0
votes
0answers
7 views

Kinematic problem (initial acceleration)

"A ball is rolling over a soccer field with constant velocity Vb (> 0) under an angle of 45° with respect to the goal line. It is starting at the corner of the field (distance d beside the middle of ...
-4
votes
0answers
16 views

How are Earth and Venus actually rotating? [on hold]

As we know something moving in circle or ellipse path cannot move forward in space. Is earth moving on a helix path with also having its own rotation in helix shape? and is venus rotating in same ...
0
votes
1answer
36 views

What does it mean for an integral's differential to be raised to a power, like e.g. $d^3r$ or $d^3u$?

I was reading Zwelfel's book on reactor physics and saw the following notation: Notice that the differential of the integral is raised to the third power. What is the meaning of this notation? ...
0
votes
1answer
20 views

Particle attached in equilibrium to two elastic strings

The question I'm trying to answer is this: This is the solution: The only part of the solution I have a problem with is $x_{ps} + x_{qs}=l$, where $x_{ps}$ is the extension of the string from $P$ ...
4
votes
1answer
35 views

How does the distribution of mass affect gravitational attraction?

For example, if a planet is considered as a point mass, then an object inside the planets' gravitational field experiences an equal attraction from all of the planets' mass. However if the planet is ...
0
votes
0answers
18 views

Are Axinos an attractive candidate for Dark Matter and why?

Out of the SUSY DM candidates Gravitinos and Neutralinos are considered more likely than Axinos however I cannot find much on these. NB: Note the difference between axions and axinos.
0
votes
2answers
31 views

Is the magnetic field zero inside an ideal conductor carrying a current?

By an ideal conductor, I mean one with zero resistance. The question is not about a superconductor. As I know superconductor and conductor with zero resistance are not the same thing. The question ...
1
vote
0answers
20 views

Why would be axions be a candidate for warm/cold dark matter?

Axions are the current main favoured candidate for the identity of dark matter. While their masses are sub-$\mathrm{eV}$, why is it that they would be cold or possibly warm dark matter candidates ...
2
votes
2answers
36 views

Does electron absorb energy?

According to my teacher, an electron is point sized and it does not absorb or release energy. Moreover, my teacher says their orbital absorbs energy rather than the electron. If that is the case, then ...
2
votes
0answers
12 views

How would shape noise be distinguished from weak gravitational lensing?

Weak gravitational lensing distorts the image of galaxies by making them elliptical and non elliptical, but this we see in every day effects. So how do you determine what is just the shape noise of ...
-1
votes
0answers
19 views

What is the physical meaning of relative equilibrium in nonholonomic systems?

I know the physical intuition of a nonlinear system equilibrium point, but I now want to know the physical meaning of relative equilibrium in non-holonomic systems. I have read some mathematical ...
-3
votes
0answers
20 views

Calculation of stone dropping [on hold]

A stone dropped from a building of height $h$ reaches the ground after $t$ seconds in the air. From the building top, if two stones are thrown, one upwards, the other downwards, with same velocity $u$...
1
vote
0answers
19 views

Converting (time domain) Fluctuations to Power Spectral Density (PSD)

I have a Voltage signal, $V$, with fluctuations that go as: $$ \langle\delta V(\tau)^2\rangle=\ln f_a\tau $$ Here $f_a$ is an attempt frequency from an Ahrennius Law. According to many papers, "...
0
votes
0answers
19 views

Existence of effective Hamiltonian for variational ansatz

I recently saw on Wikipedia that in perturbation theory one can define in a systematic way effective Hamiltonian $\hat{H}_{\rm eff}$ that produces the same kind of states and energies as if one ...
0
votes
1answer
24 views

Scalar fields and general coordinate transformations

In classical mechanics, a scalar field is characterised by the fact that its value at a particular point must be invariant under rotations and reflections of coordinates. That is, one requires that $\...
-1
votes
0answers
13 views

What does “Field theory limit” means in D/M-branes or supergravity theories? [on hold]

What does "Field theory limit" means in D/M-branes or supergravity theories? Reading some papers related with D/M-branes, they often mention field theory limit, $i.e$, limit of $\alpha\rightarrow 0$,...
1
vote
0answers
21 views

Conformal group in 2D being a subgroup of Diff/Weyl - Polchinksi's 'String Theory' [on hold]

In the appendix on page 364 of 'String Theory', Polchinski defines the conformal group in two dimensions to be the set of all holomorphic maps. On page 85 he explains how this 2d conformal group is a ...
2
votes
1answer
22 views

Cold dark matter halos and cusps

Cold dark matter is one of the preferred candidates for dark matter. Yet, models such as the NFW and isothermal predict that halos will contain cusps, where the density tends towards infinity, despite ...
0
votes
0answers
34 views

Are 3 waves that have the same frequency (and wavelength) but different phase differences coherent?

Waves 2 and 3 have different phase differences which remain constant (since the frequency and wavelength is the same) as compared to wave 1 so to get to the point, are the 3 waves coherent?
0
votes
1answer
34 views

Is the relation between expansion of a liquid with temperature linear?

Say I have a liquid with certain volume. If I heat it, will it expand with a constant rate? $$ \frac{T}{V} = k.$$ It is true for gases, is it also true for liquids? And if yes then: is it true for ...
2
votes
0answers
35 views

Calculating the ground state energy in an electron gas (Jellium)

$\renewcommand{\phi}{\varphi} \newcommand{\vec}[1]{\textbf{#1}}$ This is pretty lengthy because I kept having ideas while writing this. Consider an electron gas in a cube of side length $L$, $V=L^...
0
votes
0answers
20 views

Coin frequency distribution [on hold]

When considering the coin frequency distributions for coins of different masses, does the surface on which the coins are dropped influence the power spectral analysis of the sound waves thus produced?
0
votes
0answers
20 views

A fundamental theory of superunification [on hold]

So, an year ago I was searching over the Internet about anti gravity (just out of curiosity).. And I stumbled upon this article: http://theoryofsuperunification-leonov.blogspot.bg/2015/01/russia-...
-1
votes
0answers
15 views

Photoelectric effect - elastic collision

In an elastic collision, since the electron leaves with the same amount of energy as it originally had, does that mean the photon receives no energy? Does this even result in a photon emission, if so, ...
-1
votes
0answers
20 views

How to calculate position of object that have linear and angular acceleration at the same time?

Let's imagine that we have a boat with two engines: main and rotary engine. Main engine gives boat acceleration $a$ m/s² up to constant linear speed $V$ m/s. When engine turns off, boat slows down ...
-1
votes
0answers
21 views

How to calculate the heating power of a metal plate in nature?

I like to heat up a part of a metal plate to a given temperature. For that I want to use an electric heater. The metal plate is located outside in nature. For that I need to take in account the wind ...
-2
votes
0answers
26 views

Gas diffusion (book request)?

I want to know the permeation conductivity K of air/Steel and air/Aluminium and I could not find it in internet!! Does anyone know where to find such information (books,articles..etc.) ? $$ Q = {kA\...
0
votes
0answers
16 views

Electrical field in coaxial cavity

I already asked this question at electrical engineering SE, but I got the recommendation that in the Physics SE there will be a better chance to get answers. I have a geometry as follows: This is ...
0
votes
1answer
43 views

How can we detect electric field in electromagnetic wave?

Electromagnetic wave have magnetic and electric component but what is the proof for that? How "non electrostatic" electric field can be detected around coil?
2
votes
1answer
38 views

Why does Higgs field have 4 components and written in a doublet?

I'm studying the Higgs field and I encountered some problems. My book says that the Higgs field has four components which are conveniently arranged into a two-component vector as: $$\phi=\binom{\phi^{+...
1
vote
0answers
47 views

Lagrangian of a coupled pendulum

I am trying to find the Lagrangian for a coupled pendulum: the two pendulums have the same characteristics (length $l$ and mass $m$) and are attached to the same roof at a distance $d$. In addition, ...
1
vote
0answers
15 views

Is there an analog of the Komar mass for conformal Killing Fields?

Is there an analog of the Komar mass for conformal timelike Killing vector Fields? For a stationary spacetime M, the Komar mass may be given as: $$M=\oint_{\partial M}\sqrt{g_{00}}(2T_{\mu\nu}-g_{\...
1
vote
0answers
37 views

What are the different definitions of torsion-free connections in GR?

What are the different definitions of torsion-free connections in GR? I am summarizng torsion-less condition in various context, if you know anything about it please let me know. One typical ...
0
votes
4answers
84 views

Can a person in a car hitting the interior of the car move the car?

As I remember, on old day explanation, a person in a car hitting the interior of the car cannot move the car, because there is no action and reaction force between the car and ground. But I doubt the ...
0
votes
0answers
35 views

Experiment using a laser beam [on hold]

I need to come up with an experiment to conduct for my physics class. So far, I'm stuck at the use of lasers. What plausible experiments can be done using lasers that haven't been done before, and ...
0
votes
1answer
36 views

Do Black Holes emit Hawking radiation while engulfing normal mass?

As I read on various sites ,all of them say that Black Holes emit Hawking radiation as one of the instantly created virtual particles near Event Horizon escapes from it.One goes inside it and other ...
-2
votes
0answers
52 views

Linear motion in a constant acceleration [on hold]

a car start to move from rest and travels along a straight horizontal road with a constant acceleration. Velocity of the car after t seconds is vms-1. Find the displacement of the car during the ...
0
votes
0answers
32 views

Where I can find quantum entanglement, real experimental raw data

For analysis purpose, I am looking for raw data from real entanglement experiment with spin measured at two detectors, at various combinations of angles, but preferably at a single combination of ...
0
votes
1answer
45 views

Universe spawned from the death of a hyper black hole?

Some Cosmologists have speculated that the Universe formed from the debris ejected when a four-dimensional star collapsed into a black hole a scenario that would help to explain why the cosmos seems ...
2
votes
3answers
87 views

Finding the Expectation value of harmonic oscillator

What is the expectation value for $e^{{\alpha}a^{\dagger}}e^{-\alpha^*{a}}$ of any two states of harmonic oscillator (let say $|n\rangle$ and $|m\rangle$) given below, $$\langle n|e^{{\alpha}a^{\...
7
votes
2answers
1k views

Green dot on photos when taking photo facing the sun

When taking a photo towards the sun, I found there is a green dot on the photo. I'm pretty sure this is caused by the sun, the camera has no problem. Question: what is the cause of this green dot? why ...
0
votes
0answers
16 views

Explanation of a match between shadows and wet floor at Niagara Falls

The question is about the cause of a wet-floor phenomenon. My vacation trip started at Niagara Falls (Canadian side, horseshoe fall on the upper left corner). It was around 10-11 AM, not too sunny yet....
1
vote
3answers
29 views

Do all smoothly curved pieces of transparent material have a focal point?

I understand that a lens by definition has a focal point but do all pieces of glass with smoothly curved surfaces have a single point at which all parallel rays of light passing through it in a ...
0
votes
1answer
24 views

Applying Ampere's Law for Two Parallel Wires

This seems a simple question but I'm not able to understand it properly. Say we have two parallel wires carrying same current I in different directions. We need to calculate the magnetic field at any ...
0
votes
0answers
17 views

Find velocity of ambulance from the observed frequencies?

I have a problem where an ambulance with a siren is traveling past me (a stationary observer) at a constant velocity. When the ambulance is approaching, I measured the frequency at 1000 Hz and as it ...
-3
votes
0answers
60 views

Skeptical of the “Cannon Shot Rule” [on hold]

What I consider a highly suspect figure was imparted to me today in a lecture and it very immediately did not sit well with me. To wit, this cannon shot rule (see here for a reproduction of the ...
-3
votes
2answers
56 views

Can the Copenhagen interpretation and the many-worlds theory be somehow reconciled? [on hold]

Is it possible that, at the moment of observation, a timeline is created where an object is in a state which contrasts its state in the current timeline? Using Schrodinger's cat as an example, let's ...
1
vote
0answers
26 views

Experimental tests of electric and magnetic fields in a gravity field

Has anyone experimentally verified that the measured values of the electric and magnetic fields do not change due to gravity, that there is no post-Newtonian effect on the strength of either $E$ or $B$...
0
votes
1answer
22 views

Do III-V based photovoltaics “glow” (photo-luminesce) when illuminated but not loaded?

In this nice answer I learned that when the silicon photovoltaics cells on the International Space Station are exposed to the sun, they tend to be cooler when electrically loaded than when no current ...
0
votes
0answers
16 views

Lightning, Electrical breakdown, and Current

Recently a discussion came up about this gif: http://i.imgur.com/r9Q8M4G.gifv This lead to a few questions about electrical breakdown of insulators. The disagreement we're having is whether or not a ...

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