Scalar Quantities
Those quantities which can be completely specified by their magnitude only are called the scalar quantities such as mass, length and time etc. A scalar is a real number.
Vector Quantities
Those quantities which have magnitude as well as directions and obey the vector laws of addition are called the vector quantities like velocity, force, weight and momentum etc.
The vector 
is called the position vector of P with respect to the origin O. Its modulus is represented by 