How heavy is a kilogram? International scientific effort to redefine the kilo makes breakthrough

[Gloria]

http://www.independent.co.uk/news/science/how-heavy-is-a-kilogram-international-scientific-effort-to-redefine-the-kilo-makes-breakthrough-10388391.html

An international effort to re-define the kilogram in terms of a mathematical constant instead of it being based on a cylinder of high-grade metal locked in a vault in France has achieved a minor breakthrough, scientists have said.

The present definition of a kilogram goes back more than 125 years when a solid cylinder of platinum-iridium alloy was agreed by everyone to weigh precisely one kilo – it is now kept under lock and key at the International Bureau of Weights and Measures in Sevres.

However, the standard kilo is literally losing weight for some unexplained reason, probably related to the loss of gas locked inside it when the cylinder was made. As a result, scientists are no longer satisfied that this physical object is accurate enough of such a fundamental measurement and want to re-define it by 2018 in terms of a mathematical constant.

The original cylinder of platinum and iridium used as the standard weight for one kilogram is thought to be losing mass The original cylinder of platinum and iridium used as the standard weight for one kilogram is thought to be losing mass (Getty) To do this they decided to replace the metal block, known as the International Prototype Kilogram, with a new definition of the kilo based on Planck’s constant, which represents the size of the quanta in quantum physics and is as reliable as a mathematical constant as the speed of light in a vacuum.

However, in order to do this they need to devise a way of estimating yet another constant, called Avogadro’s number, which is the number of discreet particles – molecules or atoms – in a “mole” of substance. A mole of water, for instance, is just a few teaspoons in volume but it contains approximately 6.002 by 10 to the power of 23 (10 with 23 zeros after it) molecules – Avogadro’s number – which is greater than the number of grains of sand in the world.

Giovanni Mana and colleagues of Italy’s National Institute of Metrology Research in Turin have now obtained what they believe to be the most accurate estimate of Avogadro’s number to date, which can now be used to quantify Planck’s constant and hence help to re-define the kilogram in purely mathematical terms.

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[pansypoo53219]

1. THAT is why i can no longer believe in the metric system.

[longship]

3. That is why you will likely never be a scientist.

The metric system is elegant and, above all, simple. That is why every single country in the world, except the USA, uses it. And even in the USA, scientists universally use only metric.

[muriel_volestrangler]

5. What alternative do you have to believe in?

The pound mass (abbreviated as lbm or just lb) is also a fundamental unit within the Imperial
system. It is equal to exactly 0.45359237 kilograms by definition.

http://www.durhamcollege.ca/wp-content/uploads/Pounds-Mass-and-Pounds-Force.pdf

[Erich Bloodaxe BSN]

2. Typo in Avogadro's number there.

It should read 6.022, not 6.002.

[Javaman]

4. heavier than an eth and lighter than a fom. nt

[passnobuck]

6. Haven't physicists been working on a more precise measurement for years?

I thought I had read something about this kind of re-definition of precision back in the days of the first space flight explorations, when measurements of mass had to be ultra precise.

[Gloria]

7. Yes, but apparently now they've figured out away to

really do a precise, math based approach....