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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.
Basic, or pure, physics is a study of the behavior of the universe and is organized into a series of related laws. Basic physics can be studied from two points of view: experimental and theoretical. A physicist may work from one 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 establish new ideas where no theories existed before.
The theoretical physicist constructs theories to explain experimental results. If the theories are to stand the test of time, 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. Applied physicists develop useful devices and procedures and may hold alternative job titles. 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.
The various laws of physics attempt to explain the behavior of nature in a simple and general way. Even the most accepted laws of physics, however, are subject to change. Physicists continually 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.
At the beginning of the 20th century, the laws of physics were tested extensively and found to be too narrow to explain many of the new discoveries. A new body of theories was needed. The older body of laws is called classical physics; the new is called modern physics.
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. Hydromechanics studies the mechanics of liquids and gases. Optics is the study of the behavior of light. Physicists in this field study such things as lasers, liquid crystal displays, or light-emitting diodes. Thermodynamics is the study of heat. Acoustics is the study of sound, such as in recording studio acoustics, underwater sound waves, and electroacoustical devices such as loudspeakers. The study of electricity and magnetism also forms a branch of classical physics. Research in this area includes microwave propagation, the magnetic properties of matter, and electrical devices for science and industry.
Modern physics is also 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. Nuclear physics is the study 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 energy. The characteristics of these various particles are studied using particle accelerators, popularly called atom smashers.
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. Research in solid-state physics has produced transistors, integrated circuits, and masers that have improved computers, radios, televisions, and navigation and guidance systems for satellites. Plasma physics is the study of the properties of highly ionized gases. Physicists in this field are concerned with the generation of thermonuclear power.
Astrophysics is the study of the solar system, stars, galaxies, and the universe.
Condensed matter physics is the study of the physical properties of condensed phases of matter, such as solids and liquids.
Those who specialize in medical physics work in the health care industry to develop new medical technologies and radiation-based treatments, or to improve current imaging technologies, such as magnetic resonance imaging and ultrasound imaging, that use various forms of radiant energy.
Although biology and geology are separate sciences in their own right, the concepts of physics can also be applied directly 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). Similarly, the sciences of chemistry and physics sometimes overlap in subject matter as well as in viewpoint and procedure, creating physical chemistry. In astrophysics, the techniques of physics are applied to astronomical observations to determine the properties of celestial objects.
Most physicists are engaged in research, and some combine their research with teaching at the university level. Some physicists are employed in industries, such as petroleum, communications, manufacturing, and medicine.