Plane Kinematics of rigid bodies

   Thus, all lines on a rigid body in its planes of motion have the same angular displacement , the same angular velocity, and the same angular acceleration.

When a particle in a body move from position A to B in a circular path, the angular displacement q occurs. This displacement is a vector quantity since it has magnitude as well as direction. The direction is a rotation- either clockwise or counter clockwise.

The rate of change of angular displacement with itme is called angular velocity and is denoted by .
Thus
The unit of in SI system are radian / second².