Q stringlengths 18 13.7k | A stringlengths 1 16.1k | meta dict |
|---|---|---|
Muon lifetime determination My colleagues and I performed several experiments to determine the lifetime of the muon (from secondary cosmic rays) using scintillator detectors coupled to multi-channel analysers. The results invariably showed a muon lifetime lower than the standard 2.2 microseconds. Apart from poor statis... | As you suggested in your comment, the $\mu^-$ and $\mu^+$ that stop in matter do not have the same lifetimes. The $\mu^+$ come to rest between the atoms of your stopper (eg: scintillator?) and decay into $\nu_{\mu}e^+\nu_e$ with the standard 2.2 usec lifetime. However, the $\mu^-$ get captured into Bohr orbits about ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/258961",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Coherence length of a single photon If I pass individual photons through a M-Z interferometer with equal arms I will observe interference (eg only one detector will respond). As I increase the path length of one arm I will observe the two detectors responding alternately as I pass through each phase cycle. Eventually I... | CuriousOne makes a good point in comments and I will elaborate on that.
While you are asking about the coherence length of a single photon, in the experiment that you describe you will have to detect many photons to judge if they are detected in both arms with equal probability. Where do this photons come from?
If you... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/259116",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 5,
"answer_id": 3
} |
What is a stroboscopic map? I have an assignment where I'm supposed to generate a "stroboscopic map" of some orbits of a dynamical system. I have a hard time finding information about exactly what this kind of map is on the Internet and in my course book, but I suspect it might be the same thing as a Poincaré map or a ... | A stroboscopic map is indeed a special case of a Poincaré map for driven systems. The distinguishing feature is that a given phase of the driver’s period is used for mapping (instead of some other marker event like a local maximum or a zero crossing). If, e.g., your driving term is $\sin(t)$, you would obtain the strob... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/259186",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 1,
"answer_id": 0
} |
Does the sign of imaginary part of complex permittivity have any physical meaning? I have noticed some papers having written complex permittivity as $e' + je'' $
and others as $e' - je''$. The data in literature does not specify the sign. What should I use and does the sign of $e''$ implies anything?
| Work out how a plane wave propagates. If its intensity grows in the direction of propagation, then you need to switch the sign of the imaginary part! It depends on whether you define $e^{+i\,k\,z}$ or $e^{-i\,k\,z}$ as your diffraction operator in the direction of propagation. If it's $e^{+i\,k\,z}$, then a lossy die... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/259324",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Meaning of the phase space in statistical physics I have a silly question about the phase space. I am confused with the meaning of points in phase space. Does the each point in phase space represent concrete particle of the system, or does it represent the whole state of the system? Our teacher told us, that we use the... | It represents the "space occuped" by the hypervolume momentum-position of a particle.
If you integrate the three components of position you get volume; if you integrate the three components of momentum you get kind of a momentum volume. If you integrate both together you get the space phase volume
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/259412",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 1
} |
Why is oil a better lubricant than water? How come mineral oil is a better lubricant than water, even though water has a lower viscosity?
When two surfaces slide over each other with a gap filled with a fluid, the different layers of the fluid are dragged at different speeds. The very top layer touching the top metal ... | Your derivation is composed of correct statements and indeed, if something is known to act as a lubricant, we want the viscosity to be as low as possible because the friction will be reduced in this way. For example, honey is a bad lubricant because it's too viscous.
However, your derivation isn't the whole story. The ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/259501",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "109",
"answer_count": 6,
"answer_id": 5
} |
Is a spacetime of constant positive curvature just a 4-hypersphere? In discussions of basic cosmological models, I don't see "spacetime of constant positive curvature" described more simply as a "4-hypersphere". What am I missing?
| You are presumably thinking of the FLRW metric for a universe with greater than critical density i.e. a closed universe.
We normally use comoving coordinates to describe this, in which case the time coordinate is not curved and at every point along this time coordinate the three spatial coordinates have the topology of... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/259592",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
How was the half-life of Uranium 235 determined and by whom? Wikipedia says that the half-life of Uranium-$235$ is $7.038 \times 10^8$ ($\text{703 800 000}$) years.
This is very long. Therefore, on a human time scale, the decay is very small, posing difficulty for determining the half-life.
So Who and how was the half-... | The earliest reference I've been able to find on the half-life of 235U is in The Uranium Half-Lives: A Critical Review, by Norman Holden, which reviews various early studies of each of the common isotopes of uranium (232U, 233U, 234U, 235U, 236U, and 238U). The earliest study he cites is Nier (1939) (A. 0. Nier, The is... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/259716",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Product of two Pauli matrices for two spin $1/2$ In the lecture, my professor wrote this on the board
$$
\begin{equation}
\begin{split}
(\vec{\sigma}_{1}\cdot\vec{\sigma}_{2})|++\rangle &= |++\rangle \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;(\blacktriangledown)\\
(\vec{\sigma}_{1}\cdot\vec{\sigma}_{2})(|+-\rangle+|-+\rangle) &... | Your expression for:
$$(\vec \sigma_1 \cdot \vec \sigma_2) |+\rangle_1 \otimes |+\rangle_2=\vec \sigma_1 |+\rangle\otimes \vec \sigma_2 |+\rangle_2$$
Is wrong. It sould read:
$$(\vec \sigma_1 \cdot \vec \sigma_2) |+\rangle_1 \otimes |+\rangle_2=\sigma_{1x}|+\rangle_1\otimes \sigma_{2x}|+\rangle_2+\sigma_{1y}|+\rangle_... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/260916",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Would an HI or HII region have a color? That is, if we were approaching an HI or HII region in a spaceship, would the cloud have a color visible to the naked eye? Of the HI region, Wikipedia says:
These regions do not emit detectable visible light (except in spectral
lines from elements other than hydrogen) but are ... | "Requires large amounts of hydrogen to be seen" means simply that the light is extremely weak, so you need lots of hydrogen available to get a reasonable number of photons created the 21-cm line. That's a microwave line, by the way, so wouldn't be visible to the eye.
As far as "except in spectral lines from elements ot... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/261147",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
How to pour water from a bottle as fast as possible? When one pours water out of a bottle, it first flows smoothly but then a pressure 'blockage' develops and the pouring becomes interrupted and turbulent, so that the water comes out in splashes. This seems to slow down the flow of water from the bottle.
What is the op... | The question is: what is the optimal way to pour the water so that it [the bottle] completely empties fastest? I conclude the aim is to have the empty bottle, not the water in another container.
Solution: Create a centrifuge-like setup, bottle opening to the outside. The setup will generate artificial gravity for the w... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/261303",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
"answer_count": 15,
"answer_id": 8
} |
What is meant by rest in rest-mass? As far as I know only photons are considered to have no rest-mass. In common words when it doesn't move it 'disappears'.
*
*Electrons and quarks should have a rest-mass. But are they really at rest?
In atoms and molecules is always a kind of zero-point energy left which implie... | Rest mass means the mass which would appear if a paricle were at rest. Do not confuse between particles and photons. These particles are metarialistic particles behaving as energy in some circumstances. Being matter they possess rest mass. While photon is a bundle of energy behaving sometimes as a particle and hence ca... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/261400",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
How the data or models given in physics or mathematics problems can be obtained in real life? When ever there is physics or mathematics problem. we are already given a mathematical model. Can't we make own models from given diagrams or data collected from the problem? sometimes angle is given in the problems like a pla... | There are essentially two ways in which we obtain functions and models ourselves: through the use of an appropriate measuring instrument (ruler, protractor, scale, clock...) or via mathematical logic.
Measuring instruments can give us an excellent but imperfect approximation, while mathematical logic provides us an exa... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/261559",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
If the speed of light is constant, why can't it escape a black hole? When speed is the path traveled in a given time and the path is constant, as it is for $c$, why can't light escape a black hole?
It may take a long time to happen but shouldn't there be some light escaping every so often?
I'm guessing that because tim... | The explanation I like is thus:
In GR, all things, from planets to photons, travel in straight lines through curved space bent by mass. Black holes bend and distort spacetime so severely that the curvature captures the photon.
Scale things down and it behaves much the same way passing asteroids can be captured by a sta... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/261650",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "74",
"answer_count": 9,
"answer_id": 3
} |
What are some resources for learning about x-ray powder diffraction? I am looking for up-to-date, applied resources to learn about x-ray powder diffraction. There is a lot of jargon with which I am unfamiliar. I am trying to refine theoretical curves to collected data using the program Maud using the Rietveld Method b... | I'd prefer myself to start from an introductory book or a lecture before diving into research papers.
The most often recommended book on the rietveld_l mailing list (which is the biggest mailing list about powder diffraction) is:
Fundamentals of Powder Diffraction and Structural Characterization of Materials by Vitalij... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/261726",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Rolling motion of a rigid object I have the situation described in this picture
I know the speed of the ball at the top of the loop ($v_{top} = 2.38 m/s$), and I have to demonstrate that the ball does not fall from the track at the top of the loop.
From what I understand, the two forces acting on the ball are the grav... | At the top of the loop if the normal reaction on the ball due to the track is $F_n$ down and the weight of the ball is $F_g$ down then using Newton's second law
$$F_n + F_g = m\frac {v^2}{R}$$
where $v$ is the speed of the ball, $m$ is the mass of the ball and $R$ is the radius of the loop.
This equation tells you that... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/261844",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What is the color of a group of trillions of electrons, protons, and neutrons Since an electron is smaller than visible light, then what what color would a group of electrons (trillions of electrons) be if there were enough of them to be seen by the eye? What color would a group of trillions of protons be? Color of tri... | I cant comment on large groups of electrons, but we do actually have two real world examples of groups of neutrons, and one of groups of protons.
Neutrons
*
*In labs, we have Bose-Einstein condensates. But since they evaporate with the slightest motion or exposure to light, I dont know how we could ever see them.
*... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/261946",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 3,
"answer_id": 2
} |
Is conservation of momentum and energy valid for non-inertial frames? Conservation laws of momentum and energy are said to be the most basic principles of physics. Are they also valid for non-inertial frames, and in what way?
| Regarding total momentum conservation, the point is that in non-inertial reference frames inertial forces are present acting on every physical object. Momentum conservation is valid in the absence of external forces.
However, if these forces are directed along a fixed axis, say $e_x$, or are always linear combinations ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/262058",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 1,
"answer_id": 0
} |
Can interference occur between two waves that are parallel but separated by a small distance?
This is a image of diffraction in crystal. My doubt is how the parallel waves coming out interfere if they are seperate?
| In answering your question, a lot could be said about the art of mathematical modeling, but, the short answer is: They don't.
But, the rays in the scheme are only an approximation, and one that fails at the atomic scale - a beam of light, no matter how laser like or faint, is never exactly a 1-D mathematical line, it s... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/262160",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 1,
"answer_id": 0
} |
Specific heat of the classical ferromagnetic Heisenberg model I have simulated the classical ferromagnetic Heisenberg model on a cubic lattice using Monte Carlo and I get a finite specific heat near zero temperature. My understanding is that from the magnon theory,
we should get a specific heat that behaves like ~ $T^... | This is essentially a result of the equipartition theorem where each degree of freedom contributes $k_B T/2$ to the energy. Given that the specific heat in this context is just ${\partial E}/{\partial T}$ then each degree of freedom contributes $k_B/2$ to the specific heat. For the classical model of lattice vibrations... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/262442",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 1,
"answer_id": 0
} |
Could a "living planet" alter its own trajectory only by changing its shape? In Stanislaw Lem's novel Solaris the planet is able to correct its own trajectory by some unspecified means. Assuming its momentum and angular momentum is conserved (it doesn't eject or absorb any mass), would this be possible (in Newtonian me... | By conservation of momentum and energy, the only possible way to change a planet's trajectory is to eject some (large) mass at high velocity in specific direction, like rockets do. But you are also correct that by increasing the moment of inertia, the rotational speed can be changed. But this cannot influence the movem... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/262530",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "85",
"answer_count": 8,
"answer_id": 2
} |
What is the angular velocity of the electron? An electron has angular momentum. Shouldn't it also have angular velocity?
Ignoring the g-factor (just for the order of magnitude approximation) and the fact that an electron is not a sphere the electron's angular velocity should be around:
$$ \omega \approx \frac{\mu}{er^2... | You can't generate spin 1/2 from motion in space, so no, there is no way to assign an angular velocity to the electron. Orbital angular momentum only comes in integer multiples of h-bar.
This situation actually doesn't change very much even if we do discover substructure to the electron. Google "preon" and "confinement... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/262661",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Can I recirculate water from an open reservoir to the bottom of a bigger, closed one, without a pump? A fountain head pumps water out of the main tank into a 'pond' reservoir. Can the water recirculate back into the main tank without the help of another pump?
I'm sorry if this a dumb question. I'm guessing it would not... | The set up shown will work just fine, though to be safe I'd put the check valve on the pump so as to prevent water and or air from flowing back into the tank from above.
I also made a few assumptions:-
*
*The free space in the top of the tanks is small enough
*The tank is not too tall (less than about $9~\text{m}$ ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/262838",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 7,
"answer_id": 0
} |
System rigidity What is the meaning of system rigidity in mechanics? I can't understand how to classify the system as rigid or not, and what is the effect of rigidity on the whole system.
If you know anything about system rigidity... Please let me know
| It simply means that the object is so stiff that it can only move by proper Euclidean isometries. At any time, the whole body can only be a combination of rotations and translations of itself at any other time. In particular:
This means that the distance between every pair of points within the body stays the same at al... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/263004",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
How to find entropy production of opening the windows in the winter? Every time you open the windows in the winter (to bring in healthy and fresh air), room's warm air goes outside into the atmosphere.
How to find entropy production of opening the windows in the winter?
The room's volume is denoted by $V_r$ and its tem... | Note: We need one property of the room's air for example mass or pressure of it.
From "THERMODYNAMICS An Engineering Approach, Fifth Edition, by YUNUS A. CENGEL and MICHAEL A. BOLES":
Irreversibilities such as friction, mixing, chemical reactions, heat transfer through a finite temperature difference, unrestrained ex... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/263106",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Why does the frequency of a wave remain constant? They say the frequency of a wave is its fundamental character, thus remain constant throughout its propagation regardless the medium through which it travels. Could anyone explain why frequency of wave is fundamental character but its wavelength isn't?
| When source and receiver are moving away or towards each other, the observed frequency changes. This effect is called a "doppler shift".
The frequency becomes lower ("red shift) when the source moves away. The frequency becomes higher ("blue shift") when the source moves towards the observer.
So yes, one can change the... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/263288",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 6,
"answer_id": 5
} |
looking for a technique for conducting experiment I have used a servomotor and a controlling circuit to produce oscillatory motion for an experiment that involves flapping of a tiny metal plate (~few mm) inside liquid. I could not be very successful in controlling the amplitude and the frequency precisely.
Is there an... | I would reach for an Arduino or similar microcontroller to do the job. You can set the amplitude and frequency of the vibration in code which, in my experience, is always easier than tweaking an electronic circuit.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/263727",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
The analytical result for free massless fermion propagator For massless fermion, the free propagator in quantum field theory
is
\begin{eqnarray*}
& & \langle0|T\psi(x)\bar{\psi}(y)|0\rangle=\int\frac{d^{4}k}{(2\pi)^{4}}\frac{i\gamma\cdot k}{k^{2}+i\epsilon}e^{-ik\cdot(x-y)}.
\end{eqnarray*}
In Peskin & Schroeder's bo... | As alluded to in the other answer here, the integral can basically be evaluated in several ways. One of them is the one that OP has himself followed. (PS - OP, congratulations on completing that feat!)
Let me present here a way of computing this using Schwinger parameterization. We will use
$$
\frac{1}{a} = \int_0^\inf... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/263846",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 4,
"answer_id": 1
} |
Should the complex conjugate of a derivative of a Grassmann number include a sign? Take a real Grassmann variable, by which I mean $\theta=\theta^*$. We have
$$\int d\theta~ \theta =1,\qquad \frac{\partial}{\partial\theta}\theta=1$$
If I define the conjugation of Grassmann variables to invert their order, $$(\eta\thet... | Yes. OP is right. There is a minus. Since by convention the complex conjugation obeys
$$ (z w)^{\ast} ~=~ w^{\ast}z^{\ast}~=~(-1)^{|z|~|w|} z^{\ast}w^{\ast} \tag{1}$$
for any two supernumbers $z$, $w$ (of definite Grassmann parities $|z|$,$|w|$), we should also have
$$ (A f)^{\ast} ~=~(-1)^{|A| ~|f|} A^{\ast}f^{\ast}... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/263979",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 1,
"answer_id": 0
} |
Why do thin films need to be thin? No matter what thickness a piece of glass is wouldn't its optical thickness be close to an integer multiple of a wavelength such that it could create interference effects? I feel like I am missing something here.
| You are completely right in stating that the same effect should occur for thicker slabs. There are however at least 3 practical reasons why the effect is more easily observed in thin films.
*
*Light sources are typically not completely monochromatic. They emit slightly different colours at the same time. Imagine a l... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/264082",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 2,
"answer_id": 1
} |
Why must $v$ be $< c$ in the Lorentz transformations? Do these equations not apply to light? I was trying to understand how things look from the perspective of light. Looking at the Lorentz transformations, it seems that the universe would contract along the direction of movement into a plane, and time would stop. But ... | Lorentz transformations apply to objects with nonzero mass. For an object with mass, it would require an infinite amount of energy to reach light speed.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/264337",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
Is there any effect on mechanical waves by electromagnetic waves (and vise versa)? Do electromagnetic waves like light and gravitational waves (due to moon for instance) affect on mechanical waves like sound?
Can sound change the path of light?
| I can answer half your question in that a sound can change the path of light.
A change in the density of the air produces a change in the refractive index of the air and so a Schlieren photograph can make this visible.
Here is a YouTube video to show a sound wave produced by clapping.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/264441",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 1
} |
Force of water hitting a wall If you had a 8" pipe with 500psi stream of water exiting it and hitting a wall at 90 degrees 8 feet away, what would the force of the water on the wall be?
Thank you all.
Non-mathematician.
|
Using Bernoulli's equation and the momentum conservation equation, we can show that water flowing out of a pipe with cross-section $A$ at speed $v$ exerts a force $F$ on a wall (at 90 degrees), acc.:
$$F=\rho Av^2$$
With $\rho$ the density of the water.
But your specification of "8" pipe with 500psi stream of water ex... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/264524",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Torque on electric dipole placed in non uniform electric field When electric dipole placed in non uniform electric field, what is the approach to calculate torque acting on it? Can it be zero?
| The torque $ \tau $ on an electric dipole with dipole moment p in a uniform electric field E is given by $$ \tau = p \times E $$ where the "X" refers to the vector cross product.
Ref: Wikipedia article on electric dipole moment.
I will demonstrate that the torque on an ideal (point) dipole on a non-uniform field is ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/264655",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Relation between entropy and internal energy I am confused as to what is the relation between entropy and internal energy. Entropy is always presented as a measure of the randomness in a system. So when we supply heat to a well insulated system say ideal gas in a container with fixed boundary, the internal energy and t... | Entropy is the order of disorderness of a system, which means greater will be the irreversibility of a process.
Internal energy is the sum of kinetic and potential energies of particles.
Entropy increases only if there is enough energy in particles. Thus, if there is no internal energy there won't be any entropy.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/264757",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 1
} |
Is the energy needed for a current through a straight and a coiled wire different? When you add current to a straight piece of wire does it use less electricity than if it was coiled? The power wire on telephone pole's are curved while buried cables are pretty strait in comparison. Does the curve of the wire and proxim... | I may be wrong, but I think Lenz's Law might provide an answer.
The circuit with the straight wire takes in current i(suppose) once the switch is closed.
The one with the looped wire, will having a changing flux through it once the switch is closed. Since any change is to be opposed, the current drawn this time will be... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/264870",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Does the use of $\gamma=\left(1-v^{2}/c^{2}\right)^{-1/2}$ automatically assume a (+ - - - ) metric? In Special Relativity, does the use of $\gamma=\left(1-v^{2}/c^{2}\right)^{-1/2}$
automatically assume a (+ - - - ) metric convention? For introductory textbooks, the Lorentz factor is is always defined the same. For ... | This definition doesn't depend on the metric signature convention. Note that in definition of $\gamma$ the metric doesn't appear anywhere. It is defined purely in terms of "3-vectors" and "3-scalars" measured by particular observer. So it is impossible for metric to appear here explicitly.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/265421",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Quantum master equation and off-diagonal terms I have a couple of related questions
*
*What is exactly the difference between the quantum master equation and the regular master equation? My understanding is that the normal master equation is used to find a "vector" of state probabilities (like in a regular Markov ch... | The off-diagonal terms appear when you analyze the measurement problem. Say you have a system S with some observable $\hat{S}$ such that it haves eigenvalues $s_i$ and you wish to measure the state. In order to do that you consider an apparatus $\hat{A}$ wich is initially in a pointer state $| a_0 \rangle$ so the initi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/265517",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Reciprocal Time Dilation in Special Relativity I'm trying to understand theory of special relativity, but there is one thing that really makes me confused which is reciprocal time dilation in special relativity.
In special relativity, the time dilation effect is reciprocal: as observed from the point of view of either ... | Yes, Einstein's postulates entail symmetrical (reciprocal) time dilation, but in 1905 Einstein deduced, invalidly (in the sense that this does not follow from the postulates), asymmetrical time dilation - when the moving clock passes the stationary one, the former lags behind the latter. Nowadays you can often hear the... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/265715",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Electric field dependence on distance How can it be proved that for a point charge, $E$ is proportional to $$1/r^2$$ using the concept of Electric field lines (or lines of force)? I tried to show that if field lines are close, then magnitude of Electric field is higher. But, I couldn't show the given dependence.
| You can prove it using the concept of electric flux. For instance. If you surround a point charge with a sphere if r=1, or a sphere with r =10, you know that the electric flux ( field strength times area) must be the same. A sphere is easy because every point is equidistant to the charge.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/265816",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 1
} |
Mass dropped on a spring I thought this would be a particularly simple problem but it is turning out to be quite the opposite. I am sure I am doing a very simple mistake.
The problem statement is that there is a mass which is just barely kept on the spring (help by the force equal to the weight of the spring) such tha... | When the spring reaches maximum compression, the mass is instantaneously at rest but it is not in static equilibrium. The net force on it is not zero : $kx \ne mg$. Like a pendulum at the end of each swing, there is a net force on the mass causing it to accelerate towards the equilibrium position - at which the net f... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/266129",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
How did physicists know that there are two kind of charges? Problems
The question I am about to make is either too stupid or hasn't bothered anyone because its obvious because I can't really find the answer anywhere.
I am currently studying electricity and magnetism and my book starts by telling that matter consists of... | Among competing hypotheses, the one with the fewest assumptions should be selected.
Some electrified objects repel, some attract. This can be explained by two kinds of charge. Nothing that cannot be explained by two charges can be explained by adding a third kind of charge. So we continue to describe electricity as ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/266246",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "51",
"answer_count": 5,
"answer_id": 4
} |
Sign mistake calculating electrostatic potential energy formula! I have a problem calculating the electrostatic potential energy.
I rely on these equations coming from mechanics:
\begin{equation}
U_{B}-U_{A} = -W_{A \ \rightarrow \ B} (done\ by \ the \ field \ force)
\end{equation}
\begin{equation}
U_{B}-U_{A} = W_{A ... | You are doing a "backwards" integration. From higher to lower rather than from lower to higher x-axis values.
Integrating "backwards" from $\infty$ to $r$ (backwards because $\infty>r$) is the "flipped" and "opposite" version of the one from $r$ to $\infty$,
$$\int_\infty^r \dots dx=-\int_r^\infty \dots dx\,.$$
$\int$ ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/266435",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Why can we see the moon when it is between the Earth and the Sun? A rather stupid question, why can we see the moon when it is between the Earth and the Sun?
| The premise of this question is wrong.
If the moon is in between the earth and the sun (as shown on your diagram), and you can see the moon, then it is day, not night:
If on the other hand, you are on the opposite side of the earth during that configuration (so that it is night), then you can't see the moon because th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/266492",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 6,
"answer_id": 4
} |
Extension of Schrödinger's cat thought experiment My question is quite simple. In the thought experiment of Schroedinger's cat: When the scientist measures the state of the cat, its wavefunction collapses into either the alive or dead state. But wouldn't then the scientist in turn be in a superposition of measuring dea... | It depends of what interpretation of quantum mechanics you are using. By interpretation it is meant that the mathematical predictions of the quantum mechanics formalism are the same, but the philosophical meaning of each is what differs. In the copenhagen interpretation that you seem to describe, the wave function coll... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/266606",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "46",
"answer_count": 9,
"answer_id": 0
} |
Plotting hydrogen wave functions This may sound a bit dumb but how do I plot the hydrogen wave functions? For example, what is exactly being represented in this image? Is it just the norm-squared of the wave function and is the z-axis sticking out of the page?
I'm not sure how to use any other application but I'm usin... | The plots you see in the Wiki images, are, as their title suggests, probability density plots ($\psi^2$, for Real $\psi$). Light shaded areas represent high probability areas, darker areas lower probability density.
Furthermore, they've been sliced, e.g. with an $x,y$-plane. For radially symmetric functions like $\psi_... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/266678",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Is there a prohibited region in $P-V$ plane? Polytropic process generalize the particular thermodynamic processes with
$$P V^{n}= \mathrm{constant}$$
Where, if $n$ changes, the curve on $P-V$ plane changes, as shown in the diagram.
The orange region is not touched by any curve, so there is no value of $n$ for which t... | In a polytropic process other than adiabatic, you are controlling the temperature in tandem with P and V in such a way that n is constant. You can certainly achieve negative values of n by controlling the temperature appropriately.
From the ideal gas law, if T and P are expressed parametrically in terms of V, then:$$\... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/266980",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 1
} |
Why don't high pressure gases stored in containers lose energy? Containers holding gas at a high pressure don't slowly lose the internal energy of the gas. It seems like the high speed particles would collide with the metal walls and slowly transfer their energy to the slower particles outside the container.
Even if th... | re: "Why don't high pressure gases stored in containers lose energy?"
They can gain & lose energy:
Energy (heat) is lost from a gas as the gas is compressed (whether thru mechanical compression or thru cooling compression (e.g. passing a gas thru a tube that is immersed in a very cold liquid -- like liquid nitrogen).
... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/267146",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 4,
"answer_id": 2
} |
If change in position over time is average velocity, why doesn't change in position over time squared equal average acceleration? For example, let's say a car is experiencing an acceleration of $1$m/s$^2$, for $6$ seconds so it goes $18$m. Now the average velocity is found through dividing $18$m by $6$s which is in lin... | The glitch in your logic is that you supposed acceleration to be distance/time squared while using your formula: $$ \Delta x = v_0t+\frac{1}{2}at^2 $$
The above formula gives $$ a= \frac{2\Delta x}{t^2}$$ supposing that vo is equal to zero.
This makes the acceleration equal to the average acceleration in your case s... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/267430",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Problem on Emissivity and absorptivity I have read the radiation chapter, where I have been introduced with the terms emissivity and absorptivity. emissivity tells about the ability to emit heat energy as thermal radiation compare to a black body. and absorptivity is the amount of heat absobed by body devided by the in... | The figures below support Jim's statement.
Figure 1: The specific spectral radiation of a black (Schwarzer Strahler), grey (grauer Strahler) and real body (realer Strahler) at the same temperature and different wavelengths $\lambda$.
Figure 2: Specific spectral radiation of black bodies ($\varepsilon=1$) at different... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/267660",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Harmonic oscillator in quantum mechanics I have brief questions regarding the attachments, which are notes from the book Introduction to Quantum Mechanics by Griffiths which explains the harmonic oscillator case. Any assistance would be appreciated. The attachments don't look healthy but the questions are quite simple.... | *
*$A$ is constant in the approximate solution at large $\xi$. So Griffiths makes the ansatz that for general $\xi$, the solution is of the form for some function $A(\xi)$ that becomes "constant" compared to the exponentation at large $\xi$. It's an ansatz, it is not derived.
*Look at the condition on $K$ that termin... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/267754",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Does the speed of light in vacuum define the universal speed limit?
*
*Is light the thing causing the universal speed limit to be $299\,792\,458\,\mathrm{m/s}$? So the universal speed limit would be different if light travelled faster or slower?
*Or, is $299\,792\,458\,\mathrm{m/s}$ the universal speed limit anyway ... | It's the second one: the reason the speed $299792458\ \mathrm{m/s} = c$ is special is because it's the universal speed limit. Light always travels at the speed $c$, whatever that limit may be.
The reason there is a "universal speed limit" at all has to do with the structure of spacetime. Even in a universe without ligh... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/267852",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "32",
"answer_count": 6,
"answer_id": 2
} |
Why decrease in velocity will increase pressure? According to the Bernoulli's equation, if velocity decreases, then pressure increases.
I am trying to understand the Bernoulli's effect based on a situation.
Suppose we have a stream of water. Let's assume it is an ideal fluid. Imagine the water flows out from a wider ... | Pressure is momentum transfer due to molecular collisions once you have subtracted out their average motion. So decrease in pressure due to increase in average speed may be construed as transfer of kinetic energy from random molecular motion to mean motion. This means that random molecular motion (by which I only mean ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/267967",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Standard convention for $x$ error bars What is the standard convention regarding the error bars of the independent quantity in a graph? In what situations should I show the $x$ error bars? In case both $x$ and $y$ uncertainties are comparable or neither can be disregarded, should I show both or only the greater one?
I... | If you are measuring y at some value x, and both quantities have uncertainty, then in principle you should show the uncertainties on both axes.
In some circumstances you might omit the x error bars. This would be the case if the y value depends on x such that
$$\Delta y \gg |dy/dx| \Delta x,$$
where $dy/dx$ is your bes... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/268032",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Large-scale antimatter production From what I can find, presently the only known means of producing antimatter consist of directing particle accelerators at various targets, and only infrequently getting positrons or anti-protons as byproducts of particle interactions.
Assuming a sufficiently large source of energy: Ha... | Magnetic field containers can be used for the storage of antimatter. Also, increasing the size of the particle accelerator will increase the volume output of antimatter, the key fuel in warp drives. The size of particle accelerator can be 100 miles around by diameter and 30 stories high.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/268126",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 1
} |
Water droplet lensing Suppose I have a camera that is looking straight down at a single droplet of water resting on a flat surface. The droplet is small enough that surface tension forms it into a rounded shape. Inside the water, there is suspended an object that I'd like to image and measure. Is it possible to some... | The curvature of the drop is influenced by the liquid-solid, solid-air and liquid-air interface forces. It can be determined by the Young-Laplace equation. For more details see this article
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/268227",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Does a wave function describe the motion of electrons or atoms? I took the course of quantum mechanics a while ago. I do not quite remember all the detail on how to derive the wave function for hydrogen but I still remember the general picture. I think the text always start the discussion with hydrogen because this ato... | Atoms.
We sometimes use somewhat loose language when we speak of the wave function of the electron. We typically either have chosen the center of mass frame, or pretended that the nuclei are fixed (as you point out). It's the atom that has energy levels.
We can get away with the loose language because if we rea... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/268321",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
What is the measure of distance in higher dimensions? In our world we are using kilometers to measure distance. What measurement is used to measure distance in higher dimensions?
| Distance measurements in $n$ dimensional flat space follows the same pattern for $n$ equal 1,2,3, or higher values.
I'm going to assume a straight line, change in position to simplify the math (that is we're measuring what a introductory book would call the "displacement" $s$ rather than distance. But then distance is ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/268489",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
Jones formalism for calculating quarter waveplate angle for circular polarized light I am planning to change the polarization of a vertically linear polarized laser to circular polarized light with the help of a quarter waveplate.
I know the final result: I have to rotate the fast axis of the waveplate 45° to the incid... | Hints:
*
*The Jones matrix for e.g. right circular polarized light is: $$\frac{1}{2} \begin{pmatrix}
1 & i \\ -i & -1
\end{pmatrix}$$ To see this try applying this matrix to your linearly polarized Jones vector. It will give a right circularly polarized Jones vector.
*The Jones matrix for a quarter wave plate is:$$... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/268685",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
How do I calculate a upward-pulling force on a swinging pendulum? I'm trying to implement a simple pendulum using a 2d physics system that can model rigid bodies with gravity. The problem is that I don't know how to calculate the upward-pulling force of the rope, as in this image:
I've only found equations for calcula... | The rope pulls just enough that the pendulum doesn't fall to the ground, but follows an arc.
The following picture shows you how work out the force for the static case (no motion of the pendulum):
However, you need to take account of the fact that the pendulum is moving in an arc. When something moves in an arc, you ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/268755",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Principle of Least Action Question Let's say we have a particle with no forces on it. The path that this classical particle takes is the one that minimizes the integral
$$\frac{1}{2}m\int_{t_i}^{t_f}v^2dt.$$
So if we graph this for the actual path a particle takes it is a straight, horizontal line on the $(t,v^2)$ pl... | Your proposed path has a VERY LARGE action. As @tparker pointed out, you have to minimize the path subject to the constraint that the average velocity doesn't change. Now, the action is quadratic in velocity. A little fiddling around with the math should convince you that to minimize the integral of $v^2$ subject to th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/268941",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
Does the universe expand in every direction evenly? I've heard that the universe is expanding constantly and that galaxies are moving further and further away from each other because of this. However, does the universe expand in every direction evenly or does it expand in one direction more than another direction?
| It is an assumption that the universe expands evenly in all directions, and the experimental evidence so far confirms the assumption.
Our mathematical description of the expanding universe is based on the assumption that on a very large scale the universe is homogeneous and isotropic, which basically means it's the sam... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/269236",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 4,
"answer_id": 0
} |
Spring behaviour under high atmospheric pressure We have a spring inside a chamber. We compress the spring and then let it decompress freely. Will its decompression (its speed and displacement) be the same if the air pressure of the chamber is $1\;\mathrm{atm}$ or $3000\;\mathrm{atm}$? If not, how will it be affected?
| Damping
The density of atmospheric air is approximately 1.225 kg/m$^3$. At 3000 atm, the density would be 3675 kg/m$^3$ compared to the density of water of 1000 kg/m$^3$. I don't know the viscosity of high density air, but as @DirkBruere answered, it could be a significant factor in the damping of the spring decompres... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/269346",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Bell inequality violations evidence for 1935 EPR claims? Is it possible that Bell inequality tests provide experimental evidence in support for the EPR claims in their 1935 paper titled "Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?", where Bell tests eliminate local realism as cause f... | Yes - these experiments have been conducted, most famously by Aspect et al., but also by others, see Wikipedia. They all observed violations of Bell's inequalities - Our world is therefore not local-realistic in the sense of Einstein.
An extension of Bell's inequalities by Legett (Legett inequalities) holds for non-loc... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/269406",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Why is the resistance in a parallel circuit smaller than the resistance in a series circuit? So I was told in the physics class that the resistance in a parallel circuit is smaller than the resistance in a series circuit. Why does that happen?
Is this statement also true for circuits which have no resistors or resistan... | Question: Which of two pipes of equal length offers less resistance to the flow of water, one of which has twice the cross sectional area of the other?
Answer: The one of twice the cross sectional area.
But the one of twice the cross sectional area can be thought of as two of the smaller cross sectional area pipes in p... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/269492",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 7,
"answer_id": 5
} |
Plane waves in special relativity I don't understand how there can be plane waves that by definition are spread through all of space if nothing can travel faster than light.
Wouldn't every wave have to spread over time with at most the speed of light?
I could understand when they are only appearing in the mathematics o... | Plane waves are not real, they are just a mathematical device.
In quantum mechanics, particles are represented by wave packets, which do not have infinite amplitude and allow a collection of plane waves to group together by interfering constructively within a certain area and destructively outside that area.
From Wi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/269575",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
Principal moment of inertia for a rotating body My major is not in physics.
I am reading the following paper: (my problem is simple and not related with any optimization)
http://arxiv.org/abs/1410.2841 (p.5~p.6)
Suppose
*
*The body angular velocity is $\Omega(t_0) = [\omega \ \ 0 \ \ 0]^T$, $\omega$ is... | No you cannot assume that. The initial rotation is about the major axis, and it will continue to be so (in the absence of torque, and since you were already rotating about the major axis). Instead, since $\omega_2=\omega_3=0$, your equations for the evolution of the angular momentum don't require the moments of inertia... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/269649",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Can we exit the event horizon of merging black holes? I have an intuitive scenario. Consider we have a spaceship just below the event horizon of a BH, which is merging with another black hole.
Finally, the singularities merge and we have a single black hole again.
But, in the transient stage, it is unclear to me if a t... | No. When they merge their horizons will change shape, and eventually become the static or stationary shape of a BH horizon. Nothing inside either horizon while this is happening can escape. At all times the timelike curves stay inside, and the deformed horizons are where the lightlike curves end up. In each, and after ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/269922",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Mechanism for collapse of iron stars into black holes via quantum tunnelling In the wikipedia page "Future of an expanding universe" it refers to the scenario of a future without proton decay.
The page talks about how processes would lead to stellar-mass cold spheres of iron, calling these objects "iron stars":
In 101... | Well iron stars will collapse due to quantum tunneling. Iron from the surface of the iron star over a really really really really really long time will go to the core. This will happen to all the iron atoms. Then the iron star will be so dense that it collapses into a neutron star. This neutron star then has the abilit... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/270004",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 2
} |
What frequency is the scratching of finger nails on a blackboard? This is the frequency/intensity that sets my teeth on edge.
Does anybody know what frequency (roughly) it is? I am guessing it is near the top of normal human hearing, 20kHZ, but I'm not sure if that's why it affects me.
I am sure the same frequency is ... | From http://www.livescience.com/16967-fingernails-chalkboard-painful.html:
Interestingly, the most painful frequencies were not the highest or lowest, but instead were those that were between 2,000 and 4,000 Hz. The human ear is most sensitive to sounds that fall in this frequency range, said Michael Oehler, professor... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/270085",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 2,
"answer_id": 0
} |
How does the LHC explore extra dimensions? The Large Hadron Collider (LHC) has been smashing particles for a long time and sometimes people say that it has found new dimensions. How is it even possible for a particle accelerator to find new dimensions?
| First, no evidence for other dimensions has been found.
However, there are ways for particle colliders to detect other dimensions. One of the main ones is to see if any energy "disappears" under very certain circumstances...then it could've possibly gone into another dimension.
Another way is to look for particles th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/270376",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 2,
"answer_id": 0
} |
Coleman-Mandula theorem and mass gap I had a couple of naive questions about Coleman-Mandula theorem.
*
*One of the assumptions of the theorem is the non-existence of massless particles in the spectrum. Since we do have massless photons in the standard model, how is the theorem relevant?
*Why aren't there example... | The Coleman-Mandula theorem (CMT) does not rule out theories with massless particles. What it rules out is a theory with only massless particles. If you only have massless particles you either:
*
*End up with a free theory. This theory has trivial S-matrix, thus, the CMT does not apply here
*Have conformal symmetry... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/270458",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 1,
"answer_id": 0
} |
Largest Mass Diffraction I have read "Matter-wave interference with particles selected from a molecular library with masses exceeding 10000 amu" which claims to observe diffraction patterns in objects of around 10'000 amu. What is the largest mass objects shown to have diffraction patterns and show wave-particle dualit... | According to this website, photons, electrons, atoms, and some molecules, including buckyballs, have displayed wave-particle duality. Here is a paper that talks about some of the experimentation for larger molecules. This paper talks about molecules with over 6,000 amu showing a wave-particle duality, and this article ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/270588",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 0
} |
Satellite revolving problem gives two different answer Assume there's a satellite revolving about the Earth. If I would like to decrease its radius, should I increase or decrease its velocity?
I know the answer apparently should be decreasing its speed, but the following two formulas give different answers. Can someon... | You cannot simply pluck equations out of your textbook and apply them to any situation. Just because they both contain radius $r$ and speed $v$ does not mean that they are necessarily valid for your situation. You have to think about what you are doing.
The 1st equation applies for circular motion. It tells you that ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/270691",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
How to find static friction coefficient and the applied force's angle of inclination with a horizontal plane? Okay so I have this weird problem in my statics book that wouldn't come to a solution no matter what I tried. It states the following:
A body of weight $4$ kg.wt is placed on a horizontal rough plane. If a for... | Here's how I interpret this question:
We have two equations: The horizontal projection of the 2 kg force equals $\mu$ times the sum of gravity and the vertical projection, i.e. $$2 \cos(\theta) = \mu(4-2\sin(\theta));$$ and similarly for the 4 kg force, except it's projection on the vertical direction is $+\sin(\theta... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/270774",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What is the difference between the blackness of a Black Hole and the blackness of a Black Body?
*
*Light cannot escape the gravitational pull of the black hole and hence the 'black hole' is black.
*Any object that is black in color, absorbs all wavelengths of light and reflects none. So it appears black.
Could someo... | A black body is a system that does not reflect photons. A black body can only emit photons, which is often fabricated as a hot cavity with a small hole. A razor blade can also approximate a black body if the sharp edge is smaller than the wavelength of photons of interest and is at a temperature so short wavelength pho... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/270994",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Are there higher genus equivalent of spherical harmonics? So the equation of a surface with topology S2 can be expanded out in terms of spherical harmonic functions. (I believe).
A torus T2 which is just S1xS1 can be expanded out in terms of ordinary harmonics which is just Fourier analysis.
But what about surfaces of ... | If your surface has a metric, you can expand in eigenfunctions of the Laplace operator. This is kind of like the spherical harmonic expansion for g = 0 or 1, but it's not as nice. The sphere and torus are both homogeneous spaces, which allows you to use representation theory to organize the expansions. None of the h... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/271107",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 1,
"answer_id": 0
} |
Ground state of local parent Hamiltonians and invariance under local unitaries Assume that a finite-dimensional pure state $|\psi\rangle\in \mathcal{H}\simeq \mathbb{C}^m$, $m<\infty$, is the (unique) frustration-free ground state of a local parent Hamiltonian and suppose that the locality notion is given in terms of a... | Isn't simple translation symmetry an example?
E.g. suppose you have a one-dimensional ring of $L$ spins described by $|\psi\rangle = \sum_{\{\sigma_i\}} \psi_{\sigma_1,\sigma_2,\cdots,\sigma_L} \; |\sigma_1,\sigma_2,\cdots,\sigma_N\rangle$. Then this wavefunction could be invariant under the unitary transformation $\ps... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/271230",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 0
} |
Why aren't trigonometric functions dimensionless regardless of the argument? Consider this equation :-
$$y = a\sin kt$$
where $a$ is amplitude, $y$ is displacement, $t$ is time and $k$ is some dimensionless constant.
My instructor said this equation is dimensionally incorrect because the dimension of $[kt] = [\tex... | The sine function $\sin(\theta)$ is defined as a function of an angle $\theta$ (measured in radians). So the question amounts to asking why an angle must be dimensionless. (Of course, the answers invoking properties of Taylor series are also correct.) The angle $\theta$ between two directions is defined as the ratio $\... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/272599",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 6,
"answer_id": 0
} |
Does an object float more or less with more or less gravity? This might be a stupid question, but I'm a newbie to physics.
An object less dense than water (or any other fluid, but I'm going to use water for this example) floats normally on Earth when placed in water. But if the object was placed in a hypothetical place... | Assuming both the water and the object are rigid and incompressible (pretty good approximation for water, may or may not be so good for the object) and that we can ignore surface tension (good approximation for large objects, not so good for tiny ones) then in equalibrium the same proportion of the object will be above... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/272918",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
"answer_count": 5,
"answer_id": 0
} |
Do all rays of light from an object a being imaged by a camera pass through the focal point before being recorded on the image plane? Basically I'm trying understand the limitations of using the pin-hole model for a camera.
| In thin-lens optics, one often assumes that the center of the lens (whose faces by symmetry are locally perpendicular to the line of sight) does not refract light from distant objects, so one can ray-trace from the source to the image plane a straight line through that central point. It requires more calculation to r... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/273097",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
How is potential energy lost when a water droplet is dropping down slowly on a wall? When a water droplet is on a vertical wall, it usually drops slowly, which is different from free falling. As the dropping speed is slower than free drawing, so I guess some energy must be lost.
I guess it is lost as internal energy, ... | The energy loss is frictive in nature. As the drop slides down the surface, there is a complex interaction at the interface between the droplet and the wall. This will go into changing the temperature of the water droplet, kicking some molecules off, etc...
Perhaps someone with a litter better skills in thermodynamics ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/273192",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 3,
"answer_id": 1
} |
How increased current carrying capacity / ampacity affects wire gauge size In selecting a suitable wire size for manufacturing:
If I have a material that has the same resistivity and density as Copper, but has a higher current carrying capacity / ampacity for the same gauge (i.e. diameter and area), would I be able to... | It's all about heat buildup. A superconductor will, occasionally, lose coolant and quench, and you need enough conductivity of the windings to prevent that quench event from melting, straining or otherwise damaging your device. In non-superconducting wiring, the wire must not heat its surroundings (or itself) beyond... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/273479",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Spring force on both sides of spring I am a little confused about springs. I just wanted to know that if I pull an ideal spring of spring constant $k$ such that the spring has been symmetrically pulled and its elongation (total) comes out to be $x$ then would the force on one side by $$F=kx$$ or $$F=kx/2$$ I am a litt... | There is no such thing as a non-symmetrical pull of a string or some non-"total" elongation. $x$ is elongation, and that's it. $F=kx$ is the spring force, and that's it.
An object tied to one end of the spring experiences this spring force. The whole force. Something tied to the other end experiences by Newton's 3rd l... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/273829",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 4,
"answer_id": 1
} |
Heat pump intuition What is an intuitive explanation for the concept of heat pumps? I know that it is basically a reversed Carnot process. We can for example take an amount of heat $Q_1$ out of a warmer system and transform part of it into work W. The rest goes to the colder system. If we now reverse that process we ne... | You use a pump on a separate fluid (gas) system which is connected to the freezer (for example). The pump lowers pressure while the pipe system controls the volume of the fluid gas, and then this fluid can reach a smaller temperate than the internal of the freezer.
The freezer thus passes heat to the fluid system and ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/273919",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 1
} |
Does the mass of water molecule increase when its just converted from ice to water? When we heat some object and its temperature raised then the K.E of molecules increased it means increase in velocity and according to $m=\frac{m०}{{(1-\frac{v^2}{c^2}})^{1/2}}$ mass is increased in very small amount.but when latent hea... | In the past, we might have said that any increase in molecular mass due to velocity increase would only be significant at speeds near that of light, but that is not how we view mass today at those velocities. No amount of heat we could put into water would ever result in molecular velocities anywhere near the speed of ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/274029",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Does empty space have energy? My physics friend suggested that "the answer to why matter exists in the universe" is because all massive particles are just the fabric of space excited into little packets. To illustrate, imagine a blanket on the ground. Then, pinch a small bit of the blanket and twist it. This is a parti... | Particles are not regarded as bits of curved spacetime, but rather as excitations of quantum fields.
It has been suggested that spacetime curvature can cause structures that behave a bit like objects (though not fundamental particles) and these objects are called geons. However it remains unclear whether these would be... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/274104",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 0
} |
What is the difference between these two ways to calculate average velocity? Average velocity:
$$v_{\rm avg,1}=\frac{v_{\rm final}+v_{\rm initial}}{2}$$
and average velocity:
$$v_{\rm avg,2} =\frac{\rm total\;displacement}{\rm time \;taken}=\frac{\Delta x}{\Delta t} $$
What is the difference between them and when do ... | Taking the average of the initial velocity and final velocity is not necessarily, you are assuming a linear change in the velocity which is not the general situation. So only the second formule specifies the average velocity.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/274300",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 1
} |
How many 'recursive' gravitational orbits are possible? I was thinking about how the moon orbits around Earth, which orbits around the Sun, which orbits around the center of the Milky Way.
I think of these kinds of orbits as recursive. For each body $B_n$, we can imagine adding another smaller body $B_{n+1}$ which orbi... | The other answers have nicely addressed the scale of increasing size. This answer provides detail on the scale of decreasing size. There are no known cases of moons having moons in the solar system. Two key things get in the way of moons having moonlets having even smaller moonlets (etc.).
One issue is the ever-decreas... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/274372",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 1
} |
Could a black hole pulling on a neutron star temporarily create a quark star? I believe a quark star is a hypothesized star that is composed of quark matter. If I'm correct then an even large gravitational pull than a neutron star has would be required to break down the individual neutrons forming a star made of quarks... | No and maybe a yes. Quark stars formation from a neutron star in this is hard to conceive.
Yes it might be possible for black hole to collapse a neutron start into a quark star hybrid exotic star under different circumstances.If a small but significantly massive black hole collided and acted like a strangelet.
A shini... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/274474",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Why is 3D stress tensor acting only on three surfaces? I'm trying to learn about the stress tensor (in 3D)
The tensors are said to have directions (the first subindex $i$ in $\sigma_{ij}$) and specify the surface upon which they act (the second subindex $j$ in $\sigma_{ij}$).
What confuses me is why is it defined only... | We do consider other 3 faces, as we take into account (Sigma x), it means other opposite face of it is also taken but written only once which means the magnitude is same but direction is opposite, i.e. you will see 9 components but still there are 18 components, we only write 9 since other 9 will have same magnitude. S... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/274829",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Why doesn't Helium freeze at 0K? I have read that Helium does not freeze at absolute zero under normal pressures.
How could this be possible given that the absolute zero is the lowest attainable temperature and at that temperature, all random movements of the atom stop?
Shouldn't the atoms just stop vibrating and soli... | You have been misled by the idea that temperature is a measure of energy. While this is approximately true at high temperatures, it is not correct at low temperatures. Temperature is actually a measure of entropy; the derivative of entropy with respect to internal energy at constant particle number and volume is invers... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/274910",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 4,
"answer_id": 0
} |
Unitary translation in phase space coordinate If we suppose that we can translate one point to another point in phase space $(x,p)$ through the following operators,
$$T(\Delta x) = \exp(-i p~\Delta x ) $$
and
$$T(\Delta p) = \exp(-i x~\Delta p ) ,$$
I want to see if there is any common point between these transformatio... | Let us stick to Quantum mechanics, so, then, use P and Q for operators, and, to avoid confusion, s=Δx and t=Δp for classical shift parameters.
You then evidently wrote down the (conjugates of) celebrated U and V Weyl operators (1927), useful in the braiding form of the canonical commutation relations,
$$
e^{itQ} e^{isP... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/275015",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Does a higher water volume increase pressure? I am constructing a gravity flow water system. I have 100ft point where I can put my tank. My question is does the size of my tank matter? I am using a 1" pipe. Will I get more pressure if I use a bigger tank? For example what is the difference in pressure if I use a 10 gal... | The pressure experienced at the bottom of the pipe depends on the diameter of the pipe, the flow rate, the total height difference between the surface of the water and the point where you measure the pressure, and the density of the liquid.
When the flow rate is zero (no liquid flows: before you open the valve) the onl... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/275134",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 4,
"answer_id": 2
} |
When should you jump off a falling ladder? If you stand on the top of a falling ladder you will hit the ground at a higher speed (and therefore presumedly sustain more injury) if you hold on to the ladder than if you jump off it.
This was solved
here.
Where is the "break even" height on the ladder, from where you will ... | You people are crazy with your useless calculations.
Doesnt take science to realise that if you hold on the ladder you will have a higher chances of falling on your back or ass and hit your head against the ground now I wouldnt know peoples preferences but yesterday I was at the top of the ladder which is about 3 meter... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/275219",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "30",
"answer_count": 4,
"answer_id": 3
} |
What is a phase arrow? Feynman say's that a photon takes every path while reflecting off a mirror when going form A to B, but we only see the middle one(where incident angle = reflected angle) because all the others are cancelled out as they have longer routes and while following them their phase arrows cancel out each... | This question is based, as pretty much everyone knows, on the book "QED, the strange theory of light and matter", by Feynman.
My answer is based on my limited understanding of the book.
Phase Arrows has a good description of Feynman's analogy.
As well the above source, if you visit Feynman Lecture Using Phase Arrows , ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/275304",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Why does the food in the microwave heat up but the bowl doesn't? I put a 1/4 inch thick clear glass container into the microwave with a plate on top and put it in for almost 5 minutes (there was lots of soup). When It came out the soup was really hot but I could still hold the top parts of the container. After measurin... | The microwaves are primarily designed to vibrate/heat the water molecules in the food, as a way of ensuring that the foods gets cooked evenly. An aid to this process is the rotating plate within the machine.
Microwaves that cook your food pass through plastics, glass, and ceramics, with mimimal heating, as their wate... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/275430",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 1,
"answer_id": 0
} |
Why doesn't the adiabatic reduction of first law of thermodynamics, $W = -\Delta U,$ hold for non-conservative forces? The first law of thermodynamics is$$
\Delta U~=~Q-W
\tag{1}
\,,$$where:
*
*$\Delta U$ is change in internal energy;
*$Q$ is the amount of heat supplied to the system;
*$W$ is the amount of work do... | The above form is not the most general form of the 1st law of thermodynamics, which is:
$$ dU = \delta Q - \delta W $$
Here $\delta Q$ is the change in heat, i.e., the heat flowing into or out of the system. This is a statement of energy conservation.
Now, if the heat flow is zero, it reduces to your above equation. ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/275521",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Deceptively simple mass-spring problem? This question is inspired by two other, similar, so far unanswered questions (posed by different OPs).
Mass $m_2$ sits on a incline with angle $\theta$ that provides just enough friction for it not to start sliding down. It is connected by a massless string $S$ and perfect sprin... | Let me try to do this without using any formulas. First consider what would happen if $m_2$ were glued to the incline. Then we would have a simple harmonic oscillator consisting of $m_1$ suspended from the spring $k$ (clearly it does not matter on which side of the pulley the spring is). In this situation the average t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/275604",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 9,
"answer_id": 2
} |
The meaning of covariant but not manifestly covariant What is the most general meaning of the expression covariant, but not manifestly covariant? Suppose I have a general (local) change of coordinates, $x^{\prime} = f(x)$, on an $(n+1)$-dimensional smooth manifold on which some classical fields are defined, say $A_{\al... | I'll expand on jjc385's answer with an example of how equations of motion can arise in a non-manifestly covariant form. In curved spacetime, the Lagrangian density can be written as $\mathcal{L}=\sqrt{\left| g\right|}\mathcal{L}_0$, with $\mathcal{L}_0$ a scalar called the scalar Lagrangian density. The action is then ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/275657",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"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.