Pressure is the force per unit area that is applied on the surface of an object. It arises from the collision of molecules or particles with the surface. Pressure (P) is defined as the ratio of the force (F) applied perpendicular to the surface to the area (A) over which the force is distributed: P = F/A.
In a gas or liquid, pressure is the result of molecules or atoms colliding with the walls of the container. The SI unit for pressure is the pascal (Pa), but other common units include atmospheres (atm) and pounds per square inch (psi).
