تور (وحدة)
ملليمتر زئبق أو تور هي وحدة قياس للضغط مبنية على مقارنة الضغط المقاس بضغط عمود من الزئبق يبلغ إرتفاعه كذا ملليمتر.
يبلغ الضغط الجوي = 760 ملليمتر زئبق .
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عوامل التحويل
The millimetre of mercury by definition is 133.322387415 Pa (13.5951 g/cm3 × 9.80665 m/s2 × 1 mm), which is approximated with known accuracies of density of mercury and standard gravity.
The torr is defined as 1/760 of one standard atmosphere, while the atmosphere is defined as 101325 pascals. Therefore, 1 Torr is equal to 101325/760 Pa. The decimal form of this fraction (133.322(368421052631578947)...) is an infinitely long, periodically repeating decimal (repetend length: 18).
The relationship between the torr and the millimetre of mercury is:
- 1 Torr = 0.999999857533699... mmHg
- 1 mmHg = 1.000000142466321... Torr
The difference between one millimetre of mercury and one torr, as well as between one atmosphere (101.325 kPa) and 760 mmHg (101.3250144354 kPa), is less than one part in seven million (or less than 0.000015%). This small difference is negligible for most applications outside metrology.
Other units of pressure include:
- The bar (symbol: bar), defined as 100 kPa exactly.
- The atmosphere (symbol: atm), defined as 101.325 kPa exactly.
- The torr (symbol: Torr), defined as 1/760 atm exactly.
These four pressure units are used in different settings. For example, the bar is used in meteorology to report atmospheric pressures.[1] The torr is used in high-vacuum physics and engineering.[2][3]
پاسكال (Pa) |
bar (bar) |
ضغط جوي تقني (at) |
atmosphere (atm) |
torr (Torr) |
رطل-قوة لكل بوصة مربعة (psi) | |
|---|---|---|---|---|---|---|
| 1 Pa | ≡ 1 N/m2 | 10−5 | 1.0197×10−5 | 9.8692×10−6 | 7.5006×10−3 | 145.04×10−6 |
| 1 bar | 100,000 | ≡ 106 داين/cm2 | 1.0197 | 0.98692 | 750.06 | 14.5037744 |
| 1 at | 98,066.5 | 0.980665 | ≡ 1 kgf/cm2 | 0.96784 | 735.56 | 14.223 |
| 1 atm | 101,325 | 1.01325 | 1.0332 | ≡ 1 atm | 760 | 14.696 |
| 1 torr | 133.322 | 1.3332×10−3 | 1.3595×10−3 | 1.3158×10−3 | ≡ 1 Torr; ≈ 1 mmHg | 19.337×10−3 |
| 1 psi | 6,894.76 | 68.948×10−3 | 70.307×10−3 | 68.046×10−3 | 51.715 | ≡ 1 lbf/in2 |
Example reading: 1 Pa = 1 N/m2 = 10−5 bar = 10.197×10−6 at = 9.8692×10−6 atm, etc.
- ^ Note that a pressure of 1 bar (100000 Pa) is slightly less than a pressure of 1 atmosphere (101325 Pa).
- ^ Cohen E.R. et al. Quantities, Units and Symbols in Physical Chemistry, 3rd ed. Royal Society of Chemistry, 2007 ISBN 0-85404-433-7 (IUPAC pdf copy)
- ^ DeVoe H. Thermodynamics and Chemistry. Prentice-Hall, Inc. 2001 ISBN 0-02-328741-1