Pascal
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The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is defined as one newton per square metre, and is equivalent to 10 barye (Ba) in the CGS system. The pascal is also equivalent to the SI unit of energy density, the joule per cubic metre. The unit of measurement called standard atmosphere (atm) is defined as 101,325 Pa.
The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced the pounds per square inch (psi) unit, except in some countries that still use the imperial measurement system or the US customary system, including the United States.
Multiples
Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa), which is equal to one millibar, and the kilopascal (1 kPa = 1000 Pa), which is equal to one centibar.
In engineering the megapascal (MPa) is the preferred unit for these uses, because the pascal represents a very small quantity.
Geophysicists use the gigapascal (GPa) in measuring or calculating tectonic stresses and pressures within the Earth.