Detailed Summary of the International System of Units
The International System of Units (SI), known as Système Internationale d'Unités, is the modern form of the metric system and is widely used in scientific and technical disciplines. Initially, different countries used various systems like CGS (centimetre-gram-second), FPS (foot-pound-second), and MKS (metre-kilogram-second) for measurements. This diversity was problematic for international communication and standardization.
To streamline measurements, the SI system was developed, which adopts a standard set of units universally accepted. The SI consists of seven base units:
- Length - Metre (m): Defined using the speed of light.
- Mass - Kilogram (kg): Defined using the Planck constant.
- Time - Second (s): Based on the hyperfine transition frequency of caesium-133.
- Electric Current - Ampere (A): Defined by the elementary charge.
- Thermodynamic Temperature - Kelvin (K): Defined using the Boltzmann constant.
- Amount of Substance - Mole (mol): Contains exactly the Avogadro number of entities.
- Luminous Intensity - Candela (cd): Based on specific radiation.
Beyond these, SI also includes plane and solid angles, measured in radians (rad) and steradians (sr), respectively. The simplicity of the SI system stems from its base-10 structure, facilitating conversions between units. As technological advancement continues, the definitions of these units are refined to maintain accuracy and consistency in measurements.