Rotation about a Fixed Axis

Here the motion of the point used to describe the body's motion in the plane is fixed. Therefore, the line used to describe the body's motion is all that is needed to fully describe the motion.

1. Motion of a Line in Fixed Axis Rotion
   

   In fixed axis rotation, the motion of the body can be described by simply giving the angular position of any line in the plane of motion, so the angular velocity and acceleration of the rigid body are given by

   

2. Motion of a Point in Fixed Axis Rotation
   

   In fixed axis rotation, points not on the axis of rotation travel on circular paths centered at the axis. If r_P is defined as the position vector of point P measured relative to the fixed axis of rotation, then angular velocity can be written as

   

   

   Similarly, angular acceleration can be written as