## B1 SI UNITS AND SYMBOLS

The following formulae are based on the International System of Units, known as SI (Systeme Internationale d'Unites) which is used throughout this book. SI was adopted in February 1969 by a resolution of the CGPM (Conference Generale de Poids et Mesures) as ISO Recommendation R1000.

A base unit exits for each of the dimensionally independent physical quantities: length, mass, time, electric current, thermodynamic temperature and luminous intensity. The SI unit of any other quantity may be derived by appropriate simple multiplication or division of the base units without the introduction of numerical factors.

The system is independent of the effects of gravity, making a clear distinction between the mass of a body (unit of mass = kilogram) and its weight, i.e. the force due to gravity (unit of force = Newton).

Example:

A force of 1 N acting on a mass of 1 kg results in an acceleration of 1 m s ?2.

Conversion factors from non SI units to SI units are to be found in Appendix C.

### SI BASE UNITS

Quantity

Unit symbol

Unit name

Length

m

meter

Mass

kg

kilogram

Time

s

second

Electric current

A

Ampere

Temperature

K

Kelvin

Luminous intensity

cd

candela

### DECIMAL MULTIPLES AND SUBMULTIPLES

Factor

Prefix

Symbol

10 12

tera

T

10 9

giga

G

10 6

mega

M

10 3

kilo

k

10 2

hecto

h

10

deca

da

10 ?1

deci

d

10 ?2

centi

c

10 ?3

milli

m

10 ?6

micro

?

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