There are several equations that apply when an object's acceleration is constant.  Since acceleration is a vector quantity, this means that both the direction and the magnitude of the acceleration are unchanged over the time interval.

The equations are potential useful when the sought quantity is

Tip: To avoid making sign errors, always write these equations in terms of the vector components, then rewrite it in terms of magnitudes if necessary by substituting in projection equations.)

Given any 3 of these quantities, the remaining 2 can be derived.  Thus, there are many equations relating the quantities.  It suffices to remember a few of them and derive the other equations as needed.  Because they are most frequently used, the following equations are recommended for memorization (they are written in terms of the x-components, but similar equations exist for y-components):

 where vi_x and vf_x are the x-components of  the initial and final velocities of the object and d_x is the x-component of the displacement of the object

The first equation is also the definition of average acceleration, so it can be used when the object is moving in a curved path. If the acceleration is along the same line as the initial velocity or if the initial velocity is zero, then the motion will be along a straight line.  If, however, the acceleration is not along the same line as the initial velocity, then the motion will not be along a straight line, as in projectile motion.