4
votes
3answers
322 views

Why do sand dunes, hills and mountains assume the shape they normally do?

What about something taken in a tablespoon? This shape, as I understand, could be explained by gravity, friction and similar concepts, but why the shape isn't cubical or cylindrical couldn't be ...
3
votes
1answer
593 views

Path Integral on a circle (calculation of phase and linear independance)

I am reading Schulman's "Techniques and applications of path integration" chapter on Path integrals on multiply-connected spaces. In the first section he calculates the path integral of a free ...
3
votes
1answer
76 views

How is black hole affected by gravity of nearby bodies?

I run into wikipedia articles about ergosphere of rotating black holes. What if some massive body passes nearby some black hole: is something like ergosphere produced, or is the event horizon ...
1
vote
1answer
73 views

regarding nuclear magnetic resonance

In NMR experiment we provide an external radio frequency signal which will induce transition of nuclear spins to higher states,and then it returns to ground state precessing around the magnetic field ...
0
votes
3answers
2k views

Is a phase difference of 180 degree possible between emf and current?

While studying alternating currents I could read and observe through an oscilloscope that there can be phase difference between emf and current. But, is a phase difference of 180 degrees possible in a ...
1
vote
3answers
305 views

Will the rms current be affected by inserting dielectric in the capacitor in an LCR circuit?

MY thoughts: I think it will not be as the expression for RMS value is dependent only on the peak value of current. Is my thinking correct?
7
votes
3answers
994 views

The reference frame of $c$

I don't have a lot of knowledge of special relativity and associated topics; some of the few things I know are that "all motion is relative" (that is, there is no 'stationary reference frame'), and ...
1
vote
2answers
282 views

Forces, Incline, and Mass

A farm tractor tows a $3900 kg$ trailer up a $16^\circ$ incline with a steady speed of $3.0 m/s$. What force does the tractor exert on the trailer? (Ignore friction.) I am having trouble ...
2
votes
3answers
918 views

Nature of frictional force

I was thinking about a situation where a person in standing on the ground with some friction. The frictional force is directly proportional to the normal reaction acting on him by the ground. Assume ...
4
votes
2answers
903 views

The relation between electric field and magnetic potential

In every electrodynamics book there is one chapter on special relativity which includes one section about" covariant formulation of electrodynamics" which uses tensor to describe the two fields and ...
6
votes
1answer
271 views

The double-trace deformation effect in AdS/CFT

Let me use this paper as the reference for this. I want to understand better the argument at the bottom of page 6. If the bulk $AdS$ metric is written as $\frac{1}{r^2}(dr^2 + ...
1
vote
2answers
756 views

Does the heat produced in an inductor affected by the total current in the resistance in the circuit?

The energy stored in an inductor depends on the inductance of the inductor and the current flowing through it. But, assume that the switch is opened. Then, does the heat generated in the inductor ...
2
votes
1answer
3k views

Estimate temperature and pressure of steam in a pot of boiling water

Suppose we have a pot of known dimensions filled to level L with boiling water on a stove, covered by a lid with a vent of known dimensions. Given the steady-state temperature of the stove (bottom of ...
5
votes
0answers
479 views

Time Reversal, CPT, spin-statistics, mass gap and chirality of Euclidean fermion field theory

In Minkowski space even-dim (say $d+1$ D) spacetime dimension, we can write fermion-field theory as the Lagrangian: $$ \mathcal{L}=\bar{\psi} (i\not \partial-m)\psi+ \bar{\psi} \phi_1 \psi+\bar{\psi} ...
4
votes
0answers
90 views

Can the correlation for the Potts model be bounded?

I am studying a $d$-state Potts model. A configuration $\sigma$, which assigns for each $x\in \mathbb{Z}^2$ a value $\sigma(x)\in [1,2,\ldots,d]$, with the probability on a finite lattice defined as ...
2
votes
0answers
363 views

Dimensional analysis to estimate order of magnitude of quantities

In the Coursera course From the Big Bang to Dark Energy on several occasions dimensional analysis was used to estimate the scale of quantities. This almost seems like a contradiction in terms to me, ...
3
votes
4answers
639 views

Experimental evidence of Pauli's exclusion principle

A fermion is described by a set of quantum numbers, this set of numbers lead us to a unique wave function. If two fermions are described by the same wave function (violating the Pauli's exclusion ...
1
vote
0answers
64 views

Reconciling Different Vapor Pressure Definitions

In describing vapor pressure, I have often heard the following intuition: Assume a closed container that is partially filled with water. Above the water lies a vacuum. The water will vaporize until ...
4
votes
2answers
216 views

Will a telescope show a more magnified image if the object is brighter?

I have a small telescope which shows me the moon's craters a little bit magnified. Consider a situation where the moon is very very brighter than its current brightness, so that the telescope's ...
4
votes
1answer
1k views

Why same formula describing Doppler effect in the case of light in different situations?

I made comparison between Doppler effect in light and sound and one interesting thing that I saw was that in the case of sound there are different formulas to find the apparent frequency in different ...
2
votes
0answers
123 views

Does light initially accelerate? [duplicate]

Light travels with a speed of $3\times10^8{m\over s}$. My question is that was the light initially accelerating or it archived the speed in an instance? If it was accelerating then why it did not ...
13
votes
5answers
835 views

Proof that Our Planet is 1D

I have took a discrete mathematics course this summer and there we talked about power of groups and functions,and yesterday I though and realize that if we can map all the 3D coordinates with a one on ...
1
vote
0answers
766 views

Forces on two boxes

This is a problem from my problem sheet but we haven't yet covered the material or received our books. There is a small box of mass $m_{1}$ resting on a plank, of mass $m_{2}$ and length $L$, which ...
1
vote
2answers
920 views

Horizontal Gravitational Force

So I was writing a lab report for Physics I, where I was describing projectile motion. I had written Since gravity on Earth does not have a horizontal force, the object will not lose horizontal ...
2
votes
3answers
2k views

Does serving food on a hot plate really keep it warm longer?

I live in Ireland where serving food on hot plates is considered “good cooking practice” to ensure the food remains warm – I come from France where I have rarely seen it done. I am wondering if this ...
1
vote
0answers
332 views

What are the values of effective mass approximation

For my research work i am trying to calculate band gap of zinc oxide theoratically and found this paper (Determination of the Particle Size Distribution of Quantum Nanocrystals from Absorbance ...
1
vote
3answers
799 views

Relationship between Stoke's law of sound attenuation and the inverse square law

In attempting to find a reference for explaining sound propagation, I came across this article in Wikipedia: Stokes law(sound attenuation) What I learnt in high school is that sound is propagated by ...
4
votes
1answer
1k views

Galilean invariance of a subset of Maxwell equations

I read in Feynman's proof of Maxwell equations the statement that the subset of Maxwell equations comming from the Bianchi identity: $$ \nabla \cdot {\bf B} = 0, \quad \nabla \times {\bf E} + ...
2
votes
0answers
93 views

How to travel between tidally locked binary planets

Two planets of roughly the same volume and mass are orbiting each other. What would be the most efficient way to travel from one to the other? Seems unlikely, but could a rocket positioned at the ...
0
votes
1answer
901 views

Height of projectile above the inclined plane and above the horizontal.

I am trying to work out the maximum height of a projectile above the incline plane and above the horizontal plane but I am not sure how to do this. I have worked out all the equations of motion, $ax, ...
1
vote
0answers
224 views

Calculation of effective action

For a massless Dirac particle by integrating fermion degree of freedom in path integral, effective action is resulted for guage field $l$($\psi$,$\bar\psi$,$A$)=$\bar\psi( \gamma^\mu (i \partial_\mu ...
2
votes
1answer
174 views

Deriving the condtion for spontaneity using gibbs free energy

While deriving the condition for spontaneity, $\Delta$G$\leqslant$0, we start by saying that $\Delta S_{tot}$ $\ge$0 $\Rightarrow$ $\Delta S_{sys}$ + $\Delta S_{surr}$ $\ge0$ If $Q$ is the heat ...
10
votes
2answers
2k views

Dynamics of counter-rotating flywheels

I've wondered about this for ages. If we create a pair of flywheels that rotate in the opposite direction with the same angular momentum, but are co-located and have the same mass and inertial moment ...
2
votes
2answers
122 views

Integration of 3-momentum

During a lecture that I missed, I was trapped when the lecturer uses the relation $$dp_x~ dp_y ~dp_z ~=~d^3\mathbf{p} ~=~ 4\pi p^2 dp.$$ Can I know how is this relation derived please?
0
votes
2answers
1k views

Punching - Force or Momentum?

If I want to punch a person inflicting maximum damage, what do I need to care about? My force of punching, i.e, do I need more acceleration? Or do I need momentum, i.e my velocity for punching?
6
votes
1answer
327 views

Why Negative refractive index is negative

$n=\sqrt{\epsilon \mu }$ Negative refractive index happens when permittivity ($\epsilon $) and permeability ($\mu $)of a material is negative. My question is, if permittivity and permeabilitity of a ...
8
votes
3answers
3k views

Calculating Atmospheric Pressure on an Imaginary Planet

I am planning a series of science fiction novels that take place on an imaginary binary planet system. Both planets have a lower surface gravity than the Earth and one has slightly more mass than the ...
4
votes
2answers
163 views

Diffraction pattern when wavelength tends to zero

While studying about Fresnel and Fraunhofer diffraction, I came across a statement which says that the fringes disappears and the image would take on the limiting shape of the aperture when wavelength ...
0
votes
4answers
12k views

Why is distance between two successive nodes equal to $\frac{1}{2} \lambda$ in standing wave

I'm reading my textbook and it says the distance between two successive nodes is equal to $\frac{1}{2} \lambda$ in standing wave. If $\lambda$ here means the wavelength of the standing wave ...
1
vote
1answer
324 views

Magnetic induction in Relativity

As we know magnetic phenomenon is a mere relativistic effect.My question is how to explain the magnetic induction in a relativistic manner?
0
votes
1answer
93 views

Vector Summation [closed]

When two vectors are sketched from a single point, the angle between them is θ. Show that the size of their vector summation is given in the expression: $ \sqrt{A^2 + B^2 +2ABcosθ} $. Any ...
2
votes
1answer
758 views

If the source of sound is vibration, why can't we “hear” a object whose molecules are vibrating?

According to our physics textbook, the source of sound is vibration. According to our chemistry textbook, substances in solid state have molecules vibrating in a fixed position. So why can't I hear my ...
4
votes
1answer
263 views

Why is there a gravitational attraction between two objects at rest with respect to each other?

From my understanding of relativity, gravity is not a force, but a result of the curvature of spacetime. If Object1 moves past Object2, even though it's moving in a straight line, its direction may ...
6
votes
1answer
466 views

Schwarzschild solution in arbitrary dimensions

Is there any generalized Schwarzschild solution for an arbitrary number of dimensions? Is it necessary to calculate each individually, or is there a relationship between them?
-2
votes
1answer
437 views

Basic Physics Question [closed]

I'm having a difficult time answering this question. I think I'm just converting the units wrong somewhere: You're the CEO of a courier company, and you decide to select an electric car for your ...
1
vote
1answer
68 views

What happens when a bacteria tumble? Is it an active or a passive process? [closed]

I was wondering what actually happens during the tumbling process of a "run and tumble" process. When the bacteria stops to tumble and reorient itself, is that an active process, or is the ...
2
votes
2answers
221 views

Scalar QFT Fock Space

I want to demostrate the following relation of the normal ordered product: $\Omega\equiv:\exp{\left(-\int d^3k~a^{\dagger}(k)a(k)\right)}:=|0\rangle\langle0|.$ I proved the commutation relation ...
2
votes
1answer
186 views

Wick's theorem again

Could someone please elaborate on the accepted answer to this mathoverflow post? I'm working on a problem that looks like this \begin{equation}I=\int d^{n} x\, f(\vec x)\, e^{-\frac{1}{2} \vec x ...
1
vote
1answer
51 views

Is there a heuristic argument for the expression $ \textbf{g} = \frac {\mathbf{S}}{c^2}$?

Electromagnetic momentum density and the Poynting vector are related by the simple expression: $$ \textbf{g} = \frac {\mathbf{S}}{c^2}$$ It can be rigorously derived from Maxwell's equations, but is ...
0
votes
1answer
425 views

How does volume of water in closed system relate to humidity at 25(C) degrees

If I have a closed system with a volume of 100L, at ~24(C) or ~75(F) degrees, what volume must be filled with water to reach a humidity of 90%? I imagined if you fill it 100% with water, humidity is ...

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