Definition of kilogram set to change to physical constant

[gary]

In an article in today's Sydney Morning Herald, Marcus Storm reports that
at the 104th meeting of the International Committee for Weights and
Measurements (CIPM), which was held last week in Paris, that they
were satisfied after years of experiment that they found a new
method to define the kilogram.

Originally Posted by Marcus Storm Sydney Morning Herald

The current definition of the kilogram is based on the "International Prototype", or Le Grand K.

It is a cylindrical lump of platinum-iridium alloy sitting in a vault in the Pavillon de Breteuil, Sevres, near Paris. Six other near-identical alloy masses were made with it in 1889 to establish an international standard for the kilogram.

The problem is that after 126 years the seven kilogram masses no longer weigh the same: they are out by about 60 micrograms. And because the International Prototype is deemed the standard, it is unclear whether it has become lighter or the others heavier. Most likely it is Le Grand K losing mass through minute amounts of radioactive decay or atoms leaving the artefact from handling or in the form of gas.

Originally Posted by Marcus Storm, Sydney Morning Herald

The metric system now encompasses seven base units: mass (kilogram), distance (metre), time (seconds), electric current (ampere), temperature (Kelvin), substance (mol) and luminosity (candela).

Of those seven, six are based on universal constants of nature. For example, a metre is defined as the length of the path travelled by light in a vacuum during a time interval of 299,792,458ths of a second.

The kilogram has been the hold-out.

To shift from Le Grand K, two methods have been developed.

Article here -
http://www.smh.com.au/technology/sci...16-gkbg9s.html

[Eratosthenes (Peter)]

This Perfect Silicon Sphere is the Most Precise Kilogram Ever

http://motherboard.vice.com/read/thi...kilogram-ever-

Scientists look to define kilogram with a super-round silicon sphere

http://ceramics.org/ceramic-tech-tod...silicon-sphere

[Eden (Brett)]

Now all that remains is for the U.S. (Outside of NASA) to finally make the transition to the Metric system.

[Eratosthenes (Peter)]

Originally Posted by Eden

Now all that remains is for the U.S. (Outside of NASA) to finally make the transition to the Metric system.

...don't forget the great nations of Liberia and Myanmar

the USA isnt alone on this front.

You may very well owe the USA, its people and administration a written apology

[SimmoW (SIMON)]

Does this mean I can go down a size in my jeans? :-)

[leon]

With the discovery of this what is really going to change, v and does it really matter.
Surely time spent on this type of research could be better spent.

Leon

[speach (Simon)]

Originally Posted by Eden

Now all that remains is for the U.S. (Outside of NASA) to finally make the transition to the Metric system.

you must remember that the SI system is a socialist plot to over throw the great us of a!!!!

[Steffen]

Originally Posted by leon

With the discovery of this what is really going to change, v and does it really matter.

Well, I'll be sure to let my butcher know

Seriously though, I'd love to know why exactly the reference kilogram bars can go "out of sync" by 60µg, especially since they are presumably made of the same material and kept under similar conditions?

[Kunama]

I'm going to try lose lose a few silicon spheres by Christmas......

[FlashDrive (Poppy)]

Originally Posted by Kunama

I'm going to try lose lose a few silicon spheres by Christmas......

[gary]

This 2012 presentation by the Bureau International des Poids et Mesures
describes the process by which the prototypes are manufactured and
how they are washed and cleaned and then calibrated.

The platinum-iridium mass standards are cleaned with chamois leather
soaked for 48 hours in a mixture of equal parts ethanol and ether after
which the absorbed solvent is wrung out of the leather.

They are then steam cleaned with water.

Cleaning the prototypes can remove between 5ug and 60ug of "contamination"
depending upon when they were last cleaned.

http://www.bipm.org/ws/CCM/MeP_2012/...1nov_final.pdf

[mjfitzhenry (Matthew)]

Originally Posted by gary

Cleaning the prototypes can remove between 5ug and 60ug of "contamination"
depending upon when they were last cleaned.

It really is ridiculous that the fundamental unit of mass is defined by some random chunk of metal held in Paris. It's about time they based it on some physical constant like the rest of the fundamental units are.

[Steffen]

I wonder whether the alloy can absorb gases. Palladium, for example, which is in the same group of the periodic table as platinum, can absorb 900x its volume of hydrogen.

[KenGee]

Originally Posted by leon

With the discovery of this what is really going to change, v and does it really matter.
Surely time spent on this type of research could be better spent.

Leon

Leon whats going to change is the kg. If we keep our current system then we will have to adjust all calibrated scales. They are effectively trying to move away from weights and measures being a relative scale to being an absolute scale.
For example time is a absolute scale now the second is defined as

"the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom ".

it used to be based on the mean solar day that varies through out the year by about 30 seconds.