Themes > Science > Physics > About Physics, Generalities > Introduction
Physics, major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. Sometimes in modern physics a more sophisticated approach is taken that incorporates elements of the three areas listed above; it relates to the laws of symmetry and conservation, such as those pertaining to energy, momentum, charge, and parity. Physics is closely related to the other natural sciences and, in a sense, encompasses them. Chemistry, for example, deals with the interaction of atoms to form molecules; much of modern geology is largely a study of the physics of the earth and is known as geophysics; and astronomy deals with the physics of the stars and outer space. Even living systems are made up of fundamental particles and, as studied in biophysics and biochemistry, they follow the same types of laws as the simpler particles traditionally studied by a physicist.
Acoustics	Propagation of sound.
Atomic Physics	Structure and properties of atoms.
Cryogenics	Properties and behavior of matter at extremely low temperatures.
Electromagnetism Electric and magnetic force fields	Behavior of electrically charged particles in electromagnetic fields; propagation of electromagnetic waves. Also known as electrodynamics
Elementary Particle  Physics	Properties of elementary particles such as electons, photons, etc. Also known as high energy physics. .
Fluid Dynamics	Fluid Dynamics Properties and behavior of moving fluids and gasesProperties and behavior of moving fluids and gases.
Geophysics	Application of physics to the study of the earth. Includes atmospheric physics, meteorology, hydrology, oceanography, geomagnetism, seismology, and volcanology.
Mathematical Physics	Application of  mathematical techniques to problems in physics.
Mechanics	Forces, interactions, and motions of material objects.
Molecular Physics	Structure and properties of molecules.
Nuclear Physics	Structure, properties, reactions, and evolution of atomic nuclei.
Optics	Propagation of light, electromagnetic waves.
Plasma Physics	Behavior of ionized (electrically charged) gases.
Quantum Physics	Quantum nature of matter, energy, and light. Behavior of systems composed of small numbers of elementary particles.
Solid State Physics	Physical properties of solid materials. Includes crystallography, semiconductors, superconductivity.  Also known as condensed matter physics.
Statistical Mechanics	Application of statistical methods to model the behavior of systems composed of many particles.
Thermodynamics	Temperature and energy; heat flow; transformation of energy; phases of matter (solid, liquid, gas, plasma).
The emphasis on the interaction between particles in modern physics, known as the microscopic approach, must often be supplemented by a macroscopic approach that deals with larger elements or systems of particles. This macroscopic approach is indispensable to the application of physics to much of modern technology. Thermodynamics, for example, a branch of physics developed during the 19th century, deals with the elucidation and measurement of properties of a system as a whole and remains useful in other fields of physics; it also forms the basis of much of chemical and mechanical engineering. Such properties as the temperature, pressure, and volume of a gas have no meaning for an individual atom or molecule; these thermodynamic concepts can only be applied directly to a very large system of such particles. A bridge exists, however, between the microscopic and macroscopic approach; another branch of physics, known as statistical mechanics, indicates how pressure and temperature can be related to the motion of atoms and molecules on a statistical basis Physics emerged as a separate science only in the early 19th century; until that time a physicist was often also a mathematician, philosopher, chemist, biologist, engineer, or even primarily a political leader or artist. Today the field has grown to such an extent that with few exceptions modern physicists have to limit their attention to one or two branches of the science. Once the fundamental aspects of a new field are discovered and understood, they become the domain of engineers and other applied scientists. The 19th-century discoveries in electricity and magnetism, for example, are now the province of electrical and communication engineers; the properties of matter discovered at the beginning of the 20th century have been applied in electronics; and the discoveries of nuclear physics, most of them not yet 40 years old, have passed into the hands of nuclear engineers for applications to peaceful or military uses.