EM102 Topic 1

8/17/2019 EM102 Topic 1

1/28

Statics, Fourteenth EditionR.C. Hibbeler

Copyright ©2016 by Pearson Education, Inc.All rights reserved.

EM102 Engineering Statics

1. Introduction

2. Force vectors

3. Rigid bodies

4. Equilibrium of rigid bodies

5. Structural analysis

6. Friction

7. Distribution of forces

Dr. Elango Natarajan

Assistant Professor

Aug 2015

8/17/2019 EM102 Topic 1

2/28



References

• ENGINEERING MECHANICS/STATICS (12th Edition), by R.C. Hibbler.

Prentice Hall. 2010.

• VECTOR MECHANICS FOR ENGINEER: STATICS, by F.P. Beer, E.R.

Johnston. McGraw Hill. 2012.

8/17/2019 EM102 Topic 1

3/28



EM102 Engineering Statics

Topic 1: Introduction

Fundamental concepts,

unit of measurements,procedure for analysis,

numerical accuracy.

8/17/2019 EM102 Topic 1

4/28



In-Class activities:

• Reading Quiz

• What is Mechanics?• System of Units

• Numerical Calculations

• Concept Quiz

• Problem-Solving Strategy

• Attention Quiz

Today’s Objectives:Students will be able to:

a) Explain mechanics/statics.

b) Work with two types of units.

c) Round the final answer appropriately.

d) Apply problem-solving strategies.

MECHANICS, UNITS, NUMERICAL CALCULATIONS &GENERAL PROCEDURE FOR ANALYSIS

8/17/2019 EM102 Topic 1

5/28



Study of what happens to a “thing” (the technical name is“BODY”) when FORCES are applied to it.

Either the body or forces can be large or small.

WHAT IS MECHANICS?

8/17/2019 EM102 Topic 1

6/28



Recap

•Load or Force - a push or pull exerted by a body.

•Types of loads – static load and dynamic load

•Stress - pressure or tension exerted on a

material or object.

•Strain – the relative change occurred due to the

application of force on a body or object.

8/17/2019 EM102 Topic 1

7/28



Recap

•Modulus of elasticity

•Stiffness

8/17/2019 EM102 Topic 1

8/28



Statics Dynamics

Rigid Bodies

(Things that do not change shape)

Deformable Bodies

(Things that do change shape)

Incompressible Compressible

Fluids

Mechanics

BRANCHES OF MECHANICS

8/17/2019 EM102 Topic 1

9/28



Rigid body

•Rigid body can be considered as a combination of

large number of particles in which all the particles

remain at a fixed distance from one another both

before and after applying a load.

•The deformation of such bodies is very small.

•Machines, mechanisms are considered to be rigid

bodies.

8/17/2019 EM102 Topic 1

10/28



Statics & Dynamics

•Statics deals with the equilibrium of bodies that are

either rest or move with a constant velocity.

•Dynamics is concerned with the accelerated motion

of bodies.

8/17/2019 EM102 Topic 1

11/28



1. The subject of mechanics deals with what happens to a bodywhen ______ is/are applied to it.

A) a magnetic field B) heat C) forces

D) neutrons E) lasers

2. ________________ still remains the basis of most of today’s

engineering sciences.

A) Newtonian Mechanics B) Relativistic Mechanics

C) Greek Mechanics C) Euclidean Mechanics

READING QUIZ

8/17/2019 EM102 Topic 1

12/28



Four fundamental physical quantities (or dimensions).

• Length

• Mass

• Time

• Force

Newton’s 2nd Law relates them: F = m × a

We use this equation to develop systems of units.

Units are arbitrary names we give to the physical quantities.

UNITS OF MEASUREMENT(Section 1.3)

8/17/2019 EM102 Topic 1

13/28



Force, mass, time and acceleration are related by Newton’s 2nd law. Three of these are assigned units (called base units)

and the fourth unit is derived. Which one is derived varies by

the system of units.

UNIT SYSTEMS

We will work with two unit systems in statics:

• International System (SI)

• U.S. Customary (USCS)

8/17/2019 EM102 Topic 1

14/28



Table 1-1 in the textbook summarizes these unit systems.

8/17/2019 EM102 Topic 1

15/28



COMMON CONVERSION FACTORS

Work problems in the units given unless otherwise instructed!

Answer is 209.06 N

Can you convert a force value of 47 lb into SI units?

8/17/2019 EM102 Topic 1

16/28



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

• Separate units with a • (e.g., meter second = m • s )

• Most symbols are in lowercase.

• Key exceptions are N, Pa, M and G.

• Exponential powers apply to units, e.g., cm • cm = cm2

• Compound prefixes should not be used.

• Table 1-3 in the textbook shows prefixes used in the SI

system

THE INTERNATIONAL SYSTEM OF UNITS(Section 1.4)

8/17/2019 EM102 Topic 1

17/28



Table 1 – 3 shows some of the prefixes usedin the SI system.

8/17/2019 EM102 Topic 1

18/28



DIMENSION

Dimension is a measure of physical quantity without numerical values.

Example: Length, Area, Diameter, Weight

Unit is a way to assign a number to the dimension.

Example: mm, kg.

8/17/2019 EM102 Topic 1

19/28



NUMERICAL CALCULATIONS(Section 1.5)

Be consistent when rounding off.

- greater than 5, round up (3528 3530)- smaller than 5, round down (0.03521 0.0352)

- equal to 5, see your textbook for an explanation.

Use an appropriate number of significant figures (3 foranswer, at least 4 for intermediate calculations). Why?

Must have dimensional “homogeneity.” Dimensions have to be the same on both sides of the equal sign, (e.g. distance =

speed time.)

8/17/2019 EM102 Topic 1

20/28



1. Evaluate the situation in which mass (kg), force (N), and

length (m) are the base units and recommend one of the

following.

A) A new system of units will have to be formulated.

B) Only the unit of time have to be changed from second to

something else.

C) No changes are required.D) The above situation is not feasible.

CONCEPT QUIZ

8/17/2019 EM102 Topic 1

21/28



2. Give the most appropriate reason for using three significantfigures in reporting results of typical engineering calculations.

A) Historically slide rules could not handle more than three

significant figures.

B) Three significant figures gives better than one-percent

accuracy.

C) Telephone systems designed by engineers have area codes

consisting of three figures.

D) Most of the original data used in engineering calculations do

not have accuracy better than one percent.

CONCEPT QUIZ (continued)

8/17/2019 EM102 Topic 1

22/28

8/17/2019 EM102 Topic 1

23/28



2. In the three-step approach to problem solving called IPE,

what does P stand for?

A) Position B) Plan C) Problem

D) Practical E) Possible

1. For a static’s problem, your calculations show the final answer as12345.6 N. What should you write as your final answer?

A) 12345.6 N B) 12.3456 kN C) 12 kN

D) 12.3 kN E) 123 kN

ATTENTION QUIZ

8/17/2019 EM102 Topic 1

24/28



example_01_01

8/17/2019 EM102 Topic 1

25/28



example_01_02

8/17/2019 EM102 Topic 1

26/28



example_01_03

continued on next slide

8/17/2019 EM102 Topic 1

27/28



example_01_03 (continued)

Documents

EM102 Topic 1