# Pascal - Pressure unit

The pascal (symbol: Pa) is a unit derived from the International System used to measure internal pressure, mechanical stress, Young's modulus and tensile strength. It is defined as one newton per square meter. It is called in honor of the French mathematician Blaise Pascal.

Some common multiples of the pascal are the hectopascal (1 hPa = 100 Pa), which is equivalent to one millibar, the quilopascal (1 kPa = 1000 Pa), the megapascal (1 MPa = 1,000,000 Pa) and the gigapascal (1 GPa = 1,000,000,000 Pa).

The unit of measure called standard atmosphere (atm) is defined as 101,325 Pa and approximates atmospheric pressure at sea level at a latitude of 45 ° N.

## Applications of the pascal as a unit of measurement

Pascal (Pa) or kilopascal (kPa) as a pressure measurement unit is widely used throughout the world and has largely replaced pounds per square inch (psi), except in some countries that still use the measurement system imperial or in the USA UU.

Geophysicists use the gigapascal (GPa) to measure or calculate tectonic stresses and pressures within the Earth.

Medical elastography measures tissue stiffness non-invasively with ultrasound or magnetic resonance imaging, and often shows the Young's modulus or the tissue shear modulus in kilopascals.

In science and engineering of materials, the pascal measures the rigidity, the resistance to the traction and the resistance to the compression of the materials. In the use of engineering, because the pascal represents a very small amount, the megapascal (MPa) is the preferred unit for these uses.

The pascal is also equivalent to the unit of the international system of energy density measurements, 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 measurements of sound pressure or sound intensity, a pascal equals 94 decibels SPL.

The waterproofing of buildings is measured at 50 pascals (Pa).

The atmospheric pressure units 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 units of the international measurement system (SI), meteorologists generally measure pressures in units of hectopascals (hPa), equivalent to 100 pascals or 1 millibar.

The exceptions include Canada, which uses kilopascals (kPa). In many other fields of science, SI is preferred, which means that Pa is preferred with a prefix (in multiples of 1000).

Many countries also use millibars or hectopascals to make adjustments to the aviation altimeter. In practically all other fields, the kilopascal (1000 pascals) is used instead.

## Blaise Pascal

Blaise Pascal (Clermont-Ferrand, June 19, 1623 - Paris, August 19, 1662) was a Occitan philosopher, mathematician, physicist, inventor, writer, moralist, mystic and theologian, considered one of the Brilliant characters of Western wisdom and probably the only one who holds front-line positions in the manuals of all the disciplines he cultivated.

In his maturity, however, he approached Jansenism, and, faced with the prevailing rationalism, undertook the formulation of a philosophy of a Christian sign (truncated by his premature death), in which his reflections on the human condition, especially the one who appreciated both his great dignity and his miserable insignificance.

### Inventions and discoveries of Blaise Pascal

In 1642, inspired by the idea of making his father's tax calculation work easier, Blaise Pascal began working on a calculator called Pascaline. (The German scholar William Schickard had developed and manufactured an earlier version of the calculator in 1623). Pascaline was a numerical wheel calculator with moving spheres, each one representing a numeric digit. The invention, however, was not exempt from technical problems: there was a discrepancy between the design of the calculator and the structure of the French currency at that time. Pascal continued working on the improvement of the device, with 50 prototypes produced in 1652, but the Pascaline was never a great sales success.

In 1648, Pascal began writing more of his theorems in The Generation of Conic Sections, but pushed the work aside until the following decade.

At the end of the 1640s, Pascal temporarily focused his experiments on the physical sciences. Following in the footsteps of Evangelista Torricelli, Pascal experienced how atmospheric pressure could be estimated in terms of weight. In 1648, by asking his brother-in-law to take readings of barometric pressure at various altitudes on a mountain (Pascal was too poor to do the walk himself), he validated Torricelli's theory of the cause of barometric variations.

In the 1650s, Pascal devoted himself to trying to create a perpetual motion machine, whose goal was to produce more energy than he used. In the process, he stumbled on an accidental invention and in 1655 Pascal's roulette machine was born. Appropriately, he drew his name from the French word for "little wheel".

The superimposition of his work on roulette was Pascal's correspondence with the mathematical theorist Pierre de Fermat, which began in 1654. Through his letters about the game and Pascal's own experiments, he discovered that there is a fixed probability of a Particular result when it comes to the roll of the dice. This discovery was the basis of the mathematical theory of probability, with Pascal's writings on the subject posthumously published.

Although the specific dates are uncertain, Pascal also invented a primitive form of the wristwatch. It was an informal invention, to say the least: it was known that the mathematician placed his pocket watch on his wrist with a piece of string, presumably for convenience while retouching with other inventions.

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