# All Questions

37 views

### Error measurement barycenter of the Solar System - NASA data

What are the possible measurement error barycenter of the Solar System in NASA data? In the data JPL's HORIZONS system for NASA (http://ssd.jpl.nasa.gov/?horizons): Target Body: Solar System ...
57 views

### Why do we say gravitational waves are analogous to sound?

In every popsci discussion of gravitational waves, the waves are said to be like "sound", and that gravitational waves allow us to "hear" the universe. Despite this, I have no idea how gravitational ...
18 views

### A question about glossy paint

Once I made drip paintings, that made themselves. I dropped an amount of glossy paint on a carton, and one time a piece of paper fell on the drying paint. When I came home I pulled off carefully the ...
543 views

### How should I think about reciprocal lattice and Miller indices?

When I hear someone talking about a (100) plane or a (111) plane or an (hkl) in general, my first thought is, is the system cubic. The reason I think this is because I tend NOT to think of the planes ...
77 views

### If we could perfectly control gravitational waves, could we play music with them? [closed]

Sound is just a kinetic wave propagating through a medium, right? In that case, if we had the ability to make gravitational waves exactly as we want them, could we play music to an observer some ...
19 views

### Current flow in absence of a potential difference

What if at two different points in a wire connected to a system of capacitors and resistors, the electric potential is equal. Will the current flow? There is also a battery connected.
24 views

### Force between the plates of a capacitor

As we know that the electric field between two parallel plates of a capacitor is $$E=\frac{\sigma}{\epsilon_0}$$, so the magnitude of force exerted by one plate on the other should have been $$F=QE$$. ...
14 views

### What do echo and reverbation have in common?

What do echo and reverbation have in common? They are the reflection of sound waves, they are formed when sound waves meet a hard surface, they cause a repetition of the sound. The waves keep having ...
6 views

### 2D slab model for LJ potential

I have a program implementing a LJ(Lennard-Jones) molecular Dynamics(MD) simulation with isokinetic thermostat. I want to modify that program to study the phase characteristics of LJ particlesin 2D ...
85 views

### Validity of the 'photon wavetrain' model of coherence

In some optics textbooks, coherence is introduced with the "photon wavetrain" model. In this model, we consider light generated by many atoms each making the same transition. During each transition, a ...
19 views

### Can additional charge be put on plasma?

We all know that plasma is electrically conductive. My question is that is it possible to somehow place more charge on it (lets say like a capacitor) such that it produces its own electric field ...
115 views

### How to draw a velocity curve from Engine power, weight and traction?

Not sure if this is the right forum but I would like to plot a velocity curve of a train, starting at 0km/h and accelerating up to a max speed. The data I have for the locomotive engines are: ...
25 views

### Glauber formula, Baker

somewhere I read here: $[A,F(B)]=[A,B]F'(B)$ is used to prove Glauber's formula $\exp(A+B).\exp([A,B]/2)$ I have tried and looked everywhere to try and understand this to no avail. The first is in ...
26 views

### Confusion with calculating electric potential [on hold]

V = kQ/r I understand that this equation is a product of electric field and the distance through which the electric force acts, to calculate electric potential. Is not electric field non constant ...
2k views

### What would actually happen to a person jettisoned into space?

Alright, so we have all seen the movies where someone gets blasted out of the airlock on their starship, or their suit decompresses while on a space walk. The poor schmoe usually either decompresses ...
260 views

### What happened to this folded paper in a hydraulic press?

The video below apparently shows a man folding an A3 size piece of paper 7 times, putting it under the hydraulic press each time. After 7 folds, on the last press, the paper sort of explodes. What's ...
48 views

### Quantum mechanics: Path integrals vs normal

What are the similarities and differences in the theory for quantum mechanics using path integrals versus the normal method using wave functions?
45 views

### Relativistic mass of electron in a potential [on hold]

An electron is accelerated through a 6 MV potential difference. what is the mass of the electron at the end of the path?
239 views

### Doppler effect of matter waves

We all know that the relativistic mass of a moving object in Special relativity increases for an observer who is measuring it for a moving object. We also know the the concept of particle-wave ...
56 views

### What are the problems in the idea that a person would freeze to death in outer space?

It is said that the body would freeze to death, if left in outer space, which is true, since the temperature is around $3$K. But what are the flaws in this theory, in terms of thermodynamics (if we ...
17 views

### Magnetism and straight conductors [on hold]

Through two long, parallel straight conductors gårströmmarna 3.0 A and 2.0 A, as illustrated below. The distance between the wires is 4.0 m. Is there a point where the flux density is zero? Where? ...
48 views

### Velocity of a body in a pulley problem involving a spring fixed to the ground

So the picture shows the whole situation. My question is, how do you find the velocity of the object after it had descended 10 cm (0.1 m) ? Pulley's radius 0.2 m, moment of inertia 0.2 kg/m I ...
7 views

### 16 Volt on a 12 Volt LM317 Regulated Power Supply [migrated]

I recently purchased a 1,2-12V regulated power supply with an LM317 chip and accordingly, a 220V to 12V transformer. Because I did not need the added functionality of the "logic pen" facilitated by ...
8 views

### Relation of rate of decay of a function with width of peaks of its Fourier transform

Consider a function $f(t)=θ(t)e^{−σ_0 t}sin(ω_0 t)$, where $θ(t)$ is $1$ for positive $t$ and $0$ for negative $t$. Its Fourier transform can be easily computed and has the form:  ...
58 views

### Spacetime background of Quantum mechanics

Why is it said that the Schrodinger equation suggests a fixed, non-dynamical background spacetime, with time as an external parameter? How does this interpretation come about from the Schrodinger ...
170 views

### Expression for Atmospheric Pressure with Altitude, including Tidal Forces

Is this simple to obtain? I've tried to modify the constant-gravity model to use the $GM/r^2$ form instead, but my result was shown to be wrong with some testing. Constant Gravity Model You can ...
26 views

### Gas permeation through solid metal?

if i make a box from aluminum ( 0,5 mm thickness ) and put air in it ( about 2 bar or 3 bar). would the box lose the air over time (10 years period) or not ? assuming the temperature will change ...
40 views

15 views

### Polarized Moller scattering cross section

When doing a computation of scattering cross sections of particles with spin, one usually averages over the initial spins and sums over the final ones. I'm a bit puzzled as to how to do the ...
2k views

### Why are LIGO's beam tubes so wide?

Gravitational wave detectors and particle accelerators have at least one thing in common -- they require long vacuum tubes through which a narrow beam is fired (a laser in the gravitational wave case, ...
21 views

### What do interference and diffraction have in common

What do interference and diffraction have in common? We are learning the sound waves, but I would like to know all the things they have in common. The waves have the same frequency, after the process ...
22 views

### If $T_{kl}=\epsilon_{kil}m_i$, how to show $m_i=0.5\epsilon_{ilk}T_{lk}$? [on hold]

In a book I am reading (about magnetic dipole), it is given that $T_{kl}=\epsilon_{kil}m_i$. Then, it says since $T_{kl}=-T_{lk}$, it can be shown that $m_i=0.5\epsilon_{ilk}T_{lk}$. I understand that ...
186 views

### Relativity gedanken experiment

Lets consider the following thought experiment: A spaceship is in circular orbit around Earth traveling at 99% of $c$ (the orbital distance is chosen in such a way that inside the ship there are no ...
6 views

### How to suspend cube computer in magnetic field?

I honestly have no clue which forum to post this in but believe this group will likely have some of the best feedback at least on approaches for what I'd like to accomplish. My questions are really ...
300 views

### Determing Velocity of Moons

I have a question that I believe is relatively easy to answer, I am working on an $N$-body simulation of a fictional star system and am having trouble finding the velocity of moons so that they will ...
25 views

### Is this a valid way for deriving the ODE for a lattice vibration of a one dimensional crystal?

Consider the following lattice: I want to derive a differential equation that describes the forces acting on the $n$-th atom in the lattice. Each atom is coupled to its neighbour ($n+1,n-1)$ by a ...
71 views

### Prove energy conservation using Noether's theorem

I wonder how you prove that energy is conserved under a time translation using Noether's theorem. I've tried myself but without success. What I've come up with so far is that I start by inducing the ...
91 views

### Two dimensional spacetime and the Gauss Bonnet theorem

Generally two dimensional spacetimes are deemed to be static, as the Gauss Bonnet theorem implies that the Einstein Hilbert action would be a constant independent of $g$. But as far as I can tell, ...
774 views

### Is it true that the Schrödinger equation only applies to spin-1/2 particles?

I recently came across a claim that the Schrödinger equation only describes spin-1/2 particles. Is this true? I realize that the question may be ill-posed as some would consider the general ...
110 views

### How much noise is in the Cosmic Background Radiation, especially from Cosmic Rays

Do we have an estimate of how much noise, if any, say caused by cosmic rays in particular, is present in the CMB datasets and the maps based upon them? Can we extrapolate a figure from the cosmic ray ...
91 views

### Validity of the Lyapunov exponent approximation

I was trying to get the Lyapunov exponent for some dynamical nonlinear systems and found that it is not true (as I had expected) that the distance between two trajectories with slightly different ...
40 views

### How frequently do accelerating electrons emit photons?

In the quantum 2-slit experiment with light, we know that as the source intensity is turned down, individual photons arrive at the detector. I would like to know if there is a formula which tells us ...
45 views

### Justification of the State Postulate

I have just started thermodynamics (not with statistical approach but with macroscopic approach), in which the state postulate reads Only two independent intensive properties of a simple ...
674 views

### Is it possible to use induction ampermeter to measure power consumption of electric water heater and dryer?

I hope this practical question is not OT and not too trivial for this forum. I am renting an apartment in a duplex with a shared water heater and dryer. Turns out, both water heater and the dryer are ...
15 views

### How to derive torque from a velocity dependent potential? [on hold]

In Jackson's Classical Electrodynamics, the rate of change of the angular momentum of the electron in its rest frame in constant external electric field $\textbf{E}$ and magnetic field $\textbf{B}$ is ...
12 views

### Variation of spin in the rest frame of an electron in an external magnetic field

In Jackson's Classical Electrodynamics, the equation of motion for the angular momentum $\textbf{s}$ of an electron in an external magnetic field is given by (eq. 11.101) ...
21 views

### What is meant by negative direction of velocity? [duplicate]

What is negative velocity and negative direction of the velocity?
22 views

### Self studies reagarding physics [duplicate]

Firstly, i would like to apologize for the off-subject thread,but I am in desperate need for help.I am a 12th grader at a very good high school in eastern europe ,but ,unfortunately, i didn't have the ...
This question arises from the classical example: imagine a laboratory frame, and a space shuttle frame, the space shuttle moving in the laboratory frame with a constant velocity, let's say in the $x$ ...