What makes a pascal

The pascal symbol: Pa is the SI derived unit of pressure , internal pressure , stress , Young's modulus and tensile strength , named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square meter.

On Earth, standard atmospheric pressure is One hectopascal is equivalent to one millibar ; one standard atmosphere is exactly equal to The corresponding Imperial unit is pounds per square inch psi. The pascal can be expressed using SI derived units , or alternatively solely SI base units , as:. Where N is the newton , m is the meter, kg is the kilogram, and s is the second. The unit is named after Blaise Pascal , the eminent French mathematician , physicist , and philosopher noted for his experiments with a barometer , an instrument to measure air pressure.

Template:SI unit lowercase. The same definition is used in the compressor and the pneumatic tool industries ISO 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.

Tectonophysicists use the gigapascal GPa in measuring or calculating tectonic forces within the earth. The SI was established in and is based on the metre-kilogram-second system rather than the centimetre-gram-second system. The units are divided into two classes: base units and derived units.

There are seven base units, each representing a different kind of physical quantity. Pressure, the effect of a force applied to a surface, is a derived unit. The unit of pressure in the SI system is the pascal Pa , defined as the force of one newton per square meter:. Another unit of pressure used in meteorology is the bar:. Since the quantities measured can have such a wide range, a standardized prefix system has been set in place.

This allows us to easily write out very small and very large numbers, such as 1 mPa millipascal, 10 -3 or 1 GPa gigapascal, 10 9 , e. This works because the net force is assumed to act vertically downward with respect to this chosen system.

As hinted at already, atmospheric pressure is a measure of the weight of air molecules at ground level over a particular surface area. You are not aware of this pressure because, like all organisms on land, the species to which you belong is adapted to perceive this pressure as "neutral. The atmosphere consists mainly of the diatomic gas molecules nitrogen N 2 and oxygen O 2.

Other players include CO 2 carbon dioxide methane CH 4 and locally varying mounts of water vapor H 2 O ; while constituting only a small percentage of the air overall, methane and carbon dioxide exert significant effects as greenhouse gases. A device called a barometer is used to measure air pressure.

A panoply of pressure gauges exist; the old-style one used to measure blood pressure goes by the easy-to-recall name of sphygmomanometer. The principle is simple; because air has mass, it will tend to push other fluids liquids or gases out of its way with its own weight. A barometer contains a base reservoir of mercury into which a tube sealed at the top has been inserted.

The top of the mercury column naturally rests at the level of normal atmospheric pressure, which is about , pascal Pa or If the pressure drops, this is reflected by a lower mercury level, as the liquid is being pushed upward less forcefully; when pressure rises, so does the mercury level.

Pa units are not actually convenient for measuring pressure on the scale of most everyday things. As you just saw, you need over a hundred grand of them to equal atmospheric pressure. The metric system does make it easy to convert within its own units; for example, to convert hpa to pa hectopascals to pascals , just multiply by Units typically used to express atmospheric pressure and the value of normal atmospheric pressure in these units include millimeters of mercury , also called torr mm Hg or torr ; inches of mercury