0
votes
0answers
3 views

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 ...
3
votes
8answers
1k views

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?
-1
votes
0answers
18 views

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 ...
0
votes
1answer
19 views

Point-like nature of particle interaction and wave function non-locality

Let us consider the Hamiltonian for the hydrogen atom $$ ...
0
votes
0answers
9 views

Pummelling a Girder into the Ground

A pile driver is used to drive a vertical steel girder of mass $900 kg$ into the ground. The pile driver is comprised of an $80kg$ steel hammer which is raised $4.0m$ above the top end of the girder, ...
1
vote
0answers
5 views

Why does a cooling car engine crackle?

Why does a cooling car engine crackle? What determines the frequency of the crackles?
2
votes
2answers
20 views

Interpretation of systems in different state of matters BUT almost identical configuration

For a start, let me clarify that by "almost identical configuration" I mean same volume, temperature and number of molecules (but different pressure). One could for instance take two identical systems ...
0
votes
2answers
25 views

If a photon is exists in 'timeless' state, how can objects around it move?

My understanding is that light does not experience time. In attempting to understand what the universe would be like from the perspective of a photon, the answer I get is that the universe would be ...
0
votes
1answer
183 views

Why is the magnetic field stronger at the edges of a bar magnet?

I have been performing an experiment at school in which I test the force on an iron surface from the magnetic field of an electromagnet. The electromagnet has a rectangular iron core. The theory ...
0
votes
1answer
80 views

Why doesn't a changed particle ever lose energy by interacting with others by radiation of virtual photons? Are all virtual photons exchanged?

I've had it explained to me in a separate post that charged particles are constantly exchanging virtual particles with other charged particles and their energy is a steady state. How it is a surety ...
-2
votes
0answers
10 views

How to write Laplace equation for this problem?

How to write Laplace equation in below example. we have two plate with surface S,If we have charge surface density in boundary,obtain potential between two plate. explicitly explain for me how to ...
1
vote
2answers
47 views

How do two electrical charged particles know to repel or attract each other?

Now per QED, electrical charges interactions are effected by photons. Suppose you are one of the two charges. How do you know to attract or repel the other charge? In other words, how do you know if ...
0
votes
1answer
71 views

Total and partial derivatives in thermodynamics and Maxwell relations

Start with $$dS=\left(\frac{\partial S}{\partial T}\right)_VdT+\left(\frac{\partial S}{\partial V}\right)_TdV$$ Using the notes shown here Method 1: i) Divide both sides by dV ...
7
votes
2answers
427 views

Falling into a black hole

I've heard it mentioned many times that "nothing special" happens for an infalling observer who crosses the event horizon of a black hole, but I've never been completely satisfied with that statement. ...
0
votes
0answers
4 views

What is harmonic and fundamental bands in IR spectroscopy?

What is harmonic and fundamental bands in IR spectroscopy? I'm trying to find exact definitions. I guess that fundamental is $1\leftarrow 0$ transition (the most intense and energetic) and harmonic ...
2
votes
1answer
23 views

How does low entropy in the distant past translate into the observed entropy increases?

One of the explanations of the second law of thermodynamics is that it goes back to the low entropy in the early universe (How do you prove the second law of thermodynamics from statistical ...
3
votes
1answer
61 views

Does ordinary refraction exert a couple on the refracting medium?

Refraction gives rise to a momentum change orthogonal to the propagation direction. This must result in an equal and opposite change to the medium at the boundary. Entry and exit cancel, and the ...
0
votes
0answers
18 views

Capillary action height

How to calculate height of the liquid (let's say it's water) in the capillary (so height of capillary action) if you only have r given, r = 0.3 mm - r is radius of capillary. The equation I would use ...
0
votes
0answers
8 views

Postion of a cylinder rolling down an inclined plane [on hold]

I know that the acceleration of a uniform cylinder of known mass rolling down an inclined plane WITHOUT slipping with an inclination of $\theta$ is: $\frac23 g \sin\theta$. Suppose this term is called ...
0
votes
0answers
26 views

Green function integration problem [on hold]

When I'm trying to find the Green Function of Helmholtz equation for a cube $0≤x,y,z≤L$ $$\nabla^2u+k^2u=\delta(\vec{x}-\vec{x}')$$ where $u=0$ on the surface. I set to find the green function where ...
5
votes
4answers
102 views

In a radioactive Bose-Einstein condensate, would all the atoms disintegrate simultaneously?

They're all supposed to do the same thing - so I suppose they would? Also, would the resulting half-life be the same as that of the individual atoms it is made up of?
0
votes
1answer
40 views

Time for a particle undergoing brownian motion to reach a point in a volume

I was wondering how one could calculate the average time a particle needs to reach a random point in a small sphere (filled by water) with a radius of maybe $10 \mu m$. I thought of using the ...
1
vote
3answers
304 views

Bloch wave function orthonormality?

there is this text book that is giving me a hard time for a while now: It shows that Bloch wave functions can be written as $$\Psi_{n\vec{k}}\left(\vec{r}\right) = \frac{1}{\sqrt{V}}e^{i\vec k \vec ...
10
votes
3answers
632 views

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?
8
votes
6answers
735 views

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. ...
1
vote
1answer
23 views

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 $$V(r,\theta)=\sum_{l=0} \left[A_l r^l +\frac{B_l}{r^{l+1}} \right]P_l(\cos{\theta}).$$ ...
3
votes
1answer
34 views

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 ...
0
votes
0answers
8 views

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 ...
2
votes
3answers
43 views

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 ...
3
votes
2answers
293 views

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 ...
1
vote
0answers
24 views

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, ...
2
votes
1answer
113 views

Proof of the conservation of the energy functional for the Gross-Pitaevskii equation?

From the Gross-Pitaevskii equation \begin{equation}i\hbar\frac{\partial\psi}{\partial t}=\left(-\frac{\hbar^2}{2m}\nabla^2+V+g|\psi|^2\right)\psi\end{equation} using the variational relation ...
7
votes
1answer
198 views

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 ...
15
votes
2answers
169 views

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 ...
0
votes
0answers
14 views

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 ...
2
votes
2answers
2k views

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 ...
0
votes
0answers
9 views

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 ...
0
votes
1answer
69 views

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: ...
2
votes
1answer
25 views

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 ...
0
votes
2answers
31 views

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 ...
0
votes
0answers
8 views

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 ...
0
votes
2answers
51 views

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?
1
vote
0answers
9 views

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 ...
4
votes
0answers
17 views

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 ...
1
vote
1answer
67 views

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 ...
0
votes
0answers
10 views

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 ...
0
votes
2answers
68 views

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 ...
0
votes
2answers
51 views

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. ...
1
vote
1answer
14 views

Why are unilateral Laplace transforms suitable for causal systems and bilateral aren't?

https://en.wikipedia.org/wiki/Two-sided_Laplace_transform#Causality The above section says that bilateral transforms will not necessarily make sense for causal systems. In the course of advanced ...
1
vote
3answers
29 views

What is the meaning of pre-tension for a stiff membrane?

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 $k_{ij}$ ...

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