$Revision: 1398 $ An ontology about physical quantities and the expression of their magnitude in a chosen unit of measure. The QUDT Ontologies are issued under a Creative Commons Attribution Share Alike 3.0 United States License. Attribution should be made to NASA AMES Research Center and TopQuadrant, Inc. Quantity The NASA NExIOM Quantity Ontology Measurable Quantities James E. Masters $Id: n1quantity.n3 1398 2009-09-03 20:36:42Z cmasters $ $Date: 2009-09-03 22:36:42 +0200 (Thu, 03 Sep 2009) $ Energy per Electric Charge Electrostatic Potential σ Electrical Conductivity Inductance E Electric Field M Mass The electromagnetic system of units is used to measure electrical quantities of electric charge, current, and voltage, within the centimeter gram second (or "CGS") metric system of units. In electromagnetic units, electric current is derived the CGS base units length, mass, and time by solving Ampere's Law (expressing the force between two parallel conducting wires) for current and setting the constant of proportionality (k_m) equal to unity. Thus, in the CGS-EMU system, electric current is derived from length, mass, and time. J J Electric Current Density Magnetic Flux per Unit Length Electric Flux Q Electric Charge Magnetic Flux T Time Time is a basic component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects. I Electric Current Electric Current is the flow (movement) of electric charge. The SI unit of electric current is the ampere (A), which is equal to a flow of one coulomb of charge per second. The amount of electric current (measured in amperes) through some surface, e.g., a section through a copper conductor, is defined as the amount of electric charge (measured in coulombs) flowing through that surface over time. Capacitance Permeability Permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Permittivity Permittivity is a physical quantity that describes how an electric field affects, and is affected by a dielectric medium, and is determined by the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material. M Electric Current per Unit Length M Magnetization Length per Unit Electric Current Electromotive Force U Dimensionless Electric Dipole Moment CGS-EMU System of Quantities B Magnetic flux density is the amount of magnetic flux per unit area of a section, perpendicular to the direction of flux. B Magnetic Flux Density Magnetic Dipole Moment The magnetic dipole moment quantifies the contribution of an electromagnetic system's (such as a loop of electric current, a bar magnet, an electron, a molecule, or a planet) internal magnetism to the external dipolar magnetic field produced by the system (i.e. the component of the external magnetic field that drops off with distance as the inverse cube). H Magnetic Field D Electric Charge per Unit Area D Electric Flux Density Magnetomotive Force Magnetomotive Force is the ability of an electric circuit to produce magnetic flux. Just as the ability of a battery to produce electric current is called its electromotive force or emf, mmf is taken as the work required to move a unit magnet pole from any point through any path which links the electric circuit back the same point in the presence of the magnetic force produced by the electric current in the circuit. Resistance L Length Density Absolute Humidity Absolute humidity is the mass of water in a particular volume of air. It is a measure of the density of water vapor in an atmosphere. Force Per Area Energy Density Energy density is defined as energy per unit volume. The SI unit for energy density is the joule per cubic meter. Power Power is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time. As a rate of change of work done or the energy of a subsystem, power is: P = W/t where P is power W is work t is time. [Wikipedia] Currency Thermal Resistivity The reciprocal of thermal conductivity is thermal resistivity, measured in kelvin-metres per watt (K*m/W). Z ψ Dimensionless Ratio Compressibility Factor The compressibility factor (Z) is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behaviour. The closer a gas is to a phase change, the larger the deviations from ideal behavior. Values for compressibility are calculated using equations of state (EOS), such as the virial equation and van der Waals equation. The compressibility factor for specific gases can be obtained, with out calculation, from compressibility charts. These charts are created by plotting Z as a function of pressure at constant temperature. Thrust to Mass Ratio Power per Area Angle Absorbed Dose Rate Electric Charge per Amount of Substance Mass per Length Heat Flow Rate per Unit Area Mass per Time International System of Quantities Volume The volume of a solid object is the three-dimensional concept of how much space it occupies, often quantified numerically. One-dimensional figures (such as lines) and two-dimensional shapes (such as squares) are assigned zero volume in the three-dimensional space. Volumetric Heat Capacity Temperature Amount of Substance Electric Charge per Mass Specific Heat Volume Specific heat per constant volume. Velocity Linear Velocity Specific Impulse by Mass Specific Heat Pressure Specific heat at a constant pressure. Coefficient of Heat Transfer Linear Thermal Expansion When the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds. As a result, solids typically expand in response to heating and contract on cooling; this dimensional response to temperature change is expressed by its coefficient of thermal expansion. Different coefficients of thermal expansion can be defined for a substance depending on whether the expansion is measured by: * linear thermal expansion * area thermal expansion * volumetric thermal expansion These characteristics are closely related. The volumetric thermal expansion coefficient can be defined for both liquids and solids. The linear thermal expansion can only be defined for solids, and is common in engineering applications. Some substances expand when cooled, such as freezing water, so they have negative thermal expansion coefficients. [Wikipedia] Power Area per Solid Angle Moment of Inertia Thermal Conductivity Specific Heat Capacity Catalytic Activity J Luminous Intensity Luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit. [Wikipedia] Momentum Quantity of motion. Linear momentum is the quantity obtained by multiplying the mass of a body by its linear speed. Angular momentum is the quantity obtained by multiplying the moment of inertia of a body by its angular speed. The momentum of a system of particles is given by the sum of the momentums of the individual particles which make up the system or by the product of the total mass of the system and the velocity of the center of gravity of the system. The momentum of a continuous medium is given by the integral of the velocity over the mass of the medium or by the product of the total mass of the medium and the velocity of the center of gravity of the medium. Angular Momentum Quantity of rotational motion. Linear momentum is the quantity obtained by multiplying the mass of a body by its linear speed. Angular momentum is the quantity obtained by multiplying the moment of inertia of a body by its angular speed. The momentum of a system of particles is given by the sum of the momentums of the individual particles which make up the system or by the product of the total mass of the system and the velocity of the center of gravity of the system. The momentum of a continuous medium is given by the integral of the velocity over the mass of the medium or by the product of the total mass of the medium and the velocity of the center of gravity of the medium. In physics, the angular momentum of an object rotating about some reference point is the measure of the extent to which the object will continue to rotate about that point unless acted upon by an external torque. In particular, if a point mass rotates about an axis, then the angular momentum with respect to a point on the axis is related to the mass of the object, the velocity and the distance of the mass to the axis. While the motion associated with linear momentum has no absolute frame of reference, the rotation associated with angular momentum is sometimes spoken of as being measured relative to the fixed stars. Mass per Area Temperature per Magnetic Flux Density Square Energy Frequency Frequency is the number of occurrences of a repeatiing event per unit time. The repetition of the events may be periodic (i.e. the length of time between event repetitions is fixed) or aperiodic (i.e. the length of time between event repetitions varies). Therefore, we distinguish between periodic and aperiodic frequencies. In the SI system, periodic frequency is measured in hertz (Hz) or multiples of hertz, while aperiodic frequency is measured in becquerel (Bq). Stochastic Process Activity Activity is the term used to characterise the number of nuclei which disintegrate in a radioactive substance per unit time. Activity is usually measured in Becquerels (Bq), where 1 Bq is 1 disintegration per second. Area Angle Length Mass Absorbed Dose Absorbed dose (also known as Total Ionizing Dose, TID) is a measure of the energy deposited in a medium by ionizing radiation. It is equal to the energy deposited per unit mass of medium, and so has the unit J/kg, which is given the special name Gray (Gy). Note that the absorbed dose is not a good indicator of the likely biological effect. 1 Gy of alpha radiation would be much more biologically damaging than 1 Gy of photon radiation for example. Appropriate weighting factors can be applied reflecting the different relative biological effects to find the equivalent dose. The risk of stoctic effects due to radiation exposure can be quantified using the effective dose, which is a weighted average of the equivalent dose to each organ depending upon its radiosensitivity. When ionising radiation is used to treat cancer, the doctor will usually prescribe the radiotherapy treatment in Gy. When risk from ionising radiation is being discussed, a related unit, the Sievert is used. Electric Quadrupole Moment Electric Current per Angle Time Squared Length Temperature Heat Flow Rate Mass per Electric Charge Power Area Energy per Square Magnetic Flux Density Thermal Insulance Inverse Volume Pressure or Stress Pressure or stress is a measure of the average amount of force exerted per unit area. Area Thermal Expansion When the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds. As a result, solids typically expand in response to heating and contract on cooling; this dimensional response to temperature change is expressed by its coefficient of thermal expansion. Different coefficients of thermal expansion can be defined for a substance depending on whether the expansion is measured by: * linear thermal expansion * area thermal expansion * volumetric thermal expansion These characteristics are closely related. The volumetric thermal expansion coefficient can be defined for both liquids and solids. The linear thermal expansion can only be defined for solids, and is common in engineering applications. Some substances expand when cooled, such as freezing water, so they have negative thermal expansion coefficients. [Wikipedia] Power per Angle Electric Current per Unit Energy Length Force Viscosity Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In general terms it is the resistance of a liquid to flow, or its "thickness". Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. [Wikipedia] Dynamic Viscosity Inverse Energy Luminance Concentration Amount of Substance per Unit Mass Area per Unit Tme Kinematic Viscosity Time Temperature Force Per Area Time N Amount of Substance Inverse Magnetic Flux Temperature per Time Energy per Area Power per Area Quartic Temperature Molar Mass Area Temperature Inverse Permittivity ν ν Specific Volume Specific volume (ν) is the volume occupied by a unit of mass of a material. It is equal to the inverse of density. Electric Charge Volume Density Gravitational Attraction Length per Unit Magnetic Flux Energy per Area Electric Charge Acceleration Acceleration is the (instantaneous) rate of change of velocity. Acceleration may be either linear acceleration, or angular acceleration. It is a vector quantity with dimension length/time^2 for linear acceleration, or in the case of angular acceleration, with dimension angle/time^2. In SI units, linear acceleration is measured in meters/second^2 (m·s^-2) and angular acceleration is measured in radians/second^2. In common speech, the term acceleration is only used for an increase in speed. In physics, any increase or decrease in speed is referred to as acceleration and similarly, motion in a circle at constant speed is also an acceleration, since the direction component of the velocity is changing. Linear Acceleration Length Energy Molar Heat Capacity Force per Unit Length Inverse Square Energy Inverse Amount of Substance Thermal Resistance Cubic Electric Dipole Moment per Square Energy Length Molar Energy Exposure Entropy Entropy is a measure of the unavailability of a system’s energy to do work. It is a measure of the randomness of molecules in a system and is central to the second law of thermodynamics and the fundamental thermodynamic relation, which deal with physical processes and whether they occur spontaneously. Spontaneous changes, in isolated systems, occur with an increase in entropy. Spontaneous changes tend to smooth out differences in temperature, pressure, density, and chemical potential that may exist in a system, and entropy is thus a measure of how far this smoothing-out process has progressed. It can be seen that the dimensions of entropy are energy divided by temperature, which is the same as the dimensions of Boltzmann's constant (kB) and heat capacity. The SI unit of entropy is joule per kelvin. [Wikipedia] Heat Capacity and Entropy Specific Energy Power per Area Electric Charge Line Density Angular Acceleration Angular acceleration is the rate of change of angular velocity over time. Measurement of the change made in the rate of change of an angle that a spinning object undergoes per unit time. It is a vector quantity. Also called Rotational acceleration. In SI units, it is measured in radians per second squared (rad/s^2), and is usually denoted by the Greek letter alpha. Amount of Substance Per Unit Volume Volume per Unit Time Mass per Area Time Angle The inclination to each other of two intersecting lines, measured by the arc of a circle intercepted between the two lines forming the angle, the center of the circle being the point of intersection. An acute angle is less than 90°; a right angle 90 °; an obtuse angle, more than 90° but less than 180 °; a straight angle, 180°; a reflex angle, more than 180° but less than 360°; a perigon, 360°. Any angle not a multiple of 90° is an oblique angle. If the sum of two angles is 90°, they are complementary angles; if 180°, supplementary angles; if 360°, explementary angles. Two adjacent angles have a common vertex and lie on opposite sides of a common side. A dihedral angle is the angle between two intersecting planes. A spherical angle is the angle between two intersecting great circles. Solid Angle The solid angle subtended by a surface S is defined as the surface area of a unit sphere covered by the surface S's projection onto the sphere. A solid angle is related to the surface of a sphere in the same way an ordinary angle is related to the circumference of a circle. Since the total surface area of the unit sphere is 4*pi, the measure of solid angle will always be between 0 and 4*pi. Luminous Flux Force Force is an influence that causes mass to accelerate. It may be experienced as a lift, a push, or a pull. Force is defined by Newton's Second Law as F = m · a, where F is force, m is mass and a is acceleration. Net force is mathematically equal to the time rate of change of the momentum of the body on which it acts. Since momentum is a vector quantity (has both a magnitude and direction), force also is a vector quantity. Linear Momentum Linear momentum is the product of mass and linear velocity. The SI unit for linear momentum is meter-kilogram per second (m-kg/s). Volume Thermal Expansion When the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds. As a result, solids typically expand in response to heating and contract on cooling; this dimensional response to temperature change is expressed by its coefficient of thermal expansion. Different coefficients of thermal expansion can be defined for a substance depending on whether the expansion is measured by: * linear thermal expansion * area thermal expansion * volumetric thermal expansion These characteristics are closely related. The volumetric thermal expansion coefficient can be defined for both liquids and solids. The linear thermal expansion can only be defined for solids, and is common in engineering applications. Some substances expand when cooled, such as freezing water, so they have negative thermal expansion coefficients. [Wikipedia] Thermal Diffusivity Mass Temperature Molar Energy Energy and Work Inverse Length V_m Molar Volume μ Standard Gravitational Parameter Polarizability Force per Electric Charge Inverse Time Temperature Electric Charge Area Density Dose Equivalent Inverse Length Temperature Plane Angle Θ Temperature Area Area is a quantity expressing the two-dimensional size of a defined part of a surface, typically a region bounded by a closed curve. Quartic Electric Dipole Moment per Cubic Energy Angular Velocity The change of angle per unit time; specifically, in celestial mechanics, the change in angle of the radius vector per unit time. Power per Electric Charge Illuminance Molar Angular Momentum Atomic Charge Thermal Energy Length Γ In fluid dynamics, circulation is the line integral around a closed curve of the fluid velocity. It has dimensions of length squared over time. Circulation Respiratory Rate Length Temperature Time First Moment of Area The first moment of area is the summation of area times distance to an axis. It is a measure of the distribution of the area of a shape in relationship to an axis. Thermal Energy Video Frame Rate Serum or Plasma Level Thrust Thrust is a reaction force described quantitatively by Newton's Second and Third Laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a proportional but opposite force on that system. 1. The pushing or pulling force developed by an aircraft engine or a rocket engine. 2. The force exerted in any direction by a fluid jet or by a powered screw, as, the thrust of an antitorque rotor. 3. (symbol F). Specifically, in rocketry, F = mv where m is propellant mass flow and v is exhaust velocity relative to the vehicle. Also called momentum thrust. Specific Impulse by Weight Mass Amount of Substance Temperature Enthalpy Static enthalpy per unit mass. The specific enthalpy of a working mass is a property of that mass used in thermodynamics, defined as h=u+p . v where u is the specific internal energy, p is the pressure, and v is specific volume. In other words, h = H / m where m is the mass of the system. The SI unit for specific enthalpy is joules per kilogram. [Wikipedia] Mole Fraction In chemistry, the mole fraction of a component in a mixture is the relative proportion of molecules belonging to the component to those in the mixture, by number of molecules. It is one way of measuring concentration. Heat Capacity Ratio The heat capacity ratio, or ratio of specific heats, is the ratio of the heat capacity at constant pressure (C_P) to heat capacity at constant volume (C_V). For an ideal gas, the heat capacity is constant with temperature (Θ). Accordingly we can express the enthalpy as H = C_P*Θ and the internal energy as U = C_V*Θ. Thus, it can also be said that the heat capacity ratio is the ratio between enthalpy and internal energy Reynolds Number The Reynolds number (Re) is a dimensionless number defined as the ratio of inertial forces to viscous forces and, consequently, it quantifies the relative importance of these two types of forces for given flow conditions. Q Pressure Dynamic Pressure In fluid dynamics dynamic pressure (indicated with q, or Q, and sometimes called velocity pressure) is the quantity defined by: q = 1/2 * ρv^2 where (using SI units): q = dynamic pressure in pascals ρ = fluid density in kg/m3 (e.g. density of air) v = fluid velocity in m/s Heat Energy transferred by a thermal process. Heat can be measured in terms of the dynamical units of energy, as the erg, joule, etc., or in terms of the amount of energy required to produce a definite thermal change in some substance, as, for example, the energy required per degree to raise the temperature of a unit mass of water at some temperature ( calorie, Btu). Data Rate The frequency derived from the period of time required to transmit one bit. This represents the amount of data transferred per second by a communications channel or a computing or storage device. Data rate is measured in units of bits per second (written "b/s" or "bps"), bytes per second (Bps), or baud. When applied to data rate, the multiplier prefixes "kilo-", "mega-", "giga-", etc. (and their abbreviations, "k", "M", "G", etc.) always denote powers of 1000. For example, 64 kbps is 64,000 bits per second. This contrasts with units of storage which use different prefixes to denote multiplication by powers of 1024, e.g. 1 kibibit = 1024 bits. Molecular Viscosity Linear Energy Transfer Curvature The canonical example of extrinsic curvature is that of a circle, which has curvature equal to the inverse of its radius everywhere. Smaller circles bend more sharply, and hence have higher curvature. The curvature of a smooth curve is defined as the curvature of its osculating circle at each point. The osculating circle of a sufficiently smooth plane curve at a given point on the curve is the circle whose center lies on the inner normal line and whose curvature is the same as that of the given curve at that point. This circle is tangent to the curve at the given point. That is, given a point P on a smooth curve C, the curvature of C at P is defined to be 1/R where R is the radius of the osculating circle of C at P. The magnitude of curvature at points on physical curves can be measured in diopters (also spelled dioptre) — this is the convention in optics. [Wikipedia] Mass Amount of Substance Planck System of Quantities Atmospheric Pressure The pressure exerted at a point due to the presence of an atmosphere. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location. Similarly, as elevation increases there is less overlying atmospheric mass, so that pressure decreases with increasing elevation. [Wikipedia] Signal Strength In telecommunications, particularly in radio, signal strength refers to the magnitude of the electric field at a reference point that is a significant distance from the transmitting antenna. It may also be referred to as received signal level or field strength. Typically, it is expressed in voltage per length or signal power received by a reference antenna. High-powered transmissions, such as those used in broadcasting, are expressed in dB-millivolts per metre (dBmV/m). [Wikipedia] RF-Power Heart Rate Information Capacity or Entropy Gain A general term used to denote an increase in signal power or signal strength in transmission from one point to another. Gain is usually expressed in decibels and is widely used to denote transducer gain. An increase or amplification. In radar there are two general usages of the term: (a) antenna gain, or gain factor, is the ratio of the power transmitted along the beam axis to that of an isotropic radiator transmitting the same total power; (b) receiver gain, or video gain, is the amplification given a signal by the receiver. u Strain Energy Density Potential Energy Energy possessed by a body by virtue of its position in a gravity field in contrast with kinetic energy, that possessed by virtue of its motion. γ Gyromagnetic Ratio Weight 1. The force with which a body is attracted toward an astronomical body. 2. The product of the mass of a body and the acceleration acting on a body. In a dynamic situation, the weight can be a multiple of that under resting conditions. Weight also varies on other planets in accordance with their gravity. CGS-ESU System of Quantities The electrostatic system of units is used to measure electrical quantities of electric charge, current, and voltage within the centimeter gram second (or "CGS") metric system of units. In electrostatic units, electric charge is derived from Coulomb's Law (expressing the force exerted between two charged particles separated by a distance) by solving for electric charge and setting the constant of proportionality (k_s) equal to unity. Thus, in electrostatic units, the dimensionality of electric charge is derived from the base CGS quantities of length, mass, and time. Area Time Temperature Energy and Work per Mass Amount of Substance Electrical Power Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt. P = VI where P is the power (watt or W) V is the potential difference (volt or V) I is the current (ampere or A). Area Time CGS System of Quantities Turbidity Turbidity is the cloudiness or haziness of a fluid, or of air, caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air. Turbidity in open water is often caused by phytoplankton and the measurement of turbidity is a key test of water quality. The higher the turbidity, the higher the risk of the drinkers developing gastrointestinal diseases, especially for immune-compromised people, because contaminants like virus or bacteria can become attached to the suspended solid. The suspended solids interfere with water disinfection with chlorine because the particles act as shields for the virus and bacteria. Similarly suspended solids can protect bacteria from UV sterilisation of water. Fluids can contain suspended solid matter consisting of particles of many different sizes. While some suspended material will be large enough and heavy enough to settle rapidly to the bottom container if a liquid sample is left to stand (the settleable solids), very small particles will settle only very slowly or not at all if the sample is regularly agitated or the particles are colloidal. These small solid particles cause the liquid to appear turbid. CGS-Gauss System of Quantities Mach Number Mach number (Ma) is the speed of an object moving through air, or any fluid substance, divided by the speed of sound as it is in that substance: M = V_o/V_s where M is the Mach number V_o is the velocity of the object relative to the medium and V_s is the velocity of sound in the medium The Mach number is commonly used both with objects traveling at high speed in a fluid, and with high-speed fluid flows inside channels such as nozzles, diffusers or wind tunnels. As it is defined as a ratio of two speeds, it is a dimensionless number. [Wikipedia] Second Moment of Area The second moment of area is a property of a physical object that can be used to predict its resistance to bending and deflection. The deflection of an object under load depends not only on the load, but also on the geometry of the object's cross-section. Polar moment of inertia The polar moment of inertia is a quantity used to predict an object's ability to resist torsion, in objects (or segments of objects) with an invariant circular cross-section and no significant warping or out-of-plane deformation. It is used to calculate the angular displacement of an object subjected to a torque. It is analogous to the area moment of inertia, which characterizes an object's ability to resist bending. Torque In physics, a torque (τ) is a vector that measures the tendency of a force to rotate an object about some axis [1]. The magnitude of a torque is defined as force times its lever arm [2]. Just as a force is a push or a pull, a torque can be thought of as a twist. The SI unit for torque is newton meters (N m). In U.S. customary units, it is measured in foot pounds (ft lbf) (also known as 'pounds feet'). Mathematically, the torque on a particle (which has the position r in some reference frame) can be defined as the cross product: τ = r x F where r is the particle's position vector relative to the fulcrum F is the force acting on the particles, or, more generally, torque can be defined as the rate of change of angular momentum, τ = dL/dt where L is the angular momentum vector t stands for time. [Wikipedia] Signal Detection Threshold Kinetic Energy Internal Energy n In physics, astronomy, and chemistry, number density (symbol: n) is a kind of quantity used to describe the degree of concentration of countable objects (atoms, molecules, dust particles, galaxies, etc.) in the three-dimensional physical space. Number Density US Customary System of Quantities Liquid Volume Dry Volume M Molecular Mass The molecular mass, or molecular weight of a chemical compound is the mass of one molecule of that compound, relative to the unified atomic mass unit, u. Molecular mass should not be confused with molar mass, which is the mass of one mole of a substance. Friction Friction is the force of two surfaces In contact, or the force of a medium acting on a moving object (i.e. air on an aircraft). When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy. Speed Speed is the magnitude of velocity. Kinetic Energy The energy which a body possesses as a consequence of its motion, defined as one-half the product of its mass m and the square of its speed v, 1/2 mv^2. The kinetic energy per unit volume of a fluid parcel is the 1/2 p v2 , where p is the density and v the speed of the parcel. See potential energy. For relativistic speeds the kinetic energy is given by Ek = mc^2 - m0c^2 where c is the velocity of light in a vacuum, m0 is the rest mass, and m is the moving mass. Force Magnitude Tension Tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. It is the opposite of compression. Thermal Efficiency Thermal efficiency is a dimensionless performance measure of a thermal device such as an internal combustion engine, a boiler, or a furnace. The input to the device is heat, or the heat-content of a fuel that is consumed. The desired output is mechanical work, or heat, or possibly both. Strain In any branch of science dealing with materials and their behaviour, strain is the geometrical expression of deformation caused by the action of stress on a physical body. Strain is calculated by first assuming a change between two body states: the beginning state and the final state. Then the difference in placement of two points in this body in those two states expresses the numerical value of strain. Strain therefore expresses itself as a change in size and/or shape. [Wikipedia] ω Angular Frequency Angular frequency is a scalar measure of rotation rate. It is the magnitude of the vector quantity angular velocity. Microbial Formation TBD Capacity In computer operations, (a) the largest quantity which can be stored, processed, or transferred; (b) the largest number of digits or characters which may regularly be processed; (c) the upper and lower limits of the quantities which may be processed. In other contexts, the amount of material that can be stored, such as fuel or food. h 0.00000033E-27 6.62606885E-27 CGSValue_Planck constant 0.00000033E-34 5.0E-8 6.62606896E-34 SIValue_PlanckConstant S S Action Planck constant The Planck constant (denoted h), is a physical constant used to describe the sizes of quanta in quantum mechanics. μ_B Bohr magneton The Bohr Magneton (symbol μB) is a physical constant of magnetic moment of electrons. SI units for this constant are Joule per Tesla. 0.000023E-24 2.5E-8 9.27400915E-24 SIValue_BohrMagneton Z_0 Characteristic impedance The impedance of free space, Z_0 is a physical constant with a defined (not measured) value that relates the magnitudes of the electric and magnetic fields of electromagnetic radiation travelling through free space. 376.73031346177 SIValue_CharacteristicImpedance N_A Avogadro constant The Avogadro constant, also called Avogadro's number, is the number of "elementary entities" (usually atoms or molecules) in one mole. That is (from the definition of the mole), the Avogadro constant is the number of atoms in exactly 12 grams of carbon-12. 0.00000030E23 5.0E-8 6.02214179E23 SIValue_Avogadro constant G Newtonian gravity constant The gravitational constant, denoted G, is an empirical physical constant involved in the calculation of the gravitational attraction between objects with mass. 0.00067E-11 1.0E-4 6.67428E-11 SIValue_UniversalGravityConstant α Fine structure constant The fine-structure constant is a fundamental physical constant which characterizes the strength of the electromagnetic interaction. The numerical value of α is the same in all systems of units, because α is a dimensionless quantity. 0.0000000050E-3 6.8E-10 7.2973525376E-3 SIValue_FineStructureConstant c Speed of light The speed of light in free space is a physical constant defined as 299,792,458 metres per second. 299792458 SIValue_SpeedOfLight μ0 12.566370614E-7 SIValue_MagneticConstant Magnetic constant The magnetic constant, μ0, is the permeability of free space (vacuum). In SI, the magnetic constant is expressed in units of henry per meter. k_B 0.000024E-23 1.7E-6 1.3806504E-23 SIValue_Boltzmann constant Boltzmann constant The Boltzmann constant is the physical constant relating energy at the particle level with temperature observed at the bulk level. It has dimensions of entropy. ε0 Electric Constant The electric constant, ε0, is the permittivity of free space (vacuum). In SI, the electric constant is expressed in units of farad per meter. 8.854187817E-12 SIValue_ElectricConstant k_e 8.9875517873681764E9 SIValue_CoulombConstant Coulomb constant The Coulomb Constant is the constant of proportionality in Coulomb's Law. R 0.000015 1.7E-6 8.314472 SIValue_Ideal gas constant Ideal Gas Constant The gas constant (also known as the molar, universal, or ideal gas constant, usually denoted by symbol R) is a physical constant which is featured in a large number of fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation. It is equivalent to the Boltzmann constant, but expressed in units of energy (i.e. the pressure-volume product) per kelvin per mole (rather than energy per kelvin per particle). Its value in SI units is: R = 8.314472(15) J · K^(-1) · mol^(-1) The two digits in parentheses are the uncertainty (standard deviation) in the last two digits of the value. e Elementary charge The elementary charge is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. To avoid confusion over its sign, e is sometimes called the "elementary positive charge". 0.000000040E-19 2.5E-8 1.602176487E-19 SIValue_ElementaryCharge F Faraday constant The Faraday constant (named after Michael Faraday) is the magnitude of electric charge per mole of electrons. While most uses of the Faraday constant, denoted F, have been replaced by the standard SI unit, the coulomb, the Faraday is still widely used in calculations in electrochemistry. 0.0024 2.5E-8 96485.3399 SIValue_Faraday constant