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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Matter not observed directly but inferred to exist based upon its gravitational effects
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The four fundamental fundamental equations of electromagnetism.
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just because your question involves math! If your question is on simplification of a mathematical expression, please ask it at math.stackexchange.com The mathematics tag covers non…
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a layer of gases that surround it, permitting life and protecting life by absorbing ultraviolet solar radiation, warming the surface by retaining the heat and mitigating the temp…
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the quantum field theory believed to describe the strong nuclear force.
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an almost perfectly symmetric yellow dwarf star [spectral class G2V] which is at the center of our Solar System.
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quantify location in space.
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To be used for questions on geometry closely pertaining to physics. Includes differential geometry and euclidean geometry.
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any of several principles that find the physical trajectory of a system by minimizing or maximizing some value computed over the proposed path (for instance geometric optics can be reproduced by insis…
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astronomical bodies that are (usually) mainly composed of Hydrogen, Helium, and Lithium. They are massive enough that their gravity compresses the matter to the point where nuclear fusion oc…
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The force on a body resulting from it's motion through a fluid (gas or liquid). This force is directly opposed to the direction of travel.
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The time rate of change of energy
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A vector space $\mathfrak{g}$ over some field $F$ and kitted with a bilinear, antisymmetric and Jacobi-identity-fulfilling product ("Lie Bracket" or "commutator"). In physics, most often arises as the…
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A law in Classical Electromagnetism and Newtonian Gravity.
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a set of agreed, stipulated, or generally accepted norms. It typically helps common efficiency or understanding but is not required, as opposed to a strict standard or protocol.
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for dimensions of a manifold, typically the space-time. DO NOT USE THIS TAG for dimension of a physical quantity.
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Polarization characterizes the oscillations in time the electromagnetic field is doing in the plane perpendicular to the propagation direction of a wave
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The Sun plus the collection of bodies in orbit around the Sun such as planets, dwarf planets, moons, asteroids, comets, etc.
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A research field within general optical physics concerned with light and its material interaction: where light is modelled by full quantum mechanical description.
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particles with an intrinsic angular momentum (i.e. spin) equal to a "half integer" number of fundamental units: $\frac{(2n+1)}{2} \hbar$ for integer $n$. Fermions are required to be in a …
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Analogous to matter, but with charge of the particles opposite to their ordinary matter counterparts.
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A tag for questions about rotational motion, including angular velocity and angular acceleration.
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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 magnitude of velocity.
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For questions about problems related to physics that involve evaluating integrals. Purely mathematical questions should be asked at math.SE.
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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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light, uncharged leptons. The neutrino tag should be applied to question relating to neutrino properties or interactions involving neutrinos.