# Tag Info

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The photons released are individually massless, but all of them together have an effective mass equal to the original masses of the particle and antiparticle; see my answer here. This isn't some mathematical abstraction either -- you can put the photons in a reflective box and weigh it, and it'll have extra weight. It's safe to say that the phrase ...

1

This is an every day term, with no meaning for physics. In the Oxford dictionary for "energy" one gets: Physics The property of matter and radiation which is manifest as a capacity to perform work (such as causing motion or the interaction of molecules) In science fiction one might separate zero mass particles, like the photon and the graviton ( ...

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I would look at this in a slightly different way. Rearranging it: $$m \ddot{x} = -(a|\dot{x}|+k) x = -k_{eff} x$$ If you look at it that way, it is really a variable, non-linear stiffness $k_{eff}$ that depends on the velocity, rather than a damping that depends on the position. In this respect (assuming $a > 0$), the stiffness coefficient has a lower ...

9

Your question is not specific to inflation, and really applies to any case where a bosonic quantum field behaves semiclassically due to macroscopically large occupation numbers. One very simple example of this is the Stark effect in quantum mechanics, where a Hyrodgen atom is placed in a uniform electric field. The atom is treated as a quantum mechanical ...

0

The Gravitaional Potential Energy is calculated taking the potential at Infinty as zero, ie , if you come from infinity to the point at which you are calculating gravitational potential (say point P), Energy will continuously decrease because $$E \varpropto -\frac{1}{r}$$ (r is distance from the center of object to P) as r decreases, the fraction increases, ...

0

Electromotive force is not a mechanical force, but a driving electrical force for charges or the potential energy per unit charge stored in the electrical source. It can be seen as the work that can be done by the source to drive off electrons in a circuit, provided there is no internal resistance of the source. This potential is the gradient of the ...

1

International Handbook of Research in History, Philosophy and Science Teaching quotes the English translation of Guisasola et al. (2008), which discusses some of the early history of the EMF. The man who coined the term "electromotive force" was Alessandro Volta, who stated that there was a force separating the charges in current flowing in a closed circuit. ...

0

There is no fundamental difference between the two terms, except that in certain situations one or the other have come to be used more often. Gravity is more often used to describe the concept ("Newtonian Gravity"), the force (the "Force of Gravity"). Gravitation is more often used for phenomena resulting from gravity ("Gravitational Waves", "Gravitating ...

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Gravity is the physical phenomena by which bodies attract themselves. It is the effect we observe. Gravitation is a model, a theory to explain the observed phenomena. The Newtonian Gravitation explains this phenomena in terms of attractive forces generated by massive bodies. It dos not depend whether the bodies are terrestrial or celestial. General ...

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The adjoint of an operator is obtained by taking the complex conjugate of the operator followed by transposing it. i.e., $(A)^\dagger_{ij}=\left((A)^T_{ij}\right)^*=\left((A_{ij})^*\right)^T=A_{ji}^*$ You can do it in any order. The adjoint of an operator is the infinite dimensional generalization of conjugate transpose, where you find the transpose of ...

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when a signal is analyzed in time domain they are called spectrum or you can say that signal is in spectral domain. but when the signal is analyzed in frequency domain and amplitude of such signal is taken to analyzed the signal then they are said to be in cepstral domain.

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They both refer to the same thing. The habitable zone is also called the Goldilocks zone, a metaphor of the children's fairy tale of Goldilocks and the Three Bears, in which a little girl chooses from sets of three items, ignoring the ones that are too extreme (large or small, hot or cold, etc.), and settling on the one in the middle, which is ...

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The 6V in 6V battery is a label which gives an indication of the sort of voltage which might be obtained from such a battery. For example if your ^ V battery was an lead-acid battery and it was fairly new and fully charged its voltage would be 6.3 volt and if older or partially discharges then it is more likely to be 6 V. A 1.5 V alkaline battery at the ...

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EMF or Terminal voltage will be considered same if battery has no internal resistance. If battery has some internal resistance then terminal voltage will be different(less) from the EMF or potential difference from the battery. If a battery has internal resistance then what will be considered if the same statement is given.

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In your questions all the cases are assumed to be ideal unless mentioned. Therefore the electromotive force and the terminal voltage are equal in that case as internal resistance of the battery is considered negligible(if not given) . If the battery has internal resistance then the emf remains constant,but the terminal voltage decrease by a value which is ...

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The meaning you quote is only one of several. From the same dictionary, others which are now obsolete or not often used are 3: importance in influence or effect 4 obsolete : a cause or motive of action and it is from these that the scientific meanings derive : 6a : tendency or measure of tendency to produce motion especially about a ...

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In the language of physics, a moment is a physical quantity which accounts for how a physical property is located or arranged. We do NOT use the colloquial meaning of the term moment. This "moment" we are referring to is derived from the latin word momentum which is also a physical quantity equal to the product of the mass and velocity.

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The moment of a vector $\vec v$ applied in the point $\vec p$ with respect to the pole $\vec q$ is by definition $$\vec M = (\vec p - \vec q) \times \vec v$$ With $\times$ vector product.

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Diffeomorphism Invariance Let $M$ be a smooth manifold. Let $\phi: M \to M$ be a diffeomorphism. A simple property of the Einstein equations is $$g \in \otimes^2 TM \text{ is solution to vacuum Einstein equation} \implies \text{ so is } \phi^*g$$ To see that this is true, simply pull back both sides of the Einstein equation by $\phi$, and use the ...

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