External pressure

An external pressure is understood to be the total pressure that acts on a substance or a system from the outside and thus strives to compress it. This system can be a disturbance within a hydrostatic pressure field , for example a submarine under water ( water pressure ) or an airplane in the earth's atmosphere ( air pressure ). The contact pressure and dynamic pressure can also be parts of this total pressure, but in contrast to hydrostatic pressure act very locally, such as the weight of a solid on a substrate.

In contrast to this, there are pressures that prevail within the system and are directed outwards, thus counteracting the external pressure. Such a pressure is called internal pressure . In the examples above, this would be the outward counterpressure of the pressure hull inside the submarine or the cabin pressure of the aircraft.

The external pressure also plays a role in thermodynamics , since it is of decisive importance in interaction with the saturation vapor pressure , the internal pressure of the gas within a liquid or solid, for the existence of a boiling point or sublimation point and also defines this.