A Basic Primer on Horse Power and Torque

was there a question in that?

This was not a question but was entered under "start a discussion."

Seems to be working,even if it only generates humor.

It's good thread. At the very least, if people bother to use the little search window to the right, it will reduce the number of redundant and dumb threads.

Kramarat:

I appreciate your optimistic outlook. I'm much less confident any reduction in 'dumb and redundant' will materialize.

Granted, I probably see the front page every morning before the mods are out of bed, but for cryin' out loud................even with my limited knowledge, it's just embarrassing.

can we argue the speed of light next?

Well that sure is confusing.

I always figured that horsepower referred to how many horses it took to do a unit of work.

5HP = 5 well fed horses.

Hmm, that brings in the idea of types of horse power....

...

''...This baby has 450 BDHP (Belgian Draft Horse Power) under the hood, 450 SPP (Shetland Pony Power) just wouldn't have done the trick...''

I think the original word had to do with horses.

I guess I do need to explain the origin of the term HORSEPOWER:

A Scottish engineer named James Watt derived this term by observing the average amount of work performed by draft horses used in mining operations.It amounted to 33000 foot pounds per minute.

The mining horses were quite a bit smaller than standard horses,but the term stuck and was applied across many disciplines.

Now if he had used mules, it would have been mule power,or if camels were used to move cargo, it would have been camel power.

I am sure alien species will have a similar weird term for their power.

"HEY! How many Jabbas you got under the cowling of that space ship?"

Good information is always welcome.

A pound-foot (lb·ft or lb_f·ft) is a unit of torque (a vector). One pound-foot is the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point.

One pound-foot is exactly 1.3558179483314004 newton meters.

The name "pound-foot", intended to minimize confusion with the foot-pound as a unit of work, was apparently first proposed by British physicist Arthur Mason Worthington. However, foot-pound (ft·lb or ft·lb_f) is also sometimes used interchangeably with "pound-foot" to express torque.

From Wikipedia

that confused meI thought you just kept pulling on the wrench til it "clicked

Don't be silly, if they wanted you to pulll on it manually, the unit would be called something like a 'Yank-Hand'.

Anything labled 'Pound-Foot' is obviously instructing you to kick it.

(alternately 'Pound-Feet' is specifying much more commitment for proper operation)

I deliberately stayed away from pound-feet to prevent confusion with foot pound.

I stated the radius in inches and inch pounds in my description to avoid the often confused similarity between foot pound and pound feet.

In Russia, they use another unit called "Shoe Pound" which is a vector of a shoe pounding on a desk from a specified height at a certain repetition rate.The unit has been renamed in honor of Nikita Kreuschev as K POUNDS

You may or may not remember the incident to which I refer,(1960) but I am sure someone on this forum will.

Never threaten with a shoe, to do a shovel's job.

There are some unnecessary inconsistencies in units in this description.

It is a common convention (in the US) to describe torque in lb-ft and work in ft-lb. Suggesting that inches somehow apply to torque but feet apply to work confuses the issue. For Joe average in the US, the most often quoted torque (that of automotive engines) is measured in lb-ft. Torque wrenches read in lb-ft, unless they are for use by sissies on very small screws.

Thus the HP formula is more often seen like this:

HP = lb-ft x rpm /5252.

Thinking in these units has the advantage that 5252 is easier to remember than a figure 12 times as big. It also means that when looking at a dyno chart, the HP and torque numerical values are always the same at 5252 rpm. So even if you forget the easy-to-remember number 5252, you can look on a dyno printout to refresh your memory.

You make some valid points, especially if talking about automotive engines.What if you are talking about gear boxes and calculating pulley or gear sizes,where the pulleys are measured in inches(or millimetrs,etc)?

You will find most electric gear reducers rated in inch pounds(or metric equivalent) of torque, as it is most convenient to calculate pulley sizes.

The information I gave is valid regardless of the area of usage,as is yours, but a conversion has to be made regardless if you are changing the application from one field of endeavor to another.

Once you become accustomed to the calculations in your field, they become automatic and instinctive.

Remember, this is a PRIMER,not a full blown encyclopedia, and I did not attempt to cover all possible permutations of measurement units.

If the terms are unfamiliar to you, feel free convert to more comfortable units, as I indicated in the text

As for inch pounds, there are used when adjusting critical components, as in automatic transmissions,instrumentation, etc., and special torque wrenches are made for such applications.Of course,being an automotive oriented person, you already know this.

I also have experience in automotive, and I built an 11 second 1/4 miler back in the 60's,using the now impossible to find Z28 302 Camaro engine, and yes, foot pounds were common terms.

My field of experience has grown over the last 50 years to include many areas of mechanics and electronics,pneumatics, and hydraulics,and unit conversions are a routine thing.We did not even use the metric system at all in the 1960's,so when I think metric, I have to mentally convert to English units to get a mental"feel" for what the unit is, unless it is a unit I use regularly.Such as: .03937 x5 x last 2 digits of a ball bearing will give the shaft size for a press fit of that bearing in inches.Do you carry that number around in your head?I do. Just like you do with 5252.

I have seen a 1/16 hp electric gearbox motor pull 1/2 anchors out of a concrete floor,and it's output was rated in inch pounds.Definitely not a sissy.Of course the speed was almost like a clock motor.

I am sorry you are confused by the use of this term which is unfamiliar to you,however it may be common to other users.I cannot speak for every Joe Average in the USA,because I do not presume to know their mind,but they too are free to convert as they please.

To each his own

Don't worry,be happy!

Remember, this is a PRIMER,not a full blown encyclopedia, and I did not attempt to cover all possible permutations of measurement units.

That is why I brought up the distinction. If one says, to someone who slept through high school, that torque is measured in inch-pounds and work is measured in foot-pounds, then that person could assume that the difference between work and torque has something to do with the difference between inches and feet -- which is of course completely wrong. My point was not that you were incorrect in your math, but instead that it is poor instruction technique for a primer. An instructor would not, for an audience needing a PRIMER, say that torque is measured in newton-meters and work is measured in oz-inches. Although both assertions are correct (if one ignores the word order convention), it does not aid instruction.

The other issue, the ft-lb vs lb-ft distinction is one that is more subtle, but used to be observed by virtually all engineers and every physics teacher. In a PRIMER, maintaining the distinction is helpful, because it highlights the fact that torque and work are completely different concepts.

If you were providing a primer on electrics, you would not (I hope) use VA and Watts interchangeably, because they have different, specific meanings, despite both being the product of volts and amps. The reason teachers are "pedantic" is that they don't want to start bad habits by encouraging sloppiness with terms. Once you know this stuff, you can often figure out if 500 ft lb means work or torque from the context. But if you already know this stuff, you don't need a primer.

So, my point is that in a PRIMER (in which the intent is to be instructive) it is good to use the correct terminology. There will be plenty of time later in life for becoming sloppy.

Happiness to you too.

Please feel free to submit your own version as it should be, ATF (According To Fry)

I will not be offended or insulted in any way,and will welcome the corrections and illumination of my erroneous methods, although I would appreciate feedback from a beginner that is just getting his feet wet in the engineering discipline.I will not assume or presume how they will intepret the knowledge as I presented it.I am not a teacher.I would fall short in many areas of that endeavor.I hope I have not muddied the water for beginners.

By the way, here is a link to gearmotors,where inch-pounds is the normal specification.

There may be more gearboxes in the world than gasoline engines.

http://www.bisongear.com/category.asp_Q_catID_E_1

Who knows which field of endeavor a newbie will pursue?

Only a psychic could know.

6 of 1; 1/2 dozen of the other I say.

I constantly ask myself every day,when faced with a problem:WWFD?

"What Would Fry Do?"

PEACE! Live long and prosper.

HT has the formula down and despite a few terminology variences due to application, the numbers don't lie. Still there seems to be some confusion betwe foot pounds and pound feet which I think I can clear up. See below.

Foot pounds

Pounds Feet

See, not that hard after all. (wink wink nudge nudge)