My new spreader beam plan (visited steel yard)

That's not all she told Jane Curtain after one of her off topic rants. ;-)

Not till you clean all the dead slugs off the wall, young man!

And it seems it's you Brits who have come up with all those confusing units. (Though, much as I'd like to, I can't blame you for the pyong and the ping.)

*****************************************************************slug a unit of mass in the English foot-pound-second system The British physicist A. M. Worthington first called it a slug in a 1902 textbook.

poundal (pdl or pl) an English unit of force used in engineering The poundal was invented in the 1870s by the British mathematician James Thomson, who also named the radian.

*****************************************************************

I propose a new system, the GPS system, based on these fundamental units:

- the Gee, gravitational acceleration at sea level here in Harpswell, ME

- the pound, mass as currently defined by the NIST

- the second, as currently defined

derived units:

- the notweN is the force required to accelerate one pound at one Gee

- the grinch (gravity inch) is the distance travelled by a body accelerating from rest at one Gee after sqrt(2) seconds

If you care to bring the GPS system to the attention of the Royal Society there's no need to attribute it to me; feel free to take the credit yourself.

Define the Gee at Greenwich if you think it'll make for an easier sell.

Ned Simmons

Latin: libra

Don't laugh: femtosecond laser pulses are used for machining:

OK, so it's micromachining...

Soon to come: Grouchosecond pulses, to be followed by harposeconds...

-- Ed Huntress

So "cuba libra" means "pound Cuba"?

They've already got an 'Ohnosecond'.

-->--

That's a mighty short period of time, I'll bettcha. Shorter than a zepposecond, longer than a chicosecond, eh?

-- Ed Huntress

1) It might mean to castrate Fidel. 2) Pound Cuba? With bombs? Might accomplish 1. 3) Cuba Libra may refer to Gooding Jr.'s astrological sign. 4) Depending on the latin meaning of cuba... who knows. 5) Sounds like a rum drink. 6) Phrase not found in the Dictionary and Encyclopedia. Did you mean: Cuba Libre; see 5

I myself like Yotta = 10^24 ohms Zetta = 10^21 meters or zettameters zepto = 10-21 zeptometers yocto = 10-24 joules yoctojoules

I agree the sounding of the Marx brothers - long thought that and think those who developed the extended set of SI units had a sense of humor.

ISBN : 0780310500 Amazon has it so they say. Martin

Mart>

And I'll bet you "can't see" the D in "penny" or "Pence" either. You better stick to machining.

I think I'd better "killfile" this thread there are just way too many "clowns" in it. :-) ...lew...

On Mon, 06 Nov 2006 11:32:31 -0600, with neither quill nor qualm, Don Foreman quickly quoth:

The Cuba Libre is a free-range Cubano drink. ;)

--- -If thy poster offends thee, *PLONK* it out.-

Comprehensive Website Development

Total nonsense.

Weight is not, and never has been, a force, when we talk about the "net weight" of somethign when we buy and sell goods by weight.

Those pounds always were units of mass.

It is the pound force which is a recent spinoff, a different unit of measure, one that was NEVER a well defined unit before the 20th century, and one which even today doesn't have an official definition.

We often borrow the one that is official (adopted by the CGPM in 1901) for purposes of defining the kilogram force. But not always. Other values are used as well, such as 32.16 ft/s=B2.

One of of four. Almost. More specifically, stick to the International System of Units (SI), the modern preferred subset of the metric system. After all, many users of the metric system have gone far out of their way to show that they can be every bit as silly as those using English units. Witness a unit of mass, known by various names since it has been reinvented many times over, known as a hyl, or a metric slug, or mug, or TME from a German acronym, equal to 1 kgf=B7s=B2/m, the mass which a force of 1 kgf will accelerate at a rate of 1 m/s=B2..

Gene Nygaard

======================================================== Gyngaard sez:

Total nonsense.

Weight is not, and never has been, a force, when we talk about the "net weight" of somethign when we buy and sell goods by weight.

======================================================== Ed sez:

And how does your grocer measure the "mass" of a pound? Does he accelerate it with a force and measure its velocity? Until fairly recent times there was no practical way to measure mass. When you "weigh" something on a scale, you're measuring force, not mass.

Traditionally, it is the force exerted by gravity on a unit of mass. Check your high school physics book.

Or check an engineering text. How do you get "pounds per square inch" (psi) except as force? How do you get "pound-feet"? The pound is a unit of force in most of engineering today, and it has been for a very long while.

When engineering became more scientific -- and when science became more scientific -- the identity of the pound as a unit of force became distinguished from the FPS unit of the "slug" for mass. That was in the late

19th or early 20th century. "Pound" was reserved to mean a unit of force in most of engineering.

At about the same time weights and measures were being established for commerce, and it was recognized that most people didn't know mass from force, and cared even less. What they were interested in was a lump of whatever, and it was more easily thought of as a unit of mass than of force. So the weights and measures standard-makers in the US and the UK established a unit of mass for the pound, defined in terms of the kilogram...exactly as I said. But it was derived from the unit of force that had always, throughout modern history, been measured by a balance of some sort -- which reacts to force, not to mass.

========================================================

Gyngaard sez:

Those pounds always were units of mass.

========================================================= Ed sez:

Total nonsense. Again, before spouting off, go look it up. The history of it is readily available on the Web.

========================================================= Gyngaard sez:

It is the pound force which is a recent spinoff, a different unit of measure, one that was NEVER a well defined unit before the 20th century, and one which even today doesn't have an official definition.

========================================================= Ed sez:

"Never well-defined"? Maybe you mean, "never precisely defined in a universally agreed way." That would fit. Traditionally, most measurements were never precisely defined.

=========================================================

Gyngaard sez:

We often borrow the one that is official (adopted by the CGPM in 1901) for purposes of defining the kilogram force. But not always. Other values are used as well, such as 32.16 ft/s².

=========================================================

Ed sez:

That's nice.

=========================================================

Gyngaard sez:

One of of four. Almost. ========================================================= Ed sez:

Pffffftt! Baloney.

========================================================= Gyngaard sez:

More specifically, stick to the International System of Units (SI), the modern preferred subset of the metric system.

=========================================================

Ed sez:

No thanks. I write for medical professionals, and I spent 30 years writing for mechanical engineering professionals. The standards in those two institutions use a variety of non-SI, m.k.s. units -- as does most of the world.

It all depends on whether you want to be understood or you want to have something to argue about. SI is a sidebar in the world of scientific communication. Even the French don't especially like it.

-- Ed Huntress

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D

Nonsense. You have a weird notion of what it means "to measure" something.

What you measure is the thing you can assign a numeric value to. Consider, for example, the classic balance scale--which were the only types of scales anybody used for the first 7,500 years after people started weighing things, the only scales used by anybody more than two centuries ago.

Let's use a classic two pan, equal arm balance--the same thing applies to other scales as well.

When you put your known weights in one pan of the balance, what is it you know about them? It is their mass. You don't know how much force they exert due to gravity. They are manufactured, to varying degrees of precision, by a series of copyings from whatever is considered the standard, and that was as true when Hammurabi included regulations along this lines in his Code of Law 3,750 years ago as it is today.

So you balance them, and then what do you know about what you are measuring? Those scales will work anywhere, and variations in the strenght of the local gravitional field will not change the results of that weighing. The gravitational acceleration affects both sides of the balance in the same way. You do not "measure" the force exerted, because you cannot assign a precise number to it. You do measure the mass.

Those are pounds force. Different units.

Tit for tat: How do you get a "pound mole"? How much water will a British thermal unit raise the temperature of by 1 =B0F?

Pounds force have been used in low-precision measurements back from old steam boiler measurements a couple of centuries ago, but other than that, pounds force were hardly ever used before the 20th century. Note that the first English coherent system of mechanical units, dating back to 1879, was the absolute foot-pound-second system of units. What exactly was the unit of force in that oldest coherent English system, the amount of force which would accelerate a pound at a rate of 1 ft/s=B2?

That took place a few decades after scientists started using the foot-pound-second-poundal system.

It doesn't matter what we know or what we care about. What matters is what the regulators who look out for our interest do. They do care, and they never get confused about what they are measuring; nobody has ever though that a 401.23 troy ounce bar of gold weighed at Hammerfest would suddenly lose three ounces or whatever if you moved it to Quito.

Balances _measure_ mass, not force. Don't throw out any red herrings about "reacts to" and all that nonsense. A ruler doesn't do you much good in the dark. That doesn't mean we use a ruler to "measure" light.

What exactly do we, in your weird view of the meaning of "measure", measure with a clock? With an ammeter? With a voltmeter? With a nilometer?

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

So, if someone made a copy of the London pound troy, and took it to be the standard for measurements in Philadelphia, or in Sydney, what exactly is it about that troy pound that is the same in Philadelphia, and the same in Sydney, as it was in London? It certainly isn't the amount of force it exerts due to gravity.

Those pounds are, and ALWAYS WERE, units of mass, not units of force.

Don't you know anything at all about how measurements work?

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

Never precisely defined in hardly any usage, rather a variable about of force, equal the force that an even-then-precisely-defined pound would exert at some place on the Earth's surface, something which, even if you limit yourself to sea level on Earth, varies by 0.53%.

In the U.S., the pound was already precisely defined as an exact fraction of a kilogram before anybody ever started using any value whatsoever for a "standard acceleration of gravity" to define grams force or pounds force. Furthermore, the kilogram was even then (1893) defined exactly as it is today, was every bit as precise then as it is now, and it had been defined precisely to within parts per million 1889 definition still in use today ever since the Kilogramme of the Archives was put into use back at the end of the 1700s. So let's not have any nonsense implying that precision in some measurements didn't exist long before the 20th century.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D

Well, duhhh. Yes, many people do use "kilograms force", even today. You often see it in connection with the pre-1990 Russian space program when these were the standard units used, and even today in connection with thrust of ESA and Chinese rockets. The point is, that if you do so, it isn't one damn bit different from using pounds and pounds force. But your observation that "This is one good reason to stick to the metric system when you're doing anything serious" goes right out the window if kilograms force are used. That's my point.

Gene Nygaard

[I changed the subject]

F = m * a You do _compare_ forces with a two-arms-balance. No acceleration, no way to compare them. And I'm not aware of any direct way to meassure mass. Mass-o-meter anyone? Oh no! Two masses attract. A quite unhandy setup. But then again, the attracting force has to be measured to find out the mass.

Anyhow, I googled a bit in the last few days, and I do have to stand corrected. The American system doesn't distinguish exactly between pound mass and pound force. It is a bit puzzling for me, but that's the way it is. Maybe they know why not all their satellites reach the mars. :-))

Nick

Sure, but you do not "MEASURE" the forces.

You need enough acceleration to overcome friction, and not so much to reduce your scale to a heap of rubble.

But within that range, you get the same results, no matter how much that acceleration varies. Ignoring minor complications of buoyancy in air, your balance will "measure" the same weight on the Moon or on Mars as it does on Earth, for example.

Balance.

Torsion balance.

Whatever. Almost all of our measuring instruments, of any sort whatsoever, are indirect to some extent.

There are lots of ways to distinguish force from mass, and also lots of ways distinctions are ignored--it has nothing to do with any "American system". People talk abour rocket thrusts in kilograms, too, don't they?

But the standards-keepers recommend distinguishing normal pounds (symbol lb) from pounds force by identifying the latter as such an using symbol lbf for them (sumetimes the f is a subscript when that is available, but often just lbf).

Gene Nygaard

Actually they do not use kilograms to describe rocket thrusts. They use Newtons.

Dan