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jbird3000
03-02-2001, 10:48 PM
Can't we think of a better system than metric? I mean, a system based on water is fine and dandy, but can't we think of something that ties in to some sort of constant, like the speed of light, the weight of an electron, or something like that? Also, can't we get something better for time than seconds?

friedo
03-03-2001, 12:09 AM
I'm not sure what you mean. Water is a constant. At STP, one gram of water takes up exactly one mililiter which is equivelent to one cubic centimeter.

The official definition for a meter is in fact based on the speed of light. A meter is "the distance traveled by light in a vacuum in 1/299,792,458 of a second."

Protesilaus
03-03-2001, 12:27 AM
And the official definition of a second is the amount of time it takes for 9,192,631,770 oscillations of cesium to occur.

Mikahw
03-03-2001, 12:32 AM
There is a better system. It's called.. Well, The American system. :D

Seriously though, do we really need another system? It's hard enough communicating with the 2 we have now. Why make another one that will probably be adopted by less than 1/3 of the countries, making it even harder to share data?

Fernmeldetruppe
03-03-2001, 10:47 AM
The metric system is quite versatile, and using water as one of the "standards" is about as intuitive as you can get. (The actual standard is "a weight" (a mass) in France.) One way that you could make THE SYSTEM better is if there were some sort of naturally occurring object with a very standard length. (Cesium oscillations can't be measured with your eyes, hands and a pencil.) The only improvement I would make (having to do it over) would be to make the gram 1000 times heavier than it is, but this would just allow the gram (instead of the kg) to be more of an everyday and intuitive base measurement. I don't think the weight of an electron is all that intuitive either and it would force us to learn many more prefixes to weight ourselves or food using the electron scale.

I'm OK with seconds, but I could go for changing minutes, hours, months and years to more of a decimal format. (This wouldn't really change the metric system unless we actually go to megaseconds. Likely, a third system would be better for everyday usage.) (I'm OK with days (intuitive-wise), but I might be convinced otherwise with some very, very compelling arguments.)

In what instances, does the metric system not work well, but still maintains standardization? (Thumbs are intuitive, but are not standard across the population.) (I am confining this question to non-relativisticly different timeframes, of course.)

Enola Straight
03-03-2001, 11:12 AM
A more natural scale of measurement does exist...
the Planck scale...but its based on the fundamental physical constants of nature, which are too small to use in normal life.
i.e.
Planck mass=10^-11 gram ( molecules weigh more than this)
Planck distance=10^-32 meter (size of an electron)
Planck interval=10^-44 second (amount of time light takes to travel along the Planck distance)

Real awkward, ain't it?

But hey, a cubic centimeter of water=milliliter=gram.
Thats a great starting point for measurement.
True, you,d have to define meter (299,792,458 M/Sec)
and second (9,192,631,770 occilations of cesium),

jbird3000
03-03-2001, 02:41 PM
The official definition for a meter is in fact based on the speed of light. A meter is "the distance traveled by light in a vacuum in 1/299,792,458 of a second."

Can't we make it something to the power of 10? Like one millionth of the speed of light?

And the official definition of a second is the amount of time it takes for 9,192,631,770 oscillations of cesium to occur.

We came up with the second long before we knew how many oscillations of cesium it took, didn't we? And why cesium?

"Planck distance=10^-32 meter"... Exactly? I don't think so.

We don't we use the Planck stuff, but start it at something useful in every day life, like starting at a Plank length times 10^32, and that would be the base unit for distance.

By the way, what are the base measurements anyway? Which ones cannot be derived from other ones? For example, a Newton is really just mass times acceleration....

So there's mass, time, distance, temperature....

jbird3000
03-03-2001, 02:43 PM
Also, for water, why doesn't a cubic meter = liter = gram? Seems they all start at different points.

BobT
03-03-2001, 02:59 PM
But 1 milliliter = 1 cubic centimeter of which I thought that water at STP would weigh 1 gram.

But I may have forgotten some of this through the years.

Alphagene
03-03-2001, 03:43 PM
Originally posted by jbird3000
Can't we make it something to the power of 10? Like one millionth of the speed of light?
We could, but we don't because it would make things more confusing. Ever since the meter was defined back in the late 18th century, we haven't changed is length, just the precision by which we define it. To suddenly change the length of the meter would mean that we would have to redefine most of the derived units of metric measurement.

Originally posted by jbird3000
We came up with the second long before we knew how many oscillations of cesium it took, didn't we? And why cesium?
Again, the length of the second hasn't changed much since it was defined, but the precision by which we measure it has. Why cesium? AFAIK, it's because we knew at that time that cesium clocks were very accurate and could measure time with great precision.

Originally posted by jbird3000
By the way, what are the base measurements anyway? Which ones cannot be derived from other ones? For example, a Newton is really just mass times acceleration....
Well you should probably understand the fundamentals of the metric system before you decide it's not convenient. Check out this site (http://physics.nist.gov/cuu/Units/index.html). The base units are currently length (meter), mass (kilogram), time (second), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole), and luminous intensity (candela).

Originally posted by jbird3000
Also, for water, why doesn't a cubic meter = liter = gram? Seems they all start at different points.....
Again, check out the site I listed above. The metric system wasn't "based on water", it was based on the meter. The meter originally defined both the liter (it equals one-thousandth of a cubic meter) and the gram (one cubic centimetre of water at its maximum density, 4ºC, IIRC). Arbitrary? Sure. But it was probably more useful to make the base unit of volume around the size of a present liter than a cubic meter. That's my WAG. Anyway, IMO, the arbitrary defenitions of the base units doesn't take away from the utility and elegance of the SI units.

Keep your eyeballs peeled for my upcoming Staff Report on the metric system! It's gram-tastic!

[Edited by Alphagene on 03-03-2001 at 03:46 PM]

jbird3000
03-03-2001, 08:47 PM
Originally posted by Alphagene
Ever since the meter was defined back in the late 18th century, we haven't changed is length, just the precision by which we define it. To suddenly change the length of the meter would mean that we would have to redefine most of the derived units of metric measurement.

I'm talking about a whole new set of measurements, not a change in the metre.

Anyway, IMO, the arbitrary defenitions of the base units doesn't take away from the utility and elegance of the SI units.

We could say the same about the Imperial system. Don't get me wrong, I think the Imperial system is much more confusing than the metric system, but can't we think of something EVEN BETTER? Sure, it'll be confusing for people for a while to have a new set, but in the long run it'll be better, just like switching to metric has made stuff easier.

So basically I'm saying:

Use the Plank length, time, mass, and whatever else to make a new system. Make the units relate to each other well, unlike "1,000,000 grams of water=1 cubic metre". And if not, can we PLEASE get rid of this Imperial crap??

Looking forward to that metric Staff Report.

Alphagene
03-03-2001, 09:43 PM
OK I see where you're going with this. It seems like the point that bothers you is the definition of the base units. I don't think it's terribly important, though. Would it be any more convient to define the basic unit of time as an even 109 oscillations of a cesium atom as opposed to 9,192,631,770?

Think of it this way. If the French Academy of Sciences took this approach in the 18th Century, they would have defined the second as, let say, 10-4 solar day. The problem is, a century and a half later we developed a much more precise and uniform way of measuring time: atomic clocks.

Now in order to shift to this more precise method, we would have to do one of two things. We could base the unit of time on a power of ten of the oscillation of cesium but this would change the length of base unit of time. Alternately, we could keep the length of the traditional second and use the new method to simply fine tune the definition. You probably won't get a round number with the new definition, but it will be consistent with the old definition and you won't have to change the length base unit every time technology makes increased precision possible. Demanding that your base units always be a factor-of-ten multiple of a natural event unnecessarily restricts you.

The meter was originally defined as one ten-millionth of the distance from the North Pole to the equator. 100 years after the French computed this value and made it the prototype for the meter, an international committe realized that the length was actually about 0.2mm too short. The French miscalculated the quadrant from which they based the meter. Despite this discovery, the commitee kept the length of the meter as it was to be consistent. I think that by limiting yourself with what a base unit should be, you're defeating the flexibility and ease that the metric system is supposed to provide.

[Edited by Alphagene on 03-03-2001 at 09:49 PM]

MattTheCroc
03-04-2001, 12:42 AM
The base units are currently length (meter), mass (kilogram), time (second), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole), and luminous intensity (candela).

Shouldn't that be coulomb, instead of ampere? Seeing as amps are just coulomb/second, it seems that amps are derived from coulombs...

Mikahw
03-04-2001, 12:50 AM
Miles/Hr is derived from Miles, but Mi/Hr doesn't measure distance, now does it?

IIRC, Current is a measure of how many electrons per second, while colomb is a simple count (number of electrons) right?

tv snake
03-04-2001, 01:41 AM
Wasn't the original metre meant to be based on something nice and standard like the polar circumference of the earth?

The Ryan
03-04-2001, 01:44 AM
Originally posted by jbird3000

By the way, what are the base measurements anyway? Which ones cannot be derived from other ones? For example, a Newton is really just mass times acceleration....

So there's mass, time, distance, temperature....
Temperature is just average energy, so that's derived. Distance is just imaginary time (and vice versa). And if you really wanted to, you could define mass in terms of distance (e.g. amount of mass required to produce a black hole with radius 1 meter= 1 black-hole-mass). So the number of basic units is actually very small.

Alphagene
The base units are currently length (meter), mass (kilogram), time (second), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole), and luminous intensity (candela).
While these are indeed basic units, they are not base units in the sense of being independent. I see only two (maybe three) independent units in your list: second, and ampere (and maybe mass). And I'm not sure about ampere. A mole is not, strictly speaking, a unit, any more than "dozen" or "pi" is a unit. A mole is simply a number. A very, very large number, but a number nonetheless. It is dimensionaless. Intesity is just energy divided by time. The rest I have already dealt with.

MattTheCroc
Shouldn't that be coulomb, instead of ampere? Seeing as amps are just coulomb/second, it seems that amps are derived from coulombs...
Well, a kilowatt(energy) is derived from a watt(power) and an hour(time). On the other hand, a joule-per-second(power) is derived from a joule(energy) and a second(time). Which is more valid? As long as your basic units are independent and span the needed dimensions, it doesn't matter what they are. Amperes are easier to meaure than Coulombs, so physicists have decided to declare Coulombs the derived unit.

Mikahw
Miles/Hr is derived from Miles, but Mi/Hr doesn't measure distance, now does it?
Huh?

Mikahw
03-04-2001, 01:53 AM
Mikahw
Miles/Hr is derived from Miles, but Mi/Hr doesn't measure distance, now does it?
Huh? [/B][/quote]

I was commenting on this post:
origonally posted by MattTheCroc

Shouldn't that be coulomb, instead of ampere? Seeing as amps are just coulomb/second, it seems that amps are derived from coulombs...

If coulombs measure Current, then Mi/Hr would measure Distance, right?

Hint: I'm saying that Colombs do not measure Current, as subtly as I can..

tv snake
03-04-2001, 02:26 AM
The coulomb is a quantity like the mole, equal to some absurdly large amount of charge?

Protesilaus
03-04-2001, 02:47 AM
e = 1.602x10-19 Coulombs, where e is the charge of a single proton (an electron has a negative charge of equal strength). So 1 Coulomb is the charge from 1.602x1019 protons.

tv snake
03-04-2001, 02:51 AM
Thankyou for that. I didn't know exactly what value the aforementioned absurdly large number had.

Mikahw
03-04-2001, 02:55 AM
Actually, I've never heard of colomb before, I just ran to google and looked at what it had to say.

I do know that 1 dimentional measurements (miles, for example) Don't measure the same thing as 2 dimentional measurements (miles per hour)

MattTheCroc
03-04-2001, 05:08 AM
Amperes are easier to meaure than Coulombs, so physicists have decided to declare Coulombs the derived unit.

So how do you get coulomb from amps? I mean, knowing there are 5 amps running through a circuit isn't gonna help you figure out how much *charge* that is, is it? Unless you know the 1.602x10^-19 figure to start with, which would defeat the point...

Seems to me that it'd just be simpler to use coulombs :)

RM Mentock
03-04-2001, 05:39 AM
Originally posted by Alphagene
Originally posted by jbird3000
Can't we make it something to the power of 10? Like one millionth of the speed of light?
We could, but we don't because it would make things more confusing.

Hey, let's use one billionth of the distance that light travels in one second! We could call our system the Fundamental Orthometry Of Time system.

sewalk
03-04-2001, 08:51 AM
Originally posted by Alphagene
Arbitrary? Sure.

Umm, aren't all units of measurement arbitrary by nature? The flaw in the OP is that while a metric system based on the circumference of the Earth and the density of water is inconvenient when measuring the speed of light, the converse would also be true. Considering that engineering problems deal more often with water than with any other single substance, a system that is convenient for dealing with masses and volumes of water is inherently more useful than one that is not.

Alphagene
03-04-2001, 09:27 AM
Originally posted by The Ryan
While these are indeed basic units, they are not base units in the sense of being independent.
I see what you're saying. If you want units that aren't based at all on other units, there's the kilogram (based soley on the mass of the protoype), the second (based solely on counting cesium oscillations), the mole (great show), and the kelvin (based solely on a fraction of water's triple point). Originally, the meter was an independent unit (based solely a fraction of the earth's circumference) and so was the candela (based solely on the luminous intensity of carbon filament lamps, IIRC). So 6 out of 7 ain't bad. If we lose some "independence" for the sake of precision, I have no problem with that.

But I based my definition of independent on the definitions provided by the BIPM and I don't think that's what the BIPM mean by independent. Sure, in order to know the length of a meter you need to know the length of a second. But think of it this way. Every derived unit is a combination of the base units. Force is measured in newtons, a derived unit, and can be expressed in a combination of base units, namely: m•kg•s-1. The meter can't be expressed as simply a combination of base units. Neither can the candela, it's not "is just energy divided by time". Correct me if i'm wrong, but energy divided by time is an merely a generic expression of power, not of luminous intensity.

A mole is not, strictly speaking, a unit, any more than "dozen" or "pi" is a unit. A mole is simply a number. A very, very large number, but a number nonetheless. It is dimensionaless.
I am perfectly correct to say that the mole is a unit, simply because the International Bureau of Weights has defined it as such. You disagree with the Bureau's definition? Write them a letter :) AFAIK, they consider it a basic unit because you need it to express derived units, like the katal (mol•s-1).

robby
03-04-2001, 11:32 AM
Originally posted by MattTheCroc
So how do you get coulomb from amps? I mean, knowing there are 5 amps running through a circuit isn't gonna help you figure out how much *charge* that is, is it? Unless you know the 1.602x10^-19 figure to start with, which would defeat the point...

Seems to me that it'd just be simpler to use coulombs :) [/B]

The coulomb (measure of charge) is a more fundamental quantity. However, it is more practical to define the coulomb in term of the ampere, as opposed to defining it in in terms of the actual charge of an electron or proton.

An ampere is the amount of electric current in each of two long, parallel wires that give rise to a magnetic force per unit length of 2 x 10-7 N/m on each wire when the wires are separated by one meter. The coulomb is thus defined as the quantity of electric charge that passes a given point in one second when the current is one ampere (or one coulomb per second).

If you now want the charge of a single electron, you must conduct an experiment (such as Robert Millikan's oil drop experiments of 1909-13).

Thus the coulomb, in and of itself, has nothing to do with the charge of an electron (or proton).

Chronos
03-04-2001, 02:38 PM
Quoth enolancooper:
A more natural scale of measurement does exist...
the Planck scale...but its based on the fundamental physical constants of nature, which are too
small to use in normal life.
i.e.
Planck mass=10^-11 gram ( molecules weigh more than this)
Planck distance=10^-32 meter (size of an electron)
Planck interval=10^-44 second (amount of time light takes to travel along the Planck distance)Not quite, on the Planck distance: The size of the electron has nothing to do with this. The Planck units are chosen in such a way that c (the speed of light), G (Newton's gravitational constant), and hbar (the quantum constant) are all equal to one. If you like, you can extend the Planck system by also requiring that ke (Coulomb's electrostatic constant) and k[sub]b[/b] (Boltzman's constant, relating energy and temperature) also equal one, so now you've got fundamental units for charge and temperature, too. It should be noted that the fundamental charge thus derived is not the same as the charge of the electron: In this system, the electron has a charge of approximately 0.085 Planck charges. It's also worth noting that this means that theoretical physicists looking for a Theory of Everything can get away with using no units at all for their calculations: All quantities are considered to be in the appropriate combination of Planck units. Hence statements like "The temperature of a black hole is equal to one fourth its surface gravity", even though surface gravity is usually meters/second2 and temperature is usually Kelvins.

Quoth jbird3000:

So basically I'm saying:

Use the Plank length, time, mass, and whatever else to make a new system. Make the units relate to each
other well, unlike "1,000,000 grams of water=1 cubic metre". And if not, can we PLEASE get rid of this Imperial
crap??You can't have it both ways. If you want to use the Planck units, then the density of water is some silly-looking number that nobody would ever remember (don't have my references handy, so I can't get the exact number).

jbird3000
03-04-2001, 03:39 PM
Originally posted by Chronos

Quoth jbird3000:

So basically I'm saying:

Use the Plank length, time, mass, and whatever else to make a new system. Make the units relate to each
other well, unlike "1,000,000 grams of water=1 cubic metre". And if not, can we PLEASE get rid of this Imperial
crap??You can't have it both ways. If you want to use the Planck units, then the density of water is some silly-looking number that nobody would ever remember (don't have my references handy, so I can't get the exact number). [/B]

I know that. What I meant was the Planck system would make sense, instead of doing something silly like saying 1 "distance-Planck" is the distance something can travel at the speed of light in *2* "time-Plancks".

The Ryan
03-04-2001, 11:25 PM
Originally posted by Mikahw
If coulombs measure Current, then Mi/Hr would measure Distance, right?
Who has said that coulombs measure current?

tv snake
The coulomb is a quantity like the mole, equal to some absurdly large amount of charge?
No. The coulumb is an absurdly large number of electrons (or rarther, their charge). The mole is just an absurdly large number. It's not an absurdly large number of atoms, or an absurdly large number of molecules, or of anything else. It's just an absurdly large number. It does not represent anything physical.

MattTheCroc
So how do you get coulomb from amps? I mean, knowing there are 5 amps running through a circuit isn't gonna help you figure out how much *charge* that is, is it? Unless you know the 1.602x10^-19 figure to start with, which would defeat the point...
If you have 5 amps for 10 seconds, then there are 5*10=50 coulumbs that passed through the wire. You don't need to know the 1.602x10^-19 number unless you want to know how many individual electrons passed through, which is different from the charge.

Alphagene
Correct me if i'm wrong, but energy divided by time is an merely a generic expression of power, not of luminous intensity.
Can you explain to me what the difference is? It seems to me that this is like saying that "meter" is just a generic measure of distance, not of the distance between Paris and London. Do we need a new unit for every application?

I am perfectly correct to say that the mole is a unit, simply because the International Bureau of Weights has defined it as such.
Well then, I guess "dozen" and "pi" are units, too.

AFAIK, they consider it a basic unit because you need it to express derived units, like the katal (mol•s-1).
Either you're wrong or they are, because the katal has the same dimension as the hertz. Anything that can be measured in katals can be measured in hertz (although you need much larger numbers).

RM Mentock
03-05-2001, 12:12 AM
Originally posted by enolancooper
Planck mass=10^-11 gram ( molecules weigh more than this)
Planck distance=10^-32 meter (size of an electron)
Planck interval=10^-44 second (amount of time light takes to travel along the Planck distance)

OK, I missed this one the first few times.

You seem to have gone the wrong way in converting kilograms to grams in presenting the Planck mass (http://www.treasure-troves.com/physics/PlanckMass.html). In grams, a Planck mass would be around 10^-5 gram. Actually, pretty hefty, no?

Coldfire
03-05-2001, 07:40 AM
Originally posted by The Ryan
Alphagene
Correct me if i'm wrong, but energy divided by time is an merely a generic expression of power, not of luminous intensity.
Can you explain to me what the difference is? It seems to me that this is like saying that "meter" is just a generic measure of distance, not of the distance between Paris and London. Do we need a new unit for every application?Hopefully not!

A meter is a one-dimensional unit, as Mikahw pointed out above. We use it to measure distance. Period.
What Alphagene's discussing is the interpretation of a two-dimensional unit (energy per time unit). The difference is, therefore, that they're two different things altogether.

Which brings me to another quote of yours in this thread:
Distance is just imaginary time (and vice versa).I'm not sure if I understand you. But I'd say that distance has nothing to do with time. London - Paris (to use your example) will be 500 kilometers, no matter how long it will take you. How is distance "imaginary time"?

Mikahw
03-05-2001, 07:50 AM
Originally posted by The Ryan
Originally posted by Mikahw
If coulombs measure Current, then Mi/Hr would measure Distance, right?
Who has said that coulombs measure current?

Eh, you're probably right. I probably assumed too much.

LazarusLong42
03-05-2001, 09:29 AM
Originally posted by The Ryan
The coulomb is a quantity like the mole, equal to some absurdly large amount of charge?
No. The coulumb is an absurdly large number of electrons (or rarther, their charge). The mole is just an absurdly large number. It's not an absurdly large number of atoms, or an absurdly large number of molecules, or of anything else. It's just an absurdly large number. It does not represent anything physical.

I must respectfully disagree. The mole measures an amount--not a mass, mind you, but an amount. One Avogadro's number of something is one mole. But that doesn't mean that's the same as the mole just being a large number.

I work with a unit called molarity rather often, being a biochemist. A one molar solution of X is defined as having one mole of X per liter of solution. By what you've been saying, this could be simply defined as NA L-1 of X. Great. NA what of X per liter? Grams? Kelvins? Submarine sandwiches?

The mole very simply defines this. In one mole, there are NA formula masses of X. If one wanted, one could define the gram as: the mass of one-twelfth of a mole of Carbon-12 atoms.

From the NIST page on this: "When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles." (Bolding mine)

I will freely admit that the mole is a convenience unit--it gives us the ability to say "One mole of carbon" rather than "6.022045×1023 atoms of carbon." But that doesn't make twelve a unit--because you can't say "One twelve of carbon." You can say "Twelve atoms of carbon," which is something different.

Correct me if i'm wrong, but energy divided by time is an merely a generic expression of power, not of luminous intensity.
Can you explain to me what the difference is? It seems to me that this is like saying that "meter" is just a generic measure of distance, not of the distance between Paris and London. Do we need a new unit for every application?

We don't need a new unit for every application, but light has its own special properties that make measuring it rather important--see the derivation of the length of a meter from the speed of light.

Energy divided by time gives power. That's simple enough. But it's completely different from luminous intensity, for this basic reason: The wavelength of the light is a factor in determining the power.

In other words, if you have a red light and a blue light of equal luminous intensity, the blue light will have about 1.6 times the power as the red light, by virtue of having more energy per photon. I suppose if you wanted to be picky, you could say that a candela was a certain number of photons, but we've yet to be able to count those, so for now I'll stick with a candela.

LL

The Ryan
03-05-2001, 02:48 PM
Originally posted by Coldfire
The difference is, therefore, that they're two different things altogether.
The difference is that they're different? That sounds rather circular. Why are they different?

I'm not sure if I understand you. But I'd say that distance has nothing to do with time. London - Paris (to use your example) will be 500 kilometers, no matter how long it will take you. How is distance "imaginary time"?
Time squared minus space squared is invarient. So since their squares differ by a factor negative one, space and time differ by a factor of imaginary one. For instance, if you measure one event in London as happening one millisecond before one in Paris, then the total distance is sqr((5/3)^2-(1)^2)=4/3 (500km=~ 5/3 light milliseconds). If I'm traveling at half of light speed, I will measure the same distance, even though time and space dilations will cause each individual meaurement to be different. Relativity says that not only is time another dimension, but it's essentially the same dimension.

LazarusLong42
I must respectfully disagree. The mole measures an amount--not a mass, mind you, but an amount. One Avogadro's number of something is one mole. But that doesn't mean that's the same as the mole just being a large number.
Yes it does. If one NA of carbon = a large number of carbon, then one NA is a large number.

A one molar solution of X is defined as having one mole of X per liter of solution. By what you've been saying, this could be simply defined as NA L-1 of X. Great. NA what of X per liter? Grams? Kelvins? Submarine sandwiches?
If there is one mole of submarine sandwiches for every liter of your solution, then you have one molarity of submarine sandwiches. Of course you have to specify what you're talking about. Try coming into work tomorrow and asking for one molarity. If someone asks "One molarity of what?" just say "One molarity. Give me one of whatever a molarity measures."

In one mole, there are NA formula masses of X.
No, in one mole of X, there are NA of X. One mole, in itself, with no substance specified, represents absolutely nothing. It's just a number.

But that doesn't make twelve a unit--because you can't say "One twelve of carbon."
I never said that twelve is a unit. I said that a dozen is a unit. And one can indeed ask for one dozen carbon molecules.

I suppose if you wanted to be picky, you could say that a candela was a certain number of photons, but we've yet to be able to count those, so for now I'll stick with a candela.
If that is so, is it not of the same nature as the mole? Could we not as easily talk of one mole of photons?

tv snake
03-06-2001, 02:12 AM
And wouldn't it be much easier to define 'room temperature' as 300K instead of the current 298K (25 degrees)?