Question

Pressure can be defined as a force acting on a perpendicular area, so what if the force direction acts on an area slantly?

Answer 1

we resolve the force in two components..one perpendicular to area and other parallel to area..the perpendicular component applies pressure while parellel component is called shear stress..

Answer 2

pressure is actually defined as thrust per unit area. thrust means perpendicular force. if it is slant, as quarkine said, force has to be resolved into components.