Units Concept Scheme based on QUDT version 3.1.6

Concepts

Label	Definition	Actions
acceleration 0112/2///62720#UAD002	$\textit{Acceleration}$ 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 $angle/time^{2}$. $$$$ In SI units, linear acceleration is measured in $meters/second^{2}$ ($m \cdot s^{-2}$), and angular acceleration is measured in $radians/second^{2}$. $$$$ 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.	View
Acidity	Chemicals or substances having a pH less than 7 are said to be acidic; lower pH means higher acidity.	View
Activity A	$\textit{Activity}$ is the number of decays per unit time of a radioactive sample, 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, in honor of the scientist Henri Becquerel.	View
amount of substance n	$\textit{Amount of Substance}$ is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units (SI) defines the amount of substance to be proportional to the number of elementary entities present. The SI unit for amount of substance is mole. It has the unit symbol $mol$. The mole is defined as the amount of substance that contains an equal number of elementary entities as there are atoms in 0.012kg of the isotope carbon-12. This number is called Avogadro's number and has the value $6.02214179(30) \times 10^{23}$. The only other unit of amount of substance in current use is the $pound-mole$ with the symbol $lb-mol$, which is sometimes used in chemical engineering in the United States. One $pound-mole$ is exactly $453.59237 mol$.	View
Angle	The abstract notion of angle. Narrow concepts include plane angle and solid angle. While both plane angle and solid angle are dimensionless, they are actually length/length and area/area respectively.	View
angular velocity 0112/2///62720#UAD009	Angular Velocity refers to how fast an object rotates or revolves relative to another point.	View
area 0112/2///62720#UAD182	Area is a quantity expressing the two-dimensional size of a defined part of a surface, typically a region bounded by a closed curve.	View
area per length	No definition available	View
Area per Time	No definition available	View
Concentration	In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Furthermore, in chemistry, four types of mathematical description can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration. The term concentration can be applied to any kind of chemical mixture, but most frequently it refers to solutes in solutions.	View
Conductivity 0112/2///62720#UAD025	$\textit{Conductivity}$ is a scalar or tensor quantity the product of which by the electric field strength in a medium is equal to the electric current density. For an isotropic medium the conductivity is a scalar quantity; for an anisotropic medium it is a tensor quantity. $$\mathbf{J} = \sigma \mathbf{E}$$ Where $\mathbf{J}$ is electric current density, and $\mathbf{E}$ is electric field strength.	View
Count	"Count" is the value of a count of items.	View
Density 0112/2///62720#UAD029	The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is $\rho$. Mathematically, density is defined as mass divided by volume: $\rho = m/V$, where $\rho$ is the density, $m$ is the mass, and $V$ is the volume. In some cases, density is also defined as its weight per unit volume, although this quantity is more properly called specific weight.	View
Dimensionless Ratio	No definition available	View
efficiency	Efficiency is the ratio of output power to input power.	View
electric charge 0112/2///62720#UAD037	"Electric Charge" is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The electric charge on a body may be positive or negative. Two positively charged bodies experience a mutual repulsive force, as do two negatively charged bodies. A positively charged body and a negatively charged body experience an attractive force. Electric charge is carried by discrete particles and can be positive or negative. The sign convention is such that the elementary electric charge $e$, that is, the charge of the proton, is positive. The SI derived unit of electric charge is the coulomb.	View
electric current I	The quantity kind $\textit{Electric Current}$ is the flow (movement) of electric charge. The amount of electric current through some surface, for example, a section through a copper conductor, is defined as the amount of electric charge flowing through that surface over time. Current is a scalar-valued quantity. Electric current is one of the base quantities in the International System of Quantities, ISQ, on which the International System of Units, SI, is based.	View
energy E	Energy is the quantity characterizing the ability of a system to do work.	View
Energy Density 0112/2///62720#UAD047	Energy density is defined as energy per unit volume. The SI unit for energy density is the joule per cubic meter.	View
enthalpy H	In thermodynamics, $\textit{enthalpy}$ is the sum of the internal energy $U$ and the product of pressure $p$ and volume $V$ of a system. The characteristic function (also known as thermodynamic potential) $\textit{enthalpy}$ used to be called $\textit{heat content}$, which is why it is conventionally indicated by $H$. The specific enthalpy of a working mass is a property of that mass used in thermodynamics, defined as $h=u+p \cdot 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 $\textit{Specific Enthalpy}$ is $\textit{joules per kilogram}$	View
entropy S	When a small amount of heat $dQ$ is received by a system whose thermodynamic temperature is $T$, the entropy of the system increases by $dQ/T$, provided that no irreversible change takes place in the system.	View
Equivalent Density	"Equivalent Density" is the mass of a substance that reacts with (or is equivalent to) an arbitrary mass of another substance in a given chemical reaction, per volume.	View
Flux	Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. [Wikipedia]	View
force F	"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 \times 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.	View
frequency 0112/2///62720#UAD056	"Frequency" is the number of occurrences of a repeating event per unit time. The repetition of the events may be periodic (that is. 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). In spectroscopy, $\nu$ is mostly used. Light passing through different media keeps its frequency, but not its wavelength or wavenumber.	View
heat Q	"Heat" is the 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).	View
Inverse Length	Reciprocal length or inverse length is a measurement used in several branches of science and mathematics. As the reciprocal of length, common units used for this measurement include the reciprocal metre or inverse metre ($m^{-1}$), the reciprocal centimetre or inverse centimetre ($cm^{-1}$), and, in optics, the dioptre.	View
reciprocal mass 0112/2///62720#UAD157	No definition available	View
irradiance 0112/2///62720#UAD068	Irradiance and Radiant Emittance are radiometry terms for the power per unit area of electromagnetic radiation at a surface. "Irradiance" is used when the electromagnetic radiation is incident on the surface. "Radiant emmitance" (or "radiant exitance") is used when the radiation is emerging from the surface.	View
length l	In geometric measurements, length most commonly refers to the longest dimension of an object. In some contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured.	View
Length Mass	No definition available	View
Linear Force 0112/2///62720#UAD077	Another name for Force Per Length, used by the Industry Foundation Classes (IFC) standard.	View
Logarithm of Octanol Water Partition Coefficient	A dimensionless ratio that is the logarithm of the ratio of a compound's concentration within a two phase mixture of octanol and water at equilibrium. More simply, it is a comparison of the solubilities of the compound solute in these two immiscible liquids. This property is used to measure the lipophilicity and the hydrophilicity of a substance.	View
Magnetic Field B	The Magnetic Field, denoted $B$, is a fundamental field in electrodynamics which characterizes the magnetic force exerted by electric currents. It is closely related to the auxillary magnetic field H (see quantitykind:AuxillaryMagneticField).	View
mass m	In physics, mass, more specifically inertial mass, can be defined as a quantitative measure of an object's resistance to acceleration. The SI unit of mass is the kilogram ($kg$)	View
Mass Concentration	The "Mass Concentration" of substance B is defined as the mass of a constituent divided by the volume of the mixture .	View
Mass per Energy	Mass per Energy ($m/E$) is a physical quantity that bridges mass and energy. The SI unit is $kg/J$ or equivalently $s^2/m^2$.	View
Mass per Length	Linear density, linear mass density or linear mass is a measure of mass per unit of length, and it is a characteristic of strings or other one-dimensional objects. The SI unit of linear density is the kilogram per metre ($kg/m$).	View
Mass per Time	No definition available	View
Mass Ratio 0112/2///62720#UAD109	In aerospace engineering, mass ratio is a measure of the efficiency of a rocket. It describes how much more massive the vehicle is with propellant than without; that is, it is the ratio of the rocket's wet mass (vehicle plus contents plus propellant) to its dry mass (vehicle plus contents)	View
molar mass M	In chemistry, the molar mass M is defined as the mass of a given substance (chemical element or chemical compound) divided by its amount of substance. It is a physical property of a given substance. The base SI unit for molar mass is $kg/mol$.	View
moment of inertia 0112/2///62720#UAD128	The rotational inertia or resistance to change in direction or speed of rotation about a defined axis.	View
momentum p	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.	View
Number Density 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.	View
Population	Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world, but can also represent the number of any kind of entity.	View
power P	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 and {t} is time.	View
pressure 0112/2///62720#UAD142	Pressure is an effect which occurs when a force is applied on a surface. Pressure is the amount of force acting on a unit area. Pressure is distinct from stress, as the former is the ratio of the component of force normal to a surface to the surface area. Stress is a tensor that relates the vector force to the vector area.	View
ratio 0112/2///62720#UAD154	No definition available	View
Resistance R	The electrical resistance of an object is a measure of its opposition to the passage of a steady electric current.	View
Sound intensity I	Sound intensity or acoustic intensity ($I$) is defined as the sound power $P_a$ per unit area $A$. The usual context is the noise measurement of sound intensity in the air at a listener's location as a sound energy quantity.	View
Specific Energy e	$\textit{Specific Energy}$ is defined as the energy per unit mass. Common metric units are $J/kg$. It is an intensive property. Contrast this with energy, which is an extensive property. There are two main types of specific energy: potential energy and specific kinetic energy. Others are the $\textit{gray}$ and $\textit{sievert}$, which are measures for the absorption of radiation. $$$$ The concept of specific energy applies to a particular or theoretical way of extracting useful energy from the material considered that is usually implied by context. These intensive properties are each symbolized by using the lower case letter of the symbol for the corresponding extensive property, which is symbolized by a capital letter. For example, the extensive thermodynamic property enthalpy is symbolized by $H$; specific enthalpy is symbolized by $h$.	View
Stoichiometric Number	Chemical reactions, as macroscopic unit operations, consist of simply a very large number of elementary reactions, where a single molecule reacts with another molecule. As the reacting molecules (or moieties) consist of a definite set of atoms in an integer ratio, the ratio between reactants in a complete reaction is also in integer ratio. A reaction may consume more than one molecule, and the "Stoichiometric Number" counts this number, defined as positive for products (added) and negative for reactants (removed).	View
Surface Density	The area density (also known as areal density, surface density, or superficial density) of a two-dimensional object is calculated as the mass per unit area.	View
Temperature 0112/2///62720#UAD374	Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot. Heat spontaneously flows from bodies of a higher temperature to bodies of lower temperature, at a rate that increases with the temperature difference and the thermal conductivity.	View
Temperature Gradient	The temperature gradient measures the difference of a temperature per length, as for instance used in an external wall or its layers. It is usually measured in K/m.	View
Temperature Ratio	No definition available	View
time 0112/2///62720#UAD197	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.	View
torque 0112/2///62720#UAD200	In physics, a torque ($\tau$) is a vector that measures the tendency of a force to rotate an object about some axis. The magnitude of a torque is defined as force times its lever arm. 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.	View
velocity v	In kinematics, velocity is the speed of an object and a specification of its direction of motion. Speed describes only how fast an object is moving, whereas velocity gives both how fast and in what direction the object is moving.	View
Voltage U	$\textit{Voltage}$, also referred to as $\textit{Electric Tension}$, is the difference between electrical potentials of two points. For an electric field within a medium, $U_{ab} = - \int_{r_a}^{r_b} E . {dr}$, where $E$ is electric field strength. For an irrotational electric field, the voltage is independent of the path between the two points $a$ and $b$.	View
Volume 0112/2///62720#UAD238	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.	View
Volume Flow Rate q_V	Volumetric Flow Rate, (also known as volume flow rate, rate of fluid flow or volume velocity) is the volume of fluid which passes through a given surface per unit time.	View
Volume per Unit Area	No definition available	View

Scheme Information

IRI

https://vocab.sentier.dev/units/

Description

The QUDT, or "Quantity, Unit, Dimension and Type" schema defines the base classes properties, and restrictions used for modeling physical quantities, units of measure, and their dimensions in various measurement systems. The goal of the QUDT ontology is to provide a unified model of, measurable quantities, units for measuring different kinds of quantities, the numerical values of quantities in different units of measure and the data structures and data types used to store and manipulate these objects in software. Except for unit prefixes, all units are specified in separate vocabularies. Descriptions are provided in both HTML and LaTeX formats. A quantity is a measure of an observable phenomenon, that, when associated with something, becomes a property of that thing; a particular object, event, or physical system. A quantity has meaning in the context of a measurement (i.e. the thing measured, the measured value, the accuracy of measurement, etc.) whereas the underlying quantity kind is independent of any particular measurement. Thus, length is a quantity kind while the height of a rocket is a specific quantity of length; its magnitude that may be expressed in meters, feet, inches, etc. Or, as stated at Wikipedia, in the language of measurement, quantities are quantifiable aspects of the world, such as time, distance, velocity, mass, momentum, energy, and weight, and units are used to describe their measure. Many of these quantities are related to each other by various physical laws, and as a result the units of some of the quantities can be expressed as products (or ratios) of powers of other units (e.g., momentum is mass times velocity and velocity is measured in distance divided by time).

Creator

https://www.linkedin.com/in/ralphhodgson/

Version

3.1.6

Created

2011-04-20