November 30, 2021

The kilogram (symbol: kg) is the basic unit of mass in the International System of Units (SI) and is defined as the mass of the international prototype kilogram (IPK, also known as the “Big K”). The platinum-iridium alloy cylinder is kept by the International Bureau of Weights and Measures in Saint-Cloud, France. A kilogram was originally defined as the mass of a liter (decimetre of cubic) of water in a solid state. It was an unfavorable amount for precise replication, so at the end of the 18th century, the platinum artifact was declared the standard for the kilogram. That artifact, or its exact replica, was then the standard unit of mass for the metric system. IPK is the current primary artifact and its replicas are stored in carefully controlled laboratory conditions. Their masses are subject to fluctuation as a result of insufficiently studied factors, which may include handling, cleaning and contamination. IPK separated from its replicas by 50 μg from the time of their production, at the end of the 19th century. This led to the requirement to replace the artifact with a standard defined on the basis of invariant natural constants. The Awadipua (international) pound, used in the imperial and American steady systems, is defined to be exactly 0.453,592.37 kg, making one kilogram roughly equal to 2.2046 pounds. Other traditional units of weight and mass around the world are defined per kilogram making IPC the primary standard for almost all units of mass on Earth.


A gram, 1/1000 kilograms, was temporarily defined in 1795 as the mass of one centimeter of cubic water at the melting point of ice. The final kilogram, produced as a prototype in 1799 and from which the international prototype kilogram (IPK) in 1875 was derived, had a mass equal to the mass of 1 dm3 of water under atmospheric pressure and at the temperature of its maximum density, which is about 4 ° C. A kilogram is the only SI unit with the SI prefix (kilo) within its name. It is also the only SI unit that is still directly defined by an artifact, rather than a basic physical property that can be reproduced independently in different laboratories. Three other basic units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, floor, Gy, Sv, lm, lx) in the SI system they are defined in relation to the kilogram and therefore its stability is important

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