Pressure
Content
Pressure (the symbol: P) is the force per unit area applied in a direction perpendicular to the surface of
an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure. Pressure is the effect of a force applied to a surface. Pressure is the amount of force acting per unit area. The symbol of pressure is P. Mathematically:
where:
P is the pressure, F is the normal force, A is the area of the surface area on contact The SI unit for pressure is the pascal (Pa), equal to one newton per square meter (N/m2 or kg·m−1·s−2). This special name for the unit was added in 1971;[3] before that, pressure in SI was expressed simply as N/m2.
Fluid pressure is the pressure at some point within a fluid, such as water or air.
Fluid pressure occurs in one of two situations: 1. an open condition, called "open channel flow" 1. the ocean, or 2. swimming pool, or 3. the atmosphere. 2. a closed condition, called closed conduits 1. water line, or 2. gas line.
Stagnation pressure is the pressure a fluid exerts when it is forced to stop moving. Consequently,
although a fluid moving at higher speed will have a lower static pressure, it may have a higher stagnation pressure when forced to a standstill. Static pressure 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 (note: Bernoulli's equation only applies for incompressible, inviscid flow). The pressure of a moving fluid can be measured using a Pitot tube, 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 pressures or stagnation pressures.
Surface pressur
There is a two-dimensional analog of pressure – the lateral force per unit length applied on a line perpendicular to the force.Surface pressure is denoted by π and shares many similar properties with threedimensional pressure. Properties of surface chemicals can be investigated by measuring pressure/area isotherms, as the two-dimensional analog of Boyle's law, πA = k, at constant temperature.
Pressure of an ideal gas
Main article: Ideal gas law In an ideal gas, molecules have no volume and do not interact. Pressure varies linearly with temperature, volume, and quantity according to the ideal gas law,
where: P is the absolute pressure of the gas n is the amount of substance T is the absolute temperature V is the volume R is the ideal gas constant. Real gases exhibit a more complex dependence on the variables of state.
Vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its
condensed phases in a closed system. All liquids and solidshave a tendency to evaporate into a gaseous form, and all gases have a tendency to condense back to their liquid or solid form. The atmospheric pressure boiling point of a liquid (also known as the normal boiling point) is the temperature at which the vapor pressure equals the ambient atmospheric pressure. With any incremental increase in that temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form vapor bubbles inside the bulk of the substance. Bubble formation deeper in the liquid requires a higher pressure, and therefore higher temperature, because the fluid pressure increases above the atmospheric pressure as the depth increases.
The vapor pressure that a single component in a mixture contributes to the total pressure in the system is called partial vapor pressure. Liquid pressure or pressure at depth
Used with liquid columns of constant density or at a depth within a substance (example: pressure at 20 km depth in the Earth).
P = ρgh
where: P is Pressure g is gravity at the surface of overlaying material ρ is density of liquid or overlaying material h is height of liquid or depth within a substance
Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air
above that surface. In the diagram below, the pressure at point "X" increases as the weight of the air above it increases. The same can be said about decreasing pressure, where the pressure at point "X" decreases if the weight of the air above it also decreases.
Thinking in terms of air molecules, if the number of air molecules above a surface increases, there are more molecules to exert a force on that surface and consequently, the pressure increases. The opposite is also true, where a reduction in the number of air molecules above a surface will result in a decrease in pressure. Atmospheric pressure is measured with an instrument called a "barometer", which is why atmospheric pressure is also referred to as barometric pressure.
In aviation and television weather reports, pressure is given in inches of mercury ("Hg), while meteorologists use millibars (mb), the unit of pressure found on weather maps
T sea level standard temperature 288.15 K P sea level standard atmospheric pressure 101325 Pa M molar mass of dry air 0.0289644 kg/mol g Earth-surface gravitational acceleration 9.80665 m/s2
Dynamic pressure is a defined property of a moving flow of gas or liquid and can be expressed as.
where (using SI units): q = dynamic pressure in pascals ρ = fluid density in kg/m3 (such as the density of air) v = fluid velocity in m/s
Partial pressure refers to the pressure exerted by an individual gas in a mixture of
gasses.
Pressure sensor measures pressure, typically of gases or liquids. Pressure is an expression
of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical. Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators and piezometers, manometers, among other names.
Static pressure is the pressure that is exerted by a liquid or gas, such as water or air.
Specifically, it is the pressure measured when the liquid or gas is still, or at rest. Several different industrial and scientific applications exist for this term, but most have to do with air pressure rather than water pressure. In aviation, for example, a static pressure system is how a plane's altimeter and airspeed indicator operate. In construction, it refers to thepressure which a fan must exert in a ventilation system in order to cause air to flow. The concept of static pressure is also an essential one in the science of fluid mechanics. Scientifically, static pressure is distinguished from dynamic pressure, both of which are components of a system's total pressure. This relationship is defined in Bernoulli's equation, and relates to the study of the flow and motion of fluids. The principle of Bernoulli's equation is that static pressure and dynamic pressure may vary greatly in different areas of a fluid in motion, but the total pressure remains constant.
Water pressure is a term used to describe the flow strength of water through a pipe or
other type of channel. Water pressure depends on water flow. The more water being pushed through a pipe, the more pressure there will be naturally.
Absolute pressure sensor
This sensor measures the pressure relative to perfect vacuum pressure (0 PSI or no pressure). Atmospheric pressure, is 101.325 kPa (14.7 PSI) at sea level with reference to vacuum.
Gauge pressure sensor
This sensor is used in different applications because it can be calibrated to measure the pressure relative to a given atmospheric pressure at a given location. A tire pressure gauge is an example of gauge pressure indication. When the tire pressure gauge reads 0 PSI, there is really 14.7 PSI (atmospheric pressure) in the tire.
Vacuum pressure sensor
This sensor is used to measure pressure less than the atmospheric pressure at a given location. This has the potential to cause some confusion as industry may refer to a vacuum sensor as one which is referenced to either atmospheric pressure (i.e. measure Negative gauge pressure) or relative to absolute vacuum.
molecule refers to two or more atoms which have chemically combined to form a single
species.
compound is a chemical species that is formed when two or more atoms join together
chemically, with covalent or ionic bonds.
ATOMis a particle of matter that uniquely defines achemical element. An atom consists of a
central nucleus that is usually surrounded by one or more electrons. Eachelectron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons. A proton is positively charged. The number of protons in the nucleus ofan atom is the atomic number for the chemical element. A proton has a rest mass, denoted mp, of approximately 1.673 x 10-27 kilogram (kg). A neutron is electrically neutral and has a rest mass, denoted mn, of approximately 1.675 x 10-27 kg. The mass of a proton or neutron increases when the particle attains extreme speed, for example in a cyclotron or linear accelerator.
Ion: An atom or a group of atoms that has acquired a net electric charge by gaining or losing
one or more electrons.
macromolecule is a very large molecule commonly created by some form
ofpolymerization.The constituent molecules from which macromolecules are assembled are calledmonomers
Nobel Gas: The noble gases are a group of chemical elements with very similar properties:
under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).
Chemical bonding:
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of adipole attraction.
Inonic and covelent bond:
A molecule or compound is made when two or more atoms form a chemical bond, linking them together. The two types of bonds are ionic bonds and covalent bonds. In an ionic bond, the atoms are bound together by the attraction between oppositely-charged ions. For example, sodium and chloride form an ionic bond, to make NaCl, or table salt. In a covalent bond, the atoms are bound by shared electrons. If the electron is shared equally between the atoms forming a covalent bond, then the bond is said to be nonpolar. Usually, an electron is more attracted to one atom than to another, forming a polar covalent bond. For example, the atoms in water, H2O, are held together by polar covalent bonds.
chemical compound is a pure chemical substance consisting of two or more
different chemical elements[1][2][3] that can be separated into simpler substances by chemical
reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together in a defined spatial arrangement by chemical bonds.
an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure. Pressure is the effect of a force applied to a surface. Pressure is the amount of force acting per unit area. The symbol of pressure is P. Mathematically:
where:
P is the pressure, F is the normal force, A is the area of the surface area on contact The SI unit for pressure is the pascal (Pa), equal to one newton per square meter (N/m2 or kg·m−1·s−2). This special name for the unit was added in 1971;[3] before that, pressure in SI was expressed simply as N/m2.
Fluid pressure is the pressure at some point within a fluid, such as water or air.
Fluid pressure occurs in one of two situations: 1. an open condition, called "open channel flow" 1. the ocean, or 2. swimming pool, or 3. the atmosphere. 2. a closed condition, called closed conduits 1. water line, or 2. gas line.
Stagnation pressure is the pressure a fluid exerts when it is forced to stop moving. Consequently,
although a fluid moving at higher speed will have a lower static pressure, it may have a higher stagnation pressure when forced to a standstill. Static pressure 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 (note: Bernoulli's equation only applies for incompressible, inviscid flow). The pressure of a moving fluid can be measured using a Pitot tube, 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 pressures or stagnation pressures.
Surface pressur
There is a two-dimensional analog of pressure – the lateral force per unit length applied on a line perpendicular to the force.Surface pressure is denoted by π and shares many similar properties with threedimensional pressure. Properties of surface chemicals can be investigated by measuring pressure/area isotherms, as the two-dimensional analog of Boyle's law, πA = k, at constant temperature.
Pressure of an ideal gas
Main article: Ideal gas law In an ideal gas, molecules have no volume and do not interact. Pressure varies linearly with temperature, volume, and quantity according to the ideal gas law,
where: P is the absolute pressure of the gas n is the amount of substance T is the absolute temperature V is the volume R is the ideal gas constant. Real gases exhibit a more complex dependence on the variables of state.
Vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its
condensed phases in a closed system. All liquids and solidshave a tendency to evaporate into a gaseous form, and all gases have a tendency to condense back to their liquid or solid form. The atmospheric pressure boiling point of a liquid (also known as the normal boiling point) is the temperature at which the vapor pressure equals the ambient atmospheric pressure. With any incremental increase in that temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form vapor bubbles inside the bulk of the substance. Bubble formation deeper in the liquid requires a higher pressure, and therefore higher temperature, because the fluid pressure increases above the atmospheric pressure as the depth increases.
The vapor pressure that a single component in a mixture contributes to the total pressure in the system is called partial vapor pressure. Liquid pressure or pressure at depth
Used with liquid columns of constant density or at a depth within a substance (example: pressure at 20 km depth in the Earth).
P = ρgh
where: P is Pressure g is gravity at the surface of overlaying material ρ is density of liquid or overlaying material h is height of liquid or depth within a substance
Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air
above that surface. In the diagram below, the pressure at point "X" increases as the weight of the air above it increases. The same can be said about decreasing pressure, where the pressure at point "X" decreases if the weight of the air above it also decreases.
Thinking in terms of air molecules, if the number of air molecules above a surface increases, there are more molecules to exert a force on that surface and consequently, the pressure increases. The opposite is also true, where a reduction in the number of air molecules above a surface will result in a decrease in pressure. Atmospheric pressure is measured with an instrument called a "barometer", which is why atmospheric pressure is also referred to as barometric pressure.
In aviation and television weather reports, pressure is given in inches of mercury ("Hg), while meteorologists use millibars (mb), the unit of pressure found on weather maps
T sea level standard temperature 288.15 K P sea level standard atmospheric pressure 101325 Pa M molar mass of dry air 0.0289644 kg/mol g Earth-surface gravitational acceleration 9.80665 m/s2
Dynamic pressure is a defined property of a moving flow of gas or liquid and can be expressed as.
where (using SI units): q = dynamic pressure in pascals ρ = fluid density in kg/m3 (such as the density of air) v = fluid velocity in m/s
Partial pressure refers to the pressure exerted by an individual gas in a mixture of
gasses.
Pressure sensor measures pressure, typically of gases or liquids. Pressure is an expression
of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical. Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators and piezometers, manometers, among other names.
Static pressure is the pressure that is exerted by a liquid or gas, such as water or air.
Specifically, it is the pressure measured when the liquid or gas is still, or at rest. Several different industrial and scientific applications exist for this term, but most have to do with air pressure rather than water pressure. In aviation, for example, a static pressure system is how a plane's altimeter and airspeed indicator operate. In construction, it refers to thepressure which a fan must exert in a ventilation system in order to cause air to flow. The concept of static pressure is also an essential one in the science of fluid mechanics. Scientifically, static pressure is distinguished from dynamic pressure, both of which are components of a system's total pressure. This relationship is defined in Bernoulli's equation, and relates to the study of the flow and motion of fluids. The principle of Bernoulli's equation is that static pressure and dynamic pressure may vary greatly in different areas of a fluid in motion, but the total pressure remains constant.
Water pressure is a term used to describe the flow strength of water through a pipe or
other type of channel. Water pressure depends on water flow. The more water being pushed through a pipe, the more pressure there will be naturally.
Absolute pressure sensor
This sensor measures the pressure relative to perfect vacuum pressure (0 PSI or no pressure). Atmospheric pressure, is 101.325 kPa (14.7 PSI) at sea level with reference to vacuum.
Gauge pressure sensor
This sensor is used in different applications because it can be calibrated to measure the pressure relative to a given atmospheric pressure at a given location. A tire pressure gauge is an example of gauge pressure indication. When the tire pressure gauge reads 0 PSI, there is really 14.7 PSI (atmospheric pressure) in the tire.
Vacuum pressure sensor
This sensor is used to measure pressure less than the atmospheric pressure at a given location. This has the potential to cause some confusion as industry may refer to a vacuum sensor as one which is referenced to either atmospheric pressure (i.e. measure Negative gauge pressure) or relative to absolute vacuum.
molecule refers to two or more atoms which have chemically combined to form a single
species.
compound is a chemical species that is formed when two or more atoms join together
chemically, with covalent or ionic bonds.
ATOMis a particle of matter that uniquely defines achemical element. An atom consists of a
central nucleus that is usually surrounded by one or more electrons. Eachelectron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons. A proton is positively charged. The number of protons in the nucleus ofan atom is the atomic number for the chemical element. A proton has a rest mass, denoted mp, of approximately 1.673 x 10-27 kilogram (kg). A neutron is electrically neutral and has a rest mass, denoted mn, of approximately 1.675 x 10-27 kg. The mass of a proton or neutron increases when the particle attains extreme speed, for example in a cyclotron or linear accelerator.
Ion: An atom or a group of atoms that has acquired a net electric charge by gaining or losing
one or more electrons.
macromolecule is a very large molecule commonly created by some form
ofpolymerization.The constituent molecules from which macromolecules are assembled are calledmonomers
Nobel Gas: The noble gases are a group of chemical elements with very similar properties:
under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).
Chemical bonding:
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of adipole attraction.
Inonic and covelent bond:
A molecule or compound is made when two or more atoms form a chemical bond, linking them together. The two types of bonds are ionic bonds and covalent bonds. In an ionic bond, the atoms are bound together by the attraction between oppositely-charged ions. For example, sodium and chloride form an ionic bond, to make NaCl, or table salt. In a covalent bond, the atoms are bound by shared electrons. If the electron is shared equally between the atoms forming a covalent bond, then the bond is said to be nonpolar. Usually, an electron is more attracted to one atom than to another, forming a polar covalent bond. For example, the atoms in water, H2O, are held together by polar covalent bonds.
chemical compound is a pure chemical substance consisting of two or more
different chemical elements[1][2][3] that can be separated into simpler substances by chemical
reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together in a defined spatial arrangement by chemical bonds.
