# what is the conversion between lbs and kg

i think there are both force units, right?

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1 kg = 2.206 lbs
They are strictly speaking units of mass.
They become forces when these masses are subjected to gravity. In this case, the units should be distinguished as kgf and lbf.
But the force due to gravity on a mass of 1 kg is 1 kgf, anwhen subjected to gravity

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Sometimes. Not very often. Not very often even on plant Earth, depending on how accurate you want to be.
The gravitational force on 1 kg mass is approximately 1 kgf, to within 1%, on the surface of the Earth, at sea level, might be a better way of putting it.
"The sea-level gravitational acceleration is 9.780 m/s� at the equator and 9.832 m/s� at the poles, so an object will exert about 0.5% more force due to gravity at sea level at the poles than at sea level at the equator (http://curious.astro.cornell.edu/question.php?number10 )."
That's a quote from this: http://en.wikipedia.org/wiki/Gravity
Cheers
Greg Locock
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john smith wrote:

No, kilogram is a mass unit. Newton is the force unit in SI system. There pounds mass, lbm and pounds force, lbf. On the earth's surface 1 lbm weighs 1 lbf.
2.205 lbm = 1 kg
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Jeff Finlayson wrote:

To be really precise (unnecessarily so for most purposes), the pound mass is defined as exactly 0.45359237 kg. See: http://physics.nist.gov/Pubs/SP811/appenB.html which is a good source for such things.
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A.H. wrote:

Same basic answer except twice as many significant figures.
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On Thu, 16 Jun 2005 00:17:21 -0500, Jeff Finlayson

No. Infinity divided by four is infinity, an infinite number as many significant figures. Not twice.
Gene Nygaard
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Gene Nygaard right on cue trolls:

Infinity, great counting skills there, LOL!
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john smith wrote:

There are semantic arguments for just about any combination. As has been pointed out, you sometimes see lbm units for mass and lbf units for force. There are even kgf units for metric force!
Strictly speaking, however, if you're going to use English units for engineering (slug-ft-s), you must think of "pounds" as a unit of *force* and "slugs" as a unit of *mass*. The rest of the derived units of the system won't work out unless you do.
psi (pressure), ft-lb (energy/work), lb-ft (torque), ft-lb/s (power), etc. All of these units depend on lbs being a *force* unit. If you're going to use all the same simple formulas as you use for metric calculations, you have to think this way.
For example, the everyday Newtonian formula
F = m*a
or "force equals mass multiplied by acceleration", requires that force be in pounds, mass be in slugs and acceleration be in feet per second squared. If you don't use these units, you can't use F=ma as it is. You would have to add some sort of conversion coefficient to the formula for it to render the correct answer.
You have to be very careful, though, since you will see units such as lbm and kgf at times in manufacturers' literature. As long as you don't try to plug kgf into the 'F' of an equation, or lbm into the 'm' of an equation you should be OK.
Don Kansas City
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1) No. Thus there is no conversion between pounds and kilograms any more than there is a conversion between pounds and hours or between kilograms and newtons. Only units of the same parameter are convertible.
pounds (lbs) are units of force, and kg (1000 grams) are units of mass.
2) They are alike only in that each is a fundamental unit in their respective measurement systems.
The pound is one of the three fundamental units in the British system - force (lb), time (second), and distance (foot). The British system has no fundamental mass unit. That unit in the British system, the slug, is a secondary (derived) unit. Secondary (derived) means it is derived from one of the three fundamental units.
The kilogram is one of the three basic units in the mks (metric) system -mass (kilogram), distance (meter), and time (second). The two/three metric systems have no fundamental unit of force. The force unit in the mks metric system, called the newton, is a secondary (derived) unit. The force unit in the cgs metric system (cgs, for the fundamental units centimeter, gram, second) is the dyne, a secondary (derived) unit. The force unit in the new ISS metric system is the newton, a secondary (derived) unit.
3) There is a conversion between kilograms-FORCE and pounds. A kilogram-force is a mass of one kilogram acted on by the acceleration of earth's gravity divided by 9.8.
that conversion is 1 kilogram-force = 2.205 pounds.
------------------
Note: the term "pounds-force" is a redundancy, like saying "force-force".
For some reason, a great many of the metric adherents seem unable to buy their butter by weight, i.e., as in "a half-newton of butter". So when they say kilo, they mean a newton divided by 9.8.
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Dear --:

The pound has been defined as a unit of mass since before 1959. It is directly relatable to the kilogram, by convention. It has hysterically been defined as a unit of force also.
For the former: URL:http://physics.nist.gov/Pubs/SP447/app5.pdf ... it is 2 Mb, and is an image, not searchable text.
For a further abomination, you can procure pressure gauges with the units "kg/cm^2".
David A. Smith
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message

This thread has been going on a particularly long time without Green getting involved. Do you think he's ok?
Fred Klingener
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Dear Fred Klingener:

Do you mean "Gene Nygaard"? He last posted on 2005jun11, on alt.sci.physics, thread "Engineers vs physicists and other scientists".
David A. Smith
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dlzc:
Thanks for the research that I was too lazy to do.
I'm so relieved that he's ok. I guess he's just been too busy to do his daily Googling for 'mass'.
Fred
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Federal Standard 376B, Preferred Metric Units, states that weight is mass, and then contradicts itself on page 13 when it says that in science and engineering and technical fields, weight is mass acted on by the acceleration of gravity, and weight shall then be measured in newtons rather than kg.
http://www.lhup.edu/~dsimanek/scenario/errorman/units.htm
http://www.ccb.org/docs/FEDMIL/Fs376b.pdf
I know all too well how they are in a box and they are forced to either accept "kg" as weight the force and mess up the "clean" SI system, or they have to redefine "pounds as mass" - they have to do one of them in order to make sense of the metric countries' use of metric's mass terms for weight in commerce. They are damned if they do and damned if they don't. But they are politicians making sure commerce is served, so a few details can be overlooked.
And if you plan to take your country to the metric IS system and abandon the FPS for purposes of commerce, you will of course choose to abandon the expendable fps definition because it won't make a difference in a 100 years, even if your reasoning is BS and you make up the "mass is weight" stories for expediency and plausibility - commerce requires commonality, even if it is dead wrong scientifically. So instead of being rigorous and differentiatng between weight and mass as scientists do, the polsd of commerce says weight and mass are the same, and the problem of buying butter in kgs now makes perfect sense by making a backwards definition, since now all the previous time we really bought things by mass rather than by weight - oops, they are the same, now, so "rather" is wrong- except by law they aren't the same in the technical areas-
If the metric countries had used newtons in their day to day commerce instead of kg, the "mass is weight" snow job would never have seen the light of day.
To be honest, I cannot see how anyone but a politician can hold that all weight/mass measures in the US weights and standards are masses "because measures use a balance beam, and balance beams use a reference mass". That crap is refuted plain and simple by the removal-of-the-element argument - If you remove the acceleration of gravity, (and thus the force) a balance beam will not measure anything. At all. No force, no measurement. It cannot work with just mass. It does not measure mass. It can be used to determine mass, true, if an acceleration is present, but it does not measure mass.
Besides, mass is not measured with balance beams - it is measured with spheres on strings using m1 m2 /d^2. And that measurement method works without gravity or other acceleration.
ah, well, at least we have the simplicity of the metric system - the new one, without tor or gauss or oersteds or dynes or angstroms.
I have some pressure measurements and some thermodynamics facing me today - what the hell are those metric units again?

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-- wrote:

Don't worry about it, metrics are on their way out, there's another revolution brewing here in Philadelphia and the battle is on - follow us!
"Furlongs, stone and fortnights or die!"
<sigh>
If you really enjoy going crazy diddle with the heap of metric "standards" for torque.
Brian
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Dear --:

...
Which is of course incorrect, as you have noted. Do you have a page reference?
...

You can accelerate the "balance beam system" linearly, and its validity is restored. Gravity is not required, but it is pervasive. And it provides the same relative "mass reading" if the value of g varies... all it affects is the settling time.

Mass is a relative measure. Of course, if you can count and type the atoms...

What pulls the spheres to the ends of their strings? What then attracts one sphere to the other? Obviously gravity plays a strong part.
Just FYI, they also drop small test masses past a large reference mass, and see how much the test mass's path is altered by the presence (and distance) of the reference mass. This also one of the current methods.

Just a little less than a "bar", just FYI.
David A. Smith
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it was in the post you referenced, as was the link.

the tester

I would think it is "universal" gravity from the mm/r^2 equation, rather than earth gravity. I believe the idea for the string-and-sphere is to remove the third body mass (earth), remove the fluctuations in the earth gravity field, and remove the centripetal force effect. Although your observation that some type of gravity needs to be in play is well taken.

and a lot easier since my college days, given the accesibility to the accuracies of lasers, and likely the use of laser interferometers?

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clarification nuance -- the balance beam needs the acceleration created by earth's gravity acting on the two masses, or it needs some other acceleration acting equally on the two masses, in order to work. The adjacent sphere method does not need an acceleration - it uses universal gravitation. It does, however, need a spring-pair or like restraint to keep the mutually attracting spheres from touching.
Are they different "gravities"? Yes and no - the sphere method "uses" the universal gravitation constant (f= G*M1*M2/d^2 -I think) acting between the two masses, and the balance beam uses the earth gravitation constant (f=mg) acting on the two masses in mechanical opposition. ------------
It's as confusing as new-metric thermodynamics. Thus I am leaving this mess to others.
Thank God the politicians had the foresight to pass that law that made pi 4. It makes geometry so much simpler, and I have faith that they will do the same for metrics -again. Or has that (yes, it was real) Indiana law regarding pi been repealed?

remove
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No. It was not real. Go retake your political science classes, and learn what it means to "pass a law" in a bicameral legislature. There never was anything to "repeal".
Furthermore, the bill in Indiana did not say anything at all about pi.
The only remaining question is, where is your education most deficient? In political science, or in metrology?
Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard / Gentlemen of the jury, Chicolini here may look like an idiot, and sound like an idiot, but don't let that fool you: He really is an idiot. Groucho Marx