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isobar
isobar or isobaric line , line drawn on a weather map through points of equal atmospheric pressure. Isobars are used to define cyclones (low-pressure regions) and anticyclones (high-pressure regions). Weather maps are designed to depict the horizontal pressure distribution across an area of land...
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barograph
barograph instrument used to make a continuous recording of atmospheric pressure. The pressure-sensitive element, a partially evacuated metal cylinder, is linked to a pen arm in such a way that the vertical displacement of the pen is proportional to the changes in the atmospheric pressure. The pen ...
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vapor pressure
vapor pressure pressure exerted by a vapor that is in equilibrium with its liquid. A liquid standing in a sealed beaker is actually a dynamic system: some molecules of the liquid are evaporating to form vapor and some molecules of vapor are condensing to form liquid. At equilibrium the rates of t...
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decompression sickness
decompression sickness physiological disorder caused by a rapid decrease in atmospheric pressure, resulting in the release of nitrogen bubbles into the body tissues. It is also known as caisson disease, altitude sickness, and the bends. It is an occupational hazard of persons who work under greatly...
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manometer
manometer A device for measuring pressure differences, usually by the difference in height of two liquid columns. The simplest type is the U-tube manometer, which consists of a glass tube bent into the shape of a U. If a pressure to be measured is fed to one side of the U-tube and the other is open ...
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pressure
pressure in mechanics, ratio of the force acting on a surface to the area of the surface; it is thus distinct from the total force acting on a surface. A force can be applied to and sustained by a single point on a solid. However, a force can only be sustained by the surface of an enclosed fluid,...
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air lock
air lock compartment connecting two different environments, usually at different pressures, that enables personnel to transfer from one environment to the other. Space capsules have air locks to enable astronauts to move between the pressurized cabin and the near vacuum of space. A more common exam...
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STP
STP or standard temperature and pressure, standard conditions for measurement of the properties of matter. The standard temperature is the freezing point of pure water, 0°C or 273.15°K. The standard pressure is the pressure exerted by a column of mercury (symbol Hg) 760 mm high, often d...
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siphon
siphon , tube through which a liquid is lifted over an elevation by the pressure of the atmosphere and is then emptied at a lower level. To start the siphon, it must first be filled with the liquid before it is placed into position. The elevation over which a siphon will lift a liquid is limited by ...
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boiling point
boiling point temperature at which a substance changes its state from liquid to gas. A stricter definition of boiling point is the temperature at which the liquid and vapor (gas) phases of a substance can exist in equilibrium. When heat is applied to a liquid, the temperature of the liquid rises un...
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