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Pressure is the application of force to a surface, and the concentration of that force in a given area. A finger can be pressed against a wall without making any lasting impression; however, the same finger pushing a thumbtack can easily damage the wall, even though the force applied is the same, because the point concentrates that force into a smaller area. A thumbtack is a short nail or pin with a large, slightly rounded head made of metal which is used to fasten documents to a background for public display and which can easily be removed by hand. ...
More formally, pressure (symbol: p or P) is the measure of the normal component of force that acts on a unit area, see also stress (physics): A surface normal, or just normal to a flat surface is a three-dimensional vector which is perpendicular to that surface. ...
In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ...
This article explains the meaning of area as a physical quantity. ...
Stress tensor In physics, stress is the internal distribution of forces within a body that balance and react to the loads applied to it. ...
where: - p is the pressure
- F is the normal component of the force
- A is the area
Often F is taken to be the magnitude of the mean vector force normal to the surface of area A upon which it exerts; the "surface" not necessarily being a that of a body, but for example the cross sectional area of a conduit. In physics, a force is what changes the velocity of a material body. ...
This article explains the meaning of area as a physical quantity. ...
The gradient of pressure is force density. In vector calculus, the gradient of a scalar field is a vector field which points in the direction of the greatest rate of change of the scalar field, and whose magnitude is the greatest rate of change. ...
In fluid mechanics, the force density is a vector field representing the flux density of the hydrostatic force within the bulk of a fluid. ...
Pressure is sometimes measured not as an absolute pressure, but relative to atmospheric pressure; such measurements are sometimes called gauge pressure. An example of this is the air pressure in a tire of a car, which might be said to be "thirty PSI", but is actually thirty PSI above atmospheric pressure. In technical work, this is often written as "30 PSIG" or, more commonly, "30 psig", though other methods which avoid attaching this information to the unit of pressure are preferred. 1 diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure above any area in the Earths atmosphere caused by the weight of air. ...
In the human body, pressure is measured by baroreceptors. Baroreceptors (or baroceptors) in the human body detect the pressure of blood flowing though them, and can send messages to the central nervous system to increase or decrease total peripheral resistance and cardiac output. ...
"Pressure is a scalar quantity, but teachers and authors do not appear to believe this in their hearts." (McClelland, 1987)
Scalar quantity
Let us look at a static gas; one that does not appear to move or flow. While the gas as a whole does not appear to move, the individual molecules of the gas, which we cannot see, are in constant random motion. Because we are dealing with a nearly infinite number of molecules and because the motion of the individual molecules is random in every direction, we do not detect any motion. If we enclose the gas within a container, we detect a pressure in the gas from the molecules colliding with the walls of our container. We can put the walls of our container anywhere inside the gas, and the force per area (the pressure) is the same. We can shrink the size of our "container" down to an infinitely small point, and the pressure has a single value at that point. Therefore, pressure is a scalar quantity, not a vector quantity. It has a magnitude but no direction associated with it. Pressure acts in all directions at a point inside a gas. At the surface of a gas, the pressure force acts perpendicular to the surface.
Hydrostatic pressure Hydrostatic pressure is the pressure due to the weight of a fluid. Hydrostatic pressure is the pressure exerted by a fluid due to its weight. ...
Weight is the force exerted upon an object by virtue of its position in a gravitational field. ...
where: - ρ (rho) is the density of the fluid
- g is the acceleration due to gravity
- h is the height of fluid above the point being measured
Also see Pascal's Law. 1. ...
Density (symbol: Ï - Greek: rho) is a measure of mass per unit of volume. ...
g (also gee, g-force or g-load) is a non-SI unit of acceleration defined as exactly 9. ...
Pascals Law gives the hydrostatic pressure of a fluid at mechanical equilibrium (see also hydrostatics), on which only gravity forces are taken into account. ...
Stagnation pressure Stagnation pressure is the pressure a fluid exerts when it is motionless. Consequently, although a fluid moving at higher speed will have a lower static pressure, it may have a higher stagnation pressure. Static and stagnation pressure are related by the Mach number of the fluid. In addition, there can be differences in pressure due to differences in the elevation (height) of the fluid. See Bernoulli's equation. Mach number (Ma) is defined as a ratio of speed to the speed of sound in the medium in case. ...
In fluid dynamics, Bernoullis equation, derived by Daniel Bernoulli, describes the behavior of a fluid moving along a streamline. ...
The pressure of a moving fluid can be measured using a Pitot probe, or one of its variations such as a Kiel probe or Cobra probe, connected to a manometer. Depending on where the inlet holes are located on the probe, it can measure static pressure or stagnation pressure. A Pitot tube is a measuring instrument used to measure fluid flow. ...
A Kiel probe is a device for measuring pressure in fluid dynamics. ...
A Cobra probe is a device to measure the pressure of a moving fluid. ...
A manometer is a pressure measuring instrument. ...
Units The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N·m-2 or kg·s-2·m-1). This special name for the unit was added in 1971; before that, pressures in SI were expressed in units such as N/m² The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ...
The pascal (symbol Pa) is the SI unit of pressure. ...
In physics, the newton (symbol: N) is the SI unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics. ...
A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ...
Non-SI measures (still in use in some parts of the world) include the pound-force per square inch (PSI) and the bar. The pound-force is a non-SI unit of force or weight (properly abbreviated lbf or lbf). The pound-force is equal to a mass of one pound multiplied by the standard acceleration due to gravity on Earth (which is defined as exactly 9. ...
Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ...
Psi has multiple meanings: Psi (Ψ ψ) is a letter of the Greek alphabet. ...
The bar is a measurement unit of pressure, equal to 1,000,000 dynes per square centimetre (baryes), or 100,000 newtons per square metre (pascals). ...
The cgs unit of pressure is barye (ba). It is equal to 1 dyn·cm-2. CGS is an acronym for centimetre-gram-second. ...
The barye (symbol: Ba)is the CGS unit of pressure. ...
Pressure is still sometimes expressed in kgf/cm² or g/cm² (often as kg/cm² and g/cm² without properly identifying the force units). The technical atmosphere (symbol: at) is 1 kgf/cm². A technical atmosphere (symbol: at) is a non-SI unit of pressure equal to 1 kilogram-force per square centimeter, i. ...
In the United States air pressure is still measured in inHg — inches of mercury (as in the mercury barometer). Some meteorologists prefer the hectopascal (hPa) for atmospheric air pressure, because it gives the same numbers as the older millibar (mbar). General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery white Atomic mass 200. ...
Schematic drawing of a simple mercury barometer with vertical mercury column and reservoir at base A barometer is an instrument used to measure atmospheric pressure. ...
Meteorology is the scientific study of the atmosphere that focuses on weather processes and forecasting. ...
Blood pressure is still measured in millimetres of mercury in most of the world, and lung pressures in centimeters of water are still common. These obsolete manometric units of pressure are based on the pressure exerted by the weight of some "standard" fluid under some "standard" gravity. They are effectively attempts to define a unit for expressing the readings of a manometer. When millimetres or inches of mercury are used today, they have precise definitions which can be expressed exactly in terms of SI units, though there were considerable minor variations in earlier usage. The water-based units depend on the density of water, a measured rather than defined quantity. Blood pressure is the pressure exerted by the blood on the walls of the blood vessels. ...
The torr is a unit of pressure. ...
A manometer is a pressure measuring instrument. ...
The standard atmosphere (atm) is an established constant. It is approximately equal to typical air pressures at sea level and defined to be Atmospheric pressure is the pressure caused by the weight of air above any area in the Earths atmosphere. ...
- standard atmosphere = 101 325 Pa = 101.325 kPa = 1013.25 hPa.
A rule of thumb commonly used by Scuba divers is that one atmosphere is approximately equal to the pressure exerted by ten metres of water. The pascal (symbol Pa) is the SI unit of pressure. ...
A rule of thumb is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. ...
Early ideas of autonomous under-water systems appear in Twenty Thousand Leagues Under the Sea Scuba diving is the use of independent breathing equipment to stay underwater for long periods of time for recreational diving and professional diving. ...
Non-SI units presently or formerly in use include the following:
- Atmospheres
- Manometric units:
- Customary and foot-pound-second units:
- Kips, tons-force (short), tons-force (long), pounds-force, ounces-force, and poundals per square inch
- Pounds-force, tons-force(short) and tons-force (long) per square foot
- Non-SI metric units:
- bars and millibars
- Kilograms-force (kiloponds), grams-force, tonnes-force (metric tons-force), newtons and dynes per square centimetre
- Baryes = dyn/cm² and technical atmospheres = kgf/cm²
- Kilograms-force and tonnes-force per square metre
When expressed as a measurement, an atmosphere or standard atmosphere is a unit of pressure roughly equal to the average atmospheric pressure at sea level on the earth. ...
The torr is a unit of pressure. ...
The title given to this article is incorrect due to technical limitations. ...
In the United States, a kip is sometimes a unit of mass that equals 1,000 avoirdupois pounds (used to compute shipping charges), or more often a unit of force that equals 1,000 pounds force (used to measure engineering loads). ...
The word ton or tonne is derived from the Old English tunne, and ultimately from the Old French tonne, and referred originally to a large cask with a capacity of 252 wine gallons, which holds approximately 2100 pounds of water. ...
The poundal is a non-SI unit of force. ...
The bar is a measurement unit of pressure, equal to 1,000,000 dynes per square centimetre (baryes), or 100,000 newtons per square metre (pascals). ...
A millibar (mb) is 1/1000th of a bar, a unit for measurement of pressure. ...
In physics, the dyne is a unit of force specified in the centimetre-gram-second (cgs) system of units, symbol dyn. One dyne is equal to exactly 10-5 newtons. ...
The barye (symbol: Ba)is the CGS unit of pressure. ...
A technical atmosphere (symbol: at) is a non-SI unit of pressure equal to 1 kilogram-force per square centimeter, i. ...
Conversion table Some popular pressure units and conversion factors | | Pascal | bar | N/mm2 | kp/m2 | kp/cm2 (=1 at) | atm | torr | | 1 Pa (N/m2)= | 1 | 10-5 | 10-6 | 0.102 | 0.102×10-4 | 0.987×10-5 | 0.0075 | | 1 bar (daN/cm2) = | 105 | 1 | 0.1 | 10,200 | 1.02 | 0.987 | 750 | | 1 N/mm2 = | 106 | 10 | 1 | 1.02×105 | 10.2 | 9.87 | 7,501 | | 1 kp/m2 = | 9.81 | 9.81×10-5 | 9.81×10-6 | 1 | 10-4 | 0.968×10-4 | 0.0736 | | 1 kp/cm2 (1 at) = | 98,100 | 0.981 | 0.0981 | 10,000 | 1 | 0.968 | 736 | | 1 atm (760 torr) = | 101,325 | 1.013 | 0.1013 | 10,330 | 1.033 | 1 | 760 | | 1 torr (mmHg) = | 133 | 0.00133 | 1.33×10-4 | 13.6 | 0.00132 | 0.00132 | 1 | The bar is a measurement unit of pressure, equal to 1,000,000 dynes per square centimetre (baryes), or 100,000 newtons per square metre (pascals). ...
diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure above any area in the Earths atmosphere caused by the weight of air. ...
The torr is a unit of pressure. ...
One way of defining pressure is in terms of the height of a column of fluid that may be supported by that pressure; or the height of a column of fluid that exerts that pressure at its base. ...
See also Approximately, the partial pressure of a gas in atmospheres in a mixture or solution is what would be the pressure of that gas if all other components of the mixture or solution suddenly vanished without its temperature changing. ...
The kinetic theory of gases is a theory that explains the macroscopic properties of gases by consideration of their composition at a molecular level. ...
diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure above any area in the Earths atmosphere caused by the weight of air. ...
Sound pressure p (or acoustic pressure) is the measurement in pascals of the root mean square (RMS) pressure deviation (from atmospheric pressure) caused by a sound wave passing through a fixed point. ...
Inside a condenser microphone. ...
Timeline of temperature and pressure measurement technology 1592 - Galileo Galilei builds a crude thermometer using the contraction of air to draw water up a tube 1612 - Santorre Santorio puts thermometer to medical use 1643 - Evangelista Torricelli invents the mercury barometer 1714 - Daniel Gabriel Fahrenheit invents the mercury in glass thermometer...
This article lists conversion factors between a number of units of measurement. ...
Blood pressure is the pressure exerted by the blood on the walls of the blood vessels. ...
In physics and mechanics, shear refers to a deformation that causes parallel surfaces to slide past one another (as opposed to compression and tension, which cause parallel surfaces to move towards or away from one another). ...
External links - Online Unit Converter - Conversion of many different units
- An Exercise in Air Pressure
- Pressure being a scalar quantity
Pressure can also be psychological, political, etc.; see also peer pressure. Psychology (ancient Greek: psyche = soul and logos = word) is the study of mind, thought, and behaviour. ...
Peer pressure comprises a set of group dynamics whereby a group in which one feels comfortable may override personal habits, individual moral inhibitions or idiosyncratic desires to impose a group norm of attitudes and/or behaviors. ...
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