Chapter I: Preface

In the preparation of this text, the _pupil_, his experience, needs, and interests have been constantly kept in mind. The order of topics, illustrations, and problems have been selected with the purpose of leading the _pupil_ into a clear understanding of the physical phenomena continually taking place about him.

The recommendations and conclusions reached by the "New Movement in the Teaching of Physics" have been incorporated into the book as a whole. These conclusions indicate that the most efficient teaching in physics involves a departure from the quantitative, mathematical methods of presentation that were in general use a dozen or more years ago, toward a method better adapted to the capabilities, interests, and requirements of the young people in our physics classes.

The older methods are effective with a portion of the student body which has the greater mathematical ability and training, but they discourage a large majority of the pupils who are not gifted or prepared for severe mathematical analysis. For this reason, many of the more difficult mathematical demonstrations often given in physics texts are omitted. Most of the problems involve only the units employed in practical every-day measurements.

The portions of Mechanics that are ordinarily so difficult for the average pupil are not taken up until he has covered considerable ground with which he is more or less familiar and not until he has become somewhat accustomed to the methods of study and the technical terms of the subject.

The pupil comes to the study of physics with a great number of experiences and impressions of physical phenomena continually occurring about him. In recognition of this fact, it has been thought best to consider first the explanation of common things well known to all pupils, such as the diffusion of gases, evaporation of liquids, expansion of bodies when heated, and capillary action. Since the molecular theory of matter is now supported by so many conclusive evidences, we have not hesitated to make free use of it in the early chapters. The applications of this theory are extremely helpful in explaining every-day phenomena. Our experience shows that beginners in physics understand and apply this theory without difficulty.

The illustrations and drawings have been selected from a pedagogical rather than a spectacular point of view. Practically all of them are new. The problems and exercises have been selected for the distinct purpose of illustrating the principles taught in the text and for their practical applications.

Many direct applications to common every-day experiences are given in order to connect the subject matter with the home environment and daily observation of physical phenomena. Some phenomena are mentioned without detailed explanation as it is felt that the presentation of these subjects in this manner is better for this grade of student than a complete analysis.

Some of the special features of the text may be briefly summarized as follows:

(A) _Simplicity of presentation_ is emphasized. The methods of attack, the illustrations and examples employed in developing the subjects are particularly adapted to beginners in physics.

(B) The text is divided into some _seventy-seven sections_, each containing material enough for one recitation.

(C) Each of these sections is summarized by a list of _important topics_ which point out to the pupil the principles and subject matter requiring most careful attention. The lists of important topics are also of assistance to the teacher in assigning recitations.

(D) The _problems and practical exercises_ emphasize physical principles as distinguished from mathematical training. A list of exercises is placed at the end of the several sections. They are in sufficient number to permit testing at many points and of a choice of problems by teachers.

The authors wish to express their appreciation for suggestions and helpful criticisms to many who have read the text in manuscript or proof. Especially to Professor A. P. Carman of the University of Illinois and his associate, Professor F. R. Watson, who have gone carefully over the whole text; and to Mr. Chas. M. Brunson, Scott High School, Toledo, Ohio, Mr. Frank E. Goodell, North High School, Des Moines, Iowa, and to Mr. Walter R. Ahrens, Englewood High School, Chicago, for assistance in reading the proofs. Also to Mr. W. H. Collins, Jr., Bowen High School, Chicago, who supervised the preparation of drawings for the diagrams and figures; and to many firms and individuals that have courteously furnished material for illustrations.

WILLIS E. TOWER.
CHARLES H. SMITH.
CHARLES M. TURTON.

ON THE STUDY OF PHYSICS

When a pupil begins the study of Physics he has in his possession many bits of knowledge which are fundamental in the science. He has learned to throw a ball and can tell how a thrown ball moves. He has drawn out nails with a claw hammer. He has seen wood float and iron sink. He has sucked liquids up through straws. In his mother's kitchen, he sees water as ice, liquid, and steam. On a wintry day he reads the temperature on a thermometer. He sees sparks fly from car wheels when the brakes are applied. He has played with a horseshoe magnet, and has found the north by means of a compass. The telephone, the electric light and the motor he sees, and perhaps uses, many times a day. He dresses before a mirror, focuses his camera, watches the images at a moving picture show, and admires the colors of the rainbow. He has cast stones into water to watch the ripples spread, has shouted to hear the echo, and perhaps plays some musical instrument. These, and a thousand other things, are known to the intelligent and normal boy or girl who has reached the age at which the study of Physics is properly begun.

To a great extent even the terms used in the science are familiar to the beginner. He speaks of the horse-power of an engine, reads kilowatt-hours from the meter in the cellar, and may know that illuminating gas costs one dollar per thousand "cubic feet." "Ampere" and "volt" are words he frequently hears and sees.

When he takes up the study of Physics, the attitude of the student toward these familiar things and words must undergo a change. Casual information about them must be changed to sound knowledge, purposely acquired. Hazy notions about the meanings of words must be replaced by exact definitions. Bits of knowledge must be built into a structure in which each fact finds its proper place in relation to the others.

The only agent which can accomplish these changes is the student himself. He must consciously and purposely seek the truth and must reflect upon it until he sees it in its relation to other truth. Upon him, and upon him alone, rests the final responsibility for the success or failure of his study.

But the student is not without assistance. In his teacher he finds a guide to stimulate, to direct, and to aid his efforts, and a critic to point out wherein his efforts have failed and wherein they have succeeded. Weights, measures, and other apparatus are furnished to enable him to answer for himself questions which have arisen in his studies.

In addition to these the student has his text book, his teacher for his hours of private study. A good text book is an inspiring teacher in print. It directs attention to things familiar to the student through long experience, and inspires him to make a closer scrutiny of them. It invites him to observe, to analyze, to compare, to discover likenesses and differences in behavior. It questions him at every turn. Its ever repeated challenge reads, "Weigh and consider." It furnishes him needed information that he cannot otherwise acquire. It satisfies his desire to know, "By whom, where, when, and how was this first discovered?"

The student of Physics must never forget that he is studying not pages of text but the behavior and properties of iron, water, mica, moving balls, pumps, boiling liquids, compressed air, mirrors, steam engines, magnets, dynamos, violins, flutes, and a host of other things. His studies should, whenever possible, be made first hand upon the things themselves. The text is an aid to study, never a substitute for the thing studied.

It is an excellent plan for each student to select some one thing for special study, the telephone for example. By observation, experiment, and reading, he may acquire a large amount of valuable information about such a subject while pursuing his course in Physics. Every part of the science will be found to bear some relation to it.

The student who takes up the study of Physics in the way suggested will find himself at the end of a year of study in possession of much new and valuable knowledge about the physical world in which he lives. By virtue of this knowledge he will be better able to enjoy the world, to control it, and to use it.

THOMAS D. COPE.

PHILADELPHIA.

CONTENTS

CHAPTER I. INTRODUCTION AND MEASUREMENT. PAGE

(1) Introduction 1
(2) States of Matter 4
(3) The Metric System 8

CHAPTER II. MOLECULAR FORCES AND MOTIONS.

(1) Molecular Motions in Gases 13
(2) Molecular Motions in Liquids 18
(3) Molecular Forces in Liquids 21
(4) Molecular Forces in Liquids and Solids 27
(5) Molecular Forces in Solids 31

CHAPTER III. MECHANICS OF LIQUIDS.

(1) Liquid Pressure 36
(2) Transmission of Liquid Pressure 41
(3) Archimedes' Principle 47
(4) Density and Specific Gravity 52

CHAPTER IV. MECHANICS OF GASES.

(1) Weight and Pressure of the Air 55
(2) Compressibility and Expansibility of the Air 62
(3) Pneumatic Appliances 66

CHAPTER V. FORCE AND MOTION.

(1) Force, how Measured and Represented 79
(2) Motion. Newton's Laws 85
(3) Resolution of Forces 96
(4) Moment of Force and Parallel Forces 99
(5) Gravitation and Gravity 103
(6) Falling Bodies 109
(7) The Pendulum 115

CHAPTER VI. WORK AND ENERGY.

(1) Work and Energy 119
(2) Power and Energy 123
(3) The Lever and Simple Machines 129
(4) Wheel and Axle and Pulley 136
(5) Efficiency and the Inclined Plane 142
(6) Friction and its Uses 147
(7) Water Power 152

CHAPTER VII. HEAT, ITS PRODUCTION AND TRANSMISSION.

(1) Sources and Effects of Heat 159
(2) Temperature and Expansion 162
(3) Expansion of Gases, Liquids and Solids 167
(4) Modes of Transmitting Heat 173
(5) Convection, Heating and Ventilation 179
(6) The Moisture in the Air, Hygrometry 191
(7) Evaporation 196

CHAPTER VIII. HEAT AND WORK.

(1) Heat Measurement and Specific Heat 200
(2) Heat and Changes of State 205
(3) Heat and Work 212
(4) Heat Engines 222

CHAPTER IX. MAGNETISM.

(1) General Properties of Magnets 228
(2) Theory of Magnetism, Magnetic Fields 232
(3) The Earth's Magnetism 238

CHAPTER XI. STATIC ELECTRICITY.

(1) Electrification and Electrical Charges 243
(2) Electric Fields and Electrostatic Induction 247
(3) Electric Theories, Distribution and Electric Charges 252
(4) Potential, Capacity, and the Electric Condenser 257
(5) Electrostatic Generators 262

CHAPTER XI. ELECTRIC CURRENTS PRODUCED BY VOLTAIC
CELLS.

(1) Electrical Currents and Circuits 267
(2) The Simple Voltaic Cell and its Action 270
(3) Practical Voltaic Cells 274

CHAPTER XII. MAGNETIC EFFECTS OF ELECTRIC CURRENTS,
AND ELECTRICAL MEASUREMENTS.

(1) The Magnetic Effect of Electric Currents 279
(2) Electrical Measurements 289
(3) Ohm's Law and Electrical Circuits 298
(4) Grouping of Cells and Measuring Resistance 302

CHAPTER XIII. CHEMICAL AND HEAT EFFECTS OF ELECTRIC
CURRENTS.

(1) The Chemical Effect of Electric Currents 307
(2) The Storage Battery and Electric Power 312
(3) The Heat Effect of Electric Currents 318

CHAPTER XIV. INDUCED CURRENTS.

(1) Electromagnetic Induction 326
(2) The Dynamo and the Motor 335
(3) The Induction Coil and the Transformer 343
(4) The Telephone 349

CHAPTER XV. SOUND.

(1) Sound, Source, Speed, Media 354
(2) Waves and Wave Motion 357
(3) Intensity and Pitch of Sound 363
(4) Musical Scales and Resonance 368
(5) Interference, Beats, Vibration of Strings 374
(6) Tone Quality, Vibrating Plates and Air Columns 384

CHAPTER XVI. LIGHT.

(1) Rectilinear Propagation of Light 388
(2) Photometry and Law of Reflection 393
(3) Mirrors and Formation of Images 400
(4) Refraction of Light 410
(5) The Formation of Images by Lenses 416
(6) Optical Instruments 423
(7) Color and Spectra 430
(8) Nature of Light 442

CHAPTER XVII. INVISIBLE RADIATIONS.

(1) Electric waves and Radioactivity 448

CHAPTER XVIII. WIRELESS TELEPHONY AND ALTERNATING
CURRENTS.

(1) Wireless Telephony 460
(2) Alternating Currents 466

INDEX 487

PHYSICS