All Questions

1
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2answers
50 views

Work done by friction when object is rolling WITH slipping

So if I have an object that is rolling with slipping like a bowling ball, if I use W=F•dr definition, then work done by friction has to be negative. But if I use the W=τ•dθ definition, then work is ...
0
votes
0answers
22 views

Ball collison in 2D in Java [on hold]

For a course in my university the final project is basically making a program with java that simulates some particles moving in a 2D frame.We should consider that the collision may not be completely ...
0
votes
1answer
28 views

Dark Matter gamma-ray flux from hadronic annihilation channels?

For a project I am currently reading into indirect detection of Dark Matter via gamma-rays from DM subhalo's. I understand that there is a possibility of DM annihilating with each other in these ...
0
votes
0answers
40 views

Peskin's QFT chapter 6 contour integral

In page 178 of peskin QFT textbook equiation (6.5) gives us a contour integral: \begin{equation} A^{\mu}(x) = \int \frac{d^4k}{(2 \pi)^4} e^{-ikx} \frac{-ie}{k^2}\Big ( \frac{p'^{\mu}}{k \cdot p' + i ...
-3
votes
0answers
34 views

Has anyone tried the double slit experiment with materials of different densities? [on hold]

I'm not able to find a study with the following set up so if anyone is aware of such a study please let me know Test: Do micro gravitational fields influence particle trajectory? Setup: Double slit ...
3
votes
0answers
20 views

Sound emitted by droplets hitting a liquid surface

when a liquid jet (e.g. water) hits a water surface sound may be produced if, due to Plateau Rayleigh instability, the water jet has formed into droplets. But what exactly causes the sound? Is it the ...
1
vote
1answer
24 views

Cyclotron motion for an arbitrary velocity and constant magnetic field

I understand the classic examples of taking the magnetic field along the direction of a certain axis, and then analyzing the motion of a charged particle. This gives helical motion (for a general ...
0
votes
1answer
35 views

How can we prove that correlation function depends only on the spatial difference if Hamiltonian is translationally invariant?

If $H$ is a translationally invariant Hamiltonian, how can I convince myself that the correlation function (on the ground state $\left|G\right\rangle$) $\left\langle G|\psi(x)\psi(x’)|G\right\rangle$ ...
2
votes
0answers
24 views

Strange sound of low frequency produced from 2 steel balls

When two steel balls collide, or any metal objects collide, a high frequency sound is produced. However, what was strange is that when I held two metal balls in my hand, and moved them around, it ...
0
votes
0answers
16 views

Why do we consider spin degeneracy in graphene quantum hall effect and not in the conventional one?

When dealing with quantum hall effect in graphene we say that each landau level (with $n\neq 0$) has 4 times the degeneracy of a simple landau level derived for an electron in a magnetic field because ...
0
votes
1answer
38 views

Isothermal expansion of real gas - pressure change

I have been studying isothermal expansion process, the heat change particulary for a real gas. On the internet is many solved problems about this, but it's always about changing volume from $v_i$ to $...
1
vote
2answers
84 views

Can the future affect the past in general relativity? [on hold]

Hypothetically, let us suppose that a black hole were to suddenly appear at time $t=1$ at position $x$. Can the effect of the black hole be felt at time $t = 1-\epsilon$ near $x$ due to the bending of ...
0
votes
0answers
34 views

Derivation of the formula for the fundamental frequency of a stretched string [on hold]

I'm trying to derive the formula: $$f=\frac{1}{2L}\sqrt{\frac{T}{\mu}}$$ but I'm running into trouble with a $\theta$. Taking a string of length $L$ vibrating at the fundamental frequency $f$ we get ...
2
votes
1answer
48 views

can entangled photons produce an interference pattern?

Suppose you have a laser that emits entangled photons in opposite directions towards a double-slit screen setup as shown below. The photons are entangled such that if a photon on the left travels ...
0
votes
1answer
28 views

Can I find out magnitude and direction (+starting point) of a vectror using only one method? (graphical or mathematical)

Let's say I need to find out the magnitude and direction (by the direction i mean "position of a vector"/"starting point + direction") in uniform circular motion. When I draw it into a diagram and ...
-1
votes
1answer
24 views

Higher frequency waves

Can we artificially create extremely high frequency waves in the ( order of 10^60 )? how hard is it to create high frequency waves, and what limits are potential in doing so...
3
votes
2answers
118 views

Circular orbit in a central force field

Considering a motion of a body under a attractive central force, $\textbf{F}(\textbf{r}) = -\frac{k}{r^3} \hspace{1mm}\hat{\textbf{r}}$ with $k>0$. Is it possible for a body to move in an at ...
-1
votes
1answer
34 views

Free particle in Rindler metric

I have to discuss the motion of a free particle in Minkowski using the Rindler metric $$ds^2=e^{2ap}(-d\tau^2+dp^2)$$ So it has to satisfy the geodesic condition $\frac{d^2x^\mu}{d\tau^2}+\Gamma_{\rho\...
0
votes
0answers
18 views

What is the criteria for two fermions to behave as composite boson? [duplicate]

Other than that overall spin for pair of fermions is integral, what are properties needed to make composite boson. In some articles they say fermionshave to be in compact form , so what happens when ...
1
vote
0answers
24 views

How to make two fermions entangled with each other?

How to make two fermions entangled with each other. When we say two particles have to interact with each other to get entangled, what kind of interaction is that?
1
vote
0answers
54 views

Energy of an event for a human observer at a distance of 1 astronomical unit to physically feel the gravitational waves using inverse square law?

I'm asking this question to satisfy my curiosity about how much energy (in joules) it would take for a human astronaut to feel a gravitational wave from a distance of 1 astronomical unit (AU) from two ...
0
votes
0answers
38 views

If the amount of matter is an unchangeable end value, then we can represent any point of the time? [on hold]

Considering the matter conservation law, we know that matter can't be created or destroyed, also, from the Pauli's principle we know that one point of the space can be occupied only by one fermion, ...
0
votes
0answers
12 views

Restricted Rotation using electromagents [on hold]

I was wondering if I could restrict the rotation of a part over another in one direction alone using an electromagnet but allowing me to have a continuous rotation if forced (maybe by using some ...
1
vote
0answers
63 views

What optical system could perform a multiplication/convolution of several rectangular pulses with different widths?

Statement There is a following multiplication/convolution of $n$ rectangular pulses with different widths $$ f(x)=\mathrm{rect}(c_1x)\ast\mathrm{rect}(c_2x)\ast\ldots\ast\mathrm{rect}(c_mx) $$ or $$ ...
-2
votes
3answers
59 views

Why do energy transfers always result some heat loss?

explain that energy transfers and transformations in mechanical systems always result in some heat loss to the environment. Like why is it necessary for a heat loss?
0
votes
4answers
101 views

Basics of electric current

I am a mathematician who never took a physics class besides classical mechanics. Recently I have been looking at biophysics for a small project and I have a hard time understanding the basics of ...
1
vote
3answers
110 views

Is there any intuitive reason behind why should the eigenfunctions of observables form a basis for our Hilbert space?

Is there any intuitive reason behind why should the eigenfunctions of observables form a basis for our Hilbert space ? For example, in the case of Stern-Gerlach experiment, sending the beam that has ...
1
vote
1answer
46 views

Why only 2 derivatives in classical mechanics? [duplicate]

The title conveys my true question, but for the sake of clarity I will now rephrase it in a more mathematical flavor using the Hamiltonian formalism of classical mechanics and the terminology of ...
-1
votes
0answers
17 views

Kinematics problem…? [on hold]

Two points A and B are moving in X-Y plane with constant velocity of $V_a=(6i-9j)$ m/s and $V_b=(i+j)$ m/s respectively. At time t=0 they are 15 m apart and both of them lie on y axis with A lying ...
0
votes
0answers
5 views

How does an MRgFUS machine work?

As a medical application, magnetic resonance guided focused ultrasounds, is new I the treatment of some parkinsonian diseases, prostate cancer, none problems, and more. However, I am not sure how this ...
0
votes
0answers
37 views

Proving two space-time intervals are equivalent with matrix algebra

η=$ \begin{bmatrix} -1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 1 \end{bmatrix} $ v=$ \begin{bmatrix} ct\\ x\\ y\\ z \end{...
0
votes
0answers
7 views

Confused with the reduced density matrix and EE of TPS [on hold]

In my textbook, the writer gives such a question: Considering a L×L square lattice TPS with bond dimension D, and this system is divided into l × l small square at the center of the lattice and the ...
0
votes
1answer
40 views

What if we set Hamilton-Jacobi mechanics as an axiom?

We postulate principle of least action then we get Lagrange mechanics, after we can get Hamilton mechanics either from postulate or lagrange mechanics. Then we get HJE. But what if we have HJE as ...
2
votes
1answer
66 views

Is a stable orbit possible inside the ergosphere of a Kerr (spinning) black hole?

I have heard that it's "impossible to hover" inside of an ergosphere, but everywhere I read this seemed to be speaking in the context of "relative to a stationary observer outside of the ergosphere". ...
0
votes
1answer
24 views

Waveguide wave equation

Consider a wave guide built from two parallel slabs at $x=0, x=L$. between the slabs there is a dielectric material with $\mu=\epsilon=1$ and electric conductivity with a frequency of $\sigma(\omega)=\...
1
vote
1answer
101 views

Why are my interference patterns completely out of phase?

DIY physics enthusiast here doing a double slit eraser experiment at home with a laser pointer, double slit diaphragm, and few linear polarizers (horizontal at one slit, vertical at the other, +/-45 ...
-1
votes
0answers
18 views

Is it possible to “override” the electromagnetic field from an MRI scan? And how do you do it? [on hold]

I know electro conductors lose their charge if you heat them. Is there a better way to negate it and how?
3
votes
1answer
23 views

How are free electrons produced in a gas?

I'm aware about ionisation but even to ionise a gas you need an electron. So how in a discharge tube, which has a low pressure gas and a high voltage, does current flow? How is the first electron ...
1
vote
1answer
36 views

Can a strong electric field cause the electrons to come out of the atoms?

Can a strong electric field cause the electrons to come out of the atoms, is this how free electron are obtained in a discharge tube?
-4
votes
0answers
28 views

Im getting answer as t=5wR/8ug and w.f. =w/4 but its not in the options please help [on hold]

31* A solid disc of mass m and radius R is spun with an angular velocity w about its axis and then set into motion on a rough horizontal plane with a horizontal velocity v = Rw/4 while keeping the ...
0
votes
1answer
18 views

Magnetic Field lines within the cylindrical soft iron core within a galvanometer

I know that magnetic field lines are radial in a galvanometer because of the soft iron core. My question is if they are indeed radial then they should meet at the centre of the cylindrical iron core, ...
0
votes
1answer
20 views

Derive an equation for the minimum vertical distance needed by the string connected to masses to start accelerating [on hold]

It would be helpful if someone could help with this problem. Let us consider a mass m1 on a horizontal surface which has friction between the mass and the surface. It is attached to another mass m2 ...
0
votes
2answers
39 views

Is (DC/battery) voltage a result of charge? or energy? or both?

Backstory: I’m a software engineer just getting into electronics and it seems that everything I’ve ever been told about electricity my whole life is a candy-coated lie. I can’t find consistent logical ...
-1
votes
1answer
28 views

What is the term for a particle spin's uncollapsed position? What is the orbiting “thing”?

I'm not sure if I have the correct visual model, but I imagine that a particle spin can be represented by a single point on the orbit, or by a superposition state (like a random plane through a corner ...
0
votes
2answers
40 views

Basic First Law of Thermodynamics Question [on hold]

$2$ kg of water is heated by stirring. If this process raises the temperature of water from $15^{\circ}$ C to $25^{\circ}$ C, how much work, in joules, was done to the water by the stirring? I ...
1
vote
4answers
89 views

How does resistance *really* work? (DC, battery, LED, atoms, electrons)

Backstory: I’m a software engineer just getting into electronics and it seems that everything I’ve ever been told about electricity my whole life is a candy-coated lie. I can’t find consistent logical ...
0
votes
0answers
29 views

Can velocity wrap around?

Thermodynamics often plays out in $2n$ dimensional space. It is convenient for some numerical simulations to treat this space as if it was toroidal, wrapping around in every dimension (the fast ...
0
votes
0answers
24 views

What's the opposite of spin collapse? Superposition as a verb?

With regard to photon spin, I'm trying to figure out what the word is for being "more random" as opposed to collapsing and being "more determined" If I were to say "the spin collapsed", how would I ...
0
votes
0answers
13 views

what is the electrical conductivity tensor for AC magnetic field and DC electric field in a metal?

I need to define electrical conductivity anisotropic tensor in a metal caused by Hall effect. My problem is that i don't know how to define it in case of oscillating magnetic field and static electric ...
0
votes
0answers
33 views

Conservation of information

From the classical and quantum mechanical viewpoint, is information conserved in an expanding universe or not?

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