Units of Measurement
- In order for people around the world to agree
on quantiative observations, a system of measurement must be defined. Today,
scientists worldwide agree on the SI (le Systéme International) system,
also known as the metric system.
The fundamental units of the SI sytem are:
-
| Physical Quanitity |
Name of Unit |
Abbreviation |
| Mass |
kilogram |
kg |
| Length |
meter |
m |
| Time |
second |
s |
| Temperature |
Kelvin |
K |
| Electric current |
ampere |
A |
| Amount of substance |
mole |
mol |
| Luminous intensity |
candela |
cd |
But since the fundamental units are not always
convenient (i.e. expessing the mass of a sheet of paper in kilograms is ridiculous),
prefixes are used to change the size of the unit.
Common prefixes are:
| Prefix |
Symbol |
Factor |
| exa |
E |
1018 |
| peta |
P |
1015 |
| tera |
T |
1012 |
| giga |
G |
109 |
| mega |
M |
106 |
| kilo |
k |
103 |
| hecto |
h |
102 |
| deka |
da |
101 |
| --- |
--- |
100 |
| deci |
d |
10-1 |
| centi |
c |
10-2 |
| milli |
m |
10-3 |
| micro |
 |
10-6 |
| nano |
n |
10-9 |
| pico |
p |
10-12 |
| femto |
f |
10-15 |
| atto |
a |
10-18 |
For example, 1000 meters (or 103 m)
can be expressed as 1 km (kilometer).
In addition to fundamental units, there are also derived units, which get
their units from the fundamental units. An important derived unit in chemistry
is the liter (L), which expresses volume. A liter is the volume that a cube
with sides of 1 dm (decimeter) takes up. In other words, 1 L = 1 dm3.
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