Environmental Engineering Reference
In-Depth Information
1.5 UNITS AND DIMENSIONS
The SI (International System of Units) is the standard set of units for engineering and
science. The International Union of Pure and Applied Chemistry (IUPAC) produced
a document (Cohen et al., 2007) entitled
Quantities, Units and Symbols in Physi-
cal Chemistry
, which recommended a uniform set of units for all measurements in
physical chemistry. This document should be consulted for a more elaborate discus-
sion of the various units. However, in a number of cases, environmental engineers
still prefer to use the CGS (centimeter-gram-second) system of units. Table 1.4 gives
the seven
base quantities
and their symbols that SI units are based on. All other
physical quantities are called
derived quantities
and can be algebraically derived
from the seven base quantities by multiplication or division.
TABLE 1.4
Base Quantities, Units, and Symbols in SI Units
Physical Quantity
Name
Symbol
Length
Meter
m
Mass
Kilogram
kg
Time
Second
s
Electric current
Ampere
A
Thermodynamic temperature
Kelvin
K
Amount of substance
Mole
mol
Luminous intensity
Candela
cd
Source:
Mills, I., Cvitas, T., Homann, K., Kallay, N., and
Kuchitsu, K. (Eds). 1988.
Quantities,UnitsandSymbols
inPhysicalChemistry
, IUPAC Physical Chemistry Divi-
sion. Oxford: Blackwell Scientific Publications.
TABLE 1.5
Relations between SI and CGS Units for Some Derived Quantities
Derived Quantity
Unit
CGS Symbol
Equivalent SI Unit
10
5
newtons (N)
Force
Dyne
dyn
10
5
pascals (Pa)
Pressure
Bar
bar
Atmosphere
atm
101,325 Pa
Torr
torr
133.32 Pa
Millimeter of mercury
mm Hg
133.32 Pa
6.89
×
10
3
Pa
Pounds per square inch
psi
10
−
7
joules (J)
Energy, work, heat
Erg
erg
Calories
cal
4.184 J
Liter atmospheres
L atm
101.325 J
10
3
mol/m
3
1 mol/dm
3
Concentration
Molar (mol/L)
M
10
−
3
kg/m s
Viscosity
Centipoise
cP
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