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Quantum mechanics (QM – also known as quantum physics , or quantum theory ) is a branch of physics dealing with physical phenomena at microscopic scales, where the action is on the order of the Planck constant . Quantum mechanics departs from classical mechanics primarily at the quantum realm of atomic and subatomic length scales. Quantum mechanics provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter .
Quantum mechanics
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Statistical mechanics
Statistical mechanics or statistical thermodynamics [ note 1 ] is a branch of physics that applies probability theory , which contains mathematical tools for dealing with large populations, to the study of the thermodynamic behavior of systems composed of a large number of particles . Statistical mechanics provides a framework for relating the microscopic properties of individual atoms and molecules to the macroscopic bulk properties of materials that can be observed in everyday life, thereby explaining thermodynamics as a result of the classical- and quantum-mechanical descriptions of statistics and mechanics at the microscopic level. Statistical mechanics provides a molecular-level interpretation of macroscopic thermodynamic quantities such as work , heat , free energy , and entropy .
Annotated color version of the original 1824 Carnot heat engine showing the hot body (boiler), working body (system, steam), and cold body (water), the letters labeled according to the stopping points in Carnot cycle Thermodynamics is a branch of natural science concerned with heat and its relation to energy and work . It defines macroscopic variables (such as temperature , internal energy , entropy , and pressure ) that characterize materials and radiation, and explains how they are related and by what laws they change with time. Thermodynamics describes the average behavior of very large numbers of microscopic constituents, and its laws can be derived from statistical mechanics . Thermodynamics applies to a wide variety of topics in science and engineering —such as engines , phase transitions , chemical reactions , transport phenomena , and even black holes .
Thermodynamics
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Theory of relativity
The theory of relativity , or simply relativity , generally encompasses two theories of Albert Einstein : special relativity and general relativity . [ 1 ] (The word relativity can also be used in the context of an older theory, that of Galilean invariance .) Concepts introduced by the theories of relativity include: Measurements of various quantities are relative to the velocities of observers. In particular, space and time can dilate .
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Electromagnetism
The word Electromagnetism is a compound from two Greek terms, ἢλεκτρον, ēlektron , " amber " (as electrostatic phenomena were first described as properties of amber by the philosopher Thales ), and μαγνήτης, magnētēs , "magnet" (the magnetic stones found in antiquity in the vicinity of the Greek city of Magnesia , in Lydia , Asia Minor ). The science of electromagnetic phenomena is defined in terms of the electromagnetic force, sometimes called the Lorentz force , which includes both electricity and magnetism as elements of one phenomenon. The electromagnetic force is one of the four fundamental interactions in nature , the other three being the strong interaction , the weak interaction and gravitation . This force is described by electromagnetic fields , and has innumerable physical instances including the interaction of electrically charged particles and the interaction of uncharged magnetic force fields with electrical conductors.
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In physics , classical mechanics is one of the two major sub-fields of mechanics , which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces. The study of the motion of bodies is an ancient one, making classical mechanics one of the oldest and largest subjects in science , engineering and technology . Classical mechanics describes the motion of macroscopic objects, from projectiles to parts of machinery , as well as astronomical objects , such as spacecraft , planets , stars , and galaxies .
Classical mechanics
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