# FUNDAMENTAL AND DERIVED UNITS

Fundamental (or base) units and derived units
The metre, kilogram, second and ampere are called
fundamental units or base units. See: Base units
From these units we can derive some more units
that are called derived units.
These units are built up step by step from the base
units and usually given a distinct name.
Examples of derived units are those for velocity,
acceleration, force (Newton), work (Joule), energy
(Joule), charge (Coulomb), pressure (Pascal) and
density
As an example we will look at how the unit for
potential difference (volt) is derived from the four
base units
The volt is defined as the work done per unit
charge
1. Combining two base units, metre and second,
we have the derived unit for velocity (ms -1 )
2. Combining two base units, amp and second, we
have the derived unit for charge (As) (simply called
the Coulomb)(C)
3. Combining the base unit second with the
derived unit for velocity we have another derived
unit for acceleration (ms -2 )
4. Combining the base unit kilogram with the
derived unit for acceleration we have another
derived unit, this time for force (ms -2 ) (simply
called the Newton)(N)
5. Combining the base unit metre with the derived
unit for force we have another derived unit, this
time for work (or energy) (kgm 2s -2 ) (simply called
the Joule)(J)
6. Combining two derived units, that for work
(kgm 2s -2 ) with that for charge (As) we have the
derived unit for potential difference (kgm2 s -3 A-1 )
(simply called the volt)(V)

DIFFERENCES BETWEEN FUNDAMENTAL AND DERIVED UNITS.

Derived units are made up of fundamental units.
Fundamental units cannot be broken down into a
different form.
For example Distance (meters), Mass (kg), and
Time (seconds) can not be broken down into a
simpler form. While Force is measured in newtons
(N) which can be broken down into its fundamental
units of (kg * m) / s^2.

Fundamental Units is independent of any other units while Derived units depend on Fundalmental units 