0
votes
0answers
11 views

Why can we leave off half of the general solution?

In this pdf, it says at the bottom of the first page and beginning of the second: ... whose solution is: $$\Psi(\theta) = c_1 e^{i\omega\theta} + c_2 e^{-i\omega\theta}$$ Since we are ...
-1
votes
1answer
14 views

Finding expectation value of $p^2$ without integrals

So the expectation value of momentum, if you know the expectation value of position is $$\langle p \rangle = m \frac{d\langle x \rangle}{dt}$$ Is there a nice formula like this for $\langle p^2 ...
1
vote
1answer
24 views

Why do rockets jettison fuel tanks?

I'm trying to understand why rockets have multistages releasing their fuel tanks. Say a rocket $R$ has two fuel tanks $A$ and $B$, which respectively have masses $m_a$ and $m_b$, and the mass of the ...
2
votes
2answers
27 views

$ε_0$ affects electric field intensity, but $μ_0$ doesn't affect magnetic field intensity?

I'll be honest: this question is actually a homework problem. I've spent the past hour going through Google and several textbooks trying to answer the question "Why does $ϵ_0$ affect electric field ...
3
votes
2answers
113 views

FRW metric and its validity througout the age of the universe

Why do we think that the FRW metric should be valid throughout the entire history of the universe?
2
votes
1answer
146 views

If distant observers never see a black hole form in finite time how can the information paradox be a problem?

So, at least as reported in the media, the physics community is still struggling with the problem of resolving the impossibility of retrieving information from beyond the event horizon of a black hole ...
0
votes
0answers
17 views

Physical simulation in python

Is there a "standard" python package used to aid in physical simulations? What is the most popular?
0
votes
1answer
20 views

Potential Difference between two glass spherical shells

Say I have two spherical shells, let's call them sphere 1 and sphere 2. Sphere 1 has a uniform charge of +Q and sphere 2 has a uniform charge of -Q. Sphere 1 and sphere 2 are separated by a distance ...
0
votes
0answers
15 views

Rigorous definition of pressure in a fluid

We briefly introduced some terms at the start of my Fluids class, and one of them was pressure. I'm looking for a rigorous definition of pressure. Wikipedia gives this definition for pressure: $p = ...
0
votes
2answers
102 views

Does the formula $ \theta = \frac{v}{c} $ to find out deflection of light make sense?

I read in reliable sites that GR and classical physics calculate the angle of deflection in the same manner. The formula is almost identical: $$\theta = \frac{4GM}{c^2*r} \rightarrow \frac{4GM}{c*r} = ...
3
votes
1answer
24 views

Physical Meaning of Divergence of Convective Velocity Term

When taking the divergence of the convective velocity term, I get the following: I know the first term on the right hand side represents the convective term for the dilatation component of the ...
1
vote
2answers
36 views

Homemade Spectrometer

Recently I have had ideas of how to build a spectroscope, but I'm not sure if it will work. As can be seen in the diagram, the experiment is simple: it consists of a laser that generates the light ...
6
votes
1answer
218 views

Is it possible to determine particles' velocities from their crossings on a ring?

2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at ...
0
votes
0answers
9 views

Should S always be more than 2 to violate CHSH inequality?

Is it always should be about $2\sqrt{2}$ or it's just a maximum value and it's possible to measure something like S = 1.90, 1.8, 2.0, 2.4, 2.6, 1.8 (with average = 2) in different sub-experiments to ...
-1
votes
0answers
11 views

Quadrature method (vertically falling particle)

Consider a particle, that in the presence of the force of gravity, moves only vertically. Obtain the equation of motion of the particle from its mechanical energy(quadrature method). Consider the ...
1
vote
1answer
50 views

How does gravity's space time distortion access energy to induce freefall?

An observer, standing on top of a building, has a gravity switch (use your imagination) which allows him to turn gravity on and off. He turns the switch off, then releases a pool ball over the edge ...
0
votes
2answers
31 views

What is a 'moist greenhouse effect'?

What is a moist greenhouse effect? I've heard that this is where all the water on a planet is quickly driven into space. However, I cannot find much information on this- is it a relatively new (or ...
-2
votes
2answers
50 views

How does the human eye knows how far the object from which the photon was reflected?

A photon is emitted from a source and reflected off an object (or objects) until it hits the human eye. The color of the object we see depends on the photon wavelength. If photon travels with constant ...
0
votes
1answer
15 views

Explanation for Homogeneous Nucleation Temperature?

What is homogeneous nucleation temperature (for water this is listed as -42C); is it simply the lowest experimental temperature you can go before supercooled liquid turns into solid, or is it that ...
-1
votes
1answer
28 views

Why & What extra dimensions in M-theory?

I am not into String or M theory. Recently I am again reminded that M-theory "requires extra dimensions" beyond the usual string theories, beyond the usual space-time dimensions. To me, dimensions ...
0
votes
1answer
135 views

Semiclassical description of EM waves reflection from metallic surfaces

Imagine an EM wave impinging on a metal. Fresnel's formulas tell us that no wave can propagate through the metal, or that the transmitted field is an evascent wave with some penetration depth ...
36
votes
2answers
1k views

Why does my wooden door disperse light into a rainbow color spectrum?

On a clear morning, light comes through this window (viewed from the inside) It then hits the door on the opposite side (so viewing from the outside the door straight on the other side) There is ...
1
vote
0answers
16 views

Keplerian Telescope Exit Pupil Location - Whats the Basis for It's Formula?

For a simple two lens Keplerian telescope, this is the formula for the location of the exit pupil: $$z'=\frac{f_2}{f_1}(f_1+f_2)$$ Where $z'$ is the distance to the exit pupil location (i.e. eye ...
0
votes
1answer
2k views

Is this pseudo science or real: code found in superstring

Article in question: http://humansarefree.com/2013/01/science-strange-computer-code.html Problem: no credible looking or sounding site has anything on it. Only bunch of youtube videos. And some ...
1
vote
0answers
18 views

Derivation of apparent location of image in water

In the I am just trying to find out the equation to determine where an object (represented by the blue circle in the image) would actually be located if it appears to be where it is in this image. ...
0
votes
1answer
259 views

Coercivity of a ferromagnetic material?

I understand that coercivity is the field/force required to demagnetize/magnetize a ferromagnetic material. What if we had two opposite magnetic fields of different strengths values H acting on the ...
1
vote
1answer
28 views

Definition respective derivation of angular momentum formula

I am reading An Introduction to Mechanics by Kleppner and Kolenkow (2014). On page 241 is the definition of the angular momentum: Here is the formal definition of the angular momentum $\vec{L}$ ...
1
vote
2answers
41 views

What is the speed of an electric spark/arc in vacuum?

I am just curious about the nature of an electric spark, how fast are the electrons moving? Will these electrons slow down when the spark occurs through a dielectric? (e.g., air)
2
votes
3answers
97 views

Why does a bubble take a spherical shape?

I suspect this has something to do with thermodynamics and the isoperimetric inequality and I'm interested in a mathematical derivation of this result.
0
votes
1answer
36 views

Phase diagram of water v/s other substances

Why for water increase in pressure decreases solidification temperature? The fusion curve of water is not same as that of other substances and for other substances specific volume increases during ...
0
votes
3answers
206 views

Confused about Newton's 3rd law

I am confused about Newton's 3rd Law. If a person jumps off the ground a force is applied both to the person and to the ground. However, as $F=ma$ acceleration experienced by the Earth is much less ...
3
votes
7answers
162 views

Is it possible to cut harder material with a less hard material?

Is it possible to cut harder material with a less hard material - for example cut a steel rod with iron blade ?
0
votes
0answers
38 views

Lorentz factor, derivation from 4-velocity vector [on hold]

How do I derive the Lorentz factor $\gamma=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}$, from the fact, that the velocity 4-vector $(-c,v_1,v_2,v_3)$ has length (norm) equal to 1?
5
votes
2answers
863 views

Solving the Young-Laplace equation for arbitrary axisymmetric geometry

Say I have a non-ellipsoidal soap bubble and I want to numerically analyse the pressure in the inner lobe of this bubble here: The Young Laplace equation gives the pressure difference across a ...
17
votes
1answer
222 views

What are the equations of motion of a hole in a soap bubble?

Imagine the following situation: I have a thin stationary water film, like a soap bubble, suspended inside a large ring. I throw a small loop of string onto the film and punch a hole inside it. How ...
4
votes
4answers
1k views

What is the physics behind a soap bubble?

A soap bubble is an extremely thin film of soapy water enclosing air that forms a hollow sphere with an iridescent surface. What fluid dynamical process occurs during the popping of a soap bubble?
1
vote
3answers
37 views

How can we minimize the coefficient of static/kinetic friction?

Static frictional force depends on the coefficient of static friction; kinetic frictional force depends on the coefficient of kinetic friction. To minimize friction, one of two things could happen: ...
3
votes
2answers
131 views

Quantum entanglement on cosmological scales

This may be a foolish question given my limited understanding of QM but here it is. As I understand quantum entanglement basically means that two particles evolve as a single "unit", i.e., are ...
0
votes
1answer
29 views

Motivating the importance of energy [on hold]

I'm working on a project right now and part of the introduction is about energy, and I'm trying to introduce the notion of energy in an unconventional way. Right now, I am looking for examples of ...
1
vote
2answers
77 views

Is the Moon freely falling towards the Earth?

The Moon is revolving around the Earth and its centripetal acceleration is towards the Earth. Does it mean that the Moon is freely falling towards Earth? What is the cause of the Moon orbiting around ...
5
votes
2answers
441 views

What properties would the ideal material for spacecraft construction possess?

Assuming we develop the capability to send a robot to study Gliese 518, or any of the Earth-like planets discovered in the neighbourhood; the spacecraft would need to travel through the Solar System ...
3
votes
2answers
336 views

Linearity of Quantum Mechanics?

The proof of the No-Cloning Theorem states "By the linearity of quantum mechanics, ..." -- Could someone please give me a rough sketch/outline of what this means? Does it have to do with the Hilbert ...
1
vote
1answer
86 views

Closed expression for the Green's function for 2D Helmholtz equation over rectangular domain

I have to use the Green's function for the 2D Helmholz equation $$(-\nabla^2 - E) \psi(x, y) = 0$$ on the rectangular domain $[0, L_x] \times [0, L_y]$ with Dirichlet boundary conditions: $$\psi(0, y) ...
0
votes
0answers
32 views

Correct approach for calculating excited states of circular quantum dot under effective mass approximation

From Asnani, Mahajan et al, Pramana Journal Of Physics 73 #3 (2009) p574-580 "Effective mass theory of a two-dimensional quantum dot in the presence of magnetic field", which can be seen here: ...
1
vote
1answer
71 views

Group Theoretic definition of a particle

We intuitively have a sense of what a particle means in the conventional sense. But is it possible to have a group theoretical definition of a particle, I mean in terms of irreducible representations ...
2
votes
1answer
87 views

Simple systems whose classical and quantum Hamiltonians differ

Dirac remarked in his quantum mechanics book: One can usually assume that the Hamiltonian is the same function of the canonical coordinates and momenta in the quantum theory as in the ...
3
votes
0answers
20 views

AdS/CFT dual of $N$ D$p$-branes at finite temperature

The gravity dual of $N$ D$p$-branes at zero temperature is $$ ds^2= H^{-1/2}(r)(-dt^2+dx_p^2) + H^{1/2}(r)(dr^2 + r^2d\Omega_{8-p}^2) $$ with $$ H(r) = 1 + \left(\frac{R}{r}\right)^{7-p} $$ what ...
0
votes
0answers
20 views

Question on pressure required on a fire hose pump [on hold]

Not entirely sure of how I transfer a pressure value to speed to reach the top of the building and also unsure of how the height of the fire hose affects the question.
1
vote
3answers
151 views

Joules to do something

If my very limited understanding is correct then, not accounting for gravity: 1 Newton can move 1 kilogram 1m But, can 2 Newtons move 1 kilogram 2 meters? Is this because 1 Newton = acceleration of ...
0
votes
2answers
1k views

Can you help me solve a difficult kinematics problem? [on hold]

I've been working on this problem for a while now, but I still don't know how to solve it. It involves 2D kinematics, which aren't in themselves hard, but this one threw me for a loop. A ball is ...

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