2
votes
3answers
183 views

Why photons reflect off glass?

Why photon reflects and refracts through glass? Some photons pass through glass and some reflects.I know this is due to energy levels of electrons of glass, an incoming photon is unable to excite the ...
0
votes
1answer
129 views

Einstein on a train paradox: what's the resolution?

Okay, so Einstein is on a train looking at a mirror. The train is moving at $c - 1 \frac ms$. Einstein is facing in the direction of motion. All along the side of the train are stationary clocks. ...
0
votes
2answers
98 views

Conservation of Energy vs Conservation of Momentum in Rotational Dynamics

It is clear to me why angular momentum is always conserved, and how in some cases energy is not necessarily conserved within the system (in those cases where bodies deform, or friction is involved). ...
0
votes
0answers
40 views

Need help piecing together football trajectory equations

I've done some studying of the physics involved when estimating the trajectory of an arcing football; that is, in American football, not world futbal, per se. I have all the basic building blocks I ...
1
vote
0answers
43 views

Exponent rule for Grassmann numbers

I would like to ask if the following statement is legit for the Grassmann numbers $\eta^*,\xi_1,\xi_2,\xi_3$ and real parameters $A,B$ and $C$? $$e^{A \eta^*\xi_1} e^{B \eta^*\xi_2}e^{C \eta^*\xi_3} ...
1
vote
2answers
85 views

If light travels along null-like geodesics, does that mean it remains at the same point on a spacetime manifold? [duplicate]

I know my question doesn't make sense all ready. Suppose I have points $(0,0,0,0)$ and $(1,1,0,0)$. The distance traveled is zero since $ds^2 = 0$ in this case. And light has moved from one point to ...
0
votes
0answers
31 views

Isospin states of deuteron

I have a stupid question to ask being the newbie amateur that I am to physics. Deuteron in the ground state normally exists in the isospin singlet state at least according the wiki site: ...
1
vote
0answers
44 views

Integral derivation [closed]

Somebody know how to derive this integral? \begin{equation} \int \frac{d^Ds}{(2\pi)^D} \frac{s_\mu (p-s)_\nu}{s^2(p-s)^2} = \frac{i}{(4\pi)^2} \left(\frac{4\pi ...
0
votes
0answers
14 views

Measured versus Predicted Energy gain in Tokamaks with size

Does there exist a known relationship between the energy gain of Tokamaks in dependence of their size? How do fusion engineers can predict how much gain will a given Tokamak size deliver? Do they just ...
2
votes
0answers
24 views

Inertial frames and Sagnac interferometers

Let's posit: I am in orbit around a large body, like a planet, and I am close enough to be tidally locked to the large body. Am I in an inertial frame? Even without looking at the stars, couldn't ...
1
vote
1answer
40 views

How to begin using SDSS data?

SDSS has gone through so many updates, it's difficult to find out how to access the data today in 2015. How can I use SQL and Python to access SDSS data, e.g. the photometry and spectra of quasars, ...
-2
votes
2answers
119 views

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum?

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum? What is the intuition behind $p=mv$? I had trouble finding any sources that state the actually ...
2
votes
1answer
32 views

The effects of special relativity when accounting for two reference frames

If reference frame A is travelling past reference frame B could one argue that it is in fact B that is motionless as their motion is relative to each other? If this is the case then how does one ...
0
votes
2answers
79 views

Simulation of a simple robot [closed]

I'm a programmer and I'm working on a simple robot simulator. Of course, the most important part of this simulator, is the physical simulation of the robot. Unfortunately, I have a little knowledge ...
4
votes
2answers
124 views

Could you view yourself in high gravity situations?

I'm trying to understand what effects gravity can have on light. First of all, I don't understand how gravity can even affect it, since it doesn't have mass, right? That is probably a separate ...
0
votes
0answers
15 views

Optics Simulation Software for Airy Beam Generation [duplicate]

I have been trying to simulate the generation of Airy Beams using a simple two-cylindrical lens setup as shown by Papazoglou et al. http://journals.aps.org/pra/abstract/10.1103/PhysRevA.81.061807 I ...
0
votes
2answers
53 views

Would an ordinary or fluorescent lightbulb generate electricity when exposed to light?

I was wondering whether the physic laws or the nature in which lightbulbs are constructed would allow for lightbulb to generate electricity when subjected to strong (intensive and concentrated) ...
1
vote
1answer
64 views

A closed 1-form as a potential of electromagnetic field? [closed]

With first variation of an action (my action is formed naturally by scalar curvature of a semi-Riemannian transitive lie algebroid which I used as a framework for forces unification). I derived an ...
2
votes
1answer
151 views

Why isn't the time-derivative considered an operator in quantum mechanics? [duplicate]

Based on my understanding when doing quantum mechanics we deal with a small set of mathematical objects: namely scalars, kets, bras, and operators. But then in the Schrodinger equation we have this ...
0
votes
1answer
23 views

Spatial probability density of single atom in a crystal at low temperature?

I'm working in gravitational physics, unfortunately my solid state physics lecture is already a while a go. My question will probably sound quite trivial to solid state physicists, but I couldn't find ...
1
vote
0answers
44 views

Normalising a massive propagator?

If you take a propagator Greens function for a massless photon from the origin as $$G(0,x) = \frac{1}{x^2-t^2 +i \varepsilon}$$ then the normalisation factor at time t is: $$ N = \int |G(0,x)|^2 ...
0
votes
0answers
20 views

How would the fermi energy of an element inside of crystal affect its fermi level?

If I had a substitutional crystal of nickel atoms inside of a copper fcc lattice, how would this affect the Fermi level of the material?
2
votes
2answers
111 views

Why is rainbow always circular?

From the article that I read on physics classroom website on rainbow, rainbow is formed with red on the top and violet on the bottom because violet refracts more, and has a smaller angle of deviation ...
3
votes
1answer
318 views

Simpler derivation of Sackur-Tetrode equation

Is there a reason the following derivation for the Sackur-Tetrode equation is not common? I am teaching a lower undergraduate level class and would like to derive it with simpler terms of only using ...
0
votes
1answer
41 views

What are the limitations of using instantaneous axis of rotation? [closed]

I know when the body rotatates as well as translates IAR or ICR shouldn't be used but I am not able to understand why?
1
vote
0answers
49 views

Integral over a surface in kinetic theory [closed]

I am working with some kinetic theory. I have the distribution function $\Psi (\vec{r},\vec{p},t)$, Where $\vec{r}$ is the radius vector, $\vec{p}$ is the unit vector of orientation, and $t$ is the ...
7
votes
2answers
306 views

Is there a reason why a relativistic quantum theory of a single fermion exists, but of a single scalar not?

When we try to construct the relativistic generalization of non-relativistic time dependent Schroedinger equation, there are at least two possible completions - Klein-Gordon equation and Dirac ...
1
vote
1answer
92 views

If the Sun were smaller but had the same surface temperature, would it still have the same luminance?

Let's assume we have two stars that have the same surface temperature but very different size. I understand how luminosity depends on surface area so the two stars will have different luminosity, but ...
2
votes
2answers
85 views

Can a GPS system detect the decline in the rotational velocity of the Earth?

From Wikipedia: Rotation in Angular Velocity of Earth Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth's ...
6
votes
2answers
132 views

What does it mean to observe? [duplicate]

This is a layman's question. The only thing I know about quantum physics is from casual reading and documentaries. I can imagine electrons being probabilistic waves. Their position is an infinite ...
0
votes
0answers
40 views

What is the first topic on mathematics,that an undergraduate physics student must study? [duplicate]

I aspire to become a theoretical physicist. I like to understand about infinite series and so on. Could you please recommend me any book?
0
votes
0answers
61 views

Calculating atomic forces from total force and torque on molecule in molecular dynamics (MD)

I guess this problem applies to any body that is composed of a small number of particles, but for the sake of simplicity and concreteness, let's consider a classical model of a molecule consisting of ...
1
vote
2answers
52 views

Some confusion pertaining to direction of static friction on stationary object

Consider a stationary object of mass $m$ on a horizontal table. Since the object does not move relative to table, $f_s=0$. So it seems that we first consider $mg$ and normal reaction force,$N$ ...
0
votes
2answers
108 views

Convert an equation for acceleration into one for velocity

A sledge is pushed in a straight line. Assume surface is smooth. When the sledge is x distance away from the start the magnitude of its acceleration is given by $0.08e^{-4x}$ and is going in the same ...
1
vote
1answer
109 views

Geometric meaning of spin connection

A very short question: Does the spin connection that we encounter in General Relativity $$\omega_{\mu,ab}$$ have a geometric meaning? I am supposing it does because it comes from mathematical terms ...
3
votes
2answers
167 views

How to understand the lifespan of large-scale cosmological structures?

When a star is said to live for 1 billion years, is that relative to the 'average cosmological time unit' or local time in the star's gravitational field? Also, if the sun is said to have 5 billion ...
1
vote
3answers
191 views

Why can't we find a true inertial frame?

From one book, I read that if we release a ball horizontally on earth, its velocity does change in very accurate observations. If we track its motion, we get full information of its motion (incl. ...
0
votes
3answers
281 views

Determine direction of friction on a block held stationary against a vertical wall [closed]

A block of mass $m$ is pushed up against a wall and held stationary by a force $ F$ that makes an acute angle $\theta $ with the horizontal. May I know how to determine the direction of the static ...
0
votes
0answers
74 views

Quantitative understanding of excess heat capacity in ferroics

I'm looking to understand what an excess heat capacity in a ferroelectric (FE) can correspond to qualitatively. Typically one starts with a Landau expansion of the free energy if you want to study the ...
1
vote
2answers
1k views

How can be the neutral wire at 0 volts when current flowing through it?

Voltage is potential difference, and current flows because of voltage. So if the voltage is zero, how can current flow through the neutral wire.
1
vote
1answer
56 views

Issues with the chain rule in derivatives in chiral perturbation theory [duplicate]

I realize that this is a purely math question, which however has arisen in a physics computation. The reason to post it here is that I want a fast dirty answer. Not something cluttered with ...
-1
votes
1answer
42 views

What is the minimum acceleration that stops the rod from sliding in the frictionless surface? [closed]

What should be the block's acceleration 'a' such that the rod present inside, inclined at at the angle 'theta' and mass 'm' will be obstructed from sliding down. From car's frame of reference, a ...
1
vote
1answer
93 views

Magnetic force paradox

Suppose a current carrying wire Is placed in vertical direction. A charged rod is placed is placed nearly horizontally.It is clear that magnetic field due to current carrying wire is inside the ...
-1
votes
1answer
90 views

work and energy dilemma in an inclined [closed]

An example problem done in my book: A driver was driving a car of mass 1000 kg through an inclined plane which makes an angle of 30° with plane with a velocity of 25 m/s . Then he saw a boy 50 m ...
-2
votes
2answers
434 views

Why is the speed of light limited to (only) 299.792.458 m/s? [closed]

The speed of light (in a vacuum) is limited to 299.792.458 m/s. This sounds very fast, and it is on a global scale. But if you look at the Universe on a larger scale than it sounds quite slow, For ...
0
votes
1answer
85 views

Why do charges move at the rim of the “charged-disk” conductor in response of the field created by themselves?

Okay, one statement from Purcell's book goes like: [...]Thus, we find the potential at $P_2$: $$\phi = \frac{1}{4\pi\epsilon_0} \int_{-\pi/2}^{\pi/2} 2\sigma\cos\theta d\theta = \frac{\sigma ...
0
votes
0answers
88 views

How much of this 'Slow Death of the Universe' was predicted?

In short: the energy generated in today's universe, is "about half of the produced two billion years ago" and found that "this fading occurs at all wavelengths" as yesterday news: ESO - Charting the ...
0
votes
0answers
102 views

Neutron energy inside reaction of proton-boron fusion

While proton-boron fusion is considered 'aneutronic' (apparently aneutronic actually means that less than 1% of the energy produced is via neutrons) I believe that it is expected that proton-boron ...
3
votes
1answer
175 views

Can operators be argument of Dirac Delta function

In one part of Marc Bee's book on Quasielastic Neutron Scattering, he defines the pair correlation function $$ G(\textbf r,t) = \frac{1}{(2\pi)^3}\int I(\textbf Q,t)\text e^{-i\textbf Q.\textbf r}\ ...
2
votes
2answers
53 views

Are there hypothetical processes which allow the existence of a fission powered star?

I know this is impractical given the rarity of heavy fissile elements in the universe (contrary to the abundance of fusion friendly elements like hydrogen), but is there any process via which a ...

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