To explain the difference we use two words: **'magnitude'** and
**'direction'**. By magnitude we mean *how much of the
quantity is there*. By direction we mean *is this quantity
having a direction* which defines it.

Physical quantities which are completely specified by *just giving out
there magnitude* are known as **scalars**. Examples of scalar quantities are distance,
mass, speed, volume, density and temperature.

Other physical quantities *cannot be defined by just their magnitude*. To define
them completely we *must also specify their direction*. Examples of these are velocity,
displacement, acceleration, force, torque and momentum. These are called **vectors**.

If we were to represent the magnitude and direction of two vectors by two adjacent sides of a parallelogram.
The *resultant can then be represented in magnitude and direction by the diagonal*.
This diagonal is the one which passes through the point of intersection of these two sides.

It is often necessary to split a vector into its components. *Splitting of a vector into its components
is called resolution of the vector*. The original vector is the resultant of these components.
When the components of a vector are at right angle to each other they are called the rectangular components of a vector.

In the figure above the green vector has been resolved into two vectors: blue and red.
These vectors are at right angles to each other. The are the *rectangular components* of the green vector.