# All Questions

132,853 questions
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 ...
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 ...
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 ...
40 views

### Peskin's QFT chapter 6 contour integral

In page 178 of peskin QFT textbook equiation (6.5) gives us a contour integral: A^{\mu}(x) = \int \frac{d^4k}{(2 \pi)^4} e^{-ikx} \frac{-ie}{k^2}\Big ( \frac{p'^{\mu}}{k \cdot p' + i ...
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 ...
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 ...
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 ...
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 $\left|G\right\rangle$) $\left\langle G|\psi(x)\psi(x’)|G\right\rangle$ ...
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 ...
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 ...
38 views

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 ...
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?
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 ...
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, ...
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 ...
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  ...
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?
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 ...
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 ...
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 ...
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 ...
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 ...
37 views

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 ...
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?
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 ...
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?
28 views

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 ...
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, ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...