Pulling a Door Open by Pushing on It

Ordinarily, opening a door by pulling on the knob or handle causes a net torque on the door, and hence an angular acceleration, about a vertical axis. However, it may be that the top or bottom of the door sticks to the door frame; this horizontal force perpendicular to the plane of the door causes a torque on the door about a horizontal axis. This latter torque is countered by an opposite torque caused by horizontal forces exerted by the hinges; the result is that the door is deformed but does not readily open. The horizontal forces between the door and the hinges can potentially tear loose the hinges. When the sticking is released, the elastic potential energy stored in the deformation of the door becomes the alternating kinetic and potential energy of an annoying oscillation.