Units of pressure

Pressure results from a force exerted on an area. The SI unit of force is the newton (N) 1 N = 1 kg m/s. The SI unit of pressure is the pascal (Pa), which equals a force of one newton exerted on an area of one square meter  

A much larger unit is the standard atmosphere (atm), the average atmospheric pressure measured at sea level and 0°C. It is defined in terms of the pascal  

A metal can filled with air has equal pressure on the inside and outside. 

When the air inside the can is removed, the atmospheric pressure crushes the can. 

Another common unit is the millimeter of mercury (mmHg), mentioned above, which is based on measurement with a barometer. In honor of Torricelli, this unit has been named the torr  

Pressure due to weight of y/atmosphere (atmospheric pressure, farm) 

The unit of pressure in the International System of Units (SI) is newtons per meter squared (N m 2), which is called the pascal (Pa). In terms of pascals, the atmospheric pressure at the surface of the Earth, the so-called standard atmosphere, is 1.01325 x 105 Pa. Another commonly used unit of pressure in atmospheric science is the millibar (mbar), which is equivalent to the hectopascal (hPa) (see Tables A.5 and A.8). The standard atmosphere is 1013.25 mbar. 

Because instruments for measuring pressure, such as the manometer, often contain mercury, commonly used units for pressure are based on the height of the mercury column (in millimeters) that the gas pressure can support. The unit mm Hg is often called the torr in honor of the scientist, Evangelista Torricelli. A related unit for pressure is the standard atmosphere (abbreviated atm). 

Standard atmosphere 1.01325 x 105Pa = 1013.25hPa = 1013.25 mbar = 760 torr The variation of pressure and temperature with altitude in the standard atmosphere is given in Table A.8. Because the millibar (mbar) is the unit most commonly used in the 

The units typically used for pressure are greatly varied, depending on the particular field of science involved. Since pressure is defined as a force per unit area, one would expect the units to be that of force divided by area. In many cases we find this to be true however, in others we find some very unexpected units. 

In the British system, a common set of units for pressure is pounds per square inch (psi). The SI unit of pressure is the pascal, which is the pressure exerted by a force of 1 newton over 1 square meter of area. 

The pascal represents a very small pressure, and therefore the most common applications, such as tire pressure, will use kilopascals (kPa) instead of Pa. Other units of pressure include the torr (or millimeter of mercury, mmHg), inches of mercury, the atmosphere (atm), and the bar. A torr is an amount of pressure necessary to support a column of mercury 1 mm in height. One atmosphere of pressure is loosely defined by the atmospheric pressure at sea level, but is more precisely defined as the pressure necessary to support a column of mercury 760 mm in height. One bar of pressure is equal to 100 kPa. The relationships between the various units of pressure are given below  

For example, if a barometer, which is a device used to record atmospheric pressure, reads 735 mmFlg, what is this pressure in units of bar, torr, atm, and kPa  

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The principal type of shear test specimen used in the industry, the lap shear specimen, is 2.54 cm wide and has a 3.23-cm overlap bonded by the adhesive. Adherends are chosen according to the industry aluminum for aerospace, steel for automotive, and wood for constmction appHcations. Adhesive joints made in this fashion are tested to failure in a tensile testing machine. The temperature of test, as weU as the rate of extension, are specified. Results are presented in units of pressure, where the area of the adhesive bond is considered to be the area over which the force is appHed. Although the 3.23-cm ... 

The equihbrium partitioning of a chemical solute between a Hquid and vapor phase is governed by Henry s law when the Hquid mixture is very dilute in the solute. Henry s law generally is vaHd at concentrations below 0.01 mol/L of solution, although the upper limit can sometimes extend to 0.1 mol/L or higher (10). Over this concentration range, a direct proportionaHty, ie, Henry s constant, is observed between the partial pressure of the chemical in the gas phase and its mole fraction in the Hquid phase. Henry s constant, when expressed in this way, has units of pressure (3). 

The above is valid for a liquid flow, when the effect of compressibility can be ignored when calculating gas flows with small pressure differences. For instance, in ventilating duct work, air is not compressed, so the density is considered as constant. In HVAC technology a unit of pressure frequently used for convenience is a water column millimeter, 1 mm H.O=10Pa. 

Dnick-einfluss, m. influence of pressure, -ein-hflit, /. unit of pressure, -elektrizitat, /. piezo ctricity. dnickea, v.t. pH int stamp, driicken, v.t. press squeeze push oppress. Druckentwickelung, /. development of pressure. 

R = gas constant, depends on units of pressure, volume, and temperature... 

In the International System (Appendix 1), the standard unit of pressure is the pascal (Pa). A pascal is a very small unit it is approximately the pressure exerted by a film of water 0.1 mm high on the surface beneath it. A related unit is the bar (I05 Pa). A bar is nearly but not quite, equal to an atmosphere ... 

Pascal An SI unit of pressure the pressure exerted by the force of 1 newton on an area of 1 square meter, 104,635 Paschen series, 138 Pasteur, Louis, 601 Pauli exclusion principle, 141-143 Pauling, Linus, 185 Pentyl propionate, 596t Peptide linkage The—C—N—group... 

Absolute unit of pressure = Statical units of j>ressure = ... 

Traditionaiiy, chemists define the units of pressure in terms of the Earth s atmosphere and the mercury barometer. The standard atmosphere (atm) is the pressure that wiii support a coiumn of mercury 760 mm in height. 

Throughout this chapter the torr. millibar, and pascal are used as units of pressure, according to the original data rather then converting the first two to the SI unit. Note than 1 Pa = 0.01 mbar = 0.0076... 

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