# Introduction

*Physics* (from the Greek word *physis*, meaning *nature*) is a branch of science that involves the study of physical phenomena. Physicists are interested in literally everything, from the smallest particles of matter to the origins of the universe itself. Since the dawn of history, man has delved into the secrets of the world and what lies beyond it. Even so, physics is not just about exploring the unknown. It impacts on every aspect of our lives. Power supplies, communication networks, transport systems - in fact just about everything we rely on in the modern world is only possible thanks to our understanding of the laws of physics.

Like chemistry, biology and mathematics, physics was for a very long time simply one aspect of a general philosophy of nature that attempted to find rational explanations (as opposed to supernatural ones) for the mysteries of the natural world. Only in the last few centuries has physics evolved into a science in its own right. In fact, the branch of science we call physics was referred to as "natural philosophy" until as recently as the late eighteenth century. There are now many specialised branches of physics, but they are all underpinned by the same basic principles. Physics is often referred to as the *fundamental science*, because if forms the foundation for all other branches of science.

It would not be possible to study physics in any meaningful way without a reasonable grasp of mathematics. Mathematics is the language that allows us to accurately and precisely describe the behaviour of physical systems. If the mathematics required to describe some physical system does not exist, it will be invented. The English physicist, mathematician and astronomer *Sir Isaac Newton* is credited with developing *infinitesimal calculus* in the seventeenth century order to describe phenomena such as planetary motion. The German mathematician and philosopher *Gottfried Wilhelm Leibniz* developed his own version of infinitesimal calculus independently, together with a rigorously defined system of notation. Both men are today considered to have made significant contributions to the development of this branch of mathematics.

Even at an introductory level, the study of physics covers a broad range of topics. These topics can generally be broken down into two groups. The first group falls under the heading *classical physics*, while the second belongs to the realm of *modern physics*. Classical physics is mainly concerned with those physical systems we can see, touch, and measure with relatively unsophisticated instruments. It deals with objects that are not too small to be seen with the aid of a microscope, and that move at speeds considerably slower than the speed of light. Predominant themes in classical physics include *mechanics*, *electromagnetism*, and *thermodynamics*.

The ancient Greeks made some early contributions to the theories of classical physics. In the third century BCE, the Greek mathematician, astronomer and inventor *Archimedes of Syracuse* articulated the *principle of levers*, and explained why some objects float when submerged in water while others sink. For several hundred years, however, very little further progress was made. A period in history known as the *scientific revolution* changed all that. The revolution in question is generally considered to have begun with the publication by Polish astronomer *Nicolaus Copernicus* of his *De revolutionibus orbium coelestium* (*On the Revolutions of the Celestial Spheres*) in 1543, and was to last until the late eighteenth century.

A feature of this period was the rigorous application of mathematical principles to the study of physics, which was pioneered chiefly by the Italian mathematician and astronomer *Galileo Galilei*, and by *Sir Isaac Newton* (to whom we referred earlier). Galileo is perhaps best remembered for his improvements to the design of the telescope, his numerous astronomical observations, and his support for a heliocentric view of the solar system. He spent the last few years of his life under house arrest because his views conflicted with those of the Catholic Church, whose doctrine clearly stated that the *Earth*, and not the sun, was at the centre of the universe. Newton's achievements included the formulation of the *law of universal gravitation* and the three *laws of motion*.

The nineteenth century saw many important contributions, including that of English scientist *Michael Faraday*. Faraday was pretty much responsible for making the connection between magnetism and electricity, and established the concept of the *electromagnetic field*. His discoveries include *electromagnetic induction*, *diamagnetism* and the *laws of electrolysis*. Other achievements included the invention of an electromagnetic rotary device that would ultimately inspire the development of the electric motor, and some notable discoveries in the field of chemistry. Interestingly enough, Faraday was not very good at mathematics, having had little formal education and possessing only a rudimentary understanding of algebra.

Much of Faraday's work was later revisited and given a more rigorous mathematical interpretation by the Scottish mathematician and physicist *James Clerk Maxwell*. Maxwell took the work of Faraday and others working in the field of electromagnetism, and turned it into a set of theories and equations that are still used as the basis for our understanding of electromagnetic phenomena. He was largely responsible for the discovery that light, just like radio waves and x-rays, is a form of electromagnetic radiation. He was further able to demonstrate that all electromagnetic waves propagate through space at the speed of light. Maxwell also made important contributions in the fields of optics and thermodynamics.

*Classical physics* is the first of two broad areas of physics, the other being *classical physics* (which we shall look at elsewhere). Modern physics deals with (among other things) the behaviour of matter and energy at the sub-atomic level, whereas classical physics, whilst also concerned with the behaviour of matter and energy, deals with *macroscopic* objects - in other words, things that we can (usually) see with our own eyes, and which are relatively easy to measure.

The study of physics in one form or another has been going on for thousands of years and is perhaps one of the oldest and most wide-ranging areas of scientific study. We begin by looking at *Newtonian Mechanics* - the physical laws that describe the behaviour of bodies under the influence of one or more forces. The name reflects the fact that many of its principles can be derived, either directly or indirectly, from the physical laws formulated by Sir Isaac Newton.

The number of topics that are now considered to fall under the general heading of "classical physics" has increased considerably since the days of Newton. The field of classical mechanics alone now provides us with an explanation for virtually every kind of phenomenon involving motion of some kind. Newton's laws deal with *force*, *mass* and *motion* and the relationship between them. They are certainly still relevant, and provide us with a good place to start, but they are only the beginning of the story.

Equally important are the laws concerning the conservation of *energy* and *momentum* which, although certainly derived from Newton's work, were not formulated by Newton himself but by those who followed. And there is plenty more. Those studying classical physics can expect to learn, for example, about the behaviour of *solids*, *liquids* and *gases* in different environments, or about the thermodynamic characteristics of various materials. The aim of these pages is to provide a starting point for further study.