# All Questions

974 views

### Euler equation of fluid dynamics

I'm trying to obtain Euler equation for a perfect fluid in laminar or stationary flow. A particle fluid is submitted at volume forces and surface force. The fist, in my case, is giving only by gravity ...
413 views

### Rayleigh-Benard Convection

I found this nice paper about RB convection. However I am confused by what is going on page 6. In particular why we are suddenly using Helmholtz equation to find spatially periodic solutions. Aren't ...
115 views

### Lorentz Transformations and Aberration

Why does the azimuthal angle, $\phi$, remain unchanged between reference frames in special relativity? Edit: Here is a link from "Radiative Processes in Astrophysics": ...
1k views

### Can bosons that are composed of several fermions occupy the same state?

It is generally assumed that there is no limit on how many bosons are allowed to occupy the same quantum mechanical state. However, almost every boson encountered in every-day physics is not a ...
2k views

### Calculating partition function of ultra-relativistic 1D gas

This is a problem (Problem 3.16) from the book Statistical Mechanics 2nd Ed. by Pathria. In the problem I have to calculate the partition function of an ultra-relativistic 1D gas ($E_i=cp_i$) ...
2k views

### Finding Rotational Kinetic Energy Of A Clock

The problem I am working on is: Big Ben, the Parliament tower clock in London, has an hour hand 2.70 m long with a mass of 300 kg, and a minute hand 4.20 m long with a mass of 100 kg (see figure ...
492 views

### Temperature dependence of the relaxation time in Boltzmann equation for impurity scattering in metals

Is there any temperature dependence of relaxation time in impurity scattering of conducting electrons? It seems to me that there is none. But, some people claim that there is. So if you could ...
5k views

### Fermi surface nesting and CDW/SDW/SC orders

Fermi surface nesting and CDW/SDW/SC orders. What is the definition of a nesting vector? And why Fermi surface nesting gives rise to different orders at $T=0$? (CDW: charge density wave; SDW: spin ...
2k views

### What is the meaning of the word “particle” in particle physics?

I want to use Matt Strassler's definition of the word "particle" as a specific example: Matt Strassler writes: (1) "...all the elementary “particles” (i.e. quanta) of nature are quanta of waves ...
999 views

### Does the Chandrasekhar Limit scale for a Black Hole?

No physicist/astrophysicist I; All I know about the Chandrasekhar limit is that it apparently limits the mass a star may survive, beyond which it degenerates to a neutron star, or a black-hole. Does ...
287 views

### Is shear elasticity the same as shear modulus?

I've encountered both the terms "shear elasticity" and "shear modulus". Are these the same?
472 views

### Doubts with levers

I'm studying for a test of static rigid body and I'm having doubts on how to solve problems involving levers with weight. If I have, for example, a lever 10 kilograms and 3 meters long and one support ...
144 views

### How to get energy of collision if you know force of gravity of an object($m \rightarrow F=mg$)?

How to get energy of collision if you know force of gravity of an object($m \rightarrow F=mg$)? You get energy of collision by kinetic energy $E_k= \frac{1}{2}mv^2$, but if you use just force of ...
1k views

### Diffraction through a single slit?

I'm having some trouble finding the answer to this homework question: A wide beam of light from a laser with a wavelength of 450.0 nm is incident on a long narrow opening that is 0.300 mm wide. ...
424 views

### Alcubierre warp bubble effect on gravity and space

I read the question Faster-than-light communication using Alcubierre warp drive metric around a single qubit?, and these questions came to mind: What kind of impact would an Alcubierre warp bubble ...
896 views

### Thorium radioactivty vs Uranium radioactivty nuclear power

May i please open this question by asking that if you intended to answer this please could you provide links based on your answer. I have read ( and posted one ) on thorium and a lot of the answers ...
2k views

### Electric Potential of a Charged Sphere

Problem Consider a sphere with radius $R$, and with a charge distribution $\rho(r)=\rho_0r$. Using Poisson's equation, calculate the electric potential inside and outside the sphere. Solution I don't ...
2k views

### Nuclear fusion: what causes this “resonance” peak?

Can anyone explain why the $^{11}\mathrm{B}\mathrm{H}$ fusion cross-section has a peak near 150 keV, and why $\mathrm{D}\mathrm{D}$ and $\mathrm{D}\mathrm{T}$ have no such sharp peaks?
216 views

### In QM, does random data “come from anywhere”? Also, what are the properties of the data?

I have only taken a basic quantum mechanics course (this book, so you know where I'm coming from), but I've been wondering about something. If we set up a quantum system in a known state and take a ...
1k views

### Tensor product notation [closed]

In the image there is a tensor product: $$F_{\mu\nu}F^{\mu\nu}=2(B^2-\frac{E^2}{c^2})$$ It's about how this operation on the co- and contravariant field strength tensors can give one of the ...
1k views

### Chern number in condensed matter physics

In mathematics, the Chern number is defined in terms of the Chern class of a manifold. What is the exact definition of Chern number in condensed matter physics, i.e. quantum hall system?
689 views

### Question about the refraction of light in a swimming pool

Here is a homework question that I'm having a hard time understanding: Out of pure intellectual curiosity you have donned a snorkeling face mask and allowed yourself to sink to the bottom of the ...
275 views

### Cosmology questions from a novice

These ideas/questions probably represent a lack of understanding on my part, but here they are: 1) Cosmologists talk about the increasing speed of expansion of the universe and talk of dark energy as ...
167 views

### What are some fields where physics is leading mathematics? [closed]

I know developments in physics and mathematics often nourish each other, and at different points in history, physics and math have taken turns leading each other. An example of a physicist "inventing" ...
1k views

### Solving a Statically Indeterminate Truss with Energy Equations (Tricky)

Okay, first off, I know that there is a very similar problem about statically indeterminate trusses here, but my problem was a bit different and I didn't know how to adapt the answer for that problem ...
56k views

### Is two cars colliding at 50mph the same as one car colliding into a wall at 100 mph?

I was watching a youtube video the other day where an economist said that he challenged his physics professor on this question back when he was in school. His professor said each scenario is the same, ...
818 views

### Multi-loop beta function of gauge theory (*without* Feynman diagrams)

I would like to point to the beautiful section 4.3 (page 42) of these lecture notes. I think this is the most educative exposition I have ever seen anywhere about Yang-Mill's beta function. What I ...
520 views

### Will I recieve a shock if I charged a capacitor then i touch the 2 poles in same time?

What happens if I charged a capacitor then i touch the 2 poles in same time?
2k views

### How do we know particles exist? Aren't they just waves?

In the book "A Briefer History of Time" Stephen Hawking wrote: The unpredictable, random element comes in only when we try to interpret the wave in terms of the positions and velocities of ...
108 views

### Wire morphing shape?

Can one morph a wire by electrical current into a shape different than static shape at beginning? As in the beginning shape being in a spiral, then when electrical energy is passed through the wire it ...
448 views

### (Co)homology of the universe

In this post let $U$ be the universe considered as a manifold. From what I gather we don't really have any firm evidence whether the universe is closed or open. The evidence seems to point towards it ...
2k views

### Is there a mathematical derivation of potential energy that is *not* rooted in the conservation of energy?

For simplicity I'll consider only gravity, but in general this question only applies to conservative forces. As per my understanding, the way one gets to the equation for gravitational potential ...
219 views

### Angle of rays leaving a light source

I'm working on ray tracing and I'm trying to understand the impact of the angle at which a light-path intersects the surface of a light source on the amount of light that source delivers to the path ...
171 views

### Why can we analyse force balance on a dislocation?

Dislocation (like screw or edge dislocation) is not a 'real' thing, while Newton's laws only apply to a real object (no matter macroscopic, like stars, or microscopic, like atoms). In the derivation ...