gauge = 20.8 psi. It is approximately equal to typical air pressure at Earth mean sea level and is defined as 101325 Pa. Because pressure is commonly measured by its ability to displace a column of liquid in a manometer, pressures are often expressed as a depth of a particular fluid (e.g., centimetres of water, millimetres of mercury or inches of mercury). (The total force applied to the longer dam will be greater, due to the greater total surface area for the pressure to act upon. Mathematically: Some meteorologists prefer the hectopascal (hPa) for atmospheric air pressure, which is equivalent to the older unit millibar (mbar). Pressure is depth dependent, not volume dependent, so there is a reason that water seeks its own level. Problem 2: The psia pressure instrument gives the reading as 35.8 psi. In a static gas, the gas as a whole does not appear to move. Differential pressure is expressed in units with "d" appended; this type of measurement is useful when considering sealing performance or whether a valve will open or close. While pressures are, in general, positive, there are several situations in which negative pressures may be encountered: Stagnation pressure is the pressure a fluid exerts when it is forced to stop moving. The vacuum level is the difference in pressure between atmospheric pressure and pressure in the evacuated system: 0% vacuum = 760 torr = 14.7 psia = 29.92 inc mercury abs = 101.4 kPa abs 50% vacuum = 380 torr = 7.3 psia = 15 inc mercury abs = 50.8 kPa abs Diagram showing absolute pressure, vacuum and gauge. At sea level, it is around 14.7 pounds per square inch. At the surface of a gas, the pressure force acts perpendicular (at right angle) to the surface. 0 A submerged triangular block has water forced against each point from many directions, but components of the force that are not perpendicular to the surface cancel each other out, leaving only a net perpendicular point. = 14.2 psi + 31 psi There is a two-dimensional analog of pressure – the lateral force per unit length applied on a line perpendicular to the force. This is one example of a practical application of pressure. Surface tension is another example of surface pressure, but with a reversed sign, because "tension" is the opposite to "pressure". Further, both spellings are often used, CS1 maint: multiple names: authors list (, National Institute of Standards and Technology, Fluid statics § Pressure in fluids at rest, Timeline of temperature and pressure measurement technology, "14th Conference of the International Bureau of Weights and Measures", "U.S. Navy Diving Manual (Chapter 2:Underwater Physics)", "Rules and Style Conventions for Expressing Values of Quantities", wikiUnits.org - Convert units of pressure, Cleaning and disinfection of personal diving equipment, Swimming at the 1900 Summer Olympics – Men's underwater swimming, Confédération Mondiale des Activités Subaquatiques, Fédération Française d'Études et de Sports Sous-Marins, Federación Española de Actividades Subacuáticas, International Association for Handicapped Divers, Environmental impact of recreational diving, Table Mountain National Park Marine Protected Area, Finger Lakes Underwater Preserve Association, Maritime Heritage Trail – Battle of Saipan, Use of breathing equipment in an underwater environment, Failure of diving equipment other than breathing apparatus, Testing and inspection of diving cylinders, Association of Diving Contractors International, Hazardous Materials Identification System, International Marine Contractors Association, List of signs and symptoms of diving disorders, European Underwater and Baromedical Society, National Board of Diving and Hyperbaric Medical Technology, Naval Submarine Medical Research Laboratory, Royal Australian Navy School of Underwater Medicine, South Pacific Underwater Medicine Society, Southern African Underwater and Hyperbaric Medical Association, United States Navy Experimental Diving Unit, List of legislation regulating underwater diving, UNESCO Convention on the Protection of the Underwater Cultural Heritage, History of decompression research and development, Basic Cave Diving: A Blueprint for Survival, Bennett and Elliott's physiology and medicine of diving, Code of Practice for Scientific Diving (UNESCO), IMCA Code of Practice for Offshore Diving, ISO 24801 Recreational diving services — Requirements for the training of recreational scuba divers, The Silent World: A Story of Undersea Discovery and Adventure, List of Divers Alert Network publications, International Diving Regulators and Certifiers Forum, List of diver certification organizations, National Oceanic and Atmospheric Administration, World Recreational Scuba Training Council, Commercial diver registration in South Africa, American Canadian Underwater Certifications, Association nationale des moniteurs de plongée, International Association of Nitrox and Technical Divers, International Diving Educators Association, National Association of Underwater Instructors, Professional Association of Diving Instructors, Professional Diving Instructors Corporation, National Speleological Society#Cave Diving Group, South African Underwater Sports Federation, 14th CMAS Underwater Photography World Championship, Physiological response to water immersion, Russian deep submergence rescue vehicle AS-28, Submarine Rescue Diving Recompression System, Artificial Reef Society of British Columbia, Diving Equipment and Marketing Association, Society for Underwater Historical Research, Underwater Archaeology Branch, Naval History & Heritage Command, International Submarine Escape and Rescue Liaison Office, Submarine Escape and Rescue system (Royal Swedish Navy), Submarine Escape Training Facility (Australia), Neutral buoyancy simulation as a training aid, https://en.wikipedia.org/w/index.php?title=Pressure&oldid=977514352, Articles with incomplete citations from July 2020, Short description is different from Wikidata, Articles with unsourced statements from January 2013, Creative Commons Attribution-ShareAlike License, This is derived from the definitions of pressure and weight density.