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This is a discussion of a present category of science. For the work by Aristotle , see “ Physics (Aristotle) ”. levitating above a High-temperature Superconductor demonstrates the Meissner Effect .]] Physics (" and '''' (''phusiké''), "knowledge of nature") is the branch of Science concerned with discovering and characterizing universal laws that govern Matter , Energy , Space , and Time . Discoveries in physics resonate throughout the Natural Science s, and physics has been described as the "fundamental science" because other fields such as Chemistry and Biology investigate systems whose properties depend on the laws of physics.'' The Feynman Lectures On Physics '' Volume I, Chapter III. Feynman, Leighton and Sands. ISBN 0-201-02115-3 For the philosophical issues of whether other sciences can be "reduced" to physics, see Reductionism and Special Sciences . The development of physics as a Science distinct from Natural Philosophy began with the Scientific Revolution of the 16th and 17th centuries, and continued through the dawn of Modern Physics in the early 20th century. The field has continued to expand, with a growing body of Research leading to discoveries such as the Standard Model of fundamental particles and a detailed History Of The Universe , along with revolutionary new technologies like Nuclear Energy and Semiconductor s. Research today progresses on a vast array of topics, including high-temperature Superconductivity , Quantum Computing , the search for the Higgs Boson , and the Attempt to develop a theory of Quantum Gravity . Grounded in observations and Experiment s and supported by deep, far-reaching Theories , physics has made a multitude of contributions to Science , Technology , and Philosophy . CORE THEORIES Although physics encompasses a wide variety of phenomena, all physicists are expected to be familiar with the basic theories of Classical Mechanics , Electromagnetism , Thermodynamics , Quantum Mechanics , and Relativity . Each of these theories has been tested in numerous experiments and proven to be an accurate model of nature within its domain of validity. For example, Classical Mechanics correctly describes the motion of objects in everyday experience, but it breaks down at the atomic scale, where it is superseded by Quantum Mechanics , and at speeds approaching the Speed Of Light , where Relativistic effects become important. While these theories have long been well-understood, they continue to be areas of active research—for example, a remarkable aspect of classical mechanics known as Chaos Theory was developed in the 20th century, three centuries after the original formulation of mechanics by Isaac Newton (1642–1727). The basic theories form a foundation for the study and research of more specialized topics. A table of these theories, along with many of the concepts they employ, can be found Here . Classical mechanics See Also: Classical mechanics uses the principle of Mechanical Advantage so that a small force can lift a heavy weight.]] Classical Mechanics is a model of the physics of Force s acting upon bodies. It is often referred to as "Newtonian mechanics" after Newton and his Laws Of Motion . Mechanics is subdivided into Statics , which models objects at rest, Kinematics , which models objects in motion, and Dynamics , which models objects subjected to forces. The classical mechanics of continuous and deformable objects is Continuum Mechanics , which can itself be broken down into Solid Mechanics and Fluid Mechanics according to the state of matter being studied. The latter, the mechanics of Liquid s and Gas es, includes Hydrostatics , Hydrodynamics , Pneumatics , Aerodynamics , and other fields. Classical mechanics produces very accurate results within the domain of everyday experience. It is superseded by Relativistic Mechanics for systems moving at large velocities near the Speed Of Light , Quantum Mechanics for systems at small distance scales, and Relativistic Quantum Field Theory for systems with both properties. Nevertheless, classical mechanics is still very useful, because it is much simpler and easier to apply than these other theories, and it has a very large range of approximate validity. Classical mechanics can be used to describe the motion of human-sized objects (such as tops and baseballs), many astronomical objects (such as planets and galaxies), and certain microscopic objects (such as organic molecules.) An important concept of mechanics is the identification of conserved Energy and Momentum , which lead to the Lagrangian and Hamiltonian reformulations of Newton's laws. Theories such as Fluid Mechanics and the Kinetic Theory of gases result from applying classical mechanics to macroscopic systems. A relatively recent result of considerations concerning the dynamics of nonlinear systems is Chaos Theory , the study of systems in which small changes in a variable may have large effects. Newton's Law Of Universal Gravitation , formulated within classical mechanics, explained Kepler's Laws Of Planetary Motion and helped make classical mechanics an important element of the Scientific Revolution . Electromagnetism See Also: Electromagnetism Electromagnetism describes the interaction of charged particles with electric and magnetic fields. It can be divided into Electrostatics , the study of interactions between electric Charge s at rest, and Electrodynamics , the study of interactions between moving charges and Radiation . The classical theory of electromagnetism is based on the Lorentz Force law and Maxwell's Equations . Electrostatics is the study of phenomena associated with charged bodies at rest. Such bodies exert forces on each other, as described by Coulomb’s Law , and their behavior can be analyzed in terms of the concept of an Electric Field surrounding any charged body such that another charged body located at any point in the field is subject to a Force proportional to the magnitude of its charge and its attraction or repulsion, depending on the Polarity of the charge. Electrostatics has many applications, ranging from the analysis of phenomena such as thunderstorms to the study of the behavior of electron tubes. Electrodynamics is the study of phenomena associated with Charge d bodies in motion and varying Electric and Magnetic Field s. Since a moving charge produces a magnetic field, electrodynamics is concerned with effects such as magnetism, electromagnetic Radiation , and Electromagnetic Induction , including such practical applications as the Electric Generator and the Electric Motor . This area of electrodynamics, known as classical electrodynamics, was first systematically explained by James Clerk Maxwell , and Maxwell’s equations describe the phenomena of this area with great generality. A more recent development is Quantum Electrodynamics , which incorporates the laws of Quantum Theory in order to explain the interaction of electromagnetic radiation with matter. Dirac , Heisenberg , and Pauli were pioneers in the formulation of quantum electrodynamics. Relativistic electrodynamics accounts for Relativistic corrections to the motions of charged particles when their speeds approach the speed of light. It applies to phenomena involved with Particle Accelerators and electron tubes carrying high Voltages and Currents . Electromagnetism encompasses various real-world electromagnetic Phenomena . For example, Light is an oscillating Electromagnetic Field that is radiated from accelerating charged particles. Aside from Gravity , most of the forces in everyday experience are ultimately a result of electromagnetism. The principles of electromagnetism find applications in various allied disciplines such as Microwave s, Antenna s, electric machines, Satellite Communication s, bioelectromagnetics, Plasma s, Nuclear research, Fiber Optic s, electromagnetic interference and compatibility, electromechanical energy conversion, Radar Meteorology , and Remote Sensing . Electromagnetic devices include Transformer s, electric Relay s, Radio / TV , Telephone s, Electric Motor s, Transmission Line s, Waveguide s, Optical Fiber s, and Laser s. Thermodynamics and statistical mechanics See Also: Thermodynamics ''' - heat moves from hot (boiler) to cold (condenser) and Work is extracted]] Thermodynamics studies the effects of changes in Temperature , Pressure , and Volume on Physical System s at the Macroscopic scale, and the transfer of energy as Heat .12 Historically, thermodynamics developed out of need to increase the Efficiency of early Steam Engine s.3 The starting point for most thermodynamic considerations are the Laws Of Thermodynamics , which postulate that Energy can be exchanged between physical systems as heat or Work .4 They also postulate the existence of a quantity named Entropy , which can be defined for any system.5 In thermodynamics, interactions between large ensembles of objects are studied and categorized. Central to this are the concepts of System and Surroundings . A system is composed of particles, whose average motions define its properties, which in turn are related to one another through Equations Of State . Properties can be combined to express Internal Energy and Thermodynamic Potentials , which are useful for determining conditions for Equilibrium and Spontaneous Process es. Statistical Mechanics analyzes Macroscopic Systems by applying Statistical Principles to their microscopic constituents. It provides a framework for relating the microscopic properties of individual atoms and molecules to the macroscopic or bulk properties of materials that can be observed in everyday life, therefore explaining Thermodynamics as a natural result of statistics and mechanics (classical and quantum) at the microscopic level. In particular, it can be used to calculate the thermodynamic properties of bulk materials from the spectroscopic data of individual molecules. Relativity See Also: Special relativity General relativity space probe (artist's impression): Radio signals sent between the Earth and the probe (green wave) are Delayed by the warpage of Space And Time (blue lines).]] Relativity is a generalization of classical mechanics that describes fast-moving or very massive systems. It includes Special and General Relativity . The theory of Special Relativity was proposed in 1905 by Albert Einstein in his article " On The Electrodynamics Of Moving Bodies ". It is based on Two Postulates : #The mathematical forms of the Laws Of Physics are invariant in all Inertial Systems . #The Speed Of Light in a Vacuum is constant and independent of the source or observer. Reconciling the two postulates requires a unification of Space and Time into the frame-dependent concept of Spacetime . Special relativity has a variety of surprising consequences that seem to violate common sense, but all have been experimentally verified. It overthrows Newtonian Notions Of Absolute Space And Time by stating that distance and Time depend on the observer, and that time and space are perceived differently, depending on the observer. The theory leads to the assertion of change in Mass , Dimension , and Time with increased Velocity . It also yields the equivalence of Matter and Energy , as expressed in the Mass-energy Equivalence formula ''E'' = ''mc''&2, where ''c'' is the speed of light in a vacuum. Special relativity and the Galilean Relativity of Newtonian mechanics agree when velocities are small compared to the speed of light. Special relativity does not describe gravitation; however, it can handle accelerated motion in the absence of gravitation.
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