0
votes
0answers
2 views

If the universe has no center, how it can collapse?

After reading Does the universe have a center? and trying to find a place in my mind for "There exists no center", I asked my self: If there is no center, in what direction our universe will ...
0
votes
0answers
9 views

Is a trebuchet a physics problem with spherical symmetry?

I am investigating the physics behind a sling trebuchet in order to derive the equations of motion for the payload m (as seen in the figure.) To begin I have to define what generalized curvilinear ...
0
votes
0answers
8 views

Solutions for Kittel's Introduction to solid state physics 6th edition?

I'm looking for the solutions of Kittel's 'Introduction to solid state physics' 6th edition. I can only seem to find the solutions for the 8th edition online. Does anyone have the pdf to it? Or ...
-2
votes
0answers
8 views

Why capacitor charging is taken from negative infinity?

Why in Engineering disciplines ,when finding voltage across capacitor the time as limit of integral is taken from negative infinity to t and not zero? The same can be seen for signals,Laplace though ...
-4
votes
0answers
6 views

Two point charges of the same absolute value Q = 50x10 ^ -6 , but of opposite sign

Two point charges of the same absolute value Q = 50x10 ^ -6 , but of opposite sign , generate fields at P , the vacuum as shown in Fig . Characterize the resulting electric field in P. OBS: I ...
-1
votes
0answers
14 views

Two resistances are joined in parallel and their equivalent resistance is 3/5 ohm

Two resistances are joined in parallel and their equivalent resistance is 3/5 ohm One of the resistances is disconnected and the effective resistance becomes 3 ohm What is the resistance of the wire ...
0
votes
1answer
10 views

dot product of two vectors in spherical polar coordinates, do I have to convert to cartesian coordinates?

For two vectors $p1=(r1,\theta_1, \phi_1)$ and $p2=(r2, \theta_2, \phi_2)$ I want the dot product p1.p2. However, the solutions I have seen, involve finding the components in Cartesian coordinates and ...
0
votes
0answers
4 views

Conditions for supersonic flat plate problem

I am interested to solve "supersonic flat plate problem". I want to ask that how do conditions for this problem set?
2
votes
1answer
20 views

What is the singularity of an actual collapsing black hole?

In most general relativity texts, the singularity is treated as a point removed from the manifold, to avoid having to deal with the infinite curvature of the Ricci scalar. But in the case of a more ...
1
vote
1answer
15 views

Second covariant derivative, computation problem

I am having a question on the wikipedia article http://en.wikipedia.org/wiki/Second_covariant_derivative Using the notation therein I don't get why $(\nabla_{u}\nabla_{v}w ...
1
vote
0answers
9 views

Wavefunctions “adapted” to the perturbation ? Relation to Faraday effect

I came accross the following statement in a book: If one wants to switch on a magnetic field, one must first choose the appropriate complex unperturbed wave functions (that are "adapted" to the ...
0
votes
1answer
15 views

find the density of water only by its pressure?

Is it possible to find the density or specific volume of water, by only knowing its pressure? Or we need to know its temperature as well? I can't find any relevant table, so can you advise me please? ...
0
votes
0answers
16 views

Meaning of a Dirac delta speed in 1d shallow-water equations

A 1d thin layer of a fluid of constant density in hydrostatic balance can be modeled by shallow-water equations: $$\begin{align*}\partial_tu+\partial_x\left(v+\frac{u^2}{2}\right)&=0,\\ ...
2
votes
2answers
35 views

What is the kinetic energy of a quantum particle in forbidden region?

I have read that if a particle is trapped in a finite potential well, it has a finite chance to tunnel out from it. Therefore, one can find a particle in a region where its potential energy is greater ...
0
votes
3answers
41 views

Covariant Derivative of Kronecker Delta

I am reading Carroll's book on GR right now, and I ran into a little trouble in his chapter 3 on curvature. He is establishing the properties of the covariant derivative, and claims that the fact that ...
-1
votes
0answers
16 views

What happens when a magnet is dropped through a solenoid with a current running through it?

I know when a magnet is dropped through a copper tube or a copper solenoid it induces a current in the copper and the magnet actually slows down as it falls through the tube, but if I did this with a ...
0
votes
0answers
9 views

Active light polarization filter

I want to realise a (fast) active light polarization filter. I just need two states: 0° and 90° rotation of the filtering plane. Is it possible to use a "normal" LC film like in displays and just put ...
0
votes
0answers
15 views

What is the pressure that supports boson star?

What is the pressure that supports boson star? I noticed that for a Bose-Einstein condensate $$ p = k_BT\frac{g}{\lambda^3}\zeta(5/2) $$ where $g$ is the degeneracy and $\lambda$ is the thermal ...
0
votes
1answer
19 views

Different between space of reference and system of reference

In the book "The meaning of the relativity" by A. Einstein, it is referring to two different concepts: space of reference and system of coordinates. What it is the difference? It says: "we cannot ...
1
vote
1answer
22 views

Spectroscopic properties of hydrogen: H vs. H2

One of the basic experiments everybody learns about when it comes to physics is the spectroscopy of hydrogen gas. The typical set-up has a charge discharge lamp containing the hydrogen. The resulting ...
1
vote
0answers
4 views

How does bilayer 2d materials break inversion symmetry and how does it lead to a bandgap?

Some (?) monolayer 2d materials have inversion symmetry, however bilayer materials don't (?). This opens up a bandgap in bilayer graphene. 1) How does bilayer break inversion symmetry? In which cases ...
0
votes
0answers
12 views

Static spatial current

I experemeted with 3d printing on titanium and found strange thing to me. There is electromagnetic field as purposed to increase heating effect. But when the heating bed was not isolated with capton ...
1
vote
1answer
27 views

What is an incoherent state?

I am reading through a recent paper which speaks frequently of "incoherent states" without ever defining what such a state is. I gather from the context of the paper that it has something to do with ...
0
votes
1answer
22 views

Equations of motion acceleration doubt

So i was going through some text today morning. Where it said $$ a = \frac{vdv}{dx} $$ So they then went on to, $$ vdv = adx \\ \implies \int vdv = \int adx$$ But,I am very certain acceleration is ...
0
votes
0answers
16 views

Global Hyperbolicity IN SpaceTime

why space time which admits a Cauchy surface is called globally hyperbolic. I didn't actually understand what does globally hyperbolic physically means.
1
vote
2answers
15 views

Does a flame put off a windlike force

When I hold a flame above a flame the one on top flickers and waves as if its about to go out. What is the cause of this?
0
votes
0answers
23 views

Lagrangian of tautochrone curve and its solution

Why is that when I apply the Euler-Lagrange equation to a ball moving down a cycloid, that is $$L = \frac{1}{2}mr^2\dot{\theta}^2(1-\cos (\theta ))^2 + \frac{1}{2}mr^2\dot{\theta}^2\sin (\theta )^2 - ...
0
votes
0answers
10 views

Sedov-Taylor blastwave resources

What are some resources for learning about blast waves? Particularly the Sedov-Taylor solution? The specific application is modeling supernovae.
0
votes
1answer
30 views

The relationship between height of water and the rotational speed inside a cup

When I stir the water inside a cup with a speed $v$ ( using a stick), I find that a vortex will be formed inside the cup, with the middle part of the water at the lowest point ( with the height ...
-1
votes
1answer
33 views

Electrostatic Potential

In any region, if electric field is defined as E(vector)=(i +2j +k) V/m, then the potential difference between two points A(0,0,0) and B(2,3,4) in that region is?
-1
votes
0answers
11 views

Best book introducing Chaos Theory [duplicate]

My question is very simple: which is the best book (in your opinion), for a physicist in senior year, to introduce Chaos Theory? I prefer a book with programming applications (i.e., MATHEMATICA, ...
0
votes
1answer
21 views

Ground state metric?

In kaluza-klein theory, there's a notion of a "ground state metric" after compactification. What is the meaning of the term "ground state metric"?
2
votes
1answer
47 views

How do physicists find the speed of neutrinos?

I have heard that there is evidence for neutrinos traveling close to the speed of light, but how is that done? Since neutrinos barely react with anything, and the only evidence for them is indirect ...
2
votes
1answer
31 views

Charge without charge and non-traversable wormholes

My question concerns the theory proposed in this classic paper by Misner and Wheeler. In the paper, the authors propose the idea of "charge without charge"--namely, that positive and negative ...
0
votes
0answers
14 views

Causal networks and “local” entanglement

On his Opus Maximus, a new kind of Science, Stephen Wolfram suggests that causal networks can create behaviour similar to entanglement because the local structure of space is only an averaged ...
5
votes
0answers
21 views

How much of water's surface tension is entropic?

Water molecules on the surface of an air-water interface have preferred orientations that lower their energy. This implies that these molecules are not uniformly distributed in orientation space, ...
1
vote
0answers
12 views

What are the dynamics of the “break the surface tension with a drop of soap” experiment?

There's a common experiment exemplified in the first few seconds of this video: https://www.youtube.com/watch?v=WsksFbFZeeU You put some food coloring in the center of a plate of milk, then put a ...
2
votes
1answer
17 views

Why does Bernoulli's equation only apply to flow along a streamline that is in viscid, incompressible, steady, irrotational?

I am learning about hydrofoil on this website. In a later video I watched, I learned that in the process of deriving Bernoulli's equation, $$constant=P/d+gh+1/2v^2$$ has to multiplied through by ...
1
vote
1answer
41 views

Are neutrinos affected by electromagnetic forces?

I know they don't interact with matter nor any electromagnetic forces, but I know they have mass, very little mass but they have. When something has mass it must be attracted by gravity and other ...
3
votes
2answers
55 views

Does Unitary operator take a pure state to a pure state or can it take a pure state to a mixed state?

Does Unitary operator take a pure state to a pure state or can it take a pure state to a mixed state? I think so but why? I assume the Unitary operator acts on a pure state only.
0
votes
2answers
31 views

Why does electromagnetic induction creates both voltage and current but static electricity only creates voltage and no current?

Why is it that electrons do not move the same way in triboelectric as in magnetic induction when both creates voltage? Triboelectricity can even create tens of thousands of volts like Van De Graf ...
2
votes
0answers
28 views

When does $E=\frac{3}{2}pV$ hold?

I only know that it holds for classical (monatomic) ideal gas and quantum ideal gas. But does it hold for interacting classical gas (e.g. van der Waals gas)?
0
votes
0answers
43 views

Wavefunction of electron in 3D infinite well with non-zero potential

Consider an electron moving in a potential $V$ defined by $$V(x,y,z) = \left \{ \begin{array}{ll} \alpha(x^2 + y^2) & 0 \leq z \leq a \\ \infty & \text{otherwise} \end{array} \right. $$ ...
2
votes
2answers
19 views

How do I draw the force field lines of an isotropic oscillator?

In general, how do I draw the force field lines (in the sense of Faraday, i.e. continuous curves whose tangents give the directions and the density of lines give the intensity of the field) of a ...
0
votes
1answer
21 views

Very Basic Circular motion question

I was asked to draw a diagram of the forces acting on a ball in vertical circular motion when it is at a horizontal point. I drew the weight of the ball acting straight down and the centripetal force ...
0
votes
0answers
23 views

Transformation law for the eigenfunction representation of dilations (scale transformations) in CFT

On page 32 section 2.1.2. of http://arxiv.org/abs/hep-th/9905111 a representation $\phi(x)$ for the conformal group is chosen such that $D\phi(x) = -i \Delta\phi(x) $. After that it is stated that ...
1
vote
0answers
14 views

Why is the velocity of fluid on top a hydrofoil higher than that on the bottom? What keeps enlarging the difference in these 2 velocities?

I am trying to learn how hydrofoil works. A big part of it is Bernoulli's principles. I found this article on MIT website. There are two explanation for how it works: The conservation of linear ...
1
vote
0answers
7 views

Ionospheric electron density measurements

I've been working on measuring total electron column density (TEC) with multi frequency GPS data. In theory, signal delay caused by TEC differences should affect the code and carrier nearly evenly in ...
2
votes
1answer
65 views

How much Gravity is required to stop time?

Clocks free of gravitational influence run faster than those experiencing gravity. Is it possible for gravitational influence to bring time to a stop? Additionally can acceleration affect clocks in ...
2
votes
2answers
63 views

Mathematical Formulation of Classical Spacetime

I have seen two formulations of Classical Mechanics: Newtonian spacetime (learned it from the lectures of Professor Frederic P. Schuller): Definition: A Newtonian spacetime is a quintuple $(M, ...

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