Mechanics for Engineers

302 Pages·2005·16.233 MB·English

by  A. Morley

MECHANICS FOR ENGINEERS

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MECHANICS FOR
ENGINEERS
A TEXT-BOOK OF INTERMEDIATE
STANDARD
BY
ARTHUR MORLEY
M.Sc., UNIVERSITY SCHOLAR (VICT.)
SENIOR LECTURER IN ENGINEERING IN UNIVERSITY COLLEGE
NOTTINGHAM
WITH 200 DIAGRAMS AND NUMEROUS EXAMPLES
LONGMANS, GREEN, AND CO.
PATERNOSTER ROW, LONDON
39
NEW YORK AND BOMBAY
Allrightsreserved

PREFACE
ENGINEERING students constitute a fairly large proportion of
those attending the Mechanics classes in technical colleges
and schools, but their needs are not identical with those
of the students of general science. It has recently become
a common practice to provide separate classes in Mathematics,
adapted to the special needs of engineering students, who are
in most institutions sufficiently numerous to justify similar
provision in Mechanics. The aim of this book is to provide
a suitable course in the principles of Mechanics forengineering
students.
With this object in view, the gravitational system of
units has been adopted in the English measures. A serious
injustice is often done to this system in books on Mechanics
by wrongly denning the pound unit of force as a variable
quantity, thereby reducing the system to an irrational one.
With proper premisesthe gravitationalsystem is just asrational
as that in which the "poundal" is adopted as the unit of
force, whilst it may be pointed out that the use of the latter
system is practically confined to certain text-books and exami-
nation papers, and does not enter into any engineering work.
Teachers of Engineering often find that students who are
learning Mechanics by use of the "poundal" system, fail to
apply the principles to engineering problems stated in the
only units which are used in such cases the gravitational
vi Preface
units. The use of the dual system is certainly confusing
to the student, and in addition necessitates much time being
spent on the re-explanation of principles, which might other-
wise be devoted to more technical work.
Graphical methods of solving problems have in some
cases been used, by drawing vectors to scale, and by esti-
mating slopesand areas under curves. It is believed that such
exercises, although often taking more time to work than the
easy arithmetic ones which are specially framed to give exact
numerical answers, compel the student to think of the relations
between the quantities involved, instead of merely performing
operations by fixed rules, and that the principles so illustrated
are more deeply impressed.
The aim has not been to treat a wide range of academic
problems, but rather to select a course through which the
student may work in a reasonable time say a year and
the principles have been illustrated, so far as the exclusion
of technical knowledge and terms would allow, by examples
likely to be most useful to the engineer.
In view of the applications of Mechanics to Engineering,
more prominence than usual has been given to such parts
of the subject as energy, work of forces and torques, power,
and graphical statics, while some other parts have received
less attention or have been omitted.
It is usual, in books on Mechanics, to devote a chapter
to the equilibrium of simple machines, the frictional forces
in them being considered negligible: this assumption is so far
from the truth in actual machines as to create a false impres-
sion, and as the subject is very simple when treated experi-
mentally, it is left for consideration in lectures on Applied
Mechanics and in mechanical laboratories.
The calculus has not been used in this book, but the