2
votes
3answers
115 views

How to do linear stability analysis on this system of ODEs?

I was trying to do linear stability analysis of spring pendulum. I arrived at the differential equations which describe the system. But I am unable to proceed to linear stability analysis. Is it ...
3
votes
1answer
161 views

Graph Theory and Feynman Integrals

In Vladimir A. Smirnov's book Analytic Tools for Feynman Integrals, Section 2.3, the alpha representation of general Feynman integral takes the form $$ F_{\Gamma}(q_1,\ldots,q_n;d) = ...
0
votes
3answers
225 views

Does the magnitude of an electrical field change with frequency?

I am trying to model the frequency response of a force (dielectrophoresis) that is based on gradient of an electric field. One of the components is the CM factor which has a frequency component, but ...
0
votes
0answers
26 views

Quantum mechanics for macroscopic charges?

OK first off tell me if my understanding of the following is correct: In a Hydrogen atom, one would expect that the opposite charges (electron and nucleus) to attract each other, according to ...
4
votes
4answers
510 views

Quantum mechanics threshold

First of all I beg your forgiveness as I am not a physicist and the question I am going to ask may sound silly. I am aware that beyond a certain threshold in the hierarchy of building blocks of ...
1
vote
1answer
375 views

Can someone explain LO-TO Splitting?

LO-TO splitting occurs in an ionic (i.e. polar) solid such as GaAs or NaCl. What happens is that the degeneracy of the transverse optical (TO) and longitudinal optical (LO) phonons at $k=0$ is broken ...
20
votes
2answers
2k views

What exactly do we see on the famous neutrino image of the sun?

An answer to the question If we could build a neutrino telescope, what would we see? contains a link to a neutrino image of the sun by the Super-Kamiokande neutrino detector. There it says that ...
3
votes
1answer
255 views

Does the electron have spin in its own reference frame?

In our atomic physics class, we saw that the spin-orbit coupling term arises from the scalar product of the magnetic moment of the electron (proportional to its spin), and the magnetic field created ...
1
vote
1answer
38 views

In real laser applications, how big is the complex parameter (i.e. <n>) of the corresponding coherent state of the field?

In quantum optics, the output from a laser is modelled using a coherent state; what are some orders-of-magnitude for the complex parameter (usually denoted $\alpha$) of the coherent state ...
2
votes
1answer
84 views

Faster spinning moon

Let's say we somehow speed up the moon's rotation. (I'm thinking about a big asteroid smashing into it, but I'm open to better ideas.) Here are some questions: How fast could we get the moon to spin ...
4
votes
6answers
25k views

Why are volume and pressure inversely proportional to each other?

It makes sense, that if you have a balloon and press it down with your hands, the volume will decrease and the pressure will increase. This confirms Boyle's Law, $ pV=k=nRT $. But what if the ...
0
votes
1answer
363 views

How to calculate the buoyant force on a balloon at different altitudes [duplicate]

For a project into balloon simulation I'd like to know how the force on a balloon changes with altitude: I know that the Buoyant force on a balloon is: $F = (\rho_{air} - \rho_{helium})gV$ Using ...
0
votes
1answer
58 views

DO the condensed photon particles-waves-longitudinal-waves exist? [closed]

This is kind of hard to explain, because weird as it sounds, i have experienced a phenomenon that i would like to see if it exists and if i can explain it mathematically. The longitudinal waves of ...
1
vote
1answer
64 views

How do you actually cool the atoms to create the Bose-Einstein Condensate?

What is the actual way you cool atoms to a low enough temperature that you can observe their quantum behavior at a macroscopic level, like in the Bose-Einstein Condensate? ...
0
votes
0answers
18 views

Change in momentum [duplicate]

A cube has a side length of 20 cm. An atom in the gas moves around the cube as shown. It continually bounces off the four lateral walls of the cube. The atom has a mass of 6.6×10−27 kg. Because of the ...
0
votes
1answer
67 views

Earth-Moon system

While learning about motion of centre of mass, I came across this statement online, It is also more accurate to say that the Earth and Moon together revolve about their common center of mass. ...
1
vote
1answer
287 views

How to use accelaration data of moving object to calculate distance?

I read couple of similar question on this forum and few blogs on web, though I am still confused,I am determined to calculate object displacement using accelerometer data. So, I tried using ...
1
vote
1answer
218 views

Pressure and Buoyancy [closed]

It is well known that you can trap water in a drinking straw by placing the tip of your finger over the top while the straw is in the water, and then lifting it out. The inner diameter of the straw is ...
1
vote
1answer
881 views

Has NASA confirmed that Roger Shawyer's EmDrive thruster works? [duplicate]

This article states: But somehow, despite all of the reasons it shouldn’t work, it does. Scientists at NASA just confirmed it. Now in this question - it is strongly suggested that this ...
1
vote
0answers
45 views

Elastic Collision [closed]

A cube has a side length of 20 cm. An atom in the gas moves around the cube as shown. It continually bounces off the four lateral walls of the cube. The atom has a mass of 6.6×10−27 kg. Because of the ...
5
votes
3answers
472 views

Energy not conserved with accleration by a constant force

Suppose I have an object with mass $m$ in vacuum that I propel by applying a constant force, $F$, on it, with a rocket engine that I supply a constant amount of energy, $\frac{\delta ...
2
votes
0answers
158 views

Mathematical Prerequisites for QFT [closed]

I am curious about which areas of mathematics one should be comfortable with before learning QFT. I am familiar with the "learn-it-as-you-go" approach often advocated in physics, but would like to ...
0
votes
2answers
44 views

Is in this case distance same as displacement? [closed]

I have this graph, and I need to know the displacement in the interval from 0 to 5 seconds, so I found the area of the rectangle that you can see there. A = w*h, which means X = (5 seconds)*(20 m/s), ...
1
vote
1answer
150 views

Feynman's explanation of parallel axis theorem

In the book Feynman's Lectures on physics volume 1 chapter 19, He explains prallel axis theorem as follows. Suppose we have an object, and we want to find its moment of inertia around some ...
0
votes
1answer
54 views

Difficulty with Feynman's chapter on kinetic theory of gases

I have been reading Chapter 39 of the Feynman Lectures in Physics. In this section he argues that collision between gas molecules will mix up their directions of motion such that ultimately any ...
3
votes
0answers
62 views

How would water drain out of a sealed pipe?

While hiking through the Grand Canyon, I started wondering. Say we have a pipe for the purpose of transporting water across a canyon, with the bottom submerged in a pool of water. Like the blue line ...
2
votes
2answers
293 views

What happens to a photon after it is absorbed by an antenna?

I recently have read about interception of wireless information, however this mentions that people can intercept the information, and then somehow the recipient also gets the information. Regardless ...
0
votes
2answers
67 views

How to define a convex surface in case of refraction?

In an exam at high school level, it was said, "ray goes from optically denser to rarer medium through a convex surface. It forms a real image...." this was a part of the question. Now I thought that ...
0
votes
1answer
64 views

Estimating the effect of radiant barrier on the radiant and conductive heat transfer through a metal roof

The basic question is -- Will a radiant reflective coating be more effective applied to the upper surface or the lower surface of a metal? Case 1: Imagine a metal roof subject to solar heating. The ...
1
vote
2answers
127 views

What is a measurement in MWI

I was reviewing the MWI, and couldn't figure what a measurement is in the MWI? Everett claims that split happens when you measure, but what is it for MWI (not for general QM)? Yes, I know about ...
1
vote
2answers
62 views

U.S. Standard Atmosphere

My textbook states that "Ideally, we would like to have measurements of pressure versus altitude over the specific range for the specific conditions (temperature, reference pressure) for which the ...
2
votes
1answer
144 views

In QFT, why do fermions have to anticommute in order to insure causality?

I have seen this question and I believe I understand the answer to it. However, AFAIK, only for bosons the causality condition is a vanishing commutator. For fermions we expect the anticommutator ...
0
votes
1answer
261 views

How a fan moves air? [duplicate]

How does a fan moves air towards you (I mean in 1 direction). Also propeller and fan have different shapes, does it mean they work different?
-1
votes
1answer
105 views

A particle has $\overrightarrow{r}(0)=4m(\hspace{2pt}\hat{j}\hspace{2pt})$ and $\overrightarrow{v}(0)=(2m/s^2)\hat{i}$ [closed]

I am having trouble with these problems, and I want to gain a understanding of how to solve these. I'll put what I have tried at the end, even though I don't think it'll be of help. A particle has ...
3
votes
3answers
144 views

The Universe as a four-dimensional sphere?

I was chatting with my 12yo cousin yesterday and we got to the Universe, its size and stuff like that. Then he came up with the idea (I'll rephrase it), that the Universe could basically be a 4d ...
23
votes
4answers
7k views

Birds sitting on electric wires: potential difference between the legs

We have seen birds sitting on uninsulated electric wires of high voltage transmission lines overhead without getting harmed, because sitting on only one wire doesn't complete any circuit. But what ...
7
votes
2answers
238 views

Mathematical physics text with plenty of applications

I'm looking for texts on mathematical physics. I've seen various other threads, but the texts recommended in those threads were mathematical methods of theoretical physics texts, that is to say those ...
1
vote
1answer
81 views

How is free energy built into a Metropolis Monte Carlo simulation of an Ising model?

In the Metropolis algorithm, the change in the energy given by the hamiltonian is compared for flipping a spin. This is not the free energy, but for systems above absolute zero you are trying to ...
1
vote
1answer
90 views

Radial and tangential velocities of a star

(source) Early in this piece it states that the radial and tangential velocities are: $$V_r = V_c \cos(\alpha) -V_{c,0} \sin (l)$$ $$V_t = V_c \sin(\alpha) -V_{c,0} \cos (l)$$ but I am struggling ...
1
vote
2answers
84 views

Blackbody radiation Color

An ideal blackbody absorbs all incident radiation. Josef Stefan found that the intensity $R$ (power per unit area) radiated by an ideal blackbody is given by $$ R = \sigma T^4 $$ Q1) Since an ideal ...
2
votes
2answers
192 views

A whole lot of doubts on Lorentz representation

Can someone tell me in layman's language how the $(1/2,1/2)$ represents a vector field and $(0,1/2)$ or $(1/2,0)$ represents spinors and $(0,0)$ represents scalar field. Please don't be pedantic on ...
0
votes
1answer
39 views

Rayleigh-Jeans Equation

According to my textbook, the power radiated of a small hole in a cavity (an ideal blackbody) is given by $$R = \frac{1}{4}cU$$ where $U$ is the total energy density per unit volume, $R$ is the ...
0
votes
1answer
368 views
0
votes
1answer
32 views

Mie theory “upper limit”?

I have read most often that objects experimented with in Mie theory are on a scale not much larger than the incident wavelength (usually a fiber of diameter $5$ microns with an incident wavelength of ...
0
votes
0answers
91 views

An electron is an excitation of the electron field. So when we observe a higgs boson that means we've excited the higgs field?

See this related question: If particles are excitations what are their fields? I ask this question because, according to a lecture, the higgs boson was frozen into a "matrix" at some point before ...
3
votes
0answers
39 views

Mechanical waves edge between material and vacuum

I have been thinking about the propagation of EM waves vs. mechanical waves and some of their odd cases. One such case that I haven't been able to puzzle out is what happens when a mechanical wave ...
33
votes
9answers
11k views

Can Jupiter be ignited?

Our solar system itself contains two candidate "Earths" One is Jupiter's moon Europa and another is Saturn's moon Titan. Both of them have the problem of having at low temperature as Sun's heat ...
1
vote
0answers
64 views

$G$-parity in an electromagnetic decay

I am looking at the decay $\eta\rightarrow\pi^+\pi^-\gamma$ and I would assume that the decay itself (ignoring the $\pi\pi$ final state interaction that is obviously strong) is electromagnetic since ...
2
votes
1answer
66 views

Moment of inertia as a tensor

A professor at my university briefly stated that moment of inertia is a tensor and can be represented by a $3×3$ matrix. I don't have a good idea of what a tensor is, so I would be grateful if someone ...
3
votes
3answers
239 views

Escape velocity of satellites

I know that the equation for it is $$v^2 = \frac{2GM}{r},$$ and with that, the rocket should be launched at that speed. But could it go much slower spending much more fuel to escape from gravity ...

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