# All Questions

2answers
22 views

### How does rotational energy transfer to linear energy?

So I have recently started looking into moments of inertia, and all that stuff. I have come to a question which has a plane inclined at some angle theta and a sphere at the peak. The G.P.E at the top ...
1answer
54 views
+50

### Prove that Laughlin's 3-electron states are a complete set of states

In R. B. Laughlin's 1983 Physical Review B article, Quantized motion of three two-dimensional electrons in a strong magnetic field, Laughlin separates out the center of mass motion of the electrons, ...
1answer
193 views

### spooky nonlocal communication, or bad abstract?

I'm referring to this recent paper, "Experimental Proof of Nonlocal Wavefunction Collapse for a Single Particle Using Homodyne Measurements" by Fuwa et al. published in Nature Communications. ...
0answers
10 views

### error propagation with an integral

My question here is about how to determine the error of an integral given individual uncertainties in two parameters defining the function being integrated. I used a curve fitting function to ...
1answer
13 views

### Velocity change of air down a cone?

Does the velocity of fluids(specifically gasses) change when traveling down a cone from the wide opening to the narrow opening? If so, is there an equation used to calculate the acceleration or ...
0answers
16 views

### Is Dark Energy and or Dark Matter directly proportional to EMR?

Is Dark Energy directly proportional to Electromagnetic radiation (EM radiation or EMR)?
3answers
1k views

### Eliminating IR light reflection perceived by a steep viewing angle

I am having a problem with reflection on an acrylic surface, in the IR part of the spectrum. This reflection is interfering with an algorithm that looks at objects, as it makes two show up when only ...
0answers
16 views

### On the connection between forces and the principle of stationary action

Feynman tries to account for the relation between the principle of stationary action, which is a statement about the whole path of a particle, and Newton's second law, which is a statement about the ...
4answers
117 views

### Why does time evolution operator have the form $U(t) = e^{-itH}$?

Let's denote by $|\psi(t)\rangle$ some wavefunction at time $t$. Then let's define the time evolution operator $U(t_1,t_2)$ through $$U(t_2,t_1) |\psi(t_1)\rangle = |\psi(t_2)\rangle \tag{1}$$ and ...
1answer
296 views

### Rigid body problem in 2d

I have some questions about this exercise: In an horizontal plane, a $OA$ bar with mass $m$ and length $a$ moves, with another bar $AB$ (same mass, double length) attached in the point A. In the ...
3answers
81 views

### Isn't the aether existant

Before you say I'm wrong consider this, Einstein is supposively the first person to get completely get rid of the various aether models that were proposed. But didn't Einstein actually prove them ...
1answer
137 views

### What is the angular distance between Ptolemaic perigees of Mercury?

In his excellent treatment of the history of the science of astronomical distances and sizes, Albert van Helden says (p.29) that The complicated [Ptolemaic] model of Mercury has the curious ...
4answers
63 views

### Why spinning a pen makes it easier to remove it from the stand?

I have a ballpoint pen stand on my desk. The pens are held inside their caps with the point down, like this one (but not as fancy): If I try to simply pull up one pen, the friction between cap and ...
2answers
75 views

### “If the astronaut found that light slowed down relative to his motion, he would have detected the very ether wind that Michelson failed to detect”?

The following extract is from Relativity Simply Explained by Martin Gardner (Amazon link): Consider an astronaut in a spaceship that is racing alongside a light beam. The ship is traveling with ...
2answers
218 views

### How to get the magnetic field strength in space near a solenoid

I am trying to find the magnetic field strength along the axis of a solenoid. If I know the strength of the field at the center of the solenoid, and I know the distance from the center of the ...
1answer
35 views

### Eddy currents Vs. Inducing EMF in opposing the change?

In the following circuit there is a power supply applying a voltage(+$V$) to a circuit with resistance ($R$), current($I$) is now flowing in the circuit, and there is a movable part like so: The ...
1answer
37 views

### The Riemannian Curvature in Deformations

Is there a direct correlation between the Riemannian Curvature tensor and the deformation gradient tensor in continuum mechanics?
2answers
34 views

### Will the gravitational pull of air affect the falling rate of an object?

After looking at this question: Don't heavier objects actually fall faster because they exert their own gravity? A thought occurred to me that due to the increased gravitational pull of the ...
1answer
38 views

### Do the eigenstates of the Pauli operators correspond to the six directions of the 3D world?

I understand that the six eigenstates of the three Pauli operators $X, Y, Z$ correspond to the six poles of the Bloch sphere. By fixing an orthonormal basis of our physical word, does "measuring Pauli ...
2answers
54 views

### Would a person gain or lose weight after expelling a flatus?

Considering the chemical composition, mass, and pressure range of typical human flatulence, would a person gain or lose weight after passing gas?
0answers
37 views

### Intro Mechanics: Finding ball speeds after collision

So I'm reading about conservation of energy, momentum, balls colliding etc. and unsurprisingly there are hundreds of questions in my textbook where essentially they give me some of the variables (m1, ...
0answers
20 views

### Rotational dynamics Lagrangian problem

I am trying to construct the Euler-Lagrange equation for a non-inertial reference frame. I have two questions, the first is with regard to the discussion of the transformation properties of the ...
0answers
8 views

### When to use lateral magnification vs angular magnification?

What is the essential difference between lateral and angular magnification (like why do we need to use both and when do we use which)? Also, is there a relationship between the two magnifications?
2answers
864 views

I want to solve bound states (in fact only base state is needed) of time-independent Schrodinger equation with a 2D finite rectangular square well V(x,y)=\cases{0,&$|x|\le a ... 0answers 8 views ### Electric field in a non-uniformly charged sheet So if we have a large sheet that is not uniformly charged and is NOT a conductor, how can I find an expression for the electric field everywhere? Things we know about the sheet: the width is 2b it ... 2answers 540 views ### Force required to move a fluid out of piston at depth I have a cylinder filled with water in it at the bottom of the ocean. Say 100 meters down. In this cylinder is a piston that moves up and down. Its job is to squish the water out the bottom of the ... 1answer 25 views ### How does gravitational time dilation work in artificial gravity made by rotating a cylinder? Concerning gravitational time dilation in artificial gravity (made by a rotating torus like in many sci-fi movies) how would you go about calculating the effect? 3answers 128 views ### How does the conductor knows which side is outside? For a electrostatic equilibrium state, we know charges only stay on the outer surface of the conductor. But, how does the conductor know which side is outside? If it's about the curvature, then ... 0answers 14 views ### Aplications of algebraic topology/pure mathematics in nuclear fusion I am planning on working on an independent research class this fall at a community college. My instructor wants to focus it around pure mathematics/topology/homotopy. I think she has done a phd in ... 1answer 32 views ### Minima & maxima of Laplace's equation I don't get the following sentence from David J. Griffiths' Introduction to Electrodynamics (the ambiguous sentence is in bold) Laplace's equation tolerates no local maxima or minima; extreme ... 0answers 8 views ### Electrical resistivity: the effect of adding electrons Consider a copper wire of fixed length and cross-sectional area, and apply an electric field to the wire induced by a fixed potential difference$V$across the two endpoints of the wire. The intensity ... 1answer 60 views ### Flow in diverging channel is unstable according to Bernoulli's equation So let's say we have a circular pipe with a variable cross section with an inviscid incompressible fluid flowing through it. The areas of the two ends are$A_1$and and$A_2$. Let's say we also ... 0answers 41 views ### In how lmuch time will the year be exactly 365 days? [on hold] I understand that the number of days per year has changed throughout the history of the Earth. Apparently there were once over 400 days per trip around the sun. How long will it take approximately ... 0answers 22 views ### Gedanken experiment: Does it collapse to a black hole or not? Imagine that I am a stationary far-off observer of a massive star that is minutely larger than its Schwarzschild radius (in other words, its on the verge of collapsing). My spacecraft accelerates ... 0answers 15 views ### Books of dynamo theory I wanted recommendations of dynamo theory pdfs to make a report about magnetic fields of planets and stars with all the math behind it, like vector calculus, Lagrange functions, partial differential ... 2answers 90 views ### If a vehicle (bus, train) rapidly stops (or accelerates, or turns), why don't our hair or clothes move from the inertial force? Many times I was sitting in a train, watching closely nearby people. If the vehicle changes it's movement rapidly (brakes, turns, etc), then obviously, people feel the inertial pseudo-force that ... 3answers 51 views ### How does a converging-diverging nozzle not violate conservation of energy? Disclaimer: I know absolutely nothing about fluid dynamics, and very little about physics in general. THis may be a really dumb question. Now, at subsonic speeds, converging and diverging nozzles ... 2answers 65 views ### Faster than speed of light [duplicate] I was watching a Physics TV show, When someone called Alex Filippenko said that when there was the Big Bang, the Space extended at a speed faster than speed of light. He said that it wasn't against ... 1answer 14 views ### Number of classical oscillation modes of a Lattice and number of quantum phonons In solving the Classical model for lattice dynamics [Rossler pag 38] we find that the lattice admits $$d\cdot N\cdot r = \#modes$$ where$d=$dimension of the problem$N=$number of atoms$r=$... 3answers 44 views ### Question about intensity of EM waves For electromagnetic wave if it's reflected from a perfect conductor standing wave can be form. I wonder why Poynting vector can be used to describe the intensity of standing EM wave. (see p.19 of ... 3answers 254 views ### Is it true that spring has more force acting on it at its positive maximum amplitude than than at the negative one? Am I missing something? It seems obvious to me that at$+A$and$-A$, the spring has restorative forces equal in magnitude but opposite in direction. But since gravity is always pulling it down, ... 4answers 50 views ### Why does a current-carrying conductor behave like a magnet? I have heard that a current-carrying conductor behaves like a magnet, the reason why the magnetic needle of a compass kept near the circuit, deflects. Why is it so? 2answers 27 views ### How are standing waves a result of constructive and destructive interferences? For constructive I can understand. But destructive I can't. I can not picture the shape of two pulses or waves maybe that form the resulting standing wave. The places where waves are canceled just ... 1answer 169 views ### Difference between directional and omnidirectional transmission or reception? It is suggested that the next generation wireless technology will be highly directional since this increases the signal gain (MIMO) and decreases interference. How will the receiver still be able to ... 2answers 110 views ### Square root of a matrix appears in massive gravity. How to solve$\sqrt{A+B}$perturbatively$A=\text{diag}\{\lambda_1,...,\lambda_n\}$, where$\lambda_i$can be any number and not necessarily a small number,$\lambda_i>0$,$B$is a positive definite symmetric matrix, and ... 0answers 36 views ### How do I calculate momentum for a particle in a box, using the momentum quantum operator? For a particle in a one dimensional box with$U(x) = 0$between$x = 0$and$x = L$(infinite Potential well) the momentum for$n = 1,2,3,...$is given by: $$p_n = \frac{nh}{2 L}$$ The wave ... 0answers 41 views ### Angle sum of triangle in Schwarzschild solution Curvature of space is often intuitively explained as angles of a triangle not adding up to 180 degrees. My questions concerns that. Suppose you have a perfectly spherical star of uniform density - so ... 1answer 75 views ### Is a Plutonium gun-type atomic bomb really “impossible”? I caught a pretty well done 2 hour documentary on atomic bomb history yesterday on the local PBS station. In it, they go over the paths taken for design of the first bombs, including the Thin Man ... 2answers 87 views ### What is the fastest way to heat up a piece of metal at home? Let's start with a torch and a piece of titanium. What is the fastest way to get the titanium up to red hot? Whenever I ask my science-y friends they like to point out that the bright blue tip is ... 1answer 38 views ### How can we account for a friction force changing sign in a conservation of energy equation? I want to solve a simple mechanical problem whereby three forces act upon an object.$F_1 = (10 - x)$N$F_2 = -3 N$(friction force)$F_3 = -10x$N So at$x$= 0 we see that$F_1$+$F_2$+$F_3\$ ...

15 30 50 per page