J A Townsend
Peter Murray-Rust
Jim Downing
Sam Adams
Nick England
Type of each unit. In general there is one SI unit for eachunitType.
The term maps closely onto
Quantity. However there
can be many quantities
which share the same
unitType. Thus enthalpy and free energy are distinct concepts and
quantities
but share the same unitType (energy)
unitType
represents a computable quantity and
should not be used loosely for quantity.
unitType
does not currently point to the
corresponding SI unit, but every SI unit MUST have a
unitType
from which a mapping could be
devised.
In many cases unitTypes have well-used terms (e.g. "mass", "velocity") but some unitTypes arise from
combination
of simpler concepts and do not have well defined terms. Examples occur in high powers of dimensions (e.g. in
Virial
coefficients or high order rate constants). In these cases there is no meaningful natural language term
and we use a combination of dimensions (e.g. "ML-5T-5". The reason for including these in dictionaries is to
force the inclusion of units in documents and dictionaries.
Some unitTypes may have the same dimensions but represent different mathematical quantities. Thus energy
and torque both
have dimension ML2T-2 but represent the scalar (dot) and vector (cross) products respectively.
Some units are formed by ratios or multiplication. Thus energy-per-mass (various "specific heats") have the
units
ML2T-2.M-1 => L2T-2 , i.e. velocity-squared. However we may provide separate entries for these, while we do
not
provide different forms of energy.
unitType
MUST not be used to define quantities or other concepts. Thus entropy and specific heat have the same
unitType but may be thought of as separate quantities. Heat and work (free energy) are similar.
unitType
provides
dimensions and this can be used for dimensional analysis and unit conversion.
THIS DICTIONARY IS NOT COMPLETE or validated. There may be duplicate entries and some may be wrong.
PLEASE CONTRIBUTE TO THIS DICTIONARY, e.g. by transcribing or linking to Wikipedia, and adding your own
comments
An unreported unit
Used when a document has failed to provide units but where it is clear that there should be some sort
of units.
It is sometimes very difficult to work out the units, but
unknown
should not be used as an excuse for
not trying. By contrast
none
means that the concept does not carry units.
Cannot be used in units algebra.
Peter Murray-Rust
A quantity without an associated physical dimension
This is a difficult concept and users should read the Wikipedia article and further references.
dimensionless
can be used for numeric quantities which formally have no units such as
dimensionless constants. It can also be used for ratios of quantities with units (e.g. mg/kg).
Cancelling
units loses semantic information and we shall try in CML to avoid this if possible.
dimensionless
MUST not be used for concepts which are not numeric (e.g. algorithms) or pure numbers
and
none
SHOULD be used.
Dimensionless
in Wikipedia
Peter Murray-Rust
Wikipedia
A term signifying that the concept cannot carry units.
Use for dictionary concepts that cannot carry units. These include methods, names of programs, authors.
none
MUST not be used for concepts which should carry units or which can be formally classified as
dimensionless.
See also dimensionless.
Peter Murray-Rust
Mass used as a type of unit corresponding to dimension
M
.
Mass is a difficult concept. In Chemistry the three types of mass (inertial mass, active gravitational
mass,
and passive gravitational mass) are generally used interchangeably. Here
mass
is used as the type of the
unit and can be linked to the fundamental
M
dimension.
Mass should never be used as a synonym for weight.
see
Mass
in Wikipedia
Peter Murray-Rust
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Wikipedia
Length is a measure of one dimension
Length is a measure of one dimension, whereas area is a measure of two dimensions (length squared) and
volume is a measure of three dimensions (length cubed). In most systems of measurement, the unit of
length is a fundamental unit, from which other units are defined.
In the physical sciences and engineering, when one speaks of "units of length", the word "length" is
synonymous with "distance".
The metre (or meter), symbol m, is the base unit of length in the International System of Units (SI).
Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole
(at sea level), its definition has been periodically refined to reflect growing knowledge of metrology.
Since 1983, it is defined as the length of the path travelled by light in vacuum in 1⁄299,792,458 of a
second.
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the rate at which work is performed or energy is converted
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decay per unit time
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Amount per time T-1A
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moles of substance per volume of solution
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moles of substance per mass of solution
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area or squared length
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Volume or cubic length
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Reciprocal volume.
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Length power -4.
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Rate of change of length or position
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The radioactive equivalent dose is found by multiplying the radioactive absorbed dose by a
dimensionless "quality factor" Q dependent of radiation type and by another dimensionless number, N,
dependent on all other pertinent factors
The radioactive equivalent dose has the same dimensions as the gray (
i.e.
joules per kilogram - or m2s-2),
it measures a different quantity. To avoid confusion between the absorbed dose and the equivalent dose,
the corresponding special units, namely the gray for absorbed dose and the sievert for the dose
equivalent, are used. For a given amount of radiation (measured in gray - the plural of gray is gray),
the biological effect (measured in sievert) can vary considerably as a result of the radiation weighting
factor WR. This variation in effect is attributed to the Linear Energy Transfer [LET] of the type of
radiation, creating a different relative biological effectiveness for each type of radiation under
consideration. Per most government regulations, the RBE [Q] for electron and photon radiation is 1, and
varies for other types of radiation
Rate of change of velocity
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Rate of change of angle
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mass times velocity
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mass times angular velocity
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cross product of length and force
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Reciprocal length or inverse length is often used in spectroscopy as a measure of energy but in other
areas it could be the absorption coefficient or attenuation coefficient in materials science or
the curvature of a line in mathematics.
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.
mass per unit volume
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Volume per unit mass
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Amount per unit volume
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Volume per mole
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Energy per unit temperature
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Energy per mole per unit temperature change or molar Entropy
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Heat capacity or entropy per unit mass
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Energy or work per mole
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Force per mole
Molar force is a unit type often used as an abort criterion in minmization
procedures. In those cases it defines the maximal force per mole that is allowed
to accept a certain configuration as final.
Energy or work per unit mass
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Energy or work per unit volume
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Energy per unit area or force per unit length
Surface tension has the dimension of force per unit length, or of energy per unit area.
The two are equivalent—but when referring to energy per unit of area, people use the term
surface energy—which is a more general term in the sense that it applies also to solids
and not just liquids.
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Charge per unit volume
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Luminous intensity per area
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Gradient of energy with respect to length.
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Amount per unit volume
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Reciprocal molar mass
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Rate of change of angular velocity
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Reciprocal area
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area per unit mass
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Mass per unit area
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Rate of change of areal mass density
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Rate of change of areal mass density
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Current per unit area
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The electric dipole moment vector.
The electric dipole moment is a measure of the separation of positive and negative
electrical charges in a system of charges, that is, a measure of the charge system's overall
polarity.
wikipedia article
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A measure of how strongly a material opposes the flow of electric current.
Electrical resistivity (also known as resistivity, specific electrical resistance,
or volume resistivity) is a measure of how strongly a material opposes the flow of electric current.
A low resistivity indicates a material that readily allows the movement of electric charge.
Resistivity is commonly represented by the Greek letter ρ (rho).
Electrical resistivity
in Wikipedia
Wikipedia
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Rate of change of mass MT-1
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Hannah Barjat
Rate of change of in molar concentration with time.
This unit type may be used in the measurement of a change of molar concentration, due to physical or chemical process over time.
Hannah Barjat
Inverse of molar concentration per second.
These are the units of a second order rate coefficient.
Hannah Barjat
Inverse of molar concentration squared per second.
These are the units of a third order rate coefficient.
mass per mass
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Disintegrations per second
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Charge per unit area
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volume per unit area L3L-2
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Reciprocal volume L-3
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Rate of change of volume L3T-1
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