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New defintion of kilogram


Edwina Lee

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3 hours ago, Strange said:

It is not quite as simple as that. 

More here: https://www.nist.gov/si-redefinition/kilogram-kibble-balance

The mass is defined in terms of other factors that can all be measured independently of the mass: voltage, current, velocity and g (acceleration).

It looks like you do a velocity measurement as a calibration, and then the mass determination as a static measurement. With an independent measurement of g.

The good thing is that you eliminate the issue of who gets a secondary kilogram standard. Any country can, in principle, realize the standard, though I don't know how they will communicate the information back and forth, like they(we) do with time. But that may be embedded in the calibration info and the new definition of h (and possibly other terms), which would mean that the kilogram will be defined by a certain current, given a certain value of g, and modified by some constant you get from calibration (which accounts for differences in the geometry of the coils and details of the magnets) But I haven't seen any of this kind of detail yet.

 

edit: Nope. Looks like there will still be physical objects, known as "transfer standards"
https://www.nist.gov/si-redefinition/kilogram-disseminating-new-kilogram

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