ENGINEERING
STATICS
ENGR-202
Chapter 1:
General Principles
Pearson Education
Engineering Mechanics by R. C. Hibbeler
Prepared by: Dr. Rawa Aljarallah
Main Objectives
Explain mechanics/statics.
Convert between two types of units.
Round the final answer appropriately.
Apply problem-solving strategies.
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What is
“mechanics” ?
The study of what happens to
a “body” when forces are
applied to it.
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What is “statics” ?
The study of force systems in equilibrium σ 𝐹 = 0
Mechanics
Rigid Bodies
Statics
Deformable Bodies
Dynamics
Fluids
Inompressible
Compressible
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Basic Quantities
Length
Time
Mass
Force
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Rigid body
Idealizations
A particle has a mass, but a size
that can be neglected
A rigid body is a large number of
particles that remain at a fixed distance
from one another.
Particle
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Newton’s Laws of Motion
1st Law
2nd Law
3rd Law
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Newton’s
First Law
A particle originally at rest (or moving with
constant velocity) tends to remain in the
same state, provided it is not subjected to
an unbalanced force.
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Balanced Force
Unbalanced Force
𝑭 = 𝑭𝟏 + 𝑭 𝟐 + 𝑭𝟑 = 𝟎
𝐹 = 𝑭1 + 𝑭2 + 𝑭3 ≠ 0
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Newton’s
Second Law
A particle acted upon by an unbalanced force
(F) experiences an acceleration (a) that has
the same direction as the force and the
magnitude is directly proportional to the
force.
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If F is applied to a particle of mass (m), this law can be expressed as:
F = ma
Where m is the mass and a is the acceleration
Force and acceleration are
related as follows:
a
F
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Newton’s
Third Law
The mutual forces of action and
reaction between two particles
are equal, opposite, and
collinear.
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Newton’s Law of Gravitational Attraction
This law governs the gravitational attraction between any two particles.
𝒎𝟏 𝒎𝟐
𝑭=𝑮
𝒓𝟐
Where,
F = Force of gravitation between the two particles
G = Universal constant of gravitation ( 𝑮 = 𝟔𝟔. 𝟕𝟑 × 𝟏𝟎−𝟏𝟐 𝒎𝟑 /𝒌𝒈 𝒔𝟐 )
m1, m2: Mass of each of the two particles
r = Distance between the two particles
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Weight
What quantity is different on the
moon than on earth?
Mass or Weight?
w = mg
Where,
m: Mass of particle or body
g = gravitational acceleration ( 𝒈 = 𝟗. 𝟖𝟏 𝒎/𝒔𝟐)
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The International System of Units
Base (measured)
Derived (calculated)
Can you think of examples?
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The International System of Units
Name
Length
Time
Mass
Force
Newton (N)
SI
meter (m)
second (s)
kilogram (kg)
𝑘𝑔. 𝑚
𝑠2
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SI System Prefixes
Exponential Form
Prefix
SI Symbol
1 000 000 000
𝟏𝟎𝟗
giga
G
1 000 000
𝟏𝟎𝟔
mega
M
1 000
𝟏𝟎𝟑
kilo
k
0.001
𝟏𝟎−𝟑
milli
m
0.000 001
𝟏𝟎−𝟔
micro
𝛍
0.000 000 001
𝟏𝟎−𝟗
nano
n
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Rules of Use
Dimensional Homogeneity:
Dimensions have to be the same on both sides of the equal sign
𝒎
(distance = speed x time → 𝒎 = • 𝐬 )
𝒔
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Rules of Use
Rounding Off Numbers
o Greater than or equal to 5, round up (0.3267 → 0.327)
o Smaller than 5, round down (0.3262 → 0.326)
o Equal to 5, round to an even number (0.325 → 0.32) or (0.325 → 0.33)
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Rules of Use
Significant Figures:
Use an appropriate number of significant figures
(3 for answer, at least 4 for intermediate calculations)
Express the following numbers in the required number of significant figures.
a) 1.83945 in 4 figure
b) 24.7768 in 3 figures
c) 0.08723 in 3 figures
d) 0.07059 in 3 figures
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Rules of Use
Significant Figures:
Use an appropriate number of significant figures
(3 for answer, at least 4 for intermediate calculations)
Express the following numbers in the required number of significant figures.
a) 1.83945 in 4 figures: 1.839
b) 24.7768 in 3 figures: 24.8
c) 0.08723 in 3 figures: 0.0872
d) 0.07059 in 3 figures: 0.0706
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Problem Solving Steps
Interpret
Read carefully and determine what is given and what is to be
found, and make assumptions if necessary.
Plan
Think about major steps to solve the problem and think of
alternative solutions to choose the best one.
Execute
Carry out your steps. Use appropriate and relevant diagrams and
equations. Estimate your answers and revise your work.
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Example
Convert 100 km/h to m/s and 24 m/s to km/h.
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Example
Convert 100 km/h to m/s and 24 m/s to km/h.
𝟏𝟎𝟎𝒌𝒎 𝟏𝟎𝟎𝟎 𝒎
𝟏𝟎𝟎𝐤𝐦/𝐡 =
𝒉
𝒌𝒎
𝟐𝟒 𝒎 𝟏 𝒌𝒎
𝟐𝟒 𝐦/𝐬 =
𝒔
𝟏𝟎𝟎𝟎 𝒎
𝟏𝟎𝟎 𝟏𝟎𝟑 𝒎
𝟏𝒉
=
= 𝟐𝟕. 𝟖 𝒎/𝒔
𝟑𝟔𝟎𝟎 𝒔
𝟑𝟔𝟎𝟎 𝒔
𝟖𝟔. 𝟒 𝟏𝟎𝟑 𝒌𝒎
𝟑𝟔𝟎𝟎 𝒔
=
= 𝟖𝟔. 𝟒 𝒌𝒎/𝒉
𝟏𝒉
𝟏𝟎𝟎𝟎 𝒉
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Example
Evaluate each of the following and express with SI units having an
appropriate prefix:
a) (𝟓𝟎 𝒎𝑵) (𝟔 𝑮𝑵)
b) 𝟒𝟎𝟎 𝒎𝒎 𝟎. 𝟔 𝑴𝑵 𝟐
c) 𝟒𝟓 𝑴𝑵𝟑 /𝟗𝟎𝟎 𝑮𝒈
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Solution
a) 𝟓𝟎 𝟏𝟎 −𝟑 𝑵 • 𝟔 𝟏𝟎 𝟗 𝑵
= 𝟑𝟎𝟎 𝟏𝟎 𝟔 𝑵𝟐
= 𝟑𝟎𝟎 𝟏𝟎
𝟔
𝟐
𝑵 •
𝟏 𝒌𝑵
𝟏𝟎𝟑 𝑵
•
𝟏 𝒌𝑵
𝟏𝟎𝟑 𝑵
= 𝟑𝟎𝟎 𝒌𝑵𝟐
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Solution
b) 𝟒𝟎𝟎 𝟏𝟎
−𝟑
𝒎 • 𝟎. 𝟔 𝟏𝟎
𝟔
𝑵
𝟐
= 𝟒𝟎𝟎 𝟏𝟎 −𝟑 𝒎 •
𝟎. 𝟑𝟔 𝟏𝟎 𝟏𝟐 𝑵𝟐
= 𝟏𝟒𝟒 𝟏𝟎 𝟗 𝒎 • 𝑵𝟐
= 𝟏𝟒𝟒 𝑮𝒎 • 𝑵𝟐
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Solution
C)
𝟑
𝟔
𝟒𝟓 𝟏𝟎
𝑵𝟑
𝟗𝟎𝟎 𝟏𝟎 𝟑 𝒌𝒈
=
𝟒𝟓 𝟏𝟎 𝟏𝟐 𝑵𝟑
𝟗𝟎𝟎 𝒌𝒈
=
𝟒𝟓 𝟏𝟎 𝟑 𝒌𝑵𝟑
𝟗𝟎𝟎 𝒌𝒈
= 𝟓𝟎 𝒌𝑵𝟑 /𝒌𝒈
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Check your understanding!
1. The subject of mechanics deals with what happens to a body when
______ is/are applied to it.
A) a magnetic field
B) heat
D) neutrons
E) lasers
C) forces
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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Check your understanding!
3. 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
D) 12.3 kN
E) 123 kN
C) 12 kN
4. In the three-step approach to problem solving called IPE, what does P
stand for?
A) Position
B) Plan
D) Practical
E) Possible
C) Problem
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Thank You!
Questions?
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