Pressure

From Simple English Wikipedia, the free encyclopedia

Pressure means how much something is pushing on something else expressed as force per unit area.

To measure the amount of pressure, people use these units:



Pounds per square inch - (psi, PSI, lb/in2, lb/sq in)

Commonly used in the U.S., but not elsewhere. Normal atmospheric pressure is 14.7 psi, which means that a column of air one square inch in area rising from the Earth's atmosphere to space weighs 14.7 pounds.


Atmosphere - atm

Normal atmospheric pressure is called 1 atmosphere. 1 atm = 14.6956 psi = 760 torr.


Torr - torr

This is called the Torr because it is based on the original Torricelli barometer design. One atmosphere of pressure will push the column of mercury (Hg) in a mercury barometer to a height of 760 millimeters. A pressure that causes the Hg column to rise 1 millimeter is called a torr. 1 atm = 760 torr = 14.7 psi.


Bar - bar

The bar is almost the same as the atmosphere unit. One bar = 750.062 torr = 0.9869 atm = 100,000 Pa.


Millibar - mb or mbar

There are 1,000 millibar in one bar. This unit is used by meteorologists who find it easier to refer to atmospheric pressures without using decimals. One millibar = 0.001 bar = 0.750 torr = 100 Pa.


Pascal - Pa

1 pascal = a force of 1 Newton per square meter (1 Newton = the force needed to accelerate 1 kilogram one meter per second per second = 1 kg.m/s2; this is actually quite logical for physicists and engineers, honest). 1 pascal = 10 dyne/cm2 = 0.01 mbar. 1 atm = 101,325 Pascals = 760 mm Hg = 760 torr = 14.7 psi.


Kilopascal - kPa

The prefix "kilo" means "1,000", so one kilopascal = 1,000 Pa. Therefore, 101.325 kPa = 1 atm = 760 torr and 100 kPa = 1 bar = 750 torr.


Megapascal - MPa

The prefix "mega" means "1,000,000", so one megapascal = 1,000 kPa = 1,000,000 Pa. This high pressures does not happen very often.


Gigapascal - GPa

The prefix "giga" means "1,000,000,000", so one gigapascal = 1,000 MPa = 1,000,000 kPa = 1,000,000,000 Pa = 9,870 atm = 10,000 bar. Pressures of several gigapascals can change graphite to diamond or make hydrogen a metallic conductor!