes the narrower sense like machine torque and cars, but of course there would be liberal overlap and cross-referencing between the new torque article and the moment article. :-) --Steve (talk) 19:19, 12 April 2011 (UTC)

• Comment: The term moment by itself is slightly ambiguous with the most common meaning probably being bending moment but it does depend on context with it also being used for moment of force. There are quite a few moments in engineering such as: first moment, second moment, moment of inertia, polar moment, product moment of area, etc.. I am a physicist that teaches 2 intro level engineering classes, so I am far from an expert. From a physicists point of view engineers seem to like to add the word 'moment' randomly to various semi-related topics. (The only worse word in engineering is 'modulus' which engineer's like tossing around like its a Frisbee.) Neither of my intro level engineering textbooks use the word torque as far as I recall but prefer moment of force. If it is going to be moved it should be moved to moment of force. One problem with using torque is that many people will come looking for what it means with respect to the output of motors and engines. A article that covers the torque due to a motor seems to be missing, though. TStein (talk) 01:32, 19 April 2011 (UTC)
  • Honestly, I never learned the "engineering definition" in college either. Wizard191 (talk) 13:31, 19 April 2011 (UTC)
• Oppose I think we should stick to standard physics nomenclature whenever talking about basic physics concepts such as torque. Dauto (talk) 19:33, 18 April 2011 (UTC)
• Oppose per WP:COMMONNAME Ng.j (talk) 03:01, 19 April 2011 (UTC)
• Out of curiosity, could you enlighten us to what is the word torque used for within the engineering lingo? Dauto (talk) 19:40, 18 April 2011 (UTC)

  Yeah, from the article: ""Torque" is a special case of this: If the applied force vectors add to zero (i.e., their "resultant" is zero), then the forces are called a "couple" and their moment is called a "torque".[3]" Wizard191 (talk) 13:29, 19 April 2011 (UTC)

  So if two equal and opposite forces were directed towards each other along the line connecting them, i.e. a compressive couple of forces, then this would be called a "torque" even though it imparts no torque (angular momentum per unit time) to the compressed object? JRSpriggs (talk) 19:12, 19 April 2011 (UTC)

  If I understand it correctly, it would be called a couple with zero torque.TStein (talk) 19:19, 19 April 2011 (UTC)

  It's really not worded the best, but it makes a little more sense in context. The following would be better: ""Torque", in engineering terms, is the special case of two forces that individually induce a moment of force but act in equal and opposite directions (i.e., their "resultant" is zero); this set of forces is known as a "couple" in physics." Wizard191 (talk) 19:39, 19 April 2011 (UTC)

The most reliable source for Moment of force

Since the subject of proposal pertains to quantities and units, BIPM is the most authoritative source on the subject. SI brochure p 119 says Moment of force.--79.116.73.155 (talk) 20:02, 12 April 2011 (UTC)

The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Nonsense?

As far as I can see, the 'proof' in section 3.1 is incorrect. We cannot assume that dr/dt is zero. The article says that r is the 'radius', but it is the entire radius (position) vector of the particle! But even if it were only the scalar 'radius', it would be an unnecessary assumption. Indeed, dr/dt is the velocity of the particle, and so produces the zero vector when crossed with the linear momentum. --Andreas Rejbrand (talk) 16:41, 22 June 2011 (UTC)

It used to be correct but someone messed it up...I fixed it. --Steve (talk) 02:46, 23 June 2011 (UTC)

Moment and Torque are NOT the same

I move to change this entire article from torque to moment, and create a subsection called torque, because a torque is a special case of a moment.

Moment, also known as the moment of force, is the "rotational effect" of a force on a body about a given point. A torque (or moment couple) is a special case of a moment, when forces applied to a body cause rotation but are equal and opposite (i.e., the resultant is zero). Hence, a moment is more general than a torque. Additionally, a torque can be applied anywhere on a body and is not necessarily associated with a point. Hence a moment arm cannot be associated with a torque. This explanation comes from Dynamics, Theory and Applications by T.R. Kane and D.A. Levinson, 1985, pp. 90-99: http://ecommons.library.cornell.edu/handle/1813/638 Samner (talk) 17:25, 16 June 2009 (UTC)

The definitions of "torque" and "moment" used by physicists is different than the ones used by mechanical engineers (like Kane and Levinson). In the physics definition, for example, it's not true that torque is a special case of moment.

My own preference would be to keep the title, but have the first section of the article be "Torque vs Moment". Right now, the explanation of torque vs moment is a mere two sentences in the second paragraph, which isn't enough. --Steve (talk) 00:35, 17 June 2009 (UTC)

I added a section, can you check that I got everything right?

More work is needed, particularly in the intro, but I hope this is a start. --Steve (talk) 18:44, 4 July 2009 (UTC)

I think it's all set now, agreed? Also please take a look at my expansion of couple (mechanics). --Steve (talk) 02:53, 8 July 2009 (UTC)

Hey guys there may be a mistake here. That's because the true definition of Torque is "the rate of change of angular momentum" - in other words, the angular momentum is accelerating. Tau = dL/dt. If the angular momentum is not accelerating, for example any scenario in statics, then that is properly called Moment. Both are also called "twisting force". The diagrams with pivot point are all incomplete. That's because it shows a force acting on the end of a body relative to the pivot, but it doesn't show the "equal and opposite" force being applied by the pivot onto the body. So all pivot systems are also force-couple systems, its just that the diagrams here don't show the missing force. Think of it, you apply a force to a body and by Newton's 2nd law it will accelerate in that direction, except for the action of the pivot. What is the action of the pivot? It applies an equal and opposite force that causes the body to change its angular momentum, in other words, start to rotate. What is it called when dL/dt is equal to zero? That is a state of zero torque. That's what happens on your truck driveshaft when you are driving at a constant speed. The driveshaft is rotating with a constant speed therefore constant angular momentum therefore dL/dt = 0. The twisting force in that driveshaft is therefore MOMENT. Else we must delete tau = dL/dt because now you are saying sometimes torque means rate of change of angular momentum, and sometimes it means something else. Which is it? — Preceding unsigned comment added by 12.148.70.200 (talk) 18:27, 29 July 2011 (UTC)

I think we should delete tau= dL/dt as a definition. Of course NET tau = dL/dt, but tau = r x F is true for the component taus and not just the total tau, so it's more general. Anyway stating one definition is simpler than stating two definitions, and tau=rxF is far more common in textbooks. We can have net tau = dL/dt as a "theorem" (something we demonstrate/prove) instead of a definition. Again, I believe this is the usual approach.

If something is "properly called moment" than it is the proper subject of this article...the consensus is that this article is the wikipedia article on the concept that engineers call moment (despite the fact that this article is not called "moment"). (At least I think that's the consensus...it's definitely what I think!)

Also, I just looked at your edits (I presume you're Grunchy) -- right now there's only one citation in the "Terminology" section about the definitions of torque and moment and it does NOT seem to agree with the text you added surrounding it. It's a free download, you can check it out. It seems to me that it agrees with the text you deleted but disagrees with the text you wrote. What do you think? Also, have you seen any other textbooks that agree with the definitions of torque and moment that you are using? --Steve (talk) 20:46, 29 July 2011 (UTC)

metricate derivation

Torque is not something specific to one system of measurement. The section is biased towards North America by using imperial system. Cantaloupe2 (talk) 11:20, 12 September 2011 (UTC)

Stuck on a basic free-body problem

I have been through this and related pages, but have been unable to find the answer to the question: "If you have a number of forces acting on different parts of a free-floating rigid body, how can you calculate the resultant rotation and translation?" This seems to me to be a fundamental generalised question in mechanics and I'm disappointed Wikipedia and I couldn't work it out together. (The same problem but with a fixed axis of rotation, i.e. a pivot, is also interesting, but I think that is covered well.)

So far the best I have come up with is:

• For each force, calculate its torque and divide by moment of inertia (about centre of mass), and sum all these to get the total torque, and thereby rotational acceleration.
• Also sum all forces together to get linear acceleration.

This works in the case of balanced forces (translation only, or rotation only), but I feel it must be wrong when both translation and rotation occur, because in the sums above the same force is being used twice to add energy to the system. If you can point out what I am missing, perhaps I can update the appropriate article to clarify this. — Preceding unsigned comment added by 82.32.31.166 (talk) 05:50, 17 January 2012 (UTC)

Sounds like you have the right idea. (Your procedure is OK in the first bullet point but the wording is a bit confused. [Fixed. 82.32.31.166 (talk) 22:42, 24 January 2012 (UTC)] "Total torque i.e. rotational acceleration" implies that they're the same. You can add the torques to get total torque, then divide by moment of inertia to get rotational acceleration. Or, equivalently, you can divide each torque by moment of inertia to get a contribution to rotational acceleration, then add those up to get actual rotational acceleration.)

It's OK that a force is adding energy to the body by increasing its translational motion and also adding energy to the body by increasing its rotational motion. That's not double-counting, it's two effects. :-) --Steve (talk) 13:02, 17 January 2012 (UTC)

Thanks Steve. My problem is more easily stated by considering a single plank of wood lying on a frictionless surface. Pushing it in the middle will cause it to accelerate linearly but not rotate. When pushing anywhere other than the centre, some rotation and some acceleration will occur. So my question: How do we work out how much of each occurs? (I am doubting whether my solution above is correct!)

If I understand correctly, the linear acceleration is always the same (for the same force). Is that true? What is counter-intuitive then is how the extra rotational energy enters the system - presumably it must be down to the force working over a longer time period and distance. This explanation would satisfy me if someone knowledgeable can confirm it!

(This is actually for a game, which has a space-ship with boosters on it. What seems wrong is that the same boosters firing for the same amount of time could add more or less energy to the ship.)

Wondering if I should move this over to Talk:Rigid Body Dynamics. 82.32.31.166 (talk) 22:42, 24 January 2012 (UTC)

Energy is related to work, which is force times distance. You have to push a bigger distance (per time) if the object is rotating away from the force than if its orientation is fixed... --Steve (talk) 01:01, 25 January 2012 (UTC)

Confusion

The last two paragraphs of the units section are contradictory:

This is an example of the confusion caused by the use of traditional units that may be avoided with SI units because of the careful distinction in SI between force (in newtons) and mass (in kilograms).

Sometimes one may see torque given units that do not dimensionally make sense. For example: gram centimetre. In these units, "gram" should be understood as the force given by the weight of 1 gram at the surface of the earth, i.e., 0.00980665 N. The surface of the earth is understood to have a standard acceleration of gravity (9.80665 m/s2).

If using "pounds" causes confusion, then "gram" must also do so. If the weight of a gram is to be "understood" then the same is true for "pound."

IMO, a discussion of advantages of a unit systems ("This is an example of the confusion caused by the use of traditional units that may be avoided with SI units ...") is unrelated to the physical phenomenon of torque, especially when SI units can be abused & become equally bastardized. It should be deleted from the article. 69.174.87.100 (talk) 15:02, 26 April 2012 (UTC)

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.

The Torque#Definition and relation to angular momentum section now starts with the sentence "Torque is defined about a point, not specifically about an axis as mentioned in several books.". Those several books have a good reason for defining a torque about an axis. In general a torque is about a point, but in many cases only one component is important and it is then both easier and more usefull to talk about the torque around an axis. In many practical cases (e.g. the torque produced by a motor, or that used to tighten a bolt) the axis to use is obvious, but choosing a single point is not as easy and it will give you a torque vector when you are only interested in the magnitude. I think that the definition section (and the lead) should contain both the general definition and the practical one (about an axis), starting with the practical one since readers not familiar with vector algebra will stop reading when they find a cross product. Ulflund (talk) 22:55, 14 July 2012 (UTC)

That line was added by an IP back in 2010 [1]. It seems confused and misleading to me. Any instantaneous rotation will be around an axis so even if you have a situation where you might possibly have multiple posible direction of rotations, say a joystick, as soon as you apply a force you have a axis. I'm removing the sentence.--Salix (talk): 08:07, 15 July 2012 (UTC)

"Lever arm"

This article defines "lever arm" as the distance r from the center of rotation to the point of application of the force. However, it is more common to define it as the perpendicular distance between the center of rotation and the line of force. In other words, lever arm is r sin θ, not r. Arjenvreugd (talk) 02:22, 11 August 2012 (UTC)

Lever arm can be defined either way but it makes more sense to define it as the distance to the point of application as that is where the lever would be if there was a lever. The other definition is called the moment arm (r sin θ). The θ in the equation can equally refer to the angle between the line of the force and the lever arm or the component of the force that is perpendicular to the lever arm (r × F sinθ) Dger (talk) 03:50, 22 October 2012 (UTC)

Does the GIF fit to the text?

I just received a message from a new user, who expressed concerns about the GIF:

Hi, I'm a new user to Wikipedia but not a new 'consumer'. So I'm not sure if you are the correct person to send this message - if not, apologies. I noticed in the Torque page an animated gif http://wiki.riteme.site/wiki/File:Torque_animation.gif This diagram is inconsistent for the given equations of torque. The diagram describes a rotational constraint in one plane only. The equations describe torqe without constraint. The sinθ term in τ = rFsinθ is incosistent with the diagram. Imagine a force acting parallel to the turning axis. Because of the constraint, there would be no resultant rotation although sinθ=1. Although the equation is correct it does not correctly explain the resultant motion in the diagram. I suggest either losing the diagram, adding a caveat or asking the author to address. Thanks! Quitequick (talk) 09:52, 12 December 2008 (UTC)

Quitequick is correct in that the illustration has a constraint which the formula doesn't have, as the ball's motion is limited by the hinge. However, this is no different from any classroom physics demonstrations. When you use an air track, you have a similar limitation. Of course, a smart student might ask: "But what happens if I push the cart sideways? According to the formula we learned, it should move sideways, shouldn't it? The formula you taught us and the experiment are inconsistent!", to which I would reply "You are correct. The reason we're using a constraint is to simplify reality. Please go along with me and, for the moment, just think in one dimension. Once you completely understand one dimension, you can much better understand three dimensions." Up until now, I thought that was understood with physics experiments, but it obviously isn't for everyone among our readers. Maybe someone has an idea how to word this in this article, so that Quitequick's concern is addressed? — Sebastian 19:43, 12 December 2008 (UTC) For a more relevant to common users article on torque and horsepower the following link is a must read: http://www.4x4abc.com/jeep101/torque.html —Preceding unsigned comment added by Ravilaa (talk • contribs) 05:31, 23 January 2009 (UTC)

I would disagree that the image is in any way inconsistent with the formula. The image simply illustrates one possible application of the formula, in which the applied force is perpendicular to both the arm and the axis. This is certainly a valid application of the formula, so no inconsistency here. If the applied force had had components parallel to the arm and/or the axis, then these components would have had no effect, because the mechanical constraints of this particular setup would have provided equal and opposite forces to cancel out the additional components, so we would have been back to having a resulting force identical to the one shown in the image, and again there would be no inconsistency with the formula. Certainly, there are other possible ways to illustrate the formula - even ones employing motion in more than 2 dimensions - but how much additional insight would they provide, and how easy would it be to grasp what was going on? Let's be honest, this 2-dimensional example is already quite complex for someone who doesn't already understand the concept. Yawe (talk) 23:21, 18 March 2009 (UTC)

The definition of torque is erroneous. Torque is the action of a force couple; therefore, it reflects a state of force equilibrium. On the other hand, a moment is not force equilibrated. Consequently, the equivalent of a moment is a torque plus a force parallel to the force creating the moment that passes through the point the moment is taken about. (Rethc (talk) 19:25, 9 February 2009 (UTC))

The textbooks that I've read, which are all English-language physics textbooks, define "torque" in such a way that you can have a single push that provides both force and torque. Maybe the definition is different in mechanical engineering or other fields? Or other languages? Where did you learn this definition of torque, Rethc? --Steve (talk) 19:35, 9 February 2009 (UTC)

---

I would like to add another concern about the diagram. This concerns the way in which Torque (and Angular Momentum) are visualised. They are both represented by vertical arrows. This gives the impression that the things they refer to actually have a vertical character, which they don't. To my mind, it would be better if Torque and Angular Momentum were indicated separately. Willbown (talk) 14:34, 10 November 2012 (UTC)

The directions of the arrows are correct according to the right-hand rule. In some texts a moment of force (or torque) is differentiated from a force by putting a small circular arrow around the main arrow and in a plane normal to the arrow. This is very difficult to add to an animated GIF and there it is reasonable not to be included. Of course, there is another easier method, that of using different colours for each type of dimension. This is what the author of the GIF did and it is effective. The only problem with the GIF is that the force and torque are shown simultaneously. In fact only one, or the other, is needed to create the motion and momenta. Dger (talk) 19:59, 10 November 2012 (UTC)

displacement vector vs. lever arm vector

From the opening section: "r is the displacement vector (a vector from the point from which torque is measured to the point where force is applied), and r is the length (or magnitude) of the lever arm vector". Are these terms synonyms? If so, the same term should be used both times to avoid confusion. — Preceding unsigned comment added by 132.210.201.57 (talk) 17:15, 21 December 2012 (UTC)

Equations for moment arm formula is confusing

The equation for the special moment arm case is confusing. The formula uses a centering dot for the formula, which is also the vector symbol for the dot product. Torque is often expressed in vectors and so it is not obvious whether the centering dot is multiplication or a dot product.

Since the dot product of any perpendicular vectors (moment arm and force) is equal to 0, moment arm (dot) force is incorrect. I suggest the equation is rewritten without using symbols that suggest vector operations (x is also out, as it could mean cross product). Perhaps the equation could be written, simply "|\tau| = (moment arm)force"

Multiplication is implied by such use of the parenthesis. —Preceding unsigned comment added by 209.94.128.117 (talk) 08:11, 2 February 2009 (UTC)

Done. OK? --Steve (talk) 15:38, 2 February 2009 (UTC)

In the "Moment arm diagram", I believe the force vector is mislabeled; the direction of force is the vector currently labeled as "Axis", no? Patrickwooldridge (talk) 22:17, 30 January 2013 (UTC)

Sorry; just noticed that the torque point is being indicated by what I had interpreted as a vector labeled "Axis" (rather than the point r:F, which I had interpreted as the torque point). Still, I find the diagram confusing and I am not sure it is accurate, as the the perpendicularity of the force vector to the moment arm is arbitrary. I am no expert in moment arm, so I will not try to clean it up. Patrickwooldridge (talk) 22:27, 30 January 2013 (UTC)

OK; I think I finally noodled it out. When the force exerted on the lever is perpendicular to the lever (and in the plane of rotation), then the moment arm is equivalent to the distance from the pivot point to the point of force exertion, but if the force exerted on the lever is not perpendicular to the lever, then the moment arm becomes a line segment from the pivot point perpendicular to the (extension of the) force vector. If this understanding is correct, then perhaps we should include some wording like this in the text and also redo the diagram for clarity. Patrickwooldridge (talk) 01:08, 31 January 2013 (UTC)

Gyroscopic Torques

After the section discussing rotation about a fixed axis there should be something clarifying that the inertia tensor of a freely rotating body changes relative to the inertial frame as a function of time and therefore the torque includes the extra gyroscopic terms.

In a 3d inertial frame,

${\boldsymbol {\tau }}_{\mathrm {net} }=I{\boldsymbol {\alpha }}+{\boldsymbol {\omega }}\times I{\boldsymbol {\omega }}.$

Jcooperation (talk) 17:16, 12 April 2013 (UTC)

Formula and info to add

• τ = r x F is also written as M = d x F
• M = d x F is also the same as W = s x F (the latter signifies labour = force x displacement; whereby labour is in Joule)
  

The latter hence also means that labour equals moment of force or simply that 1 Joule equals Newtonmeter KVDP (talk) 12:52, 29 September 2013 (UTC)

Labour should be work in English. No work and torque, or moment of force, are not the same thing even though their dimensions are equivalent. The work of a moment of force is the product of torque and angular displacement (in radians). By the way, spell joule with a small J. Dger (talk) 23:28, 29 September 2013 (UTC)

"Tendency" to rotate ??

This article uses the word "tendency" to define torque in the first sentence. What does "tendency" mean in physics, math, or engineering? Tendency is a term that is based on some unknown probability that is greater than 0.5. In this case, it is based on the distribution of mass in the rigid body, and other torques acting on it, which does not need to have a probability of greater than 0.5 of causing a rotation. There is also a "tendency" to want to know the rotation contribution caused by a specific torque, but that human desire should not be part of the definition. Ywaz (talk) 13:07, 27 January 2013 (UTC)

Torque, moment or moment of force (see the terminology below), is the tendency of a force to rotate an object about an axis,[1] fulcrum, or pivot. Tendency may not be the right word, as an applied force will always rotate an object around an axis (excluding frictional resistance). Perhaps another description would be that torque is an extension of the concept of force to account for rotational motion. In this sense, torque has no "physical" meaning, rather it is only "force" that has physical meaning. However I don't know if this is actually correct. Perhaps yet another definition: torque is the effectiveness of a force in producing rotation motion, given the same force applied at a greater distance produces a greater angular acceleration. The problem is, torque is one of those things we've been taught how to use without really understanding what it is. — Preceding unsigned comment added by 58.173.113.116 (talk) 10:09, 22 March 2014 (UTC)

Moment of force vs momentum

Do these things mean the same, its not quite clear.

No. For example, units don't match. Moment of force = r F (N.m or kg.m²/s²) but linear momentum = m v (kg.m/s) or angular momentum = I ω (kg.m²/s).

Dger (talk) 00:57, 5 November 2014 (UTC)

UK relationship between torque and moment of a force

This article follows US physics terminology by using the word torque. In the UK and in US mechanical engineering,[3] this is called moment of force[4] shortened usually to moment.

In US mechanical engineering, the term torque means 'the resultant moment of a Couple',[5] and (unlike in US physics), the terms torque and moment are not interchangeable. Torque is defined mathematically as the rate of change of angular momentum of an object.

In UK physics, torque is defined mathematically as the rate of change of angular momentum of an object. It is the resultant of all the individual moments of forces. So in UK physics, torque and moment of a force are not interchageable because a body in rotational equilibrium can have several moments acting on it but cannot have a torque acting on it. This seems to match the US mechanical engineering use.

So maybe the second para. should read "In US mechanical engineering, and in the UK, the term torque means 'the resultant moment of a Couple'..."

I'm not sure whether UK mechanical engineering matches UK physics or whether UK mechanical engineering matches US physics, which is why I haven't edited the article. I think that a UK mechanical engineer would happily state that a torque was being applied to a driveshaft even if the driveshaft wasn't turning (because the torque wasn't big enough). Come to that, a UK physicist might well do the same, but they would always fall back on the definition "rate of change of angular momentum" if pressed Matt perks (talk) 06:49, 1 February 2013 (UTC)

I find the first paragraph of the section Terminology to be ambiguous:

"This article follows US physics terminology by using the word torque. In the UK and in US mechanical engineering,[3] this is called moment of force,[4] usually shortened to moment. In US mechanical engineering, the term torque means "the resultant moment of a couple,"[5] and (unlike in UK physics), the terms torque and moment are not interchangeable."

Main assertions I could infer are:

• From the first part: "This article follows US physics terminology by using the word torque. In the UK and in US mechanical engineering,[3] this is called moment of force, usually shortened to moment." So, the term torque in US physics terminology translates to the term moment of force (or simply moment) in US mechanical engineering terminology and in the UK terminology (the whole UK, as implied).
• From the second part: "In US mechanical engineering, the term torque means "the resultant moment of a couple,"[5] and (unlike in UK physics), the terms torque and moment are not interchangeable." So, in US mechanical engineering, torque and moment are not interchangeable. But, in UK physics, they are interchangeable. So, even though US_Physics/torque actually refers to UK/moment, the two terms are still interchangeable in UK Physics (although not in the rest of the UK, as implied, when combined with the previous assertion).

So, in short, I see a problem that needs to be fixed;

• US_Physics: The terms torque and moment are interchangeable.
• US_Mechanical_Engineering: The terms are not interchangeable.
• UK_Physics: The terms are interchangeable (?)
• UK: The terms are not interchangeable (?)

85.110.84.238 (talk) 18:57, 31 October 2014 (UTC)

I agree this is a mess. IMHO, having studied from US engineering texts, moment of force is the preferred term for a torque. In the UK and various US sources "torque" means the moment of force about the "torsional axis" of an object where forces act to rotate or attempt to rotate the object. No actual rotation is necessary. For example, a torque wrench may be used to test the static torsion on a nut or bolt. Whenever, rate of change of angular momentum is used the correct term should be "resultant moment" or "resultant torque" not simply torque. There can be many forces and consequently many torques acting on an object but it is only the resultant torque that is equal to the rate of change of angular momentum. This is called Euler's Second Law. The reference to Kane and Levinson is to a old text (1985) that may not reflect current engineering practice. For example, they don't define a force couple the way that it is currently understood. See Couple (physics) for example. A couple is generally considered to be a moment of force or torque caused by one or many pairs of parallel forces of equal magnitudes and opposite directions. Such forces have a zero resultant force but a nonzero resultant moment of force. They produce or attempt to produce pure rotation of an object. Dger (talk) 03:11, 1 November 2014 (UTC)

To be honest, my primary objection to those three sentences I wrote in blue up there was/is not lack of normative consistency, but rather lack of (paragraph's) self consistency. I think it is quite understandable that slightly different terminology may co-exit (without threatening scientific health); US mechanical engineering terminology calls it moment when there is no change in angular momentum and calls it torque when there is a change in angular momentum. On the other hand, US physics terminology considers the two terms to be synonymous in all cases. That's perfectly fine in my opinion (maybe even necessary). My point was that those three sentences cause ambiguity/contradiction within themselves, which is arguably a more critical issue than establishing a normative consistency, which may not even be possible in short term perhaps. — Preceding unsigned comment added by 85.110.45.230 (talk) 14:34, 1 November 2014 (UTC)

What I was trying to say, which is also stated in earlier discussions on this page, is that it is inaccurate to define torque as dL/dt. Only, the resultant torque or resultant moment of force is equal to dL/dt. Dger (talk) 01:04, 5 November 2014 (UTC)

Although what I wrote at first was (maybe) lengthy, the gist of it can be reduced to a single sentence: Just can somebody please clarify UK's terminology? Four lines I wrote were:

US_Physics: The terms torque and moment are interchangeable.

US_Mechanical_Engineering: The terms are not interchangeable.

UK_Physics: The terms are interchangeable (?)

UK: The terms are not interchangeable (?)

These "(?)" indicate the problematic ones causing (logical!) ambiguity/contradiction in the article's current version, and needs to be clarified. A very simple, tiny, logical ambiguity.

I understand and appreciate your concern, but please; there are 49 sections in this talk page(!), and the one belonging to the space we're currently populating, which is already over-populated as it is, is "UK relationship between torque and moment of a force", and that's precisely why I wrote what I wrote under this section in the first place. I don't think anybody has time to read a (severely) over-populated talk page. This is another thing I keep seeing over and over in wikipedia; apparently sometimes we love filling pages so inefficiently.. and arguing in an infinite loop.

You don't like $\tau =dL/dt$? well, I checked out a few recent teaching materials from MIT and Berkeley, all of which includes that equality, which considers torque to be change in angular momentum, and honestly it is quite natural to me. This isn't US books vs. Soviet era Russian books, we are just talking about "torque". The whole point of rotating gyrsocopes and the associated precession motion upon application of a torque perpendicular to the axis of rotation is the change of angular momentum, which is explained by this very equality everywhere I looked. Apart from the right or wrong perspective, it exists in very many respectable references. It is just that the article should be clear about UK's terminology; UK_Physics is okay with the terms being interchangeable, but other disciplines in UK are not? Because that's what article says currently, right?

If a system interacts with its environment in the sense that there is an external torque on the system, the net external torque acting on the system is equal to the time rate of change of its angular momentum:

$\sum {\overrightarrow {\tau }}_{ext}={\frac {d{\overrightarrow {L}}_{tot}}{dt}}\quad :$ The rate of change in the angular momentum of a nonisolated system is equal to the net external torque on the system.

And now after all I just wrote, the section is even more overloaded! More importantly, the article is not even in a really good shape in the current version. I created the last section in this talk page, "Misleading example at section Relationship between torque, power, and energy", but I couldn't get any feedback.

78.162.6.38 (talk) 03:26, 5 November 2014 (UTC)

The references for this paragraph where placed after the wrong sentences and the reference to the SI brochure didn't add anything since it uses both terms (torque and moment of force) but defines neither. I have moved the refs to their correct positions and edited the paragraph to be clearer but saying the same thing (except stating plainly that the terms are interchangeable in US physics). We do not have any sources on UK usage but from what I could see by googling the terms seems to be used more or less interchangeably, possibly with torque denoting either a moment of force or a moment of a couple. Ulflund (talk) 17:11, 5 November 2014 (UTC)

Force?

My feeling is that this article is confusing with regard to the notion of force. I may be mistaken, but I don't believe a torque is a force. However, the article uses terms like turning force, and never fully clarifies whether or not torque is a force. The sense I get is that torque is a rotational projection of a force, which happens to have a rotational character. — Preceding unsigned comment added by 75.139.254.117 (talk) 16:26, 13 October 2016 (UTC)

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

Level of technical talk in the article. This is one of several articles that should have two versions, a layman's version, and a second version for a person with a start of a technical background.

74.214.42.26 (talk) 23:18, 18 July 2010 (UTC)

I understand almost nothing in this article. Far too technical. I'm no idiot, but I am a layman trying to learn about torque, and learned nothing reading this. 71.171.89.90 (talk) 20:40, 15 December 2013 (UTC)

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

Removed "Loosely speaking, torque is a measure of the turning force on an object such as a bolt or a flywheel. For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque (turning force) that loosens or tightens the nut or bolt." Potentially confusing example. For the example of tightening a bolt into a plate, the text implies that a force is created acting through the axis of the bolt which causes tightening into the plate. As far as I understand it, the wrench causes a rotation around an axis of the bolt and it is the spiraled groove itself that caused the bolt to move further into the plate. While it is very common practice to define torque as acting perpendicular to both the force applied and the distance from the rotation point, I think these examples may cause an incorrect assumption that there exists a force in the direction we define torque. Perhaps further clarification is needed when defining that torque is and the direction it acts in. — Preceding unsigned comment added by 2A02:C7D:522B:2500:108:2E10:C99E:6647 (talk) 22:24, 15 September 2017 (UTC)

Overuse of the "×" symbol

In parts of the article, the "×" symbol is used for the vector cross product of three-dimensional vectors and in other parts of the article the "×" symbol is used for the ordinary multiplication of numbers. Can one of those uses be replaced by something else, perhaps "∧" for the cross product or "⋅" for the ordinary multiplication? 64.132.59.226 (talk) 16:23, 15 November 2017 (UTC)

Infobox needed

Article could use {{Infobox physical quantity}}. - DePiep (talk) 09:28, 11 January 2018 (UTC)

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)

I'm not so hot on that idea, because different sources use different symbols. It's all well and good using tau for torque, most people will figure that out, but in two of my textbooks inertia and rotational energy have opposite symbols (i.e. the symbol for inertia in one book is that of rotational energy in the other) —The preceding unsigned comment was added by 204.220.135.214 (talk) 14:50, 5 April 2007 (UTC).

Absolutely NOT! Symbols make everything totally confusing! Remember, those people who understand the symbols, do not need this article. — Preceding unsigned comment added by 115.70.29.185 (talk) 14:46, 9 April 2018 (UTC)

Need a short summary

The whole article is waaaay too detailed for the non-experts. It may be good for physics PhD students but for the rest of us is useless. We need a short, to the point summary at the top. An equation on a year 12 level. A "this is how you calculate it". — Preceding unsigned comment added by 115.70.29.185 (talk) 14:51, 9 April 2018 (UTC)

M·L^2·T^−2 vs kg·m^2·s^-2

I switched M·L^2·T^−2 to kg·m^2·s^-2 in the infobox here with comment

switch from M·L^2·T^−2 to kg·m^2·s^-2 - they convey the same information, and my experience (talking to many people both in and out of physics) is that the latter is more likely to be understood

Then Andy Dingley (talk · contribs) reverted with comment:

Dimensional analysis. MLT? Undid revision 853448172 by Sbyrnes321 (talk)

I mostly don't understand this comment, but I'll try to address it anyway. I have nothing against helping people solve dimensional analysis problems involving torque—I would say that it's a lower priority than conveying virtually any of the other information in this article—but whatever, fine, I'm not against it. But my proposed change will not stop anyone from solving dimensional analysis problems involving torque. One can do dimensional analysis with kg, m, s instead of M, L, T. Trust me, I do it all the time! And if a reader really wants to use M, L, and T for some reason, they only need enough physics knowledge to know that kg is a unit of mass, m is a unit of length, and s is a unit of time. That's really not asking much! Beyond that, see my original edit comment above. I'm happy to discuss more and I am interested what other people think. :-D --Steve (talk) 23:04, 4 August 2018 (UTC)

• Dimensional analysis. It's always good to at least read a lightweight encyclopedia article on a topic before breaking it. Andy Dingley (talk) 23:10, 4 August 2018 (UTC)

OK I just read that article. It is not new to me. I am a professional physicist, I do dimensional analysis all the time, I even wrote a widely-used computer program that automates dimensional analysis violation testing for arbitrarily-complicated computations. So ... what exactly do you think I broke, and why do you think I broke it? I really don't understand you. Can you please read what I wrote and respond to it in a substantive way? --Steve (talk) 00:33, 5 August 2018 (UTC)

There is a convention that, when discussing dimensional analysis, MLT are used as identifiers for the dimensions, rather than the symbols for the conventional units. This is twofold: to avoid questions of magnitude (which have no place here - it's purely dimensional analysis); secondly to avoid problems of unfamiliar units and errors over interpreting their dimensions. I have no idea offhand (at least not a reliable one) what the dimensions of a slug, erg, dyne or poundal are. Now if we operate in a sensible pure SI world, then this problem becomes a little theoretical. But in engineering, rather than science, and engineering which involves the US, it's still a very real one.

I'm sorry if my responses were rude, but I'm surprised to see a professional physicist making such a change. Andy Dingley (talk) 20:48, 5 August 2018 (UTC)

Do you think that there are a lot of readers of the article who are simultaneously (1) capable of using and applying dimensional analysis, (2) not familiar off-hand with the fact that kg is a unit of mass, that m is a unit of length, and that s is a unit of time? If so, can you talk a bit about who you think these readers are? High school students? Professionals? Physicists? Engineers? Nurses? Are you personally in this category? I mean, if I tell you, Andy, that torque can be written in SI base units as kg·m^2·s^-2, would you have trouble figuring out that the dimension of torque is M·L^2·T^-2?

Also, how many times in your life have you, Andy, pulled up this wikipedia article for the purpose of finding the dimension of torque in MLT?

My experience is that dimensional analysis comes in two flavors:

• The extremely common type of dimensional analysis, which does not involve MLT, is things like factor-label method, e.g. figuring out that sqrt(1 btu / 1 slug) is 19 miles per hour. This is the kind of dimensional analysis that I do every day, and that every scientist I know does every day. The MLT decomposition is not helpful for that: it can tell you that sqrt(1 btu / 1 slug) has units of velocity, but not what velocity it is, which makes it pretty much useless for everyday physics and engineering calculations.
• Applying the Buckingham Pi theorem is extemely rare in my experience. I can think of 2 times in my life that I have done so, outside of homework problems (and I guess arguably certain extremely simple cases where you do it in your head, like defining a "dimensionaless length parameter" by dividing one length by another length). And I have never seen anyone else apply the Buckingham Pi Theorem either, outside of homework problems. I think of it as a tool to be used in unusually strange and challenging physics problems. (For the record, the rare times I've used Buckingham Pi, I did so with kg,m,s instead of M,L,T.)

So that's why (1) I see the MLT decomposition as useful to very small niche audience in the first place, and (2) those very few readers who do want to know the MLT decomposition are all people who are very capable of figuring it out themselves if given a kg,m,s SI base unit decomposition.

Again, this is based on my experience. Is yours different? Maybe I'm missing something. I'm interested to learn. --Steve (talk) 23:28, 5 August 2018 (UTC)