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Millimetre of mercury
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Millimetre of mercury
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. Currently, it is defined as exactly 133.322387415 pascals, or approximately 1 torr = 1/760 atmosphere = 101325/760 pascals. It is denoted mmHg or mm Hg.
Although not an SI unit, the millimetre of mercury is still often encountered in some fields; for example, it is still widely used in medicine, as demonstrated for example in the medical literature indexed in PubMed. For example, the U.S. and European guidelines on hypertension, in using millimeters of mercury for blood pressure, are reflecting the fact (common basic knowledge among health care professionals) that this is the usual unit of blood pressure in clinical medicine.
The millimetre of mercury is defined as the pressure exerted by a column of mercury 1 millimetre high with a density of 13595.1 kg/m3 (approximate density at 0 °C or 32 °F) at standard gravity (9.80665 m/s2), i.e. precisely 133.322387415 pascals.
The use of an actual column of mercury for precise measurement of pressure requires corrections for the actual gravity at given location (±0.44%) and the density of mercury at the actual temperature (−0.45% at 25 °C or 77 °F). Precision may be further improved by taking account of the density of the fluid whose pressure is being measured.[clarification needed][verification needed]
A torr is a similar unit defined as exactly 1/760 of a standard atmosphere (1 atm = 101325 Pa), i.e. 133.322368421… pascals.
The torr is about one part in seven million or 0.000015% smaller than the millimetre of mercury; such difference is negligible for most practical uses.
Each millimetre of mercury can be divided into 1000 micrometres of mercury, denoted μmHg or simply microns.
For much of human history, the pressure of gases like air was ignored, denied, or taken for granted, but as early as the 6th century BC, Greek philosopher Anaximenes of Miletus claimed that all things are made of air that is simply changed by varying levels of pressure. He could observe water evaporating, changing to a gas, and felt that this applied even to solid matter. More condensed air made colder, heavier objects, and expanded air made lighter, hotter objects. This was akin to how gases become less dense when warmer and more dense when cooler.
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Millimetre of mercury AI simulator
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Millimetre of mercury
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. Currently, it is defined as exactly 133.322387415 pascals, or approximately 1 torr = 1/760 atmosphere = 101325/760 pascals. It is denoted mmHg or mm Hg.
Although not an SI unit, the millimetre of mercury is still often encountered in some fields; for example, it is still widely used in medicine, as demonstrated for example in the medical literature indexed in PubMed. For example, the U.S. and European guidelines on hypertension, in using millimeters of mercury for blood pressure, are reflecting the fact (common basic knowledge among health care professionals) that this is the usual unit of blood pressure in clinical medicine.
The millimetre of mercury is defined as the pressure exerted by a column of mercury 1 millimetre high with a density of 13595.1 kg/m3 (approximate density at 0 °C or 32 °F) at standard gravity (9.80665 m/s2), i.e. precisely 133.322387415 pascals.
The use of an actual column of mercury for precise measurement of pressure requires corrections for the actual gravity at given location (±0.44%) and the density of mercury at the actual temperature (−0.45% at 25 °C or 77 °F). Precision may be further improved by taking account of the density of the fluid whose pressure is being measured.[clarification needed][verification needed]
A torr is a similar unit defined as exactly 1/760 of a standard atmosphere (1 atm = 101325 Pa), i.e. 133.322368421… pascals.
The torr is about one part in seven million or 0.000015% smaller than the millimetre of mercury; such difference is negligible for most practical uses.
Each millimetre of mercury can be divided into 1000 micrometres of mercury, denoted μmHg or simply microns.
For much of human history, the pressure of gases like air was ignored, denied, or taken for granted, but as early as the 6th century BC, Greek philosopher Anaximenes of Miletus claimed that all things are made of air that is simply changed by varying levels of pressure. He could observe water evaporating, changing to a gas, and felt that this applied even to solid matter. More condensed air made colder, heavier objects, and expanded air made lighter, hotter objects. This was akin to how gases become less dense when warmer and more dense when cooler.
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