The pascal (symbol: Pa) is a unit derived from the International System of Units (SI) used to measure internal pressure, mechanical stress, Young's modulus, and tensile strength. It is defined as one newton per square meter (N/m²).
The unit is named after Blaise Pascal, noted for his contributions to hydrodynamics, hydrostatics, and his experiments with barometers. The 14th General Conference on Weights and Measures in 1971 officially adopted the pascal as the SI unit of pressure.
Equivalences of the Pascal with other pressure units
Below is a table with conversions of pascals to other pressure units:
| Unit of pressure | Equivalence in Pascals (Pa) |
|---|---|
| 1 N/m² | 1 Pa |
| 1 atmosphere (atm) | 101325 Pa |
| 1 bar | 100000 Pa |
| 1 kg/m² | 9.80665 Pa |
| 1 mm water column (mm H₂O) | 9.80665 Pa |
| 1 mm of mercury (mm Hg) | 133.322 Pa |
Some common multiples of the pascal are:
- Hectopascal (hPa) : 1 hPa = 100 Pa (equivalent to one millibar).
- Kilopascal (kPa) : 1 kPa = 1,000 Pa.
- Megapascal (MPa) : 1 MPa = 1,000,000 Pa.
- Gigapascal (GPa) : 1 GPa = 1,000,000,000 Pa.
The standard atmosphere (atm) is defined as 101.325 Pa, which is equivalent to the average atmospheric pressure at sea level at a latitude of 45°N.
Examples of how pascal is used
The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced pounds per square inch (psi), except in a few countries that still use the imperial measurement system or in the US.
Geophysicists use the gigapascal (GPa) to measure or calculate tectonic stresses and pressures within the Earth.
Medical elastography measures tissue stiffness noninvasively with ultrasound or magnetic resonance imaging, and often displays the Young's modulus or shear modulus of the tissue in kilopascals.
In materials science and engineering, the pascal measures the stiffness, tensile strength, and compressive strength of materials. In engineering usage, because the pascal represents a very small quantity, the megapascal (MPa) is the preferred unit for these uses.
The pascal is also equivalent to the SI unit of energy density, J/m3. This applies not only to the thermodynamics of pressurized gases, but also to the energy density of electric, magnetic, and gravitational fields.
In sound pressure or sound intensity measurements, one pascal equals 94 decibels SPL.
The air tightness of buildings is measured at 50 pascals (Pa).
The units of atmospheric pressure commonly used in meteorology were previously the bar, which was close to the average air pressure on Earth, and the millibar. Since the introduction of the International System of Measurement (SI) units, meteorologists generally measure pressures in units of hectopascals (hPa), equivalent to 100 pascals or 1 millibar.
Exceptions include Canada, which uses kilopascals (kPa). In many other fields of science, SI is preferred, meaning Pa with a prefix (in multiples of 1000) is preferred.
Many countries also use millibars or hectopascals to give aviation altimeter settings. In virtually all other fields, the kilopascal (1000 pascals) is used instead.
Pascal's principle
Pascal's principle, formulated by Blaise Pascal in the 17th century, states that the pressure exerted on a confined, incompressible fluid is transmitted in its entirety and with equal intensity in all directions. This means that any change in pressure applied at one point in the fluid affects all points in the fluid equally.
This principle is fundamental to fluid mechanics and has applications in devices such as hydraulic presses, hydraulic brakes, and lifting systems. In a hydraulic press, for example, a small force applied to a piston of smaller area is translated into a large force on a piston of larger area, allowing the force to be efficiently amplified.
Thanks to this principle, hydraulic systems can move large loads with relatively little effort, making them essential in engineering and industrial machinery.
Biography and merits of Blaise Pascal
Blaise Pascal (Clermont-Ferrand, June 19, 1623 - Paris, August 19, 1662) was an Occitan philosopher, mathematician, physicist, inventor, writer, moralist, mystic and theologian, considered one of the most brilliant figures of Western wisdom and probably the only one who occupies leading positions in the manuals of all the disciplines he cultivated.
In his maturity, however, he approached Jansenism, and, in contrast to the prevailing rationalism, he undertook the formulation of a philosophy of Christian character (cut short by his premature death), in which his reflections on the human condition stand out, of which he was able to appreciate both its grandiose dignity and its miserable insignificance.
Inventions and discoveries of Blaise Pascal
The Pascaline
In 1642, inspired by the idea of making his father's tax calculations easier, Blaise Pascal began work on a calculator called the Pascaline. (The German polymath William Schickard had developed and manufactured an earlier version of the calculator in 1623.)
The Pascaline was a numerical calculator with wheels with movable dials, each representing a numerical digit.
The invention, however, was not without technical problems: there was a discrepancy between the calculator's design and the structure of French currency at the time. Pascal continued to work on improving the device, with 50 prototypes produced by 1652, but the Pascaline was never a big sales success.
The generation of conic sections
In 1648, Pascal began writing down more of his theorems on The Generation of Conic Sections, but pushed the work aside until the following decade.
Torricelli's theory
In the late 1640s, Pascal temporarily turned his experiments to the physical sciences. Following in the footsteps of Evangelista Torricelli, Pascal experimented with how atmospheric pressure could be estimated in terms of weight.
In 1648, by asking his brother-in-law to take barometric pressure readings at various altitudes on a mountain (Pascal was too poor to make the trek himself), he validated Torricelli's theory on the cause of barometric variations.
Pascal's Roulette Machine: The Basis of the Mathematical Theory of Probability
In the 1650s, Pascal set about trying to create a perpetual motion machine, the aim of which was to produce more energy than it used.
In the process, he stumbled upon an accidental invention and in 1655, Pascal's roulette machine was born. Appropriately, he derived his name from the French word for "little wheel."
Overlapping his work on roulette was Pascal's correspondence with mathematical theorist Pierre de Fermat, which began in 1654. Through their letters about the game and Pascal's own experiments, he discovered that there is a fixed probability of a particular outcome when it comes to the roll of the dice.
This discovery formed the basis of the mathematical theory of probability, with Pascal's writings on the subject published posthumously.
Wristwatch
Although specific dates are uncertain, Pascal also invented a primitive form of the wristwatch. It was an informal invention, to say the least: the mathematician was known to strap his pocket watch to his wrist with a piece of string, presumably for convenience while he tinkered with other inventions.