digplanet beta 1: Athena
Share digplanet:

Agriculture

Applied sciences

Arts

Belief

Business

Chronology

Culture

Education

Environment

Geography

Health

History

Humanities

Language

Law

Life

Mathematics

Nature

People

Politics

Science

Society

Technology

This article is about the unit of pressure. For the informal unit of signal strength, see Mobile phone signal.
"Kbar" redirects here. For the knife, see KA-BAR.
An aluminium cylinder
(5 mm or 0.197 in thickness) after 700 bar (10,153 psi) pressure.

The bar is a metric (but not SI) unit of pressure, defined by the IUPAC as exactly equal to 100,000 Pa.[1] It is about equal to the atmospheric pressure on Earth at sea level, and since 1982 the IUPAC has recommended that the standard for atmospheric pressure should be harmonized to 100,000 Pa = 1 bar ≈ 750.0616827 Torr.[2] The same definition is used in the compressor and the pneumatic tool industries (ISO 2787).

The bar and the millibar were introduced by the British meteorologist William Napier Shaw in 1909, while he was the director of the Meteorological Office in London.[3]

Units derived from the bar are the megabar (symbol: Mbar), kilobar (symbol: kbar), decibar (symbol: dbar), centibar (symbol: cbar), and millibar (symbol: mbar or mb). These are not SI or cgs units, but they are accepted by the BIPM for use with the SI.[4] The bar is legally recognized in countries of the European Union.[5]

The bar unit is considered deprecated by some entities. While the BIPM includes it under the class "Non-SI units accepted for use with the SI",[4] the NIST includes it in the list of units to avoid and recommends the use of kilopascals (kPa) and megapascals (MPa) instead.[6] The IAU also lists it under "Non-SI units and symbols whose continued use is deprecated."[7]

Bar(g) is a unit of gauge pressure, i.e., pressure in bars above ambient or atmospheric pressure; see absolute pressure and gauge pressure below.

Definition and conversion[edit]

The bar is defined using the SI unit pascal, namely: 1 bar100,000 Pa. 1 bar is therefore equal to:

  • 100 kPa (in SI units)
  • 1×105 N/m2 (alternative representation in SI units)
  • 1,000,000 dyn/cm2 (barye) (in cgs units)
  • 0.987 atm
  • 14.5038 psi absolute
  • 29.53 inHg
  • 750.06 mmHg
  • 750.06 torr
  • 1,019.72 cmH2O

Origin[edit]

The word bar has its origin in the Greek word βάρος (baros), meaning weight. The unit's official symbol is bar; the earlier symbol b is now deprecated, and conflicts with the use of b as a unit symbol to denote the barn, but it is still encountered, especially as mb (rather than the proper mbar) to denote the millibar.

Usage[edit]

Atmospheric air pressure is often given in millibars where standard sea level pressure is defined as 1000 mbar, 100 (kPa), or 1 bar. This should be distinguished from the now deprecated unit of pressure, known as the "atmosphere" (atm), which is equal to 1.01325 bar. Despite the millibar not being an SI unit, meteorologists and weather reporters worldwide have long measured air pressure in millibars as the values are convenient. After the advent of SI units, some meteorologists began using hectopascals (symbol hPa) which are numerically equivalent to millibars; for the same reason, the hectopascal is now the standard unit used to express barometric pressures in aviation in most countries. For example, the weather office of Environment Canada uses kilopascals and hectopascals on their weather maps.[8][9] In contrast, Americans are familiar with the use of the millibar in US reports of hurricanes and other cyclonic storms.[citation needed]

In fresh water, there is an approximate numerical equivalence between the change in pressure in decibars and the change in depth from the water surface in metres. Specifically, an increase of 1 decibar occurs for every 1.019716 m increase in depth. In sea water with respect to the gravity variation, the latitude and the geopotential anomaly the pressure can be converted into meters depth according to an empirical formula (UNESCO Tech. Paper 44, p. 25).[10] As a result, decibars are commonly used in oceanography.

Many engineers worldwide use the bar as a unit of pressure because, in much of their work, using pascals would involve using very large numbers.

In the automotive field, turbocharger boost is often described in bars in the metric part of the world (i.e. outside the USA).

Unicode has characters for "mb" (, U+33D4) and "bar" (, U+3374), but they exist only for compatibility with legacy Asian encodings and are not intended to be used in new documents.

The kilobar, equivalent to 100 MPa, is commonly used in geological systems, particularly in experimental petrology.

Absolute pressure and gauge pressure[edit]

Bourdon tube pressure gauges, vehicle tire gauges, and many other types of pressure gauges are zero-referenced to atmospheric pressure, which means that they measure the pressure above atmospheric pressure (which is around 1 bar); this is gauge pressure and is often referred to in writing as barg or bar(g), spoken as "bar gauge". In contrast, absolute pressures are zero-referenced to a complete vacuum and when expressed in bars are often referred to as bara or bar(a). Thus, the absolute pressure of any system is the gauge pressure of the system plus atmospheric pressure. The usage of bara and barg is now deprecated, with qualification of the physical property being preferred, e.g., "The gauge pressure is 2.3 bar; the absolute pressure is 3.3 bar".[5]

In the United States, where pressures are still often expressed in pounds per square inch (symbol psi), gauge pressures are referred to as psig and absolute pressures are referred to as psia. Gauge pressure is also sometimes spelled as gage pressure.

Sometimes, the context in which the word pressure is used helps to identify it as meaning either the absolute or gauge pressure. However, for best practice, whenever a pressure is expressed in any units (bar, Pa, psi, atm, etc.), it should be denoted in some manner as being either absolute or gauge pressure to avoid any possible misunderstanding. One recommended way of doing so is to spell out what is meant, for example as bar gauge or kPa absolute.[11]

See also[edit]

References[edit]

This article incorporates material from the Citizendium article "Bar (unit)", which is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License but not under the GFDL.
  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "IUPAC Gold Book - bar".
  2. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "IUPAC Gold Book - standard pressure".
  3. ^ Sir William Napier Shaw
  4. ^ a b International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), p. 127, ISBN 92-822-2213-6 .
  5. ^ a b British Standard BS 350:2004 Conversion Factors for Units
  6. ^ NIST Special Publication 1038, Sec. 4.3.2 NIST Special Publication 811, 2008 edition, Sec. 5.2
  7. ^ International Astronomical Union Style Manual. Comm. 5 in IAU Transactions XXB, 1989, Table 6
  8. ^ Environment Canada Weather Map
  9. ^ Weather - Environment Canada
  10. ^ http://unesdoc.unesco.org/images/0005/000598/059832eb.pdf
  11. ^ FAQ (from the website of the National Physics Laboratory, United Kingdom)

External links[edit]

Pressure units
Pascal Bar Technical atmosphere Standard atmosphere Torr Pounds per square inch
(Pa) (bar) (at) (atm) (Torr) (psi)
1 Pa ≡ 1 N/m2 10−5 1.0197×10−5 9.8692×10−6 7.5006×10−3 1.450377×10−4
1 bar 105 ≡ 106 dyn/cm2 1.0197 0.98692 750.06 14.50377
1 at 0.980665×105 0.980665 ≡ 1 kp/cm2 0.9678411 735.5592 14.22334
1 atm 1.01325×105 1.01325 1.0332 p0 760 14.69595
1 Torr 133.3224 1.333224×10−3 1.359551×10−3 1.315789×10−3 ≈ 1 mmHg 1.933678×10−2
1 psi 6.8948×103 6.8948×10−2 7.03069×10−2 6.8046×10−2 51.71493 ≡ 1 lbF/in2

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Bar_(unit) — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
861978 videos foundNext > 

Uno Bar Unit

SKU CODE: NC271HA48IODINDFUR-26782 A wonderful product from the house of Uno. You can buy this product here: http://www.fabfurnish.com/Uno-Bar-Unit-23351.html.

chikki bar unit 1

Watts Bar Unit 2 Reactor Filling Time Lapse

Cool time lapse video showing 185000 gallons of water in about 23 minutes filling the Watts Bar Unit 2 reactor vessel. The water filled a space 60 ft. long ...

The Paul Oxley's - Unit Spanish bars

The Paul Oxley's - Unit Spanish bars.

Watts Bar Nuclear Station Unit 2 Open Vessel Testing

A major milestone in the completion of Watts Bar Unit 2 is open vessel testing. Basically all the pumps, pipes and valves that circulate reactor cooling wate...

Bar (unit)

The bar is a metric (but not SI) unit of pressure, defined by the IUPAC as exactly equal to 100000 Pa. It is about equal to the atmospheric pressure on Earth at sea level, and since 1982...

English Conversation - Learn english speaking 2 - Unit 6: At the Bar

english conversation,english speaking,learn english,english online,speak english,learn, english, conversation, speak, speaking.

Watts Bar Unit 2 Update - October 26, 2012

TVA' s quarterly update on construction progress on the Watts Bar Unit 2 nuclear reactor verifies performance is consistent with detailed completion cost and...

Ryan Bailey // Watts Bar Unit 2

Meet Ryan Bailey and hear how his work at Watts Bar Unit 2 is important to the future of the Valley.

SpringRTS - Fancy Unit Selection Widget - BAR

Now has an open / close animation aswell.

861978 videos foundNext > 

7 news items

Chattanooga Times Free Press

Chattanooga Times Free Press
Tue, 24 Jun 2014 21:02:21 -0700

TVA's critical path toward starting the Watts Bar Unit 2 still requires regulators to also adopt a court-accepted plan for storing or disposing of highly radioactive wastes generated at nuclear plants. Macfarlane said the NRC will present such a plan ...

Environment & Energy Publishing

Environment & Energy Publishing
Tue, 22 Jul 2014 07:44:46 -0700

"All of this can be used to prevent a Fukushima event," said Bob Williams, the Fukushima project manager for Watts Bar Unit 2. The FLEX buildings are the nuclear industry's answer to the Nuclear Regulatory Commission's safety directives that followed ...

Chattanooga Times Free Press

Chattanooga Times Free Press
Thu, 10 Jul 2014 05:37:49 -0700

TVA filled the new reactor vessel in the Watts Bar Nuclear Plant reactor being built near Spring City, Tenn., this week with 185,000 gallons of water in just over 23 minutes. The flow filled 18 feet of water into a space 60 feet long and 22 feet wide ...

New York Times

New York Times
Thu, 10 Jul 2014 03:52:30 -0700

There also is an open-plan living area, with a large kitchen and Deco-style bar unit made of maple wood standing in the center. “It's top of the range because we thought we would be here for good,” said Jimmy James, who, with his wife, Theresa, is ...

Chattanooga Times Free Press

Chattanooga Times Free Press
Thu, 26 Jun 2014 20:56:15 -0700

At the Watts Bar Unit 2 reactor under construction, for instance, 3,200 construction workers are now on site and the average pay for those in the nuclear industry is 36 percent above the U.S. median, Whitman said. While nuclear power will add jobs, a ...

MMA Corner

MMA Corner
Mon, 07 Jul 2014 15:02:08 -0700

Rob would like to thank Haleo, Muscle Bar, Unit 27, Phuket Top Team, Phuket Pro Nutrition, Vicious Circle and Pokerstars. He would also like to thank God and his family, who believe in him and support him so much. He adds, “I love them with all my heart.

Båtliv

Båtliv
Mon, 23 Jun 2014 02:08:46 -0700

The first 122' Mythos yacht features a large Jacuzzi, sided by a comfortable aft sun pad and a bar unit to the bow. In front of the bar another spacious C-shaped aft-facing sofa. Steering from the forward flybridge offers perfect viewing of yacht ...
Loading

Oops, we seem to be having trouble contacting Twitter

Talk About Bar (unit)

You can talk about Bar (unit) with people all over the world in our discussions.

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!