Introduction to Physics
Physics, the science that deals with matter and energy and the relationships that exist between them. Physics is the most comprehensive of the natural sciences because it includes the behavior of all kinds of matter—from the smallest particles to the largest galaxies.
The word physics originates from a Greek word meaning natural things. Physics was originally called natural philosophy and included all natural science. As a large amount of knowledge was collected on a particular subject within natural philosophy, that subject branched off and developed into a separate science. This trend is still continuing. Those sciences, such as chemistry, that branched off long ago have developed theories and procedures that seem to have little direct connection with physics. Those, such as electronics, that branched off recently have theories and procedures that still show their close connection to the parent science. Regardless of when the branching took place, however, all the natural sciences exist within the framework of the laws of physics.
Although such sciences as biology and geology have their own viewpoints and experimental procedures, the viewpoint and procedures of physics can also be directly applied to them. Where this application has been made, a new series of sciences has developed. To separate them from their parent sciences, they are known by such names as biophysics (the physics of living things) and geophysics (the physics of the Earth). The sciences of chemistry and physics sometimes overlap in subject matter as well as in viewpoint and procedure. The result is physical chemistry. In astrophysics, the techniques of physics are applied to astronomical observations to determine the properties of celestial objects.
The Study of Physics
The purpose of basic, or pure, physics is to extend human knowledge of the behavior of the universe and to organize this knowledge into a series of related laws.
The work in basic physics is done from two points of view—experimental and theoretical. A physicist may work from one, or the other, or both of these points of view. The experimental physicist performs experiments to gather information. The results of the experiments may support or contradict existing theories or the experiments may be in a field where no theories exist.
The theoretical physicist tries to construct theories that will explain the experimental results. If the theories are to stand, they must also predict the results of future experiments. Both the experimental physicist and the theoretical physicist try to extend the limits of what is known.
Not all physicists are concerned with testing or developing new theories. Some physicists work in applied physics, the purpose of which is to develop useful devices and procedures. Various types of engineers, such as electrical and mechanical engineers, are trained in physics. Applied physics and engineering have led to the development of such devices as television sets, airplanes, washing machines, satellites, and elevators.
Physicists rely heavily on mathematics. Mathematical statements are more precise than statements in words alone. Moreover, the results of experiments can be accurately compared with the various theories only when mathematical techniques are used.
Some knowledge of physics is necessary for even a casual understanding of science. The study of physics is therefore important for anyone wishing to understand the world of today, a world in which science plays a role of ever-increasing importance. Elementary-school science programs include much simple physics. A general introductory course on physics as a separate subject is usually first offered in high school.
The Laws of Physics
The various laws of physics are attempts by physicists to explain the behavior of nature in a simple and general way. Even the most accepted laws of physics, however, are subject to change. Nature's behavior does not change, but techniques for determining its behavior do change and become more accurate. In addition, observations are made under new conditions, such as from orbiting satellites. Physicists, therefore, must subject the laws of physics to new tests to see if, under new conditions, they still hold true. If they do not hold true, changes must be made in the laws or entirely new theories must be proposed. New theories must explain not only all phenomena that the old laws explained but also results of the new tests.
At the beginning of the 20th century, the laws of physics were tested extensively and were found to be too narrow to explain many of the new discoveries. A new body of theories was started. The older body of laws is called classical physics; the new is called modern physics.
Classical Physics
Classical physics is based primarily on the laws of motion and gravitation of Sir Isaac Newton and the theory of electromagnetic radiation of James Clerk Maxwell. In classical physics matter and energy are two separate concepts.
Matter is anything that occupies space and has mass. It exists in three basic forms. Plasma—highly ionized gas—has been called a fourth form.
Energy is the capacity to move matter; as more commonly stated, it is the capacity to do work. Energy exists as mechanical energy, chemical energy, radiant energy, and nuclear energy. Radiant energy, which travels in waves, includes electricity and light and other forms of electromagnetic radiation, such as radio waves.
Some of the most important laws in classical physics are the conservation laws. The law of conservation of mass states that matter cannot be created or destroyed. The law of conservation of energy states that energy cannot be created or destroyed. The law of conservation of momentum states that the momentum of an object is unchanged unless a force acts on it.
Classical physics is usually divided into several branches, each of which deals with a group of related phenomena. Mechanics is the study of forces and their effect on matter. Dynamics is the study of change in motion because of force. Hydromechanics is the mechanics of fluids; that is, of liquids and gases. Hydromechanics is also known as fluid mechanics. Statics deals with how force affects bodies in constant motion and moving in a constant direction. Optics is the study of the behavior of light. Thermodynamics is the study of heat, and how heat energy is stored, transmitted, and converted to other forms of energy. Acoustics is the study of sound. The study of electricity and magnetism also forms a branch of classical physics.
Modern Physics
Modern physics is based on the theory of relativity of Albert Einstein and the quantum theory of Max Planck and others. Matter and energy are not separate concepts, but are alternate forms of each other.
The theory of relativity states that matter and energy are interchangeable and that mass and time can vary.
Quantum theory states that light and other forms of electromagnetic radiation behave as though they have a double nature. Sometimes they behave as waves; at other times they behave as particles. Small particles of matter also have a double, or wave-particle, nature.
Modern physics is broken up into various fields of study. Atomic physics is the study of the structure of atoms and the behavior of electrons, one of the kinds of particles that make up the atom. Because different substances have different atomic structures and therefore, electromagnetic activity, they can be identified on the basis of this activity.
Nuclear physics is the study of the structure of the nucleus, or center, of the atom and of the forces that hold the nucleus together.
High-energy physics, or particle physics, is the study of the production of subatomic particles from other particles and from energy. The characteristics of the various particles, including the antiparticles associated with antimatter, are also studied. Particle accelerators, popularly called atom smashers, are important tools in high-energy physics.
Ultrasonics deals with sound at very high frequencies.
Solid-state physics is the study of the behavior of solids, particularly crystalline solids. Cryogenic, or low-temperature, techniques are often used in research into the solid state.
Plasma physics is the study of the properties of highly ionized gases.
Conservation laws are an important part of modern physics. Since mass and energy can be converted into each other, neither is necessarily conserved, but the total amount of energy and mass is conserved. Momentum is conserved, as in classical physics. Other conservation laws, which apply to certain subatomic particles, have no counterparts in classical physics.
Modern Versus Classical Physics
Modern physics provides a wider, and therefore more accurate, picture of the behavior of the universe than does classical physics. Because classical physics is easier to understand and use, however, it remains valuable in several situations. Classical physics is directly related to everyday experience and, therefore, provides a good introduction to the study of physics. Most high school and introductory college physics courses are primarily classical physics. In most everyday occurrences classical physics is as accurate as modern physics; as in, for example, computing the force needed to move a heavy object, or determining the speed of a train. Classical physics, therefore, is still useful.
Modern physics is reserved for situations where classical physics does not apply. These situations arise particularly when extremely small masses or high speeds (speeds approaching the speed of light) are involved. Even when not used directly, modern physics provides the theoretical basis for the work done in physics.
History
Prehistoric monuments such as Stonehenge are a testimony to the study of physics in those times. These monuments were, in all probability, made for the purpose of studying the motion of heavenly bodies. When the numeral system was developed in ancient civilizations such as Babylon and Sumeria, mathematical formulas were used for studying heavenly bodies. They also helped in more practical areas such as building monuments and developing cities. The study of physics was begun by the Greeks about the fifth century BC. However, because they depended primarily on speculation rather than on observation and experimentation, most of the theories they developed were incorrect.
In the fourth century BC, Aristotle wrote the first treatise on physics. His influence was very great throughout the Middle Ages and his work was accepted without question. A hundred years later, another Greek, Eratosthenes, estimated the circumference of the Earth. Important contributions to physics were made by Archimedes in the third century BC. He found that a solid immersed in a liquid loses weight equal to the weight of the liquid displaced. He also invented many mechanical devices. Ptolemy in the second century A.D. calculated the position of the planets and stars. His theory, however, was incorrect because he postulated that Earth lay at the core of the universe. His theory held sway till Galileo disproved it in almost a thousand years later.
The theories developed by Greeks were introduced to the Arabs, who translated the Greek texts into Arabic. Through the Arabs, these theories were introduced to the West. The Renaissance was the period when new viewpoints toward the study of physics were developed. Leonardo da Vinci of Italy, in the 15th century, did experiments to find out more about movement and mechanics. Nicolaus Copernicus hypothesized that the sun, and not Earth, was the center of the universe. His work was published in the 16th century; and earned strong disapproval within religious and scientific circles.
The first physicist in the modern sense was Galileo Galilei (1564-1642). He based his theories on experiments and measurements. He observed the sky and heavenly bodies through telescopes. His observations conflicted with the Greek theories regarding the motion of Earth and other planets of the solar systems. Galileo made several discoveries in the study of moving bodies. About the same time, William Gilbert made the first experiments in magnetism and electricity. Galileos work was taken further by Johannes Kepler and Rene Descartes in the 17th century. While Kepler postulated a new theory to explain the position of planets and sun in the solar system, Descartes stated that all matter has inertia; it remains in the state of motion or inactiveness till force is applied to it.
Sir Isaac Newton (1642-1727) discovered the law of universal gravitation and stated mathematically the laws of motion. Newton's laws are the basis for much of classical physics. Newton also discovered that white light can be broken up into its constituent colors by a prism. Newton is also credited with having developed the calculus for mathematical calculations related to the study of motion and gravitation.
In 1662, Robert Boyle stated the law, now bearing his name, that describes how the pressure and volume of a gas are related. In 1643, Evangelista Torricelli invented the mercury barometer, which provided one of the first steps in the application of physics to the study of the weather. In 1675, Olaus Roemer became the first to measure the speed of light.
Otto von Guericke, about 1665, made the first device for continuously producing a charge of static electricity. In 1752, Benjamin Franklin made his kite experiment, which showed that lightning is a discharge of electricity. Charles Augustin de Coulomb formulated the laws of electrostatic and magnetic attraction and repulsion in 1785.
Electrical currents were discovered by Luigi Galvani about 1780. Count Alessandro Volta invented the first electric batteries in about 1800. Hans Christian Oersted in 1820 found that an electric current produces a magnetic field. This fact makes possible electromagnets and electric motors. Andr Ampre's law concerning forces between current-carrying electrical conductors, formulated between 1820 and 1825, was the basis for James Clerk Maxwell's theory (about 1865) of electromagnetic waves. The work of Thomas Young in the early nineteenth century, and that of Augustin Fresnel a few years later, proved that light was a kind of electromagnetic wave. This theory clashed with the Newtonian theory of the particle form of light, which was finally discarded. In the late nineteenth century, Heinrich Hertz discovered radio waves. Apart from practical uses in the field of radio and television broadcast, the discovery of radio waves was also of value to theoretical physicists. They could now detect a common factor underlying magnetism and light: their wave nature.
Michael Faraday (1791-1867) is known for his discovery of electromagnetic induction. He also did work in electrochemistry that furthered the atomic theory of matter. This theory had been revived from an early Greek concept by John Dalton in 1808 to account for the way in which substances combine chemically.
Count Rumford showed, about 1798, that a given amount of mechanical energy always produces the same amount of heat. The foundations for the mechanical theory of heat were laid about the middle of the 19th century by the work of James Joule, Julius von Mayer, and Hermann Helmholtz. Thermodynamics was developed by Helmholtz, Rudolf Clausius, and Lord Kelvin. It was Helmholtz who, in 1847, first clearly stated the principle of conservation of energy.
In the late 19th century, Sir William Crookes studied the cathode rays produced in a vacuum tube, finding that they behaved as if they were electrically charged particles. In 1897, J. J. Thomson established the existence of these particles, today known as electrons.
The study of the atom gained great importance following the discovery of x-rays by Wilhelm Konrad Roentgen in 1895 and the discovery of radioactivity by Antoine H. Becquerel in 1896. Two years later, Marie and Pierre Curie discovered radium, a radioactive substance. In 1911, Lord Rutherford developed the theory that an atom consists of one or more electrons revolving about a positively charged nucleus. Niels Bohr, in 1913, added the condition that the electrons in the atom could have only certain orbits, and that electromagnetic radiation was the result of electrons jumping from one orbit to another. This behavior could not be explained by classical physics, and the quantum theory, which had been originated by Max Planck in 1900, was applied to explain it. Quantum mechanics as a field of study came into its own after Erwin Schrodinger and Werner Heisenberg refined the ideas already introduced by Planck, Bohr, Louis de Broglie, and other scientists.
In 1887, Albert A. Michelson and Edward Morley performed an experiment to determine the motion of Earth relative to a substance called ether that was thought to pervade all space and to be the medium through which light waves traveled. The experiment involved detecting changes in the speed of light as measured in different directions. No changes were found, however, indicating that the ether did not exist. The failure of the experiment to detect any changes in the speed of light was later accounted for by the theory of relativity. This theory, introduced by Albert Einstein in 1905 and later expanded, revolutionized the way in which scientists and the general public perceive the universe.
The first experiment in nuclear bombardment was made by Lord Rutherford in 1919. Using the particles emitted by a radioactive material, he produced nuclear reactions in which nitrogen atoms were transmuted (changed) into oxygen atoms. Using this experiment, Rutherford postulated the atomic model where electrons in an atom orbited a dense, positively charged nucleus. The first transmutation of a nucleus by artificially accelerated particles was accomplished in 1932 by Sir John D. Cockroft and Ernest T. S. Walton. Soon after, James Chadwick and Hideki Yukawa found protons, subatomic particles that carry a positive charge, and mesons, respectively.
In 1938, Lise Meitner and Otto Frisch showed that experiments conducted by Otto Hahn and Fritz Strassmann had succeeded in causing the fission (splitting) of the uranium nucleus with neutrons. Further experiments indicated that the neutrons released during the fission of a uranium atom could in turn cause the fission of other atoms, releasing large amounts of energy. In the United States on December 2, 1942, a team of scientists under the direction of Enrico Fermi achieved the first controlled self-sustaining chain reaction. This accomplishment led to the building of the first nuclear weapons, used on two cities in Japan, and later to the construction of nuclear power reactors for producing electricity.
Further studies in nuclear energy led to the development of fusion weapons (hydrogen bombs) in the early 1950s. Physicists built devices to study the properties of plasmas to try to achieve controlled fusion reactions for use as a source of energy.
Teams of physicists used ever more powerful particle accelerators to investigate the inner structure of the nucleus and the basic structure of matter. The collisions of subatomic particles in these accelerators produced a large variety of previously unknown subatomic particles. Owen Chamberlain and Emilio Segre found the existence of a proton with a negative charge, called an antiproton. In the 1950s and 60s, Murray GellMann and George Zweig independently showed how the properties of many of the particles could be accounted for if they were composed of yet smaller particles, which Gell-Mann called quarks. Physicists working with theories concerning elementary particles predicted the existence of particles that were discovered in the 1970s and 1980s. One of them, gluon, helps quarks join together to form protons and neutrons. Other particles discovered include W particle and Z particle.
In the late 1950s rockets carried the first artificial satellites into space. During the following decades, many scientific satellites were placed into orbit or sent through the solar system, providing enormous amounts of data about Earth and the solar system as a whole. Observations of astronomical objects gave astrophysicists an increased understanding of the physical processes that take place in stars, in interstellar matter, and in such objects as pulsars. Astrophysicists found evidence that the universe had begun at one point in a single cosmic explosion—the Big Bang—and, using information obtained from the study of elementary particles, they determined how the universe could have evolved into its present-day form.
Scientists studied the properties, such as superconductivity, exhibited by certain kinds of matter at extremely cold temperatures. Superconducting magnets were developed for use in scientific instruments and other devices. In the mid-1980s, J. Georg Bednorz, K. Alex Mller, and others created materials that exhibit superconductivity at temperatures much higher than previously known materials. Many physicists believed that these new materials would lead to the development of important energy-saving applications.
In the decades following World War II, scientists made a number of important discoveries in electronics that led to the development of such devices as the transistor and the laser. Methods were found for miniaturizing electronic components and for placing large numbers of them on single small chips of silicon.
By the late 1980s computers had come into general use in physics. They were used to run experiments and analyze large amounts of data, making it possible, for example, to simulate extremely complex physical phenomena such as the motion of flowing liquids. Their increased use with particle accelerators helped yield additional discoveries about subatomic matter, including—in 2000—the first direct evidence for the existence of a type of subatomic particle called a tau neutrino. Today, scientists are working toward grand unified theories that can explain the relationship between the elemental forces, primarily the forces between subatomic particles, affecting the universe. The supergravity approach is based on the assumption that gravity is also a fundamental force that affects the universe.
Physics As A Career
Those who wish to have physics as a career should take mathematics and physics at the high school level. A graduate course will include physics, mathematics, and chemistry. Majoring in physics involves a lot of work in the laboratory. Postgraduate or doctoral degrees in physics will enable one to find work in government or private research laboratories. Physicists can also teach in universities. One of the best international research laboratories is the European Organization for Nuclear research (CERN) in Geneva, Switzerland.
The American Institute of Physics works to advance and spread the knowledge of physics and to employ it for human welfare. To this end the institute publishes journals, encourages physics education, provides information about physics to the news media, promotes cooperation among associations devoted to physics, and presents awards. Among its many publications is Physics Today, a monthly journal. The institute was founded in 1931 and has about 75,000 members. Headquarters are in New York City.