# All Questions

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### Physical Meaning Of $dQ/T$ Regarding Clausius Inequality: Is it related to Energy Loss in form of heat or Something Else?

What is the physical meaning of term $dQ/T$ in Clausius Inequality $dQ/T <= dS$ ? Physically we can relate entropy to number of microstates of a system, which relates to number of possible ...
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### Why does the Sun always rise in the East?

Why does the Sun always rise in the East? Earth is rotating on its own axis & also revolves around the Sun, then how come the Sun always rises in the East?
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### Can you debunk this “Perpetual” (ie, very long term) motion machine?

In the following design, gravity is "always" pulling down. There's a parallelogram-shaped box containing a magnet, and underneath the lowest corner of the box is another magnet to repel the first ...
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### Why do leptons and quarks mix?

Is the fact that weak eigenstates are not mass eigenstates completely arbitrary? Or is there a deeper reason for the existence of the PMNS and CKM matrices?
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### What was the need for doing experiments to prove quantum entanglement?

This question comes from someone who is interested in Physics but with no theoretical background. In 1936, EPR presented the thought experiment which later came to be known and quantum entanglement. ...
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### Finding the potential between two spherical shells [on hold]

How to find the potential in region $a<r<b$ I know that the general solution for Laplace's equation is $$V(r,\theta)=\sum_{l=0} \left[A_l r^l +\frac{B_l}{r^{l+1}} \right]P_l(\cos{\theta}).$$ ...
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### A true singularity at $t=0$, coordinate independent Big Bang

Consider a flat Robertson-Walker metric. When we say that there is a singularity at $t=0$, clearly it is a coordinate dependent statement. So it is a "candidate" singularity. In principle there is ...
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### States in valence and conduction band

I often see a Hamiltonian in second quantization written for the valence and conduction band. Now, I was wondering: What are the single-electron states that form the prouct state they act on? So what ...
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### Question of Conservation of Momentum

I think I understand the concept of conservation of momentum in an inelastic collision. However, what if two objects, one being more massive than the other, started out together and then separated ...
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### Why don't global coordinates always exist for a manifold?

Let $M$ be a manifold and $(\phi,U)$ a patch. Then $\phi(P)=\bar{x}=\begin{bmatrix} x^1\\ x^2\\ \vdots\\ x^n \end{bmatrix}$ for each $P$ in $U$. But each $P$ in $M$ is in some patch, so this ...
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### What makes Lattice Yang-Mills hard?

I've been reading up on non-perturbative Yang-Mills, and have found the following equation: $$Z[\gamma, g^2, G]=\int \! \prod e^{-S}\mathrm{d}U_i$$ Now I don't know much about computational physics, ...
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### Proof of the conservation of the energy functional for the Gross-Pitaevskii equation?

From the Gross-Pitaevskii equation $$i\hbar\frac{\partial\psi}{\partial t}=\left(-\frac{\hbar^2}{2m}\nabla^2+V+g|\psi|^2\right)\psi$$ using the variational relation ...
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### Intersecting Wilson loops in 2D Yang-Mills

I am currently trying to understand 2D Yang-Mills theory, and I cannot seem to find an explanation for calculation of the expectation value of intersecting Wilson loops. In his On Quantum Gauge ...
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### Hourglass on the Moon

Someone asked me this, and I was surprised to find I couldn't answer it: suppose I have an hourglass / egg timer that times two minutes in Earth's gravity. If I used it on the Moon, how long would it ...
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### Distanced covered when projected with escape velocity?

A body is projected from the center of the Earth with escape velocity, at what distance it will rise from the surface of the Earth? [Please do not give negative rating to my question. Tomorrow is my ...
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### Slingshot Projectile motion calculation [on hold]

If I have distance the sling was dragged and the angle of the drag; then I require to calculate the projectile motion this sling shot would make. What are the equations that would enable this ...
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### What concepts/rules apply for multi-stage pumping of water

For single stage (ie one pump) water transfers calculations for pressure loss are commonly done by adding the elevation difference of the start and end of the pipe line to the friction losses that ...
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### Applying Euler Homogenous Function Theorem to $df$ or $f$

I am currently reading Demirel's Nonequilibrium Thermodynamics in order to learn more about entropy and nonequlibrium thermodynamics However I and stumped on how the author's do the following step: ...
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### Viscosity and surface tension

Both viscosity and surface tension are dependent on the intermolecular forces between the molecules of the liquid. Supposing from this, shouldn't there be a directly proportional relationship between ...
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### Current lagging voltage by more then 90 degrees

According to Wikipedia https://en.wikipedia.org/wiki/Leading_and_lagging_current An alternating current that reaches its maximum up to 90° behind the voltage producing it is said to be lagging. and ...
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### Excitation probability given pulse bandwidth and atom linewidth

Consider photon source producing photon pulses with a frequency distribution $f(\omega)$ and a glass tube filled with a gas. The atoms of the gas can be excited by photons with a frequency of ...
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### A model that unifies the strong, EM, weak and gravity forces?

Does there exist such a model that explains the force clusters (their origin, relations between them): the strong, EM, weak and gravity forces?
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### Evaluation of the anomalous dimensions of fields in SUSY $SU(5)$

The general formula for the anomalous dimension can be found in Martin΄s review article (hep-ph/9709356v6), on page 62 relation (6.5.4). In the case of $SU(5)$ and especially in the paper of ...
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### What is the largest number of bosons placed in a BEC?

What is the record for the largest number of bosons placed in a Bose-Einstein condensate? What are the prospects for how high this might get in the future? EDIT: These guys reported 20 million ...
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### Visualisation of electron

first things first, I'm not by any means a physicist nor a student of physics. I study graphic design. Theme of my bachelor thesis is visualisation of physical and mathematical phenomenons, long story ...
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### Equal volumetric rate versus area open to flow [on hold]

A vertical water disposal well has been drilled and cased. There are two horizontal rock formations that the wellbore intersects and these formations will be targeted for water disposal. To allow ...
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### How to use an accelerometer to correctly quantify the magnitude of vibrations

Consider the following setup, an accelerometer is placed inside a helicopter, measuring "g" values along 3 axes (x,y,z) every 10 ms (100 times a second), during a helicopter flight. If one, wants to ...
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### On which basis we think there is something more than just super dense matter in black holes?

Apparently physicists think that there is something inside black holes. Like a new universe or a link between dimension... But for me a black hole is no more than supermassive supercompacted matter. ...
On one hand, I know that the tighter a drum head is stretched, the higher its natural frequencies. This relation is given by: $$f_{ij}=\frac{k_{ij}}{2\pi R}\sqrt{\frac{T_0}{h\rho}}$$ where $k_{ij}$ ...