From today the kilo stops weighing a kilo. The change affects not only the kilogram, but also the ampere, kelvin, and mole.
What is actually a kilogram?
In the 19th century, a cylinder-shaped mold would be the original shape in which the “Great Kilo” would be born; specifically in 1889. The international prototype of the kilogram has been the reference for the basic unit of mass ever since.
For almost 130 years, that piece of metal has been locked in a locked vault at the Pavillon de Breteuil, Saint-Cloud, near Paris. However, representatives from 60 nations, including Australia, have now voted on a proposal to define the humble unit using pure, unadulterated physics.
It is not a change that we will notice when shopping, but it is necessary if we want to keep pace with technology now and in the future.
History of the kilogram
In the 18th century, a kilogram was equivalent to a certain volume of water, but in 1889 it was replaced by a cylinder of platinum and iridium known as the international prototype kilogram or Big K, the Great Kilo.
“We are only talking about micrograms. Not enough to worry us in our measurements of daily life, but enough to see, and enough to want a better kilogram,” explains Bruce Warrington, CEO of the National Measurement Institute.
So what will change?
Instead of using the classical kilogram as the yardstick, scientists will use one of the fundamental laws of nature known as Planck’s constant to define a kilogram, which varies by about 50 micrograms less. The new value of the kilogram is derived from Planck’s constant using a power balance.
Planck’s constant is the amount of energy released in the light when electrons in atoms jump from one energy level to another. That number will now be exactly 6.62607015 x 10 ^ -34 J · s. To make their measurements, the scientists will use a sensitive electromagnetic instrument known as a Kibble balance.
A historical redefinition
“This is a historic step, bigger than any similar change made in the past,” says Warrington.
The International Office of Weights and Measures, which regulates changes in measurements, has already updated several of its units.
After the approval of the changes, they will enter into force on the next World Metrology Day : May 20, 2019. The objective is, therefore, to achieve the numerical accuracy of the kilogram and, with this, the International System of Units will be adapted better to new technologies.
Revised units
-The second , which occurs at a fixed frequency of 9,192,631,770 Hz.
-The meter, the distance traveled by light in a specific fraction of a second, defined using the speed of light in a vacuum of 299,792,458 meters / second
-The Kelvin is the unit of temperature, defined by the Boltzmann constant for the energy of gas particles at a given temperature, established at: 1,380 649 × 10–23 joules / Kelvin
-The kilogram is a quantity of mass, defined using Planck’s constant established in: 6.626 070 15 × 10–34 joules-second
-The ampere is a current flow, quantified using the elemental charge of electrons established in: 1,602 176 634 × 10–19 Coulomb
-The candela measures the intensity of light and is defined using the constant Kcd: the brightness, per watt, of monochromatic radiation at a specific frequency (540 × 1012 Hz), that is, 683 lumen / watt
-The mole is a number of atoms or particles, defined by Avogadro’s constant established at: 6.022 140 76 × 1023 mol – 1
