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The International System of Units, internationally known by the abbreviation SI (from French Système international d'unités), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official status in nearly every country in the world, employed in science ...
This list of international units is subsidiary to the list of units article and lists widely used modern units in a form of sortable table. Unit system Domain
The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science and technology. [ citation needed ] The names and symbols of SI base units are written in lowercase, except the symbols of those named after a person, which are written with an initial capital letter.
jiffy (physics) 3 × 10 −24 s: The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum. zeptosecond: 10 −21 s: One sextillionth of a second. Time measurement scale of the NIST and JILA strontium atomic clock. Smallest fragment of time currently measurable is 247 zeptoseconds. [3] attosecond: 10 −18 s
The SI system after the 2019 definition: Base units as defined in terms of physical constants and other base units. Here, means is used in the definition of . The SI system after 1983, but before the 2019 redefinition: Base unit definitions in terms of other base units (for example, the metre is defined as the distance travelled by light in a specific fraction of a second), with the constants ...
A form of energy transferred from one body to another by thermal interaction. heat transfer Helmholtz free energy hertz The SI unit of frequency, defined as the number of cycles per second of a periodic phenomenon. Higgs boson homeokinetics The physics of complex, self-organizing systems. horsepower (hp) Huygens–Fresnel principle hydrostatics
[a] This system underlies the International System of Units (SI) [b] but does not itself determine the units of measurement used for the quantities. The system is formally described in a multi-part ISO standard ISO/IEC 80000 (which also defines many other quantities used in science and technology), first completed in 2009 and subsequently ...
Physics is the scientific study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. [1] Physics is one of the most fundamental scientific disciplines. [2] [3] [4] A scientist who specializes in the field of physics is called a physicist.