Q stringlengths 18 13.7k | A stringlengths 1 16.1k | meta dict |
|---|---|---|
Which temperature to evaluate fluid properties in pipe? I am always confused about which temperature to evaluate fluid properties at. Let's say I have a helical pipe and I know the inlet temperature, outlet temperature, and surface temperature and the inlet Reynold's number. I must determine the length of the pipe need... | Usually the properties are taken at mean temperature (and pressure) between in- and outlet, often by iteration. If your problem is that sensitive to changes in thermal properties I would calculate the problem sectionwise to account for the non-linearity.
When calculating Nusselt Numbers, often the wall temperature need... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106048",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Why Do Sausages Always Split Lengthwise? Sausages universally split parallel to the length of the sausage. Why is that?
| This behaviour is well explained by Barlow's formula, even though the English Wikipedia article is incomplete in this context. The German version, on the other hand, gives the full picture (which I will quote in the following).
The walls of a pipe (or a similar cylindric container, say, a sausage) experience two types... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106098",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "49",
"answer_count": 2,
"answer_id": 0
} |
Speed of light originating from a star with gravitational pull close to black-hole strength? Imagine you have a star which is on the brink of turning into a black hole. Lets say it is infinitely close to become a black hole, but not there yet.
Since there is no event horizon, but a great gravity pull. Will the speed of... | The speed of light is a constant regardless of where or when you measure it. The speed of the light as it leaves the star will be $c=299792458\frac{m}{s}$. The speed of the same light far from the star will also be $c$.
Instead of slowing down like newtonian objects, the light will instead lose energy as it attempts to... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106224",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Can entropy of Universe be constant? If I understand entropy correctly, then for example two objects orbiting a centre of mass have lower entropy than when said objects eventually crash into each other and form a new one.
So let's say that a typical galaxy spirals around its centre of mass and eventually objects within... | Yes it can be, if the Universe attains equilibrium.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106376",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 5,
"answer_id": 4
} |
Non-unique pressure for Navier-Stokes for incompressible fluid The Navier-Stokes system for incompressible fluid says
$$
\begin{aligned}
\dot{\mathbf{u}} + (\mathbf{u}\cdot\nabla)\mathbf{u}-\nu\Delta\mathbf{u}+\nabla{p} &= 0,\\
\nabla\cdot\mathbf{u}&=0.
\end{aligned}
$$
The non-slip boundary condition for the velocity ... | As long as we are far from compressible effects (low Mach) and the 0 pressure under which cavitation may appear, yes, pressure is defined up to a constant if boundary conditions are given in terms of velocity. If you provide boundary condition in terms of normal stress (e.g. at an inlet), then you provide a pressure va... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106518",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 1
} |
Has the collapse of wave function due to observation been recorded? I've seen pictures like this one,
which depict the outcome of the Double-slit experiment with wave-like or particle features, depending how measurement has taken place.
The graphic showing multiple 'straight' lines on the detecting screen depicts the... | You will not easily find the second one because in a sense it is trivial.
Here is the single slit and double slit pattern from wikipedia
.
If you try to detect which slit the particle went through you get two single slits except for some experiments that are very careful not to disturb too much the wave functions of ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106560",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 2,
"answer_id": 1
} |
How to express magnetic field vector in terms of force on current I am preparing for an exam and one of the questions I have come across asks:
Define the electric field $\mathbf{E}$ and the magnetic flux density $\mathbf{B}$, in terms of the force on charges and currents.
By the Lorentz force law we have:
$$\mathbf{F... | The Biot-Savart law expresses the magnetic field in terms of the current as,
$$
\mathbf{B}=\frac{\mu_0}{4\pi}\int_C\frac{I\,d\mathbf{l}\times\mathbf{r}}{|\mathbf{r}|^3}
$$
which does not account for any forces, just the current, $I$. You might be able to solve $\mathbf B$ in terms of $\mathbf F$ and $\mathbf I$ using s... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106781",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 1
} |
Majorara mass and fermion number violation How can it be shown that the Majorana mass violates the fermion number by two units? Can even a Noether charge be defined in presence of Majorana mass term?
| In the Standard Model, fermion number is not conserved. Lepton number is conserved, because of an accidental symmetry. One cannot write down a renormalizable, gauge and Lorentz invariant operator that violates lepton number conservation in the Standard Model.
A Majorana neutrino would violate lepton number conservation... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106866",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 0
} |
Electrostatic and gravitational forces? Electrostatic force between two charged particles depends on the magnitude of the charges and the distance between them. If the charges have mass $m$ and $m'$ then, what will be the total force including gravitational and electrostatics forces? Distance between them is $d$.
| The magnitude of gravitational force between them would be: $$G\frac{mm'}{d^2}$$
The magnitude of electrostatic force, if the magnitude of charge on them is $q$ and $q'$ respectively, would be: $$\frac{1}{4\pi \epsilon _o}\frac{qq'}{d^2}$$
The net force would just be the vector sum of the two.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/106947",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Would QM be detectable in a all boson universe If there was a universe with the same laws as this one, but there were only bosons in it, would QM 'do anything'?
Would there be any QM effects - such as an energy level (but that would require fermions..).
| The existence of "bosons" is already a consequence of QM -- the notion of indistinguishable particles and the resulting Bose-Einstein (as opposed to Maxwell-Boltzmann) statistics is manifestly not a classical phenomena. Classical particles are always distinguishable, since "that particle there" has a complete set of ob... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107029",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
CCD's and the photoelectric effect Do charge coupled devices as found in telescopes use the photoelectric effect if not what eles librates the electons. Also what is charge intergration in reation to CCD's.
| First question: depends on your definition of photoelectric effect. In a CCD a photon is absorbed, and the energy given to an electron which is then promoted out of the Fermi sea, just as happens in the traditional experiment of a metal in a vacuum. However, in a CCD, the electron has only enough energy to get to th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107104",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Will an anti-neutron annihilate a regular neutron even though they have no charge Since neutrons have no electric charge will an anti-neutron annihilate when it comes into contact with a regular neutron as protons and anti-protons do? if so what causes it to annihilate?
| Yes it will. Annihilation is a form of interaction which only happens between a particle and its anti-particle. You can sort of imagine it even though its not completely true I think, as destructive interference of the same particle field. Its independent of charge.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107186",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Force exerted on ceiling by a simple mecahnical system I have a simple static mechanical system, but I reach a conclusion that seems to me counter-intuitive:
There is a pulley fixed to the ceiling and there is a weight fixed to a rope which goes through the pulley and is fixed to a point on the floor. I denote by $T$ ... | The rope on the left pulls the weight and the pulley towards each other. The rope on the right pulls the floor and the pulley towards each other. Each of these pull downwards on the pulley with force $T$. The total downward force on the pulley is $2T$.
The pulley doesn't move because the ceiling pulls upward on it hard... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107259",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Sum of acceleration vectors If a point mass has some accelerations $\mathbf{a_1} $ and $\mathbf{a_2} $, why is mathematically true that the "total" acceleration is $\mathbf{a}= \mathbf {a_1}+\mathbf {a_2}$?
| It makes no sense for a point mass to have 2 accelerations. What you might have done is find accelerations due to 2 forces separately. You can add them as when $m= \text{constant}$,
$\vec{F}=\vec{F_1}+\vec{F_2}=m(\vec{a_1}+\vec{a_2})$
When using vectors symbol, its automatically takes care of their directions.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107383",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 0
} |
Minkowski Metric Signature When I learned about the Minkowski Space and it's coordinates, it was explained such that the metric turns out to be $$ ds^{2} = -(c^{2}dx^{0})^{2} +(dx^{1})^{2} + (dx^{2})^{2} + (dx^{3})^{2} $$ where $ x^0,x^1,x^2,x^3 $ come from $ x^{\mu} : \mu = 0,1,2,3 $, and $ c $ is the speed of light... | Someone gave me the following nice picture that always stuck afterwards:
A light source in vacuum turned on at the point $(x_0,y_0,z_0)$ at time $t_0$ will form a sphere growing at the speed of light with radius $r = c (t-t_0)$. The equation for the sphere for $x = x(t)$, $y = y(t)$, $z = z(t)$ is
$$
r^2 = c^2(t-t_0)^2... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107443",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "19",
"answer_count": 9,
"answer_id": 2
} |
Significant digits of time divided by 10 We're testing the period of a pendulum in physics class by measuring the time it takes to complete 10 periods then dividing that by 10. Our timing equipment measures to the nearest 100th of a second.
There's a big debate at school over whether or not we can go into precision of ... | Yes, if you measure 10 periods at four digits precision, then after dividing by the 10 (an exact integer) you're still good to four digits.
Imagine if instead of a pendulum, you were measuring radio waves at several MHz. You measure let's say exactly one billion cycles using your timer good to 100ths of a second. Div... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107497",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
When do stars become red giants? I am a bit confused when do stars become red giants? Is it just after they have finished core H burning and the core contracts creating high temperatures which result in core He burning to occur which creates outward pressures pushing the outer lowers apart or something different? Also ... | Red giants are caused as outward forces become greater than gravity can pull inwards. This could be caused by stars loosing mass as the reactions take place or through more energetic reactions starting.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107574",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Maxwell's Equations: Induction What is the reason for some writing Faraday's Induction Law as $$ \nabla \times E= -\frac{1}{c}\frac{\partial B}{\partial t} $$ versus $$ \nabla \times E= -\frac{\partial B}{\partial t} ?$$
| Argue by dimensional analysis. The force on a charged particle is usually taken to be $$\mathbf F = q(\mathbf E + \mathbf v \times \mathbf B)$$ and this defines the $\mathbf E$ and $\mathbf B$ fields. With this definition $[\mathbf E] = [c][\mathbf B]$. However you could take as definition $$\mathbf F = q(\mathbf E + \... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107672",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Pseudocubic unit cells: how to construct one? I keep coming across the term pseudocubic unit cell while reading about orthorhombic perovskite structures. No clear explanation is given in papers. Can someone please tell me how these structures are generated and what exactly is meant by them?
| I personally think the introduction of the pseudo-cubic unit cell is for the purpose of better reflecting the phase transition. For example, when you have cubic to orthorhombic transition, you can say that the unit cell is still "cubic", with respect to the changing of the unit vectors length. Then if looking at the di... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107757",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Friction fire lighting Having watched a few youtube guides on making a fire by friction, namely the spindle and fireboard method, I've heard many of the instructors talk about how the shape of the spindle at its ends should be point-like at the top and blunt/round at the bottom. They then go attribute this to the idea ... | Well, I'm not sure if you can use the ideal friction for this case. But the surface area does matter, if you want to light something up.
Given the same normal force over 2 different surface areas, you would experience the same resistive force right? So given the same moving velocity (simplification), the power dissipat... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107838",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Why is the black body radiation so important? In the derivation of the black-body radiation formula the assumption is made that the system is an electromagnetic cavity, so that it can be considered in thermal equilibrium.
Leaving aside the fact that I don't see why one would make that assumption (what are its mathemati... | Among other reasons stated in the answers and the commments, here is another very important reason for why we care about blackbody radiation:
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/107907",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 3,
"answer_id": 2
} |
Interpretation of Heisenberg's uncertainty principle Heisenberg's uncertainty principle is one of the most fundamental principles on which quantum mechanics is based on. But it is also one of the most confusing laws we encounter. My doubt is whether the uncertainty is due to observation error or due to dual nature of m... | Uncertainty principle is due to intrinsic uncertainty of nature.
Yes, at any given time a particle exists both as a particle and a wave combined. Following part of your question is related to the complementarity principle (of the most accepted Copenhagen interpretation of quantum mechanics) claims that wave and particl... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/108071",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Diagonalization of Hamiltonian Typically, one way of understanding the physics of an interacting quantum system is by diagonalizing the Hamiltonian. In principle, can we always diagonalize a Hamiltonian, such that it is expressed in terms of non-interacting particle states? If so, is the diagonalization unique?
| In Mahan may-particle physics P15:
(for bilinear Hamiltonian)It is only necessary to find the eigenvalues of the Hamiltonian matrix. Usually the matrix is of infinite dimensionality. But one may often diagonalize it exactly for many problems. Computers allow very accurate solutions for any case of interest. If all Ham... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/108154",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 1,
"answer_id": 0
} |
How come a whistling kettle starts whistling only when water boils, and not long before - due to hot air escaping under pressure? A whistling kettle will start to whistle when the water boils and turns into a jet of steam which then exits the small aperture in the spout.
But why doesn't this happen much earlier - when ... | Before the water boils, the rate that the water becomes water vapor is slow compared to after it is boiling. The pressure inside the kettle does not increase significantly until after the water is boiling. Only after the water is boiling, is there enough pressure inside the kettle to send a stream of air through the wh... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/108282",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 2,
"answer_id": 1
} |
What is the notion of a spatial angle in general relativity? Is there a notion of spatial angles in general relativity?
Example:
The world line of a photon is given by $x^{\mu}(\lambda)$. Suppose it flies into my lab where I have a mirror. I align the mirror in such a way, that I measure a right angle between the incom... | If it is a photon, then you know that $x^{a}x_{a}$ is always zero. You have measured the spatial direction of the photon with your mirror apparatus, so you know the values of the $x^{i}(0)$ at some time${}^{1}$, which we will call zero. Furthermore, we can infer the value of $x^{0}$ at this time from the fact that $x... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/108359",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 0
} |
Intuitively what's the relationship between forces and connections? In Einstein's General Relativity we relate the effects of gravity with the curvature of the Levi-Civita connection on the spacetime manifold. Also, when we get the electromagnetic tensor $F = dA$ where $A$ is the $4$-potential, I've heard it's possible... | Following Cunningham's Law, here is a probably somewhat wrong answer:
When spacetime/our gauge bundle is flat, we do not really need
connections. Even if we write down our theory in general terms which
includes connections, there is a choice of local coordinate systems where the
connection vanishes everywhere. The d... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/108550",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 2,
"answer_id": 1
} |
Uncertainty of permittivity of vacuum Question: The value of permittivity of vacuum, $\epsilon_0$, is given with absolutely no uncertainty in NIST
Why is this the case?
More details:
The permeability of vacuum can be given by
$$\mu_0=\frac{1}{\epsilon_0 c^2}$$
which comes from the definition of a magnetic field in sp... | Just to add to Danu's Answer, which I believe to be right. The relative scalings of the "electro" and "magnetism" parts of the unified electromagnetism whole are somewhat arbitrary; we're only required to ensure that $c=\frac{1}{\sqrt{\mu_0\,\epsilon_0}}$ to achieve a valid set of Maxwell equations.
As we change these... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/108626",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 2
} |
Why must spacecraft reach escape velocity to escape Earth (or any other big object)? I think I have learned in physics that escape velocity is defined as the speed at which objects going ballistic in the opposite direction of the main gravitational force are able to finally overcome that force (assuming the simplest ca... | You're absolutely correct - objects do not need to ever reach earth's escape velocity of 11.2 km/s, and many spacecraft that leave orbit, don't.
That being said, note that escape velocity depends on where you are: the velocity that a cannonball 1000 km above the earth's surface would need to escape is substantially low... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/108865",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Constant of motion An exercise from Goldstein (9.31-3rd Ed) asks to show that for a one-dimensional harmonic oscillator $u(q,p,t)$ is a constant of motion where
$$
u(q,p,t)=\ln(p+im\omega q)-i\omega t
$$
and $\omega=(k/m)^{1/2}$. The demonstration is easy but the physical significance of the constant of motion is not s... | It is a functional combination of other constants: the energy (another constant of motion) and the initial condition. This would be the same as proving that, in classical mechanics, $E^2 + \log(L)$ with $L$ being the total angular momentum is a constant. It does not hold any new physical meaning, further than what you ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/108928",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Simulating electrical sublimation of aluminium foil When i apply high voltage (through a capacitor bank) across an aluminium foil, it gets converted into plasma. I want to simulate this process and study the properties of the plasma produced henceforth. I would then like to change my experimental parameter and see if m... | That's a lofty goal for someone with no knowledge of plasma physics. I suggest you contact a group that has already been working on this and offer their code for free use:
Our most recent, popular and well kept up codes are on bounded plasma,
plasma device codes XPDP1, XPDC1, XPDS1, and XPDP2. The P, C, and S
mea... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109013",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What are threshold corrections? As the title goes, what are threshold corrections in quantum field theory?
In particular, I would be glad if a good reference is provided. Standard QFT books such as Peskin, Weinberg, etc seem to have nothing to say about them.
| Threshold corrections are the finite renormalization corrections coming from fields that were integrated out in an effective field theory (EFT).
First you have to realize that constants appearing in the Lagrangian are defined just in the given theory even if both would use the same experiments to derive their values. E... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109065",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 2,
"answer_id": 1
} |
Why maximum energy transfer at natural frequency even if max amplitude occurs below $f_0$ This is a paragraph from my book:
"For a damped system, the resonant frequency at which the amplitude is a maximum is lower than the natural frequency.However, maximum transfer of energy, or energy resonance always occurs when app... | Interesting question. Note that the power transfer is $$P=\frac{1}{\tau}\int_0^\tau F(t)v(t)\,\mathrm dt$$
where $F(t)$ is the applied force, $v(t)$ is the velocity of the oscillation, and $\tau$ is the length of the period of the oscillation (this is just a simple extension of the usual rule for work, $w=Fd$, to time-... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109242",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 0
} |
Why the generators of boosts transform like a vector under rotation? $$\left[J_i,J_j \right]=i\epsilon_{ijk}J_k$$
$$\left[J_i,M_j \right]=i\epsilon_{ijk}M_k$$
$$\left[M_i,M_j \right]=-i\epsilon_{ijk}J_k$$
where $J_i$ is the generator of rotation of Lorentz group, $M_i$ is the generator of boost of Lorentz group
In many... | The important fact is that the change of an object $O$ under an infinitesimal transformation generated by a generator $G$ can be written in terms of their commutator (infinitesimal parameter $\alpha$):
$$O\longrightarrow O + \delta O\enspace\,\,\text{where}\enspace\,\, \delta O = i\alpha [G,\,O]$$
(to prove this, see J... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109346",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 2,
"answer_id": 1
} |
Hamilton-Jacobi equation with time dependent Hamiltonian I was struggling with this exercise about Hamilton-Jacobi equation. I have to solve by means of Hamilton's principal function the system with Hamiltonian:
$$\tag{1}
H=\frac{p^2}{2m}-mAtx
$$
with $A$ constant and initial conditions $t=0$, $x=0$, $p=mv_0$. Before a... | I'm a bit late to the party, but for future reference of other students stuck in this problem, you can easily find a solution if you assume a solution for $S$ in the form of $$S(x,t) = x\cdot f'(t) + g(t)$$
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109598",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 2,
"answer_id": 1
} |
Range of poissons ratio I know the range of poisson's ratio is -1 to 0.5 but how do you arrive at this expression? I am a 11th grade student and I am not too familiar with advanced physics
| The answer is a bit lengthy, but can be arrived at using arguments about elastic strain energy. Here is a very detailed explanation:
Limits of Poisson's ratio in isotropic solid
This was written at a graduate mechanical engineering level, so I'll simplify it here.
Imagine that there exists a function $\psi$ that descri... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109705",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Could you theoretically map the internal distribution of mass in a black hole using Hawking radiation? Assuming you could measure the qualities of the radiation emanating from all around a black hole, could this be used to determine the internal geometry or makeup of the mass inside?
| In principle yes. But it is very, very hard:
Computational Complexity and Black Hole Horizons
Quote from the paper:
Representing bulk physics by boundary data at a fixed time is difficult
for well known reasons. It is especially difficult to represent the bulk
degrees of freedom behind the horizon. And finally it is
e... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109759",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 2,
"answer_id": 0
} |
Infinite potential well with barrier in the middle- symmetric So I'm having problems with the double infinite potential well given by
$$V(x)= \left\{\begin{array}{ll}
\infty & -\infty < x < -a-b \\
0 & -a-b< x < -a \\
V_0 & -a < x < a \\
0 & a < x < a + b \\
\infty & a+b < x < \infty \\
\end{array}\right.$$
I have to u... | One of the important condition to get the relationship between $A$ and $B$ in the left region (or in other words to get that the wave function there is proportional to $\sin(x-(-a-b))$ is to realize that the wave function must be zero for $x<-a-b$, because the potential is infinite there. Thus we have that $\psi_1|_{x=... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109851",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Does electricity flow on the surface of a wire or in the interior? I was having a conversation with my father and father-in-law, both of whom are in electric related work, and we came to a point where none of us knew how to proceed. I was under the impression that electricity travels on the surface while they thought ... | As already mentioned, the conductivity is both theoretically and empirically proportional to the cross-sectional area, not the circumference. An intuitive explanation (for DC or low frequency AC) results from the forces between moving electrons as opposed to static ones. Think of it as Ampere's Law, Maxwell's Equatio... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109897",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "64",
"answer_count": 9,
"answer_id": 4
} |
How can a star emit light if it is in Plasma state?
*
*I understand that star is in Plasma state (all nucleus and electrons are not bound to each other and moving around freely)
*Photon is emitted when an excited electron moves back to lower orbit.
*So in a star if electrons are not in any orbit then how can photon... | Thanks for a great question, and thanks to everyone for great answers! :-)
A very simple answer is, as someone above has already mentioned, there are lots of collisions of nuclei happening in a star. When these nuclei fuse, the binding energy is given off (this is the energy we get from fusion); and photons are also gi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/109964",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "20",
"answer_count": 4,
"answer_id": 3
} |
Is the neutral pion a singlet? In Griffiths' Introduction to Elementary Particles, it is mentioned p. 179 that the $\pi^0$ is a singlet under $SU(2)$ isospin. But it is also part of the $\pi^-,\pi^0,\pi^+$ isospin triplet. How can it be both?
Don't particles of a given $SU(2)$ multiplet mix under a corresponding trans... | The pi zero is not a singlet, but part of an Ispin triplet. The eta meson and the omega meson are Ispin SU(2) singlets.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110025",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 3,
"answer_id": 2
} |
What is the difference between these two Feynman diagrams? In which direction is time flowing and what reactions do they represent?
EDIT for Gigi (I could not add a comment to your answer):
1) Do Feynman diagrams by definition only show fundamental particles?
2) why does the second diagram show how neutrons transform ... | As this is homework, the answers are supposed to guide you into thinking for yourself.
Feynman diagrams are read any logical way, if the lines represent elementary particles.
First of all one must choose the lines that comes first in time, the incoming particles.
In this simple example, if one takes the time axis as ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110112",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
Optics biconvex and plano convex What is the resultant focal length If a biconvex lens is cut into half and then the resulting 2 plano-convex lens arranged in such a way that the plane surface of one faces the curved surface of the other plano-convex lens considering the focal length of the plano-convex lens to be f.
| If the cut is perpendicular to the axis, then the combined focus length of the 2 (co-axial) lens will be the same as the original lens, whichever way you line them up.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110239",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Kolmogorov/Energy spectrum for turbulent boundary layer Previously, I have calculated energy spectrum for 3D isotropic turbulent flow data which is equally spaced in all three directions and then to compute the energy spectrum, one performs Fourier transform and then accumulates energy located in different wavenumber b... | Usually near wall turbulence is thought about using the Law of the Wall where the distance from the wall enforces a maximum length scale for isotropic motion.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110310",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 1,
"answer_id": 0
} |
Lorentz invariance? What exactly is meant by Lorentz invariance?
Is it just an experimental observation, or is there a theory that postulates it?
What quantities do we expect to be Lorentz invariant?
Charge? Charge densities? Forces? Lagrangians?
|
What exactly is meant by Lorentz invariance?
A physical quantity that is unchanged by a Lorentz transformation, i.e., a coordinate system (or frame) independent quantity that is independent of the spacetime coordinates. Another term used is Lorentz scalar.
Often Lorentz invariant quantities are prefixed with the wor... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110547",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Electric potential is zero but non zero electric field? What is the physical significance of such a point where electric field is non-zero but electric potential is zero? I mean, how can we understand this concept without mathematics?
| My thoughts on the intuition behind it:
-Think of a dipole formed by two charges with equal magnitude. Now, take a point equally distanced from both, this will lead us to a point where the electric potential is zero and non-zero electric field. Now think about a test charge in infinity and the displacement vector forme... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110610",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 5,
"answer_id": 4
} |
Is gravitational time dilation different from other forms of time dilation? Is gravitational time dilation caused by gravity, or is it an effect of the inertial force caused by gravity?
Is gravitational time dilation fundamentally different from time dilation due to acceleration, are they the same but examples of dif... | Gravity is a inertial force where reference frame is Spacetime. So, Gravitational Time Dilation and Time Dilation due to accelerated frame are both same.
And yes, you can recreate same kind of Time Dilation using centrifugal force.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110669",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "34",
"answer_count": 5,
"answer_id": 2
} |
Show that two families of curves are orthogonal (without using orthogonal trajectories) I'm reading through Hartle's General Relativity and came across this question:
Consider the following coordinate transformation from rectangular coordinates $(x,y)$, labeling points in the plane to a new set of coordinates $(m,n)$... | $$dx= ndm + m dn\:,\quad dy = mdm -ndn$$
hence
$$dx^2 + dy^2 = n^2 dm^2 + m^2 dn^2 + 2nm dn dm + m^2 dm^2 + n^2 dn^2 - 2nm dn dm \:.$$ We conclude that:
$$ds^2 = (n^2 +m^2)(dm^2 + dn^2)$$
and there is no $dn\: dm$ term in the metric as stated.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110837",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
If a neutrino has a rest frame, why can't a photon have a rest frame as well? Concerning Rest Frame Wikipedia states:
For example, in the rest frame of a neutrino particle travelling from the Crab Nebula supernova to Earth the supernova occurred in the 11th Century AD only a short while before the light reached Eart... | Disclaimer: in this answer “photon” refers to an excitation of electromagnetic field, not to a fundamental particle as understood in QED and Standard Model.
Possibly unexpectedly for some readers, a photon can have its rest frame in a homogeneous medium that moves w.r.t. the frame with speed equal to the light speed in... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/110968",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 3,
"answer_id": 2
} |
Does Feynman path integral include discontinuous trajectories? While reading this derivation of relation of Schrödinger equation to Feynman path integral, I noticed that $q_i$ can differ form $q_{i+1}$ very much, and when the limit of $N\to\infty$ is taken, there remain lots of paths, which are discontinuous (almost) e... | The discontinuous paths do 'disappear' when you take the continuum limit. They contribute nothing to the integral in the end. In the Euclidean picture, they are suppressed by the kinetic term in $e^{-S(\phi)}$, which looks like $\sum_t \frac{(\phi(t+a) - \phi(t))^2}{a}$.
The measure you define by taking this limit is... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111020",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 1,
"answer_id": 0
} |
Is there a simple layman way to explain the incompatibilities between quantum mechanics and (general) relativity to high school students? Is there a simple layman way that I can use to explain the incompatibilities between quantum mechanics and (general) relativity to high school students (people with not much knowledg... | Probably no simple explanation. It is however important to emphasize that the incompatibility applies only to general relativity. The special relativity and quantum mechanics are very compatible and were luckily married many decades ago, giving birth to the quantum field theory which is an incredibly successful framewo... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111128",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 2,
"answer_id": 1
} |
How do traveling waves pass through a standing wave node, if the node doesn't move? I'm having trouble with the explanation that a standing wave in a string is the superposition of traveling waves.
(source: physicsclassroom.com)
The nodes in the diagram above are points where the particles of the string's medium unde... | As @auxsvr says.There is a contradiction between "traveling wave", which does not have stationary nodes, and the diagram you are displaying, which is of a standing wave.
Here is a standing wave:
The energy is stationary in the x direction, that is why nodes are formed .
Here is an animation of a traveling wave:
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111260",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 6,
"answer_id": 3
} |
Do these cars rotate on themselves? I was reading about the moon rotation around earth and the tidal lock related. I found some interesting information already here and on astronomy.stackexchange.com as well. The moon is known to have a full rotation period of ~27 days.
However I really can't wrap my head about this.
L... | After reading this and this very briefly I found out that there needs to be a significantly massive body with significant variation of gravity from the near to far end, that is a gravitation gradient, since such a gradient will not be present for a small aeroplane or a bus which is pretty much blown out of proportion i... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111322",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 3
} |
How does a spinning electron produce a magnetic field? I learned in my undergraduate physics class that atoms have magnetic fields produced by the orbit of electrons and the spin of electrons. I understand how an orbit can induce a magnetic field because a charge moving in a circle is the same as a loop of current.
Wh... | I really like the explanation on or about 29:30 of this older video. He causes the electrons to start spinning around the torus with the magnet, trapping the magnetic field lines orthogonal to the spinning electrons.
https://www.youtube.com/watch?v=BFdq6IecUJc#t=1729
In his words "As the magnet is removed, the magnet... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111538",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "14",
"answer_count": 8,
"answer_id": 6
} |
How to do calculation in relativity of simultaneity I have great trouble in understanding simultaneity in special relativity. Let me illustrate it with a concrete example.
Assuming there is a train, its two end points are $A$ and $B$, the length of the train is $x$. The train moves at speed $v$. Assuming the train is m... | The Fabri's explanation is complete, but, if someone need numbers, we can use an interactive construction https://www.geogebra.org/m/duvwkba7
Now, the interactive construction is public. Sorry. The construction is the reproduction of Fabri' images (answer Oct 22 '18 at 7:08), adding numeric cohordinates. K and K' are ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111597",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 5,
"answer_id": 3
} |
Is there a giant cloud of antimatter at centre of the Milky Way Among others, this page says there is a giant cloud of antimatter at centre of the Milky Way, which was discovered in the 1970s.
My brother doesn't believe there is any such cloud. I'm prepared to believe it does exist, but can anyone explain in simple ter... | Introduction:
Yes it could be. If astronomers are sure that they can see gamma rays that are produced in matter-antimatter annihilation then yes. (unless that gamma rays are produced in star explosion). Produced energy can be described using Einstein's 'most famous' equation $E=mc^2$ (as page that you have mentioned sa... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111663",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 3,
"answer_id": 2
} |
Question about (complex) motion of Moon In an ideal situation, we can use a simple formula to determine the velocity at which a body revolves around a massive body at a particular distance. I was wondering if there is an intuitive way to understand the motion of a body influenced by two other massive bodies (say the mo... | First of all, you have to be familiar with uniform circular motion (UCM) and the law of universal gravitation. $$\Sigma F=ma$$$$G\frac{m_1m_2}{r^2}=m_1\frac{v^2}{r}$$where $G$ is the gravitational constant, or $6.67\times10^{-11}$, $r$ is the distance between the centers of the two bodies, v is the velocity, and $m_1$ ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111806",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
Radiative Electric and Manetic field from an accelerating electron Note: I've started a meta post to discuss this type of question. Yes, it looks like it's straight out of a worksheet from a physics class. That's because it is, and it's also why I posted the answer as well. Ok, now on to the question.
| a) The time it will take for the detectors to detect it will always be
$$\frac{\text{Distance from detectors}}{\text{Speed of light}} = \frac{10m}{3*10^8 \frac{m}{s}} \approx\boxed{ 3.3333× 10^-8}$$
b) We can start out using the equation:
$$\vec E_{rad} = \frac{1}{4 \pi \epsilon_0}\frac{-q \vec a_{\perp}}{c^2r}$$
$$\... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111890",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Two springs and a mass between length L I am trying to solve the problem that is depicted below;
I am writing the equations with state variables as $x_2$ and $v_2$within the matrix form as;
$$\begin{align*}\dot{x_2} &= v_2\\
\Sigma F_2 &= m_2a_2 \\
\dot{v_2} &= -\frac{k_1}{m_2}x_1-\frac{k_3}{m_2}x_3\end{align*}$$
from... | after comments of nivag and davePhD I think the answer is;
$\begin{align*}\dot{x} &= v \\
\dot{v} &=-\frac{k_1+k_3}{m}x\end{align*} $
so the matrix $A$ can be written as;
$\begin{bmatrix} \dot{x} \\ \dot{v} \end{bmatrix} = \begin{bmatrix} 0&1\\ -\frac{(k_1 + k_3)}{m}&0\end{bmatrix} \cdot \begin{bmatrix}x\\v\end{bmatri... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111938",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Faraday's Law - recursive? So we know that the EMF is induced by change of flux. The thing that was always confusing me is the following:
*
*we start changing the magnetic field
*which in turn induces electric field which makes charge carriers move
*this e-field also, in turn, makes another magnetic field that ch... | The below two equations :
$$\nabla\!\times\!\vec{E} = -\frac{\partial \vec{B}}{\partial t} $$
and
$$\nabla\!\times\!\vec{B} = \mu_0\vec{J} + \mu_0\epsilon_0\frac{\partial \vec{E}}{\partial t} $$
show how electromagnetic waves propagate. The second term in the second equation in particular is necessary for the propagati... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/111998",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 2
} |
Bending of a spline The introduction section on this page states: "the spline will take a shape that minimizes the bending", while showing the formula for curvature of a real curve.
Question is, what is the formula for the bending that is to be minimized, the curvature is a function rather than a number?! Is it some in... | The stored energy in a spline goes as the inverse square of the radius of curvature - so if you want to minimize the energy, you want to minimize
$$\int \frac{ds}{r(s)^2}$$
where $s$ is taken along the length of the spline, and $r$ is the local radius of curvature.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/112229",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What is the first non-vanishing multipole moment of this configuration? Imagine that you have a triangle where each side has the length $a$ and a charge $q$ sitting at every vertex. Additionally, we have a charge $-3q$ sitting in the center of the triangle. What is the first non-vanishing multipole moment?
I thought th... | It has a non-zero quadrupole moment. The easiest way to see this (Other then computing it) is to consider the expansion of the potential near a point perpendicular to the plane of the triangle and passing through the centre. If you place the origin of the coordinate system also at the origin then the radius vectors of ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/112360",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Why are there gapless excitations in the anti-ferromagnetic Heisenberg model while the true ground state is a singlet? The true ground state of the anti ferromagnetic quantum Heisenberg Model (nearest neighbor only)is known to be a singlet (I think this is Liebs theorem.)
Since a singlet is invariant under rotations, t... | You are correct that Goldstone's theorem does not apply to the 1-D Heisenberg chain, or indeed to any local 1-D system, because there is no continuous symmetry breaking in 1-D for local Hamiltonians. But Goldstone modes are not the only possible kinds of gapless excitations - you don't need continuous SSB for a system... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/112441",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 2,
"answer_id": 0
} |
How long does it take to optimally change position and velocity? A spaceship moving in two dimensions is at position $(x, y)$ and has a velocity $(v_x, v_y)$. It also has a maximum acceleration $a_{max}$. Its goal is to be at position $(x', y')$ with a velocity of $(v'_x, y'_x)$. What path takes the smallest amount of ... | Your hunch is correct. The optimal solution is acceleration at $a_{max}$ followed by deceleration. The correct ratio (and direction) of the two depends on the relative initial and final velocities.
For the 1D case with velocity changing from $v_i$ to $v_f$, from position $x_i$ to $x_f$, accelerating for $t_1$ and decel... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/112687",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 1
} |
If I'm floating in space and I turn on a flashlight, will I accelerate? Photons have no mass but they can push things, as evidenced by laser propulsion.
Can photons push the source which is emitting them? If yes, will a more intense flashlight accelerate me more? Does the wavelength of the light matter? Is this practi... |
Can photons push the source which is emitting them?
Yes.
If yes, will a more intense flashlight accelerate me more?
Yes
Does the wavelength of the light matter?
No
Is this practical for space propulsion?
Probably not
Doesn't it defy the law of momentum conservation?
No
In fact that last question is the key o... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/112866",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "60",
"answer_count": 4,
"answer_id": 0
} |
Significant figures in measurement with error Someone can explain me what's the rule behind the correct expression of a quantity $K$ with its error $\Delta K$ as $K \pm \Delta K$?
They must have the same number of significant figures? Or the error should have in general 1-2 significant figures? For example, if I have:... | Error is usually express as 1 or 2 significant figures.
4 significant figures are too many, because it is unreasonable to think the error could be quantified to such a degree.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113014",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
How does the boiling time depend on the amount of water? For example we have 1 electric kettle with 1 litter of water and we have another (the same type) electric kettle with 2 litters of water. How much time each kettle will need to boil and why?
How does the boiling time in electric kettle depend on the amount of wat... | lol jk, I would think that the more water the more time it would take to heat up, as the heat would reach the bottom first, then reach the top. But the Heat would try and even itself out across the water but it would thin itself out. For example, think of butter. You have a small piece of toast and you spread it evenly... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113087",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 5,
"answer_id": 4
} |
Why does light travel in straight paths? Why light travels in straight paths? What's the real cause that makes light photons to go in a straight line? and what are the factors that could change the path of light externally? (I'm excluding reflection, refraction and deviation here.)
| The Lagrangian of a light ray is given by,
$$\mathcal{L} = \mu(y) \left[ 1+ \left( \frac{\mathrm{d}y(x)}{\mathrm{d}x}\right)^2\right]^{1/2}$$
where $\mu$ is the refractive index, a function of the path. The associated equations of motion are,
$$\frac{\partial \mu}{\partial y} \frac{1}{\sqrt{1+y'^2}} + \left[ \frac{y''... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113135",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 4,
"answer_id": 2
} |
Does a light wave that has been cancelled by another light wave continue traveling forward? I imagine that if a light wave is cancelled out by another light wave, it would still continue to exist as a photon that is traveling at the speed of light--only without a wavelength. Would it behave only as a particle after it ... | According to Louis de-Broglie (December 12, 1929):
"A wave must be associated with each corpuscle and only the study of the wave's propagation will yield information to us on the successive positions of the corpuscle in space."
So, your idea of the propagation of photon alone is not true according to Broglie's pre... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113293",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Wrapping plastic in aluminium foil to protect it from heat Does it make any sense to wrap the plastic handle of a pan in aluminium foil to protect it from overheating when placing it to the hot oven?
| MSalters answer is all correct, but even in an oven the reflective nature of foil may help (as it would under a grill, but the effect is smaller in an oven). To explain, let's assume the plastic is perfectly black: Wherever the heat is coming from must be hotter than the air in the oven and the other items in the oven... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113364",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 4,
"answer_id": 1
} |
Why do lasers cut? Is this a case of light acting as matter? All I found in Google was very broad. From a physics models perspective, why can photons emitted from a laser cut? Does this cut mean that the photons are acting like matter?
| Cutting is a process when you deliver energy to break chemical bonds in material that you cut.
When you use a saw, you deliver mechanical (kinetic) energy that converts into kinetic energy of particles of the thing you cut, so they can get out of the thing.
Laser is just another way to deliver such energy, since the a ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113431",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "48",
"answer_count": 6,
"answer_id": 4
} |
Why change in internal energy is zero in isothermal process In isothermal process $\Delta U =0$. But I am having trouble understanding it.
Say we have an ideal gas, and say my temperature is constant but I move the pressure, volume from $(P, V) \to (P-dP, V+dV) $. So the volume has expanded and system has done some wor... | You might have got the answer, but this answer is for new visitors ...
When you say isothermally it means the system is somehow allowed to exchange thermal or mechanical energy. In an isothermal compression, the system is allowed to release heat otherwise (adiabatic process) change in temperature will change the intern... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113586",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 5,
"answer_id": 3
} |
Why does Minkowski space provide an accurate description of flat spacetime? What is the chain of reasoning (beginning, of course, from observations about the universe) that leads one to predict that Minkowski space provides an accurate description of space-time in the framework of special relativity?
That is, why shoul... | I think the key observation is Lorentz symmetry.
It was realized by the end of the 19th/beginning of the 20th century that the Maxwell equations adhere to a symmetry other than the Galilean symmetry of Newtonian mechanics. This is Lorentz symmetry.
Many researchers tried reconciling the difference between those symmetr... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113656",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 3,
"answer_id": 1
} |
Velocity in frame $S$ and $S'$ If I take the Lorentz position transforms between two inertial frames, $S$ and $S'$ moving with relative velocity $u$ along a common axis (say $x-x'$), then:
$$x'=\gamma(x- ut)$$
$$y'=y$$
$$z'=z$$
$$t'=\gamma\left(t-\frac{ux}{c^2}\right)$$
If the particle has velocity $(v_x,v_y,v_z)$ in $... | To see this just take the points $(t = 0, y = 0)$ and $(t = T, y = v_yT)$ in $S$ and transform them into $S'$. The point $(0, 0)$ goes to $(0, 0)$ but the point $(T, v_yT)$ goes to $(\gamma T, v_yT)$. So the velocity in $S'$ is $v'_y = v_y/\gamma$ i.e. it is reduced.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113710",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
In the case of riding a bicycle, why can the system of the bicycle and rider be accelerated if no external net force? According to Newton, if no external net force acting on a system then the system will keep its initial condition whether at rest or moving uniformly in a straight line.
Let's consider a boy riding a bic... | You're neglecting the interaction between the bicycle and the ground. If I start riding my bicycle to the east, the Earth rotates a tiny bit towards the west to compensate. Because I and my bicycle are small and the Earth is enormous, it's usually a good approximation to consider the Earth as fixed and immovable.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113799",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 3,
"answer_id": 1
} |
How to calculate the velocity of this body?
Graph of a train (the body) is provided which starts from rest. What is the velocity after the train has 10 metres displacement?
Thats the only things provided for the question, please help me out here, I find that more variables will be required but the book states that n... | The work done (per unit mass) after it has traveled a distance $x$ is the area under the acceleration curve between $0$ and $x$. $$W = 6 x - \frac{x^2}{10}$$
This work goes into kinetic energy (per unit mass) which is $K=\frac{1}{2} v^2$. Equating the two will give the velocity as a function of position
$$ v(x) = \sqrt... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/113894",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 1
} |
Fourier Coefficents in general solution to Klein-Gordon Dirac-equation? The most general solution to the Klein-Gordon equation is written as
\begin{equation} \Phi(x)= \int \mathrm{d }k^3 \frac{1}{(2\pi)^3 2\omega_k} \left( a(k){\mathrm{e }}^{ -i(k x)} + a^\dagger(k) {\mathrm{e }}^{ i(kx)}\right)
\end{equation}
whe... | You didn't write the correct general solution of the KG equation for a complex scalar field. Your $a^\dagger$ should be $b^\dagger$. See, for example, Eq. 3-37 in this PDF book by R. Klauber.
That book also motivates that the operators $a$ & $a^\dagger$ are destruction & creation operators for particles, while $b$ and ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114152",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Reflection Probability for Different Potentials - Quantum Mechanics
My question is above. Firstly, I don't actually know whether it is true or not (!). Secondly, if I were to try to prove it, then I have very little idea how to. The potential steps that I have always done are steps from a constant level to another con... | It is not necessarily true. For a zero potential $V_2$ you have $p_2=0$, whereas if $V_1$ is a rectangular pit, in general, $p_1>0$.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114350",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Which mathematical operation does the right hand rule for current come from? I am currently wondering about the famous right-hand rule for magnetic fields around currents.
Where does it come from mathematically that when you point with your thumb in the direction of the current, your curved fingers will point in the di... | The interesting thing about right-hand-rules is that they always manifest in pairs.
To find the direction of precession for a gyroscope you use a RHR to get the direction of the angular momentum and then use a RHR find the direction of the torque. Finally, you apply that torque as the time-rate-of-change of the angula... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114496",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 2,
"answer_id": 0
} |
Why Does Change of Magnetic Flux Induce an emf? Why does change in magnetic flux with time through a coil induce an emf across it? Please explain what happens to the charges in the coil when magnetic flux changes?
Also, why does a constant magnetic flux not induce an emf?
| My answer is not associated with the forces on electron and changing electric field.I am giving this answer which is just to feel what happens.
Change is the law of nature but, no one likes sudden changes. U may call it analogous to the first law of newton relating to inertias. In the similar way, suppose a loop is kep... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114536",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 4,
"answer_id": 1
} |
Cause for Power Transmission Tower "Breathing" OK, this question is not your usual one: Last night while hiking solo from the mountains back to my car at the mountain/desert interface (Lone Pine, CA), I had a rather bizarre -- and downright spooky -- experience.
The last half-mile of my return was in total darkness, wh... | I think it might be the wind. When changing direction it could have changed how some parts were impinged so these were changing emitted sound.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114621",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Is Newton's third law always correct? Newton's third law states that every force has an equal and opposite reaction. But this doesn't seem like the case in the following scenario:
For example, a person punches a wall and the wall breaks. The wall wasn't able to withstand the force, nor provide equal force in opposite ... | When a body exerts a force on another body, both being in contact, the other body also exerts an equal and opposite force at their contact.
The first body may push the second and make it move, which is because of a non-zero net external force. But the force the two bodies are exerting on each other (internally) at the... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114669",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
"answer_count": 14,
"answer_id": 5
} |
Chemical effect on gravitation? We know, that gravitation field of charged black hole is different than one of uncharged.
I this true only for objects with singularity or is true for all objects?
If true, then may we say, that gravitation field of chemical molecule has footprints of it's chemical composition and state ... | In principle it is possible for a molecule that doesnt change its axes of rotation constantly I'd say. This is because the to first-order fixed spatial structure of the molecule poses a mass density $\rho(x,y,z)$ as any other masses do, too and produces a gravitational potential $\Phi(x,y,z)$ according to Poissons equa... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114729",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Why is the ratio of velocity to the speed of light squared in the Lorentz factor? Why is the ratio of velocity to the speed of light squared in the Lorentz factor?
$${\left( {{v \over c}} \right)^2}$$
My only guess is the value must be positive.
| Same reason the speed of light is squared in the "Energy–momentum relation" equation:
$$
E^2 = m_0^2 \cdot c^4 + p^2 \cdot c^2
$$
Same as
$$
{ E \over c } = \sqrt{ m_0^2 \cdot c^2 + p^2 }
$$
It is a leg of a right triangle we cannot directly observe.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114913",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 6,
"answer_id": 0
} |
Why the trap is needed in cold atom experiment? In ultracold atomic gas experiments, the optical lattice provides a periodic optical potential to trap the atoms, why an extra trap, usually a harmonic trap is needed to trap the atoms?
| Modified: after 4 years in cold atom experiments I found my original answer of this question to be super naive.
There are quite a few types of trapping in cold atom experiments. Such as a periodic trap which we called optical lattices, a magneto-optical trap (MOT) where most experiments use for a very powerful cooling... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/114965",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Power fit to some experimental data I have to fit some data to a power law
$$ F=\alpha q^{\beta}$$
being $q$ and $F$ the experimental data points. What I usually do is taking logs so that
$$ \ln(F) = \beta \ln(q)+\ln(\alpha)$$
and apply least squares with uncertainties in both variables. How may I approach this in the ... | Are you sure that it is $q$ taking the negative value and not $\alpha$?
Non-integer powers of negative numbers are complex, so this surely is not what your experiment returned as values for $F$.
If you already know that $\beta$ can only take integer values, you could fit
$$ F_1 = \alpha q^1$$ $$ F_2 = \alpha q^2 $$ an... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/115088",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 4,
"answer_id": 0
} |
Lagrangian point or dark matter? We know that spiral galaxies spin in a way such that we have to assume that dark matter is responsible for the extra mass required to do so.
My question is, can Lagrangian points (L1 and L2) be used to describe a galaxy's rotation instead?
Can we explain that objects far away from the c... | As noted by Kyle Kanos: the derivation of the Lagrange point heavily relies on the assumption that the object can be seen as a point-like mass.
The Lagrangian points are the constant-pattern solutions of the restricted three-body problem:
(Wikipedia)
This assumption breaks down, when you consider an extended mass dis... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/115161",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Coadjoint orbits in physics I am looking for some application of coadjoint orbits in physics. If you know some of them please let me know.
| I am going to run the risk of having someone else contradict me. My short answer is
No.
There are no longer any applications of co-adjoint orbits to Physics. The topic of
co-adjoint orbits belongs to mathematical physics, which is not real Physics.
The work started by Souriau and Kostant on geometric quantisation... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/116416",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 4,
"answer_id": 3
} |
Is friction a product of Newton's third law? Newton's third law is defined as $F_{12} = -F_{21}$
Is friction a product of this law? For example, if I take my hand and slide it across the floor in the $+x$ direction... My hand exerts a force $F_1$ on the floor. According to Newton's third law, the floor should exert a... | I know this post is coming way too late, but I think the underlying confusion behind the question is one involving fundamental forces. The question was whether friction, in a case like a hand sliding across the floor, is caused by Newton's third law. The answer should be: "No, friction is caused by the electromagnetic ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/116558",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 3
} |
Online course on theoretical electrodynamics I'm looking for good online course for an introduction into theoretical electrodynamics. However, it seems that the MIT opencourseware only contains partial lectures for this topic.
Has anyone got a recommendation for me?
| These are not exactly lectures (its just a guy on youtube) but they cover the whole of Introduction to Electrodynamics book by Griffiths (which is an amazing book btw). If you want to learn about QED as well then his next book called Introduction to Elementary Particles covers a bit of QED calculations like scattering ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/116612",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
How does the viscosity (besides density) of a fluid affects sinking? If water, air of whatever fluid had a different viscosity, but the same density, would things fall/sink differently?
| Yes they would fall differently.
For example, according to Stokes' Law the drag force is proportional to dynamic viscosity and the terminal velocity of a falling sphere is:
$$\frac{2(\rho_s -\rho_f)}{9\mu}gR^2$$
where $\rho_s$ and $\rho_f$ are the densities of the sphere, $\mu$ is the dynamic viscosity, $g$ is the acce... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/116701",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
How can there be really any instantaneous velocity? I have read about Zeno's arrow paradox that tells us there is no motion of the arrow at a particular instant of its flight. It can be inferred that there can be no velocity at any instant. Moreover we cannot calculate velocity at any instant in the real world (of cour... | bright magus puts his finger on the problem when he says in a comment: There is no movement without time flow.
Physicists describe the universe as a four dimensional manifold, in which points are identified by their position $(t, x, y, z)$. The time coordinate $t$ is just a coordinate like $x$, $y$ and $z$, and there i... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/116955",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 4,
"answer_id": 1
} |
Are there any astronomical objects at night that are dangerous to look at (through a telescope)? Are there any astronomical bodies that would be dangerous to my vision to view through a telescope? Obviously the sun is dangerous, but are there other bodies at night I should avoid?
| Compared to naked eye view, a telescope image never increases surface brightness. This fact is related to the concept 'etendue'.
However, although the image formed on your retina is never brighter than the corresponding naked eye image, the image through a telescope is magnified. This means that looking through a tele... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/117003",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 2,
"answer_id": 1
} |
Why does a ball bounce lower? If a ball hits the floor after an acceleration then why does it bounces lower? I mean the Energy is passed to the floor then why does the floor give back less Energy?
| When the ball hits the floor, its center of mass needs to be decelerated. It is done by deforming the ball (and possibly the floor if it is soft enough compared to the ball). In vacuum, if the ball and floor were perfectly elastic, they would then recover their previous shape following exactly the reverse dynamics as t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/117091",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "24",
"answer_count": 4,
"answer_id": 2
} |
Deflection of magnetic compass sorrounded by alternating poles What happens to the deflection of the magnetic compass if it is surrounded by south poles and north poles in alternating direction of a magnet around it in a circular pattern. Will it be deflected in any particular direction ?
| To add to Rijul Gupta's answer: depending on the exact symmetry of the arrangement (see below), theoretically, the needle can move freely to point in any direction. Practically, there will be some direction which is one of minimum energy, so the needle will have a weak tendency to point in this minimum energy direction... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/117228",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
What's the outcome of two polarized electrons beam collide head on? Let's say that I have two electron beams targeted towards each other along x-axis. Both beams are polarized on axis (z-axis) perpendicular to x-axis. Another beam's polarization is up and another down on z-axis.
What would happen when those polarized e... | My question, concerning protons, got its answer from this document (Chapter 3), Anomalous $A_{NN}$ Spin-Spin correlation.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/117342",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
Physical Interpretation of four velocity in GR I'm confused about the physical interpretation of the four-velocity $U^\mu=\frac{dx^\mu}{d\tau}$ in General Relativity. I know that it is a tangent vector to a particle's "worldline", but what does this mean more physically?
For example, I am comfortable with what $U^\mu$ ... | There is no difference between the interpretation of the four-velocity in special relativity and general relativity. One way of stating the equivalence principle is that locally, GR reduces to SR.
Although it's true that expressions like $\Delta x^\mu$ don't make sense in GR for finite coordinate differences (displacem... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/117408",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 0
} |
Why are totally antisymmetric tensors more useful than totally symmetric tensors? In an arbitrary number of dimensions, one can naturally define two tensors, Kronecker delta and Levi-Civita epsilon tensor. However, why isn't it advantageous to define some totally symmetric tensor as well? Is there an intuitive reason f... | Isn't the Kronecker delta symmetric? Let's see:
$$\delta_{ij}=1 \, \, \, \text{if} \, \, \, i=j, \quad \delta_{ij}=0$$
otherwise. I'm pretty sure that is symmetric. The Levi-Cevita symbol is indeed anti-symmetric though.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/118451",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
With redshift, energy is lost. Where does it go? A photon emitted by a distant source billions of light years away arrives here with a lower frequency hence less energy than it started with. What happened to the energy?
| No energy is lost. The photon does not change, we just perceive it differently because of our relative velocities. The doppler effect is not a change in a wave, just the change in the apparent frequency of the wave. Technically speaking, the doppler effect changes the wavelength of the wave, which alters the apparen... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/118590",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "13",
"answer_count": 3,
"answer_id": 1
} |
Why does a large train cause the ground to shake? I work in a 4 story building that is approx. 150 feet away from a set of train tracks. When a large (40+ car) freight train goes by, the shaking in the building is perceptible. As I've watched the train go by, there does not appear to be any side to side movement and ... | According to my research into the vibrations of passing trains, flat spots on train wheels can be caused by skidding train stops. This flat spot causes vibrations. Lack of rail inspection and maintenance can cause vibrations.
We have trains with no vibrations go by so I tend to believe our vibration problems are caused... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/118734",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "30",
"answer_count": 4,
"answer_id": 2
} |
Tension in an Atwoods machine conceptual?
Assuming $T_1$ is the force that acts on box $1$ and $T_2$ is the force that acts on box $2$.
Exactly what causes the Tension? Why does $T_1 = T_2$?
The problem is we are told to memorize that $T_1 = T_2$ for mass less ropes, but I do not understand why, especially in an Atwoo... | The assumption that $T1$ and $T2$ are the same comes down to the approximation $m_{rope} = 0$. At the end, we are trying to make sense of an assumption that is not trivial to interpret physically.
Besides Brian's great answer I would like to add that the assumption $m_{rope} = 0$ leads to a force balance (FBD) about th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/118905",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 3,
"answer_id": 2
} |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.