A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.

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The central term in the hamiltonian formalism. Can be interpreted as an energy input, or "true" energy.
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A particle that emerges from the theoretical mechanism that is thought to give other particles mass.
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Massive systems held together by gravitational attraction, consisting of stellar associations, star systems, star clusters and types of interstellar clouds, stellar remnants, gasses, cosmic dust and a…
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The subfield of optics in which light propagation is approximated in terms of rays. It mainly includes reflection and refraction on surfaces.
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The property of some materials by which individual atoms decay, emitting energy or particles often transforming into different elements in the process.
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Dimensional analysis means to obtain results by analyzing the units in question, etc. DO NOT USE THIS TAG if your question is about degrees of freedom or spatial dimensions.
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A tag for questions about rotational motion, including angular velocity and angular acceleration.
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The study of the composition or dynamics of the gaseous layers around planets. See also [Earth Science Stack Exchange](http://earthscience.stackexchange.com).
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The change in position of an object relative to a frame of reference. DO NOT USE THIS TAG just because the question contains motion! Almost all physical systems contains motion. Hence it is often …
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for topological field theory (Tft) and topological string theory (tst) questions.
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To be used for linear algebra, and closely related disciplines such as tensor algebras and maybe clifford algebras.
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Analysis of a system of bodies where all forces are in balance and there is no motion relative to a chosen reference frame.
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Perturbation theory refers to methods for understanding physical systems by treating them as small modifications to exactly solvable systems.
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Surface tension occurs due to the tendency of liquid molecules to favor their own kind. Surface tension is important in fluid multiphase systems typically at small length and velocity
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A smaller body orbiting a larger, primary body, where the primary body is not a star.
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the integral of the Lagrangian over time, or the integral of the Lagrangian Density over both time and space.
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World's largest particle accelerator built by the CERN (European Organization for Nuclear Research) near the Franco-Swiss frontier near Geneva, Switzerland. It is designed to collide beams of protons…
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This higgs field breaks electroweak symmetry and provides mass to particles though a process called the higgs mechanism. The excitation of the higgs field is called a higgs boson.
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Could refer to (1) A hydrogen molecule; two hydrogen atoms bonded together or (2) A hydrogen atom; One electron electromagnetically interacting with a nucleus made of a single proton. Hydrogen atoms a…
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Gaseous layer around a planet, dwarf planet, or a star.
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defined as the mass per unit volume of a substance.