kilogrammamääritelmä

The kilogrammamääritelmä refers to the definition of the kilogram, the base unit of mass in the International System of Units (SI). Historically, the kilogram was defined by a physical artifact, the International Prototype of the Kilogram (IPK). This cylinder, made of a platinum-iridium alloy, was kept under controlled conditions at the International Bureau of Weights and Measures (BIPM) in Sèvres, France. Its mass was considered the standard kilogram.

However, the reliance on a physical object presented challenges. Over time, slight variations in the mass of the IPK were observed, making it an unstable standard. To address this, a significant change occurred in 2019 with the redefinition of the kilogram. The new definition is based on fundamental physical constants, specifically Planck's constant.

The current kilogrammamääritelmä defines the kilogram by assigning an exact numerical value to Planck's constant. This value is 6.62607015 × 10⁻³⁴ joule-seconds (J⋅s). This definition is realized through experiments that link electrical power to mechanical power, such as the Kibble balance. By precisely measuring Planck's constant, scientists can determine the mass of one kilogram to an extremely high degree of accuracy and reproducibility, independent of any physical prototype. This shift to a definition based on fundamental constants ensures a more stable, accurate, and universally accessible standard for mass.