# All Questions

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### Question about inertial mass and gravitational mass

I know that inertial mass $m_i$ is the quantity that appears in Newton's second law: $F=m_ia$ and that gravitational mass $m_{g_1}$ is the quantity that appears in Newton's gravitational law: ...
491 views

### Conversion of ideal gas to real gas via $Z$ compression factor

The ideal gas equation $PV=nRT$ can be converted into real gas equation by compression factor $Z$ i.e $PV=Z~ nRT)$. My question is what is $Z$ and how does it arise? Is $PV/nRT$ a compression ratio of ...
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### Do air particles always rush to fill a container?

I'm sitting here in the metro station, drinking a bottle of water, and watching how the flow of water out of my mouth changes as air rushes into the bottle. My questions is: in space, obviously the ...
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### Low density black holes and singularity

According to wikipedia "... the average density of a supermassive black hole (defined as the mass of the black hole divided by the volume within its Schwarzschild radius) can be less than the ...
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### Wind turbine impact on cars fuel consumption

I have question that I still can't resolve. How much cars fuel consumption rises(l/100km) if I attach 1 kW wind generator to cars body? How can I calculate that and what do I need to know? ...
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### If there are two conserved quantities that do not commute, why is there typically another?

I have come to the following conjecture: Consider two observables $A,B$ that do not commute and represent conserved quantities, there is typically a third conserved quantity. E.g. for some ...
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### Calculating rocket thrust

for my recent project I'm trying to compute somewhat accurate rocket physics (although approximations are good enough - for example for aerodynamics). The project is about making "game-like" ...
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### Critical Value for Dispersion of light

If there is a ray of light moving from $n_1$ to $n_2$ you can get dispersion if $n_1$ is a function of wavelength. What angle of incidence ($\theta_1$) will maximise the dispersion? My solution so ...
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### Is it because of curvature of time that an non-moving object starts to fall down? [on hold]

Are there two extremes in general relativity? One, in which the object is at rest, and starts to fall by time curvature, and one in which light is only influenced by the curvature of space?
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### How do (special) groups such as U(1) and SU(2) do represent the electromagnetic and weak forces? [on hold]

I don't see how groups, such as the circle group somehow representing electromagnetism, represent the fundamental forces. Where is this connection between maths and theoretical physics? Also, as a ...
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### Representing Hamiltonian in discrete position basis

I am trying to numerically find eigenstates of an Hamiltonian. Let $V(x)$ be some potential. Suppose my space is between $-L,L$ and that the allowed positions are every $\Delta x$, such that ...
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### Adiabatic approximation with scaled time?

A car is sent to take a student from coaching every day. The car arrives at the coaching 15min before the time. One day coaching gets closed one hour before the usual time. Then the student without ...
116 views

### On Thermodynamics of Spontaneity of the Reduction-Oxidation Chemical Reactions

According to the first and second law for a closed system containing different chemicals we have \begin{align} &\delta Q - \delta W = dU = T dS - p dV +\sum_i \mu_i d N_i\\ ...
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### As hot air rises is the cold air that rushes in pushed in or sucked in?

I seem to remember from high school, the state of equilibrium. Volumes of more molecules wanting to get to a volume of less molecules and causing a state of equilibrium. From this I believe cold air ...
106 views

### About de Broglie relations, what exactly is $E$? Its energy of what?

Well, you may know de Broglie relations, here they are: $$E = h\nu, \quad\quad p = \frac{h}{\lambda}$$ My question is simple: What exactly is $E$? Is it the total energy? Maybe only kinetic energy? ...
184 views
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### Confusion in Maxwell's derivation of Ampere's Force Law - Part II

I am reading Maxwell's "a treatise on electricity and magnetism, Volume 2, page 156" about "Ampere's Force Law". I have some confusion in the following pages: My question is of two parts: 1. ...
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### What does a one-photon state look like as a wave functional?

According to a post on a mailing list here: https://groups.google.com/d/msg/sci.physics.research/n7Ao7N9aeq0/wqgj20-jBQAJ In general, quatum states |Psi> of the electromagnetic field, no matter ...
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### Ohm's law and an ideal voltmeter

In an ideal voltmeter there is infinite resistance so because of which no current is flowing through it and the voltage reading is not affected. The ohm's law stated that V = I * R In an ideal ...
178 views

### Optical path difference

I have question about calculating optical path difference. $$\Delta L = \mathrm{(BC+CD)}\cdot n_2 - \textrm{BF}\cdot n_1$$ - why calculating path difference here we are subtracting $\mathrm{BF}$ ...
18 views

### Floating of a dead body [on hold]

Why does a dead body float on water? And why does it float by making head downward? The dead body floats due to the production of gases. But how are the gases produced? And which gases are produced? ...
556 views

### How can tangential acceleration from a radial force be explained?

A mass is attached to a rope, and put into a circular motion. If I pull the string from the center, the tangential speed of the mass will increase (by conservation of angular momentum). I am ...
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### Negative probabilities in quantum physics

Negative probabilities are naturally found in the Wigner function (both the original one and its discrete variants), the Klein paradox (where it is an artifact of using a one-particle theory) and the ...
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### Can charged scalar have non zero vev?

In Higgs-Kibble mechanism, if we consider a SU[2]_L doublet of complex scalar fields, then one of them is charged and the other neutral. Why does the neutral field acquire vev and not the charged one? ...
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### The state below has non-zero entanglement, but why is its discord zero?

|ψ⟩=(|00⟩+|11⟩)/√2. after calculation, I get $\delta=cos^2(\theta)\log cos^2(\theta)+sin^2(\theta)\log sin^2(\theta)$, Its minimum value is 0, therefore the discord of the state is zero. But there is ...
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### What are skeleton diagrams and what is their use in qft and many-body physics?

How does one construct skeleton diagrams from specific Feynman diagrams (e.g. for the electronic Green function in QED and in many-body gases, for the polarization function, for the vertex function, ...
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### Relation between phase of dark field and bright field images

I am trying to understand how the super-resolution technique based on Fourier Ptychography 1. In the paper, we run phase retrieval algorithms using images captured using illumination at different ...
68 views

### Proportional acceleration due to changing density of the Earth

My question has to to do with a recent video Minutephysics posted about the time it takes for a person to fall through the earth, found here http://www.youtube.com/watch?v=urQCmMiHKQk At around ...
38 views

### Has Rovelli proven that time doesn't exist? [on hold]

Has Rovelli proven that time doesn't exist? See this paper on the Arxiv for a description of his ideas. I am reading some people argue at length, and inauspiciously, that he has. I am entirely ...
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### What is the size/mass of largest metal plate that was moved by casimir effect?

I learned about Casimir effect recently. Is it applicable only on very light/thin metal plates( in terms of micro/nano meters) or is the effect large enough to be noticed on mili meters scale? What is ...
278 views

### Intro Mechanics: Finding ball speeds after collision

So I'm reading about conservation of energy, momentum, balls colliding etc. and unsurprisingly there are hundreds of questions in my textbook where essentially they give me some of the variables (m1, ...
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### Could science still exist if the nature of events in the universe would be truely random? [on hold]

Most of the science is based on the study of how something behaves in a well defined pattern. Everything follows a rule. Which is the base of all scientific studies. So, in case if there won't be any ...