Engineering Mechanics: Statics
Fifteenth Edition
Chapter 1
General Principles
Section 1.1 Mechanics
Section 1.2 Fundamental
Concepts
Section 1.3 Units of
Measurement
Section 1.4 The International
System of Units
Section 1.5 Numerical
Calculations
Section 1.6 General Procedure
for Analysis
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Mechanics, Units, Numerical Calculations
& General Procedure For Analysis
Today’s Objectives:
Students will be able to:
a. Explain mechanics/statics.
b. Work with two types of units.
c. Round the final answer appropriately.
d. Apply problem-solving strategies.
In-Class activities:
• Reading Quiz
• What is Mechanics?
• System of Units
• Numerical Calculations
• Concept Quiz
• Problem-Solving Strategy
• Attention Quiz
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Reading Quiz (1 of 2)
1. The subject of mechanics deals with what happens to a
body when __________ is/are applied to it.
A. a magnetic field
B. heat
C. forces
D. neutrons
E. lasers
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Reading Quiz (2 of 2)
2. ________ still remains the basis of most of today’s
engineering sciences.
A. Newtonian Mechanics
B. Relativistic Mechanics
C. Greek Mechanics
D. Euclidean Mechanics
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What is Mechanics?
Study of what happens to a “thing” (the technical name is
“Body”) when Forces are applied to it.
Either the body or forces can be large or small.
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Branches of Mechanics
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Section 1.3: Units of Measurement
Four fundamental physical quantities (or dimensions).
• Length
• Mass
• Time
• Force
Newton’s 2nd Law relates them: F = m × a
We use this equation to develop systems of units.
Units are arbitrary names we give to the physical quantities.
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Unit Systems
Force, mass, time and acceleration are related by Newton’s
2nd law. Three of these are assigned units (called base units)
and the fourth unit is derived. Which one is derived varies by
the system of units.
We will work with two unit systems in statics:
• International System (SI)
• U.S. Customary (USCS)
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Table 1.1 In the Textbook Summarizes
These Unit Systems
Table 1.1 Systems of units.
Name
Length
Time
Mass
Force
International
System of
Units SI
meter
m
second
s
kilogram
kg
newton*
N
 kg  m 
 2 
 s 
left parenthesis start fraction kilogram times meter over s squared end fraction right parenthesis
U.S.
Customary
FPS
foot
ft
second
s
slug*
 lb  s 2 


 ft 
pound
lb
left paranthesis start fraction pound times s squared over feet end fraction right paranthesis
*Derived unit.
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Common Conversion Factors
Work problems in the units given unless otherwise
instructed!
Table 1.2 Conversion Factors
Quantity
Unit of
Measurement (F P S)
Equals
Unit of
Measurement (S I)
blank
Force
lb
4.448 N
blank
Mass
Slug
14.59 kg
blank
Length
ft
0.3048 m
eter
Can you convert a force value of 47 lb into SI units?
Answer is 209.06 N
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Section 1.4: The International System
of Units
• No plurals (e.g., m = 5 kg, not kgs)
• Separate units with a  (e.g., meter second = m  s )
• Most symbols are in lowercase.
– Key exceptions are N, Pa, M and G.
• Exponential powers apply to units, e.g., cm  cm = cm 2
• Compound prefixes should not be used.
• Table 1.3 in the textbook shows prefixes used in the SI
system
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Table 1.3 Shows Some of the Prefixes
Used in the SI System
TABLE 1.3 Prefixes
Blank
Exponential Form
Blank
Prefix
Blank
S I Symbol
Blank
Multiple
1 000 000 000
109
giga
G
1 000 000
10 6
mega
M
1 000
10 3
ten to the power of 9
ten to the power of 6
kilo
ten to the power of 3
Blank
Blank
K
Blank
Submultiple
0.001
10 3
milli
m
0.000 001
10 6
micro
μ
0.000 000 001
10 9
nano
n
ten to the power of negative 3
ten to the power of negative 6
ten to the power of negative 9
Mu
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Section 1.5: Numerical Calculations
Must have dimensional “homogeneity.” Dimensions have to
be the same on both sides of the equal sign, (e.g. distance =
speed × time.)
Use an appropriate number of significant figures (3 for
answer, at least 4 for intermediate calculations). Why?
Be consistent when rounding off.
– greater than 5, round up (3528  3530)
– smaller than 5, round down (0.03521  0.0352)
– equal to 5, see your textbook for an explanation.
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Concept Quiz (1 of 2)
1. Evaluate the situation in which mass (k g ), force (N), and
length (m) are the base units and recommend one of the
following.
ilo
ram
A. A new system of units will have to be formulated.
B. Only the unit of time have to be changed from second
to something else.
C. No changes are required.
D. The above situation is not feasible.
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Concept Quiz (2 of 2)
2. Give the most appropriate reason for using three
significant figures in reporting results of typical
engineering calculations.
A. Historically slide rules could not handle more than
three significant figures.
B. Three significant figures gives better than one-percent
accuracy.
C. Telephone systems designed by engineers have area
codes consisting of three figures.
D. Most of the original data used in engineering
calculations do not have accuracy better than one
percent.
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Problem Solving Strategy IPE: A 3Step Approach
1. Interpret: Read carefully and determine what is given
and what is to be found/delivered. Ask, if not clear. If
necessary, make assumptions and indicate them.
2. Plan: Think about major steps (or a road map) that you
will take to solve a given problem. Think of
alternative/creative solutions and choose the best one.
3. Execute: Carry out your steps. Use appropriate
diagrams and equations. Estimate your answers. Avoid
simple calculation mistakes. Reflect on and then revise
your work, if necessary.
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Attention Quiz (1 of 2)
1. For a static’s problem, your calculations show the final
answer as 12345.6 N. What should you write as your final
answer?
A. 12345.6 N
B. 12.3456 kN
C. 12 kN
D. 12.3 kN
E. 123 kN
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Attention Quiz (2 of 2)
2. In the three-step approach to problem solving called IPE,
what does P stand for?
A. Position
B. Plan
C. Problem
D. Practical
E. Possible
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