quantités

Quantités, or quantities, is a broad concept used in science to describe properties that can be measured or counted. A quantity has a magnitude, represented by a numerical value, and a unit that expresses the scale of that magnitude. The concept applies across physics, chemistry, engineering, and everyday measurement, and it provides a common framework for comparing, adding, or differentiating properties.

Quantities are often classified as scalar or vector. Scalar quantities have only magnitude, such as mass, temperature, or distance. Vector quantities have both magnitude and direction, such as velocity, force, or displacement. The distinction matters for mathematical operations: vectors require treatment of both size and orientation, while scalars require only numerical values.

A central framework for quantities is the International System of Units (SI). SI distinguishes base quantities, such as length (meter), mass (kilogram), time (second), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole), and luminous intensity (candela). Derived quantities, like speed, acceleration, force, energy, and pressure, are formed from combinations of base quantities and have corresponding derived units.

Measurement and uncertainty are integral to quantification. All measured quantities have some degree of error, which is described by significant figures, uncertainty intervals, or statistical confidence. Dimensional analysis uses units to check the consistency of equations and to ensure that mathematical models properly reflect physical relations.

In practice, quantities enable precise description, comparison, and prediction of natural phenomena. They underpin instrumentation, data analysis, and scientific communication, and they rely on standardized units and consistent definitions to remain interoperable across disciplines and regions.