Anyone have any suggestions as to alternative definitions for the kilogram and pound- soon "Le Grand K" is to be replaced (the current standard), but with what?

I mean, for a start, could someone help me here:

what is the definition of the pound (and kilogram) in basic physics terms?


Cheers.

One of the natural constants it says there is far more accurately determinable than the others.. with the symbol 'R'.. what constant is that!?!??!

The current definition of the kg (taken from www.bipm.fr) is

<<
The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.
>>

The various national standards (which are compared to the copy kept at Sevres are accurate to about 1 part in 5*10^-6.



The pound is defined as 0.453... kg exactly. (I do not have all the figures to hand).

Martin, I don't understand how that is relevant to this thread. In fact, it is quite clearly NOT relevant. Also, I know the pound = 0.45359237kg EXACTLY, but so what?

The point is, what is this figure in terms of natural constants (the kg is NOT a natural constant)


Are you intentionally being difficult or did you simply not understand my posts?

Bryan,

I understand your post fully. However, the kg is currently defined in terms of a lump of metal that is in the custody of the BIPM at Sevres (near Paris). Please check their website: www.bipm.org. My definition in my previous post was cut and pasted from their site.

BIPM are currently considering changing the definition to one which uses N atoms of Carbon12 as the base definition of mass, but until the BIPM board is satisfied that the new definition is superior to the current definition (in particular that it is more reproducable), they are sticking to the curretn definition.

I mean not to be rude, but unless I am particularly stupid I do not see how you DID understand my post. I point you to the following:


"Anyone have any suggestions as to ******alternative definitions****** for the kilogram and pound- *****************************soon "Le Grand K" is to be replaced (the current standard)*************************, but with what?!"

That is to say that I know the definition is the lump of metal- I explicitly state that here. Your confusion may has arisen when I later asked for the "definition" in "basic physics terms". I see how this might have caused confusion if you hadn't read that first part of my message.

Let me rephrase for you, Martin:


What, in terms of planck mass, equivelant energy of various atoms etc etc etc, is the kilogram, or the pound, equal to as far as can be determined, given the present size of the kilogram (from its definition as that cylinder of metal)?


Jesus, you'ld think that we were drafting a legal document here or something.


I clearly asked some simple questions, and all I get is the usual confused answer in return. I am sad to say that very rarely do metric suppporters on this board seem to want to 'play ball' and just help a fellow out. What is a man to do...?

I have two suggestions:
1. Determine Avogadro's number (number of particles per mole) to several more significant figures, and then define the mass of that number of atoms of Carbon-12 as 12 grams, and define the kilogram from there.
2. Simply define the kilogram as the mass of a certain number of protons, neutrons, electrons, or some combination.

Where we are currently, I don't think either of these possibilities is very feasible, but in the future who knows.

Bryan

In your original post you asked

<<
what is the definition of the pound (and kilogram) in basic physics terms?
>>

There is only one "definition" of the kilogram and that is in term of a lump of metal that is kept in Sevres. There are a number of other "values" or "equivalences" of the kilogram in other physical terms - originally the gram was the mass of 1cm^3 of water at its maximum density, bu tthat has now been superceded. I think that you and I had different understandings of the word *definition*.

As regards the use of Avagardo's number, Bud is quite right.

Martin, why are you being antagonistic?

Bryan,

I think that there have been a few misunderstandings.

Further to your ideas on redefining the Kilogram, may I point you to the NIST site

http://physics.nist.gov/cuu/Constants/index.html

If you root around there you will find the relative uncertainty of many phyusical and chemical constants.

Yes, some spectacular misunderstandings. Let us brush this whole business aside and continue hating each other in Imperial-etric traditional and mutual loathing. Cheers!

So when it says that the natural mass unit is 9.109 3826 x 10-31 kg, this means it is approx. 4.132 x 10^31-lb
????????????????????????????????????????

That is about it, but more than likely they will say that 1kg is equivalent to N atoms of carbon 12 (where N is avery large number). BIPM needs of course to be sure that 1kg of graphite (made from pure carbon 12) has the same number of atoms as 1kg of diamonds (also made form pure carbon 12). It is of course possible that the energy af association is sufficient that the equation e=mc^2 comes into effect.

OK - I have made diamonds in the past (I jest not), but I do not know how much energy is assocated with the chemical bonds or whether this manifests itself in e=mc^2.

It certainly is a tricky business, metrology.