0
votes
1answer
95 views

What is the distance to the closest star similar to our Sun? [closed]

My question was inspired by this nice question. But, I recall the phenomenon of strange objects appearing on our sky, and then moving away with a velocity that seems not yet attainable by manmade ...
0
votes
1answer
25 views

Non-zero potential measured on the surface of an insulator

After driving a screw into an alumina firebrick and applying a 5kV potential, I measured a ~4.5kV potential using a high voltage probe at other locations on the brick surface. Firebrick is generally ...
0
votes
1answer
58 views

why the electromagnetic wave transmits momentum in the direction of the movement?

Ordinarily a transverse wave does not transmit momentum, as it is the case of the well-known sea wave phenomenon. But the electromagnetic radiation has both fields transversal to the movement of the ...
0
votes
0answers
33 views

Verification of mass density function in continuum mechanics

I'm having problems knowing where to go with this question: Suppose that a certain material initially fills an open region $\mathcal O\in\mathbb R^3$, with $\Omega:=[-1,1]^3\in\mathcal O$ , so ...
4
votes
1answer
65 views

Desynchronised pixels in images of the Sun?

NASA published this wonderfull video of Sun from SDO: https://www.youtube.com/watch?v=GSVv40M2aks And it occurred interesting question: Sun is very big sphere. Its so big that it took light 4,6 ...
3
votes
1answer
78 views

How can diffraction happen in the Hubble Telescope?

I've seen people talking about the angular resolution of the HST is, if using Rayleigh's criterion, equal to: $$\theta = 1.220 \frac{\lambda}{D}$$ My question is, since the diameter of the HST $D$ ...
0
votes
1answer
114 views

What forces act on an object submerged in flowing fluid in an enclosed environment (i.e pipe)?

Let's say we have a pipe with water flowing through it and obstacle is inserted into the pipe and is rigidly fixed to the inner wall so that it does not get washed away. What forces are exerted by ...
0
votes
0answers
33 views

Reference for the non-perturbative origin of the baryon masses

I'm looking for nice introductions to the non-perturbative generation of the baryon masses.
18
votes
3answers
1k views

Detectability of interstellar messages

Recently a debate started whether it is a good idea to send more messages into space in the hope of having alien civilizations receive them. There are some predecessors, most notably the 1974 Arecibo ...
1
vote
0answers
23 views

Earth's magnetic effect on my magnet

My magnet seems to work independently of, and unaffected by, the Earth's magnetic field, yet the magnetic field of my magnet changes as I introduce some other similar magnets of varied sizes into its ...
0
votes
0answers
60 views

Does this Hamiltonian have point spectrum?

Consider such a Hamiltonian $$ H = - \frac{1}{2} \frac{\partial^2}{\partial x^2} - F x + V(x) ,$$ with $F$ being some constant, and $V(x)= V(x+L)$ being some periodic potential. Does this ...
1
vote
0answers
75 views

What's the difference between “spectromicroscopy” and “microspectroscopy”? [duplicate]

Both definitions that I found are rather vague. (Related question: What's the difference between microscopy and spectroscopy?)
-1
votes
1answer
42 views

Can surrounding masses influence the speed of time (excluding the time dilation due to gravity)?

https://www.youtube.com/watch?v=ev9zrt__lec @6:22-7:22 If you removed the middle and front spaceships, will the time of the last spaceship flow differently? As this is what it appears to suggest.
0
votes
0answers
54 views

Is there any material that a magnetic field cannot penetrate? [duplicate]

Is there any way to build an enclosure that protects its contents from magnetic fields more effectively than simply keeping sources of magnetic fields away by the same distance the box would?
0
votes
0answers
19 views

My electrophorus doesn't work

I have failed in generating charge using electrophorus. The charging material was a balloon rubbed with hair until it became very full of static, as well as a small piece of Styrofoam rubbed with the ...
1
vote
1answer
103 views

What is thermodynamic equilibrium?

The state of thermodynamic equilibrium is typically defined referring to the system's behaviour in the future. Can the definition be formulated in terms of measurable quantities?
0
votes
2answers
657 views

Tricky conceptual question: ball sliding and rolling down incline [closed]

We all are familiar with the classic ball rolling down the incline exercise in rotational dynamics. Here is quite a tricky conceptual problem: You have an incline of fixed height, but the angle of ...
1
vote
1answer
69 views

Determine the value of $g$ with rolling ball

At first, I thought the value of $g$ ($9.8m/s^2$) could be determined simply by placing a ball at the top of a ramp at a known height. The ball was released with no initial velocity, and the final ...
0
votes
0answers
63 views

Differential Cross sections from amplitude scattering matrix

How can I get the differential cross sections from the amplitude scattering matrix, $S$ (2x2 matrix)? I've seen this in a Mie solution solver: Parallel Polarized Light: dCsdOp = $\frac{2}{\pi k} ...
2
votes
2answers
86 views

Air Drag in orbit

Artificial satellites don't orbit the earth forever. Eventually the Earth's atmosphere, thin as it may be up there, will bring them down. But did you know the linear speed of a satellite in a near ...
4
votes
0answers
74 views

Non-Hermitian Lagrangian in Quantum Field Theory

I have seen more than once non-Hermitian Lagrangian densities being used in effective field theories. Usually the problem of unitarity is explained away with decays into some degree of freedom not ...
1
vote
1answer
97 views

Deuteron wave function

The deuteron wave function is given by $$|\psi _d\rangle = a|^3S_1\rangle+b|^3D_1\rangle$$ where all states are normalized. How do we find $b^2$ s.t. the wave function reproduces the magnetic moment ...
0
votes
2answers
118 views

Why do we lose signal in elevators? [duplicate]

Whenever I am talking on my phone and walk into the elevator the call drops as soon as the doors close, and also the WiFi signal completely stops. Why does this happen? Note: I am asking this ...
0
votes
0answers
28 views

Stationary Perturbation Theory

We write first order correction in the wavefunction as a linear sum of eigenstates of unperturbed hamiltonian. Why is this possible?
0
votes
0answers
31 views

Rotation of Thin street sign

I am attempting to complete a home question in which a shop sign in the shape of a thin rectangle of size p x q (with q being the longer side), and mass m, that rotates about an axis that passes ...
0
votes
1answer
37 views

Electrical network of current sources - What happens if one source is defect?

Suppose you have connected in a parallel circuit a pair of, say for the sake of concretness 5 sources of 300 mA and 0,5 V each, which are themselves connected together in series. Hence, in total one ...
0
votes
0answers
35 views

On the probability of the existence of a similar observable universe

Let's assume a standard ($\Lambda$CDM + some simple inflation model) cosmology in an infinite universe. Really it doesn't matter much what cosmology we take, just that we're considering an infinite ...
0
votes
1answer
63 views

What is the relation between $\eta^{ab}x^2$ and $x^ax^b$?

What is the relation between $\eta^{ab}x^2$ and $x^ax^b$? Here $\eta$ is the Minkowski metric in $d=4$ and $x$ is a 4-vector. In particular, a tensor like $$x^a x^b x^c (\eta_{ab}x^2 - x_ax_b) ...
1
vote
0answers
25 views

Why is the potential minimum of a molecule shifted towards greater nucleii separation for excited electron states?

I know it has to do with symmetry of the wave function, but I am having trouble piecing it all together. For a positive H ion we have a symmetric wave function $\psi_{+}$, which base functions ...
1
vote
1answer
77 views

Is it correct that whenever energy change, mass also change?

Can I simply claim that, according to the mass-energy equation $E=mc^2$, whenever the energy of an physical object (not necessarily a microcosmic one) changes, its mass also change? Okay, I ...
0
votes
1answer
41 views

X-ray pulse more powerful than national grid?

There is an article today in the BBC science section on the Linac Coherent Light Source, an X-ray laser in Palo Alto: http://www.bbc.com/news/science-environment-31483781. I don't trust the news with ...
0
votes
0answers
73 views

Nodes of the ground state of a system of Schrödinger equations

In 1D, a single wave function that satisfies Schrödinger's equation representing the ground state for some $V(x)$ has no nodes. Suppose now that you have a system of $N\neq 1$ coupled Schrödinger ...
0
votes
0answers
29 views

Newtons 2nd law and longitudibal dynamics of bicycle

When a bicycle (of gross vehicle mass $m$) accelerates ($a$) forward, such that both the wheels are in pure rolling (no slipping), then: static friction ($f_{s1}$) acts on the front wheel backwards, ...
0
votes
1answer
44 views

What is the factor that controls the speed of electrons accelerating in vacuum?Won't they accelerate infinitely? [duplicate]

We all know that speed of light can not be exceeded. So the question is if electric field accelerates electron in a vacuum tube with enormous length won't the electron accelerate till a point where it ...
1
vote
2answers
69 views

Identifying a scalar function

We know that a scalar is invariant under rotations. What about a scalar function? Should it also be invariant under rotations? Therefore, under rotation $\phi(x,y,z)$ must be equal to ...
0
votes
1answer
126 views

Eigenvalues of a nearest-neighbour tight-binding Hamiltonian in (Mahan, 2003)

In this paper by G. D. Mahan, he obtains the following electron Hamiltonian in a nearest-neighbour tight binding scheme: (page 2 of the paper, top of the right column) \begin{align} H_0 &= J_0 ...
3
votes
1answer
58 views

Limits for the linear wave equation

In acoustics and continuum mechanics the following wave equation (for Speed of Sound $c$) for the pressure field $p$ is well-known: $\partial_t \partial_t p = c^2 \Delta p$. This wave equation can be ...
0
votes
0answers
16 views

Say we have the following springs and weights as given. Find the equilibrium displacement

Assume we have a ceiling and from it three springs $c_1$, $c_3$ and $c_4$ are attached to it. Mass $m_1$ is connected by $c_3$ and $c_1$. $c_2$ connects mass $m_1$ to $m_2$ below it and $c_4$ ...
0
votes
1answer
75 views

Why Levi-Civita term signal the breaking of parity and time reversal?

For example, referring to Zee's QFT book, in Chern-Simons matter theory, after writing a term $$\gamma {\varepsilon ^{\mu \nu \lambda }}{a_\mu }{\partial _\nu}{a_\lambda }$$ he said The ...
2
votes
2answers
59 views

Work done in lifting chain with nonuniform linear density

I am teaching calculus, and a natural-seeming problem type just occured to me. It would go something like: a 2m chain hangs from the top of a building. Its density at a point h meters from the edge ...
0
votes
0answers
12 views

Magnetic field generated by wires with magnetic cores

Describe the magnetic field generated by alternating current as it passes through a wire's special core of tiny, metal-coated, cylindrical rare earth magnets? Examples of real-world consequences of ...
1
vote
3answers
100 views

Position, Velocity And acceleration relations

Today we showed our physics teacher our code for a basic physics engine. He told us that this code snippet is incorrect: ...
0
votes
1answer
24 views

Writing collision equations with the help of coefficient of resistitution

Suppose we have a frictionless surface and a small particle of mass $m$ which collides with velocity of $V$ with stationary particle of $2m$ elastically. I know how to deal with this simple problem ...
23
votes
7answers
6k views

Is there a maximum frames per second (FPS)?

Take a video camera and crank up the frames per second rate. Disregarding current technological advancements, could a camera's FPS go so fast that any two captured images be identical? Would ...
2
votes
3answers
2k views

What is basically the difference between static pressure and dynamic pressure?

What is basically the difference between static pressure and dynamic pressure? While studying Bernoulli's theorem, I came before these terms. The law says: When the fluid flows through a small ...
1
vote
1answer
112 views

What properties make a good catalyst?

Specifically, I am thinking about metal catalysts that do not (apparently) take part in a direct chemical reaction. Is there any general method of either finding a catalyst for a given chemical ...
1
vote
5answers
558 views

Normalizing the solution to free particle Schrödinger equation

I have the one dimensional free particle Schrödinger equation $$i\hbar \frac{\partial}{\partial t} \Psi (x,t) = -\frac{\hbar^2}{2m} \frac{\partial^2}{\partial x^2} \Psi (x,t), \tag{1}$$ with ...
0
votes
0answers
72 views

Topology of a black hole

How many dimensions are theorized for a black hole, in view of the fact that black holes are not observed directly.
0
votes
3answers
105 views

Resistance of capacitors

Please I would like to know how the resistance of the plates of a capacitors work? Is it the same as a resistor? If yes, is there electric field inside the plates like inside a resistor?
1
vote
1answer
259 views

Zero velocity and non-zero average acceleration

Can you have a zero velocity and nonzero average acceleration? I am confused with the word "average" here. If the question would be, "Can you have a zero velocity and nonzero acceleration?" my answer ...

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