Engineering MechanicsEngineering Mechanics

Part I: StaticsPart I: Statics

Dr. El-Sayed Awad Sayed-Ahmed

elsayed_awad46@yahoo.com

Mobile: 0121778678

CHAPTERCHAPTER

11

INTRODUCTIONINTRODUCTION

Basic Information

• Code: BSM 014

• Credit hours: Lecture: 2 Tutorial: 2 Total: 4

• Assessment Schedule Assessment 1 Mid term Examination Week no. 8 (first semester) Assessment 2 Report, and Assignments During the first semester Assessment 3 Mid term Examination Week no. 8 (second semester) Assessment 4 Report, and Assignments During the second semester Assessment 5 Final Examination By the end of the second semester

• Weighting of Assessments Mid Term Examinations 50 Points Final term Examination 140 Points Semester work (Report, Oral and Assignments) 10 Points______________________________________________________ Total 200 Points

Basic Information (Special Program)• Code BSM 014 • Credit hours:

Lecture: 2 Tutorial: 2 Practical: None Total: 3

• Assessment Schedule Assessment 1 Mid term Examination Week no. 8 Assessment 2 Report, and Assignments During the second semester Assessment 5 Final Examination By the end of the first semester • Weighting of Assessments Mid Term Examination 25 %

Final term Examination 50 % Semester work (Report, Oral and Assignments) 10%

Attendance 5% Quizzes 10% _______________________________________________________ Total 100 %

List of References

Essential Books

1 - Lecturer’s Text Book (Engineering Mechanics - Statics and Dynamics).

2 - Engineering Mechanics (Statics and Dynamics): R. C. Hibbeler, 12th

Edition, 2007. http://prenhall.com/hibbeler

Recommended Books:

1 - Engineering Mechanics (Statics and dynamics): Shames.

2 - Engineering Mechanics (Statics and dynamics): A. Bedford, 4th Edition.

3 - Engineering Mechanics (Statics and dynamics): J. L. Meriam, 5th Edition.

4 - Vector Mechanics for Engineer (Statics and dynamics), F. P. Beer, 8th Edition, 2005.

Course Objectives

The objectives of this course are:

• Develop equilibrium equations for particles

• Draw free body diagrams

• Determine the resultants of a force and couple system

• Reduce a force and couple system

• Reduce a distributed load into a resultant force

• Develop equilibrium equations for rigid bodies

CHAPTER 1• Objectives:

Students will be able to:

a) Identify what is mechanics / statics.

b) Understand the fundamental concepts of Statics

c) Work with two types of units.

Contents

1.1 Engineering Mechanics Basic Concepts and Definitions

SpaceTimeMassForceConcentrated ForceParticleRigid BodyNewton’s Three Fundamental LawsNewton’s Law of GravitationWeight

1.2 The Basic Units of Mechanics U.S. Customary Units (British System of Units)

The International System of Units (SI)Conversion from One System of Units to Another PrefixesRules for Use of SI Units

1.3 General Procedure for Analysis

1.1 Engineering MechanicsWhat is Engineering Mechanics? Engineering Mechanics is that branch of applied science,

which deals with the state of rest or motion of bodies under the action of forces.

• Categories of Mechanics:- Rigid bodies

- Statics- Dynamics

- Deformable bodies- Fluids

• Statics deals with the forces and their effects, while acting upon the bodies at rest or move with a constant velocity,

• Dynamics is concerned with the accelerated motion of bodies.

1.2 Basic Concepts and Definitions

• Space - associated with the notion of the position of a point P given in terms of three coordinates measured from a reference point or origin.

• Time - is the measure of the succession of events

• Mass - is a measure of the inertia of a body the quantity of matter in a body.

- is the property of every body by which it experiences mutual attraction to other bodies.

• Force - represents the action of one body on another.

The force is characterized characterized by its point of application, magnitude, and direction, i.e., a force is a vector quantity. In Newtonian Mechanics, space, time, and mass are absolute concepts, independent of each other. Force is not independent of the other three

• Concentrated Force -A concentrated force represents the effect of a loading, which is assumed to act at a point on a body .

Fundamental Principles. Cont.

• Particle: is a body of negligible dimensions

• Rigid body: A rigid body can be considered as a combination of a large number of particles in which all the particles remain at a fixed distance from one another both before and after applying a load.

• Newton’s Three Laws of Motion

First Law: Particle originally at rest (i.e., in equilibrium), or moving in a straight line with a constant velocity v, will remain in this state provided it is not subjected to an unbalanced force.

Second Law: A particle (of mass m) 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.

F=m a

Fundamental Principles. Cont.

Newton’s first law contains the principle of the equilibrium of forces, which is the main topic of concern in statics. Third Law: The mutual forces of action and reaction between two particles are equal, opposite, and collinear. The third law is basic to our understanding of force. It states that forces always occur in pairs of equal and opposite forces.

Fundamental Principles

Newton’s Law of Gravitation: Newton postulated a law governing the gravitational attraction between any two particles. This law is known as Newton’s Law of Gravitation and is expressed mathematically by the equation:

221

rmm

GF

Weight: The magnitude w of the weight of a particle of mass m is w = m g

1.3 The Basic Units of Mechanics

• Kinetic Units: length, time, mass, and force.

• Three of the kinetic units, referred to as basic units, may be defined arbitrarily. The fourth unit, referred to as a derived unit, must have a definition compatible with Newton’s 2nd Law,

amF

• International System of Units (SI):The basic units are length, time, and mass which are arbitrarily defined as the meter (m), second (s), and kilogram (kg). Force is the derived unit,

2s

m1kg1N1

maF

• U.S. Customary Units:The basic units are length, time, and force which are arbitrarily defined as the foot (ft), second (s), and pound (lb). Mass is the derived unit,

sft1

lb1slug1

a

Fm

1.3 The Basic Units of Mechanics Cont.

System of Units

1.3 The Basic Units of Mechanics Cont.

Conversion from One System of Units to Another:

In the FPS system, 1 ft = 12 in. (inches), 1 mi (mile)= 5280 ft2000 lb =1 Tone

1 ft = 0.3048 m 1 m = 3.281 ft = 39.37 inlb = 4.4482 N 1 N = 0.2248 lb1 slug = 14.5938 kg 1 kg = 0.06852 slug

1.3 The Basic Units of Mechanics Cont.

Prefixes: represents a multiple or su-bmultiple of a unit

Prefixes

Examples: 1 μs = 10−6 s 2.3 kN = 2300 N 34.1 mm2 = 0.0000341 m2

The Basic Units of Mechanics Cont.

Rules for Use SI symbols

• No Plurals (e.g., m = 5 kg not kgs )

• Most symbols are in lowercase. Some exceptions are N, Pa, M and G.

• Separate Units with a dot (.) .For example, a Newton-meter is written as N.m, to avoid confusion with prefix notation mN , which stands for millinewton.

• Compound prefixes should not be used: e.g. ks (kilo-micro-second) should be expressed as ms (milli-second) why?

• The exponential power represented for a unit having a prefix refers to both the unit and its prefix. For example,

N2 = (N)2 =N. N.

1.3 General Procedure for Analysis

General Procedure for Analysis

• Read the problem statement carefully (identify what’s given and what’s to be found) and try to correlate the actual physical situation with the theory studied.

• Draw necessary diagrams (free-body diagrams) and tabulate the problem data.

• Apply the relevant principles (Newton’s laws), generally in mathematical form (equilibrium equations). Solve the equations algebraically as much as possible, then, making sure they are dimensionally homogeneous, use a consistent set of units and complete the solution numerically. Report the answer with no more significant figures than the accuracy of the given data.

• Study the answer with technical judgment and common sense to determine whether or not it seems reasonable.