ENGINEERING

MECHANICS
Statics and Dynamics

CIVIL AND ENVIRONMENTAL ENGINEERING DEPARTMENT– 1st STAGE

Dr. MSHEER H. ALI

Email: msheer.ali@uoz.edu.krd October - 2023
LECTURE TIME:

Wednesday 09:00 - 11:00 (Theory), 30 minutes rest.

Wednesday 11:00 - 1:00 (Tutorial), 30 minutes rest.

ASSESSMENT STRATEGY:

1. Class attendance.

2. Class work during tutorial sessions.

3. Home works and Quizzes.

4. Mid-Semester exam.

5. Final Exam.
REFERENCES

Engineering Mechanics “Statics and Dynamics" By: R. C. Hibbeler. 12th

edition. (2010).
REFERENCES

J.L. Meriam and L.G. Kraige, “Engineering Mechanics "Statics"” 8th

edition (2016).
REFERENCES

Vector Mechanics For Engineers “Statics and Dynamics" By: Ferdinand

P. Beer. 10-th edition. (2012).
 Introduction
Definition

Mechanics is a branch of the physical sciences that is

concerned with the state of rest or motion of bodies that are
subjected to the action of forces.

In general, this subject can be subdivided into three

branches:

- Rigid-body mechanics, we will study this now.!

- Deformable-body mechanics , and

- Fluid mechanics

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Rigid-body mechanics is divided into two areas:

- Statics.
- Dynamics.

- Statics deals with the equilibrium of bodies, that is, those that are
either at rest or move with a constant velocity.
- Dynamics is concerned with the accelerated motion of bodies.

We can consider statics as a special case of dynamics, in which the

acceleration is zero.

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Fundamental Concepts
Basic Quantities. The following four quantities are used
throughout mechanics.

- Length. Length is used to locate the position of a point in space and thereby
describe the size of a physical system.

- Time. Time is conceived as a succession of events. Although the principles

of statics are time independent, this quantity plays an important role in the
study of dynamics.

- Mass. Mass is a measure of a quantity of matter that is used to compare

the action of one body with that of another.

- Force. In general, force is considered as a “push” or “pull” exerted by one

body on another.
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Newton’s Three Laws of Motion.

Engineering mechanics is formulated on the basis of Newton’s three

laws of motion, the validity of which is based on experimental
observation. They may be briefly stated as follows.

- First Law.
A particle originally at rest, or moving in a straight line with
constant velocity, tends to remain in this state provided the particle
is not subjected to an unbalanced force, Fig.

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- Second Law.
A particle acted upon by an unbalanced force (F) experiences an
acceleration (a) that has the same direction as the force and a
magnitude that is directly proportional to the force, Fig. If F is applied to
a particle of mass m , this law may be expressed mathematically as

- Third Law.
The mutual forces of action and reaction between two particles are
equal, opposite, and collinear, Fig.

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Newton’s Law of Gravitational Attraction.

Eq. 1

Where;
W - is the weight of a particle.
m – is the mass.
g – is the constant of earth gravitation

“g” is determined at sea level and at a latitude of 45°, which is

considered the “standard location.”

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 Units of Measurement

The four basic quantities (length, time, mass, and force)

are not all independent from one another; in fact, they are
related by Newton’s second law of motion, F = ma.
Because of this, the units used to measure these quantities
cannot all be selected arbitrarily. The equality F = ma is
maintained only if three of the four units, called base units
, are defined and the fourth unit is then derived from the
equation.

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 Units of Measurement

SI Units.
The International System of units, abbreviated SI after the French
“Système International d’Unités,” is a modern version of the metric
system which has received worldwide recognition. As shown, the SI
system defines;

- Length in meters (m),

- Time in seconds (s),
- Mass in kilograms (kg).
- The unit of force, called a newton (N), is derived from F = ma.

Thus, 1 newton is equal to a force required to give 1 kilogram of

mass an acceleration of 1 m/𝑠 2 (N = kg . m/𝑠 2 ).

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If the weight of a body located at the “standard location” is to be
determined in newtons, then Eq. 1 must be applied. Here
measurements give g = 9.806 65 m/𝑠 2 ; however, for calculations,
the value g = 9.81 m/𝑠 2 will be used.

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U.S. Customary.
In the U.S. Customary system of units (FPS);
- Length in feet (ft),
- Time in seconds (s),
- Force in pounds (lb).
- The unit of mass, called a slug , is derived from F = ma . Hence,

1 slug is equal to the amount of matter accelerated at 1 ft/𝑠 2 when

acted upon by a force of 1 lb (slug = lb . 𝑠 2 Τ𝑓𝑡) .

Therefore, if the measurements are made at the “standard location,”

where g = 32.2 ft/𝑠 2 .

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Conversion of Units.
Table 2 provides a set of direct conversion factors between FPS and SI
units for the basic quantities.

Also, in the FPS system, recall that

• 1 ft = 12 in. (inches)
• 1000 lb = 1 kip (kilo-pound),
• 2000 lb = 1 ton.

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Prefixes.
When a numerical quantity is either very large or very small, the units
used to define its size may be modified by using a prefix. Some of the
prefixes used in the SI system are shown in Table 3. Each represents a
multiple or submultiple of a unit which, if applied successively, moves
the decimal point of a numerical quantity to every third place. For
example, 4 000 000 N = 4 000 kN (kilo-newton) = 4 MN (mega-
newton). Notice that the SI system does not include the multiple
deca (10) or the submultiple centi (0.01), which form part of the
metric system. Except for some volume and area measurements, the
use of these prefixes is to be avoided in science and engineering.
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Tutorial

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Homework 1

1-3; 1-7, 1-9 and 1-10

R. C. Hibbeler, “Engineering Mechanics Statics

and Dynamics”, 12th edition (2010).

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