Physical Quantities - Foundation Physics
PHYSICAL QUANTITY
The quantities which can be defined and measured are called physical quantities. Example: Force, distance, time, current, etc.
The laws of physics can be described in terms of these physical quantities.
Measurement of Physical Quantities and their Units
Measurement is a method of comparison of an 
unknown quantity-with a standard quantity. This fixed or definite quantity which we take as a standard and by the help of which we can measure other quantities of the same kind is defined as the unit.
The measure of a physical quantity is expressed in two parts namely the magnitude and the(unit) For example, when we say force is 12 newton, 12 is the magnitude and newton is the unit of force.
Scalar Quantity
The physical quantities which can be described completely by their magnitude only are called scalar quantities.
There is no need to know or specify their directions. Example: Distance, mass, time, speed, density, etc.
These quantities can be added according to ordinary algebraic rules.
Vector Quantity
The physical quantities which can be described completely giving/stating by both their magnitude and direction are called vectors. If we state only magnitude or only direction, then their significance is not clear.
Example: Force, velocity, acceleration, etc.
Addition of these quantities can be done by special methods of addition- Law of polygon or law of vector.
Types of Physical Quantity and its Unit
The physical quantities are classified into two categories fundamental quantities and derived quantities.
Fundamental Quantities
The physical quantities that do not depend on any other physical quantity for their measurement are called fundamental quantities. Mass, length, time, electric current, temperature, luminous intensity and amount of substance are the fundamental quantities.
Derived Quantities
The physical quantities that are derived from the fundamental quantities are called derived quantities. Area, volume, density, force, velocity, etc., are some examples of derived quantities.
