sekundi

Sekundi is a unit of time, defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. It is the base unit of time in the International System of Units (SI). The symbol for second is 's'.

The second was originally defined based on the Earth's rotation, but this proved to be inconsistent. In 1967, the definition was changed to the current atomic definition, which is highly precise and stable. This atomic second forms the basis for Coordinated Universal Time (UTC), the primary time standard by which the world regulates clocks and time.

The second is a fundamental unit used in many scientific and engineering disciplines. It is also part of other derived SI units, such as the meter per second (m/s) for velocity and the hertz (Hz) for frequency. While commonly associated with seconds, minutes (60 seconds) and hours (60 minutes) are not SI units but are widely accepted for use with the SI. The concept of a second has been used for centuries, with early mechanical clocks attempting to measure its duration.