In a world where everything strives to be the best and the biggest, scientists behind The Avogadro Project in Australia have sought a surprising superlative: the world’s roundest object.
And they aren’t just doing it for bragging rights. Instead, the remarkable sphere may provide a solution to what’s known as the “kilogram problem.”
I thought a kilogram was the weight of a litre of water at sea level and a certain temperature.
Skeptic Pete said:
I thought a kilogram was the weight of a litre of water at sea level and a certain temperature.
I think it explains somewhere why that is fallible
Skeptic Pete said:
I thought a kilogram was the weight of a litre of water at sea level and a certain temperature.
You’re only 220 years behind the times there, SP.
The Wikipedia article on the kilogram is pretty good.
The gram was originally defined in 1795 as the mass of one cubic centimeter of water at 4°C, making the kilogram equal to the mass of one liter of water. The prototype kilogram, manufactured in 1799 and from which the current kilogram is based has a mass equal to the mass of 1.000025 liters of water.The kilogram is the only SI base unit with an SI prefix (“kilo”, symbol “k”) as part of its name. It is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Four of the seven base units in the SI system are defined relative to the kilogram so its stability is important.
The International Prototype Kilogram was commissioned by the General Conference on Weights and Measures (CGPM) under the authority of the Metre Convention (1875), and is in the custody of the International Bureau for Weights and Measures (BIPM) who hold it on behalf of the CGPM. After the International Prototype Kilogram had been found to vary in mass over time, the International Committee for Weights and Measures (CIPM) recommended in 2005 that the kilogram be redefined in terms of a fundamental constant of nature. At its 2011 meeting, the General Conference on Weights and Measures (CGPM) agreed in principle that the kilogram should be redefined in terms of the Planck constant, but deferred a final decision until its next meeting, scheduled for 2014.
The International Prototype Kilogram (IPK) is rarely used or handled. Copies of the IPK kept by national metrology laboratories around the world were compared with the IPK in 1889, 1948, and 1989 to provide traceability of measurements of mass anywhere in the world back to the IPK.
Also see Proposed future definitions
The kilogram is the international disgrace of metrology. Generally I abhor the cheap jibes at the French that come from our anglophone culture, but they’ve really right republicanly fkd this one up.