statics ch1

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VECTOR MECHANICS FOR ENGINEERS:

STATICS

Tenth Edition

Ferdinand P. Beer

E. Russell Johnston, Jr.

David F. Mazurek

Lecture Notes:

John ChenCalifornia Polytechnic State University

CHAPTER

© 2013 The McGraw-Hill Companies, Inc. All rights reserved.

1Introduction




Vector Mechanics for Engineers: StaticsT en t h

E d i t i on

Contents

1 - 2

What is Mechanics?

What Can You Do with Statics Knowledge?

Systems of Units

Method of Problem Solution

Numerical Accuracy





E d i t i on

What is Mechanics?

1 - 3

• Mechanics is the study of bodies under the action of forces.

• Categories of Mechanics:

- Rigid bodies

- Statics – bodies at rest or at constant velocity - Dynamics – accelerating bodies

- Deformable bodies

- Fluids – gas and/or liquid

• Mechanics is an applied science, closely related to

physics, so many of the concepts will build on that

prior knowledge.

• Mechanics is the foundation of many engineering topics and

is an indispensable prerequisite to their study.

T





Ed i t i on

What Can You Do with Statics Knowledge?

1 - 4

Calculate the force in

each member of thisstructure (a truss) in

order to design it to

withstand the loads that

it will experience.

T E





Ed i t i on

Systems of Units

1 - 5

• 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,

am F

• 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

m1kg1 N1

ma F

• 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

F m



T E


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Ed i t i on

Numerical Accuracy

1 - 7

• The accuracy of a solution depends on 1) accuracy of the given

data, and 2) accuracy of the computations performed. The solutioncannot be more accurate than the less accurate of these two.

• As a general rule for engineering problems, the data are seldom

known with an accuracy greater than 0.2%. Therefore, it is usually

appropriate to record parameters beginning with “1” with four digitsand with three digits in all other cases, i.e., 40.2 lb and 15.58 lb.

• The use of hand calculators and computers generally makes the

accuracy of the computations much greater than the accuracy of the

data. Hence, the solution accuracy is usually limited by the dataaccuracy. That is, remember what you learned about significant

figures.

statics ch1

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