It is essential to understand the term thrust first before understanding pressure. The force acting on a surface is known as the thrust. It has both direction and magnitude. The force exerted per unit area applied in a perpendicular direction to the object surface is known as pressure. Pressure can also be defined as thrust per unit surface area. Fluid pressure is the pressure exerted by a fluid. For example, water (fluid) in a glass (container) exerts pressure in all directions, at all points. The air in the earth's atmosphere exerts a force upon all objects and also on the earth. Atmospheric pressure can be defined as, the force exerted by the atmospheric air upon a unit area. Fluid Pressure: Pascal's law: Pressure exerted anywhere in a confined liquid is transmitted equally in all directions. Atmospheric Pressure: Atmospheric pressure is the force per unit area exerted against a surface by the weight of the air.