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CIV100 – Mechanics
Module 1: Force and Moment in 2D
by: Jinyue Zhang
2011/9/9
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A Reminder
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Module Objective
•
By the end of this Module you should be able to:
–
Be familiar with the units used in this course
–
Know the requirements regarding
significant figures
in this course.
–
Know how to resolve a force in any 2 directions.
–
Know how to add two or more forces and find their resultant.
•
Graphically
•
Using algebra
–
Understand the concept of vector, their addition and product.
–
Know how to develop a free body diagram
–
Understand the concept of moment in 2D
–
Understand the concept of Equilibrium
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General Principles
•
In Chapter One, we will learn:
– What is mechanics / statics?
– Newton’s Laws
– Working with International System (SI) units
– Significant figures and rounding a calculated result
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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 the force could be large or small.
Rocket  Large
Crane – Medium
Chronograph  Tiny
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Branches of Mechanics
Statics
Dynamics
Rigid Bodies
(Things that do not change shape)
Deformable Bodies
(Things that do change shape)
Incompressible
Compressible
Fluids
Mechanics
It is the basis for the design and analysis of many engineering systems
Many objects are designed with the intention that they remain in equilibrium
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2011/9/9
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What…If…
•
What may happen if statics is not applied properly?
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Basic Quantities
•
Four fundamental physical quantities:
– Length, Time, Mass, and Force
– 3 basic units (m, s, kg) and 1 derived unit (N)
•
Idealizations
–P
a
r
t
i
c
l
e
– Rigid body
– Concentrated force
2
s
m
kg
N
⋅
=
To Remember
2
⋅
=
W
T
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Newton’s Laws
•
First Law
–
A particle originally at rest, or moving in a straight line with constant
velocity, will remain in this state provided the forces applied on the
particle is all balanced (the particle is in
Equilibrium
)
•
Second Law
–
An unbalanced force
F
is applied to a particle having a mass
m
,
then the particle has an acceleration
a
which satisfies
•
Third Law
–
The mutual forces of action and reaction between two particles are
equal, opposite, and collinear.
•
Weight: Newton
’
s Law of Gravitational Attraction
a
F
=
a
F
=
To Remember
2
2
s
m
kg
s
m
kg
N
⋅
=
⋅
=
2
2
1
r
G
F
=
2
e
mM
W
=
mg
=
=
g=9.81m/s
2
2
81
.
9
g
=
Universal constant of gravitation
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SI Units
•
International System of units
–
length:
m
, mm, km
–t
i
m
e
:
s
–
mass:
kg
, g, Mg
–f
o
r
c
e
:
N
, kN, MN
•
Some rules you need to know
–
No Plurals
(e.g.,
m = 5 kg
not kgs )
–
Separate Units with a
•
(e.g., meter second = m • s )
–
Most symbols are in lowercase ( some exception are N, Pa, M and G)
–
Exponential powers apply to units , e.g., cm
2
= cm • cm
–
Always represent the numbers in terms of their
base or derived units
by converting al prefixes to
powers of 10.
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 Force, bx

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