What are fundamental and derived units?

this answer can look lengthy but its very easy read till
thge end and u will find everything regarding ur question in a very easy
method...

Fundamental
units....i.e also called base units...u can understand it by the
following example.

consider a building...the building is
made up of bricks of different sizes..these can be considered as the units of the
building...which kind of units these may be???
fundamental units off course...the building blocks and the bricks are the
minimum components, the combination of which makes the whole building.similarly we can
define basic units.DEFINITION: the minimum number of those
physical quantities in terms of which other physical quanitites can beobtained is called
base quantities. these are decided to be seven in number by
the system
internationl...i.e

1. second


2. kilogram


3. meter


4. ampere


5. candela


6. kelvin


7. mole

DEIVED
QUANTITIES: Now take the same exapmle....this building also composed of
some other units that
is;

• rooms


• bathrooms


• kitchens


• stores
  etc etc

look at these units,,,,they are formed
by the combination of bricks or building blocks(which was considred as
fundamental units in first
case).......

these rooms,kitchens, and stores etc can be
considered as derived units,,,as its name tells that they can be derived or obtained
from other units(from 
fundamental)...so they are not
fundamental but derived from fundamentl.

Q: and how derived
are obtained from fundamental?

A: by trhe differnt
combination of fundamental....i.e multiplying or dividing two or more than two
fundamental...not subtracting or adding...

let us see in
examples.

1. velocity unit is meter/second...meter
   and second are fundamental while metr/second is
   derived.


2. newton(derived).... 1 newton = kg m /
   sec...where kg, m, and sec are
   fundamental


3. coulomb(derived)... 1 coulomb = 1 ampere *
   sec where both ampere and second are
   fundamental....

conclusion:
different fundamental units joins together (joining in terms of multiplication and
division only) and obtain derived
units.

Note: there are some
units which are neither fundamental nor derived they are called supplemenatry
units...i.e radian and steradian..