Coherent system of units

A system of measurement units in which derived units are formed from base units without numerical factors other than one.

Base unit: A unit chosen as a fundamental reference for defining other units in a system. Coherent systems derive other units from a selected set of base units.
International System of Units: The internationally agreed system of measurement units, abbreviated SI. SI is the most widely used modern coherent system.
Noncoherent system of units: A unit system in which at least some derived units require numerical factors beyond base-unit products. It is the direct opposite: derived-unit definitions include extra factors.
Newton's second law: The law stating that an object's acceleration is proportional to its net force and inversely proportional to its mass. In coherent units its familiar form is force equals mass times acceleration.
Derived unit: A unit defined as a product or quotient of powers of base units. Coherence requires derived units to use base-unit combinations without extra numerical factors.
Centimetre–gram–second system of units: A family of metric unit systems based on centimetre, gram, and second. CGS variants illustrate coherent units with different base-unit choices.
Gravitational metric system: A family of engineering systems using force rather than mass as a base quantity. Its force-based units can introduce conversion constants into mechanical equations.
Work (physics): Energy transferred when a force causes displacement along its direction. Its derived unit follows directly as force multiplied by distance.
Physical dimension: A property expressed in terms of fundamental kinds of quantity, such as length, time, or mass. Dimensions reveal the base-unit powers that define each derived unit.
Metre–tonne–second system of units: A metric system using the metre, tonne, and second as base units. Its coherent force unit is the sthène, rather than the newton.

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