2
votes
1answer
501 views

Dynamic simulation of surface tension [closed]

Is there any substantial body of work in physics on dynamically simulating effects of surface tension on liquids? The texts i found so far on fluid dynamics all seem to ignore surface tension, ...
-2
votes
1answer
171 views

How to multiply Celsius and kilograms? [closed]

I have something like this: $$\frac{0.04\,\text{kg} \times 90\,^{\circ}\text{C} + 0.06\,\text{kg} \times 50\,^{\circ}\text{C}}{0.1\,\text{kg}} = T_k$$ Where $T_k$ is a temperature, in Celsius. But ...
0
votes
0answers
55 views

can we break the speed of light [duplicate]

I know this is impossible but I just want to know where I went wrong. here's my proposal: Let us imagine that we have a source of light and a switch that are far one light year from us. so it would ...
2
votes
2answers
289 views

Bertrand's theorem

I found in Goldstein's Classical Mechanics that the condition for closed orbits is given by $\frac{d^2 V_{eff}}{dr^2}>0$.(bertrand's theorem). Can somebody explain to me, how this inequality is ...
2
votes
1answer
351 views

Online physics diagram tool

What is a suitable tool for drawing physics diagrams online? I would love to know if there is a program like the excellent schematic drawing tool that is integrated into the electrical engineering ...
2
votes
0answers
257 views

The correspondence between Poisson bracket and Commutators in Quantum Mechanics

I don't understand canonical quantization. In passing from classical to quantum, one replaces the Poisson brackets with the commutators. I don't really understand this. How can we generally show that ...
4
votes
1answer
675 views

What is the formal definition of spin-independent vs. spin-dependent scattering?

In the search for WIMPs as the dark matter particle, there is an important distinction between spin-independent and spin-dependent scattering. Roughly, WIMPs scattering from nucleons through a ...
-4
votes
2answers
6k views

Do radio waves go faster than the speed of light? [closed]

My science teacher used to say a lot of weird stuff, but I'm just making sure on this one.
0
votes
1answer
256 views

Laser action on one side mirrors (half silvered) and prisms

I know that half silvered mirrors are used in the production of laser emission. Can half silvered mirrors be used outside the instrument so the rays get reflected back on one side of the mirror and ...
4
votes
1answer
178 views

What is a set of minimal assumptions needed to interpret general relativity?

Next semester, I am going to lecture about (the mathematics of) general relativity and I am still thinking hard how to organize and even more importantly how to motivate all the stuff. I am wondering ...
20
votes
5answers
4k views

Does a car consume more fuel when it's raining?

Yesterday my wife asked me that question, and I couldn't answer. Consider a car, in a sunny day, and that is consumes x gallons per mile. Considering that everything is equal, except that it's ...
0
votes
0answers
49 views

What is the volume of electron? [duplicate]

I know that electron has mass , and that is particle( a body which has only mass and whose size is negligible) but can we ever calculate the volume of the electron . if yes how much it is . if no why? ...
-3
votes
1answer
62 views

What is the $\delta$ in fluctuation model [closed]

I found this formula : $G-G_0=\frac{-nkT}2\delta^2$ on this Site and I'd like to ask what does the $\delta$ stand for?
5
votes
3answers
312 views

Why does light seem to occlude objects in front of it

My question: why does light seem to occlude an object in front of it, especially when viewed from a distance? E.g. imagine a grid-like structure (for example an empty gasometer) viewed from a ...
4
votes
1answer
244 views

Can massive fermions have zero modes?

I'm confused about fermion zero modes in relation to instantons. I understand that instantons can create fermion zero modes, but it's not clear to me when a fermion has a zero mode. For example, ...
6
votes
2answers
619 views

Schrödinger equation in position representation

We start from an abstract state vector $ \newcommand{\ket}[1]{|{#1}\rangle} \ket{\Psi}$ as a description of a state of a system and the Schrödinger equation in the following form $$ ...
5
votes
1answer
385 views

M(atrix) theory and things other than D0-branes? And is it non-peturbative M-theory or non-peturbative Type IIA theory?

When I first read the BFSS Paper on M(atrix)-theory, I was under the impression that it was a non-peturbative formulation of M-theory. But recently, upon reading this paper of Nathan Seiberg's, I ...
0
votes
1answer
72 views

Uncertainty in approximated relation

I'll give directly an example to fix the ideas. Suppose that you're studying the acceleration of a system of masses that depends from the number $n$ of masses $m$ by the following relation: ...
2
votes
4answers
1k views

rope wrapped around a pole

I would like to solve this question without using conservation of angular momentum(because of some reason I'll elaborate later). So imagine that we have a pole with radius $r$ and a ball attached to ...
4
votes
2answers
353 views

How to promote algebraic expressions to operators in quantum mechanics?

Okay, I know that in quantum mechanics the quantum observable is obtained from the classical observable by the prescription $$ X \rightarrow x,\quad P \rightarrow -i\hbar\frac{\partial}{\partial x} ...
0
votes
1answer
312 views

does matter radiate energy? [duplicate]

Since we know that all accelerated charges radiate energy and we also know that all matter is made up of protons and electrons which are all the while doing accelerated motion.So from this can i ...
-2
votes
1answer
215 views

Is there a heuristic explanation for the derivation of Heisenbergs Uncertainty Principle from String Theory?

Heisenberg famously derived his uncertainty principle by considering the disturbance that a measurement would have on a small enough system. Of course in the mathematical formalism of Quantum ...
14
votes
1answer
447 views

What is the evidence for the super-rotation of Earth's inner core?

What are the geophysical observations that support (or contradict) the hypothesis that the Earth's inner core rotates at a faster rate than the Earth's mantle? Summary of Answers: 1) Studies of ...
20
votes
2answers
452 views

How to combine these equations of constraint?

I want to model a nonholonomic system of an arbitrary rotating disk in 3D, which rolls without slipping, and doesn't have to stay vertical. (think spinning a penny on the table) I want to use the ...
2
votes
2answers
184 views

Is a permutation of coordinates or labels really equivalent?

To construct a N-body anti-symmetric wave function some derivations start with the requirement that the N-body wave function should be anti-symmetric under a permutation of coordinates, other ...
3
votes
1answer
444 views

Electron in Magnetic Field can lead to non-Hermitian Hamiltonian?

Consider a charged quantum particle in a magnetic field. The Hamiltonian can be written using minimal coupling: $$ H = \frac{1}{2m} \left( \mathbf{p} - \frac{e}{c} \mathbf{A}(\mathbf{x}) \right)^2 $$ ...
3
votes
2answers
3k views

Time required for water to freeze

recently I was wondering if there is any specific formula in order to calculate how long it takes for certain liquids to freeze (especially water). I know this depends on: the volume of the liquid, ...
1
vote
0answers
105 views

What is the domain of validity of the Omega equation?

The Omega eqation is used in meteorology for estimate the value of the vertical velocity. Considering that the horizontal velocity field and density is given by observation. Under which condition ...
1
vote
2answers
1k views

What makes radio waves refract?

What materials cause radio waves to refract? What are the radio IOR's of these materials?
0
votes
1answer
408 views

Why cellphone cameras don't have optical zoom

I have just basic understanding of Physics from elementary school. But I still wonder, why after 10 years of cameras in cellphones, there is no "small-pack" optical zoom. I think there should be no ...
5
votes
1answer
304 views

Is this a Fata Morgana?

I took this photo. Above the horizon there is a thick layer that looks like a cloud, but it surely isn't. Is this a Fata Morgana? What do you think? EDIT: I think the more appropriate name is ...
0
votes
1answer
120 views

Time taken for collision [closed]

We have three particles at the vertices of equilateral triangle of side $d$. At $t=0$ they start moving in such away that at all instant of time each of them has a speed $v$ towards adjacent one. We ...
0
votes
1answer
110 views

Is there a way to define a function of a meniscus curvate?

If you cut a thin slit in thin opaque material and then put it into water and pull it out, the meniscus will be formed in the slit. For my research I need to know if it is analytically possible to ...
5
votes
4answers
769 views

What causes matter to initially rotate/spin/orbit?

What causes matter to initially rotate/spin/orbit? All I can find is the statement that in space particles of dust/gas/matter contract into a spinning disk due to gravity (to form stars, solar ...
1
vote
0answers
3k views

How to calculate the velocity of fluid at the outlet when density and the pressure drop are known?

I have a U- like pipe. Its inlet has atmospheric pressure $p_o=10^{5} \, Pa$. Vacuum is applied to the other end with a pressure gradient $\nabla p_v=-30 \cdot 10^{3} \, kPa/s$. The total time of the ...
2
votes
2answers
1k views

Having trouble understanding the work energy principle intuitively

I'm having trouble understanding the work energy principle intuitively. This is what I'm solid on so far: If you have a ball rolling down a hill, it loses potential energy and gains kinetic energy. ...
3
votes
2answers
886 views

Why are eigenfunctions which correspond to discrete/continuous eigenvalue spectra guaranteed to be normalizable/non-normalizable?

These facts are taken for granted in a QM text I read. The purportedly guaranteed non-normalizability of eigenfunctions which correspond to a continuous eigenvalue spectrum is only partly justified by ...
-1
votes
1answer
465 views

Why strong and weak forces are short range? [closed]

Why are the strong and weak nuclear forces short range? Are quarks confined or welded together? Why are elementary particles confined at short range? Or is color confinement color welding? the ...
0
votes
0answers
61 views

Photon detection time in NMR rotating frame

I think of an NMR experiment, but with a single spin half nucleus initially set to the excited state. When the nucleus finally returns to its ground state, it will emit a photon. An observer in the ...
-3
votes
3answers
273 views

Can you lift a basket up while standing inside it? [closed]

Suppose you stand in a basket and you try to pull the handles of the basket. Will you be able to lift the basket from ground? Similarly, Baron Münchhausen allegedly pulled himself and the horse on ...
3
votes
1answer
138 views

Object submerged in a fluid

1)A sphere of a given mass is put in a non viscous liquid. The sphere is released, and it moves down in the liquid. My doubt is, is the mechanical energy of the system decreasing? The answer given in ...
10
votes
1answer
660 views

Dimensional regularization: removing more than just logarithmic divergencies?

I have followed two courses on QFT, which both involved renormalization by dimensional regularization. My confusion is that one of the professors claimed that dimensional regularization can only be ...
5
votes
0answers
167 views

Holographic Field Theory

I am trying to read this paper http://arxiv.org/abs/1204.1780 and I don't understand how to get from eqn 91 which is, $$S_{2} = N^{2} \{V[P^{(1)}_{m}] + (J^{(1)m} - \mathcal{J}^{m})P_{m}^{(1)}\} ...
7
votes
1answer
130 views

Is it possible to derive the brane action in pure supergravity?

The branes that source the RR fields of supergravity are described by the DBI action plus a CS term. I know this only from superstring considerations. Is there a way to find this result without ...
2
votes
1answer
527 views

How much does sunlight affect inside temperature?

Suppose we have a $3\cdot 3\cdot 3\,m^3$ room of which one side is glass. And suppose that the other 5 sides have no effect on temperature (super isolation). We know from physics how to calculate ...
2
votes
1answer
150 views

Optics for projecting OLED screen DLP style

I just bought a small OLED screen and was wondering is it possible to make a screen surface a little bit bigger ( 2x ) by projecting it through some optics on translucent surface. It reminds me of ...
2
votes
1answer
188 views

Why are particles in harmonic motion in normal modes?

Why do we assume that in normal modes, particles oscillate in form cos (wt) ? How do we know that the general motion of particles can be expressed as a superposition of normal modes? In both French ...
6
votes
1answer
200 views

Can we write the electromagnetic potential covariantly in terms of the four-current?

In the Lorenz gauge, we have a beautiful relation between the four-current and the four-potential: $$\Box A^{\alpha} = \mu_0 J^{\alpha}$$ To get $A$ in terms of $J$, however, we have to use a ...
0
votes
1answer
1k views

Frame of reference of the photon? [duplicate]

In the frame of photon does time stop in the meaning that past future and present all happen together? If we have something with multiple outcomes which is realized viewed from such frame? Are all ...
6
votes
3answers
4k views

What sets a “Law” apart from a “Rule” or a “Principle”? [duplicate]

Basically, I understand the difference between a "Theory" and a "Theorem" but I am quite confused when it comes to "Law", "Rule" and "Principle". Can you make the differences clear to me?

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