# All Questions

94 views

Do paradoxes exist due to velocity addition ? .. In the above diagram, we have a very lengthy 259,627.885 km long space station. Rocket "A" is parked at the left end of the space station. Let us ...
35 views

### Would an airtight box filled with air act the same way to 1 bar of water pressure as the same box vacuum-sealed at atmospheric pressure?

Pressure On average, a column of air one square centimeter in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kg and weight of about 10.1 N (2.28 lbf) ...
44 views

### Proving a relation for representations of gauge groups [on hold]

I have asked this question in Math Stackexchange as well. However, given that it is closely related to gauge theories studied by physicists who will probably be more familiar with the language and ...
43 views

### Non-polarised light

We know the beam of light oscillates in electric field and magnetic field, both perpendicular to both the wave of propagation and each other. What does, however, a non-polarised beam of light look ...
22 views

### Positivity of Bulk modulus and shear modulus in isotropic materials

I have been searching through many resources, but could not find a proper thermodynamic reasoning for why bulk and shear moduli for isotropic materials should be positive. Some resources like eFunda ...
813 views

### Can polarized light be unpolarized again?

I was just wondering if there could be a process that could unpolarize polarazied light. Is that possible?
73 views

### Ball flying towards me - Newton's third law is violated?

I was trying to answer the question of the flying ball here on the basis of Newtons third law and Momentum conservation. Here is what I have tried. Lets take $m_1$ (the ball) hits $m_2$ (the man). ...
58 views

### Does rain jam radio signal?

I have experienced several times that heavy rain seems to jam the signal a radio of a bus receives. The only explanation I have is that the rain drops also become weak emitters, if a radio wave hits ...
24 views

### Why is radiance measured normal to the beam?

Radiance is defined as: $L=\frac{d \Phi}{\mathop{d \omega} \mathop{d A} \mathop{\cos\theta}}.$ I’m wondering why there is a $\cos \theta$ factor in the denominator of the radiance ($\theta$ is the ...
123 views

### Why is every particle a sphere?

I was wondering why is everything in this universe, I mean atoms and well quarks and photons and what not some form of sphere. Is there any exploitation to the sphere being perfect and only thing for ...
43 views

### How can a 360 Degree Rainbow be formed? [duplicate]

Just a while ago while I was reading news paper, I saw an amazing article. Someone had caught a photo of a 360 Degree Rainbow. But how is it possible. I mean after refraction the only rainbows that ...
56 views

### The Big Bang theory [duplicate]

According to big bang theory the whole universe was formed by this big explosion and it gets bigger and bigger Does that mean it has limits? and what do you think we can found beyond all that ?
80 views

### Can a discoverer give the name he wants to his finding? [migrated]

Let's assume that some scientist discovers a phenomenon that has never been noticed before. He wants to write a paper about it but he doesn't want to constantly write "effect of change of some ...
19 views

### Uniformly magnetized sphere

While working on a uniformly magnetized sphere, I have come across this problem: How does the boundary value equation $$\vec n.(\vec B_2-\vec B_1)=0$$ lead to the equation ...
25 views

### Lorentz transformation of scalar field [on hold]

How can I show that $$\phi(x^{\mu}) - \frac{1}{2}\lambda^{\sigma \rho}L_{[\sigma \rho]}\phi(x^{\mu}) = \phi(x^{\mu} + \lambda^{\mu \nu}x_{\nu}) \,\,\, ?$$ Here, $\lambda^{\rho \sigma}$ are the ...
15 views

### Relativistic non-linear Walecka model

What is meant by a relativistic non-linear Walecka model? What are some various sources to study it? [And why cannot Google show a satisfactory result to such a simple question?]
26 views

### Search materials by HOMO, LUMO and work function [on hold]

I need to search organic semiconductors for organic photovoltaics (OPV) by their HOMO, LUMO, work function (WF) at 300 K (as I understand, WF cannot be derived from HOMO and LUMO because semiconductor ...
385 views

### Can velocity be an undefined quantity?

We have the image below displaying the uniform velocity by time-distance graph. At every point velocity is constant but what if distance and time both become zero as at origin in the graph is? The ...
95 views

### Does lunar module need the same amount of fuel for landing and take off?

Let's assume there is no atmosphere and let's assume there is no change in weight due to fuel consumption, will reactive rocket need the same amount of fuel for landing on a planet as for take off? ...
41 views

### Delayed Choice Quantum Eraser [duplicate]

All delayed choice quantum eraser experiments I've seen record the signal photons reaching detector D0 and then use the data of the idler photons recorded at detectors D1, D2, D3, D4 to "filter out" ...
59 views

### Gravitational time dilation, does time of the observer at a lower gravitational potential looked slowed down in the frame of the higher one

This question is mainly inspired after watching the movie known as Interstellar We knew that for time dilation caused by relativistic motion between A and B. A will measure B's clocks slowing down, ...
82 views

### Could it be possible that the universe doesn't exist [on hold]

Could it be possible that the universe doesn't exist? That nothing exists, not even you or me? And by not existing, I mean totally not existing, as in not even existing as a computer simulation, or a ...
55 views

### How to actually account for air resistance?

What's interested me in my studies thus far is that in a lot of beginner undergrad mathematics and physics courses we're often told to calculate trajectories, velocities, etc. by "ignoring air ...
27 views

### Best book for learning Quantum Communication [duplicate]

I am new in Quantum physics. I want to do my BSc thesis on Quantum Communication. My major is Communication. So I want to learn fast. I have little idea about quantum computing. So please suggest me ...
40 views

### Inclined pulley with unknown hanging mass: when won't the system accelerate?

We have an inclined pulley with angle of $30°$ a block with mass of $10 kg$ placed upon it and It is attached by a rope over a pulley to a mass of $M_A$ which hangs vertically. If $μ_s=0.4$ and ...
721 views

### Does quantum entanglement arise from quantum theory or is it merely an experimental observation?

I assume that entanglement emerges from quantum mechanics because the idea was around before experimental verification (e.g the EPR paper). How then does entanglement emerge from the theory (please ...
13 views

### Direction, closeness and range of streamlines in a flow domain with solid boundary and free surface?

I have a flow-field with solid boundaries and a free surface, I have plotted the streamlines, however I am not sure whether my graph is correct. In fact, I drew the streamlines by taking a range of ...
35 views

### How to calculate the solid-liquid interface energy knowing the surface free energy and liquid contact angle? [on hold]

Given surface free energy something around 20mN/m, and the contact angle around 120° for water (73mN/m). How can I estimate the solid-liquid interface energy of the given solid surface to water? I ...
42 views

### Speed of a magnet

What is the speed of two magnets during the congruent moment of their attraction? Theoretically, could a large enough magnet attract a significantly smaller magnet at near the speed of light? In ...
28 views

### Why is space isotropic in the vector particle's decay?

I come across one proof the Landau-Yang Theorem, which states that a $J^P=1^+$ particle cannot decay into two photons, in this paper (page 4). The basic idea is, the photon's wavefunction should be ...
32 views

### Momentum in the frame of reference of the center of mass [on hold]

I'm a high school student who just learned this topic in class today. I don't understand why the sum of momentum is zero in the frame of center of mass. Also, how can I solve this problem: Three ...
17 views

### Critical engine failure just after rotation: what percent of accelerated slipstream lift does the wing loose? [on hold]

I have searched the web for facts about the lift created by a propeller slipstream (propwash). I have found many web sites that in fact claim that the propeller slipstream does indeed produce a lift ...
16 views

### Mutual inductance theoretically decreasing while EMF is increasing in 2 square coil system

I have a quick question regarding electricity and magnetism. I am measuring the induced emf in a square coil of wire with an inductance of 439uH (the other coil is also 439uH and is the same shape). I ...
13 views

### LOCAL Temperature Gradient and Stress

I'm investigating the thermo-migration failure mechanism in nanoscale ICs interconnects. Typically, a nano wire under thermal stress suffers from material/mass migration or void nucleation if it ...
20 views

### Calculations to Determine Force Required for Gyroscopic Stabalization

I am currently undertaking a project involving gyroscopes, the aim of which is to stabilize a large object. I have read that gyroscopes work because of conservation of angular momentum, and if you ...
39 views

### Quantum Physics, Energy States [on hold]

Which of the following transitions in a hydrogen atom absorbs a photon of the highest energy? a.) $n=2\hspace{1cm}to\hspace{1cm}n=3$ b.) $n=3\hspace{1cm}to\hspace{1cm}n=2$ c.) ...
28 views

### How to minimize the wavepacket dispersion?

This is a final exam problem. Here is what I can remember: We know that if an electron's wavefunction starts out as a narrow wavepacket, and moving in a region of constant potential, then the ...
3k views

### Why isn't length contraction permanent even though time dilation is?

It's my understanding that when something is going near the speed of light in reference to an observer, time dilation occurs and time goes slower for that fast-moving object. However, when that ...
25 views

### Short Wave UV lamp [on hold]

if I remember correctly, shortwave UV is very dangerous such that it can break DNA apart. Today I found this site, where parent can buy some scientific tools for their kids. Do not you think shortwave ...
82 views

### Force of a Train

Imagine that there are two trains and the first train is twice as long as the second train. They have the same mass per unit length and they are traveling at exactly the same speed. If the first ...
22 views

### Does the surface of austenitic steels have an especially “dynamic” phase somewhere between 100 and 200 Celsius?

There is lots of kitchen lore about pans. One popular concept are the "pores" of a steel pan surface, which are the reason why food sticks to the pan when it's not heated properly. I don't know much ...
74 views

### Why (and how) do foods stick to a pan?

We all (sooner or later) have noticed that foods relatively high in protein (especially those low in fat) are very prone to sticking to a pan, or in general to any non-specially-coated metal surface. ...
28 views

### Space formed by dot products of three vectors [migrated]

Suppose I have 3 3D unit vectors $\mathbf{v}_1$, $\mathbf{v}_2$, and $\mathbf{V}$. I define the three corresponding scalars $u_1=\mathbf{v}_1 \cdot \mathbf{V}$, $u_2=\mathbf{v}_2 \cdot \mathbf{V}$, ...
31 views

### Convert angular position to wavelength [on hold]

Can you convert angular position to wavelength in spectroscopy? I need know if it's possible. I don't have too much experience in this subject.
39 views

### Diffraction grating from first principles

I have realised that a lot of books and online resources fail to give a detailed treatment of the derivation of the diffraction grating interference pattern. Normally only the result is stated. I was ...
135 views

### About the double orthogonality of the eigenfunctions of the Hamiltonian

Consider the usual Hamiltonian describing the motion of a particle, $$\hat H = \frac {\hat P^2}{2m} + V(r),$$ where for simplicity the problem can be considered in 1D on the semiaxis $[a, \infty)$ , ...
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### Does spacetime have a “mass” value? or What is “Spacetime” made out of?

When measuring the MASS within the Universe, does "space" or "spacetime" have a value? I only ask, because when speaking of expansion, space is expanding. Could it be possible, to reverse the ...
27 views

### Confusion about conduction of electricity in a solution

I'm trying to unserstannd conduction of electricity in a solution. Is it correct that anions give their extra electrons to the anode, which transfers the electrons to the cathode, where the cations ...
Is it always possible to write interacting Hamiltonian in a second quantized matrix form like we do it for non-interacting form $$H=\sum _{\alpha\beta}C_\alpha^\dagger h_{\alpha\beta} C_\beta$$ ...