The Naked Scientists

The Naked Scientists Forum

Author Topic: Will the measure of the kilogram be changed?  (Read 4228 times)

Offline petrovitch

  • Jr. Member
  • **
  • Posts: 19
    • View Profile
Will the measure of the kilogram be changed?
« on: 22/08/2009 22:20:28 »
The weight of the standard unit of measure has recently changed.  Will this standard unit of measure be discarded for a new unchanging unit of measure or a constant?


 

Offline Madidus_Scientia

  • Neilep Level Member
  • ******
  • Posts: 1451
    • View Profile
Will the measure of the kilogram be changed?
« Reply #1 on: 23/08/2009 04:39:18 »
There's no reason for an alternative to the metric system, no.
 

Offline Chemistry4me

  • Neilep Level Member
  • ******
  • Posts: 7709
    • View Profile
Will the measure of the kilogram be changed?
« Reply #2 on: 23/08/2009 06:45:49 »
I love kilograms.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8648
  • Thanked: 42 times
    • View Profile
Will the measure of the kilogram be changed?
« Reply #3 on: 23/08/2009 10:16:24 »
They may change the definition of the kilogram (it's currently the only SI unit based on an artefact).
However if they do the new definition will mean that the kilogram is still the ssame mass as it alsways was (as near as they can measure).
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3813
  • Thanked: 19 times
    • View Profile
Will the measure of the kilogram be changed?
« Reply #4 on: 25/08/2009 10:23:48 »
Here is a useful URL on the subject (registration may be required)

http://www.nature.com/news/2009/090824/full/4601070a.html
 

Offline Nizzle

  • Hero Member
  • *****
  • Posts: 964
  • Thanked: 1 times
  • Extropian by choice!
    • View Profile
    • Carnivorous Plants
Will the measure of the kilogram be changed?
« Reply #5 on: 25/08/2009 10:53:02 »
I think a new SI unit will be deviced once a single quantum gravity theory is generally accepted.
When that will be is still very speculative
« Last Edit: 25/08/2009 10:55:59 by Nizzle »
 

Offline Madidus_Scientia

  • Neilep Level Member
  • ******
  • Posts: 1451
    • View Profile
Will the measure of the kilogram be changed?
« Reply #6 on: 25/08/2009 13:08:38 »
Why will we need a new SI unit then?
 

Offline Nizzle

  • Hero Member
  • *****
  • Posts: 964
  • Thanked: 1 times
  • Extropian by choice!
    • View Profile
    • Carnivorous Plants
Will the measure of the kilogram be changed?
« Reply #7 on: 25/08/2009 13:53:48 »
It's not a matter of need,
It's a matter of losing the artifact.

BTW, the kilo is only valid on earth no? It's the SI unit of weight, not mass right?
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3813
  • Thanked: 19 times
    • View Profile
Will the measure of the kilogram be changed?
« Reply #8 on: 25/08/2009 14:01:38 »
No the Kilogram is the unit of mass

http://physics.nist.gov/cuu/Units/units.html
 

Offline Nizzle

  • Hero Member
  • *****
  • Posts: 964
  • Thanked: 1 times
  • Extropian by choice!
    • View Profile
    • Carnivorous Plants
Will the measure of the kilogram be changed?
« Reply #9 on: 25/08/2009 14:10:57 »
So I weigh 85 Kg on earth, but if i take my scale to the moon, i won't weigh 85 Kg. But my mass hasn't changed...

So what is faulty? I thought Kg was the unit of weight :(
 

Offline Madidus_Scientia

  • Neilep Level Member
  • ******
  • Posts: 1451
    • View Profile
Will the measure of the kilogram be changed?
« Reply #10 on: 25/08/2009 14:52:46 »
I believe mass is measured as what the mass would weigh in Earth gravity

It's not a matter of need,
It's a matter of losing the artifact.

But what are we waiting for in a quantum theory of gravity that we need to devise the new SI unit?
« Last Edit: 25/08/2009 14:56:38 by Madidus_Scientia »
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3813
  • Thanked: 19 times
    • View Profile
Will the measure of the kilogram be changed?
« Reply #11 on: 25/08/2009 15:20:46 »
Mass is defined by how much inertia a body possesses, a mass of 1Kg requires a force of 1 Newton to accelerate it at 1 meter per second per second.
Weight is the force produced on a body by a gravitational field about 9.81 newtons per Kilogram on the Earth (it varies slightly depending where you are) and about one sixth that force on the moon.
 

lyner

  • Guest
Will the measure of the kilogram be changed?
« Reply #12 on: 25/08/2009 16:45:46 »
So I weigh 85 Kg on earth, but if i take my scale to the moon, i won't weigh 85 Kg. But my mass hasn't changed...

So what is faulty? I thought Kg was the unit of weight :(
If you're going to be pedantic (which is what this sort of thread has to be) you can't say you "weigh" anything in kg. You can only say you weigh so many N or your mass is so many kg. Your weight will vary all over the place and can't be used as a standard for anything. You can compare two masses on a balance, which will cancel out any force variations due to g being different.

The standard (kg) mass is still, I believe, defined in terms of the lumps of Platinum in Paris. Defining it in terms of proton masses or as the mass of so many atoms of an element is great in theory but actually counting out that number of atoms is difficult (to any degree of accuracy). How would you do it? If you did it using electrolysis, then you would have to know the current much more accurately than possible at the moment and you would also need to know the proportion of the various isotopes in your sample, too. It's a catch 22 situation and standard lumps under nice clean and stable conditions are a pretty good way of keeping a 'good' standard kg.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8648
  • Thanked: 42 times
    • View Profile
Will the measure of the kilogram be changed?
« Reply #13 on: 25/08/2009 19:28:52 »


If you're going to be pedantic (which is what this sort of thread has to be) you can't say ....

The standard (kg) mass is still, I believe, defined in terms of the lumps of Platinum in Paris.

It's a platinum iridium alloy and it's in Sevres (which I think is just outside Paris, but it may be a matter of deffinition).

The practicallities of counting that many atoms are interesting- so they plan to count them by volume. In particular they intend to use a sphere of isotopically enriched silicon.
There's a paper about (part of) the story here
http://www.iop.org/EJ/article/-ffissn=0957-0233/-ff30=all/0957-0233/20/9/092002/mst9_9_092002.pdf

though you will need to register to read it.
The plan is to get the answer right to about 1 part in 100,000,000
« Last Edit: 25/08/2009 19:32:46 by Bored chemist »
 

Offline Nizzle

  • Hero Member
  • *****
  • Posts: 964
  • Thanked: 1 times
  • Extropian by choice!
    • View Profile
    • Carnivorous Plants
Will the measure of the kilogram be changed?
« Reply #14 on: 25/08/2009 20:04:26 »
I dunnow, I'm just waiting for gravitons or Higgs Bosons or something... which might be used once completely understood
 

lyner

  • Guest
Will the measure of the kilogram be changed?
« Reply #15 on: 25/08/2009 23:58:31 »
Quote
The plan is to get the answer right to about 1 part in 100,000,000
So when are they planning to do it accurately then?
(They can do a lot better when defining time or frequency. Different problem, I know.)

I'll try to read the article tomo. Cheers for the info.
 

lyner

  • Guest
Will the measure of the kilogram be changed?
« Reply #16 on: 26/08/2009 11:32:24 »
BC
What a great article! Thanx for the reference. It would take several days to do it justice but it's well enough written to see where they're going without getting all the details.
Wall to wall with good ol' rigorous Scientific method. (Should be required reading for anyone who wants to post a BS theory)

Yes - I remember hearing the idea of using Silicon. The nice thing is that you don't need to use a particular size of sphere. The interferometric method for measurement is genius.

I never bothered to register with IOP before - can you imagine?
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8648
  • Thanked: 42 times
    • View Profile
Will the measure of the kilogram be changed?
« Reply #17 on: 26/08/2009 19:01:14 »
Quote
The plan is to get the answer right to about 1 part in 100,000,000
So when are they planning to do it accurately then?
As soon as they can, but that's already better then the stability of the lump of metal. It's believed to have changed bu about that much, but it's hard to be certain.
 

The Naked Scientists Forum

Will the measure of the kilogram be changed?
« Reply #17 on: 26/08/2009 19:01:14 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums