SI Units
In the Système Interntional d’Unitès, SI, a unit
is
chosen for a particular purpose and larger and smaller are obtained by
applying
a prefix to this unite and multiplying or dividing by 10 or power of 10.
Larger units, obtained by multiplying by 1000,
etc.,
are called ‘multiples’, smaller units, obtained by multiplying by 0.01,
etc.,
are termed ‘sub-multiples’.
SI multiples and sub-multiples
|
Prefix
|
Symbol
|
Factor by which unit is multiplied
|
Example
|
|
mega
|
M
|
1
000 000 = 106
|
meganewton,
MN
|
|
kilo
|
k
|
1
000 = 103
|
kilometer,
km
|
|
The unit
|
|
centi
|
c
|
0.01
= 1/102
|
centimeter,
cm
|
|
mili
|
m
|
0.001
= 1/103
|
millimeter,
mm
|
|
micro
|
µ
|
0.000
001 = 1/106
|
micrometer,
µm
|
SI Symbols
Only one prefix can be applied to a unit at a
time.
For example, 1000 kilonewton must not expressed 1 kilokilonewton but
as
meganewton; 0.001 millimeter must not be written as 1 millmillmeter but as
1
micrometer.
The correct use of upper and lower case
letters
(capital and small letters) is important. For example m- meter, but M- mega;
k-
kilo, but K- Kelvin.
Symbols must not made plural by adding ‘s’ since
’s’
is symbol of second.
When a prefix is attached to a unit there should
be
no space between the prefix and the unit; for example, mm- millimeter,
kW-
kilowatt, MN- meganewton.
When a complex unit is formed by multiplying
two
units together, however, the symbol should be separated by a space;
for
example, N m- newton meter (the unit of torque).