Engineering 10
Chp.16 Units
& Conversions
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering-10: Intro to Engineering
1
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Units Introduction
 People measure quantities through
comparisons with standards.
 Every measured quantity has an associated
“unit” Which is the name of the Standard.
 Need to define sensible and practical "units"
and "standards" that scientists & engineers
everywhere can agree upon
 Even though there exist an almost infinite
number of different physical quantities, we
need no more than a handful of “base”
standards.
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
SI System of Units
 Système International d'Unités
(International System of Units)
 A Completely Consistent
Set of Basic Units
• Requires NO
Conversion factors
– e.g., 18 inches = 1.5 feet
• Defined by UNCHANGING
Physical Phenomena
– Except for one...
Engineering-10: Intro to Engineering
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http://www.bipm.org/en/si/
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
SI System History
 In 1960 The 11th General Conference
on Weights and Measures (GCWM)
adopted the name SI System, for the
recommended practical system of units
of measurement.
 The 1960 GCWM Specified Seven
well-defined “Base” units which, by
convention, are regarded as
DIMENSIONALLY INDEPENDENT
http://www.bipm.org/en/si/
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
 From this List
Observe
SI Base Units
SI Base Units
Base quantity
length
mass
Name
Symbol
meter
m
kilogram
kg
time
second
s
electric current
ampere
A
thermodynamic
temperature
kelvin
K
amount of substance
mole
mol
candela
cd
luminous intensity
 All But the kg are
defined by Physical
Phenomena
• Examine the Defs
Engineering-10: Intro to Engineering
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• Very common Units
– Mass (kg)
– Length (m)
– Time (s)
• Some Not so
Common Units
– Current (A)
– Temperature (K)
• Some Uncommon
Units
– Substance amt (mol)
– Luminous Int (cd)
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Meter Defined
 Length or
Distance
(meter)
 “The path traveled by light in
vacuum during a time interval
of 1/299792458 of a second.”
1 meter
Laser
photon
Engineering-10: Intro to Engineering
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1/299792458 s
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Kilogram Defined
 Mass
(Kilogram)
 a cylinder of PLATINUMIRIDIUM alloy maintained
under vacuum conditions
by the International
Bureau of Weights and
Measures in Paris
If The ProtoType Were Cubic, its
Edge Length would be About 36.2
mm (1.42”); quite small
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Second Defined
 Time
(Second)
 The duration of 9 192 631 770
periods of the radiation
corresponding to the transition
between the two hyperfine
levels of the ground state of
the cesium 133 atom
• This is the Definition of an
“Atomic” Clock
– more than 200 atomic clocks are
located in metrology institutes and
observatories in more than 30
countries around the world
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Amp Defined
 Electric
Current
(ampere)
 That constant current which,
if maintained in two straight
parallel conductors of infinite
length, of negligible circular
cross-section, and placed
1 m apart in a vacuum, would
produce between these
conductors a force equal to
2 x 10−7 Newton per metre of
length.
• What’s a Newton?→ 1kg-m/(s2)
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Kelvin (Temperature) Defined

 Thermodynamic
temperature
(Kelvin)
The unit of thermodynamic
temperature, is the fraction
1/273.16 of the
thermodynamic temperature of
the triple point of water.
 273.16K = 0.0098 °C
 Room Temperature
(72 °F) is about 295.5
Kelvins
 NO “Degree” Sign
Used with the
Kelvin Unit
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
mole (amt of Substance) Defined
 Amount of  The mole is the amount of
substance of a system which
Substance
contains as many elementary
(mole)
entities as there are atoms in
0.012 kilogram of carbon 12.
 1 mole = 6.023x1023
entities
• entities must be specified
and may be atoms,
molecules, ions, electrons,
other particles, or specified
groups of such particles.
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Luminous Intensity Defined
 The luminous intensity, in a given
 Light
direction, of a source that emits
Brightness
monochromatic radiation (one(candela)
color light) of frequency 540 x
1012 Hertz (555 nm) and that has
a radiant intensity in that direction
of 1/683 watt per steradian
 The are 4 (12.57)
Steradians in a Sphere
• 1 Str = 7.96% of the
Sphere Surface
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Units Have Evolved
 Candela Predecessor based
on a Flame
• Hence the Name
 Temperature Based on Freezing points
• Water
• Platinum
 Second Based on the
Sidereal (standard) day
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Units Have Evolved
 History of the Meter (or Metre)
• One ten millionth of the distance
from the North pole to the equator.
• The distance between two fine lines
engraved near the ends of a
platinum-iridium bar
• 1 650 763.73 wavelengths of a particular
orange-red light emitted by atoms of
krypton-86 (86Kr).
• The length of the path traveled by light in a
vacuum during a time interval of
1/299 792 458 of a second.
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
SI Derived Units
 The Seven Base Units May be
Arithmetically Combined to Produce
“Derived Units”
units of distance
• e.g.:
Units of velocity 
units of time
meters
 Several Derived

seconds
Units have Special
Usefulness And are
 m/s
Given their OWN
Names
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Some Derived Units
Derived quantity
Name
Symbol
Expression
in terms of
other SI units
Expression
in terms of
SI base units
plane angle
radian (a)
rad
-
m·m-1 = 1 (b)
solid angle
steradian (a)
sr (c)
-
m2·m-2 = 1 (b)
frequency
hertz
Hz
-
s-1
force
newton
N
-
m·kg·s-2
pressure, stress
pascal
Pa
N/m2
m-1·kg·s-2
energy, work,
quantity of heat
joule
J
N·m
m2·kg·s-2
power, radiant
flux
watt
W
J/s
m2·kg·s-3
electric charge,
quantity of
electricity
coulomb
C
-
Engineering-10: Intro to Engineering
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s·A
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Some (more) Derived Units
Derived quantity
Name
Symbol
Expression
in terms of
other SI units
Expression
in terms of
SI base units
electric potential
difference,
electromotive
force
volt
V
W/A
m2·kg·s-3·A-1
capacitance
farad
F
C/V
m-2·kg-1·s4·A2
electric
resistance
ohm

V/A
m2·kg·s-3·A-2
electric
conductance
siemens
S
A/V
m-2·kg-1·s3·A2
magnetic flux
Weber
Wb
V·s
m2·kg·s-2·A-1
magnetic flux
density
tesla
T
Wb/m2
kg·s-2·A-1
inductance
henry
H
Wb/A
m2·kg·s-2·A-2
Celsius
temperature
degree Celsius
°C
luminous flux
lumen
lm
cd·sr (c)
illuminance
lux
lx
lm/m2
Engineering-10: Intro to Engineering
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-
K
m2·m-2·cd = cd
m2·m-4·cd = m2·cd
Bruce Mayer,
PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
SI prefixes – A form of ShortHand
Factor
Name
Symbol
Factor
Name
Symbol
1024
yotta
Y
10-1
Deci
d
1021
zetta
Z
10-2
Centi
c
1018
exa
E
10-3
milli
m
1015
peta
P
10-6
micro
µ
1012
tera
T
10-9
nano
n
109
giga
G
10-12
pico
p
106
mega
M
10-15
femto
f
103
kilo
k
10-18
atto
a
102
hecto
h
10-21
zepto
z
101
deka
da
10-24
yocto
y
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Derived Units Family Tree
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Old (and Tired) Unit Sets
 MKS
• Stands for Meter-Kilogram-Second in the
Most Common Units
– Predecessor to The SI Units
 CGS
• Means Centimeter-Gram-Second
– Still Widely Used
 IPS, FPM, FPH
• Inch-Pound-Sec, Foot-Lb-Min, Ft-Lb-Hour
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
American Engineering System,
AES – Still in (declining) Use
Fundamental Dimension
Base Unit
length
foot (ft)
mass
pound (lbm)
force
pound (lbf)
time
second (sec)
electric charge [Q]
coulomb (C)
absolute temperature
degree Rankine (oR)
luminous intensity
candela (cd)
amount of substance
mole (mol)
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Conservation of Units
 Principle of conservation of units:
• Units on the LEFT side of an equation
MUST be the SAME as those on the
RIGHT side of an Equation
 Then Have Dimensional Homogeneity
• Needed to Prevent
“Apples & Oranges” Confusion
– e.g., I Buy 100 ft of Wire at One Store and 50 m
at another; how much total Wire do I have?
(It’s NOT “150”)
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Unit Conversion by Chain-Link
 To Determine the Amount of Wire I have
Need to Convert to Consistent
(Homogeneous) Units
 Start by Thinking About the Definition of “1”
• Ref also Table 16.8 in The Text
• Now Consider a “minute” 60 Seconds  1 minute
therefore
1 min
1
60 sec
or
60 sec
1
1 min
 Read as “60 Seconds per minute”
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Chain-Link Unit Conversion
 Units can also be Multiplied and Divided
in a manner similar to Numbers
• This how we get, say, “Square Feet”
– e.g.; Consider an 8ft x 10ft Engineer’s Cubicle in
Dilbert-Land. How Much WorkSpace Does the
Engineer Have?
WrkSpc  8ft x 10 ft  8x10 ftxft   80 ft
 Now Back to the Wire
• Want to Know how many FEET of Wire
I have in Total
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
2
Chain-Link Unit Conversion cont.
 Check in Table 16.8 and Find
“3.2808 ft per meter”
• Multiply the 50m by this special Value of 1
3.2808 feet
50 meter 1  50 meter 
 164.04 feet
1 meter
 Can “Cancel” The Units by Division
 So then the Total Wire = 264 ft
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Chain Link Examples
 A World-Class Sprinter can Run 100m in 10s.
• How Fast is this in MPH?
100 m 3.2808 ft 1 mile
60 s 60 min
miles




 22.37
10 s
1m
5280 ft 1 min
1 hr
hr
 Gasoline In Seoul Costs 1840 Korean-Won
(W) for one Liter of Regular Unleaded
• How Much is this in $ per Gallon
– Find Currency Exchange Rate → $1 = 1150 W
1840 W
1$
28.317 Liter
1 ft 3
$



 6.06
3
1 liter
1150 W
1 ft
7.48 Gal
Gal
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Several Forms of “1”
 Unit Conversion Factors
1 mile = 5280 feet
1 meter = 3.281 feet
1 foot = 12 inches
1 yard = 3 feet
1 lb = 4.448 Newtons
1 m2 = 1973.5 Circular inch
1 cup = 48 TeaSpoon
$1 = 0.787 €
1 Btu = 1054.4 Joule
1 Watt = 1 Joule/sec
1 HorsePower = 2545 Btu/hr
1 km = 1000 meters
1 furlong = 220 yards
°F = 1.8x°C + 32
1 Acre = 43,560 ft2
$1 = 16,030 Viet Nam Dong
1 hour = 60 min
1 min = 60 sec
1 gallon = 3.785 liters
1 ft3 = 7.4805 gallons
1 Pascal = 1 Newton/m2
1 HorsePower = 550 ft-lb/s
1 lb = 16 ounces
$1 = 10.825 Mexican Pesos
 ANYTHING Divided by ItSelf = 1
→
43560 ft 2
550 ft  lbs  s
1054.4 J
10.825 MXNs
1
1
1
1 acre
1 HP
1 Btu
1 USD
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Ton of Refrigeration
 During his
Presentation Mr.
Ian McClaren of
SouthLand
Industries
described the
“Ice Storage”
Cooling System Behind Bldg-1800.
 He Noted that the Cooling Power
of this system was Rated in “Tons”
 What is a “Ton” of Cooling Power
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Ton of Refrigeration
 A TON of the refrigeration
is defined, roughly, as the
COOLING effect of melting 2000 lbs of
water ICE over a 24 HOUR Period
• From PHYS4C (or ASHRAE HandBook)
find that the “Latent Heat of Fusion” for ice
is 333.55 kJ/kg
 On WhtBoard Convert a
“Ton of Refrigeration” to
• kW and Btu/hr
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
White Board Examples
 A 2003 Chevy z06 corvette
• Has a 5.7 Liter V8 Engine
– What is the Engine Displacement in cubic-inches?
• Develops 410 HP
– What is the Power in Watts?
 A the Maximum recommended pressure
for many 65R15 tires is 44 psi (lbs per sqinch; NOT lbs)
• What is this Max Pressure in kPa?
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
White Board Examples cont.

The USA FDA recommends that Adults
consume 2200 Calories per Day
•
What then is the “Power Rating”
of a Grown Human Being?
– Note that there are TWO types of “Calories”
1. The Amount of Heat Required to Raise the
Temperature of 1 GRAM of water by 1 °C (or 1 Kelvin)
 Often Called the Gram-CAL; This is what is in the Text
2. The Amount of Heat Required to Raise the
Temperature of 1 KILOgram of water by 1 °C
 Often Called the KgCAL or KiloCal; This is what
you read on the side of Food Packaging
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
All Done for Today
How to
Spend
the
Calories
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt
Engineering-10: Intro to Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-10_Lec-16_Chp16_Units-Conversions.ppt