Table 4. Examples of SI coherent derived units whose names and symbols include
SI coherent derived units with special names and symbols
SI coherent derived unit
————————————————————————————
Expressed in terms of
Derived quantity
Name
Symbol
SI base units
dynamic viscosity
pascal second
Pa s
m
−
1
kg s
−
1
moment of force
newton meter
N m
m
2
kg s
−
2
surface tension
newton per meter
N/m
kg s
−
2
angular velocity
radian per second
rad/s
m m
−
1
s
−
1
= s
−
1
angular acceleration
radian per second squared
rad/s
2
m m
−
1
s
−
2
= s
−
2
heat flux density,
watt per square meter
W/m
2
kg s
−
3
irradiance
heat capacity, entropy
joule per kelvin
J/K
m
2
kg s
−
2
K
−
1
specific heat capacity,
joule per kilogram kelvin
J/(kg K)
m
2
s
−
2
K
−
1
specific entropy
specific energy
joule per kilogram
J/kg
m
2
s
−
2
thermal conductivity
watt per meter kelvin
W/(m K)
m kg s
−
3
K
−
1
energy density
joule per cubic meter
J/m
3
m
−1
kg s
−
2
electric field strength
volt per meter
V/m
m kg s
−
3
A
−
1
electric charge density
coulomb per cubic meter
C/m
3
m
−
3
s A
surface charge density
coulomb per square meter
C/m
2
m
−
2
s A
electric flux density,
coulomb per square meter
C/m
2
m
−
2
s A
electric displacement
permittivity
farad per meter
F/m
m
−
3
kg
−
1
s
4
A
2
permeability
henry per meter
H/m
m kg s
−
2
A
−
2
molar energy
joule per mole
J/mol
m
2
kg s
−
2
mol
−
1
molar entropy,
joule per mole kelvin
J/(mol K) m
2
kg s
−
2
K
−
1
mol
−
1
molar heat capacity
exposure (x and
γ
rays)
coulomb per kilogram
C/kg
kg
−
1
s A
absorbed dose rate
gray per second
Gy/s
m
2
s
−
3
radiant intensity
watt per steradian
W/sr
m
4
m
−
2
kg s
−
3
= m
2
kg s
−
3
radiance
watt per square meter steradian
W/(m
2
sr) m
2
m
−
2
kg s
−
3
= kg s
−
3
catalytic activity
katal per cubic meter
kat/m
3
m
−
3
s
−
1
mol
concentration
The values of several different quantities may be expressed using the same name
and symbol for the SI unit. Thus for the quantity heat capacity as well as the
quantity entropy, the SI unit is the joule per kelvin. Similarly for the base quantity
electric current as well as the derived quantity magnetomotive force, the SI unit is
the ampere. It is therefore important not to use the unit alone to specify the quantity.

SI Units
•
27
This applies not only to scientific and technical texts, but also, for example, to
measuring instruments (i.e. an instrument read-out should indicate both the unit and
the quantity measured).
A derived unit can often be expressed in different ways by combining base units
with derived units having special names. Joule, for example, may formally be
written newton meter, or kilogram meter squared per second squared. This,
however, is an algebraic freedom to be governed by common sense physical
considerations; in a given situation some forms may be more helpful than others.

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