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A unit of time is any particular time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI), and by extension most of the Western world, is the second, defined as about 9 billion oscillations of the caesium atom.
The SI base units are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now known as the International System of Quantities: they are notably a basic set from which all other SI units can be derived.
The SI unit of time, the second, symbol s, is easy enough to define, but time itself can only be defined in reference to other quantities. As we will see, time isn't even the steady thing that it seems to be, but can change how quickly or slowly is passes depending on speed and mass.
The SI comprises a coherent system of units of measurement starting with seven base units, which are the second (symbol s, the unit of time), metre (m, length), kilogram (kg, mass), ampere (A, electric current), kelvin (K, thermodynamic temperature), mole (mol, amount of substance), and candela (cd, luminous intensity). The system can ...
12 kwi 2010 · Learn how the second, the SI unit for time, is defined by the cesium frequency and how to measure it with atomic clocks. Find resources for students and teachers, FAQs, and links to related topics.
The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s–1.
9 kwi 2019 · Atomic clocks enable us to define the second — the international unit of time — in a precise, measurable way that doesn’t change over time. And they allow us to divide the second into extremely small parts, opening up new applications with each finer subdivision.
