0
votes
0answers
4 views

Angle sum of triangle in Schwarzchild 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 ...
0
votes
0answers
6 views

Zero Current Induced in a Loop

Consider the following two cases, Case 1 – A coil moving through a constant magnetic field Case 2 – A conductor moving through a constant magnetic field Now, in Case 1 (a coil moving through a ...
0
votes
0answers
6 views

If there are no hidden variables, what is the causal relationship, if any, between observation/measurement and the decohered result?

I am asking this question more from a logic point of view, so perhaps it belongs in the philosophy/metaphysics section. If there is no way to predict how our measurement of a particle in superposition ...
0
votes
0answers
7 views

Converting spectra to rgb colour

I am having trouble obtaining RGB colour values from the spectra of an object. I have the specific flux $F_\nu$ as a function of $\nu$ for each pixel of the image I'd like to make, but am unsure of ...
0
votes
0answers
3 views

Magnet rotor diameter effect on power output in an axial flux generator

I'm trying to determine which parameters of the magnet rotor have the greatest effect on power output of an axial flux generator. Obviously a very large diameter will have a greater tangential ...
1
vote
0answers
18 views

Conservation of momentum in Heisenberg's microscope

In working through Heisenberg's microscope, conservation of momentum for the photon and electron tells us that \begin{align} \frac{h}{\lambda}=\frac{h}{\lambda'}\sin\theta+p_x\,, \end{align} where ...
-2
votes
0answers
13 views

Stretch as a function of time

A cylinder of neglectable mass, initial radius $R_{0}$ and initial length $L_{0}$ is attached to a ceiling by one end. A mass $M$ is attached to the other end of the cylinder. Following is also ...
0
votes
0answers
6 views

Black holes – Irrotational vortex or Rigid-body-like vortex

As light enters a Black hole – does the light enter as “Irrotational vortex” or as “Rigid-body-like vortex”? https://en.wikipedia.org/wiki/Vorticity Thank You
0
votes
0answers
30 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 ...
5
votes
1answer
21 views

Is dark energy homogeneous and/or isotropic?

Shouldn't there be at least some fluctuations of dark energy in various regions, analogous to the fluctuations we observe in other forms of energy like matter?
1
vote
3answers
60 views

Conical train wheels

I've been reading about how the conical shape of train wheels helps trains round turns without a differential. For those who are unfamiliar with the idea, the conical shape allows the wheels to shift ...
3
votes
3answers
53 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, ...
0
votes
0answers
26 views

Special Relativity Paradox

A rocket passes the earth and synchronises its clock with the earth. Years later, a rocket passes it going to the earth and synchronises its clock with the first rocket. When it reached the earth, ...
-1
votes
2answers
25 views

seperate engines working vs single engine

What is more fuel efficient: Two identical cars running at 50mph or one being tied to the other and only the first dragging both at 50mph? Or what requires less fuel: Two cars to start from stop and ...
1
vote
0answers
37 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 ...
-2
votes
1answer
23 views

Can something actually be air tight? Sub unit of energy?

I thought about space travel and wondered if space crafts are 100% air tight or not. How would we even know if something is air tight or not. There could be a leak that would allow small amounts of ...
2
votes
0answers
30 views

General proof of formulas of geometric optics?

In most lf textbooks formulas of geometric optics like lens maker formula and base formula for that are proven (or rather verified from my point of view) by taking specific case (ray diagram) and ...
2
votes
1answer
27 views

Does spacetime curvature increase when an attractor's potential energy is converted to kinetic energy?

Imagine an asymptotically flat spacetime with nothing but two stars at a certain distance. They fall into each other and form one big star, so their potential energy is converted to kinetic energy. ...
-4
votes
2answers
54 views

Quantum Entanglement - How To Interpret

I have thought about quantum entanglement for some time, and I still don't quite understand the reasoning behind the conclusion that entangled particles somehow can communicate their state to each ...
-1
votes
2answers
31 views

Why do motorcycles have bigger wheels than mopped? [on hold]

I am from India. Here bikes and mopeds are used almost everywhere for the same purpose and terrain.
-1
votes
1answer
59 views

is there a situation where $|\frac{d\vec{v}}{dt}|$ is non-zero while $\frac{d|\vec{v}|}{dt}$ is zero?

Here $\vec{v}$ represents velocity and $\frac{dv}{dt}$ gives the instantaneous acceleration. $|\vec v|$ gives the magnitude of velocity. When acceleration is zero, then change in magnitude of velocity ...
2
votes
2answers
33 views

Determination of the ground state of a field theory

Consider the Spontaneous symmetry breaking in the theory $$\mathcal{L}=\frac{1}{2}\partial_\mu\phi\partial^\mu\phi-\frac{\mu^2}{2}\phi^2+\frac{\lambda}{4!}\phi^4.$$ By the ground state of a ...
1
vote
0answers
14 views

Counting modes Rayleigh-Jeans

In the derivation of the Rayleigh-Jeans Law, we count the number of EM modes in a square cavity. After calculating the number of allowed modes due to boundary conditions, we multiply it by a factor of ...
0
votes
3answers
56 views

Can the sign of metric change physics?

Consider the Lagrangian of a massless real scalar (classical field) in $\phi(\textbf{x},t)$: $$\mathcal{L}=\frac{1}{2}\partial^\mu\phi\partial_\mu\phi$$ The Hamiltonian density in two different ...
1
vote
1answer
24 views

What causes a eutectic point?

What causes the melting point depression known as a eutectic point? The temperature depression of a eutectic point can be calculated from the enthaplies and entropies of fusion of the two ...
3
votes
2answers
22 views

Why does the vortex form in the von Karman Vortex Street?

Why does the vortex form in the von Karman Vortex Street? So far I have this for the reasoning: 'It occurs when a fluid flows around a cylindrical object. The pressure on a fluid particle rises to ...
1
vote
1answer
26 views

Virtual work (generalized forces) for rotation with Euler angles

Here is what we know from virtual work: \begin{equation} \delta W=\sum_{i=1}^N{\vec F_i\cdot\delta\vec r_{i}} \end{equation} Where $N$ is the number of bodies in the system. I am considering a ...
3
votes
1answer
61 views

Crying in microgravity

So I looked around the net and found that you really cant "cry" as we do on earth in space floating around, because the tears would just stay near your eyes, because the pull of gravity is not strong ...
0
votes
1answer
26 views

Does buoyancy change on smaller scales?

For baseball size objects on the order of centimeters across we have experience with what floats and what doesn't. A stick will float and a rock will not. But what if the rock were a grain of sand? ...
-4
votes
0answers
39 views

What maximum theoretical speed can reach spaceship with EM Drive in space? [on hold]

There are several studies (by Institute of Aerospace Engineering, Technische Universität Dresden and by NASA) that are concluding that the EM Drive produces thrust. So I am wondering: if the EM Drive ...
-3
votes
2answers
48 views

Area under v-t and a-t graphs

I know that the magnitude ( i.e. considering all area as positive) of area under v-t graph gives distance travelled by the particle in the given time. But I've been told that magnitude of area under ...
3
votes
1answer
23 views

One Pion Exchange Potential properties for a two-nucleon system

I'm going through my Nuclear Physics book, and has come across a section called "Properties of OPEP for the two-nucleon system". It start out by considering the n-p system in a singlet spin state ...
-1
votes
0answers
25 views

Using Lagrangian to get the equations of motion [on hold]

The thin hollow cylinder rolls on the plane without slipping. I want to write the Lagrangian, but am confused about the degrees of freedom of the motion and the coordinate axes to consider for ...
0
votes
3answers
33 views

Pressure change with a pipe diameter change

I have a question regarding a water line from the street to a house. What happens to the pressure in a water line if it goes from a 1" diameter pipe (at street) and increases to a 1.5" diameter pipe ...
0
votes
2answers
33 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 ...
0
votes
2answers
29 views

Which centripetal force equation should I use for centripetal motion in uniform magnetic field, and why?

So far I learn two equations, doing the same thing: $$F_c = m\frac{v^2}{r} = qvB$$ It leaves me undecided when a question asks "by what factor is the force increased when velocity is double". The ...
0
votes
0answers
6 views

Visible wavelengths of fluorescence of constituents of air at sea level for school demo laser telephone

I'm seeking to find out about flourescence in visible wavelengths (390-700nm) of any of the main constitutents of air ( \$ N_2, O_2, CO_2, H_2O, CO, etc. \$, ) that can be excited with a low-cost? ...
0
votes
2answers
20 views

Calculating the drag force provided by a laminar flow [duplicate]

If I drop a ball into viscous fluid (e.g. oil), by calculation I know that the fluid flow is laminar. So which equation do I need to calculate the drag force provided by fluid? The drag equation, ...
0
votes
2answers
36 views

Does entanglement have to be verified synchronously

I am not a physicist so, first of all I like to apologise if I my question is stupid. I just want to know where I am going wrong here. But if I have understood anything about the entanglement ...
0
votes
1answer
23 views

Calculate constant acceleration for a length of track with start at rest and final velocity known [on hold]

My maths and physics are rusty... I'm a bit ashamed, but I have this problem: Let's have a 1000m linear accelerator (mass driver) propel a payload at constant acceleration, with a final velocity of ...
0
votes
0answers
4 views

Setting up superlattices in VASP based on two POSCARS

Does anyone know how to setup a superlattice in VASP/QE using the atomic simulation environment based on two materials/POSCARS?
1
vote
2answers
58 views

When we ride a bicycle, why do we tend to move left when we turn it right?

When we ride a bicycle, we tend to move our body left if we are taking a right turn and vice versa. Why is it like that?
1
vote
2answers
45 views

What is the perfect Ice Cube? [on hold]

I have a freezer with -25°C temperature and Soda with +30°C. What is the ice-cube-sized material I can put in the freezer that can bring my glas of soda to the lowest temperature? Are e.g. saltwater ...
2
votes
2answers
73 views

What is high energy physics?

Is high energy physics the same as particle physics? Does research in high-energy physics include things like quantum gravity, string theory and quantum field theory? Is unifying the four ...
0
votes
0answers
38 views

Is it worthwhile letting the Hubble Space Telescope stare at one sky point for a year before it dies?

The Hubble Space Telescope will end it's useful life, probably, around 2018. The question I have concerns it's possible uses after that time. The pictures of the Pillars of Creation shown below were ...
1
vote
1answer
47 views

Mass and Schwarzschild Radius

Do free massless particles have a Schwarzschild radius? I'm curious about the mass in the equation for the Schwarzschild radius. I know that you can calculate a Schwarzschild radius for any massive ...
0
votes
0answers
38 views

Classical mechanics explanation of Liouville's theorem [on hold]

What is the classical mechanical explanation of Liouville's theorem when density explicitly depends upon time and density implicitly depends upon time?
0
votes
0answers
22 views

Double groups in Crystallography

I'm currently studying double point groups and their applications in condensed matter physics. Let me start by giving you the definition of the double group that is used in my textbook: Let $G$ be a ...
2
votes
3answers
89 views

Travelling near the speed of light, will radar give me sufficient warning of approaching debris?

If I’m travelling in space near the speed of light, I would like to use radar to give me advance warning of approaching hazards. However, will I have enough time to be able to react? From a ...
-1
votes
0answers
26 views

Liouville's theorem in quantum mechanics

Is there any theorem in quantum mechanics which relates conservation of any physical quantity (say density) just like Liouville's theorem does in classical mechanics?

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