Newnes Engineering Science Pocket Book

363 Pages·1987·18.719 MB·English

by  J. O. Bird (Auth.)

Newnes
E n g i n e e r i ng S c i e n ce
Pocket Book
J O Bird
BSc(Hon8), CENG, MIEE, FIMA, F.CoU.P, MIElecIE
Heinemann Newnes
Heinemann Newnes
An imprint of Heinemann Professional Publishing Ltd
Halley Court, Jordan Hill, Oxford OX2 8EJ
OXFORD LONDON MELBOURNE
AUCKLAND SINGAPORE IBADAN
NAIROBI GABORONE KINGSTON
First published by Butterworth & Co (Publishers) Ltd 1983
First published by Heinemann Newnes 1987
Reprinted 1988
© Heinemann Professional Publishing Ltd 1987
British Library Cataloguing in Publication Data
Bird, J. O.
Newnes engineering science pocket book
1. Science - Dictionaries
1. Title
1.503'.21 0,121
ISBN 0 434 90154 7
Printed in England by Butler & Tanner Ltd,
Frome and London
Preface
This Engineering Science pocket book is intended to provide
students, technicians and engineers with a readily available
reference to the essential engineering science formulae, definitions
and general information needed during their studies and/or work
situation.
The book assumes litde previous knowledge, and is suitable for
a wide range of courses, and will be particularly useful for students
studying for Technician certificates and diplomas, and for GCSE
and A levels.
The author would like to express his appreciation for the
friendly cooperation and helpful advice given to him by the
publishers and by the editor Mr A.J.C. May and also to Mr. D.S.
Ayling for his agreeing to the use of some material from his
Mechanical Science Checkbook. Thanks are also due to Mrs. Elaine
Woolley for the excellent typing of the manuscript.
Finally, the author would like to add a word of thanks to his
wife Elizabeth for her patience, help and encouragement during
the preparation of this book.
J O Bird
Highbury College of Technology
Portsmouth
1 SI units
1 The system of units used in engineering and science is the
Systéme Intematíoiimle dlJiiites (International system of units),
usually abbreviated to SI units, and is based on the metric system.
This was introduced in 1960 and is now adopted by the majority
of countries as the official system of measurement.
2 The basic units in the SI system are given in Table 1.1.
Table 1.1
Quantity Unit
length metre, m
mass kilogram, kg
time second, s
electric current ampere. A
thermodynamic temperature kelvin. Κ
luminous intensity candela, cd
amount of substance mole, mol
SI units may be made larger or smaller by using prefixes
which denote multiplication or division by a particular
amount. The eight most common multiples, with their
meaning, are listed in Table 1.2.
Table 1.2
Prefix Name Meaning
Τ tera multiply by 1 000000000000 (i.e. ^ 10^^)
G giga multiply by 1 000000000 (i.e. ^ 10^)
Μ mega multiply by 1 000000 (i e. χ 10^)
k kilo multiply by 1 000 (i.e. xlO^)
m milli divide by 1 000 (i.e. χ 10"^)
micro divide by 1 000000 (i.e. χ 10"^)
η nano divide by 1 000000000 (i.e. χ 10"^)
Ρ pico divide by 1 000000000000 (i.e. ^ lO''^)
4 (i) Length is the distance between two points. The
standard unit of length is the metre, although the
centimetre, cm, millimetre, mm and kilometre, km,
are often used.
1 cm = 10 mm; 1 m = 100cm= 1000 mm;
1 km =1000 m.
(ii) Area is a measure of the size or extent of a plane
surface and is measured by multiplying a length by a
length. If the lengths are in metres then the unit of area is
the eqiwre metre, m^.
1 m2=l mx 1 m=100 cm χ 100 cm = 10000 cm^ or
10* cm^
= 1000 mm χ 1000 mm = 1000000 mm^
or 10^ mm^
Conversely, 1 cm^ = 10"* m^ and 1 mm^ = 10"^ m^.
(iii) Volume is a measure of the space occupied by a
solid and is measured by multiplying a length by a length
by a length. If the lengths are in metres then the unit of
volume is in cubic metres, m'.
1 m^ = \ mxl mxl m=100 cm χ 100 cm χ 100 cm
= 1000 mm χ 1000 mm χ 1000 mm = 10^ mm^
Conversely, 1 cm^= 10"^ m^ and 1 mm^ = 10"^ m^
Another unit used to measure volume, particularly with
liquids, is the litre (1) where 1 litre = 1000 cm'.
(iv) Mass is the amount of matter in a body and is
measured in kilograms, kg.
1 kg = 1000 g (or conversely, 1 g = 10"' kg) and
1 tonne (t) = 1000kg.
5 Derived SI units use combinations of basic units and there
arc many of them. Two examples are:
velocity — metres per second, (m/s)
acceleration — metres per second square, (m/s^).
(a) The unit of charge is the coulomb, (C), where one
coulomb is one ampere second. (1 coulomb = 6.24 χ ΙΟ'®
electrons). The coulomb is defined as the quantity of
electricity which flows past a given point in an electric
circuit when a current of one ampere is maintained for
one second. Thus
charge in coulombs, Q = !t
where / is the current in amperes and / is the time in
seconds.
(b) The unit of force is the newton, (N), where one newton
is one kilogram metre per second squared. The newton is
defined as the force which, when applied to a mass of one
kilogram, gives it an acceleration of one metre per second
squared. Thus
force in newtons, F=ma,
where m is the mass in kilograms and a is the acceleration
in metres per second squared. Gravitational force, or
weight, is mg^ where ^ = 9.81 mj^.
(c) The unit of work or energy is the joule, (J), where one
joule is one newton metre. The joule is defined as the
work done or energy transferred when a force of one
newton is exerted through a distance of one metre in the
direction of the force. Thus
work done on a body in joules, W=Fs,
where F is the force in newtons and s is the distance in
metres moved by the body in the direction of the force.
Energy is the capacity for doing work.
(d) (i) The unit of power is the watt, (W), where one watt is
one joule per second. Power is defined as the rate of doing
work or* transferring energy. Thus:
W
power in watts, P = —,
where W is the work done or energy transferred in joules
and / is the time in seconds.
Hence, energy in joules, W = Pt.
(e) The unit of electric potentiml is the volt (V) where one
volt is one joule per coulomb. One volt is defined as the
difference in potential between two points in a conductor
which, when carrying a current of one ampere dissipates a
power of one watt.
/ watts joules/second joules
i.e. volts = -
amperes amperes ampere seconds
^joul«_\
coulomb /
A change in electric potential between two points in an
electric circuit is called a potential difTerence. The
electromotive force (e.m.f.) provided by a source of energy
such as a battery or a generator is measured in volts.
2 Density
(i) Density is the mass per unit volume of a substance.
The symbol used for density is ρ (Greek letter rho) and its
units are kg/m'.
Density I.e.,
volóme'
m
m
p=— or m=pV or V= —
Ρ
υ
where m is the mass in kg, V is the volume in m' and ρ is
the density in kg/m'.
(ii) Some tvpical values of densities include:
aluminium 2 700 kg/m', copper 8 900 kg/m',
lead 11 400 kg/m', cast iron 7 000 kg/m',
steel 7800 kg/m', water 1 000 kg/m^
cork 250 kg/m', petrol 700 kg/m'.
(i) The relative density of a substance is the ratio of the
density of the substance to the density of water,
density of substance
i.e. relative density =
density of water
Relative density has no units, since it is the ratio of two
similar quantities.
(ii) Typical values of relative densities can be determined
from para. 1, (since water has a density of 1000 kg/m^),
and include: aluminium 2.7, copper 8.9, lead 11.4, cast
iron 7.0, steel 7.8, cork 0.25, petrol 0.7.
(iii) The relative density of a liquid (formerly called the
'specific gravity') may be measured using a hydrometer.
3 Atomic structure of
matter
1 There is a very large number of different substances in
existence, each substance containing one or more of a number of
basic materials called elements. 'An element is a substance which cannot
be separated into anything simpler by chemical means.'
There are 92 naturally occurring elements and 13 others
which have been artificially produced. Some examples of common
elements with their symbols are:
Hydrogen Η Helium He,
Carbon C, Nitrogen N,
Oxygen O, Sodium Na,
Magnesium Mg, Aluminium Al,
Silicon Si, Phosphorus P,
Sulphur S, Potassium K,
Calcium Ca, Iron Fe,
Nickel Ni, Copper Cu,
Zinc Zn, Silver Ag,
Tin Sn, Gold Au
Mercury Hg, Lead Pb
Uranium U.
2 Elements are made up of very small parts called atoms,
'An atom is the smallest part of an element which can take part in a
chemical change and which retains the properties of the element.'
Each of the elements has a unique type of atom.
In atomic theory, a model of an atom can be regarded as a
miniature solar system. It consists of a central nucleus around
which negatively charged particles called electrons orbit in certain
fixed bands called shells. The nucleus contains positively charged
particles called protons and particles having no electrical charge
called neutrons. An electron has a very small mass compared with
protons and neutron. An atom is electrically neutral, containing
the same number of protons as electrons. The number of protons in
an atom is called the atvunlc number of the element of which the
atom is part. The arrangement of the elements in order of their
atomic number is known as the periodic table.
The simplest atom is hydrogen which has 1 electron orbiting
the nucleus and 1 proton in the nucleus. The atomic number of
hydrogen is thus 1. The hydrogen atom is shown diagrammatically
in Figure 3.1(a). Helium has 2 electrons orbiting the nucleus, both
of them occupying the same shell at the same distance from the
nucleus, as shown in Figure 3.1(b).
The first shell of an atom can have up to 2 electrons only, the
second shell can have up to 8 electrons only and the third shell up
to 18 electrons only. Thus an aluminium atom which has 13 electrons
orbiting the nucleus is arranged as shown in Figure 3.1(c).
1st shell
2nd shell
3rd shell —
(0
3 When elements combine together, the atoms join to form a
basic unit of a new substance. This independant group of atoms
bonded together is called a molecule.
Ά molecule is the smallest part of a substance which can have a
separate stable existence.*
All molecules of the same substance are identical.
Atoms and molecules are the Imeic building blocks from
which matter is constructed.
4 When elements combine chemically their atoms interlink to
form molecules of a new substance called a compound.
Ά compound is a new substance containing two or more elements
chemically combined so that their properties are changed.*
For example, the elements hydrogen and oxygen are quite unlike
water, which is the compound they produce when chemically
combined.
The components of a compound are in fixed proportion and
are difficult to separate.
Examples of compounds include:
(i) water H2O, where 1 molecule is formed by 2 hy­
drogen atoms combining with 1 oxygen atom,
(ii) carbon dioxide, CO2, where 1 molecule is formed by