Kinematics is the science of motion, which responds to the motion of an object without looking at the forces acting on the object (mass objects are ignored). So the distance the object during its motion is only determined by the speed or acceleration of v and a.
Straight Irregular Motion is a straight-line motion in the horizontal direction with a velocity v fixed (the acceleration of a = 0), so that the distance S is determined only by the speed remains within a certain time.
An object is said to move straight changed irregularly if the acceleration is always constant. Acceleration is a vector quantity (quantities that have magnitude and direction). Means constant acceleration magnitude and direction of acceleration is always constant at any time. Although the magnitude of the acceleration of an object is always constant but if the direction of acceleration is always changing the acceleration of the object is not constant. And vice versa if the direction of the acceleration of an object is always constant but the magnitude of the acceleration is always changing the acceleration of the object is not constant.