0
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0answers
2 views

How to find the height where the collision of two balls occurs?

There was this question that got deleted (for whatever reason): Ball A is dropped from the top of a building of height h at the same instant that ball B is thrown vertically upward from the ...
0
votes
0answers
7 views

Can electricity flow through vacuum?

People say yes, and give a wonderful example of vacuum tubes, CRTs. But can we really say that vacuum (..as in space) is a good conductor of electricity in a very basic sense?
0
votes
0answers
4 views

How to show time reversal symmetry is not break in the tight binding Hamiltonian for the honeycomb lattice?

The Hamiltonian of the honeycomb lattice is $$ H=\sum_{k\sigma}t(k) a_{k\sigma}^\dagger b_{k\sigma}+h.c $$ Where $t(-k)=t^*(k)$. If we do a time reversal transformation(according the answer to this ...
0
votes
0answers
5 views

hiding joint lines of plain mirrors

For some experiment I took two rectangular pieces of front surface mirrors, and joined it at 30 degree. However, the joint line is visible clearly, how do I hide it ? I guess I need to apply some ...
1
vote
1answer
13 views

What is the idea of canonical quantization?

From what I understand, canonical quantization of a classical theory consists of replacing the observables by abstract operators, of which only the commutation rules, which have to correspond to the ...
0
votes
0answers
7 views

Does Average Lifetime even mean anything?

So today I was trying to derive an expression for the number of radioactive atoms remaining after a time $t$ if I began with $N_0$ atoms in total. At first I tried to assume that they had an average ...
1
vote
0answers
6 views

Around fixed point of renormalization group

In the general formulation of renormalization group in "statistical mechanics" by P.K.Pathria, each point in parameter space is represented by a vector $\vec{K}$ and the transformed vector would be ...
0
votes
0answers
6 views

Efficiently compute the bases functions of the Signal

Let there be 4 1D signals such that \begin{cases} x(t)=4\sin(10\pi t) \\ y(t)=8\cos(20\pi t) \\ z(t)=16\sin(30\pi t) \\ m(t)=x(t) +y(t)-z(t) \end{cases} Is there a way to compute ...
0
votes
0answers
8 views

Acceleration of an oscillating object in a frame of reference that is itself rotating!

I have been reading a paper and due to my limited knowledge of Physics, I can't move ahead. Sorry I do not know latex so, I will snip the paper and paste it here. So here goes it..... I think ...
0
votes
0answers
12 views

Equivalence of gauss's law for surface and volume distribution of charge

I have a problem about Equivalence of Gauss's law of surface and volume charge distribution. Can any one tell me about the equation which relate the surface and volume distribution of charge using ...
-1
votes
1answer
23 views

String theory $bc$ system CFT

$bc$ CFT is an example of free-field CFTs. action is $$S = \frac{1}{2\pi} \int d^2 z b \bar{\partial} c$$ How can we obtain equation of motion? Polchinski-volume 1-page 50 writes that ...
-2
votes
1answer
35 views

Is the concept of infinity valid in physics, beyond its convenience?

Is infinity a meaningful concept in physics, apart from making some of the maths easier? Especially since reality seems to be discrete.
0
votes
2answers
20 views

Double Pipe Heat Exchanger Flow Hot Cold

Based on sources I referred, I got to know that a double pipe heat exchanger operates in a way where hot water flows in a pipe and comes out as cold water and cold water flows into another pipe and ...
-1
votes
0answers
16 views

What will happen if Sun makes a trivial change in position?

What will happen if Sun makes a trivial (negligible) change in position. Will it be disastrous? Or, It will not matter?
0
votes
0answers
21 views

If my particle is a surfer on a wave and speed of wave is $c$, How can I add “the speed of particle” in relavity?

I have 3 particles which have different masses (0, 5 and 10). I have also a wave with the speed of $c$. My particles are also vibrating in $y$ axis (according to direction of waves) because of peaks. ...
-2
votes
0answers
27 views

Is Brent's accelaration zero at any point? If so, where? [on hold]

Brent is jumping on a trampoline.He leaps up into the air,and falls back again.
1
vote
2answers
232 views

Is there a way to photograph the very edge of black hole?

According to Professor Stephen Hawking, black holes emit radiation, Hawking radiation. The bigger the black hole, the fainter the radiation. That means, I personally believe, if we built large enough ...
2
votes
1answer
162 views

Is there a difference between Electric and Electrostatic Field?

Is there a difference between Electric and Electrostatic Field? All I know is that they both represented with same law suppose we have a Charge placed at the Origin: ...
0
votes
2answers
44 views

When and who by was the earliest definition of speed?

Speed is defined to be distance divided by time; when and who by was this definition first put forward? The obvious guess would be for Galileo in early modern physics; is this right, and can it be ...
0
votes
0answers
13 views

Physical interpretation of the relative displacement tensor?

I've resolved a relative displacement tensor into a strain tensor and a rotation tensor, where the strain tensor is: $$ \varepsilon_{i,j} =\begin{pmatrix} 0.2 & 0 & 0 \\ 0 & 0.8 ...
1
vote
1answer
27 views

Protons and Neutrons Overshoot Actual Mass?

When I add up the mass of 6 protons and 6 neutrons in amu, I get a mass that is greater than the mass of carbon. I thought that it should be the other way around, because I have not including binding ...
1
vote
0answers
19 views

Are there any grounds for thinking that the distribution of matter in the universe is unbounded?

Even though we can make no observations beyond the cosmological horizon, I think people tend to picture a universe that is either homogeneous to infinity, or possibly having spacelike slices that are ...
0
votes
0answers
32 views

Has the Pioneer Anomaly been experienced by Voyager?

I came across the Pioneer Anomaly recently, and a quick search here showed there now a theory that fits everything observed. My question is, should we expect a similar effect from the design of the ...
1
vote
1answer
50 views

What will happen to the Earth when Milky Way and Andromeda merge?

Hypothetically, if our solar system survived into the far future and human was still around, is the merge between 2 galaxies were a disaster for lives on Earth? Were the Sun get thrown away from the ...
0
votes
0answers
7 views

Scalar Green's function of wave equation in a multilayer medium

A point source is located somewhere $\mathbf{r}_0$ in planar stratified media that consists of $n-1 $ layers (or $n$ types of materials). The physics is governed by the scalar wave equation ...
0
votes
2answers
42 views

What sort of propulsion technology would allow spaceships to lift off the surface of the Earth and ascend into space like we see in sci-fi movies?

In many sci-fi films, spacecraft are easily capable of lifting off the surface of a planet like a Harrier and ascending into space. It's clear that the propulsion system/jet engines aren't your ...
-5
votes
0answers
31 views

Calculating the change in entropy [on hold]

What is the magnitude of the entropy change of $2~\text{kg}$ of water heated from $20^{◦} ~\text{C} \to 40^{◦} ~\text{C}$? Assume the heat capacity of water is $4186~\frac{\text{ ...
1
vote
2answers
32 views

when a steam is being liquified, does its temperature change or not?

Here is a question: When ice is being melted, its temperature doesn't change. So, when a steam is being liquified, does its temperature change or not? And is the heat transferred here calculated by ...
1
vote
0answers
21 views

Chemical Potential at Triple Point

How does one calculate the chemical potential/Gibbs Free energy at the triple point of a substance given only the temperature and pressure of the triple point, and the volume of each phase? I cannot ...
4
votes
2answers
331 views

Why do people only float in certain orientations?

If the buoyant force on an object is equal to the weight of the water displaced by the object, why do people have an easier time floating on their back than vertically with their head sticking out of ...
4
votes
3answers
77 views

In QCD mass is caused by gluons and in electroweak it is caused by the Higgs field which is it?

I am trying to understand mass. The Standard model contains an electroweak field where mass of everything comes from the Higgs field. The Standard model also contains Quantum Chromodynamics with a ...
2
votes
1answer
32 views

How does electromagnetic radiation affect the velocity of a charged particle?

I've heard that the acceleration of a charged particle releases electromagnetic waves. So let's say there is a charged electron moving forwards in a region with a downwards magnetic field. If the ...
3
votes
2answers
38 views

What is precisely the energy scale of a process?

Coupling constants run with the energy scale $\mu$. But what is exactly this energy scale. My question is, if I have a physical process, how do I compute $\mu$?
2
votes
1answer
50 views

Lorentz-invariance of step function

I was reading about the Lorentz invariant integration measure $\int \frac{d^3k}{2E_K}$, and ways to prove that this was Lorentz invariant. Many of the proofs I have read use the step function (or ...
1
vote
1answer
15 views

What is the physical meaning of $v\times n$?

What is the physical meaning of $v\times n$, where $v$ is a velocity vector and and $n$ is a unit normal vector of a interface? Why at the free surface between two fluids, $$v^{(1)}\times ...
-2
votes
1answer
18 views

Induction Oscillation [on hold]

A bar (m=100g, l=10cm) is moving in a constant magnetic field $B$ as shown above. The resistor $R$ is $1\Omega$. The bar is attached to a spring with spring constant $10N/m$, can you derive ...
3
votes
0answers
32 views

Why do rings form on microwaved CD/DVDs?

Here's a microwaved CD. As you can see, the disc has been destroyed, but there are very clear circular rings bridged with lines. Why are rings formed when microwaving discs?
0
votes
2answers
39 views

space contraction near lightspeed

I read a lot of the Time-Life Science books when I was a kid (well, mostly the pictures and captions). One of the things that always stuck in my mind was an explanation of the twin paradox, using ...
-2
votes
0answers
22 views

Why is the rotation not zero and the divergence zero in the figures below? [migrated]

Why is the rotation not zero and the divergence zero in figure 1 and figure 2 below? Figure 1 Figure 2
0
votes
0answers
56 views

Interesting approach to Kepler problem

I won't go into the explanation of this idea, because it is explained in this blog post. In this paper, which was featured on John Baez's blog, $\frac {dt}{d\lambda}$ is given as $\frac r V$, where ...
2
votes
1answer
15 views

Relationship of the volume of a plumbing system to pressure

How does the volume of water a plumbing system holds vary with water pressure? I know the ratio would include the modulus of elasticity of the plumbing material, the total surface area of the plumbing ...
2
votes
1answer
65 views

Weightless person in a cart on a rail [on hold]

In a problem I'm trying to solve I've having a conflict between my understanding and the proposed solution of the problem. A cart ($m=35kg$) is at rest in the start of a friction-less ("covered with ...
0
votes
0answers
9 views

Geophysics: Dynamic form factor and Equipotential surfaces [on hold]

I've got the following problem which I need help with. I'm used to calculating coefficients when the problem is about ellipsoids and first order approximations. But when it comes to spheres and ...
0
votes
0answers
13 views

Propagation of incertitude - specific example [duplicate]

I am setting up an experiment, where I know the force and the incertitude (delta) of that force. However, I need to graph the logarithm of that force with the incertitude of the log. Can someone help ...
1
vote
0answers
13 views

A question about genus one string amplitude

In BCOV's paper http://arxiv.org/abs/hep-th/9309140 the genus one string amplitude of a Calabi-Yau 3-fold was explained in the B-model as the Ray-Singer torsion (there is a similar discussion in the ...
0
votes
0answers
10 views

Why is the heat transferring best from within the tube within a tube-heat exchanger

If you've got gas and cooler fluid, you'd run the gas through the tubes, because the gas has a lower h-value. Inside a tube heat-exchanger it is said that the best heat transfer is from within the ...
1
vote
1answer
17 views

Moment of Inertia Calculation [on hold]

A uniform disc has centre O, radius a and mass 2m. It is free to rotate in a vertical plane about a horizontal axis through O. A particle P of mass m is placed on the highest point of the rough edge ...
2
votes
1answer
13 views

Determining straining force and reaction forces on a beam

A homogenous beam $OA$ with the length $4a$ and the mass $m$ can rotate in the vertical plane along a horizontal axis through $O$ and is kept in equilibrium by a wire running from the points A and C ...
2
votes
1answer
30 views

Point charges in a sphere

If we put N point charges (with charge +q) in a sphere with radius R and the charges can move freely in the sphere but can't get out of it, where will the charges go to and what will be the ...

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