Easein creates a linear easing curve that smoothly increases the percentage tween from zero to one hundred percent in the number of frames it takes to complete the tween. This creates an effect of linear uniform acceleration that means that the velocity of the moving body changes in by equal amounts each frame creating a uniformly accelerating object.

The exact value of the acceleration depends on the final velocity that must be achieved as the object always starts moving from rest. The final velocity of the object depends on relationship between the number of fames in the tween and the change in position on stage.

The frame rate and the size of the stage are other factors which effect the appearance of the acceleration tween and must be considered when creating a physically accurate animation.

Ease out creates the same linear easing curve as the easein function. The  Easing curve still smoothly changes the percentage tween from zero to one hundred percent in the number of frames it takes to complete the tween. However because the tween is negative it is has the effect of deceleration. This means that the object starts the animation at its maximum velocity then slows down until it is motionless.

As with the easein function the exact value of the deceleration depends on the relationship between the number of fames in the tween and the change in position on stage.