Q stringlengths 18 13.7k | A stringlengths 1 16.1k | meta dict |
|---|---|---|
Object with friction in circular motion caused by a string A physics problem in my textbook reads:
A 0.40kg ball, attached to the end of a horizontal cord, is rotated in
a circle of radius 1.3m on a frictionless horizontal surface. If the
cord will break when the tension in it exceeds 60N, what is the
maximum s... | You understand the case with no friction. Let's look at the case with friction.
There are two forces acting on the ball: tension and friciton.
The friction comes from the interaction between the string and the talbe, and the direction of friction is always opposing the direction of relative motion of the two objects i... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/77009",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Deriving the Lorentz force from velocity dependent potential We can achieve a simplified version of the Lorentz force by
$$F=q\bigg[-\nabla(\phi-\mathbf{A}\cdot\mathbf{v})-\frac{d\mathbf{A}}{dt}\bigg],$$
where $\mathbf{A}$ is the magnetic vector potential and the scalar $\phi$ the electrostatic potential.
How is this d... | Velocity-dependent potential is not strictly a potential. Lagrange equations say that
$$\frac{d}{dt}\frac{\partial L}{\partial \bf{v}} = \frac{\partial L}{\partial \bf{r}}$$
You have $L = L_0 - U$ where $L_0$ corresponds to free motion (e.g. $L_0 = mv^2/2$ or $L_0 = -mc^2\sqrt{1-(v/c)^2}$).
If $U$ does not contain $\bf... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/77325",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 0
} |
About vector form of friction I read a text on mechanics and in the chapter on friction, there written that the kinetic friction is in the form
$$f_k = \mu_k F_N$$
where $f_k$ is the kinetic friction, $\mu_k$ is the kinetic friction coefficient, $F_N=mg$ is the normal force due to the weight of the object. In anothe... | You're very close. The vector giving the friction force has magnitude $\mu_k F_N$ and is opposite the direction of travel, so it can be written as the product of $\mu_k F_N$ with a unit vector pointing in the direction opposite the direction of travel. Since the velocity $\vec v$ is in the direction of travel, the un... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/77458",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Why should nature of light(or any quantum object) depend on observation? We know that, in the double slit experiment, observation changes the behavior of a quantum object, that it behaves like a particle when observed and a wave when not observed. But why should its nature depend on observation? What if we didn't exist... | It seems that you stumbled upon the measurement problem, where if you don't observe or measure a quantum object yet, it moves in all directions.
Its nature depends on observation as if you measure it, it will disturb or interfere with it as you measure it as it changes it's direction to a specific one, the environment ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/77738",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Surface gravity of Kerr black hole I'm going through Kerr metric, and following the 'Relativist's toolkit' derivation of the surface gravity, I've come to a part that I don't understand.
Firstly, the metric is given by
$$\mathrm{d}s^2=\left(\frac{\Sigma}{\rho^2}\sin^2\theta\omega^2-\frac{\rho^2\Delta}{\Sigma}\right)\ma... | $$\nabla_\nu(-\chi^\mu\chi_\mu) =\partial_\nu(-\chi^\mu\chi_\mu)\\
=\frac{\rho^2 }{\Sigma}\partial_\nu \Delta + \Delta \partial_\nu(\frac{\rho^2 }{\Sigma})-(\Omega_H -\omega)^2 \partial_\nu(\frac{\Sigma\sin^2{\theta}}{\rho^2})$$
Now use the horizon condition you will get
$$\nabla_\nu(-\chi^\mu\chi_\mu)=\frac{\rho^2 }{\... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/77890",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 4,
"answer_id": 2
} |
By saying a physical state has some 'symmetry', what do we really mean? Here our arguments are restricted to the realm of the Projective Symmetry Group(PSG) proposed by Prof. Wen,
Quantum Orders and Symmetric Spin Liquids. Xiao-Gang Wen. Phys. Rev. B 65 no. 16, 165113 (2002). arXiv:cond-mat/0107071.
and the following... | I just found that I asked a naive question and I can answer it by myself now.
(1) and (2) are equivalent to each other. Because if $\Psi$ is a ground state of $H(\psi_i)$, then $\Psi'=D\Psi$ is the ground state of $DH(\psi_i)D^{-1}$, and $[P,D]=0$, therefore $D(P\Psi)=P\Psi'$.
Remark:
More generally, when we talk abou... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/77972",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Symmetry breaking in Bose-Hubbard model According to Landau's symmetry breaking theory, there is a symmetry breaking when phase transition occurs.
*
*What is the symmetry breaking of superfluid-Mott insulator transition in Bose-Hubbard model?
*Why metallic state to Mott insulator state transition in Fermi-Hubbard... | The Mott transition in the Bose-Hubbard model is a quantum phase transition. From the point of view of field theory, that does not change much compare to standard (finite-temperature) phase transitions. The main difference is that you now have to take into account the quantum fluctuations which correspond to the "imagi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78049",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 1,
"answer_id": 0
} |
Quantum entanglement as practical method of superluminal communication As I understand it (from a lay physics perspective), quantum entanglement has been experimentally demonstrated - it is a reality. As I understand it, you can measure something like the spin of an electron and know that its entangled pair will, in th... | To rephrase Danu answer, you can not use the correlation of these entangled particles before you have exchanged some information with another (subluminal) device.
The main problem comes from the fact that the outcome of a measurement is random, so there is no way to agree beforehand on how to interpret a measurement do... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78118",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 3,
"answer_id": 0
} |
Is there an easy way to get water at roughly 70°C in our kitchen? Some green tea requires to pour water at 70°C. I have no thermal sensor or kettle with adjustable temperature with me.
Do you know a way to get water at roughly 70°C like “boil water and wait for x minutes” or “mix x part of boiling water with 1-x part ... | Assumptions:
*
*we have a volume of water $(v_1)$ at $100^{\circ} C$ (boiling water)
*we have a volume of water $(v_2)$ at $20^{\circ} C$ (tap water)
*we want a volume of water $(v_1+v_2)$ at $70^{\circ} C$
*the pot that will finally hold the $70^{\circ} C$ water will consume a negligible amount of energy from t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78183",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 3,
"answer_id": 1
} |
Definition and motivation for Twistors What are Twistors? Why are they important?
This particular statement in Wikipedia is intriguing
According to Andrew Hodges, twistor space is useful for conceptualizing the way photons travel through space, using four complex numbers.
| Your question can be answered at many levels. I'll keep it simple; I'm not very well versed with the grand picture.
Twistors provide an efficient (and possibly natural) means to encode the kinematics of massless particles and the resulting conformal symmetry.
For a nice and clear introduction, check Witten's lecture n... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78348",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 1,
"answer_id": 0
} |
What are the assumptions of the Navier-Stokes equations? I wanted to model a real life problem using the Navier-Stokes equations and was wondering what the assumptions made by the same are so that I could better relate my entities with a 'fluid' and make or set assumptions on them likewise. For example one of the assum... | Most importantly, the Navier-Stokes equations are based on a continuum assumption. This means that you should be able to view the fluid as having properties like density and velocity at infinitely small points. If you look at e.g. liquid flows in nanochannels or gas flows in microchannels you could be in a regime where... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78416",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Frames of reference: Inertial and accelerated - and jerked, snapped, crackled and popped? There are inertial frames of reference and the accelerated frames of reference, but are there any frames of references w.r.t. higher order derivatives of velocity? [1] [2]
For example, jerked frames of reference, snapped frames o... | A frame of reference does not need to be inertial though, for a non-inertial frame of reference, there is, at any instant, a momentarily co-moving (inertial) reference frame or MCRF
Now suppose that a particle does accelerate. In that case, we can have
an inertial frame at any event in the particle’s life by definin... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78473",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Is such an orbit possible that allows a satellite on Earth and another on Mars to always be in direct line-of-sight? If not always, how much "most of the time" could it get?
Or would a multi-satellites setup be more suited?
| The best way to minimise loss of sight would be to have the satellites orbiting at a very high altitude, e.g. beyond the distance of the moon. It would then be very rare for the satellites to be eclipsed by the planets, or moon. Such eclipses could also be easily avoided with a small orbit correction or by synchronizin... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78729",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 1
} |
Is inflation deterministic? In some theories inflation is supposed to be able to turn quantum fluctuations into macroscopic inhomogeneities.
I don't understand how an isolated system such as the universe can undergo such a random transformation : if at the beginning the universe is in a state $A$, quantum mechanics say... | Ok I ask the question to some specialists and it just seems that indeed the evolution of the whole universe is not unitary in inflation theory.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78855",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Time it takes two oppositely charged particles to collide I think this is supposed to be a simple problem but I am having a hang up converting it to a one-body problem. It's one-dimensional. +q and -q a distance d apart, held stationary then let go at t=0. The potential is V(x)=kq^2/x. If I turn it into a one body prob... | The negative sign doesn't have to do with electrostatics, it's a problem with a global sign which comes from the square root.
In a 1D problem, you can write
$$t_f-t_i=\int_{x_i}^{x_f}\frac{\text dx}v,\ \text{where}\ v^2=\frac2m(E-V(x)).$$
In the present case, though, with $x$ decreasing as $t$ increases, you need to ta... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/78925",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
How does a pressure suit work? I recently learnt that a suit called pressure suit is worn by fighter plane pilots to prevent red-outs and black-outs. And it seems to be work by -
"..applying pressure to selective portions of the body."
How do these suits work; i.e. by what means, selective portions of the body are pr... | The suits are designed to provide protection from the temperatures +100F to -90F.
When pressurized to 3.5 pounds per square inch (roughly equivalent to the atmospheric pressure at 35,000 feet), the suit can help to avert symptoms of decompression sickness (the "bends").
Above about 62,000 feet, the liquid in pressure s... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79143",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
Quantum tunneling effect in a potential of the kind $V(x)=A\frac{x^2}{1+x^4}$ Given a potential: $$V(x)=A\frac{x^2}{1+x^4}$$ with $A\gt 1$ and a quantum particle inside the well around the point $x=0$. I'm stuck on the calculation of the transmission and reflection coefficients for this particle vs. its energy.
| Here's a not-so-clever answer.
The plot of the function is shown below.
The red line denotes the energy of the particle being tunneled which expressed in terms of A. The black line denotes the max value of the potential which is A/2.
The task is to evaluate the transmission coefficient of the particle through one of ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79199",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 0
} |
Question on field strength tensor in YM just a quick question on $F_{\mu\nu}^a$. I'm correct to think $F_{\mu}^{\mu,a}$ vanishes, aren't I? (Just want to make sure...) My reasoning is as follows:
The derivative terms cancel anyways - that's obvious - so the only "critical" term of $F_{\mu}^{\mu,a}$ is $f^{abc}A_{\mu}^b... | Yes, $$\sum_{\mu} F_{\mu}{}^{\mu}~:=~\sum_{\mu,\nu}F_{\mu\nu} g^{\nu\mu}~=~0$$ vanishes because it is a trace of a product of a symmetric and an antisymmetric tensor. It is irrelevant for the argument that $F_{\mu\nu}$ is Lie algebra valued.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79329",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why does vacuum have a nonzero characteristic impedance towards electromagnetic radiation? On Wikipedia, the impedance of free space $Z_0$ is defined as square root of the ratio of the permeability of free space $\mu_0$ to the permittivity of free space $\epsilon_0$, i.e.
$$Z_0 = \sqrt{\mu_0 / \epsilon_0} \, .$$
The va... | Since a finite fluctuating electric field creates a finite fluctuating magnetic field (and vice versa), their ratio must also be a finite value. In other worlds, that being a finite quantity is only a consequence of the existence of light in vacuum.
Now that value itself is merely a consequence of the definition of uni... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79364",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "23",
"answer_count": 5,
"answer_id": 1
} |
Dehn twists and topological order I am trying to understand notion of a "Dehn twist" and how it relates to topological order.
In particular refering to http://arxiv.org/abs/1208.4834 it is stated that
Xiao Gang Wen's paper on "Topological Order in Rigid States" (http://dao.mit.edu/~wen/pub/topo.pdf) is supposed to pr... | Any oriented closed surface is a torus with g holes (for an actual torus g=1, for a sphere g=0, etc.), where g is called the genus. Associated to these surfaces is the mapping class group, which is the group of equivalence classes of homeomorphisms (topological isomorphisms) of the surface to itself, where two such map... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79489",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
How to establish relation between flow rate and height of the water column of the tank? Suppose a water tank has 1" diameter drain at the bottom and is filled with water up to one meter height above the drain. What time it will take the tank to drain out completely. Now say, the tank is filled up to two meter height ab... | The issue is, what is the flow velocity?
It is not simple, and it depends on pressure, which is proportional to height.
For low pressure, viscosity will dominate, and velocity will be proportional to pressure.
For high pressure, velocity will be proportional to square root of pressure.
In any case, the geometry of the ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79644",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 1
} |
What is the most efficient way to travel between tidally locked binary planets? Suppose that there are two planets of roughly the same volume and mass are orbiting each other. What would be the most efficient way to travel from one to the other? In other words, what kind of orbits, and connecting rocket-engine burns, w... | I worked out the outline of thee solution to this problem using Newtonian mechanics and vectors. This is not an easy problem because it is a three body problem. For simplicity I have made a few assumptions: 1. Mass of the spaceship is negligible and the orbits are perfect circles.
Working out the final solution require... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79709",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "14",
"answer_count": 5,
"answer_id": 0
} |
Nature of frictional force I was thinking about a situation where a person in standing on the ground with some friction. The frictional force is directly proportional to the normal reaction acting on him by the ground. Assume that he leaned forward i.e his center of mass is not vertically up the point of contact of him... | When the person is standing perfectly upright, the frictional force on him is actually zero and the normal reaction is $mg$. The frictional force is the horizontal component of the contact force and normal reaction is the vertical component. Therefore, unless there is a horizontal force, there will not be any friction ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79775",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 0
} |
Is it possible for the entropy in an isolated system to decrease? As far as I can tell, the concept of entropy is a purely statistical one. In my engineering thermodynamics course we were told that the second law of Thermodynamics states that "the entropy of an isolated system never decreases". However, this doesn't ma... | By the Poincaré recurrence theorem, an isolated system is guaranteed to return arbitrarily close to its initial state after a sufficiently long time.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79844",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 5,
"answer_id": 2
} |
Do orbitals overlap? Yes, as the title states: Do orbitals overlap ?
I mean, if I take a look at this figure...
I see the distribution in different orbitals. So if for example I take the S orbitals, they are all just a sphere. So wont the 2S orbital overlap with the 1S overlap, making the electrons in each orbital "me... | The orbitals shown in the figure are the different eigenstates of the electronic wave functions derived from the solution of Schrodinger equation. One of the postulates of QM states that these eigenstates are independent in a free atom.
Orbitals do overlap when two atoms are close together, e.g. in a molcule and the de... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/79985",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 5,
"answer_id": 2
} |
How fast does light travel through a fibre optic cable? The principle behind a fibre optic cable is that light is reflected along the cable until it reaches the other side, like in this diagram:
Although I know that the light is slowed down somewhat because it's not going through air, I've always wondered about anothe... | We can make a 1st-order approximation by assuming the following:
*
*$L=3$ m is the length of the fibre optic cable
*$d=3\cdot10^{-6}$ m is the diameter of the cable
*the cable is perfectly straight
*$\theta=0.785$ rad (~45$^\circ$) is the angle of reflection inside the cable
*photons are classical balls
*reflec... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/80043",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "21",
"answer_count": 3,
"answer_id": 2
} |
How to find the wavefunction that solves an infinite square well with a delta function well in the middle? Solutions for the wavefunction in an infinite square well with a delta function barrier in the middle are easily found online (see here for an example). I am wondering what the wavefunction is for an infinite squ... | Consider an infinite square with free region $[0, L]$. Place a delta function potential at $L/2$ with strength $\alpha$. Then, Schrödinger's equation is
$$E\psi = -\frac{\hbar^{2}}{2m}\frac{\partial^{2}\psi}{\partial x ^{2}} + \alpha \delta(x- \frac{L}{2})\psi$$
First, note that the delta function is zero everywhere ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/80106",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 1,
"answer_id": 0
} |
Why are we not affected by the radiation of the radioactive decay going inside the Earth? I was reading the question Why has Earth's core not become solid?, and one of the answers says that
The core is heated by radioactive decays of Uranium-238, Uranium-235, Thorium-232, and Potassium-40
Why are we not affected by ... | Alphas and betas are stopped by a small amount of material. Gammas are more penetrating, but a gamma ray with a typical energy would be stopped by something like 10 cm of rock.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/80171",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 2,
"answer_id": 0
} |
2N Fermions $\stackrel{?}{=}$ N Bosons We know that we do have composite particles (for example Atoms) made of fermions or bosons or mixture of them with fermionic or bosonic statistics. So why can't a gas of $2N$ fermions become a gas of $N$ bosons and condense to the lowest state at low temperature (just like what ha... | It can. This is exactly what happens when Helium-3 becomes superfluid. It's also what happens in superconductivity, which you mention in your question, when electrons combine into Cooper pairs.
Well, it's not exactly what you ask since neither liquid Helium-3 nor electrons are a gas. It's very unlikely a gas of fermion... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/80253",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Compressible flow - subsonic to supersonic and the 2nd law of thermodynamics I'm reading chapter 16 in Fluid Mechanics by Kundu.
It is stated (figures 16.16 and 16.17) that in a constant area duct flow with heating or friction, to go from subsonic conditions to supersonic violates the 2nd law of thermodynamics. How ca... |
Somehow, one must be able to get ambient quiescent air to supersonic velocities (it's done all the time).
Of course, and that same chapter already told you how it could be done: in convergent–divergent nozzle.
The statement
... the upper left
branch of the solution $M_2 > 1$ when $M_1 < 1$ is inaccessible because ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/80348",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why is moment dependent on the distance from the point of rotation to the force? The formula for moment is:
$$M = Fd$$
Where F is the force applied on the object and d is the perpendicular distance from the point of rotation to the line of action of the force.
Why? Intuitively, it makes sense that moment is dependent o... | The best definition of torque (or moment) is the work per unit angle of rotation (in Joules per radian) that can be done by a force which is acting in a manner that tends to cause a rotation. This implies that you want the component of the force which is acting along an arc, times the arc length, divided by the angle (... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/80538",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 10,
"answer_id": 3
} |
Quantum Thrusters and Warp Drives Any reservations about the potential of this (given in the link below/title above)?
Does it seem like a helpless attempt or something which might have the potential of developing into something real?
http://news.discovery.com/space/quantum-thruster-warp-drive-physics-130823.htm
| The idea is very much possible by using exotic matter through quantum waves amongst other things of course. Besides the energy was scaled down in caparison to Voyager 1 size and achieves this by using a ring around the ship. Sure this may not be feasible now ,but so many other things were considered impossible before t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/80597",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why can't we perfectly focus light-abberations aside I don't understand why there is necessarily a diffraction limitation on optical systems. Where does this limitation in focusing light come from?
| Well I suppose by perfectly focus, you mean to a mathematical point. And if we could do that, Heisenberg's principle implies that the momentum uncertainty would be infinite. So by the time we looked where the point was supposed to be, it would have moved to someplace else, in fact it could be anywhere at all, and we ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/80808",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 4,
"answer_id": 1
} |
How accurate is Newtonian Gravity? I know that really fast moving things need Relativity rather than Newtonian physics.
I also know the quirk of the Mercury´s orbit.
But just how much more accurate is General Relativity than Newton´s Law of Gravitation for predicting say the orbit of Earth or Neptune?
Can the "slingsho... | There are several different questions embedded in here. The answer to all of them is "Newton's theory is accurate to great precision, and beyond measurement accuracy for most of your examples".
The key point is that Newtonian physics fails when, roughly, the quantity $v/c > .1$ or $\frac{GM}{c^{2}r} > .1$. You can ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81110",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 0
} |
Why does Newton's third law exist even in non-inertial reference frames? While reviewing Newton's laws of motion I came across the statement which says Newton's laws exist only in inertial reference frames except the third one. Why is it like that?
| $\newcommand{fp}[0]{\vec{F}_\textrm{phys}}$ $\newcommand{fn}[0]{\vec{F}_\textrm{non-inertial}}$ $\newcommand{fab}[0]{\vec{F}_{AB}}$ $\newcommand{fba}[0]{\vec{F}_{BA}}$In a non-inertial frame, every object feels the physical force $\fp$, that it felt in the inertial frame, plus a force $\fn$. The non intertial force fel... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81191",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 5,
"answer_id": 3
} |
How much energy does it take to simply run forward? I'm interested in tracking as much data about my runs as I can in an effort to get faster, and while I can easily estimate energy expenditure during an uphill run due to the change in elevation, I can't estimate energy expenditure due to the requirements of just keepi... | Most of the energy of running is used to move the legs of the runner. This isn't very efficient because the legs are heavy and are being quickly accelerated and deaccelerated from the running speed. The leg muscles are very powerful but runners hit a maximum speed when most of the power of their muscles is used up movi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81251",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Calculating Rotational Inertia Using Parallel Axis Theorem I am working on the following physics problem and have run into some trouble
The figure above shows particles $1$ and $2$, each of mass $m$, attached to the ends of a rigid massless rod of length $L_1 + L_2$, with $L_1 = 20cm$ and $L_2 = 80cm$. The rod is hel... | Your problem is in the calculation of the COM. You first need to define the origin from where, you will get the COM distance by using the formula. Let the left end(particle 1) be the origin. Now, defining all distances from this origin:-
$$x_{com}=\frac{1}{M_{Total}}\Sigma{m_i r_i}=m_w(L_1+L_2)/2m_w=0.5m$$ WHICH MEANS ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81433",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Oscillation of a Bose Einstein condensate in a harmonical trap We were asked to try to make a theoretical description of the following phenomenon:
Imagine a 2D Bose Einstein condensate in equilibrium in an harmonical trap with frequency $\omega$. Suddenly the trap is shifted over a distance a along the x-axis. The cond... | From the way the question is worded, I would assume you can treat this system as a BEC wavepacket in a potential barrier, where the potential barrier is given by your harmonical trap. Since the trap is harmonic, this is in analogy to the well-known vibrational wavepackets. I would also recommend reading this paper for ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81494",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Infinite Wells and Delta Functions In considering a delta potential barrier in an infinite well, I can just enforce continuity at the potential barrier-it doesn't have to go to zero. Why then does it need to go to zero at the walls of the infinite well? These two cases seem to be very similar to be, I even feel like th... | You are confining the particle into a region of $|x|< a$ with an infinite potential that extends infinitely far for $|x|\geq a$:
Image source
Since we are confining the particle to a particular region (by applying a potential outside this region), you will never find the particle outside this region, so the wave funct... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81574",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 5,
"answer_id": 3
} |
Expansion of the Universe: Conversion of gravitational potential energy to kinetic energy? Suppose there is an object floating in space which over time begins to fall toward the source of a gravitational field. As it falls, its motion happens to be such that it gets locked in orbit around the source with a greater vel... | Gravitational potential of universe can't be defined now because the universe has been expending due to this we can't find the exist value of gravitational potential.
As the diameter of universe has being expend,gravitational potential become decrease & the gravity due to sun on all the planet would be decrease, becaus... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81695",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
Anderson localization in 1d, 2d and 3d Why in 1d and 2d systems, all states will be localized for infinitesimal disorder, but in 3d only states with energy lower below mobility edge will be localized?
| *
*1D : all states are localized
*2D : all states are localized ; the length scale of localization
grows exponentially with E and marginal dimension for the Anderson
transition
*3D : mobility edge ; finite localization for $l_B <~ \lambda/(2\pi)$
Some good references
*
*LSP et al., Phys. Rev. Lett. 98, 210401... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81833",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
When can a surface charge density exist? In my syllabus about electromagnetism, they state:
"This surface charge density will not always be present, e.g. when considering two non-conducting dielectrics such surface charge density remains absent. However, at a perfect conductor, a surface charge density will be present... | A simple line is as follows:
*
*Conductor is an equipotential volume. If there were potential difference between any two points, free charges would flow to compensate for this difference, hence produce currents. If there is a current, it produces heat. However, due to energy conservation the heat cannot be produced... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/81947",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Charged spheres - help with method to work these out? Can anyone demonstrate how to get the answers to these questions? I'm just interested in the method I need to use in order to obtain the correct answer no matter what the values are.
Three small spheres are placed at fixed points along the x-axis, whose positive dir... | Since the charges are distributed on spheres they can be considered as point charges.
Both the charges A and C will attract charge B so the force is given by subtracting these two forces vectorially
The electrostatic field due to A and C at point of B comes out to be 18 × 10^6 towards A.
Correspondingly the force exper... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/82013",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Does a heavy body move with the slightest force on a frictionless surface? If I apply horizontal force on a body resting on the ground, my force will be opposed by the frictional force and the body will accelerate at the point where my force exceeds the force of friction = $\mu\, \mathrm{N}$ ($\mathrm{N}$ being the nor... | When a force is applied to a body initially at rest for a finite amount of time, the velocity of that body is given by conservation of momentum:
$$m\Delta v = F\Delta t$$
When initial velocity is zero, $\Delta v = v$ - the final velocity is equal to the change in velocity. So we can write
$$v = \frac{F\Delta t}{m}$$
Fr... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/82071",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 0
} |
Intuitively, how can the work done on an object be equal to zero? To my understanding the work done on an object is defined mathematically as:
$$W = \vec{F}\cdot\vec{S}=|\vec{F}||\vec{S}|cos\theta$$
This, I understand. My problem is that I don't understand that if the angle $\theta$ is 90 degrees how can the work done ... | Because it's not any work, but the work done by a force that produces a displacement.
In the scenario you describe, somehow that force is not doing any work on the particle. This could be because the particle is restricted by another force to not go perpendicular and then the sum of forces in the perpendicular directi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/82196",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 7,
"answer_id": 0
} |
Does our existence cost us energy? When something needs to inform its presence, such as the electromagnetic presence of charged particles , or the gravitational presence of particles due to their mass. Is this made by sending information of its existence propagated in space via some kind of electromagnetic waves or hyp... |
Anything when it needs to inform its presense such as electromagnetic presense of charged particles and gravitational presense of particles due to their mass does so by sending information of its existencs propogated in space via means of electromagnetic waves or hypothesised gravitational waves.
Not true. Maxwell's ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/82405",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Structure factor of crystals (X-ray crystallography) How can one prove that the degree of each node in a distance graph must be at least four in order to obtain a unique solution to an exact distance geometry problem with sparse distance data?
The example in the Wikipedia article has three degrees for each node, which ... | The smallest possible case where you get ambiguity is that of 5 nodes. In the complete graph on these nodes every node has degree four. If we remove a single edge we get ambiguity (in general): it contains a complete graph on 4 nodes (the edges of a tetrahedron) and the fifth node is connected to three of the others, b... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/82503",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Angular Momentum of Two Non-interacting Particles I'm reading a book (An Introduction to Mechanics by Kleppner) where they calculate the angular momentum $l$ of a system of two non-interacting particles, but I don't understant what are they doing.
Consider two non-interacting particles with $m_1$ and $m_2$ moving towar... | Elaborating on Trimok's comment, you are mixing up $\dot{\mathbf r}$ and $\dot r$. $\dot{\mathbf r}$ is the rate of change of the separation vector, while $\dot r$ is the rate of change of the separation distance.
We can quickly see they are different. By definition, we know that $ \mathbf r = r \,\hat{\mathbf r} $. Ta... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/82582",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why does the specific thrust of an ideal turbojet drop with increasing compressor pressure ratio? As the pressure ratio increases in an ideal turbojet (fixed flight Mach number), the specific thrust, $\frac{F}{\dot{m_{air}}}$ rises, reaches a peak for small pressure ratios and then starts to decrease with increasing pr... | Increased compressor pressure ratio means increased temperature in inlet of the turbine.
Turbine has limits $T_{max}$ on inlet temperature (turbine could melt). To keep temperature in operational limits the fuel/air mass ratio $f$ is lowered at high pressure ratios.
Lowered fuel/air mass ratio $f$ means that less chemi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/82774",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Resolution of identity in interacting QFT $\mathbf{Background:}$ Consider a free scalar field $\phi$ ($\mathcal{L}_0 = \frac{1}{2}\partial_\mu \phi \partial^\mu \phi + \frac{1}{2}m^2 \phi^2$).
In the Hamiltonian viewpoint, this system has a Hilbert space $\mathcal{H}_0$ (the Fock space). We can write down a resolution... | Yes, that's still a resolution of the identity.
But knowing this isn't likely to make your life easier. The observable algebra for the free theory and the observable algebra for the interacting theory are generated by unbounded operators. These algebras do not have the same domains of definition. The 'free-particl... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/82857",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Explain reflection laws at the atomic level The "equal angles" law of refection on a flat mirror is a macroscopic phenomenon. To put it in anthropomorphic terms, how do individual photons know the orientation of the mirror so as to bounce off in the correct direction?
| According to quantum electrodynamics (QED), light can be thought of as going along all paths. However, the only paths that do not experience destructive interference are those in the neighbourhood of paths with stationary (e.g., minimal) action (time), which, in your case, is the "equal angles" path.
I strongly recomme... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83105",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "31",
"answer_count": 4,
"answer_id": 1
} |
Does antimatter curve spacetime in the opposite direction as matter? According to the Dirac equation, antimatter is the negative energy solution to the following relation:
$$E^2 = p^2 c^2 + m^2 c^4.$$
And according to general relativity, the Einstein tensor (which roughly represents the curvature of spacetime) is linea... | See also: What is anti-matter?
Currently there is no reason to believe/require antimatter has negative mass. It should therefore behave exactly the same in a gravitational field.
The matter-antimatter distinction is pretty arbitrary. We found protons/neutrons/electrons first, so particles of the same families that exhi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83307",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "28",
"answer_count": 10,
"answer_id": 3
} |
How does that Boltzmann distribution interact with entropy? In an ideal gas, the Boltzmann distribution predicts a distribution of particle energies $E_i$ proportional to $ge^{-E_i/k_bT}$.
But, doesn't entropy dictate that the system will always progress towards a state of maximum disorder? In other words the system e... | In any system in equilibrium, the entropy of such system is the maximum given a set of constrains. If you think of a microcanonical ensemble, the total energy is fixed while in an canonical ensemble of particles the temperature is the one being held constant.
This distribution probability you mention, is for a canonica... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83386",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 0
} |
Why would an object appear a different size when in water? A friend of mine has a homework question and we're having some trouble figuring out what physical mechanisms come into play for this.
An underwater swimmer sees a spherical air bubble that appears to have a diameter $d=$ 1.5 cm. What is its actual diameter?
W... | Objects do appear larger (or equivalently nearer) underwater when wearing a mask or goggles. See the image below for confirmation of this fact. Why is this?
The interface between the water and your mask obeys Snell's law which can be written, in the small angle approximation, as
$$
n_1\theta_1=n_2\theta_2.
$$
Since ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83480",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 5,
"answer_id": 0
} |
How does energy transfer between B and E in an EM standing wave? I'm trying to understand how an electric field induces a magnetic field and vice versa, its associated energy, as well as relating it to my understanding of waves on a string.
Using a standing wave as an example, I came up with the equations
$\vec{E}=A\si... | The variation of the fields over a quarter of a period looks something like this.
In the left diagram it is the magnetic field which is storing the energy of the system whilst in the right hand diagram it is the electric field.
The exchange between the electric field and magnetic field follows Maxwell's equations ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83529",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 2
} |
Does the moon affect the Earth's climate? So, this morning I was talking to a friend about astronomical observations, and he told me that lately there has only been good weather when there was a full moon in the sky, which was a shame.
I jokingly said: 'maybe there's a correlation!', but then I started thinking: wait,... | There are tides in rocks and those tides affect volcanoes and volcanoes can affect climate.
Scientists have not yet found any correlations between land tides and earthquakes but they have found a relationship between the tides and volcanic eruptions because of the movement of magma or molten rock inside volcanoes (USG... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83574",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 5,
"answer_id": 2
} |
A simple conjecture on the Chern number of a 2-level Hamiltonian $H(\mathbf{k})$? For example, let's consider a quadratic fermionic Hamiltonian on a 2D lattice with translation symmetry, and assume that the Fourier transformed Hamiltonian is described by a $2\times2$ Hermitian matrix $H(\mathbf{k})=a(\mathbf{k})\sigma_... | I just found a relative rigorous argument supporting my conjecture:
The Chern number $N=\frac{1}{2\pi}\int _{BZ}b(\mathbf{k})$, where $b(\mathbf{k})$ is the Berry curvature. Since $H(-\mathbf{k})=H(\mathbf{k})$, it's easy to show that $b(-\mathbf{k})=b(\mathbf{k})$, accordingly, we can divide the $BZ$ into two halfs ca... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83650",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 2,
"answer_id": 0
} |
What constitutes displacement current? In the chapter electromagnetic waves I was introduced with the concept of displacement current inside a capacitor. Since the region inside the capacitor is a dielectric there is no charge carriers in it. Then, what constitutes displacement current if it flows over there?
I know t... | Displacement current is not formed by a changing magnetic field. Rather, it is due to a changing electric field (between the two plates of a capacitor, maybe).
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83715",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Thin lens formula Can someone help me or guide me how the thin lens formula:
$$\frac{1}{s_1}+\frac{1}{s_0}=\frac{1}{f}$$
can be proven?
I was trying to prove it on my own using similar triangles, only to fail.
| A lot depends on how much you want to learn, just to teach elementary (geometrical) optics. There are many good books, but often they cover too much that you aren't interested in.
By far the best textbook on actual geometrical optics, relating to lens design, including aberrations etc, is one that as a mathematician,... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83751",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 4,
"answer_id": 3
} |
Can air bubbles sink at extreme depths? I was thinking earlier about air bubbles in water. if you had a bubble of air (say in a balloon) then as you take it down in water the bubble shrinks because of the pressure and because it is compressible. This means its density increases.
Water on the other hand being incompress... | We need a phase diagram for the gas in the balloon. I found one for CO2
The pressure at the bottom of the ocean can be estimated as 1 atmosphere every ten meters depth. For 4000 meter that is 400 atmospheres.
Temperatures at the bottom of the ocean are above icing, a few C, so from the diagram a balloon with CO2 rele... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83845",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 4,
"answer_id": 1
} |
Classical Wave Equation - Approximations I don't understand the derivation of the wave equation given below -
$$T \sin (\theta _1) - T \sin (\theta ) = T\tan (\theta _1 )-T\tan (\theta ) = T \left. \left(\frac{\partial f}{\partial z} \right|_{z + \Delta z} - \left. \frac{\partial f}{\partial z}\right| _z \right) = T \f... | $tan(\theta) = \frac{opposite}{adjacent} = \frac {rise}{run} = gradient$
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/83925",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
Chinook Helicopter Torque The Chinook Helicopter has 2 rotors to counteract the torque generated by spinning the blade.
Theoretically, could you use a smaller "back" rotor that is farther away from the main rotor to achieve the same result, ie no twisting?
| The interchangeability of rotors for tourque might be nearly impossible because of the ma in f=ma.The rotor speeds would have to continuously vary ideally.Now if it were just a question of lift it would be in aronautical engineering. But then again as they say ,nothing is really impossible,you just have to find a way o... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/86139",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
Proper name for a thermodynamic process with constant internal energy $U$ Back in the day I learned that a few special thermodynamical processes have special names.
For example, if one keeps $P$ constant, the process is called isobaric, if one keeps $T, V$ or $S$ constant, one gets, correspondingly, isothermic, isocho... | The process with constant internal energy is called free expansion.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/86208",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
One way insulation? I know from basic physics lessons that a box painted black will absorb heat better than a box covered in tin foil. However a box covered in tin foil will lose heat slower than a black box.
So what is the best way to conserve the temperature of a box? (aiming for 0 degrees Celsius inside the box whe... | make 1 box, with the inside and outside as reflective as possible. make a second box the same way except bigger. using magnets on all sides to 'levitate' box 1 inside of box 2. suck all the air out of box 2.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/86306",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 3,
"answer_id": 2
} |
Initialize a traveling wave in a 1D gas? I am trying to initialize a traveling wave for a 1d simulation as one can see from the attached figure.
Such that it will be traveling to the right.
However, I cannot initialize the right velocity profile, and this makes the initial pressure distribution tends to be more unifo... | We are trying to get the simple wave solution, so one can assume the dependence of the functions defining the solution (namely $u$, $p$ and $\rho$) only on a single combination of variables $x$ and $t$. In case of weak sound wave this combination would be $x - c t$, but nonlinear effects would makes this more complicat... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/86527",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Thermionic Emission: Kinetic Energy Distribution of Emitted Electrons I am having a conceptual problem understanding the kinetic energy of thermionically emitted electrons.
I know that in order to escape the surface the electrons must have energies of at least the Fermi Level plus the work function ($\varepsilon \ge \v... | The electron maintains the total energy $\epsilon$ that it had while inside the material. Inside the material it has some kinetic energy and some potential energy, but we don't really care exactly what those are since we know their sum. The point is, once it enters the vacuum, its total energy is still made up of kinet... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/86615",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Molecular rotation - Energy levels for an asymmetric molecule For a molecule with spherical symmetry, the energy level of rotation for quantum number $J$ is:
$$E(J)=\frac{J(J+1)\hbar^2}{8\pi^{2}I}$$
"$I$" is the Moment of inertia for the molecule ($I_{x}=I_{y}=I_{z}$ for a molecule with spherical symmetry)
For an asymm... | Download the file at https://www.dropbox.com/s/5l3lvqbal1ch2gm/Asymmetric%20Top.nb and run in Mathematica.
Executing the command en[3,0], for example, yields the energies and vector representations of the $J=3,m=0$ wavefunctions in the basis $$\{|3,-3,0\rangle,|3,-2,0\rangle,|3,-1,0\rangle,|3,0,0\rangle,|3,1,0\rangle,|... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/86766",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why are high voltage lines “high voltage?” If I have two spheres of the same size and one sphere has a small amount of charge compared to the other that has a lot more charge, then clearly the sphere with the larger charge has a larger voltage (relative to the ground). My question is do high voltage power lines have a ... | The voltage in electric cables has almost nothing to do with the amount of electric charge on or in some portion of the cable.
The voltage is a measure of electric potential.
Charge carriers are present in all conductors, even those that have no voltage across them. Applying a high voltage does not alter the number of ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/86974",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
Angular Displacement If something is rotating about a point and it covers a complete circle, should we take its angular displacement as 360 degree or 0?
Please give link to some established material on this subject which defines your answer, whether it is that it should be taken as 0 or 360 degrees.
Question that led ... | An angle is a ratio. The ratio of arc length to radius. So if you want to consider zero arc length or full circle is really up to you. It depends on the situation. If you are using the angle for orientation it does not matter, but if you are using it for angular displacement it depends on the initial conditions.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87057",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 3,
"answer_id": 2
} |
Could there have been two "Big Bangs"? A couple of years ago, I remember seeing a documentary on the big bang theory. The theory presented was that to explain the cosmic microwave background radiation, there needed to have been two big bangs. Is this theory legitimate? I've tried searching for details without success.
... | It is not really said that there were two big bangs. However there is a theory that multiple big bangs occurred during the beginning of the universe. Each of these gave rise to multiple bubble universes. So whether two big bangs happened, well it could be legitimate however it is not widely accepted.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87289",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 4,
"answer_id": 3
} |
Infinitesimal Lorentz transformation is antisymmetric The Minkowski metric transforms under Lorentz transformations as
\begin{align*}\eta_{\rho\sigma} = \eta_{\mu\nu}\Lambda^\mu_{\ \ \ \rho} \Lambda^\nu_{\ \ \ \sigma} \end{align*}
I want to show that under a infinitesimal transformation $\Lambda^\mu_{\ \ \ \nu}=\delta... | Note that if you lower an index of the Kronecker delta, it becomes the metric:
$\eta_{\mu\nu}\delta^{\mu}_{\rho}=\delta_{\nu\rho}=\eta_{\nu\rho}$
And in your last step you got a wrong index. It should be $\omega_{\rho\sigma}$, not $\omega^{\rho}_{\sigma}$.
Then, the metric terms cancel and you neglect cuadratic terms.... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87346",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 2,
"answer_id": 1
} |
What is negative Energy/Exotic Energy? So I have been researching around a little as I am highly interested in Astrophysics and I came across an energy I have never heard of before; negative energy also commonly known as exotic energy. Now I started to research this however I found the concept rather hard to grasp due ... | Negative energy occurs when the energy level for a given space is below that which is considered zero energy. A zero energy space is not really zero but is always full of some virtual particles popping in and out of existence.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87425",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 4,
"answer_id": 2
} |
Can sound be propagated without initial mechanical interference? I have researched up a little on sound, and it seems that sound is a mechanical wave that propagates through the air as energy, and that is how we hear it through our ears.
Depending on the medium's density, the type of wave, and the amplitude, among othe... |
In the future, please search for these answers first by e.g. looking
up "how speakers work". A quick search will bring up what you want.
An electromagnet in the speaker cone is usually fixed next to a permanent magnet. Electricity is channeled through it to create a magnetic field which, by changing polarity, can... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87562",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Mean kinetic energy according to the WKB approximation
Show that in the WKB approximation, the mean kinetic energy $T_{n1}$ in a bound state $\psi_n$ in a potential $V(x)$ is given by
$\langle T_n \rangle = \frac{1}{2}\left(n+\frac{1}{2}\right) \frac{dE_n}{dn}$
This is a homework problem and I'm having trouble unders... | The notation $T_{n1}$ may come from the fact that the mean is also referred to as the "first moment", this is what the number $1$ as a lower label might stand for. For reference, see the Wikipedia article on moments in mathematics.
Regarding the derivative of the Energy: you are supposed to formally take the derivative... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87669",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Will the heat flow of Joule heat be different, if the Joule heat is dissipated in a material that has a temperature gradient beforehand? Let us assume one dimensional heat transfer, for example a finite length wire starting at point $0$ and ending at point $\ell$. If the current passes the wire, the Joule heat $I^{2}R$... | As mentioned by Programmer, saying that if the wire temperature is constant then half of the heat will flow in either direction is incorrect. It really depends on the boundary conditions on either end of the wire (since it is of finite length). Assuming that the wire is at a spatially uniform temperature (not constant ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87825",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
Reference request for exactly solved models in statistical mechanics Can someone recommend a textbook or review article that covers exactly solved models in statistical mechanics, such as the six- or eight-vertex models? If there is literature at the undergraduate level, that would be ideal. I'm only familiar with Baxt... | How familiar are you with exact solutions to the 2D Ising model? If you don't know that forwards and backwards, I would probably start with some textbooks that cover that material in depth. This would teach you some of the basics of transfer-matrix techniques and some other tricks about estimating eigenvalues, the th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87917",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 0
} |
Photons from stars--how do they fill in such large angular distances? It would seem that far-away stars are at such a distance that I should be able to take a step to the side and not have the star's photons hit my eye. How do stars release so many photons to fill in such great angular distances?
| A very non-technical answer, but in trying to get your head around this, have you thought about the speed of light?
The angle distended by the star on your eyeball (or by your eyeball on the star) is very small. So it seems like a very tiny region of space must be 'full of photons' for the star to be constantly visibl... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/87986",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "58",
"answer_count": 7,
"answer_id": 5
} |
Gradient of a two-component field I have a two-component field:
$$\phi(\vec{x}) = \left( \begin{array}{c} \phi_1(\vec{x}) \\ \phi_2(\vec{x}) \end{array} \right)$$
with $\phi^T = (\phi_1, \phi_2)$. And I am trying to evaluate:
$$(\vec{\nabla}\phi)^T(\vec{\nabla}\phi)$$
I'm pretty sure the result of that expression is s... | When you have a matrix $\Phi = \begin{pmatrix} \phi_1\\ \phi_2\end{pmatrix}$, with one column and two rows, and its transpose matrix $\Phi^T = \begin{pmatrix} \phi_1 & \phi_2\end{pmatrix}$, with one row and two columns, the product of the two matrix $\Phi^T \Phi$ is a matrix $P$ with one column and one row:
$P =\Phi^T... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88073",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Archimedes' principle for two liquid layers
Problem: I have a cylindrical vessel of height $H$ and radius $R$. There are two liquid layers in the vessel. The first has density $D_1$ and height $h_1$, the second has density $D_2$ and height $h_2$. The second liquid is floating on the first liquid (thus $D_2 < D_1$) and... | This will help for sure. Floating between two liquids
You only have to calculate the height. And the information you get for this is enough.
I used this formula to write a program in a contest in codeforces. The problem is same as yours. No change."Cocktail"
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88233",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Electromagnetism: Conductors Even though the thermal velocity of electron in a conductor is comparatively high, the thermal velocity is not responsible for current flow? Why is this the case?
| Let's change that to "thermal velocity by itself is not responsible for current flow".
Thermal differences can produce current flow. And just like with electricity, a potential or change in thermal energy is required to convert the form of the energy to something else.
The reason heat cannot simply generate electric cu... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88392",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
The velocity of a cloud? I noticed an unusually fast moving cloud this morning.
My questions:
*
*What is the average velocity of a cloud on Earth?
*What is the greatest ever recorded cloud velocity?
*What factors affect the velocity of a cloud? (e.g. do they experience inertia?)
| It looks like there can be a difference of up to 5 m/s between cloud velocity and wind velocity (http://journals.ametsoc.org/doi/abs/10.1175/1520-0450%281976%29015%3C0010%3AWEFCMP%3E2.0.CO%3B2 ).
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88458",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 1
} |
Why is the decay of a neutral rho meson into two neutral pions forbidden? Why is the decay of a neutral rho meson into two neutral pions forbidden? (Other modes of decay are possible though.)
Is it something with conservation of isospin symmetry or something else? Please explain in a bit more detail.
| As far as I understand, due to conservation of angular momentum, the resulting system of neutral pions would need to have angular momentum 1, therefore, the identical neutral pions would be in an anti-symmetric state, which does not seem possible as they are bosons. Note that a neutral rho meson can decay into two neut... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88593",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 4,
"answer_id": 1
} |
Physics of the inverted bottle dispenser
When you invert a water-bottle in a container, the water rises and then stops at a particular level --- as soon as it touches the hole of the inverted bottle. This will happen no matter how long your water-bottle is. I understand this happens, because once the water level touch... | Other answers are right, but let me put it without math:
Water can't come out of the bottle if air can't go in.
(Except: if the water in the bottle is so tall that water can come out even if air can't go in.)
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88669",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 4,
"answer_id": 3
} |
Relationship between power and max. speed I'm talking about the maximum speed if let's say I have a car with the power $P = 1000 \text{W}$ and a force of friction of $5 \mbox{N}$ acting in the opposite direction. After some googling I found that the maximum speed is given by $P=Fv$, where $P$ is the power, $F$ is the f... | *
*The expression $P=Fv$ expresses a relation between the instantaneous power, the force and the velocity. You don't have to average for it to be true.
*In your case, the velocity in constant. This implies that the net force is zero. Hence, the force propelling the car is equal and opposite to the friction force. We ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88737",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
If a spaceship was pulled toward a sun, would it spin? I was watching a movie. A spaceship was forced into "warp speed". The co-ordinates could not be set. The spaceships trajectory was that of a nearby sun. Forcing the spaceship to power down was the solution. Now out of "warp speed" and with no computer aid (steering... | The only way for a falling object to be made to rotate and translate is if there was a separate force causing this rotation.
In an atmosphere this is a net force on one side of the craft whose surface area (and therefore drag) is the highest, causing this part of the craft to rotate away from the direction the entire ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88801",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Physical intuition for independence of components of velocity in derivation of Maxwell–Boltzmann distribution Maxwell derived the shape of the probability distribution of velocity of gas particles by starting with just two assumptions.
These are:
*
*The probability distribution is rotation invariant.
*The component... | I'm just going to quote Wikipedia here:
For the case of two colliding bodies in two dimensions, the overall velocity of each body must be split into two perpendicular velocities: one tangent to the common normal surfaces of the colliding bodies at the point of contact, the other along the line of collision. Since the ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88871",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 3,
"answer_id": 1
} |
What is the physics of a spinning coin? When we spin a coin on a table, we observe 2 things:
*
*It slows down and stops after sometime.
*It does not stay at just one point on the table but its point of contact with table changes with time.
I was trying to explain quantitatively this but I am stuck at how to take fr... | I think that if you spin "perfectly" (i.e., such that the rotational axis is normal to the surface and goes through he centre of the coin), is only a rotation movement with friction. This motion is unstable though, so, the axis tilt a little bit and this cause a rotation in the axis itself, the precession. The point of... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/88965",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "13",
"answer_count": 4,
"answer_id": 0
} |
Are coherent states of light 'classical' or 'quantum'? Coherent states of light, defined as
$$|\alpha\rangle=e^{-\frac{|\alpha|^2}{2}}\sum_{n=0}^\infty \frac{\alpha^n}{\sqrt{n!}}|n\rangle
$$
for a given complex number $\alpha$ and where $|n\rangle$ is a Fock state with $n$ photons, are usually referred to as the most c... | It is all about what meaning you put into the words "quantum" and "classical". Fock space and elements of this space are notions that belong to quantum theory of radiation and have no direct relation to states of radiation in classical electromagnetic theory, so the coherent state may be called "quantum" with good reas... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/89018",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "19",
"answer_count": 7,
"answer_id": 2
} |
Visible Lines for Hydrogen Say H atoms are excited to 4th level, n=4 that is, how many lines do we see? How to decide the number of the lines?
| An excited state electron may transition to any lower level. From n=4, the electon could go to n=3, n=2 or n=1. Of these 3 transitions, only n=4 to n=2 (wavelength 486nm) is visible light. n=4 to n=1 is ultraviolet and n=4 to n=3 is infrared.
The wavelengths of the transitions are given by the Rydberg formula.
htt... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/89288",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Question on energy mass conversion I have a question regarding the energy-mass conversion. Well, when a particle starts moving with a speed comparable to that of light, its (relativistic) mass increases that means some matter is created and that too of the same particle...energy being converted to mass is ok but how do... | If you accelerate a stone to relativistic speeds, no new atoms are created in the stone. There is constant amount of atoms. If new atoms were created, that would mean than these atoms have to disappear when you decelerate the stone. And now think about someone accelerating together with the stone. From the perspective ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/89342",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
Why are roofs blown away by wind? Whenever there are high winds, such as in storms, thin metal roofs on sheds as well as concave roofs on huts are sometimes blown away.
One explanation provided to me said that the higher velocity of the air outside causes the air pressure above the roof to decrease and when it has decr... | High speed winds are accompanied by reduced air pressure
So high pressure from inside the house pushes roof to low pressure and gets blown away.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/89570",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 4,
"answer_id": 3
} |
How can one see that the Hydrogen atom has $SO(4)$ symmetry?
*
*For solving hydrogen atom energy level by $SO(4)$ symmetry, where does the symmetry come from?
*How can one see it directly from the Hamiltonian?
| It's because there is another vector quantity $A_i$ conserved in addition to the angular momentum $L_i$. Furthermore, the commutation relations of $A_i$'s and $L_i$'s are those of $SO(4)$. See for instance this reference : http://hep.uchicago.edu/~rosner/p342/projs/weinberg.pdf
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/89654",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 3,
"answer_id": 0
} |
Why do solar cells have a window layer on top of the absorber layer and not below it? In solar cells there is a p-n junction. P-type semiconductor (for example CdTe) is often absorber layer because of its carrier lifetime and mobilities. In case of CdS/CdTe,* CdS is n-type window layer and everywhere it is said that it... | When the light strikes the P-substrate, it excites an electron. This electron either is absorbed back into the P-substrate, or it can move into the N-substrate and gets absorbed there. Once the electron has moved into the N-substrate, due to the PN junction, the easier path to balance the charges is to push electrons t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/89763",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 5,
"answer_id": 1
} |
Lorentz boost matrix in terms of four-velocity As I understand it, the value of a 4-vector $x$ in another reference frame ($x'$) with the same orientation can be derived using the Lorentz boost matrix $\bf{\lambda}$ by $x'=\lambda x$. More explicitly,
$$\begin{bmatrix}
x'_0\\
x'_1\\
x'_2\\
x'_3\\
\end{bmatrix}
=
\begin... | Take units $c=1$.
You have $U_0^2-\vec U^2=1$, that is $\gamma^2(1-\beta^2)=1$. With some basic transformations, you will get : $\frac{\gamma - 1}{\beta^2}= \frac{\gamma^2}{\gamma + 1}$
Now, from your Wikipedia matrix, you have obvious term, $ U_0 =\gamma , U_i =\gamma \beta_i$
You have $(\gamma -1) \frac{\beta_i\beta_... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/89974",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
As the universe ages, will we see more stars or less? After a very long time will we see more stars (due to the fact that more light is get to us) or less stars (as the universe expends and light have to pass larger distance)?
In general, can stellar objects go outside of the scope of the observable universe or is it o... | I red some times ago about a scenario in which the number of visible objects is becoming smaller and smaller. This is basically due to the Hubble's law: the further two objects are, the faster they move away from each other and when the speed exceed the speed of light, no news can come from them any more. If you take i... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/90024",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "18",
"answer_count": 8,
"answer_id": 4
} |
If friction disregard area, why the direction you drag a long object matters? I am talking here about dry friction between solid objects, for example a ruler and a table, not anything lubricated or fluid.
I noticed that with a ruler and a table for example, if you drag the ruler like it was a knife, it is much easier t... | Deformities in the surface cause more friction. As it's rightly said friction is a necessary evil, friction between the surface helps in forward movement as well. Like when we walk on a rough surface we get more forward push.A slippery and smooth surface is really difficult to walk on. A very nice article with Free Bod... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/90114",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 1
} |
Would a black hole created on the surface burrow through the crust? If scientists created a microscopic black hole with an initial mass of one ton on the surface of the earth, would the gravitational attraction to the center be enough for it to "burrow" until it eats its way through the crust? It seems like there would... | Black holes this small will have very high Hawking temperature:
$$
T_H = \frac{\hbar c^3}{8 \pi G M k_B} \approx 10^{20}\,\text{K},
$$
So, before this black hole can fall down even the diameter of an atom it will evaporate through Hawking radiation. As a result, the 1 tonne of black hole mass would be converted into th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/90175",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
A question about T duality Normally T-duality is introduced perturbatively by computing world-sheet spectrum of fundamental strings, and one of the conclusions is that it switches between momentum mode and winding mode of fundamental strings. My question is that does this switching extend beyond fundamental strings, na... | Yes, whenever the momentum is conserved and T-duality holds, T-duality must map a conserved quantity such as this momentum to another conserved quantity, i.e. the string winding number in this case, and this fact is independent of the carrier of the momentum or the winding charge. In the general nonperturbative case, y... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/90265",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
What is the reasoning behind the Hill Sphere? According to Wikipedia, Hill Sphere is: the volume of space around an object where the gravity of that object dominates over the gravity of a more massive but distant object around which the first object orbits.
True as this may be, it just mathematically supports a phenome... | "I mean why should the gravity of a less massive object dominate the gravity of a more massive one?"
Maybe because it's closer?
"The strength of the gravitational force between two objects depends on two factors, mass and distance."
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/90319",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 3,
"answer_id": 2
} |
Experimental evidence for non-abelian anyons? Since non-abelian anyons have become quite fashionable from the point of view of theory. I would like to know, whether there has actually been experimental confirmation of such objects.
If you could cite original literature, that would be great!
| As far as I know we do not yet have definitive verification of non-abelian statistics which would indicate the existence of non-abelian Anyons. The latest results I know about are the ones mentioned by akhmeteli and An, et. al. "Braiding of Abeliana and Non-Abelian Anyons in the Fractional Quantum Hall Effect." Arxiv:1... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/90398",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 2,
"answer_id": 1
} |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.