![]() ![]() Pounds are the primary unit of weight used in the United States for everyday purposes. This definition was updated in 1959, and this pound was based on a prototype weight that could be divided into 16 ounces. It originated from the Roman libra, and went through a number of different definitions until the development of the international avoirdupois pound in the 13th century. The definition of the pound has changed throughout the course of history. It is equivalent to 16 avoirdupois ounces. The definition of the pound (lb) is based on the international avoirdupois pound, which is defined as exactly 0.45359237 kilograms. What is a poundĪ pound is a unit of mass in the US customary system of units. While the US also uses SI in many other contexts, it has still not officially adopted SI. Most countries around the world have adopted SI with one notable exception being the United States, which still largely uses the US customary system in everyday life. The kilogram is widely used throughout the world in everyday as well as scientific contexts. The reason the base unit is the kilogram rather than the gram is because when this physical standard of mass was created in 1799, there were no methods for measuring masses that were as small as a gram. The kilogram is the only SI base unit that has an SI prefix (kilo-). The prototype was created in 1875 and adopted in 1889, and this definition of the kilogram lasted until 2019, when it was redefined in terms of the Planck constant, the speed of light, and the atomic transition frequency of cesium. It was redefined a few more times, and in 1875, one of the longest-lasting definitions of the kilogram was produced: a platinum alloy object about the size of a golf ball named the International Prototype of the Kilogram. In 1795 it was defined as the mass of one cubic centimetre of water at the melting point of ice. In 1793, it was defined as the mass of 1 litre of water. The definition of the kilogram has changed a number of times throughout the course of history. The redefinition bases it on physical constants that never change. The redefinition of the kilogram is intended to improve its definition, since the physical platinum alloy degrades over time. The actual value of the mass remains mostly consistent with the previous definition, which was based on an actual physical object made of a platinum alloy. The kilogram was redefined in 2019 to be based on three physical constants speed of light, the atomic transition frequency of cesium, and the Planck constant. 170 lbs ÷ 2.204623 = 77.111 kg What is a kilogramĪ kilogram (kg) is the base unit of mass in the International System of Units. ![]()
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