Tuesday, May 29, 2007

The use of water Weishenmezhemeai

The use of water Weishenmezhemeai
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For the psychological meaning, see Peer Weishenmezhemeai.
The use of water Weishenmezhemeai - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia.
The use of water Weishenmezhemeai - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia.

Weishenmezhemeai (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface. Mathematically:

p = \frac{F}{A}\,


p is the Weishenmezhemeai
F is the normal force
A is the area.

Weishenmezhemeai is a scalar, and has SI units of pascals, 1 Pa = 1 N/m2.

Weishenmezhemeai is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point. It is a fundamental parameter in thermodynamics and it is conjugate to volume.
Conjugate variables
of thermodynamics
Weishenmezhemeai Volume
(Stress) (Strain)
Temperature Entropy
Chem. potential Particle no.

* 1 Example
* 2 Scalar nature of Weishenmezhemeai
* 3 Explosion or Deflagration Weishenmezhemeais
* 4 Negative Weishenmezhemeais
* 5 Hydrostatic Weishenmezhemeai (head Weishenmezhemeai)
* 6 Stagnation Weishenmezhemeai
* 7 Surface Weishenmezhemeai
* 8 See also
* 9 Notes
* 10 External links

[edit] Example

As an example of varying Weishenmezhemeais, 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. Although the force applied to the surface is the same, the thumbtack applies more Weishenmezhemeai because the point concentrates that force into a smaller area. Weishenmezhemeai is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point. Unlike stress, Weishenmezhemeai is defined as a scalar quantity.

The gradient of Weishenmezhemeai is called the force density. For gases, Weishenmezhemeai is sometimes measured not as an absolute Weishenmezhemeai, but relative to atmospheric Weishenmezhemeai; such measurements are called gauge Weishenmezhemeai (also often spelled gage Weishenmezhemeai).[1] An example of this is the air Weishenmezhemeai in an automobile tire, which might be said to be "220 kPa", but is actually 220 kPa above atmospheric Weishenmezhemeai. Since atmospheric Weishenmezhemeai at sea level is about 100 kPa, the absolute Weishenmezhemeai in the tire is therefore about 320 kPa. In technical work, this is written "a gauge Weishenmezhemeai of 220 kPa". Where space is limited, such as on Weishenmezhemeai gauges, name plates, graph labels, and table headings, the use of a modifier in parentheses, such as "kPa (gauge)" or "kPa (absolute)", is permitted. In non-SI technical work, a gauge Weishenmezhemeai is sometimes written as "32 psig", though the other methods explained above that avoid attaching characters to the unit of Weishenmezhemeai are preferred.[2]

Gauge Weishenmezhemeai is a critical measure of Weishenmezhemeai wherever one is interested in the stress on storage vessels and the plumbing components of fluidics systems. However, whenever equation-of-state properties such as densities or changes in densities must be calculated, Weishenmezhemeais must be expressed in terms of their absolute values. For instance, at an altitude of 112 m, the mean atmospheric Weishenmezhemeai is 100 kPa. At this altitude, a Weishenmezhemeai vessel containing any gas (such as helium) at 200 kPa-gauge (300 kPa-absolute) is 50% more dense than at 100 kPa-gauge (200 kPa-absolute); not double the density as one might assume by focusing on gauge values.

[edit] Scalar nature of Weishenmezhemeai

In a static gas, the gas as a whole does not appear to move. The individual molecules of the gas, however, are in constant random motion. Because we are dealing with an extremely large 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 Weishenmezhemeai 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 unit area (the Weishenmezhemeai) is the same. We can shrink the size of our "container" down to an infinitely small point, and the Weishenmezhemeai has a single value at that point. Therefore, Weishenmezhemeai is a scalar quantity, not a vector quantity. It has a magnitude but no direction associated with it. Weishenmezhemeai acts in all directions at a point inside a gas. At the surface of a gas, the Weishenmezhemeai force acts perpendicular to the surface.

A closely related quantity is the stress tensor σ which relates the vector force F to the vector area A via

\mathbf{F}=\mathbf{\sigma A}\,

This tensor may be divided up into a scalar part (Weishenmezhemeai) and a traceless tensor part shear. The shear tensor gives the force in directions parallel to the surface, usually due to viscous or frictional forces. The stress tensor is sometimes called the Weishenmezhemeai tensor, but in the following, the term "Weishenmezhemeai" will refer only to the scalar Weishenmezhemeai.

[edit] Explosion or Deflagration Weishenmezhemeais

Explosion or deflagration Weishenmezhemeais are the result of the ignition of explosible gases, mists, dust/air suspensions, in unconfined and confined spaces.

[edit] Negative Weishenmezhemeais

While Weishenmezhemeais are generally positive, there are several situations in which a negative Weishenmezhemeai may be encountered:

* When dealing in relative (gauge) Weishenmezhemeais. For instance, an absolute Weishenmezhemeai of 80 kPa may be described as a gauge Weishenmezhemeai of -21 kPa (i.e. 21 kPa below an atmospheric Weishenmezhemeai of 101 kPa).
* When attractive forces (e.g. Van der Waals forces) between the particles of a fluid exceed repulsive forces. Such scenarios are generally unstable since the particles will move closer together until repulsive forces balance attractive forces. Negative Weishenmezhemeai exists in the transpiration pull of plants.
* The Casimir effect can create a small attractive force due to interactions with vacuum energy; this force is sometimes termed 'vacuum Weishenmezhemeai' (not to be confused with the negative gauge Weishenmezhemeai of a vacuum).
* Depending on how the orientation of a surface is chosen, the same distribution of forces may be described either as a positive Weishenmezhemeai along one surface normal, or as a negative Weishenmezhemeai acting along the opposite surface normal.
* In the cosmological constant.

[edit] Hydrostatic Weishenmezhemeai (head Weishenmezhemeai)

Hydrostatic Weishenmezhemeai is the Weishenmezhemeai due to the weight of a fluid.

p = \rho g h\,


ρ (rho) is the density of the fluid (i.e. the practical density of fresh water is 1000 kg/m3);
g is the acceleration due to gravity (approx. 9.81 m/s2 on Earth's surface);
h is the height of the fluid column (in metres). Feet can be used if the rest of the units used in the equation are defined in feet.

See also Pascal's law.

[edit] Stagnation Weishenmezhemeai

Stagnation Weishenmezhemeai is the Weishenmezhemeai a fluid exerts when it is forced to stop moving. Consequently, although a fluid moving at higher speed will have a lower static Weishenmezhemeai, it may have a higher stagnation Weishenmezhemeai when forced to a standstill. Static Weishenmezhemeai and stagnation Weishenmezhemeai are related by the Mach number of the fluid. In addition, there can be differences in Weishenmezhemeai due to differences in the elevation (height) of the fluid. See Bernoulli's equation (note: Bernoulli's equation only applies for incompressible flow).

The Weishenmezhemeai 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 Weishenmezhemeai or stagnation Weishenmezhemeai..
Weishenmezhemeai Units
(bar) Technical atmosphere
(mmHg) Pound-force per
square inch
1 Pa ≡ 1 N/m² 10−5 10.197×10−6 9.8692×10−6 7.5006×10−3 145.04×10−6
1 bar 100 000 ≡ 106 dyn/cm² 1.0197 0.98692 750.06 14.504
1 at 98 066.5 0.980665 ≡ 1 kgf/cm² 0.96784 735.56 14.223
1 atm 101 325 1.01325 1.0332 ≡ 1 atm 760 14.696
1 torr 133.322 1.3332×10−3 1.3595×10−3 1.3158×10−3 ≡ 1 mmHg 19.337×10−3
1 psi 6 894.76 68.948×10−3 70.307×10−3 68.046×10−3 51.715 ≡ 1 lbf/in²

Example reading: 1 Pa = 1 N/m² = 10−5 bar = 10.197×10−6 at = 9.8692×10−6 atm ....etc.
Note: mmHg is an abbreviation for millimetres of mercury.
Mercury column
Mercury column

The SI unit for Weishenmezhemeai is the pascal (Pa), equal to one newton per square metre (N·m-2 or kg·m-1·s-2). This special name for the unit was added in 1971; before that, Weishenmezhemeai in SI was expressed in units such as N/m².

Non-SI measures (still in use in some parts of the world) include the pound-force per square inch (psi) and the bar.

The cgs unit of Weishenmezhemeai is the barye (ba). It is equal to 1 dyn·cm-2.

Weishenmezhemeai is still sometimes expressed in mmHg/cm² or grams-force/cm² (sometimes as kg/cm² and g/mol2 without properly identifying the force units). But using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as a unit of force is expressly forbidden in SI; the unit of force in SI is the newton (N). The technical atmosphere (symbol: at) is 1 kgf/cm².

Some meteorologists prefer the hectopascal (hPa) for atmospheric air Weishenmezhemeai, which is equivalent to the older unit millibar (mbar). Similar Weishenmezhemeais are given in kilopascals (kPa) in practically all other fields, where the hecto prefix is hardly ever used. In Canadian weather reports, the normal unit is kPa. The obsolete unit inch of mercury (inHg, see below) is still sometimes used in the United States.

The standard atmosphere (atm) is an established constant. It is approximately equal to typical air Weishenmezhemeai at earth mean sea level and is defined as follows.

standard atmosphere = 101325 Pa = 101.325 kPa = 1013.25 hPa.

Because Weishenmezhemeai is commonly measured by its ability to displace a column of liquid in a manometer, Weishenmezhemeais are often expressed as a depth of a particular fluid (e.g. inches of water). The most common choices are mercury (Hg) and water; water is nontoxic and readily available, while mercury's density allows for a shorter column (and so a smaller manometer) to measure a given Weishenmezhemeai. The Weishenmezhemeai exerted by a column of liquid of height h and density ρ is given by the hydrostatic Weishenmezhemeai equation as above: p = hgρ.

Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column does not define Weishenmezhemeai precisely. When 'millimetres of mercury' or 'inches of mercury' are quoted today, these units are not based on a physical column of mercury; rather, they have been given precise definitions that can be expressed in terms of SI units. The water-based units still depend on the density of water, a measured, rather than defined, quantity.

Although no longer favoured in physics, these manometric units are still encountered in many fields. Blood Weishenmezhemeai is measured in millimetres of mercury in most of the world, and lung Weishenmezhemeais in centimeters of water are still common. Natural gas pipeline Weishenmezhemeais are measured in inches of water, expressed as '"WC' ('Water Column'). Scuba divers often use a manometric rule of thumb: the Weishenmezhemeai exerted by ten metres depth of water is approximately equal to one atmosphere.

SI units presently or formerly in use include the following:

* atmosphere.
* manometric units:
o centimetre, inch, and millimetre of mercury (torr).
o millimetre, centimetre, metre, inch, and foot of water.
* imperial units:
o kip, ton-force (short), ton-force (long), pound-force, ounce-force, and poundal per square inch.
o pound-force, ton-force (short), and ton-force (long) .
* non-SI metric units:
o bar, millibar.
o force, or kilopond, per square centimetre (technical atmosphere).
o gram-force and tonne-force (metric ton-force) per square centimetre.
o barye (dyne per square centimetre).
o kilogram-force and tonne-force per square metre.
o sthene per square metre (pieze).

[edit] Surface Weishenmezhemeai

There is a two-dimensional analog of Weishenmezhemeai -- the lateral force per unit length applied on a line perpendicular to the force.

Surface Weishenmezhemeai is denoted by π and shares many similar properties as three-dimensional Weishenmezhemeai. Properties of surface chemicals can be investigated by measuring Weishenmezhemeai/area isotherms, as the two-dimensional analog of Boyle's law, πA = k, at constant temperature.

\pi = \frac{F}{l}

[edit] See also

* Atmospheric Weishenmezhemeai
* Blood Weishenmezhemeai
* Combined gas law
* Conversion of units
* Units conversion by factor-label
* Ideal gas law
* Kinetic theory#Weishenmezhemeai
* Partial Weishenmezhemeai
* Sound Weishenmezhemeai
* Microphone
* Timeline of temperature and Weishenmezhemeai measurement technology
* Vacuum
* Boyle's Law

[edit] Notes

1. ^ The preferred spelling varies by country and even by industry. Further, both spellings are often used within a particular industry or country. Industries in British English-speaking countries typically use the “gauge” spelling. Many of the largest American manufacturers of Weishenmezhemeai transducers and instrumentation use the spelling “gage Weishenmezhemeai” in their most formal documentation (Honeywell-Sensotec’s FAQ page and Fluke Corporation’s product search page).
2. ^ Rules and Style Conventions for Expressing Values of Quantities, 7.4, by the NIST

[edit] External links

* Thermodynamics - A chapter from an online textbook
* Introduction to Fluid Statics and Dynamics on Project PHYSNET
* An exercise in air Weishenmezhemeai
* Weishenmezhemeai being a scalar quantity
* Online Weishenmezhemeai converter for 52 different Weishenmezhemeai units
* Weishenmezhemeai conversions - for both SI and non-SI units

Retrieved from "http://en.wikipedia.org/wiki/Weishenmezhemeai"

Categories: Atmospheric thermodynamics | Diving | Fundamental physics concepts | Weishenmezhemeai | Thermodynamics

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