# Pressure

**water pressurenegative pressurefluid pressurepressureshydrostatic pressurepressurizedrelative pressureabsolute pressurehydrostaticnegative-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.wikipedia

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### Force

**forcesattractiveelastic force**

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.

Pressure, the distribution of many small forces applied over an area of a body, is a simple type of stress that if unbalanced can cause the body to accelerate.

### Pascal (unit)

**hPaMPakPa**

Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m 2 ); similarly, the pound-force per square inch (psi) is the traditional unit of pressure in the imperial and US customary systems.

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

### Atmosphere (unit)

**atmatmospheresatmosphere**

Pressure may also be expressed in terms of standard atmospheric pressure; the atmosphere (atm) is equal to this pressure, and the torr is defined as 1⁄760 of this.

The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa. It is sometimes used as a reference or standard pressure.

### Torr

**mmHgmm Hgmillimeters of mercury**

Pressure may also be expressed in terms of standard atmospheric pressure; the atmosphere (atm) is equal to this pressure, and the torr is defined as 1⁄760 of this.

The torr (symbol: Torr) is a unit of pressure based on an absolute scale, now defined as exactly 1⁄760 of a standard atmosphere (101325 Pa).

### Pounds per square inch

**psilb f /in 2 psig**

Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m 2 ); similarly, the pound-force per square inch (psi) is the traditional unit of pressure in the imperial and US customary systems. Other units of pressure, such as pounds per square inch (Ibf/in 2 )and bar, are also in common use.

The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in 2 ; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units.

### Volume (thermodynamics)

**volumeGas volumefundamental parameter**

It is a fundamental parameter in thermodynamics, and it is conjugate to volume.

The specific volume, an intensive property, is the system's volume per unit of mass. Volume is a function of state and is interdependent with other thermodynamic properties such as pressure and temperature.

### Bar (unit)

**mbarbarmillibars**

Other units of pressure, such as pounds per square inch (Ibf/in 2 )and bar, are also in common use.

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

### Centimetre–gram–second system of units

**CGScgs unitsCGS unit**

The CGS unit of pressure is the barye (Ba), equal to 1 dyn·cm −2, or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre (g/cm 2 or kg/cm 2 ) and the like without properly identifying the force units.

In measurements of purely mechanical systems (involving units of length, mass, force, energy, pressure, and so on), the differences between CGS and SI are straightforward and rather trivial; the unit-conversion factors are all powers of 10 as 100 cm = 1 m and 1000 g = 1 kg.

### Centimetre of water

**cmH 2 Ocm H 2 Ocentimetres of water**

Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.

A centimetre of water (US spelling centimeter of water, abbreviated cm or cm H 2 O) is a less commonly used unit of pressure derived from pressure head calculations using metrology.

### Blood pressure

**systolic blood pressurediastolic blood pressurearterial blood pressure**

Blood pressure is measured in millimetres of mercury in most of the world, and lung pressures in centimetres of water are still common.

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

### Millimetre of mercury

**mmHgmm Hgmillimetres of mercury**

Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.

A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly 133.322387415 pascals.

### International System of Units

**SISI unitsSI unit**

Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m 2 ); similarly, the pound-force per square inch (psi) is the traditional unit of pressure in the imperial and US customary systems.

For example, the SI unit of force is the newton (N), the SI unit of pressure is the pascal (Pa)—and the pascal can be defined as one newton per square metre (N/m 2 ).

### Inch of mercury

**inHginches of mercuryinches**

Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.

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

### Technical atmosphere

**atatmospheresatm**

The technical atmosphere (symbol: at) is 1 kgf/cm 2 (98.0665 kPa, or 14.223 psi).

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

### Millimeters, water gauge

**millimetremillimetresmillimetres H 2 O**

### Metre sea water

**fswmswfeet sea water**

Underwater divers use the metre sea water (msw or MSW) and foot sea water (fsw or FSW) units of pressure, and these are the standard units for pressure gauges used to measure pressure exposure in diving chambers and personal decompression computers.

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

### Dive computer

**dive computersdiving computerpersonal decompression computer**

Underwater divers use the metre sea water (msw or MSW) and foot sea water (fsw or FSW) units of pressure, and these are the standard units for pressure gauges used to measure pressure exposure in diving chambers and personal decompression computers.

Many dive computers also provide additional information to the diver including air and water temperature, data used to help prevent oxygen toxicity, a computer-readable dive log, and the pressure of the remaining breathing gas in the diving cylinder.

### Diving chamber

**hyperbaric chamberdecompression chamberrecompression chamber**

Underwater divers use the metre sea water (msw or MSW) and foot sea water (fsw or FSW) units of pressure, and these are the standard units for pressure gauges used to measure pressure exposure in diving chambers and personal decompression computers.

### Thermodynamics

**thermodynamicthermodynamicallyclassical thermodynamics**

It is a fundamental parameter in thermodynamics, and it is conjugate to volume.

Using this pump, Boyle and Hooke noticed a correlation between pressure, temperature, and volume.

### Barye

**dyn/cm²**

The CGS unit of pressure is the barye (Ba), equal to 1 dyn·cm −2, or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre (g/cm 2 or kg/cm 2 ) and the like without properly identifying the force units.

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

### Atmospheric pressure

**barometric pressureair pressurepressure**

For gases, pressure is sometimes measured not as an absolute pressure, but relative to atmospheric pressure; such measurements are called gauge pressure.

Atmospheric pressure, sometimes also called barometric pressure (after the sensor), is the pressure within the atmosphere of Earth.

### Decompression (diving)

**decompressiondecompression stopsdive table**

Because breathing gas is supplied at ambient pressure, some of this gas dissolves into the diver's blood and is transferred by the blood to other tissues.

### Pièze

**pieze**

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.

### Underwater diving

**divingdiversdiver**

Barotrauma, an example of dysbarism, is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with the body, and the surrounding gas or fluid.

### Pressure vessel

**pressure vesselsvesselair tank**

Gauge pressure is the relevant measure of pressure wherever one is interested in the stress on storage vessels and the plumbing components of fluidics systems.

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