Engineering Mechanics I

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Manner Guideline in this Lecture Course

❑ Be reasonable and act politely .

❑ Turn off your mobile phone. If you have urgent calls

to make or answer, kindly leave the room.

❑ No noisy chat and all other activities that can distract

the lecture should be avoided.

❑ No food. Only water are allowed.

❑ Do not disturb your classmates.

❑ Dress properly.

❑ No smoking

Course Syllabus• Engineering Mechanics I 3 (2-0-3) Credit

• Lecture Hour: Sunday Group1 08.00-10.00 -• Group2 10.00 - 12.00

• Grading Policy: Total Score: 125 point , • Homework 10 point

– Midterm Exam 15 point– Final 90 point– Class Activity 10 point

Contents

• 1- Introduction, force in level, vector algebra,Forces in a plane, Forces in space

• 2- Statics of particles

• 3- Statics of Rigid bodies

• 4- Equilibrium of Rigid bodies (2 and 3dimensions)

• 5- Analysis of structures (Trusses, Frames

• and Machines)

• 6- Friction

• 7- Centroids and Centers of gravity

• 8- Moments of inertia of areas and masses

• 9- Internal forces

Textbook

“Engineering Mechanics STATICS”

R.C. Hibbeler, Engineering Mechanics

“Engineering Mechanics, STATICS”

Meriam and Kraige

Mechanics ?

Mechanics

Statics

Dynamics-Equilibrium

-Selected Topics

Kinematics Kinetics

-Particles

-Rigid Bodies

-Particles

- Rigid Bodies

A branch of physical science

which deals with ( the states of

rest or motion of ) bodies under

action of forces

Dynamics: Motion of bodies

Statics:

Equilibrium of bodies

(no accelerated motion)

under action of Forces

PARTS OF MECHANICS

Introduction to Statics

MechanicsMechanics is the physical science which deals with the

effects of forces on objects. Mechanics plays a greaterrole in engineering analysis. The principles of mechanicshave wide applications in engineering; although they arefew. The principles of mechanics are central to researchand development in the fields of vibrations, stability andstrength of structures and machines, robotics, rocket andspacecraft design, automatic control, engineperformance, fluid flow, electrical machines andapparatus, and molecular, atomic, and subatomicbehavior.

Structures

Machines

Robotics

Introduction to Statics

Mechanics

The subject of mechanics is logically divided intotwo parts: statics, which concerns the equilibrium ofbodies under action of forces, and dynamics, whichconcerns the motion of bodies.

Mechanics #2

Mechanics

Statics

Dynamics

Mech of Materials

Fluid Mechanics

Vibration

Fracture Mechanics

Etc.

Structures

Automotives

Robotics

Spacecrafts

MEMs

Etc.

Basic Concepts

Basic Concept

The following concepts and definitions are basic to study of mechanics,

and they should be at the outset.

Space is the geometric region occupied by bodies whose positions are

described by linear angular measurements relative to coordinate system. For

three-dimensional problems, three independent coordinates are needed. For

two-dimensional problems , only two coordinates are required.

Time is the measure of the succession of events and is a basic quantity in

dynamics. Time is not directly involved in the analysis of static problems.

Mass is a measure of the inertia of a body, which is its resistance to a

change of velocity. Mass can also be thought of as the quantity of matter in a

body. The mass of a body affects the gravitational attraction force between it

and other bodies. This force appears in many applications in statics.

Force is the action of one body on another. A force tends to move a

body in the direction of its action. The action of a force is characterized by its

magnitude, by the direction of its action, and by its point of application.

Basic Concept continuedA particle is a body of a negligible dimensions. In the mathematical

sense, a particle is a body whose dimensions are considered to be near zero

so that we may analyze it as a mass concentrated at a point.

Rigid body: A body is considered rigid when the change in distance

between any two of its points is negligible.

Scalars and VectorsWe use two kinds of quantities in mechanics; scalars and vectors.

Scalar quantities are those with which only a magnitude is associated.

Examples of scalar quantities are time, volume, density, speed, energy, and

mass. Vector quantities possess direction as well as magnitude, and must

obey the parallelogram law. Examples of vector quantities are displacement,

velocity, acceleration, force, moment, and momentum.

Vectors can be classified as free, sliding, or fixed

• In dynamics, force is an action that tends to cause acceleration of an object.

• The SI unit of force magnitude is the newton (N). One newton is equivalent to one kilogram-meter per second squared (kg·m/s2 or kg·m · s – 2)

Basic Concept - Force

Force: Vector quantity that describes an action of

one body on another [Statics]

SCALARS AND VECTORS

Scalars: associated with “Magnitude” alone

Vectors: associated with “Magnitude” and “Direction”

- mass, density, volume, time, energy, …

- force, displacement, velocity, acceleration, …

: Direction

or V| |V

Magnitude:

V or V

Vector :

free vector

(“math” vector)

Vector’s Point of Application

Vectors: “Magnitude”, “Direction”

F

Free Vector

rotating motion, coupleE.g.) Force on

non- rigid body

Fixed Vector

F

F

Sliding Vector

F

FRigid Body

E.g.) Force on

rigid-body

F

F

=?

line of action

“Point of Application”

The external

consequence

of these two

forces will

be the same

if ….

- Rigid Body

Rotational motion occurs at every point in the object.point of action

rotation

vector

Principle of

Transmissibility

Internal Effect –stress

Externaleffect

The Principle of Transmissibility

“A force may be applied at any point on its given line of action

without altering the resultant effects external to the rigid body on

which it acts.”

We can slide the force along its line

of action.(force can be considered as sliding vector)

F

F

=?

The two force can be

considered equivalent if

……

If we concerns only about the external

resultant effects on rigid body.

UnitsIn mechanics we use four fundamental quantities called

dimensions. These are length, mass, force, and time. Although there are a number of different systems of units, only the two systems most commonly used in science and technology will be used in this course.

QuantityDimensional

Symbol

SI UnitsU.S. Customary

Units

Unit Symbol Unit Symbol

Mass M kilogram kg slug -

Length L meter m foot ft

Time T second s second sec

Force F newton N pound Ib