What's a grain... why do we measure with it?

[telomerase]

NO, NO, NO!!!!

>If you want to figure out the muzzle energy of a 230 grain bullet, you first have to find out that 230 grains is the same as 0.032857143 pounds.

Which won't do you any good. Pounds are a unit of FORCE, not MASS. The English-system unit of mass is the slug.

And if you're a European laughing at the dumb Americans who don't know that you can't use pounds to measure mass, go read your European tires... most of them say "kg/cm2"... which is trying to use a mass unit to measure a force.

I don't know what the moral of all this is, except that if education were private most people would know elementary physics by the time they were 12. I feel the years I was incarcerated in the American publik skools would have been better spent breaking rocks.

 

[BunsenH]

<in my best condecending teacher voice> Children lets not forget our significant digits.

230 grain is NOT equal to 14.9037493 gram unless that 230 grain was measuered acurately as 230.000000 grain. That's not very likely. 230 grain as actually more like 14.9 gram or if you prefer 149 decigram. So the rediculous strings of worthless digits are just that, rediculous.

230 grain is 14.9g.
115 grain is 7.45g.
147 grain is 9.53g.
158 grain is 10.2g.

Each is three digits to remember. Not too tough.

Significant Figures Rant Off.

Grains are used for bullet weights. It's just that way historically so as long as everyone that matters agrees, we don't really need to change.

 

[Mike Irwin]

I have a couple of European references that show weights in grams.

The one closest at hand is Jean Huon's "Military Rifle and Machine Gun Cartridges".

Shows bullet and cartridge weights in grams.

Once you remember that gr. means grams, you're on the money.

 

[Mike Irwin]

"And if you're a European laughing at the dumb Americans who don't know that you can't use pounds to measure mass, go read your European tires... most of them say "kg/cm2"... which is trying to use a mass unit to measure a force."

Telo,

Correct me if I'm wrong, but isn't that based on the same principle used to measure atmospheric pressure? X number of inches of mercury can be translated directly to atmospheric pressure in pounds per square inch, correct?

It's been such a long time since high school sciences... My head hurts. Must be an increase in cranial pressure. Or would it be mass?

BLAM!

Ouch. Cerebral blowout!

 

[BrokenPaw]

Correct me if I'm wrong, but isn't that based on the same principle used to measure atmospheric pressure? X number of inches of mercury can be translated directly to atmospheric pressure in pounds per square inch, correct?

Mike, you can use inches of mercury - to - psi comparison because both are using weight (versus mass) measurements. A column of mercury of a given height under normal earth gravity will weigh a given amount, and if you divide that weight over the surface area of the cross section of the column, you get a pounds-per-square-inch value.

You can't use kg/cm2, because kilograms are a unit of mass, not weight. A kilogram of lead on the moon is still a kilogram of lead (even though it weighs different amounts on the earth and on the moon). A pound is a unit of force (and thus, mass times acceleration). 1 pound is equal to a given amount of mass under 1G of acceleration (32.2ft/sec2), or, equivalently, less mass under greater acceleration( higher gravity), or more mass under lower acceleration (such as on the moon).

The metric unit of force is the newton, which equals 1kg (m/s2), or one kilogram of mass accelerated at 1 meter per second squared. If the tires were to be marked properly, they'd have to be marked in N/cm2, not kg.

Or they could be marked in psi, the way all right-thinking folks do it.

-BP, weighing in

 

[WheelMan]

kg/cm^2 is a just as valid a unit as psi or N/cm^2, instead of measuring pressure it measures "area density" which is a perfectly fine unit to describe the amount of air in a tire provided you have a tire gauge that reads such units. Of course you still don't need one as long as your car stays on earth because kg/cm^2 and N/cm^2 are equivalent in all but name due to the gravitational constant.

 

[Mike Irwin]

Broken,

Now wait one second...

A pound of lead on the moon would also weigh a pound.

It seems to me that a pound can be both a measure of mass and a unit of force. The pound is a unit that's doing double duty by being two measures at the same time...

 

[BrokenPaw]

Mike,

The moon has roughly the 1/6 the gravity of earth. If you took a chunk of lead that weighed 1 pound on earth, and put it on the moon, it would still have the same mass (about 1/32 slug), but you could lift it straight up using only 1/6 pound of force.

"Weight" is just the amount of force required to counteract gravity. So on the moon, an item will weigh 1/6 that of what it does on earth. And in space, free from significant gravity wells, an object becomes "weightless", but still retains its mass (and therefore the force required to accelerate it).

By definition, the "pound" is a unit of force, only, and the "slug" is the corresponding unit of mass. A slug of material, under earth gravity, weighs 32.2 pounds (approximately).

-BP (starting to feel bad about Thread Drift)

 

[C.R.Sam]

Trivia
My copy of Les Pistolets, Les Revolvers et Leurs Munitions, 1957....refers to bullet weights in grains.

Sam

 

[uglymofo]

You guys are 'way too serious....

The basic unit of weight in the British system is the grain - based on the weight of a grain of barley (but note that money was based on the grain of wheat - and that three grains of barley weigh the same as four of wheat). This grain is the troy grain - there is no other weight of the same name.

Quote taken from here:

http://home.clara.net/brianp/weights.html

CWL's damn close to the mark, but his source erred. As Skunk and I (and anyone with our eyes) know from "mother country" culture and legend, gunpowder was invented in China, and the easiest, convenient, unit of weight was rice . Some Englishman translated the idiogram incorrectly, and changed the meaning from 'rice' to 'grain'...and there you have it.

Of course, the English are guilty of many errors akin to this, and I recount another:

An English archeology expert was leading a guided tour through the Oxford museum, commenting about different artifacts as the group studied each display in turn. He came to a stone tablet, and started to discuss it.

"Here we see a stone tablet from China. This tablet was unearthed during the recent excavations at the old Christian missionary site in Beijing. As you can see, there are four pictures carved on this one tablet. The first picture on the left is a depiction of a young woman. Motherhood was revered in ancient China. The second panel from the left is a picture of a donkey. Farming and agriculture were critical to Chinese society. The third panel shows a shovel. Farming tools were highly prized in ancient times. Lastly, in the right panel, is a magnificent rendering of Jesus in prayer or contemplation. "

A tourist interrupted, "You've got it all wrong! That's not what this is at all. As we all know, Chinese is based on hieroglyphics or pictographs , and as with most Asian cultures, this is meant to be read from right to left. In fact, this is just a note. It says, "Sweet Jesus, dig the @ss on that babe!"

 

[Mike Irwin]

Broken,

"By definition, the "pound" is a unit of force, only, and the "slug" is the corresponding unit of mass. A slug of material, under earth gravity, weighs 32.2 pounds (approximately)."

That's a FOOT-pound, isn't it?

This is the definitions I'm coming up with from American Heritage...

1. A unit of weight equal to 16 ounces...

2. A unit of apothecary weight...

3. A British unit of force equalt ot the weight of a standard one-pound mass where the local acceleration of gravity is 9.817 meters per second per second (is that a foot pound?)

4. The basic monetary unit of the UK... wait, that's completely out of the picture


No, apparently that ISN'T a foot pound...

Sigh.

OK, don't trouble yourself, Broken.

Thanks for the primer, but I just don't have enough of a grasp on the concepts of physics to really integrate this stuff. Maybe it's time I took an intro to physics class at the local CC.

The one thing I definitely know, though, is that when I weigh myself, whether pounds or kilograms, my a@@ has too much mass!

 

[Steve Smith]

A foot pound is a unit of energy, or work, being equal to the work done in
raising one pound avoirdupois against the force of gravity
the height of one foot.


The standard Avoirdupois pound of the United States is equivalent to the weight of 27.7015 cubic inches of distilled water at 62[deg] Fahrenheit, the barometer being at 30 inches, and the water weighed in the air with brass weights. In this system of weights 16 drams make 1 ounce, 16 ounces 1 pound, 25 pounds 1 quarter, 4 quarters 1 hundred weight, and 20 hundred weight 1 ton. The above pound contains 7,000 grains, or 453.54 grams, so that 1 pound avoirdupois is equivalent to 1 31-144 pounds troy. (See {Troy weight}.) Formerly, a hundred weight was reckoned at 112 pounds, the ton being 2,240 pounds (sometimes called a long ton).

 

[benewton]

My best take has always been to solve the problem in terms of the units given, and skip all conversions

Thus, with lasers, one works in nanometers...

But I think in feet and inches, equating meters to yards on the first pass, and so, after all these years, am not likely to "go metric", even though I do handle it when necessary.

So, leave grains at the loading bench when you depart, but keep the system: it works, and that's enough!

 

[benEzra]

Which won't do you any good. Pounds are a unit of FORCE, not MASS. The English-system unit of mass is the slug.

The standard Avoirdupois pound of the United States is equivalent to the weight of 27.7015 cubic inches of distilled water at 62[deg] Fahrenheit, the barometer being at 30 inches, and the water weighed in the air with brass weights.

Actually, you guys are thinking of the British Gravitational System, a system that is not the legal standard in the U.S. and never has been. The U.S. pound avoirdupois is defined as a unit of MASS equal to EXACTLY 0.45359237 kilogram, per the U.S. National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards. The official U.S. pound has been defined in terms of the kilogram since 1893; before that, it was defined as the mass of a brass artifact kept in Washington. BTW, the U.S. foot is defined as exactly 0.3048 meter.

The reason engineers liked to use slugs is that if you measure mass in pounds mass and force in pounds force ( = the force of 1 standard gravity on a mass of 1 U.S. pound), then Newton's law F=ma doesn't work out; you have to make it F=kma where k is a correction constant. (If you think that's weird, NASA used an even weirder set of units in the 1960s--the pound-force as the force measure, the inch as the length measure, and the "slinch" (slug-inch) as the mass measure, 1 slinch being equal to the mass that 1 pound force would accelerate at 1 inch per second (IIRC).

The fact is, we in the U.S. are far more metric than most people think. Ever bought a 2-quart bottle of soft drink, or a 1.38" camera, or a light bulb rated in foot-pounds? The military is already mostly metric, and most technical fields. Medicine has long since abandoned apothecaries' measure (grains, drams, minims) in favor of metric units, etc. The BTU is hanging on, but it'll eventually lose to joules. (And did you know that 98.6 Fahrenheit is just the American/English translation of 37 Celsius?)

And yes, when calculating muzzle energies, I personally prefer joules.

 

[telomerase]

>U.S. pound avoirdupois is defined as a unit of MASS

Yes, Ben, for legal and commercial purposes there is a unit of mass called the "pound", which has nothing to do with the physics unit "pound" of force. Since you chose to throw a smoke bomb in front of the chalkboard, I'll leave it to you to come up with a cogent explanation of the difference between mass and force for those you have terminally confused.

 

[Mike Irwin]

"I'll leave it to you to come up with a cogent explanation of the difference between mass and force for those you have terminally confused."

Oh yeah, like you and everyone else has done a good job of UNconfusing us, Telo!

Oh, wait, that just means that I'm a dumba$$, doesn't it?

 

[C.R.Sam]

Q...What's a grain... why do we measure with it?

A...A small unit of measure......it is handy.

Sam

 

[BrokenPaw]

Benewton:

My best take has always been to solve the problem in terms of the units given, and skip all conversions

17.99885e12 furlongs per fortnight; it's not just a good idea, it's the law!
-BP

Just remember, pi seconds equals one nanocentury...

 

[Steve Smith]

benEzra, according to the U.S. National Institute of Standards and Technology website, http://ts.nist.gov/ts/htdocs/230/235/h4401/appenc.pdf General Tables of Units of Measurements, Appendix C, Table "Units of Mass Not Less than Avoirdupois Ounces" one Avoirdupois Pound is equal to .45359237 Kilograms and is the standard for US mass and weight measurement.

 

[Duncan Idaho]

17.99885e12 furlongs per fortnight; it's not just a good idea, it's the law!

[SPIT TAKE] OMG! LMFAO![/SPIT TAKE]

 

[Mike Irwin]

How much is that in rods and chains?

 

[BrokenPaw]

How much is that in rods and chains?

Chains is easy; a chain is just 0.1 Furlong. So it'd be 1.799885e13 chains per fortnight. Or 7.19954e13 rods. And, just to get it out of the way before someone asks:
1.9798735e14 fathoms per fortnight.
9.8993675e13 fathoms per se'ennight, if you prefer.

-BP

 

[M67]

Hey, I just realised something. Grain isn't measured in grains at all, it's measured in bushels, isn't it?

 

[Mal H]

Just remember, pi seconds equals one nanocentury...

Cool! I love little tidbits like that.

 

[benEzra]

Yes, Ben, for legal and commercial purposes there is a unit of mass called the "pound", which has nothing to do with the physics unit "pound" of force. Since you chose to throw a smoke bomb in front of the chalkboard, I'll leave it to you to come up with a cogent explanation of the difference between mass and force for those you have terminally confused.

That's easy. Mass is the invariant length of a particle's momentum four-vector. Weight is the three-dimensional manifestation of a particle's attempt to follow a geodesic through four-dimensional spacetime.

Actually, I'm not disputing that the pound force is commonly used in physics (in fact, it's the predominant use in most textbooks that use it at all). I'm just point out that it's a derived unit from the U.S. pound mass (which is in turn based on the kilogram) rather than a fundamental unit, and that using the pound as a mass measure is not at all incorrect, even in physics.

As far as mass vs. weight goes (for those confused), mass can be thought of as the amount of matter in an object (roughly speaking), and weight the force of gravity upon that matter. Since the earth's gravity is roughly constant (to a moderate fraction of a %) over the earth's surface, most people use them interchangeably for measuring stuff here at the earth's surface, where most of us live.