Vector Quantities: Vector quantities refer to the physical quantities characterized by the presence of both magnitude as well as direction. For example, displacement, force, torque, momentum, acceleration, velocity, etc.
Angular displacement, Angular velocity and Angular acceleration all of these are vector quantities.
The motion of a particle round a fixed axis is circular.
In order to completely specify angular displacement by a vector, it must fix
* direction of the axis of rotation
* magnitude of angular displacement
* sense of angular displacement
Amplitude is the maximum displacement of a body from its mean position. The amplitude is always equal to the radius of the circle.