Any
thing that is measurable in this physical world is called a physical quantity.
For
example,
the length of a table can be measured. Here, length is a physical quantity. The
mass
of your body can be measured, mass is a physical quantity. The time during
which
you
are reading this book can be measured, time is a physical quantity. If you
apply
force
to lift some thing, that force can be measured. So force is a physical
quantity.
There
are many such quantities in this physical world. Among these, it is seen that
there
are
a few quantities which can be measured without any help from any other
quantities.
These
quantities are `fundamental quantities’. For instance, to measure the length of
a
table,
you need to measure only the length. To measure this length, there is no need
of
measuring
any other quantity. So, length is a fundamental quantity. On the other hand,
measurement
of some quantities need the help of other quantities. For example, to
measure
the density of copper bar it is necessary to measure the mass and volume of a
piece
of copper bar and then mass is to be divided by the volume. Again, to measure
the
volume,
the length, the breadth and the height are to be measured, that is, lengths are
to
be
measured three times in three directions. So, it is seen that, there are
certain quantities
which
are fundamental. They do not depend on other quantities. These are called
fundamental
quantities.
