# All Questions

0answers
2 views

### Repelling force of magnets

What happens if I take two strong magnets and press their like-poles towards each other - does the repelling force created by them equals the force I'm exerting on them or does the repulsion force ...
0answers
4 views

### Questions on D branes and their role in the AdS/CFT correspondence

everyone! I'm a beginner in learning the AdS/CFT correspondence, and I come across two problems that I hope an answer will be given here. D branes in string theory are usually introduced through the ...
0answers
5 views

### energy, gravity and buoyancy working together

What will happen to the objects in this youtube video? https://www.youtube.com/watch?v=c5FF6DEaXTw
1answer
12 views

### Picturing electrons

I used to think that the electron is a particle orbiting the nucleus, but now I know that the electron can be also thought of as a standing wave. That's kind of like saying that a curve is both ...
0answers
7 views

### Determine path of point mass using the Hamilton's principle

I am very new in this field but I try to solve a problem by using the Hamilton's principle and afterwards I want to compare the solution by solving the same problem using conservation laws. What I ...
0answers
4 views

### Finding the maximum extension of a Spring

I have solved that after the body m1 hits m2, the velocity of m2 is going to be (3/4)*v0. I did this by using the law of conservation of momentum and using the coefficient of restitution (relative ...
1answer
23 views

### What are Stephen Hawking's main contributions to research-level physics?

Without a doubt, Stephen Hawking is the most famous living scientist; indeed, his public visibility in all of history seems to be rivaled only by Einstein and easily eclipses giants of physics such as ...
1answer
7 views

### How do I compute the angle needed to have a turning radius of $<8m$ and its wheel base with 20'' tire

I was doing a project of a vehicle, I'm assigend to the steering. I need to have a turning radius of $<8m$ however I'm limiting my space for the wheels. I've read that $>$ wheel base $=$ $>$ ...
1answer
10 views

### Tension after cutting the rope

In the image below how many times the tension in OA would change if i cut the rope where the scissor is?
1answer
7 views

### What is the formula to find the temperature at a specific location of a material as a function of time that is gaining or losing heat?

Imagine a scenario where there is a homogenous material and at a any location in that object I know the temperature at time 0. Given some properties of that material, how can I find out at any other ...
0answers
11 views

### Calculation of the Poisson bracket of a (Classical) Yang-Mills generator

This question might be too technical or minute, but I believe someone can give me the right advise. What I want to calculate is a Poisson bracket algebra of classical YM gauge generators, ...
0answers
6 views

### How to understand/derive Eq 5.5 in Geiner's Quantum Mechanics - An Introduction?

Geiner's Quantum Mechanics - An Introduction has an unnumbered equation about Eq. 6 in section 2.4 discussing density -- not sure if it is energy density -- of radiation: ... dE/dV = E/V =a ...
0answers
8 views

### How to correctly resolve forces radially in vertical circular motion?

I have always had problems at resolving forces and relating to Centripetal Force. Il show an example that I am stuck at right now. Please help me understand. This is the diagram: This is the ...
0answers
5 views

### Time reversal operator in tight-binding model with second quantization form

In tight binding model, $H=\sum_{r,r'}ta^{\dagger}_{r}a_{r'}+h.c.$.When now conducting a time reversal transformation, what form will this Hamiltonian like? Or how can I express time reversal ...
0answers
2 views

### Source of low frequency oscillation heard in ambulance siren

I have noticed that when I am standing on the street as an ambulance passes that so long as it is sufficiently close by (within 10-15 feet, so the siren is VERY loud for this to happen), I hear a ...
0answers
10 views

### Off-shell external line

In some QFT textbooks, an external line which is off mass shell also concerns us. But according to the motion equation, shouldn't the single external line be on the mass shell? Especially when we ...
0answers
9 views

### Solution to a kinetic temperature problem

I have a particular equation that needs to be solved for the kinetic temperature of a stream of gas particles. If we let the kinetic temperature be designated by the letter x, the equation becomes, ...
0answers
10 views

### What is a Chiral Algebra for a group?

What do we mean by the Chiral Algebra for a group G (SO(3) etc )? Do you know a reference suitable for physicists? Thank you
0answers
17 views

### Could you explain me how 'I*dl x r' from Biot-Savart Law works for finite long wire?

http://cnx.org/contents/416f27b6-e016-47c5-b1f1-01f470fd2907@10/Magnetic_field_due_to_current_ I am studying this problem right now but can't move forward. Biot Savart law shows that ...
0answers
19 views

### Velocity and Relativity

Hey guys I've been stuck on the question all day An interstellar race manager (M) is trying to compare the performance of two new spacecar models. Two flags are set up 39.5 m to the right and left of ...
1answer
13 views

### Gibbons-Hawking-York (GHY) boundary term for Schwarzschild metric

What is the simplest way to calculate Gibbons-Hawking-York boundary term for Schwarzschild metric? \begin{align} \int ...
0answers
19 views

### Electron can be at rest in Relativistic limit - what?

Here, I will demonstrate an astonishing fact (and thus an astonishing lack of understanding): It is well known from the uncertainty principle that an electron cannot be at rest. However, consider ...
0answers
9 views

### Callen's Second Postulate - Composite or Closed+Composite systems?

In section 1.9 of Callen's Thermodynamics he says: The single, all-encompassing problem of thermodynamics is the determination of the equilibrium state that eventually results after the removal of ...
1answer
16 views

### Exact Relation between voltage and current

I apologize before hand if this seems too naive. I'm having a really tough time understanding the relation between voltage and current. I read that 1 volt is the amount of work done to move a 1 amp ...
0answers
20 views

### Why are cameras on cell phones not designed so that we can see the images while taking our own photos? [on hold]

Why are cameras on cell phones not designed so that the camera hole and the screen are on the same side, and we can check the images while taking our own photos? Thanks.
1answer
40 views

2answers
24 views

### Adding a tracer to the surface of a water droplet

I have a 2 mm water droplet generated by a syringe and falling down. I am using two perpendicular cameras to capture simultaneous frames from it. I need to track the droplet during the time and ...
0answers
33 views

### Is Functional Analysis used at all in String Theory? [on hold]

Is functional analysis used at all in string theory? (and if so, how?)
0answers
33 views

### Analytic (or just qualitative) solution to *any* nontrivial electrodynamic dynamic problem?

I just realized that, after a basic course in electrodynamics, I have no idea whatsoever how to solve the most trivial non-static example in an "exact" way. By this, I mean the following: I know (at ...
0answers
27 views

### Which notation for the unit vectors is the most common: $\vec{u}$ or $\vec{e}$? [on hold]

I have seen both $\vec{u}$ and $\vec{e}$ used to denote the unit vectors. In Cartesian coordinates: ($\vec{u_x}$ , $\vec{u_y}$ , $\vec{u_z}$) and ($\vec{e_x}$ , $\vec{e_y}$ , $\vec{e_z}$) In ...
0answers
12 views

### Meaning of Wigner Function In a Single Variable

We know that if we integrate the Wigner function $W(x,p)$ against one of the variables, we get the marginal probability distribution. But how should we interpret say $W(x)$, i.e. its projection into ...
1answer
9 views

### Find quantity of electricity of two circular faces

So, there are two circular conductive sheets with quantities of electricity of Q and -Q. If I know that the distance d between them is 0.002 meters and their radius is 0.1m and the voltage between ...
0answers
26 views

### Why are pernament magnets pernament?

If I get it right when iron bar is attracted by pernament magnet it becomes the magnet itself because all of its magnetic domains starts to point in the same direction. When iron bar is no longer ...
1answer
32 views

### Is it possible to eliminate Van der Waals interactions?

I came to know that the friction force actually depends on the surface contact area due to weak interactions (adhesion due to Van der Waals forces) between the atoms of both materials increasing in ...
0answers
28 views

### If (relativistic) mass depends on velocity does that mean that (relativistic) mass depends on the observer's frame of reference? [on hold]

A long time ago I've read that the (relativistic) mass of an object increases if its velocity increases. If the velocity of the object becomes equal to the speed of light, then its (relativistic) mass ...
0answers
65 views

### Do these photographs depict the Higgs Field?

[PHOTO 1] Colter Dallman wrote in his paper - Space, Density, Relativity and Higgs Field Occupancy - (available online): ...
0answers
16 views

### Help in finding the pdf for Lebesque measure

The application is in signal processing but the concept is based on Physics. The model generating the observation is of the form $y_n = A^Tx_n + U_n$ where $x$ is the output of a a linear stationary ...
1answer
19 views

0answers
10 views

### Para and ortho hydrogen angular momentum values

In Wikipedia, it is said that: Orthohydrogen, with symmetric nuclear spin functions, can only have rotational wavefunctions that are antisymmetric with respect to permutation of the two protons. ...
1answer
12 views

### Does Peltier effect decrease temperature?

Does Peltier effect decrease temperature? Such as infamous flashlight from your hand temperature. It use Peltier effect to generate light while your hand has more heat than air. So, whenever ...
0answers
18 views

### Calculate Compressibility of water

I have 1 litre of water on 30 celsius, and there is a pressure of 10 mega psi affects on it. I want to calculate volume decrease that caused by pressure Thanks
0answers
31 views

### Could these hypothetical very long distance properties of light offer alternatives to an expanding universe or a finite number of galaxies? [duplicate]

Assume that there could be a property of light that it gets very gradually steadily red-shifted by traveling large astronomical distances, in exactly the same way that Doppler shift from receding ...
2answers
29 views

### Is collision in ideal gas because of physical collision or due to repulsion force

Is collision in ideal gas because of physical collision or due to repulsion force when they approach close by?
0answers
27 views

### 'Topological' Notions in Physics

So I've been trying to make sense recently of the usage of 'topological' in various fields of physics, and get sort of an intuition for what this means in context. This all boils down to my main ...
3answers
41 views

### Thought experiment about wavelength of light through a medium

Though the physical concepts and mathematics are highly rudimentary, I often try to comprehend exactly why light wants to keep it's frequency, yet alter it's wavelength as it travels through a medium, ...
0answers
9 views

### Understanding the definition of SAR value?

I am confused over the meaning of SAR values and different standards in its definitions. While checking of website a mobile manufacturer company for a mobile phone, I found this statement The SAR ...

15 30 50 per page