Pressure

Pressure
Name	Pressure
Units	pascal (Pa)
Si	Pa
Other units	atmosphere (atm), bar, torr, psi

Pressure is the scalar physical quantity defined as force per unit area, fundamental in Newtonian mechanics, hydrodynamics, electromagnetism, statistical mechanics, and relativistic contexts. It governs phenomena from atmospheric weather patterns to aeronautical lift, underpins technologies developed at institutions such as CERN and NASA, and is central to industrial standards set by organizations like International Organization for Standardization and American Society of Mechanical Engineers.

Definition and Units

Pressure is defined as the magnitude of force applied perpendicular to a surface per unit area, p = F/A, introduced in formulations by Blaise Pascal and formalized in SI units as the pascal (Pa), equal to one newton per square metre. Historical units include the standard atmosphere (atm) related to measurements by Evangelista Torricelli and the torr named for Evangelista Torricelli's work; other units prevalent in engineering contexts are the bar, the pound-force per square inch (psi) used in United States practice, and the millimeter of mercury (mmHg) used in medical settings like Mayo Clinic.

Physical Origins and Causes

Pressure arises from molecular collisions in gases as described by Daniel Bernoulli and James Clerk Maxwell's kinetic theories, from intermolecular forces in liquids characterized by work of Thomas Young on surface tension, and from mechanical contact stresses studied by Augustin-Jean Fresnel and Gustave Eiffel in structural engineering. In gravitational fields such as those of Earth and Jupiter, hydrostatic pressure gradients produce notable profiles analyzed by researchers at Jet Propulsion Laboratory and observed in planetary atmospheres during missions like Voyager program and Galileo.

Types of Pressure

Common categories include absolute pressure measured relative to a perfect vacuum (relevant in spacecraft design), gauge pressure measured relative to ambient atmospheric pressure as in Boiler and Tire systems, differential pressure used across filters and orifices in Siemens industrial applications, and partial pressures defined in Dalton's law for gas mixtures relevant to Maritime diving physiology and Aerospace life support. Specialized forms include osmotic pressure central to Wilhelm Pfeffer's botanical experiments, radiation pressure relevant to Hubble Space Telescope observations, and dynamic pressure appearing in Ludwig Prandtl-based aerodynamic analyses.

Measurement and Instruments

Pressure measurement employs devices such as manometers tracing back to Evangelista Torricelli, mechanical bourdon gauges invented by Eugène Bourdon, and electronic sensors like strain-gauge transducers used in General Electric systems. High-vacuum measurements use ionization gauges developed at Bell Labs and cryogenic techniques applied in CERN accelerators; medical monitoring relies on sphygmomanometers standardised in World Health Organization protocols and intracranial pressure monitors used in Johns Hopkins Hospital neurosurgery. Calibration and metrology are overseen by bodies like National Institute of Standards and Technology and Physikalisch-Technische Bundesanstalt.

Applications in Science and Engineering

Control and analysis of pressure enable combustion optimization in Rolls-Royce turbine design, deep-sea exploration with submersibles operated by Woods Hole Oceanographic Institution, and semiconductor fabrication in Intel cleanrooms where vacuum levels are critical. Civil engineering applications include soil consolidation theories applied in projects by Bechtel and hydraulic systems in Panama Canal lock operations. In planetary science, pressure profiling informs atmospheric entry strategies used by missions from Roscosmos and European Space Agency.

Biological and Environmental Effects

Physiological responses to pressure are crucial in Charles Darwin-inspired evolutionary contexts, diving medicine practiced by organizations like Divers Alert Network and Royal Navy research, and high-altitude medicine studied at University of Colorado School of Medicine. Environmental effects include barotrauma in marine species investigated at Scripps Institution of Oceanography, pressure-driven circulation in Gulf Stream and El Niño dynamics, and anthropogenic impacts from deep-ocean drilling by companies such as Schlumberger.

Mathematical Formulations and Laws

Key mathematical formulations include Pascal's law, Bernoulli's equation, the Navier–Stokes equations developed by Claude-Louis Navier and George Gabriel Stokes, and the ideal gas law combining constants from Robert Boyle and Jacques Charles. Thermodynamic relationships involve equations of state such as the Van der Waals equation from Johannes Diderik van der Waals and the Gibbs free energy framework of Josiah Willard Gibbs; in relativity, pressure appears in the stress–energy tensor used in Albert Einstein's field equations.

Category:Physical quantities