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For decades, metrologists have strived to retire ‘Le Grand K’ — the platinum and iridium cylinder that for 126 years has defined the kilogram from a high-security vault outside Paris. Now it looks as if they at last have the data needed to replace the cylinder with a definition based on mathematical constants.
The breakthrough comes in time for the kilogram to be included in a broader redefinition of units — including the ampere, mole and kelvin — scheduled for 2018. And this week, the International Committee for Weights and Measures (CIPM) will meet in Paris to thrash out the next steps.
“It is an exciting time,” says David Newell, a physicist at the US National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. “It is the culmination of intense, prolonged efforts worldwide.”
[...] In 2011, the CIPM formally agreed to express the kilogram in terms of Planck’s constant, which relates a particle’s energy to its frequency, and, through E = mc2, to its mass. This means first setting the Planck value using experiments based on the current reference kilogram, and then using that value to define the kilogram. The CIPM’s committee on mass recommends that three independent measurements of Planck’s constant agree, and that two of them use different methods.
(Score: 2) by bob_super on Thursday October 15 2015, @10:48PM
On a daily basis, my grandma would prefer to keep the density of milk at about 1. Makes measuring for cakes easier.
1dm3 = 1l = 1kg is nice, a cubic foot of water being about 27kg only helps if you really have a lot of guests.
(Score: 2, Interesting) by Francis on Thursday October 15 2015, @11:27PM
Why would she care about the density? We measure liquids by volume. Things like flour are generally best measured by weight just because they're easily compacted leading to uncertainties in the actual amount there.
And regardless of what system of measure you're using, the density of milk isn't going to be constant. It's going to depend upon the specifics of the milk. Whether you use whole milk or 0% fat milk is going to change the density of the milk, but in both cases the volume would be the same. That's generally why it's best to stick with the same brand and type of ingredients when possible as each brand may or may not act exactly the same way as the other options do. My mother restricts her purchases of flour to one or two varieties for that reason.
(Score: 3, Insightful) by fido_dogstoyevsky on Friday October 16 2015, @04:54AM
Why would she care about the density? We measure liquids by volume.
Not used a modern kitchen balance lately?
It's NOT a conspiracy... it's a plot.
(Score: 1) by Francis on Friday October 16 2015, @02:26PM
How is this insightful? It doesn't in any way shape or form address the question I asked.
For liquids, there's no reason not to use weight as a measure and at least one good reason not to. Weight varies a lot more than volume does globally. Needing to adjust the weights in addition to the other adjustments needed for cooking at various altitudes makes very little sense when it comes to liquid measures. Measuring flour by weight, does makes some sense as I've already acknowledged, but measuring liquids like that is stupid.
(Score: 0) by Anonymous Coward on Friday October 16 2015, @03:13PM
Well, if 1g is approximately equal to 1ml, you can use a scale to measure volume (after zeroing it with the container in place).
(Score: 0) by Anonymous Coward on Friday October 16 2015, @12:21PM
Whatever remains after removing all fat from the milk is not worthy of being called milk any more.