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The kilogram doesn't weigh a kilogram any more. This sad news was announced during a seminar at CERN on Thursday, 26 October by Professor Klaus von Klitzing, who was awarded the 1985 Nobel Prize in Physics for the discovery of the quantised Hall effect. "We are about to witness a revolutionary change in the way the kilogram is defined," he declared.
Together with six other units – metre, second, ampere, kelvin, mole, and candela – the kilogram, a unit of mass, is part of the International System of Units (SI) that is used as a basis to express every measurable object or phenomenon in nature in numbers. This unit's current definition is based on a small platinum and iridium cylinder, known as "le grand K", whose mass is exactly one kilogram. The cylinder was crafted in 1889 and, since then, has been kept safe under three glass bell jars in a high-security vault on the outskirts of Paris. There is one problem: the current standard kilogram is losing weight. About 50 micrograms, at the latest check. Enough to be different from its once-identical copies stored in laboratories around the world.
To solve this weight(y) problem, scientists have been looking for a new definition of the kilogram.
Dang. That throws the easily memorable conversion of 1kg=2.2lbs right out the window.
(Score: 3, Interesting) by requerdanos on Tuesday November 07 2017, @03:43AM
The "gotcha" is that saying, as did the headline above, "how much does it weigh?" is a question that's meaningless without an agreed-upon gravity index, as it were. So, the question, "How much does this rock weigh?" can be answered with something like "About a kg and a half" if both the asker and answerer are on the same planet or other astral body (usually Earth) and neither is in some sort of exceptional reference frame (or both are in the same).
The gotcha gets worse. A kilogram weighs what a kilogram of mass weighs in the local reference frame and gravity index, whether that's a troy ounce or a short ton. It is therefore said to weigh "about a kilogram" regardless of what that weight is, which is meaningless even with an agreed-upon gravity index and frame of reference.
Sort of why the parts written by journalist-not-knowledgeable people say "how much does it weigh" and "zomg! the weight is changing" and the parts that quote actual scientists talk about things like mass and about how the kilogram is defined, and not about weight, which as you point out is a combination of mass and other factors. They even say right in TFS/TFA that the kg is a unit of mass. sigh.