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6 views

Question regarding the angular velocity of a ball rolling off of a sphere

Here is the actual problem in its entirety: A uniform ball with radius r is rolling down from the top of a fixed sphere with the radius R. Its initial velocity is negligibly small. What will be the ...
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0answers
12 views

Masses connected with a string, one mass in unifom circular motion

A light inextensible string of length $a$ is threaded through a fixed smooth ring $R$. One end of the string is attached to a particle $A$ of mass $3m$. The other end of the string is attached to a ...
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1answer
27 views

Spontaneous symmetry breaking in the Standard Model. What is "broken"?

I know this question has been asked other times, but I am looking for a confirmation of the following. When we say that the gauge group of the standard model is $G_{SM} = SU(3)_{c} \otimes SU(2)_{L} \...
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0answers
9 views

Where is the flaw in this brownian ratchet design?

As I understand, Brownian ratchets do not work because the paddle, which is supposed to keep the gear spinning in a single direction, also oscillates with thermal noise. A the paddle can dissipate the ...
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0answers
19 views

Asking for recommended mathematical basics to cover to master Electromagnetic theory

I was trying to self read "Electrodynamics by Griffiths". However, I find it very difficult when different coordinate systems were used simultaneously. ...
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1answer
13 views

Will the force on the output piston be bigger than the force on the input piston in a confined container?

Suppose we have a confined container with two pistons on both sides filled with a fluid. Now we know that, F1/F2=A1/A2 Let's say that F1 is the input force. Now F2 should be the input force times the ...
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1answer
13 views

Hanging (without tying) a ring or any other object with a massless string

Suppose ends of a string are attached to two different points on a ceiling. If a ring is hung freely, why does that ring move to the mid point of the string usually? Is it because the tension along ...
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11 views

Question about Active, Reactive and Apparent power

I guess this is more of a basic mathematics question. Suppose I have a simple AC circuit with applied voltage $\mathbf V = a_1 + \hat j b_1=V\angle \alpha$ and current throught the circuit $\mathbf I ...
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25 views

Function of noncommutative operators: how should the powers in its Taylor expansion be arranged, and how to take partial derivatives?

Let $F:\mathbb R ^n\to\mathbb R$ be a function that has a Taylor expansion, then it can be written (expanded at $a$) as $$ F(x)=\sum_{\alpha} \frac{(x_1 - a_1)^{\alpha_1}\dots(x_n - a_n)^{\alpha_n}}{\...
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13 views

Is quark quark interaction possible under extreme heat and pressure circumstances?

Neutron rich core of neutron stars on extreme pressure and heat undergo phase transition to quark-gluon plasma. On further exceeding heat and pressure(beyond TOV limit), could QGP undergo transition ...
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2answers
32 views

Force being equal at all points in ideal string

If a person pulls an ideal massless string, why do all points in the string experience the same force? How to prove this rigorously?
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1answer
24 views

Does calculating relative uncertainty not account for the extreme values or am I wrong?

Assume two values, $A = 4 \pm 0.5$ and $B = 10 \pm 1$. When calculating $AB$, we must convert them into their percentage uncertainties. $A = \frac{0.5}{4}\times 100 = 4\pm12.5\%$ $B = \frac{1}{10}\...
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29 views

Some alternatives for the evolution of the observable universe

The observable Universe exists in a single copy, therefore all its parameters are clearly defined. My astronomy teacher sometimes advises to explore also possible alternatives to the evolution of the ...
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0answers
41 views

Momentum vs Kinetic energy

Two geometrically identical spheres A and B with different masses (A>B) are thrown vertically downward on sandy ground with different velocities such that their kinetic energies are equal but the ...
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1answer
24 views

Dissipation function is homogeneous in $\dot{q}$

We have Rayleigh's dissipation function, defined as $$\mathcal{F}=\frac{1}{2} \sum_{i}\left(k_{x} v_{i x}^{2}+k_{y} v_{i j}^{2}+k_{z} v_{i z}^{2}\right)$$ Also we have transformation equations to ...
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0answers
19 views

Find Voltage using Circuit Analysis

Hi, I been trying to find an effective way to solve the question given below I tried to solve it many times but the value is fluctuating can anyone else try to solve this
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14 views

Equivalence of simple formulations of qubit entanglement

I'm reading some very elementary treatments of quantum computation and am unsure about the correspondence among "definitions" of qubit entanglement. One definition states that (1) the bits ...
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0answers
21 views

Is there a classical limit that connects classical volume/phase space with the scalar product of momentum and position eigenstates?

The book Understanding Molecular Simulation: From Algorithms to Applications, 2002, Daan Frenkel and Berend Smit, states the following $$ \langle r|k\rangle \langle k|r\rangle = 1/V^N $$ where $|r\...
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0answers
37 views

Graviton propagator in Horndeski theory

Let $\phi$ be a scalar field and $g_{\mu \nu} = \eta_{\mu \nu}+h_{\mu \nu}/M_p$ where $M_p$ is the Planck mass (so we assume we deal with perturbations). Let $\Lambda_2,\Lambda_3$ be energy scales ...
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48 views

How to derive equation 6.1.26 in Sakurai's quantum mechanics?

I am trying to get to equation 6.1.26 in Sakurai's quantum mechanics and I am getting confused with one of the steps in the derivation. Similar questions have been asked about this question on this ...
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2answers
99 views

Are differential geometric and physics conventions for covariant derivatives consistent?

In a differential geometric setting, the covariant derivative can be defined as a map $\nabla_X:\Gamma(TM)\to\Gamma(TM)$, for any vector field $X\in\Gamma(TM)$, satisfying certain conditions. In other ...
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1answer
44 views

Informational content of a single symbol

In the communication context, every book i've started to read says: if you want to send a datum about a random experiment $X$, let it be a fair coin toss, that is $$p(tails)=p=0.5; p(heads)=q=0.5$$ ...
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0answers
16 views

The Hubble parameter of Randall-Sundrum model

It’s mentioned in this paper On the cosmological constant problem and brane-world geometry that the Hubble parameter of the Randall-Sundram model is given by: $$ H^2 = \frac{8\pi}{3m_{pl}^2} \rho + \...
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0answers
23 views

Does the fact a charge experiences a perpendicular force when moving perpendicular to a magnetic field have anything to do with EM waves?

Does the fact a charge accelerates perpendicular to a uniform magnetic field when moving perpendicular to it have anything to do with the form of an EM wave? I thought this might link because the ...
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32 views

How to count the number of microstates in this example and in general

Suppose we have $3$ energy levels $E_1,E_2,E_3$, that we need to fill up with $3$ electrons. Each of these Energy levels can be filled with two electrons - spin up and spin down. How does one ...
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25 views

The Reaction at A is ____ kN and at B is ____ kN [closed]

The Reaction at A is ____ kN and at B is ____ kN.
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1answer
38 views

"Active quantum fluctuations" due to the quantization of the gravitational field?

This is a follow-up to the question In what sense is the word quantum fluctuation used here? In arXiv:0710.3787 it is stated on page 7 that there are "active fluctuations in the intrinsic ...
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0answers
19 views

Is a scalar obtained by metric contraction invariant under Weyl transformation?

Under a Weyl transformation $g_{\mu\nu}(x)\rightarrow e^{2\omega(x)}g_{\mu\nu}(x)$ So a scalar $X_\mu X^{\mu}$ should transform as following: $$X_\mu X^{\mu}=g_{\mu\nu}X^\nu X^{\mu}\rightarrow e^{2\...
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2answers
127 views

Can we bend light ray into any closed loop?

Suppose we have a medium with varying refractive index and a source of light inside that medium emmiting rays. Then is it possible to bend the ray into any closed loop? As the medium has varying ...
2
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2answers
49 views

How to understand the time reversal symmetry of position operator?

How to understand the fact that position operator is symmetric under time reversal? I can visualize the momentum and magnetic field being odd under time reversal. Got the same doubt for Electric field ...
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1answer
46 views

Rocket orbitting Moon [closed]

The Figure shows six paths by which a rocket orbiting a moon might move from point a to point b. Rank the paths according to the net work done on the rocket by the gravitational force from the moon, ...
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0answers
33 views

What does Polchinki mean when he says identifying under involution?

I am reading chapter 7 of Polchinki's String Theory vol. 1 textbook and I am trying to understand why one obtains the cylinder (annulus) from the torus by identifying points under involution. To be ...
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1answer
38 views

Is light a single wave when we refer to frequency?

When we say that light oscillates $n$ times (frequency) in a second do we mean that the same electromagnetic field travelling through space oscillates $n$ time's? As i have seen diagrams suggesting ...
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0answers
21 views

How to generate a PDE from a discrete equation in a rice-pile like model?

I am reading Noise and dynamics of self-organized critical phenomena by Albert Díaz-Guilera Here, on an extension of the rice-pile model by Bak et al demonstrating self-organized criticality. Equation ...
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1answer
38 views

Particle- and wave-like properties

Is wave-particle duality a real concept or a pedagogical tool? In a less opinion-based way: what are particle properties and wave properties of a particle (that we speak of particle properties of ...
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0answers
22 views

How do I prove this integral solution in terms of modified Bessel function?

I came across this equation while studying about Dark Matter relic density but I can't seem to prove it. In the early universe, the number density of dark matter in the thermal bath is approximately ...
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0answers
14 views

Why don't wave packets disperse? [closed]

As the Uncertainty Principle suggests that $\Delta x\Delta p\geq h/4\pi$, a particle must have different velocities at any point in space within it's Gaussian distribution. Since wave functions ...
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2answers
31 views

A wire that is electrically neutral but carries current?

The wire described in the title is proposed in Griffiths's book on electrodynamics: ... To begin with, I'd like to show you why there had to be such a thing as magnetism, given electrostatics and ...
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0answers
11 views

What does "marginality" mean in the context of magnetically confined plasmas?

I am reading the paper-Self-organized criticality and the dynamics of near-marginal turbulent transport in magnetically confined fusion plasmas by Sanchez and Newman. Here, the term "marginality&...
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1answer
94 views

Is general relativity required from quantum mechanics?

One of the paradoxes against quantum mechanics was claimed by Einstein during one of the Solvay conferences: a paradox called the Einstein box also explained in this question. The solution proposed by ...
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1answer
24 views

Does pressure affect heat transfer between two mediums?

I'm a self-taught Coca-Cola connoisseur and try to use science to be able to have the best taste possible in every glass. I usually try to get the bottles as cool as possible before opening them. I've ...
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0answers
17 views

How do you figure out where an object between two charged objects needs to be for the net electrostatic force acting on it to be 0? [closed]

In a question such as: There are three objects (A, B, C) in a line. A has a charge of +5 microCoulombs, B has a charge of +3 microCoulombs, and C has a charge of +2 microCoulombs. A and C are 7 cm ...
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2answers
36 views

Cosmic inflation and how does it stop?

What conditions make out the probability for the Cosmic Inflation once began to stop. For instance quantum physics says that once the inflation started there was a probability say 80% for it to stop ...
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1answer
44 views

What does it mean to apply a voltage bias on a superconductor when $V = IR$ and $R = 0$ for a superconductor?

I have been reading papers about superconducting nanowire single photon detectors, and in them the voltage bias the superconductor to close to $T_c$ so that a photon has enough energy to break the ...
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1answer
56 views

$t=0$ is out of the domain of the equation of motion

At $t=0$, $Q_1$ is dropped under the influence of only the electrostatic force. I have solved the differential equation to find the equation of motion: and the distance of the 2 objects as a ...
3
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2answers
129 views

What does it mean to take GR and QM "together"?

From the "Theory of Everything" Wikipedia article (first paragraph): Over the past few centuries, two theoretical frameworks have been developed that, together, most closely resemble a TOE. ...
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1answer
27 views

Finding windspeed gave me negative time value

This is a homework question, I will make it as concise as possible: A 1-way plane trip is 2800km and the plane's airspeed is 790km/h. The plane flies with the wind on the way there, and against it on ...
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2answers
58 views

Centrifugal Force & Rotating Frames

In Thornton & Marion's Classical Dynamics, the following relation is given for the rate of change of an objects position in the two coordinate systems (according to the picture shown at the bottom)...
2
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1answer
57 views

In what sense is the word "quantum fluctuation" used here?

I found this paper: On the origin of the LIGO "mystery" noise and the high energy particle physics desert, currently only published on arXiv as far as I can tell. I do not understand any of ...
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2answers
19 views

How does the particle's total energy affect the interference pattern? Individual Particle Double Slit Experiment

Double slit experiment with individual particles has been performed with a variety of particles from photons to molecules of up to 2000 atoms. For photons, as the frequency increases (i.e. wavelength ...

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