54 Basic Engineering Mathematics
Table 8.2 Some quantities and their units that are common in engineering
Quantity
Unit
Symbol
Length
metre
m
Area
square metre
m 2
Volume
cubic metre
m 3
Mass
kilogram
kg
Time
second
s
Electric current
ampere
A
Speed, velocity
metre per second
m/s
Acceleration
metre per second squared
m/s 2
Density
kilogram per cubic metre
kg/m 3
Temperature
kelvin or Celsius
K or ◦ C
Angle
radian or degree
rad or ◦
Angular velocity
radian per second
rad/s
Frequency
hertz
Hz
Force
newton
N
Pressure
pascal
Pa
Energy, work
joule
J
Power
watt
W
Charge, quantity of electricity
coulomb
C
Electric potential
volt
V
Capacitance
farad
F
Electrical resistance
ohm
Inductance
henry
H
Moment of force
newton metre
Nm
The most common multiples are listed in Table 8.3.
A knowledge of indices is needed since all of the prefixes
are powers of 10 with indices that are a multiple of 3.
Here are some examples of prefixes used with engineering units.
A frequency of 15 GHz means 15 × 10 9 Hz, which is
15 000 000 000 hertz,
i.e. 15 gigahertz is written as 15 GHz and is equal to 15
thousand million hertz.
(Instead of writing 15 000 000 000 hertz, it is much
neater, takes up less space and prevents errors caused
by having so many zeros, to write the frequency as
15 GHz.)
A voltage of 40 MV means 40 × 10 6 V, which is
40 000 000 volts,
i.e. 40 megavolts is written as 40 MV and is equal to 40
million volts.
An inductance of 12 mH means 12 × 10 −3 H or
12
10 3 H or
12
1000
H, which is 0.012 H,
i.e. 12 millihenrys is written as 12 mH and is equal to
12 thousandths of a henry.
Table 8.2 Some quantities and their units that are common in engineering
Quantity
Unit
Symbol
Length
metre
m
Area
square metre
m 2
Volume
cubic metre
m 3
Mass
kilogram
kg
Time
second
s
Electric current
ampere
A
Speed, velocity
metre per second
m/s
Acceleration
metre per second squared
m/s 2
Density
kilogram per cubic metre
kg/m 3
Temperature
kelvin or Celsius
K or ◦ C
Angle
radian or degree
rad or ◦
Angular velocity
radian per second
rad/s
Frequency
hertz
Hz
Force
newton
N
Pressure
pascal
Pa
Energy, work
joule
J
Power
watt
W
Charge, quantity of electricity
coulomb
C
Electric potential
volt
V
Capacitance
farad
F
Electrical resistance
ohm
Inductance
henry
H
Moment of force
newton metre
Nm
The most common multiples are listed in Table 8.3.
A knowledge of indices is needed since all of the prefixes
are powers of 10 with indices that are a multiple of 3.
Here are some examples of prefixes used with engineering units.
A frequency of 15 GHz means 15 × 10 9 Hz, which is
15 000 000 000 hertz,
i.e. 15 gigahertz is written as 15 GHz and is equal to 15
thousand million hertz.
(Instead of writing 15 000 000 000 hertz, it is much
neater, takes up less space and prevents errors caused
by having so many zeros, to write the frequency as
15 GHz.)
A voltage of 40 MV means 40 × 10 6 V, which is
40 000 000 volts,
i.e. 40 megavolts is written as 40 MV and is equal to 40
million volts.
An inductance of 12 mH means 12 × 10 −3 H or
12
10 3 H or
12
1000
H, which is 0.012 H,
i.e. 12 millihenrys is written as 12 mH and is equal to
12 thousandths of a henry.