0
votes
1answer
44 views

Help recognizing partial differential equation

I would be very grateful if someone could tell me something about the following partial differential equation: $$ \frac{\partial U}{\partial t} = K * (\frac{\partial^2 U}{\partial r^2} + ...
1
vote
1answer
32 views

Are coefficients of friction invariant by switching the materials?

I don't have the ability to make the experiment to answer these questions : Let $A$ and $B$ be two materials. Is the static coefficient of friction of $A$ on $B$ equal to the static coefficient of ...
5
votes
1answer
100 views

Are the electrons at the centre of the Sun degenerate or not?

Trying to find an answer to this question, I came across two different methods of determining whether electrons at the center of the sun are degenerate or not. The first method, used here, calculates ...
4
votes
0answers
78 views

What happens to sound at speeds greater than mach 1?

We know that a moving source of sound waves produces Doppler shift, so that sound waves are closer-together in the front and farther apart behind, creating a difference in pitch. Let's consider a ...
0
votes
1answer
53 views

How do we measure thermal energy?

My textbook says "The amount of thermal energy is found by measuring the temperature of the substance." However, how is this true? Temperature measures only the average kinetic energy of the particles ...
0
votes
0answers
18 views

Initial conditions for second order ODE with complex stiffness

I tried this on Math Stack Exchange. I'm trying to find initial conditions to ensure systems of the form stay bounded $$\ddot{x}_i+\sum_{j=1}^N k_{ij} x_j = 0, \quad k_{ij} \in \mathbb{C}.$$ For ...
0
votes
0answers
16 views

heavy quark pair spin states

Apparently, heavy quark pair can have "axial-vector" spin state, "vector" spin state, and two different "tensor" spin states. Can anyone explain to me what they are and why this is the case? Thank ...
1
vote
2answers
70 views

Calculating euler number of disk

I'm trying to do exercise 3.1 from Polchinski, which should be a rather easy differential geometry problem. I have to calculate the euler number defined by $$\chi = \frac{1}{4\pi}\int_{M}d^{2}\sigma ...
3
votes
2answers
104 views

Can anyone explain me how time can bend according to Einstein in simple way? [duplicate]

I am just 16 and curious to learn about Theory of Relativity. Can any one explain it simple enough for me to understand? I read that it is bending of time-space or space-time that causes gravity. How ...
0
votes
1answer
31 views

Reversing time for a closed system of particles

For a closed system of particles, the lagrangian in classical mechanics is $$L=\sum \frac{1}{2}mv_a^2 - U(\mathbf{r_1},\mathbf{r_2}, \cdots)$$ For an arbitrary position function $x(t)$, to see the ...
0
votes
3answers
62 views

Path of light as it travels between two black holes

What would happen to light passing through a narrow space between the event horizons of two equal-mass black holes? Would it deviate or follow a straight path?
-1
votes
0answers
8 views

How to calculate the inertia tensors of an irregular polygonal right prism?

I am attempting to program a physics simulation and need to do calculate the inertia tensors of a mesh constructed of a series of irregular polygonal prisms. Now, I am aware that you can calculate ...
2
votes
2answers
73 views

Cosmological constants

I've heard that the cosmological constant is 0.[123 more zeros] and then a 1 [in some units]. Does that means that it used to be exactly zero? Is the value of this constant changing or is it fixed at ...
7
votes
1answer
66 views

Random walk recurrence term and the self-energy

Consider the "first passage problem" A random walk proceeds on a graph of connected points. On this graph, there is one "end" point $j$ meaning that if the random walker lands on this point the ...
8
votes
2answers
2k views

Can a mouse rotating a wheel violate conservation of angular momentum?

I have been thinking on the following problem. Part I. Imagine we have a mouse enclosed in a rigid box. We placed the box on a frictionless surface (ice might be a good example). Can the box start ...
-1
votes
0answers
26 views

Rotating cone magnetic field [on hold]

how to calculate the magnetic field of a rotating cone with a superficial charge distribution that varies with the altitude? It knows : height of the cone , truncated cone rays bases , there are ...
-1
votes
0answers
14 views

Reflected wave from free end

A wave pulse on a string moving from left to right towards a free end will reflect and propagates from right to left with the same speed and amplitude as the incident wave, and with the same polarity. ...
1
vote
0answers
27 views

Quantising the magnetic monopoles the make Maxwell symmetric

I don't believe this has already been asked, but I might be wrong; sorry. One can add a magnetic charge density/magnetic monopoles to Maxwell's equations to make the theory symmetric between the ...
-2
votes
0answers
45 views

Understanding sine waveform [on hold]

Hey I want to study basics of propagating periodic signal I.e. sine waveform which is a power signal. Let us write expression as $$y=A*sin(2\pi*ft)$$ There are mainly two types of energies ...
-5
votes
0answers
41 views

Particles are waves, particles are trapped in time and waves are trapped in zero time? [on hold]

So, particles are waves that have been or are being observed? A particle is trapped in time and a wave exists outside time? A wave and particle are one and the same, in time and out of time at the ...
1
vote
0answers
26 views

Fourier transformation and mode expansions [duplicate]

Sorry as this is a rather trivial question, but I'm stuck with a certain implication. I'm working on exercise 1.7 from Polchinski where we are given an open string with boundary conditions ...
0
votes
0answers
56 views

Is it true that whenever any non rigid body moves, there must be a delay between the ends? [duplicate]

Very sorry if this is still considered a duplicate to this, but unfortunately the answer to this question cannot address this because mine is a nonrigid body and involve biological locomotion concepts ...
0
votes
0answers
14 views

Refraction at Hyperbolic surface [on hold]

Could some one provide proof for the application of Snell's law of refraction at a hyperbolic surface? I understand that a ray parallel to the axis of hyperbola passes after refraction, through the ...
0
votes
1answer
26 views

Period to calculate the universal gravitational constant

To calculate the torsion constant in Cavendish experiment we need the period of it, so my question is if I need to measure the time the rod with two small spheres takes to do an oscillation (with an ...
-1
votes
0answers
24 views

Throwing the object around the Earth [on hold]

You have to throw an object to a point diametrically opposite od Earth surface, take that Earth does not rotate and that it is perfect sphere. What angle to the ground and velocity must object have? ...
0
votes
1answer
23 views

How does a Venturi Injector comply with energy conservation?

How does a Venturi Injector comply with energy conservation? When the water flow enters the narrower cross section its velocity increases and its pressure decreases. When the pressure gets lower ...
0
votes
0answers
46 views

't Hooft–Polyakov and Dirac monopoles, instantons and solitons

What is the difference between a 't Hooft–Polyakov and a Dirac monopole? (I read in the wikipedia article on the 't Hooft–Polyakov monopole: "The 't Hooft–Polyakov monopole is a topological soliton ...
-3
votes
0answers
17 views

How does one solve this problem(IOAA 2014, data anlysis)? [on hold]

http://prntscr.com/7nwjrt http://prntscr.com/7nwjvf This problem is from IOAA 2014, second problem from data analysis. I can't connect height with time without velocity or maximum height, which I ...
0
votes
0answers
44 views

Importance sampling for Coulomb potential

The integral I have to solve is: $$I=\int\int d \mathbf{r}d \mathbf{r}' \frac{\Phi(\mathbf{r})\Phi(\mathbf{r}')}{|\mathbf{r}-\mathbf{r}'|}$$ It is a six-dimensional integral which I am going to ...
4
votes
0answers
67 views

The logarithmic decay of WIFI

I have been told that Wi-Fi, LTE etc signal strength fall of as $$\propto \frac1{\log(r)}$$ where $r$ is the distance. I am wondering why this is. I better explain what I mean with this question. ...
0
votes
1answer
49 views

Stress-energy tensor on spacetime satisfying Klein-Gordon equation

Consider the stress-energy-momentum tensor $$T_{\alpha \beta}=(\nabla_\alpha \phi )\nabla_\beta \phi -\frac{1}{2}g_{\alpha \beta}((\nabla^\nu \phi ) \nabla_{\nu} \phi +m^2 \phi^2$$ where the ...
0
votes
0answers
39 views

Are there any $f(R, T)$ models of gravity?

For the past few months I have been studying $f(R)$ models of gravity. Recently I came cross $f(R, T)$ modified models of gravity. For the past few days I have tried to work out the difference between ...
0
votes
0answers
24 views

Where can I find a good theoretical treatment of conductor shielding?

Suppose one has three current carrying cylinders lying on the same plane. Some of the electric field of the first conductor ends up on the second conductor, which creates capacitance C12. But also ...
2
votes
1answer
44 views

How to find the remaining subgroup after some Higgs field gets a VEV?

Say we have a group $G$ and a set of Higgs fields in a representation $R$ of $G$. One of the Higgs fields in $R$ gets a VEV, how can I determine the remaining subgroup after this symmetry breaking? ...
1
vote
0answers
41 views

Question about Elon Musk's Hyperloop Suspension [on hold]

So one of the proposed suspension systems that will be used on the hyperloop include the externally pressurised air cushions. These cushions lift (or atleast help lift) the capsule and reduce drag ...
0
votes
0answers
35 views

I want to test a tunable optical filter that can quickly change from being a red light filter to being a blue light filter [on hold]

I want to test a tunable optical filter that can quickly change from being a red light filter to being a blue light filter. For this purpose, I am wondering about photonic crystal tunable optical ...
0
votes
0answers
32 views

entaglement experiments in laboratories for atom and photons-how to? [on hold]

My questions come splited like this: 1.How to entangle a spin and a photon in an experiment? 2.How to test for entanglement in the lab?3.There is entanglement for an atom also? 4. What does it mean ...
1
vote
2answers
27 views

electric field inside hollow conducting bodies

Let's say that there's a hollow conducting sphere placed in the presence of an external electric field and there's a + ve charge placed inside the sphere at a point other than the centre of the ...
2
votes
0answers
27 views

What is the optimal slope for Archimedes screw?

The Wikipedia article has nice image showing how the Archimedes screw work: As I understand, the red balls do not fall down because they are in minima caused by the screw. Because of material ...
0
votes
0answers
18 views

How to calibrate an ammeter and voltmeter? [migrated]

How can I calibrate an ammeter and a voltmeter. I just want to know about it. Because it might be helpful and I think it is a vital thing to know. So how can I do this?
0
votes
1answer
45 views

Question about Majorana spinor's property

I am reading the BBS, Exercise 5.1 This exercise is nothing but showing that two Majorana spinors $\Theta_1$ and $\Theta_2$ \begin{align} \bar{\Theta}_1 \Gamma_{\mu} \Theta_2 = -\bar{\Theta}_2 ...
0
votes
5answers
104 views

Does measurement change the evolution of wave function?

Basically any measurement is on wave function $|\psi\rangle$ is done by operator $X$ such that $X|\psi\rangle$ results observable $x$ with some probability. But what happens to $|\psi\rangle$? Does ...
0
votes
0answers
14 views

Is there / What is the technique to detect water on a remote object? [on hold]

For example, before human went to the moon, how could we find out if there are water underneath? How accurate will it be? Or without opening a suitcase, how could we non-destructively find out how ...
0
votes
1answer
32 views

Firing a blank vs live round from a gun [on hold]

When firing a gun, is there any difference between a blank round and a live round, aside from the obvious presence of a bullet exiting the muzzle? For example, does it sound different? Is there any ...
0
votes
1answer
36 views

What is supposed to be used as $m$ in $m\lambda = d\sin \theta $

I know that $m$ is the "order number", but I don't understand how this applies to the lab we did. We looked at Hydrogen gas through a diffraction grating (500 lines/cm or something like that) and saw ...
-1
votes
0answers
25 views

Inhomogeneous Maxwell's equations in CGS units [on hold]

What is the basis or the way of writing the given inhomogeneous Maxwell's Equations in CGS units: $$\nabla.E=\frac{\rho}{\epsilon_0}$$ $$\nabla\times B=\mu_0J+\mu_0\epsilon_0\frac{\partial E}{\partial ...
0
votes
0answers
35 views

Is there a physical interpretation of the alternating property?

A map from a vector-space to its base field is called "alternating" if each vector with repeated elements is mapped to zero. I've read that symplectic geometry is an important representation of ...
-3
votes
0answers
24 views

SHM by using cos equation [on hold]

A particle start motion according to equation $x=a\cos \left(\omega t+ \frac{\pi}{6}\right)$. Find time required for it to reach mid point. The displacement according to it must be 0 but how?
1
vote
1answer
61 views

Should the (On-shell) (2+1)d $N=2$ Chiral Multiplet Contain Two Scalars and Two Majorana Spinors?

In supermultiplets, the bosonic degrees of freedom and the fermionic degrees of freedom need to match in number. The number of degrees of freedom of a field corresponds to the number of independent ...
0
votes
1answer
27 views

renormalization subtraction point, scaling

When we use minimal subtraction scheme, for instance, we have a dependence of coupling on a scale $\mu$. Using the $\beta$ function, we can observe the behavior of the coupling at different scale ...

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