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