A door rotates around its hinges, which act as a pivot. The turning effect of a force is called its moment. Moment equals force multiplied by the perpendicular distance from the pivot. Applying the same force farther from the hinges creates a larger turning effect. That is why handles are placed near the edge of the door rather than next to the hinges. You need less force to produce the moment required to open it. The same physics explains long spanners, crowbars and many levers.

The useful part of this physics is that it helps people predict and design real things. Engineers often begin with the same simplified model used in school, test where it works, then add more detail when measurements show that the real situation is more complicated.

Turning depends not only on force but on how far that force acts from the pivot. The moment is force multiplied by perpendicular distance from the pivot, so moving the same force farther from the hinge produces a larger turning effect. Levers exploit exactly this relationship: a larger distance can reduce the force needed, although the hand then has to move through a greater distance.