To understand the meaning of the variables that appear in the equations for rotational kinematics with constant angular acceleration. rotational motion with a constant nonzero acceleration is not uncommon in the world around us. for instance, many machines have spinning parts. when the machine is turned on or off, the spinning parts tend to change the rate of their rotation with virtually constant angular acceleration. many introductory problems in rotational kinematics involve motion of a particle with constant, nonzero angular acceleration. the kinematic equations for such motion can be written as

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.