Talk:Torque/Archive 2

Archive 1

Archive 2

Units for L=Iω

We just had a long discussion about this, summarized at Talk:Angular_momentum#Bottom_line. In short, for the equation L=Iω, units of L must equal the product of the units of I and ω. I has units of ML² (mass times length squared), so any angular units in ω must match the angular units in L. I would prefer that L be expressed in ML²θ/T (mass times length squared times angle per unit time) and that angular velocity be expressed in θ/T, in which case you would be right, the L=Iω equation would be independent of angular units, as long as the angular units of L and ω were consistent.

However, the International System of Units (SI) states that angular momentum (L) has units of ML²/T and angular velocity (ω) has units of 1/T, which is actually dimensionless radians per unit time. These are the units used in the respective articles. Unit-wise this is formally correct, but it requires that the angular velocity in L=Iω be expressed in dimensionless radians per unit time. Having Wikipedia out-of-synch with SI is not a good idea, it's better to follow SI and then link to orientational analysis which treats angle as a base unit rather than a "dimensionless unit" (an oxymoron in my opinion), thereby sorting out the mess, but orientational analysis is not presently mainstream or commonly used and some might argue that its theoretical foundations need work. PAR (talk) 00:19, 19 May 2019 (UTC)

Both torque and the equation L=Iω are much older than SI, and they are independent of what units you use. The equation will still be correct if you measure the angular velocity in degrees per year as long as you keep track of your units. You are right that, if one wants to follow SI one should use units of radians/s, where the radians are dimensionless, but the article does not limit itself to the SI unit system. It is much more general than that. Ulflund (talk) 09:36, 19 May 2019 (UTC)

I'm happy to let it stand, since I basically agree with you. Just be aware that the use of some other system of units should be justified by a reference in order to be in strict accordance with Wikipedia standards and someone else might take offense. PAR (talk) 13:51, 19 May 2019 (UTC)

Misleading example at section Relationship between torque, power, and energy

$P={\boldsymbol {\tau }}\cdot {\boldsymbol {\omega }},$

Below paragraph is used to provide a practical example of the above equality:

"In practice, this relationship can be observed in power stations which are connected to a large electrical power grid. In such an arrangement, the generator's angular speed is fixed by the grid's frequency, and the power output of the plant is determined by the torque applied to the generator's axis of rotation."

However, the claim that the power output of a power plant generator is determined by the applied torque is false. For a given angular frequency such as 60 Hz, which is constant for a power plant as the paragraph emphasizes, the power output is determined by;

1. The number of turns in the generator's winding that is subjected to a varying magnetic field due to rotational motion of the rotor within the stator
2. The physical dimensions of the generator

   two of which in turn determines the ultimate rate of change of magnetic field, which yields a certain amount of electromotive force (EMF), i.e. voltage, as explained by Faradays law.

3. The resistance of the conductor, which determines the current for a given voltage.

$P=VI$

In an operating thermal power station, if the torque on the shaft that rotates the generator's rotor is changed, the angular frequency is directly changed as the rotor will rotate at either a higher or lower angular frequency as a result.

A completely misleading example; a thermal power plant generator receives mechanical power as input, which is typically supplied by a steam turbine, and it outputs electrical power. Although energy is converted among various forms in this process, it is a false claim that 'torque on the shaft determines power output'.

85.110.58.208 (talk) 00:01, 1 November 2014 (UTC)

Since I didn't receive any feedback, I went ahead and replaced the problematic example with a more appropriate one:

In practice, this relationship can be observed in bicycles: Bicycles are typically composed of two road wheels, front and rear gears (referred to as sprockets) meshing with a circular chain, and a derailleur mechanism if the bicycle's transmission system allows multiple gear ratios to be used (i.e. multi-speed bicycle), all of which attached to the frame. Cyclist, the person who rides the bicycle, provides the input power by turning pedals, thereby cranking the front sprocket (commonly referred to as chainring). The input power provided by the cyclist is equal to the product of cadence (i.e. the number of pedal revolutions per minute) and the torque on spindle of the bicycle's crankset. Bicycle's drivetrain transmits the input power to the road wheel, which in turn conveys the received power to the road as the output power of the bicycle. Depending on the gear ratio of the bicycle, (torque,rpm)_input pair is converted to (torque,rpm)_output pair. By using larger rear gear, or by switching to a lower gear in multi-speed bicycles, angular speed of the road wheels is decreased while the torque is increased, product of which (i.e. power) does not change.

78.162.6.38 (talk) 21:51, 4 November 2014 (UTC)

In this section, there is a formula that comes just after the words "Power is the work per unit time, given by". I'm just wondering why the given equation P = tau.omega appears to have absolutely no link or relation to the words "Power is the work per unit time, given by". There appears to be some kind of disconnect here. KorgBoy (talk) 00:41, 14 February 2020 (UTC)

Definition of torque

I made a slight edit to the definition. It is correct that torque is always defined with respect to a point, but the previous version said that this point was the origin of the coordinates. That is not correct, the origin of coordinates could be quite separate. And anyway, no defintion should depend on the choice of the origin of coordinates. Timb66 (talk) 22:09, 15 March 2020 (UTC)

Ok, even if the source mentions the origin of a coordinate system. No problem. Thx. - DVdm (talk) 17:17, 16 March 2020 (UTC)

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)

Isn't the correct unit of torque really newton-metres per radian. In order for this formula:

   P = τω

(where P is power, τ is torque, ω is the angular velocity)

to work, the units of torque must be newton-metres per radian. If it isn't, then the formula can't be true. Newton metres time radians per second does not equal watts, it equals watt radians. Newton metres is the unit of work and energy and not torque. Work and energy divided by the angle in radians is the torque.

Newton metres per radian times radians per second equals newton metres per second, which equals joules per second, which equals watts. It only works out this way. — Preceding unsigned comment added by 68.109.207.203 (talk) 21:10, 7 July 2011 (UTC)

You are right. This little paragraph told me more about torque than the entire article. --213.46.223.174 (talk) 23:29, 27 August 2020 (UTC)

A radian is a dimensionless ratio of arc length to its associated radius i.e. the radian is not a unit. --Izno (talk) 21:26, 7 July 2011 (UTC)

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
I think that link is dead or changed. Actually for Joe's sake - and many others - this is TOO much of High school formal education or College Physics basics, Really need a Good separate article discussing torque- and its relationship to Power for engines & vehicles- in layman's terms interest with application versus formal education terminologies.
Ok -power is -partially how fast you can go - overcome or match all existing resistances. Acceleration requires torque - increase inertia rotational speed of engine. (and that could use improvement0 19:27, 15 May 2022 (UTC) — Preceding unsigned comment added by Wfoj3 (talk • contribs)

"Infinite torque at zero rpm" listed at Redirects for discussion

An editor has identified a potential problem with the redirect Infinite torque at zero rpm and has thus listed it for discussion. This discussion will occur at Wikipedia:Redirects for discussion/Log/2022 May 17#Infinite torque at zero rpm until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Ten Pound Hammer • ^{(What did I screw up now?)} 15:19, 17 May 2022 (UTC)