The English used in this article or section may not be easy for everybody to understand.
In technology, pressure is often specified in multiples of atmospheric pressure.
It can also be defined as the thrust (compressive force acting perpendicularly to the surface of a body) acting per unit area.
Since pressure depends on both force and area, the same amount of force applied by a hand will make less pressure than when applied by something smaller, like a finger.
To measure the amount of pressure people use these units:
- Pounds per square inch (psi, PSI, lb/in2, lb/sq in). 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 (6.7 kg).
- Atmosphere (atm). Normal atmospheric pressure is called 1 atmosphere. 1 atm = 14.7 psi = 760 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. 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) is the SI unit of pressure. It was named after the French physicist Blaise Pascal. 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 mmHg = 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. Pressures in the megapascal range are common in high-pressure air compressors and hydraulic systems, where high pressure liquids are used to do useful work.
Pressure is directly proportionate to force and inversely proportionate to area.
- Pressure -Citizendium