3 ms·

>The definition of the kilogram for more than 130 years, the International Prototype of the Kilogram (IPK), a cylinder of a platinum alloy stored at the BIPM in

by sandov 8y ago

>The definition of the kilogram for more than 130 years, the International Prototype of the Kilogram (IPK), a cylinder of a platinum alloy stored at the BIPM in France, will now be retired. It will be replaced by the Planck constant Maybe I interpreted it wrong (non-native English speaker), but does it say that the Kilogram will be equal to the Planck constant? Shouldn't it be that the definition of the Kg will be based on the Planck constant? >Although the size of these units will not change (a kilogram will still be a kilogram) Are our current measurements of the IPK that exact so the old kg is exactly equal to the new Kg? How can they measeure it with 0 error?. It doesn't make any sense to me.

biotech 8y ago
It's not just you, the wording is a bit weird. Yes, they are trying to say that the definition of the kg will be based on the Planck constant. Further down, the article says: "The kilogram – will be defined by the Planck constant (h)."
m1el 8y ago
> but does it say that the Kilogram will be equal to the Planck constant? No, this statement means that Kilogram will give up its place as a fundamental unit to Planck constant. Earlier, Kilogram was used as a fundamental unit, defined by a physical object. Not anymore. The kilogram will be defined by Planck constant. Namely, m = E/c^2 = hf/c^2. > How can they measeure it with 0 error? We can't, all measurements have errors. But we can measure things better than a physical object, which has changed with time. So we only have to measure Plank constant with precision higher than variation of physical object's mass for the purpose of replacing the definition of mass.
ashwinikd 8y ago
I guess it means that we are fixing the value of the Planck constant and deriving measure of kilogram from it. Given the measure of second and metre, a kilogram is the mass so that the value of plank constant is observed to be exactly 6.626x10^−34.

by sandov 8y ago

biotech 8y ago

It's not just you, the wording is a bit weird. Yes, they are trying to say that the definition of the kg will be based on the Planck constant. Further down, the article says: "The kilogram – will be defined by the Planck constant (h)."

m1el 8y ago

> but does it say that the Kilogram will be equal to the Planck constant? No, this statement means that Kilogram will give up its place as a fundamental unit to Planck constant. Earlier, Kilogram was used as a fundamental unit, defined by a physical object. Not anymore. The kilogram will be defined by Planck constant. Namely, m = E/c^2 = hf/c^2. > How can they measeure it with 0 error? We can't, all measurements have errors. But we can measure things better than a physical object, which has changed with time. So we only have to measure Plank constant with precision higher than variation of physical object's mass for the purpose of replacing the definition of mass.

ashwinikd 8y ago

I guess it means that we are fixing the value of the Planck constant and deriving measure of kilogram from it. Given the measure of second and metre, a kilogram is the mass so that the value of plank constant is observed to be exactly 6.626x10^−34.