Scientists are set to change the way the kilogram is defined - without a referendum !!

Scientists are set to change the way the kilogram is defined.

Currently, it is defined by the weight of a platinum-based ingot called "Le Grand K" which is locked away in a safe in Paris.

Researchers are expected to vote to get rid of it in favour of defining a kilogram in terms of an electric current.

The decision is to be made at the General Conference on Weights and Measures, in Paris.

 

"laid-back-but-awfully-reassuring"

Original Post

It might sound strange to us mere earth bound mortals,  but I understand it there is a changing variation between Le Grand K & its certified copies,  so it makes sense to find another means of ensuring accuracy outside of actual mass (weight).   

 The new method will be based on the Planck constant,  & will be defined by fixing the value as the speed of light & the resonant frequency of the caesium atom in a vacuum.

The caesium atom is used in other SI definitions;  the definition of a second is the time it takes a caesium atom to oscillate 9,192,631,770 times.   

Earth shattering (not) but if the variation in a kilo equivalent to the weight of 20mm of human hair is important to you  ......  

Indeed Don,   however as much as I trust BA’s navigation systems will get me safely to Cape Town next week,  I suspect the potential of navigational errors caused by this anomaly in Le Grande K will be overcome by the application Mk-II eyeballs & the cleanliness of the cockpit window to ensure we don’t land on the rather large lump of sandstone that someone stuck in the middle of the city.

Don Atkinson posted:

Oh ! and a new "unit" of measurement, at least in my vocabulary is the "light foot". Possibly something to do with Usain Bolt

It's an approximation of course, one foot being the approximate distance that light (and other EM frequencies) travel in one billionth of a second.

You mean “one foot per nano-second”? Nothing new there for us sparkles........

Don Atkinson posted:

Hi Mike,

that human hair represents an error of about 50 parts in a billion. Now, if we apply that sort of rough and ready measurement to our gps/satnav systems, we’d be lost !

If you mean weight per unit length of generic human hair, the variation is considerably more -  it can be at least as much as +/- 60% (assuming consistent density).

Innocent Bystander posted:
Don Atkinson posted:

Hi Mike,

that human hair represents an error of about 50 parts in a billion. Now, if we apply that sort of rough and ready measurement to our gps/satnav systems, we’d be lost !

If you mean weight per unit length of generic human hair, the variation is considerably more -  it can be at least as much as +/- 60% (assuming consistent density).

Hi IB,

Le Grande K has deteriorated and the copies around the world have also deteriorated. Some of these copies were never precisely accurate in the first place.

The typical magnitude of these deteriorations and variations is represented by the mass of a human eyelash, or 20mm of typical human hair. As you say, human hair can vary in density quite a bit, but these eyelash/hair comparisons give a helpful comparison, at least IMHO.

I have simply extended the comparison to GPS to provide an alternative visualisation of how rough and ready Le Grande K is as a fundamental unit of mass.

Suzy Wong posted:
Don Atkinson posted:

Oh ! and a new "unit" of measurement, at least in my vocabulary is the "light foot". Possibly something to do with Usain Bolt

It's an approximation of course, one foot being the approximate distance that light (and other EM frequencies) travel in one billionth of a second.

You mean “one foot per nano-second”? Nothing new there for us sparkles........

..... there’s always somebody “light years” ahead of the rest of us ! ........one day we’ll catch up !

Don Atkinson posted:
Christopher_M posted:

I thought I heard something about Ava Gardner's number when this topic was mentioned on the radio yesterday.

Hi Chris,

If you're still looking for Ava Gardner's number.................

........you could try + (00) 602 214 0857................

Good of you Don, I suspect the National Physical Laboratory may have a mole. Thanks for Ava's number but I have a feeling there are a few digits missing, twenty three zeros to be precise.

Christopher_M posted:
Don Atkinson posted:
Christopher_M posted:

I thought I heard something about Ava Gardner's number when this topic was mentioned on the radio yesterday.

Hi Chris,

If you're still looking for Ava Gardner's number.................

........you could try + (00) 602 214 0857................

Good of you Don, I suspect the National Physical Laboratory may have a mole. Thanks for Ava's number but I have a feeling there are a few digits missing, twenty three zeros to be precise.

ah! that's what the .......'s were for

thebigfredc posted:

I think there is every chance I am out of my depth here but I thought a kg was the weight of 1 litre of water, hence the specific gravity of water is 1.

I’m surprised you know what a kg or litre is. You come across as a CWT and fluid ounce sort of person.

thebigfredc posted:

I think there is every chance I am out of my depth here but I thought a kg was the weight of 1 litre of water, hence the specific gravity of water is 1.

Ray, you have to keep up with the times. We are leaving the EU. Kg and Litres will be a thing of the past !

Le Grande K is over ! It's much more than a gnat's whisker out of tolerance, it's a whole 3/4 inch of a human hair out !!

And don't rely on us going back to the CWT and fluid ounces business just because JR-M can't get his head around km and Euros.

Take a look in the BBC science section, rather than the "news" compartment !

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