On this Wikipedia the language links are at the top of the page across from the article title. This article is about pressure in the physical sciences. A figure showing pressure exerted by particle collisions inside a closed container. The pressure cooker pork chops that exert the pressure are highlighted in red.

Various units are used to express pressure. Pressure is the amount of force applied perpendicular to the surface of an object per unit area. The symbol for it is “p” or P. The IUPAC recommendation for pressure is a lower-case p. The minus sign comes from the convention that the force is considered towards the surface element, while the normal vector points outward. The equation has meaning in that, for any surface S in contact with the fluid, the total force exerted by the fluid on that surface is the surface integral over S of the right-hand side of the above equation.

The pressure, as a scalar, has no direction. The force given by the previous relationship to the quantity has a direction, but the pressure does not. If we change the orientation of the surface element, the direction of the normal force changes accordingly, but the pressure remains the same. Pressure is distributed to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point. It is a fundamental parameter in thermodynamics, and it is conjugate to volume. Since a system under pressure has the potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume.

The inch of mercury is still used in the United States. Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column does not define pressure precisely. Gauge pressure is often given in units with “g” appended, e. Although the force applied to the surface is the same, the thumbtack applies more pressure because the point concentrates that force into a smaller area. If we try to cut with the flat edge, force is distributed over a larger surface area resulting in less pressure, and it will not cut.