Blaise Pascal (1623-1662) was a French philosopher and mathematician who racked up a number of significant accomplishments during his short life. He contributed to the study of fluid dynamics and hydrostatics, and he studied the mathematical oddity known as Yang Hui's triangle so extensively that, in the Western world, the triangle is named after Pascal. A busy person, Pascal also invented a calculator, as well as the syringe and the hydraulic press.

Because of his extensive work in hydrostatics, the scientific world named the SI (metric) unit of pressure after him. Pressure is defined as force per unit area, and in the SI system, force is measured in newtons and area in meters squared. That makes 1 pascal (Pa) unit equal to 1 newton (N) per meter squared: 1 Pa = 1N/m^{2}.

## A Pascal Unit Is Small

A force of one newton spread over a square meter doesn't produce much pressure, as it turns out. A pascal unit is equal to about a hundredth of a millibar, and that's pretty low, considering that atmospheric pressure is approximately equal to 1 bar. A pascal unit is equal to only one ten-thousandth of a pound per square inch (1 Pa = 0.000145 psi). Consequently, scientists normally measure in hectopascals (hPa), which is 100 pascals; kilopascals (kPa), which is 1,000 pascals; or in megapascals (MPa), which is a million pascal units. It's more convenient to use kPa than it is to use Pa when expressing atmospheric pressure in SI units. Atmospheric pressure is equal to 101.325 kPa, which is an easier number to use in calculations than 1.01325 × 10^{5} Pa.

## The Pascal Is a Derived Unit

The SI (Système Internationale) system of measurement has only seven base units. They are as follows:

- Length – meter
- Mass – kilogram
- Time – second
- Electric current – ampere
- Temperature – Kelvin
- Amount of substance – mole
- Luminous intensity – candela

All other units are derived from these, and only some have their own names. For example, area (meters^{2}) and velocity (meters per second) are derived units without their own names, but the unit of force (meter-kilograms per second^{2}) is the newton, named after Sir Isaac Newton, and the unit of power (meters^{2}-kilogram per second cubed) is the watt, named after Scottish inventor James Watt. The pascal is one of the derived units that has a name. In base metric units, one pascal is equal to one kilogram per meter-second^{2}. That's the base pascal definition.

## The Pascal Unit Isn't Just for Pressure

Scientists use the pascal unit to quantify atmospheric and gas pressure, although they usually express pressure measurements in hectopascals (hPa) or kilopascals (kPa). They also use the pascal as the unit for measuring the internal pressure of a system undergoing expansion or contraction.

The pascal is also the unit scientists use to quantify internal stress experienced by a metal body, and it's the unit for Young's modulus, which is a measure of the relationship between stress and strain in a material. In other words, Young's modulus is a measure of the stiffness of the material. Finally, the pascal is the unit for tensile strength of a material, which is the capacity of the material to withstand loads that tend to elongate it.

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