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# Units in Physics

## B.1. Multiples and submultiples of units

The multiples of units and their submultiples by powers of 10 are designated as in Table B.1.

Table B.1. Multiples and submultiples

## B.2. Fundamental and derived SI units

The units of all physical quantities are defined in terms of six fundamental (or basic) units, which are chosen by convention: length, time, mass, current intensity, temperature, and luminous intensity. The units of the other physical quantities (the so-called derived units) are defined in terms of the fundamental units by using the dimensional homogeneity of physical laws. The International System of Units (SI) used in the book has the meter (m), second (s), kilogram (kg), ampere (A), kelvin (K), and candela (cd) as fundamental units. However, some branches of science and engineering continue to use the CGS system (based on the centimeter, gram, and second) for mechanical quantities. As the whole circumference is divided into 2π radians, the unit of angles is the radian. We also use the degree (°), minute (′), and second (″), and sometimes revolution (2π radians).

## B.3. Mechanical units

Table B.2. Mechanical units

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