-4
votes
0answers
88 views

Physics major in university [on hold]

When I was 10, I started reading college-physics books; I always loved physics. I'm 17 years old and, on my own, learned calculus, real analysis, complex analysis, functional analysis, differential ...
0
votes
1answer
24 views

Few doubts about saturated vapour pressure and unsaturated vapour pressure

I have some sort of confusions towards saturated vapour pressure and unsaturated vapour pressure.. So let me give you those. What is exactly saturated vapour pressure and unsaturated vapour ...
0
votes
0answers
16 views

Anomalous diffusion dynamic exponent calculation

I'm trying to calculate this $\alpha$ (dynamic exponent, I think) from an equation from this wikipedia article. The equation (anomalous diffusion power law): $r^2 \propto t^\alpha$ The problem is ...
3
votes
1answer
89 views
+100

Approximating a target operator

I was wondering if anyone knew how the author got to equation 12 on page four of this paper, I will attempt to explain the situation below. Given $C$, a target operator, we wish to create an ...
-3
votes
0answers
9 views

How do I get 50 Reputation? [migrated]

I was going to comment that the atmosphere takes about 1/3 to 1/2 the mussel velocity based on my 1987 paper on the Flight of Passive Launch Vehicles. I am about to re-do the paper and am working from ...
0
votes
1answer
33 views

Torque Approximations Neglecting Friction

Disclaimer: I'm not asking for homework help. I don't understand how my calculations work out conceptually. If you can help me understand the connection between the concepts, I'd really appreciate it. ...
0
votes
2answers
52 views

What would happen if there was no friction on earth? [on hold]

I'm not talking about zero-g or a vacuum. If oxygen, gravity, air pressure, etc still existed but if there was suddenly no friction, anywhere.
0
votes
0answers
10 views

Particle aggregation: difference between coagulation and coalescence?

I know there are different processes involved in particle aggregation, and that depending on temperature and other factors one of them may be more significant. I know that particles can aggregate, ...
0
votes
1answer
22 views

How do I incoporate gyro information in my position and velocity calculation? [on hold]

The velocity in 1 direction can be calculated as : $V_t=V_0+at$ And position could be calculated as $P_t=V_0t+1/2at^2$. Besides time, acceleration, I was also given information from 3 axis ...
0
votes
1answer
26 views

Can I interpret Avogadro's principle of gases from the state equation (ideal gas law)?

Considering the molar form of the ideal gas law I can solve for the ratio of some gas volume, $V$ divided by the number of gas particles, $n$ in mols $$\frac{V}{n}=\frac{RT}{P}$$ And $R$ is the ...
0
votes
0answers
46 views

Julia in computational physics [on hold]

What are the benefits and drawbacks of using Julia in developing physics models? Traditionally, C/C++ and Fortran (and some Java) have been used in any serious computational physics projects, while ...
0
votes
0answers
15 views

Are x-rays in fusion plasmas mostly from collisions with high atomic number ions?

Say you have a hot (100eV-1keV) hydrogen plasma with no impurities in it and no collisional interaction with the wall. Would this plasma radiate x-rays? X-rays are from bremsstrahlung, so could ...
0
votes
1answer
18 views

Which features effect on the Reflection of things?

I'm working on something and I need to find a wire that doesn't reflect well. so, I know one feature is the color of the wire to decrease the reflection. But what other features effect on the ...
2
votes
1answer
56 views

Why do high voltage transmission line workers need a Faraday cage suit?

In this video the high voltage transmission line workers are wearing a Faraday cage suit. Why is this needed? Without the Faraday cage, the resistance of the human would be very high compared to the ...
0
votes
1answer
46 views

For an event that can occur in many ways, why is the wavefunction of the event the sum of wavevfunction for each way separately?

The wavefunction of identical particles is given as: $$\psi_{1,2} (x_1,x_2) = \psi_1(x_1)\psi_2(x_2) + \psi_2(x_1)\psi_1(x_2)$$ . Why is it so? Why is it the sum of the two states? What is the ...
-2
votes
0answers
75 views

What does cross product mean in simple words? [migrated]

Two numbers 3 and 4 their multiplication is each one from the first number is repeated a number of times as the second number i.e. 3 times 4 is (1+1+1) times four meaning 1+1+1+1 + 1+1+1+1 + 1+1+1+1 ...
1
vote
2answers
72 views

Physical meaning of divergence

While reading the section on Hamiltonian mechanics in Taylor's Classical mechanics, I realized that I didn't fully understand what he was saying when he was explaining why ...
3
votes
1answer
28 views

Simple Beam Worst Case Scenario

Part 1 If I have a simple beam with two supports and a static load, does placing the load in the center push the beam closest to breaking (catastrophic failure)? Will this be more likely to break ...
4
votes
2answers
122 views

In QFT how do you write down the most general interactions?

This past year I took a QFT class and I now feel comfortable solving scattering problems, but I am still a bit perplexed by how physicists write down a Lagrangian in the first place. In particular, ...
2
votes
1answer
50 views

Is weather cyclic?

I'm a sports amateur, and enjoy playing in Ultimate Frisbee leagues in my hometown. In the last years, I've observed some "weird" weather behavior, and wondered if it was some sort of coincidence, or ...
0
votes
0answers
25 views

Calculating center of mass after movement [on hold]

For this problem there is no change in External Forces so change in momentum to the system is 0. We have a massless boat of length $L$ with a person on either end of masses $m_1$ and $m_2$ Person 1 ...
0
votes
1answer
32 views

Energy of a system if the nuclear repulsion increases

I have calculated the optimised geometry for a molecule. I have noticed that the energy of the nuclear repulsion increases with each iteration of optimisation. What is the logic behind this?
0
votes
0answers
44 views

Resistance of a metal sphere

How would you go about calculating the electrical resistance of a sphere when you only know it's radius and conductivity? I know with cables you can use $$ R = L/(g \cdot S),$$ but I don't know how ...
2
votes
1answer
58 views

Variation of Christoffel symbol and Lie derivative

I've also asked this question on Math Overflow; I hope that asking in two separate fora is not a solecism. Under an infinitesimal diffeomorphism the Riemann metric changes by the Lie derivative $$ ...
-2
votes
1answer
39 views

Simple question about using determinant to find eigenvalues of $\hat{S_x} + \hat{S_y}$ [on hold]

The problem is: Find the eigenvalues and eigenfunctions of the operator $\hat{S_x} + \hat{S_y}$ where $\hat{S_i}$ is the spin operator in the i direction (i = x,y,z). The first step of their ...
0
votes
0answers
38 views

Photon Energy and Einstein Equation $E=mc^2$ [duplicate]

If the mass of a photon is zero and these ones travel to the light speed, how may I explain Einstein's equation $E=mc^2$? It is well known that the energy associated to a photon may be calculated ...
0
votes
0answers
44 views

Equipartition theorem and virial theorem differences?

The classical virial theorem and the classical equipartition theorem are clearly related. A version of the virial theorem is, \begin{equation} \bigg\langle \sum ^{3N}_{i=1} x_i\frac{\partial ...
1
vote
3answers
33 views

Why do the tangent holes (like in pitot-static tube) feel the static pressure?

Why do the tangent holes (like in pitot-static tube) feel the static pressure although the static pressure is in the direction of the velocity of the streamlines not normal to the surface of the hole
0
votes
0answers
29 views

Why does being unable to collect all emitted light from a source lead to the diffraction limit?

My optics textbook (Hecht & Zajac) says the following: Most commonly, the function of an optical device is to collect and reshape a portion of the incident wavefront, often with the ultimate ...
0
votes
2answers
45 views

What is the meaning of this definition of potential energy?

The isolated system of particles is being observed. In the coursebook, $\vec F_\mu$ is by definition the vector sum of forces of all other particles acting on $\mu$-th particle. Usually, potential ...
0
votes
1answer
79 views

What happens to theoretical physics if a photon has non-zero mass?

I want to know the theoretical implication if photons have a non-zero mass. What happens to the Maxwell equations? What happens to QFT? If the photon have mass it can decade?
0
votes
2answers
66 views

Confusion in understanding the proof of Uniqueness Theorem

I am having problems in comprehending the proof of contradiction used by Purcell in his book; ...We can now assert that $W^1$ must be zero at all points in space. For if it is not, it must have a ...
0
votes
0answers
27 views

What is colour-Coulomb interaction?

In several publications (e.g. http://arxiv.org/pdf/1506.06864.pdf) a "colour Coulomb interaction" between quarks was mentioned. What kind of interaction is that, is it electromagnetic or strong?
1
vote
1answer
71 views

A trace formula of two noncommutative operators

In many cases of quantum many-body problems, the Hamiltonian $H$ can always be divided into two parts, i.e. $H_0$ and $H'$. In this occasion, one can systemically calculate the partition function ...
0
votes
1answer
27 views

Inertia of a disk - axis of rotation through the x-axis [on hold]

In general one computes the inertia by the formula of: $$ I = \int r^2 dm $$ However in this case it does not work, as the mass is not equally distanced from the axis. The disk in the xy - plane ...
0
votes
0answers
23 views

Plane wave solutions of the Majorana equation

Let u(p) and v(p) be the plane wave solutions of the Dirac equation with positive respectively negative energy. In case of a solution of the Majorana equation the charge-conjugated solution is ...
0
votes
0answers
37 views

About spin 2, graviton, in the context of attractive force.

excerpt from Introduction to Black hole physics, Valeri P. Frolov and Andrei Zelnikov In this textbook, there is comment about spin of gravitons as follows For gravitating bodies the gravitational ...
0
votes
1answer
98 views

Relativity… Twin paradox

Sorry, but I have another stupid question about relativity. In the twin paradox: Let's say the travelling twin went to Proxima Centauri and back at 0,99c. However, he did not slow down to stop on ...
0
votes
0answers
22 views

Finding the amplitude of a pendulum [on hold]

I'm tring to simulate the behaviour of a pendulum. I have it in the equilibrium position, then I apply on it an initial velocity $\vec{v_{0}}$ Knowing $\vec{v_{0}}$ and its mass m, how can I find the ...
0
votes
0answers
28 views

Sign convention thermodynamics

Say a system is inside a volume $V$ with surface normal vector $n$ pointing out from the volume. Then there are force vector fields (nonconservative and conservative) depending on parameters external ...
21
votes
4answers
3k views

Is it possible to build a thermoelectric nuclear power plant?

Current nuclear power plants are essentially an enhanced version of a kettle, which seems like a stupidity caused by a lack of other options. We heat the water which turns to steam which rotates the ...
0
votes
1answer
57 views

Cylindrical capacitor in an electric circuit

I've come across a tricky question and would appreciate some hints or explanations as to why the given solution is the way it is. The question reads as follows: A coaxial cable consists of a wire ...
0
votes
1answer
42 views

Theoretical proof of the Bohr's postulates

It was proved in an experimental way that the energy of a photon equals $E = h \nu$ electrons radii satisfy the equation $mvr = n \hbar$ Is it possible to prove these properties in a theoretical ...
4
votes
1answer
90 views

Quantum Mechanics - Lowering Operator [on hold]

Let $a$ be a lowering operator. Show that $a$ is a derivative respects to raising operator, $a^\dagger$, $$a = \frac{\textrm{d}}{\textrm{d}a^\dagger}$$ Can someone please explain how to prove the ...
4
votes
5answers
1k views

I know light's speed in vacuum is constant, but what about its velocity?

Is the velocity of light in vacuum constant? It seems it would be different depending on whether it is coming toward you or away from you, but I just want to make sure. Does the direction of light ...
1
vote
2answers
52 views

Concept of a Magnetic Field

I was reading a physics book by some author and I got a little too confused with the explanation he stated about magnetic fields. A magnetic field is a field of force produced by current-carrying ...
0
votes
0answers
20 views

Collision between electrons & nucleus [duplicate]

I am new with physics and I have a confusion that since electron and nucleus has opposite charges then why they do not collide with each other inside an atom?
0
votes
0answers
16 views

Bead and Disc with a String [on hold]

I want to know about the path the bead follows, and whether tension increases , decreases or remains constant and work done by tension (along with analysis and reasoning).
1
vote
0answers
38 views

Lack of symmetry in Poynting vector

I've noticed that there's a lack of symmetry in the definition of the Poynting vector, being defined as: $$S=E\times H$$ meaning, using the electric field cross the magnetizing field instead of the ...
1
vote
3answers
101 views

How can i prove that $\frac{d\vec{p}}{dt} = \vec{F_{net}}$? [duplicate]

I could prove that $d\vec{p}/dt = m\vec{a}$, but how can I prove that $\vec{F_{net}}=d\vec{p}/dt$? Is force just defined by this expression? What is the rigorous definition of a general force? In my ...

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