SKPP 1113 Eng. Mechanics Section 09 & 10

Jusni Ali N01-275

07-5535498 jusni@petroleum.utm.my

INSPIRING CREATIVE AND INNOVATIVE MINDS

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INTRODUCTION

INSPIRING CREATIVE AND INNOVATIVE MINDS

1.0 What is Mechanic? applied science which describes and predicts

physical phenomena of the bodies at rest or motion under the action of forces.

Fluid Mechanics

Statics Dynamics

Rigid Bodies Deformable Bodies

Solid Mechanics

Engineering Mechanics

In Statics we will assume the bodies to be perfectly rigid, no deformation.

This is never true in the real world, everything deforms a little when a load is applied.

These deformations are small and will not significantly affect the conditions of equilibrium or motion, so we will neglect the deformations.

Rigid body - a body is considered rigid when the relative movement between its parts are negligible.

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What may happen if static's is not applied properly?

1.1 Fundamental Concepts and Principles

Space : Geometric region occupied by bodies whose positions are described by linear and angular measurement relative to a coordinate system.

Time : Measure of the succession of events and is a basic quantity in dynamics.

Mass : Measure of inersia of a body, which is its resistance to a change of motion.

Force : The action of one body on another. A force tends to move a body in direction of its action. The action of a force is characterized by its magnitude, by the direction of it action, and by it point of application. Force are vector quantities Particle: A body of negligible dimension and it may be analyzed as a point mass.

Rigid Body : A body is considered rigid when the relative movement between its part are negligible for the purpose at hand.

Six fundamental principle based on study of mechanic:

1-1 The Parallelogram Law This states that two forces acting on a particle may be replaced by a single force, called their resultant, obtained by drawing the diagonal of the parallelogram which has sides equal to the given forces.

2-Principle of Transmissibility This state that the conditions of equilibrium or of

motion of a rigid body will remain unchanged if a force acting at a given point of the rigid body is replace by a force of the same magnitude and same direction, but acting at a different point, provided that the two forces have the same line of action.

Newton Fundamental Laws 3- FIRST LAW

If the resultant of force acting on a particle is zero, the particle will remain at rest ( if originally at rest) or will move with constant speed in a straight line ( if originally in motion) - Figure 1.1

F1 F2

F3

v

EQUILIBRIUM

FIGURE 1.1

4- SECOND LAW The resultant force

acting on a particle is not zero, the particle will have an acceleration proportional to the magnitude of the resultant and in the direction of this resultant force.(Figure 1.2). This law may be stated as:

F a

Accelerated motion

Figure 1.2

F = ma Where:

F is Resultant force m is mass of the particle a is acceleration of the particle

5-THIRD LAW The forces of action and reaction between bodies in contact have the same magnitude, same line of action and opposite sense (Figure 1.3).

6. Newtons Law of Gravitation

Two particle of mass M and m are mutually attracted with equal and opposite forces F and F (Figure 1.1),of magnitude F given by the formula:

F = G

Mmr 2

Where: G = constant of gravitation

r = distance between the two bodies

r

M

m

F

F

m

M

F

F

r

Let say, M is the mass of the earth, m equal to mass of the particle, and R equal to radius of the earth, and introducing the constant:

g =

GMR2

Weight of a particle of mass m may be expressed as:

F =W = G

MmR2

= mg

W = mg

In most engineering computation to assume that g equal 9.81 m/s2 or 32.2 ka/s2 .

1.3 Systems of Unit

A. International System of Unit (S.I)

Quantity Dimensional symbol Unit Symbol

Mass M kilogram kg Length L meter m Time T second s Force F newton N = kg.m/s-2

B. US customary Units

Quantity Dimensional symbol Unit Symbol

Mass M slug - Length L foot ft Time T second sec Force F pound Ib

SI Prefixes

Multiplication Factor 1,000,000,000 = 109 1,000,000 = 106 1,000 = 103 0.01 = 10-2 0.001 = 10-3 0.000,001 = 10-6

Prefix Giga Mega Kilo Centi Milli micro

Symbol G M K C m

1.4 PROBLEM SOLVING STRATEGY: 3 Step Approach

1. Interpret: Read carefully and determine what is given and what is to be found/ delivered. Ask, if not clear. If necessary, make assumptions and indicate them.

2. Plan: Think about major steps (or a road map) that you will take to solve a given problem. Think of alternative/creative solutions and choose the best one.

3. Execute: Carry out your steps. Use appropriate diagrams and equations. Estimate your answers. Avoid simple calculation mistakes. Reflect on / revise your work.

Homework

Review Trigonometry Law Law of Cosines Law of Sines Right Triangle Trigonometry

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