# Of horsepower and torque **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [July 15, 2005, 8:03pm UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709 "2005-07-15T20:03:00Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![grg88](https://avatars.discourse-cdn.com/v4/letter/g/bbe5ce/32.png) [@grg88](https://boards.straightdope.com/u/grg88)\ **Post date:** [July 21, 2005, 11:17am UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/21 "2005-07-21T11:17:36Z")
\>Torque is work per (some unit of angle, such as degree, radian, grad, or revolution), If that were so, the units of torque would include an angle. They do not. \>though it is, unfortunately, traditionally regarded as force-at-radius-x. There’s a good reason it’s regarded that way, that’s because it is. One may be decieved because there’s a distance element, the “foot” in foor-pounds. But this isnt a true distance, indicating distance moved, because it’s always at right angles to the force. It’s just an indication of the length of the lever. \>It is the rotational analog of force. That’s exactly right. You can turn torque into force by putting a lever on the rotating object. 100 ft-lbs of torque will turn into 100 pounds of force at the end of a 1 foot lever. However 100 pounds of force is just that, force. Without movement, there is no work done. I hate to be sooo picky, but it’s important to get these basic things just right, otherwise physics becomes chaos. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [July 21, 2005, 12:57pm UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/22 "2005-07-21T12:57:28Z")
> [@grg88](#): > > \>Torque is work per (some unit of angle, such as degree, radian, grad, or revolution), > > If that were so, the units of torque would include an angle. They do not. The units of torque, and all related units, such as moment of inertia and angular momentum, are _wrong_, just as the older electromagnetic units in which capacitance was a length were wrong; if they were right, then torque would be interconvertible with energy, which it most certainly is not. ---
**Author:** ![grg88](https://avatars.discourse-cdn.com/v4/letter/g/bbe5ce/32.png) [@grg88](https://boards.straightdope.com/u/grg88)\ **Post date:** [July 21, 2005, 1:25pm UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/23 "2005-07-21T13:25:16Z")
\>The units of torque, and all related units, such as moment of inertia and angular momentum, are wrong, That kind of statement worked for Aristotle, but we have this new thing called “science” where one has to show, demonstrate, perhaps even prove the correctness of their statements. \>just as the older electromagnetic units in which capacitance was a length were wrong; Capacitance is proportional to the area (distance squared) divided by the separation. In units, that does simplify down to just distance. I have some old French radios here where all the capacitors are labeled inthose old units, cm. Quite startling, but physically correct. A few confirming references: > **[Answers - The Most Trusted Place for Answering Life's Questions](https://www.answers.com/redirectSearch?query=centimetre-gram-second-system-of-units)** > > Answers is the place to go to get the answers you need and to ask the questions you want > **[Centimetre–gram–second system of units](https://en.wikipedia.org/wiki/Electromagnetic_unit)** > > The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways in which the CGS system was extended to cover electromagnetism. > The CGS system has been largely supplanted by the MKS system based on the metre, kilogram, and second, w... ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [July 21, 2005, 3:13pm UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/24 "2005-07-21T15:13:30Z")
It is trivial to show that torque is not equivalent to energy. Indeed, you’ve stated it yourself. It was a mistake to regard electricity as a dimensionless quantity a hundred years ago, and the SI (and the MKSA system before it) has corrected this; it is just as much a mistake to regard rotation as a dimensionless quantity today, no matter how traditional and well established, and your own first post in this very thread makes the point for me. ---
**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\ **Post date:** [July 21, 2005, 5:40pm UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/25 "2005-07-21T17:40:28Z")
When they calculated the original horsepower number, were they including the power the horse used to move itself when pulling a load, or just the power needed to pull the load itself? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 21, 2005, 6:07pm UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/26 "2005-07-21T18:07:30Z")
How is it a mistake to regard rotation as dimensionless? If it had a dimension, then you couldn’t take the sine or cosine of a rotation. Likewise, what makes you say so confidently that Coulomb’s constant has dimension? It’s just as dimensionless as Newton’s constant or Einstein’s constant (all three of them being equal to 1). Or at least, it can be perfectly consistently treated as dimensionless, and it is often convenient to do so. Is there any more compelling argument available? Beyond, I mean, the oh-so-scientific “that’s just wrong” you’ve offered. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [July 21, 2005, 6:55pm UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/27 "2005-07-21T18:55:43Z")
> [@Chronos](#): > > How is it a mistake to regard rotation as dimensionless? If it had a dimension, then you couldn’t take the sine or cosine of a rotation. Likewise, what makes you say so confidently that Coulomb’s constant has dimension? It’s just as dimensionless as Newton’s constant or Einstein’s constant (all three of them being equal to 1). Or at least, it can be perfectly consistently treated as dimensionless, and it is often convenient to do so. Is there any more compelling argument available? Beyond, I mean, the oh-so-scientific “that’s just wrong” you’ve offered. Because it invalidates dimensional analysis; it makes it entirely possible to have equations with energy on one side and torque on the other, or with capacitance (or, alternatively, inductance) on one side and linear distance on the other. In the electromagnetic case, the problem was resolved when the cgs systems were replaced by the MKSA system (later the SI). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 21, 2005, 8:39pm UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/28 "2005-07-21T20:39:03Z")
You can’t have an equation with energy on one side and torque on the other, for the simple reason that energy is a scalar but torque is a pseudovector. But you can have an equation with energy on one side and magnitude of a torque on the other, or one with capacitance and linear distance. And I’m puzzled by your use of the past tense in referring to the hypothetical time when MKS replaces CGS… That hasn’t happened yet. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [July 22, 2005, 1:04am UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/29 "2005-07-22T01:04:25Z")
> [@Chronos](#): > > You can’t have an equation with energy on one side and torque on the other, for the simple reason that energy is a scalar but torque is a pseudovector. But that’s when you get when you define torque as ml[sup]2[/sup]t[sup]-2[/sup]. It’s adding torque apples to energy oranges, which is a Bad Thing. Torque should be defined as ml[sup]2[/sup]t[sup]-2[/sup]θ[sup]-1[/sup], which is what it really is. (Back when I was in high school physics, every time a student answered a question with a number – except for the rare occasion when that was actually the correct answer – Mr. Gralla would shoot back, “_n_ what? _n_ alligators?” a lesson I’ve never forgotten.) > [@Chronos](#): > > And I’m puzzled by your use of the past tense in referring to the hypothetical time when MKS replaces CGS… That hasn’t happened yet. Every reference I can find (not to mention my physics textbooks from back in the 1960’s) says so, not to mention that SI, which evolved from MKS, has replaced both. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [July 22, 2005, 4:48am UTC](https://boards.straightdope.com/t/of-horsepower-and-torque/312709/30 "2005-07-22T04:48:52Z")
> [@grg88](#): > > Pretty good article, marred by I think at least one blooper: > > \>" Torque is a measure of the ability of an engine to do work. " > [@John W. Kennedy](#): > > However, Una said “ability…to do work”, not “work”. I think that says it all. And even that may not be totally correct, but I believe it is reasonably correct to say in the context of the article. [Previous page](https://boards.straightdope.com/t/of-horsepower-and-torque/312709.md?page=1)