[duns]

I wish people would stop using "ft/lbs" as the measure of energy. :banghead:

The correct measure is "ft lbf". The former is wrong for two reasons: (1) the two units should be multiplied not divided, and (2) energy has the units of distance x force so the pound force (lbf) should be used rather than the pound (lb), which is a unit of mass. If you want to use the lb mass unit, the energy would need to be expressed in units of "ft^2 lb/sec^2" where 1 ft lbf = 32.174 ft^2 lb/sec^2.

Getting the units right is vital if doing one's own calculations. I also feel it's just as easy to use the right measure as the wrong one. Just my rant, feel free to call me pedantic :).

[RS14]

energy has the units of distance x force so the pound force (lbf) should be used rather than the pound (lb), which is a unit of mass.

I was always taught in school that a pound, unqualified, was a unit of force. If we needed mass, we tended to use kilograms (there is another imperial unit of mass--the slug--but it's not used much. I have seen it exactly once on an exam).

32.174 ft^2 lb/sec^2.

That's 32.174 ft^1 lb / sec^2

Or not; how embarrassing. Sorry.

[duns]

I was always taught in school that a pound, unqualified, was a unit of force. If we needed mass, we tended to use kilograms (there is another imperial unit of mass--the slug--but it's not used much. I have seen it exactly once on an exam).
If that's what you were taught in school, it's wrong. In the US System, the common units of mass are pound (lb or lbm), slug (32.174 lb), and ton (2000 lb). US force units include pound force (lbf) and ton force (tonf). There is also the kip (1000 lbf).

The kilogram mass unit is from the Metric System, an entirely different and more logical system of units. There is also a metric tonne (1000 kg). In the Metric System, common force units are the newton (N), the kilonewton (kN), the meganewton (MN), etc. The Metric System can also use kilogram force (kgf = 9.807 N), tonnes force (tonnef = 1000 kgf = 9.807 kN) etc.

That's 32.174 ft^1 lb / sec^2

Or not; .
No, it was correct as I had it. The "^2" means raised to the power 2 but I couldn't figure out how to show the power in the nicer format of a superscript. I can insert it as a picture though:

http://i943.photobucket.com/albums/ad274/riskassessor/Misc/Units.gif

PS In the Metric System, a typical unit of energy would be the newton meter (N m) or the joule (J). 1 J = 1 N m.

[RS14]

If that's what you were taught in school, it's wrong. In the US System, the common units of mass are pound (lb or lbm), slug (32.174 lb), and ton (2000 lb). US force units include pound force (lbf) and ton force (tonf). There is also the kip (1000 lbf).

The OED defines 'pound' as "A unit of weight and mass." Which is yes, absurd, but it's an absurd unit. Historically, there exist the Avoirdupois, Troy, Tower, Merchant's, London, and Wool pounds, at least.

Historically, I believe that 'pound' has been used as a unit of weight, e.g. force. Because it generally didn't matter, they also used it as a unit of mass. Thus it is archaic and ambiguous, but not entirely incorrect, to refer to a pound as a unit of force.

Better, of course, to use lbm when you mean mass and lbf when you mean force, or to simply use metric.




No, it was correct as I had it. The "^2" means raised to the power 2 but I couldn't figure out how to show the power in the nicer format of a superscript.

I just made an error in checking your work. I realized my error shortly after posting.

[Mike OTDP]

Sorry. RS14 is right. In English Engineering Units, the slug is the measure of mass. If you don't work things in slugs, you wind up dividing a truckload of stuff by 32.2 to get the right answer.

For thermodynamics, jet or rocket engine formulae, and aerodynamics, the first step is to get everything in the right units. Mass in slugs or kilograms, temperature in degrees Kelvin or Rankine. Had that pounded into me over 25 years ago.

[duns]

Historically, I believe that 'pound' has been used as a unit of weight, e.g. force. Because it generally didn't matter, they also used it as a unit of mass. Thus it is archaic and ambiguous, but not entirely incorrect, to refer to a pound as a unit of force.
Colloquially, we confuse pounds and pounds force all the time and it doesn't matter. I tell people "my weight is x pounds" when I should strictly say either "my mass is x pounds" or "my weight is x pounds force". This would be too pedantic in everyday speech especially since the number x remains the same whichever expression I use. When doing calculations one will obtain the wrong answer if one confuses pound and pound force.

When people write "ft/lbs" for muzzle energy, the more serious error I think is introducing the division sign between the units when the units are supposed to be in a multiplicative relationship.

[duns]

Sorry. RS14 is right. In English Engineering Units, the slug is the measure of mass. If you don't work things in slugs, you wind up dividing a truckload of stuff by 32.2 to get the right answer.
Ah, the good old slug. We still used those when I was doing engineering at college.

I found this definition somewhere on the net: "The slug is defined as the mass which would accelerate at a rate of 1 ft/s per second under a force of one pound-force (lbf). Since 1 lbf is the force exerted on a mass of one pound by a standard gravitational field (of exactly 9.80665 meters per square second), a slug is thus exactly equal to 196133/6096 pounds (about 32.1740485564 lb or 14.593902937206 kg)." I felt sure you all wanted to know that.

Bullets of course are measured in grains defined as 1/7000 of one pound. A grain reputedly is the average mass of a single grain of wheat. Units and their histories are really quite fascinating.

[RyanM]

I think most people that use the slash are just using it as an abbreviation. I usually say ft-lb for energy, sg-ft/sec for momentum. So mine at least is consistent dash = multiply.

In my mind, anyway, pounds are always force, and the only English mass unit is the slug. It's simpler that way.

[danez71]

Since the projectile is going X fps (speed), cant this be coverted to HP (horse power) and be easier to understand for all? :rolleyes:

[The Lone Haranguer]

I always thought it was "ft lb of muzzle 'smash.'" :evil:

[MCgunner]

I don't get ulcers over internet semantics, grammar, or spelling. :rolleyes: All that matters is I understand the point. It's sort of condescending to correct someone and, well, you'd spend all day doing it and, well, people who live in glass houses shouldn't throw stones. :D

What does tick me off a tad is the word "shotty".:fire::banghead: I mean, you got the "clip" vs "magazine" thing, the "revolver" vs "pistol" thing. You could go crazy.

[MICHAEL T]

I suggest you send letter to Guns and Ammo I see their using ft-lbs and all my Corbon Ammo boxes have ft/lbs listed better advise them also of the error . Those are 2 I found with out getting up from my computer So is this going to be a clip mag thing Or are you the only one who really cares. I will use ft/lbs have for many a year and don't see any change coming Obama might be interested in forming a committee to study this matter might be way for him to take our ammo

[Lonestar49]

...

Yikes, a math test.. :eek:


Ls

[The Lone Haranguer]

If you want to use the lb mass unit, the energy would need to be expressed in units of "ft^2 lb/sec^2" where 1 ft lbf = 32.174 ft^2 lb/sec^2.


:confused:

http://botit.botany.wisc.edu/toms_fungi/images/einstein3.jpg

"TMI!"

[Cosmoline]

I wish people would stop using "ft/lbs" as the measure of energy

Wait a second.. are you just griping about the use of the "/" symbol instead of saying "ft-lbf"

[duns]

I suggest you send letter to Guns and Ammo I see their using ft-lbs and all my Corbon Ammo boxes have ft/lbs listed better advise them also of the error . Those are 2 I found with out getting up from my computer So is this going to be a clip mag thing Or are you the only one who really cares. I will use ft/lbs have for many a year and don't see any change coming
Yes, it's a very common error. Only really matters if you are doing calculations. Otherwise, it can be regarded as no more or less important than the misspelling of any word.

[duns]

Wait a second.. are you just griping about the use of the "/" symbol instead of saying "ft-lbf"
The "/" symbol is my first gripe. It means division as in for example "ft/sec". But energy is the product of distance (e.g. ft) and force (e.g. lbf), i.e. it's a multiplicative relationship. To express the multiplicative relationship, it is conventional to leave a space as in "ft lbf" or use a small dot raised above the line as shown in the image in post #3 (I can't do the raised dot in this message text).

My second gripe is writing "lbs" instead of "lbf". I suppose the "s" is meant to indicate a plural (pounds) but conventionally units are always written in the singular when abbreviated, e.g. we write "mm" for millimeters, not "mms". But "lb" would not be correct either because that is a unit of mass, not force. It has to be "lbf".

[Cosmoline]

Good luck with that.

Results 1 - 10 of about 1,050,000 for "ft/lbs"

1 - 10 of about 73,800 for "ft lbf"

I think you're just seeing a difference between scientific nomenclature and common English.

[rcmodel]

When I grew up, car & motorcycle magazines listed engine torque in ft-lb.

Now, it is more often listed in lb-ft.

Which is it?
And who cares anyway.
I still know what they are talking about.

rc

[buck460XVR]

I think it depends on what you are measuring the energy of.....whether it's a firearm, weapon of just a plain gun. Also whether it uses a magazine or a clip.:rolleyes:


like RC said......"who cares anyway?''

[duns]

I think you're just seeing a difference between scientific nomenclature and common English.
Let's use speed as an analogy because people understand speed better than energy. Would you in common English write feet per second as "ft sec"? No, because you want to express the per, which represents a division operation (feet divided by seconds), so you write "ft/sec" or maybe "fps". Now when people write energy as ft/lbs, they are effectively saying "feet per pounds", which is both ungrammatical and scientifically wrong. Energy is distance times force (e.g. feet times pounds-force), so the unit of energy they want is the foot pound-force, which is correctly expressed as "ft lbf". It's not so much common English as lack of understanding of what energy is. Speed is understood, so is expressed correctly; energy is not understood so is expressed wrong.

[duns]

When I grew up, car & motorcycle magazines listed engine torque in ft-lb.

Now, it is more often listed in lb-ft.

Which is it?

Yes, its common to use "ft-lb" or "lb-ft" for torque. Torque is force times distance (or distance times force, same thing), so it doesn't matter which order the units come in. These common expressions for torque contain one of the errors I was ranting about -- use of pounds-mass (lb) when it should be pounds-force (lbf). So torque is correctly expressed: "ft lbf" or "lbf ft".

Although energy and torque have the same units, they are not the same thing. When you apply torque to rotate something through an angle, the energy expended is the torque times the angle in radians. The radian is a bit strange as it is a pure number not a unit, so the radian unit can always be omitted without error. So energy (in this case torque times angle) has the exact same units as torque.

[duns]

like RC said......"who cares anyway?''
Engineers and scientists doing calculations with energy have to care about using the correct units otherwise they would get the wrong numerical answers. For other people, it's akin to the misspelling of a word. If you care about spelling words correctly, then you should want to quote units correctly.

[Cosmoline]

Would you in common English write feet per second as "ft sec"?

You would if that's how it was expressed in common English. "Ft/lbs" is really just a word, not a scientific abbreviation. We use it as a word, and we all know what it means. We know that it isn't expressing a division. How that particular usage evolved I don't know, but it's been that way for a long time.

In other words, proper English does not have to be scientifically accurate or correct. It simply is what it is. That's the great thing about English.

[duns]

"Ft/lbs" is really just a word, not a scientific abbreviation. We use it as a word, and we all know what it means. We know that it isn't expressing a division.
When you use "ft/sec" you are expressing a division between one unit and the other. You intend the "/" to be pronounced as "per". So why put a "/" between the units of energy when you are not going to pronounce it as "per" but instead you are going to treat it as a space? Do you feel a space looks awkward?

[fastbolt]

Lots of folks use different terms when discussing ammunition.

Some folks like to use the abbreviation "JHP", even though it may not be the most accurate term. How about BHP, BJHP, SJHP, etc?

Some folks like to refer to the nose cavity of a JHP as the hollowpoint, even ...

So, if a manufacturer lists "FPE" or "ME" for any particular cartridge, does anyone not know to what they're referring?

Next thing you know, someone's going to want to express bullet weight in grams instead of grains ... :neener:

[duns]

So, if a manufacturer lists "FPE" or "ME" for any particular cartridge, does anyone not know to what they're referring?

When someone uses the incorrect units "ft/lbs", I know what they mean. They mean energy expressed in the US units system. The fact they didn't write it as "ft lbf" suggests they may not understand exactly how energy is calculated.

[duns]

Next thing you know, someone's going to want to express bullet weight in grams instead of grains ...
In France they do express bullet weight in grams (...and energy in joules).

[SSN Vet]

Yawn.....

that's the same response I had back in school whenever the whole lbf vs lbm vs slugs bit came up.

any one who knows anything knows that Joules is the unit for energy anyways :neener:

[duns]

any one who knows anything knows that Joules is the unit for energy anyways
LOL, I agree. There aren't too many different ways to write joule (J).

[Cosmoline]

When you use "ft/sec" you are expressing a division between one unit and the other.

Actually I'm more likely to say "fps." I don't use the slash as a solidus just as a divider. I could put "ft-lbs" yet I'm not trying to subtract pounds from feet.

[Wheeler44]

If I understand then, todays date is .000213219....

Some words have more than one meaning...apparently some symbols do as well...

[fastbolt]

The fact they didn't write it as "ft lbf" suggests they may not understand exactly how energy is calculated.

I'd be willing to consider that most people don't understand how MPG estimates are determined for motor vehicles, either, but they still seem willing to use it when comparing vehicles they're considering for potential purchase, though, don't they?

Besides, calculating the "ft lbf" for any given cartridge/load still doesn't really tell anyone the complete story when it comes to the usefulness of the load, anyway ...

[Nematocyst]

If any one needs any information about mitochondria, chloroplasts, citric acid cycle,
electron transport systems, photosynthesis and such, just let me know.

Otherwise, I'll just stand over on the side here and let the physicists slug it out.

:uhoh:

[Brian Williams]

And this has to do specifically with Handguns, HOW?

[skoro]

As I understand it, the English unit for mass is the slug. The pound measures weight, which is mass x g (acceleration of gravity). And mass x g = force. Force x distance (lb x ft) would equal energy (well, work actually but it's equivalent to energy).

It's all more clear cut in the metric system (SI) which is what we should be using in the first place. And we will, eventually. The rest of the world is way ahead of us here.

[Art Eatman]

You mean to tell me that all this fooforaw began because some folks use a slash instead of a dash? 'Scuse me? Can we identify a new career field? "Picking Flypoop out of Pepper"?

I haven't forgotten my high school physics, not completely anyway, even if that was sixty years ago. It was "ft-lbs" then and my Marks Engineering Handbook still says that.

Somebody makes a trivial goof; okay, send a polite and courteous PM if you feel the need for correcting an error.

Polite and courteous. It's the cowboy--oops, the High Road Way.

[JohnBT]

"The "/" symbol is my first gripe. It means division "

Not always. Not usually, unless you're in math class. Does "and/or" mean "and divided by or"? Of course not. That's why the symbol is called a forward slash. Or stroke, by some.

Weren't you in my junior physics class at Tech?

John

[tyme]

Reason #19035676 to use metric for everything, everywhere, all the time.

You mean to tell me that all this fooforaw began because some folks use a slash instead of a dash? 'Scuse me? Can we identify a new career field? "Picking Flypoop out of Pepper"?

http://www.cnn.com/TECH/space/9909/30/mars.metric.02/

That was of course the result of using different measurement systems rather than using one system incorrectly, but it's still the result of too-casual [lack of] use or understanding of [correct] units.

If we don't try to correct the cultural attitude that units can be written and used incorrectly or ambiguously in casual communication, we are begging for more expensive screw-ups in the future, when such casual attitudes occasionally bleed into the professional engineering world. Whether it's a government project and taxpayers pay for unit illiteracy, or whether it's a private company and customers or owners or investors pay, someone pays.

In extreme cases, insensitivity to unit accuracy can get people killed. Why is it so surprising that those who are more aware of the specter of such calamities protest vehemently when others are fast & loose with unit representations?


About the alternate uses of "/", which one are you thinking applies in the case of "ft/lbs" or "ft/lbf"?

"/" often means "or" or less commonly "subclass/subgroup/subsection", but neither of those uses makes any sense in this case.

How far does this go? If we tolerate "ft/lbs", aren't we obligated to tolerate "ft%lbs", "ft^lb", and every other unit and punctuation option that makes zero sense and/or is ambiguous, simply because "we know what it means" in context?

Is it really a bad thing to gently nudge unit manglers and inform them of their mistakes?

[msgttbar]

Kinda reminds me of the old question, "Which weighs more, a pound of feathers or a pound of gold?".

[Mal H]

Actually, the older, old question is "Which weighs more, a pound of feathers or a pound of lead?" The answer being neither, they both weigh the same.

The answer to the old question you asked is - the pound of feathers weighs more.
;)

[duns]

And this has to do specifically with Handguns, HOW?
My original post is relevant to this site because energy of bullets is frequently discussed but energy values are more often than not given with the wrong units attached. I thought it helpful to point out the correct units as it is just as easy for people to use the right ones as the wrong ones. I'm not sure if you are suggesting I posted my thread in the wrong section; if I did, I apologize.

[Jesse Heywood]

It's one of those things that I consider to be in the same category as correcting grammar and spelling. The message is usually wasted or taken as an insult. Some boards have rules against correcting spelling and grammar to help keep peoples' feelings from reaching a boil. All in all, I let those items slide.

And when I took engineering classes we had to use the SI units. But in the real world we specified force in ft-lb on the drawings. If we had used lbf the guys on the shop floor would not have understood, resulting in rejection tags and phone calls, wasting a lot of time.

What is my point? Don't sweat the small stuff.

[duns]

It's one of those things that I consider to be in the same category as correcting grammar and spelling.
I think tyme got it right in his message #39. Correct use of units is not in the same category as grammar and spelling for engineers and scientists because use of incorrect units is a common cause of incorrect analysis results, sometimes with disastrous consequences. For lay people, I agree it is in the same category as a spelling error but it is nice not to make spelling errors. I thought people on THR might like to know the correct units of energy since energy values are quoted so often.

[Mal H]

... and with that, we'll close this one. Further discussion would be pointless.