Physical quantities

A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement. A physical quantity can be expressed as the combination of a magnitude expressed by a number – usually a real number – and a unit; for example, 6973167492749999999♠1.6749275×10⁻²⁷ kg (the mass of the neutron), or 7008299792458000000♠299792458 metres per second (the speed of light). Physical quantities are measured as ${\textstyle nu}$ where ${\textstyle n}$ is the magnitude and ${\textstyle u}$ is the unit. For example: A boy measured the length of a room as 3 m. Here 3 is the magnitude and m (metre) is the unit. 3 m can also be written as 300 cm. The same physical quantity ${\textstyle x}$ can be represented equivalently in many unit systems, i.e. ${\textstyle x=n_{1}u_{1}=n_{2}u_{2}}$.

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