The fact that movements of people or objects across the screen appear to have
different degrees of difficulty and effort depending on which direction they are going , is due to our
knowledge and
understanding of the physical rules of gravity.
Movements from
top to bottom are perceived as lighter and easier than those from
bottom to
top, because our experience
tells us that although things fall down easily, it takes effort to move something against the force of
gravity.
How strenuous we perceive a direction of movement has not only to do with
our physical experiences, but also with our cultural background. In western
cultures, it is common to read from
left to right, which is why this direction of
movement is often perceived as pleasant and easy. Accordingly, the direction of
movement from
right to left is considered more strenuous. In film language, this
effect is called directionality or
directionality.