The SI system provides us seven base units but these seven units cannot describe all kinds of measurements. Some measurement quantities are quite small and some are very large. For describing measurement which cannot be described from seven base units, scientist have created a new way of deriving units which can describe such measurements. For example meter is too small to describe the length of earth from sun. Similarly litre ( 1 litre is 1/1000 m3) is too big to describe the size of a tear drop. These aspects can be described from derived units. In this tutorial we will learn about two ways of deriving units.
1. Derivation from base units
2. Derivation form metric prefixes
Let us learn these two ways step wise.
Derivation from base units
Many units have been derived from base units. For example; unit of area, density, speed, volume etc. We will take one of them to illustrate you as an example.
Derivation of unit of area and volume
Unit of area is derived from unit of length. For finding area of a rectangular plane, we need to multiply its length and breadth.
A = l x b
= m x m
= m2
Where 'A' is area 'l' is length and breadth is 'b'. As SI unit of length is meter (m), the unit become 'm2'. Similarly for volume's unit become m3. Here is the table which shows some derived units.
Type of
measurement
|
Name of
the derived unit
|
Symbol
|
area
|
square meter
|
m2
|
volume
|
cubic meter
|
m3
|
speed
|
meter per
second
|
m/s
|
acceleration
|
meter per
second squared
|
m/s2
|
density
|
kilogram per
meter cubed
|
kg/m3
|
Derivation from metric prefixes
The other way of deriving SI units is using metric prefixes. This is a way to represent very small or large number using metric prefixes . For example; kilometre means 1000 m in the base unit form. This value is derived from the prefix kilo which means 103 ( 10 x 10 x 10). These prefixes help us to describe large or small quantities easily. It is better to say distance of earth form moon is 384,703 km rather than 384, 403, 000 m. Similarly the size of a typical hair is 0.000003 metres. We can represent it in metric prefixes as 3µm. ('µ' is Greek letter 'mu'. Its name is micro and value is 10-6)
See the below table of metric prefixes.
See the below table of metric prefixes.
Prefixes
|
Abbreviations
|
Value
|
tera
|
T
|
1 000 000 000
000 or 1012
|
giga
|
G
|
1 000 000
000 or 109
|
mega
|
M
|
1 000 000 or
106
|
kilo
|
k
|
1 000 or
103
|
hecto
|
h
|
100 or 102
|
deca
|
da
|
10 or 101
|
none
|
none
|
1
|
deci
|
d
|
0.1 or 10-1
|
centi
|
c
|
0.01 or 10-2
|
milli
|
m
|
0.001 or
10-3
|
micro
|
µ
|
0.000 001 or
10-6
|
nano
|
n
|
0.000 000 001
or 10-9
|
pico
|
p
|
0.000 000 000
001 or 10-12
|
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