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# Pressure

Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. [1]

140 relations: Amount of substance, Area, Artesian aquifer, Ascent of sap, Atmosphere (unit), Atmospheric pressure, Bar (unit), Barye, Bernoulli's principle, Blaise Pascal, Blood pressure, Boiling point, Boyle's law, Brownian motion, Bubble (physics), Buoyancy, Car, Casimir effect, Centimetre of water, Centimetre–gram–second system of units, Cobra probe, Combined gas law, Condensation, Conjugate variables (thermodynamics), Conversion of units, Cosmological constant, Critical point (thermodynamics), Daniel Bernoulli, Decompression (diving), Deflagration, Density, Dimensional analysis, Discover (magazine), Dive computer, Diving chamber, Drag equation, Drawing pin, Dynamic pressure, Dyne, Electromagnetic field, Electron degeneracy pressure, Evaporation, Explosion, Fluid, Fluid dynamics, Force, Force density, Gas, Gas constant, General relativity, ... Expand index (90 more) »

## Amount of substance

Amount of substance (symbol for the quantity is 'n') is a standard-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles.

## Area

Area is the quantity that expresses the extent of a two-dimensional figure or shape, or planar lamina, in the plane.

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## Artesian aquifer

An artesian aquifer is a confined aquifer containing groundwater under positive pressure.

## Ascent of sap

The ascent of sap in the xylem tissue of plants is the upward movement of water and minerals from the root to the crown.

## Atmosphere (unit)

The standard atmosphere (symbol: atm) is a unit of pressure defined as.

## Atmospheric pressure

Atmospheric pressure, sometimes also called barometric pressure, is the pressure within the atmosphere of Earth (or that of another planet).

## Bar (unit)

The bar is a metric unit of pressure, but is not approved as part of the International System of Units (SI).

## Barye

The barye (symbol: Ba), or sometimes barad, barrie, bary, baryd, baryed, or barie, is the centimetre–gram–second (CGS) unit of pressure.

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## Bernoulli's principle

In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

## Blaise Pascal

Blaise Pascal (19 June 1623 – 19 August 1662) was a French mathematician, physicist, inventor, writer and Catholic theologian.

## Blood pressure

Blood pressure (BP) is the pressure of circulating blood on the walls of blood vessels.

## Boiling point

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.

## Boyle's law

Boyle's law (sometimes referred to as the Boyle–Mariotte law, or Mariotte's law) is an experimental gas law that describes how the pressure of a gas tends to increase as the volume of the container decreases.

## Brownian motion

Brownian motion or pedesis (from πήδησις "leaping") is the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the fast-moving molecules in the fluid.

## Bubble (physics)

A bubble is a globule of one substance in another, usually gas in a liquid.

## Buoyancy

In physics, buoyancy or upthrust, is an upward force exerted by a fluid that opposes the weight of an immersed object.

## Car

A car (or automobile) is a wheeled motor vehicle used for transportation.

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## Casimir effect

In quantum field theory, the Casimir effect and the Casimir–Polder force are physical forces arising from a quantized field.

## Centimetre of water

A centimetre of water (US spelling centimeter of water, abbreviated cm or cm H2O) is a less commonly used unit of pressure derived from pressure head calculations using metrology.

## Centimetre–gram–second system of units

The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time.

## Cobra probe

A Cobra probe is a device to measure the pressure and velocity components of a moving fluid.

## Combined gas law

The combined gas law is a gas law that combines Charles's law, Boyle's law, and Gay-Lussac's law.

## Condensation

Condensation is the change of the physical state of matter from gas phase into liquid phase, and is the reverse of vapourisation.

## Conjugate variables (thermodynamics)

In thermodynamics, the internal energy of a system is expressed in terms of pairs of conjugate variables such as temperature and entropy or pressure and volume.

## Conversion of units

Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors.

## Cosmological constant

In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) is the value of the energy density of the vacuum of space.

## Critical point (thermodynamics)

In thermodynamics, a critical point (or critical state) is the end point of a phase equilibrium curve.

## Daniel Bernoulli

Daniel Bernoulli FRS (8 February 1700 – 17 March 1782) was a Swiss mathematician and physicist and was one of the many prominent mathematicians in the Bernoulli family.

## Decompression (diving)

The decompression of a diver is the reduction in ambient pressure experienced during ascent from depth.

## Deflagration

Deflagration (Lat: de + flagrare, "to burn down") is subsonic combustion propagating through heat transfer; hot burning material heats the next layer of cold material and ignites it.

## Density

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume.

## Dimensional analysis

In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric charge) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms) and tracking these dimensions as calculations or comparisons are performed.

## Discover (magazine)

Discover is an American general audience science magazine launched in October 1980 by Time Inc.

## Dive computer

A dive computer, personal decompression computer or decompression meter is a device used by an underwater diver to measure the time and depth of a dive so that a safe ascent profile can be calculated and displayed so that the diver can avoid decompression sickness.

## Diving chamber

A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of breathing gas for the occupants.

## Drag equation

In fluid dynamics, the drag equation is a formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid.

## Drawing pin

A drawing pin (British English) or thumb tack (North American English) is a short nail or pin used to fasten items to a wall or board for display and intended to be inserted by hand, usually using the thumb.

## Dynamic pressure

Dynamic pressure (sometimes called velocity pressure) is the increase in a moving fluid's pressure over its static value due to motion.

## Dyne

The dyne (symbol dyn, from Greek δύναμις, dynamis, meaning power, force) is a derived unit of force specified in the centimetre–gram–second (CGS) system of units, a predecessor of the modern SI.

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## Electromagnetic field

An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged objects.

## Electron degeneracy pressure

Electron degeneracy pressure is a particular manifestation of the more general phenomenon of quantum degeneracy pressure.

## Evaporation

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gaseous phase before reaching its boiling point.

## Explosion

An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases.

## Fluid

In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress.

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## Fluid dynamics

In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids - liquids and gases.

## Force

In physics, a force is any interaction that, when unopposed, will change the motion of an object.

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## Force density

In fluid mechanics, the force density is the negative gradient of pressure.

## Gas

Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).

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## Gas constant

The gas constant is also known as the molar, universal, or ideal gas constant, denoted by the symbol or and is equivalent to the Boltzmann constant, but expressed in units of energy per temperature increment per mole, i.e. the pressure-volume product, rather than energy per temperature increment per particle.

## General relativity

General relativity (GR, also known as the general theory of relativity or GTR) is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.

In mathematics, the gradient is a multi-variable generalization of the derivative.

## Gravitational acceleration

In physics, gravitational acceleration is the acceleration on an object caused by the force of gravitation.

## Gravity

Gravity, or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light—are brought toward (or gravitate toward) one another.

## Hydraulic brake

A hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing glycol ethers or diethylene glycol, to transfer pressure from the controlling mechanism to the braking mechanism.

Hydraulic head or piezometric head is a specific measurement of liquid pressure above a geodetic datum.

## Hydraulics

Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids.

## Hydrogen bond

A hydrogen bond is a partially electrostatic attraction between a hydrogen (H) which is bound to a more electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F), and another adjacent atom bearing a lone pair of electrons.

## Hydrostatics

Fluid statics or hydrostatics is the branch of fluid mechanics that studies fluids at rest.

## Ideal gas

An ideal gas is a theoretical gas composed of many randomly moving point particles whose only interactions are perfectly elastic collisions.

## Ideal gas law

The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas.

## Imperial units

The system of imperial units or the imperial system (also known as British Imperial or Exchequer Standards of 1825) is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced.

## Inch of mercury

Inch of mercury (inHg and ″Hg) is a unit of measurement for pressure.

## Intermolecular force

Intermolecular forces (IMF) are the forces which mediate interaction between molecules, including forces of attraction or repulsion which act between molecules and other types of neighboring particles, e.g., atoms or ions.

## Internal pressure

Internal pressure is a measure of how the internal energy of a system changes when it expands or contracts at constant temperature.

## International System of Units

The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement.

## International Union of Pure and Applied Chemistry

The International Union of Pure and Applied Chemistry (IUPAC) is an international federation of National Adhering Organizations that represents chemists in individual countries.

## Joule

The joule (symbol: J) is a derived unit of energy in the International System of Units.

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## Kiel probe

A Kiel probe is a device for measuring stagnation pressure or stagnation temperature in fluid dynamics.

## Kilogram

The kilogram or kilogramme (symbol: kg) is the base unit of mass in the International System of Units (SI), and is defined as being equal to the mass of the International Prototype of the Kilogram (IPK, also known as "Le Grand K" or "Big K"), a cylinder of platinum-iridium alloy stored by the International Bureau of Weights and Measures at Saint-Cloud, France.

## Kip (unit)

A kip is a US customary unit of force.

## List of thermodynamic properties

Within thermodynamics, a physical property is any property that is measurable, and whose value describes a state of a physical system.

## Mercury (element)

Mercury is a chemical element with symbol Hg and atomic number 80.

## Meteorology

Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting.

## Metre

The metre (British spelling and BIPM spelling) or meter (American spelling) (from the French unit mètre, from the Greek noun μέτρον, "measure") is the base unit of length in some metric systems, including the International System of Units (SI).

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## Metre sea water

The metre (or meter) sea water (msw) is a unit of pressure used in underwater diving.

## Microphone

A microphone, colloquially nicknamed mic or mike, is a transducer that converts sound into an electrical signal.

## Millimeter of mercury

A millimeter of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high and now defined as precisely pascals.

## Millimeters, water gauge

Millimeters, water gauge, also known as a millimetre of water (US spelling millimeter of water) or millimetres water column and abbreviated to mmwg, mmH2O or mmwc, respectively, is a less commonly used unit of pressure.

## Momentum

In Newtonian mechanics, linear momentum, translational momentum, or simply momentum (pl. momenta) is the product of the mass and velocity of an object.

## Nameplate

A nameplate identifies and displays a person or product's name.

## National Institute of Standards and Technology

The National Institute of Standards and Technology (NIST) is one of the oldest physical science laboratories in the United States.

## Navier–Stokes equations

In physics, the Navier–Stokes equations, named after Claude-Louis Navier and George Gabriel Stokes, describe the motion of viscous fluid substances.

## Neutron star

A neutron star is the collapsed core of a large star which before collapse had a total of between 10 and 29 solar masses.

## Newton (unit)

The newton (symbol: N) is the International System of Units (SI) derived unit of force.

## Normal (geometry)

In geometry, a normal is an object such as a line or vector that is perpendicular to a given object.

## Normal force

In mechanics, the normal force F_n\ is that component of the contact force that is perpendicular to the surface that an object contacts.

## Orders of magnitude (pressure)

This is a tabulated listing of the orders of magnitude in relation to pressure expressed in pascals.

## Partial pressure

In a mixture of gases, each gas has a partial pressure which is the hypothetical pressure of that gas if it alone occupied the entire volume of the original mixture at the same temperature.

## Pascal (unit)

The pascal (symbol: Pa) is the SI derived unit of pressure used to quantify internal pressure, stress, Young's modulus and ultimate tensile strength.

## Phase (matter)

In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform.

## Pièze

The pièze is the unit of pressure in the metre–tonne–second system of units (mts system), used, e.g., in the former Soviet Union 1933–1955.

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## Pitot tube

A Pitot tube, also known as Pitot probe, is a flow measurement device used to measure fluid flow velocity.

## Pound (force)

The pound-force (symbol: lbf, sometimes lbf) is a unit of force used in some systems of measurement including English Engineering units and the British Gravitational System.

## Poundal

The poundal (symbol: pdl) is a unit of force that is part of the foot–pound–second system of units, in Imperial units introduced in 1877, and is from the specialized subsystem of English absolute (a coherent system).

## Pounds per square inch

The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units.

## Power (physics)

In physics, power is the rate of doing work, the amount of energy transferred per unit time.

In fluid mechanics, pressure head is the internal energy of a fluid due to the pressure exerted on its container.

## Pressure measurement

Pressure measurement is the analysis of an applied force by a fluid (liquid or gas) on a surface.

## Pressure sensor

A pressure sensor is a device for pressure measurement of gases or liquids.

## Pressure vessel

A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.

## Proportionality (mathematics)

In mathematics, two variables are proportional if there is always a constant ratio between them.

## Pythagorean cup

A Pythagorean cup (also known as a Pythagoras cup, Greedy Cup, Tantalus cup or i koupa tis dikaiosynis) is a practical joke device in a form of a drinking cup, credited to Pythagoras of Samos.

## Real gas

Real gases are non-hypothetical gases whose molecules occupy space and have interactions; consequently, they adhere to gas laws.

## Scalar (physics)

A scalar or scalar quantity in physics is a physical quantity that can be described by a single element of a number field such as a real number, often accompanied by units of measurement.

## Sea level

Mean sea level (MSL) (often shortened to sea level) is an average level of the surface of one or more of Earth's oceans from which heights such as elevations may be measured.

## Second

The second is the SI base unit of time, commonly understood and historically defined as 1/86,400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

## Solid

Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma).

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## Sound pressure

Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave.

## Specific weight

The specific weight (also known as the unit weight) is the weight per unit volume of a material.

## Square inch

A square inch (plural: square inches) is a unit of area, equal to the area of a square with sides of one inch.

## Square metre

The square metre (International spelling as used by the International Bureau of Weights and Measures) or square meter (American spelling) is the SI derived unit of area, with symbol m2 (Unicode character). It is the area of a square whose sides measure exactly one metre.

## Stagnation pressure

In fluid dynamics, stagnation pressure (or pitot pressure) is the static pressure at a stagnation point in a fluid flow.

## Static pressure

In fluid mechanics the term static pressure has several uses.

## Sthène

The sthène (symbol sn), sometimes spelled (or misspelled) sthéne or sthene (from the Greek σθένος (sthenos) meaning "force"), is an obsolete unit of force or thrust in the metre–tonne–second system of units (mts) introduced in France in 1919.

## Stress (mechanics)

In continuum mechanics, stress is a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other, while strain is the measure of the deformation of the material.

## Stress–energy tensor

The stress–energy tensor (sometimes stress–energy–momentum tensor or energy–momentum tensor) is a tensor quantity in physics that describes the density and flux of energy and momentum in spacetime, generalizing the stress tensor of Newtonian physics.

## Surface integral

In mathematics, a surface integral is a generalization of multiple integrals to integration over surfaces.

## Surface tension

Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area possible.

## Technical atmosphere

The technical atmosphere (symbol: at) is a non-SI unit of pressure equal to one kilogram-force per square centimeter.

## Tensor

In mathematics, tensors are geometric objects that describe linear relations between geometric vectors, scalars, and other tensors.

## Thermodynamic equilibrium

Thermodynamic equilibrium is an axiomatic concept of thermodynamics.

## Thermodynamics

Thermodynamics is the branch of physics concerned with heat and temperature and their relation to energy and work.

## Timeline of temperature and pressure measurement technology

Timeline of temperature and pressure measurement technology.

## Tire

A tire (American English) or tyre (British English; see spelling differences) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface traveled over.

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## Torr

The torr (symbol: Torr) is a unit of pressure based on an absolute scale, now defined as exactly of a standard atmosphere (101.325 kPa).

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## Torricelli's law

Torricelli's law, also known as Torricelli's theorem, is a theorem in fluid dynamics relating the speed of fluid flowing out of an orifice to the height of fluid above the opening.

## Turgor pressure

Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall.

## Underwater diving

Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment.

## United States customary units

United States customary units are a system of measurements commonly used in the United States.

## Vacuum

Vacuum is space devoid of matter.

## Vacuum energy

Vacuum energy is an underlying background energy that exists in space throughout the entire Universe.

## Vacuum pump

A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum.

## Van der Waals force

In molecular physics, the van der Waals forces, named after Dutch scientist Johannes Diderik van der Waals, are distance-dependent interactions between atoms or molecules.

## Vapor

In physics a vapor (American) or vapour (British and Canadian) is a substance in the gas phase at a temperature lower than its critical temperature,R.

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## Vector area

In 3-dimensional geometry, for a finite planar surface of scalar area and unit normal, the vector area is defined as the unit normal scaled by the area: For an orientable surface composed of a set of flat facet areas, the vector area of the surface is given by where is the unit normal vector to the area.

## Vertical pressure variation

Vertical pressure variation is the variation in pressure as a function of elevation.

## Viscosity

The viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or tensile stress.

## Viscous stress tensor

The viscous stress tensor is a tensor used in continuum mechanics to model the part of the stress at a point within some material that can be attributed to the strain rate, the rate at which it is deforming around that point.

## Volume (thermodynamics)

In thermodynamics, the volume of a system is an important extensive parameter for describing its thermodynamic state.

## Xylem

Xylem is one of the two types of transport tissue in vascular plants, phloem being the other.

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## References

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