Q stringlengths 18 13.7k | A stringlengths 1 16.1k | meta dict |
|---|---|---|
AGN accretion disk vs. torus The torus is the donut of dust encircling the Active Galactic nucleus. The accretion disk is inside the torus. Is there a boundary between the two? At what point does a torus become an accretion disk? What are their differences?
|
The Figure above is Figure 1 of this paper. It shows the scales of various features of the unified AGN model in units of $\log_{10}(r/\text{pc})$. Remember that a parsec is about 3.26 light-years or 200,000 AU (or 5000 times Pluto's mean orbital distance). The $10^{-5}$ mark is roughly the Schwarzschild radius for a $... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25365",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 0
} |
Color Variation in RR Lyrae I've been doing some research on RR Lyrae stars and haven't been really able to find an answer to this question.
RR Lyrae are well known for their periodic magnitude, and also are usually found in certain color ranges ("RR Lyrae Color Box"). My question is: does the color of RR Lyrae Stars (... | The short answer is that yes the color would have to change somewhat. All the stars in the instability strip (RR Lyrae, Cepheids, etc) are variable because they pulsate. Over the course of the pulsation, they vary in brightness, size and surface temperature.
It is the temperature change that is important here. As ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25414",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Exoplanet detection via space-based parasol I remember from watching Cosmos years ago, Carl Sagan suggested an interesting hypothetical method for directly seeing exoplanets. He proposed that in the 'future' we could launch a satellite designed to block the light from distant stars, effectively eclipsing them, perhaps ... | Such a method is actually a little more complex than it may seem at first glance, since light is a wave and will create an interference pattern due to the edge of the shade. Also, it's much less flexible than other deep nulling systems such as coronagraphs and interferometers, since it requires two widely separated spa... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25451",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 5,
"answer_id": 4
} |
Emission line width units What do these units mean: the large velocity widths of emission lines (in AGN) are 2,000 - 10,000 km s^-1? I've looked for the answer but keep getting swamped in myriads of details. I want to know what the term velocity means in large velocity widths and also why km s^-1. Thanks
| Velocity and wavelength shifts are connected by the Doppler effect, with which you may already be familiar. Basically, objects that are approaching appear bluer and those receding appear redder.
Now, suppose body of material emits some spectral line and that the particles of that material have line-of-sight velocities ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25542",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 1,
"answer_id": 0
} |
Figuring out which moons of Jupiter I saw through my telescope Three days ago (Sunday 11st March) in London using my new telescope I was able to see Jupiter and three of its moons. It was very clear and easy to spot. How can I determine the names of the moons I saw (and which one was which)? I would assume they were th... | There are a large number of programs called planetarium programs, which animate the solar system, so that you can view the positions of any objects, such as the Galilean moons, at any point in time. These are so accurate that you can enter the times Galileo himself observed the moons in 1609 and 1610 and see them plott... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25582",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
How fast will the sun become a red giant? I've read many accounts of our sun's distant fate, but what I've never heard is on what time scale these events occur.
For instance, when the sun runs out of hydrogen, I presume it doesn't just WHAM! become a red giant suddenly, engulfing the inner planets in seconds. But how l... | There's a nice paper by Drs. Klaus-Peter Schroder and Robert Smith on the distant future of the Sun and Earth; it's available at the arXiv:
*
*http://arxiv.org/abs/0801.4031
Table 1 in that preprint summarizes a number of parameters, but in simplified form the radii (in terms of the current value) at different time... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25622",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 3,
"answer_id": 2
} |
Can a neutron star compress until it's converted to a black hole? The Universe's densest objects are black holes. In the second place, there are neutron stars.
So, if a neutron star compresses to its Schwarzschild radius, would it appear as a black hole? That black hole would be one of the most dense objects in the uni... | An important point to make is that it is not possible for a neutron star to shrink "gradually" so that it disappears quietly inside its own event horizon. There will always be some sort of violent collapse because a neutron star becomes unstable at radii significantly larger than the Schwarzschild radius.
A neutron sta... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25708",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 3,
"answer_id": 2
} |
What was the apparent magnitude of the June 15th 2011 lunar eclipse? My plan was to observe and estimate the apparent magnitude of the Moon during totality of the June 2011 lunar eclipse, but the clouds rolled in at the exact moment, so I couldn't make any useful estimates. What was the apparent magnitude?
| Thank you for the answers! I just received an email from Dr. Richard Keen, turns out the visual magnitude of the eclipse from observers using naked eye, reversed binoculars, and photometry averaged -0.3 and the Danjon L values ranged from 0 to 1.5.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25749",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 1
} |
Is CO2 really a potent greenhouse gas for planets around M dwarfs? The thing with global warming is that it absorbs infrared (IR) radiation from the planet and reradiates much of it back to the planet (whereas the Sun's peak flux is in the visible region, that is unaffected by CO2).
But with red dwarfs - it's different... | Ah, but there are different kinds of infrared, it's a very wide spectrum of electromagnetic energy after all. It ranges from about 700 nanometers (0.7 microns) at the visible end to about 1 mm (1000 microns) at the microwave end. Wien's law states that the energy peak of blackbody radiation is at a wavelength in micron... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25787",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Can the Hubble telescope bring any star into focus? Lets say I am talking about a view like this supernova - 13 billions light year away. In short can Hubble bring any star into focus in the entire universe? And if so, to what definition?
I also wonder, how much time would time would it need to focus on a distant star... | I think what you are asking is if the Hubble telescope can "resolve" any star within 13 billion light years. The answer is "no".
Resolution is the measure of telescope performance that determines how small a detail can be resolved in the image it forms. Nearly every visible star resolves to a point of light in the ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25829",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 4,
"answer_id": 1
} |
Significance of letters in Hertzsprung-Russell (H-R) diagram The Hertzsprung-Russell diagram that categorizes star types uses the letter codes O, B, A, F, G, K, and M to indicate a star's temperature/color. Hottest (blue) is O and coolest (red) is M.
What do the letters themselves relate to?
For example, why is "O" us... | The letters used are not significant as they were assigned arbitrarily before anyone really knew anything about the subject. See the Wikipedia article here for more about it.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25871",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 3,
"answer_id": 2
} |
Why is a new moon not the same as a solar eclipse? Forgive the elementary nature of this question:
Because a new moon occurs when the moon is positioned between the earth and sun, doesn't this also mean that somewhere on the Earth, a solar eclipse (or partial eclipse) is happening?
What, then, is the difference between... | Your question makes an unstated assumption: all three bodies are always in the same plane. In fact, if this were true, there would be a solar eclipse for every new moon. So your spatial imagination is working quite correctly, indeed!
However, the unstated assumption does not hold. The plane of the Earth orbit around th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25924",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "41",
"answer_count": 5,
"answer_id": 2
} |
Use of advanced mathematics in astronomy, like topology, abstract algebra, or others I know that topology, abstract algebra, K-theory, Riemannian geometry and others, can be used in physics. Are some of these areas used in astronomy, and are some astronomical theories based on them?
I'm not considering calculus, linear... | In astronomy per se, little advanced mathematics are used, except statistics, error propagation, and in designing optical instruments. As soon as you start shading over from pure astronomy into astrophysics, however, you will have occasion to use the full range of, as a grad student acquaintance of mine once very memor... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25964",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 3,
"answer_id": 0
} |
"Blue Bumper" Stars I was recently overviewing various massive compact halo object studies (the Anglo-Australian MACHO collaboration and the French I/II EROS collaboration), and they frequently reference "blue bumper stars," irregular variable stars which produce light curves very similar to gravitational microlensing ... | I did some hunting and followed the paper trail to Cook et al. (1995). In Section 4, they identify a class of stars that brighten aperiodically. They reckon that these "blue bumpers" are Be stars: B-type stars that show strong emission lines. Then again, this is off one paper and I'm really not sure if this is a widely... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26002",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 1,
"answer_id": 0
} |
How could I translate a field of view value into a magnification value? When I zoom in with Stellarium, it indicates a field of view (FOV) value in degrees, but most binoculars and telescopes are advertised with value like "nX magnification power."
How could I translate this value so I get an idea of what I will see wi... | There is no direct translation between FOV (Field Of View) and Zoom value (or magnification, in other words). In the astronomy lab I used to teach, we had the students focus their classroom telescope first on a parking sign in the distance. I explained to them that magnification was how big a particular letter on the ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26046",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 0
} |
How does the central peak in moon craters form? The central peak in many of the moon's large craters are visible with a telescope and they seem a little odd to me. Can someone explain how they form.
| If you drop something into a pool of water, you will get a rebound effect in the middle where the object was dropped, and then waves will spread out around it. This rebound effect in the middle is the same phenomenon that causes central peaks in craters. The difference is just the scale: An impact that forms a >~15-... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26091",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 2,
"answer_id": 0
} |
What are the known relationships between rotation of planets/moons and their distance to Sun? What are the known relationships between rotation of planets/moons and their distance to Sun? Or any other known attributes? For example, the sidereal year for planets is directly related to their mass and their distance from ... | The length of the solar day is related to the sidereal day and the speed at which an object orbits the Sun, which in turn is dependent on its orbital radius.
The sidereal year is not related to the mass of the orbiting object. Any object at the same radius in a circle orbit will have the same year. It IS dependent on t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26134",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
In astronomy what phenomena have theory predicted before observations? As far as I know, astronomy is generally an observational science. We see something and then try to explain why it is happening. The one exception that I know of is black holes: first it was thought of, then it was found.
Einstein's relativity is ... | In addition to the others, there are other famous theoretical predictions that were then seen in the sky:
*
*Neptune!
*Asteroids. (from the failure of Bode's law)
*Lagrange point objects
*Inspiralling neutron star binaries
*Supernova neutrinos(Colgate and White 1966).
*GZK cutoff
The recent cosmology revolution... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26177",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 10,
"answer_id": 7
} |
How to find the Andromeda galaxy without using a go-to telescope? In other words, what is the proper technique (star-hopping or other?) in order to find and properly point a telescope to this target? Would a star atlas or other tool/reference help? Can I use the R.A. and Dec. coordinates to find such deep-space objects... | This is not a good time of year to observe the Andromeda Galaxy, because it's very low in the sky until around 3 a.m. Around that time, this chart I made some years ago may be helpful:
The starhop indicated there, from Cassiopeia, is OK, but not very exact. I prefer to use the two stars in the middle of Andromeda, Mir... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26216",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 4,
"answer_id": 2
} |
How fast is the Cosmic Microwave Background Radiation (CMBR) changing? I know that the Cosmic Microwave Background Radiation (CMBR) is the leftover radiation from the "surface of last scattering".
However, at every instant the surface is changing (at the rate of flow of time). So how constant is the CMBR?
| We can derive an order of magnitude estimate of the rate of decrease of the CMB temperature in the following way. The equation of state for a photon gas is
$$
N = \frac{16 \pi k^3 \zeta(3)}{(h c)^3} \cdot V T^3
$$
If the photon gas is confined within a cavity, it interacts with the electrons in the walls of the cavit... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26257",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 3,
"answer_id": 2
} |
Spectral energy distribution fitting tools or routines I have observed magnitudes and fluxes for an object in different wavelengths from optical to mm. Now I need a tool, routine or something like that to fit a spectral energy distribution (SED) and derive some physical parameters from the fit.
I'm looking for a ready ... | There certainly are, but it depends on what the object is?
For example, I have used the `flared disk' model of Dullemond Dominik & Natta (2001) to model the SED of hot dust around a sgB[e] star
http://www.mpia.de/homes/dullemon/ppdisks.html
where at optical wavelengths emission is dominated by a ~25kK stellar source b... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26295",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 1,
"answer_id": 0
} |
Is Jupiter a failed star? In my physics lessons, my teachers have always been keen to tell my class that Jupiter is considered a 'failed star' by scientists. Is this true?
In my own effort I wondered if maybe this could just be being regurgitated from an outdated physics syllabus that still considers the Solar System t... | Well Jupiter is not really a failed star. It is considered that because it has 2.5 times all the mass if all the other planets were added together. However Jupiter has the materials of a star it lacks the mass. It has to be a minimum 80 times more massive to even be a low mass star(red dwarf). The sun has 1000 masses o... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26339",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "28",
"answer_count": 3,
"answer_id": 2
} |
How big (compared to our moon) would Saturn look from Titan's surface? How large in the night sky would Saturn look from Titan's surface? I believe they are tidally locked.
| The angular size of the object can be calculated by basic trigonometry: $\theta=2\cdot \arctan(r/d)$, where $r$ is the radius of the object you're viewing, and $d$ is the distance between you and the object ($\theta$ is the angle).
The average (volumetric) radius of Saturn is 58,232 km. The distance between Titan and... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26386",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 1,
"answer_id": 0
} |
How can I vizualize and understand curved spaces in general relativity? I'm taking a basic physics class and the teacher described space with a special table that has curves and black holes etc. He would throw a metal ball down onto it and the class would watch it circle around a black hole and this showed the warping ... | Another way to think of curved is distorted as in distance distortion.
A basic postulate of Euclidean geometry is "The shortest distance between two points is a straight line." That's what the top figure shows (below). That would be true if space were not curved, but it is. The second figure shows a curved line. In add... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26440",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 5,
"answer_id": 3
} |
What is exactly the density of a black hole and how can it be calculated? How do scientists calculate that density? What data do they have to calculate that?
| We can't tell how matter behaves inside a black hole. I can think of at least several solutions, but there is no way to either confirm or deny them.
I'd say its most likely matter forms a sphere inside the event horizon equal to the radii of the black hole. Considering physics (as we know it) don't break down inside th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26515",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "23",
"answer_count": 6,
"answer_id": 3
} |
Mass of Milky Way Supermassive Black Hole I am looking at data from Andrea Ghez (2005; ADS link) which states the mass of the supermassive black hole in the MW. Here's what I don't understand: She reports the value as $3.7 \times 10^6 [R_0/(8~\mathrm{kpc})]^3$ solar masses.
The part I'm not clear on is the radius/8 kpc... | The largest source of error in the measurement of the black hole mass is its distance, $R_0$, which Wikipedia says is $7940\pm420$ parsec. By quoting the mass in terms of the distance, this error is isolated. So, for example, if the black hole is actually $7600$ parsec away, its mass is about $3.5\times10^6\,M_\odot$. ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26553",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
On what planar regions are the Earth, Moon.. for that matter, all astronomical bodies, placed in the Universe? When we are on Earth, we look UP in the Sky to see the Moon. How do we have to look at Earth from Moon.. Is it the way ? If so, how are these bodies actually placed in the space?
Are all astronomical objects l... | Coplanar orbits are very common in astronomy. From the small scale (moon orbits) to the large scale (galaxy discs), and this is due to the conservation of angular momentum. If you have a cloud that is being exerted upon by force (gravity), the conservation of angular momentum will cause an initial spin to be amplified.... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26599",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
How much of the Earth would a spoonful of the Sun scorch? How much of the Earth would a spoonful of the Sun scorch if held at ground level?
I basically would like to conceptualize the heat of the Sun on a smaller scale, please.
| What part of the sun? That would make a huge difference in your question. Overall, these types of hypothetical questions are rather non-nonsensical without really defining the parameters very clearly.
That said, keep in mind, we have "released the power of the sun on the surface of the earth" a few times already. No... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26690",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Energy and Matter I was watching a show about the big bang theory. They were saying that in the beginning all that existed was energy. After the big bang that energy transformed into matter which then started forming into different elements. How exactly does energy change into matter and at what point does this happ... | Mass is nothing but most concentrated form of energy. As its the most concentrated form, all attributes of energy (possessing momentum, gravitational interaction etc) get magnified. You can see the equivalence in the popular equation $E=mc^2$.
Not just in the beginning, but even today all that exist is energy (and, Spa... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26730",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
Sky-Watcher Skymax-127 (AZ) 127mm (5") f/1500 SynScan GO-TO Maksutov-Cassegrain Telescope I have not purchased the above item yet but was wondering whether or not I should? Can I hook this scope up to a monitor or laptop so I can see what my scope is seeing? Is this scope is any good at viewing planets etc., Mars and S... | Optically and mechanically, this telescope's optical tube is identical to the Orion Apex and StarMax 127mm Maksutov-Cassegrain, but on a different GoTo mount. While the SkyWatcher brand may not be familiar in the United States, it is widely known in the rest of the world as the house brand of Synta, the largest telesc... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26774",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
What is the current state of research into $v$-representability? In their proof, Hohenberg and Kohn (Phys Rev 136 (1964) B864) established that the ground state density, $\rho_\text{gs}$, uniquely determines the Hamiltonian. This had the effect of establishing an implicit relationship between $\rho_\text{gs}$ and the ... | There are three places to address the $v$-representability:
1) The Hohenberg-Kohn theorem for the one-to-one mapping from ground-state electronic density to potential $v$
2) The Hohenberg-Kohn variational theorem
3) The Kohn-Sham scheme
As far as I know,
1) The $v$-representability is automatically guaranteed. Since th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26804",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "25",
"answer_count": 1,
"answer_id": 0
} |
Is the Lagrangian of a quantum field really a 'functional'? Weinberg says, page 299, The quantum theory of fields, Vol 1, that
The Lagrangian is, in general, a functional $L[\Psi(t),\dot{\Psi}(t)$], of a set of generic fields $\Psi[x,t]$ and their time derivatives [...]
My hang-up concerns the use of the word funct... | In stead of calling a Lagrangian a functional, one should call it an operator.
Like the example in the question, physics literature is filled with loose terminology. Usually by "functional", it is meant an element of a space dual to some infinite dimensional vector space. Or some map $ V \approx \Omega_1^{\alpha_1}(M) ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27019",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 4,
"answer_id": 3
} |
Group of symmetries of Lagrange's equations Consider the following statements, for a classical system whose configuration space has dimension $d$:
*
*Lagrange equations admit a smaller group of "symmetries" (coordinate change under which equations are formally unchanged) than Hamilton's;
*The 'symplectic diffeomorf... | Here Hamiltonian systems on cotangent bundles $(T^{*}M, \omega_M, H)$ of a manifold
$M$ will be considered.
A symmetry of the Hamiltonian system is a diffeomorphism which preserves 1) The cotangent bundle structure, 2) the canonical symplectic form $\omega_M$ and 3) the Hamiltonian $H$.
A point (or Noether) symmetry ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27122",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 2,
"answer_id": 0
} |
Phase Transition in the Ising Model with Non-Uniform Magnetic Field Consider the Ferromagnetic Ising Model ($J>0$) on the lattice $\mathbb{Z}^2$ with the Hamiltonian with boundary condition $\omega\in\{-1,1\}$ formally given by
$$
H^{\omega}_{\Lambda}(\sigma)=-J\sum_{<i,j>}{\sigma_i\sigma_j} - \sum_{i\in\Lambda} {h_i\... | It seems pretty clear that if you take a very diluted subset of, say, the horizontal line through $0$, then you'll be able to make a Peierls argument.
For example, put $h=+\infty$ (worst possible case, amounting to fixing the corresponding spins to $+1$) at all vertices with coordinates (10^k,0), with $k\geq 1$. Then, ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27170",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 1,
"answer_id": 0
} |
Is this a simple Lie algebra? This question comes from Georgi, Lie Alegbras in Particle Physics. Consider the algebra generated by $\sigma_a\otimes1$ and $\sigma_a\otimes \eta_1$ where $\sigma_a$ and $\eta_1$ are Pauli matrices (so $a=1,2,3$). He claims this is "semisimple, but not simple". To me, that means we should ... | Unless I am mistaken, your algebra is $\mathfrak{so}(4)=\mathfrak{su}(2)\oplus\mathfrak{su}(2)$. The generators are $\sigma_a\otimes 1 \pm \sigma_a\otimes\eta_1$.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27217",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 2,
"answer_id": 0
} |
A nice overview (and maybe derivation) of the Poincaré transformations of the Vector Spherical Harmonics With $Y_{lm}(\vartheta,\varphi)$ being the Spherical Harmonics and $z_l^{(j)}(r)$ being the Spherical Bessel functions ($j=1$), Neumann functions ($j=2$) or Hankel functions ($j=3,4$) defining $$\psi_{lm}^{(j)}(r,\v... | The problem with Poincaré group is in the fact that it is not compact. That's why this question is non-trivial. Though, properly formulated search gives few papers on this topic. Try to find the answer in this paper http://arxiv.org/abs/math-ph/0507056 . The paper itself may be not that interesting, but there is a nice... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27279",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 1,
"answer_id": 0
} |
Holographic Renormalization in non-AdS/non-CFT In AdS/CFT, the story of renormalization has an elegant gravity dual. Regularizing the theory is done by putting a cutoff near the conformal boundary of AdS space, and renormalization is done by adding counterterms on that surface. Mathematically this is also interesting, ... | I believe one has to distinguish two kinds of dualities. AdS/CFT, even in the context where it describes an RG flow (so not the pure AdS_5xS^5 case), is an exact duality to a four-dimensional theory, which interpolates between one well-defined conformal field theory in the UV and another conformal field theory in the I... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27313",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
"answer_count": 2,
"answer_id": 1
} |
Quantum gravity at D = 3 Quantization of gravity (general relativity) seems to be impossible for spacetime dimension D >= 4. Instead, quantum gravity is described by string theory which is something more than quantization (for example it introduces an infinite number of fields). More direct approaches to quantization o... | Two quick comments:
First, having no perturbative excitations is not the same as being topological, at least with the conventional use of these terms.
Secondly, whether quantization of the metric “works” depends strongly on what your expectations are and what tests you subject your theory to, so you’ll get different s... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27443",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 1,
"answer_id": 0
} |
Rigorous proof of Bohr-Sommerfeld quantization Bohr-Sommerfeld quantization provides an approximate recipe for recovering the spectrum of a quantum integrable system. Is there a mathematically rigorous explanation why this recipe works? In particular, I suppose it gives an exact description of the large quantum number ... | This answer addresses the geometrical origin of the Bohr-Sommerfeld condition.
In geometric quantization, the additional structure required beyond the
symplectic data of the phase space is a polarization. The quantization spaces are constructed as spaces of polarized sections with respect a polarization.
The most "ob... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27492",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "19",
"answer_count": 5,
"answer_id": 0
} |
Convexity -- reference request I've been reading a few papers on generalized probabilistic theories, and have been struggling through proofs of some results that involve use of convexity and group theory, e.g. this paper on bit symmetry and many others. Is there a set of introductory lecture notes on convexity (as used... | I am currently dealing with generalized probabilistic theories too, and I had the same problem. For example, I read papers like this one: http://arxiv.org/abs/1012.1215
I don't know a good online reference for this kind of math, but a book that I liked reading very much was
*
*Charalambos D. Aliprantis and Rabee Tou... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27584",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 1,
"answer_id": 0
} |
Allowed states vis-a-vis allowed dynamics in generalized probabilistic theories (GPTs) In his work on information processing in GPTs http://arxiv.org/abs/quant-ph/0508211 Barrett speculates that the trade-off between allowed states and the allowed dynamics in a GPT is optimal in quantum theory, allowing for information... | There has indeed been some work on relating the geometry of the state space to the limitations of the theory. First, work relating the local state space to the non-locality present in a theory developed by Janotta et al. They consider the local state space to be a regular polygon. For a large number of sides, the non-l... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27673",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 1,
"answer_id": 0
} |
References for phase-transitions in supersymmetric field theory Apart from other reasons, recently my interest in this area got piqued when I heard an awesome lecture by Seiberg on the idea of meta-stable-supersymmetry-breaking.
I am looking for references on learning about phase transitions/critical phenomenon in sup... | While this isn't necessarily going to answer your request, I think it might be interesting none the less:
Phases of N=2 Theories in Two Dimensions
In a String Theory context:
The Basic Idea is to study a GLSM in 2D which exhibits the interesting property to lead to Calabi-Yau compactification in one phase and Orbifold... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27768",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 1,
"answer_id": 0
} |
Electric circuit. Slight problem with the sign on voltages
Translation first!
The figure shows an electric circuit.
a) Use Kirchhoffs 2.law on the part-circuit abed and show that $I_3$ = 0,50A.
b) Explain that $I_2 + I_5 = 2,0A$. Use Kirchhoffs 2.law on the part-curcuit befc to find another equation with $I_2$ and $I_... | The book defined the 2.law as follows.
The sum of all emf around a closed circuit is equal to the voltage over all the resistors.
I just think it fails to press that if you do just sum up all the voltages it should indeed be 0. Which is a nice thing if you don't really have an emf in a part-circuit you are analyzing.... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27814",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
What's the distinctions between Yang-Mills theory and QCD? So Yang-Mills theory is a non-abelian gauge theory, and we used a lot in QCD calculation.
But what are the distinctions between Yang-Mills theory and QCD?
And distinctions between supersymmetric Yang-Mill theories and SUSY QCD?
| From the beginning of the wikipedia page on Yang-Mills theory (have you read it?):
"Yang–Mills theory is a gauge theory based on the SU(N) group ...
... In early 1954, Chen Ning Yang and Robert Mills extended the concept of gauge theory for abelian groups, e.g. quantum electrodynamics, to nonabelian groups to provide .... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27987",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 4,
"answer_id": 3
} |
Given entanglement, why is it permissible to consider the quantum state of subsystems? Quantum entanglement is the norm, is it not? All that exists in reality is the wave function of the whole universe, true? So how come we can blithely talk about the quantum state of subsystems if everything is entangled? How is it ev... | Don't you worry about cosmic entanglement coming from the inflationary era. They've collapsed away by now. So don't worry. The wave function has already collapsed. Ordinary Schroedinger time evolution tends to produce more entanglement, but collapses tend to undo entanglement. Are we entangled? No, because the collapse... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28048",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 8,
"answer_id": 5
} |
Reference needed for Iron-based superconductors Iron-based superconductor is a class of high-$T_c$ superconductors discovered in 2008.
Are there any review papers about these superconductors yet? If not, which are the key papers in the field?
| Well, Let Me Google That For You
For specific recommendations, the review in Nature by Paglione and Greene1 is very highly cited and accessible. There is a review of the magnetic properties by Lumsden and Christianson2 and a somewhat older article is available from Hosono and collaborators3. A Nature review on the d... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28300",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Would you die if you put your hands on a powerline? You know how birds perch on powerlines without getting electrocuted? What if by some chance that I find myself falling and I grab on one of them? Let's say both of my hands are on the same line, would i get electrocuted?
I am thinking I won't because the current won't... | Hanging from a power line you should be as safe as a bird.
The voltage difference is between the lines (e.g. in a 3-phase system) and between the line and ground. This voltage difference exists across the insulators and pole, as well as through the air to ground. These voltage differences are obviously small enough to ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28350",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 3,
"answer_id": 0
} |
Any noise slowly starting to take effects? I am studying a system subject to random noise, or a system driven by some noise, for example, heat flow or wave propagation perturbed by noise. I would like to know if there is a real system where the noise take effects slowly instead from the very beginning.
| There are many possible examples of this, and you may need to be more specific in what you want. Here are two that immediately come to mind:
1) A bead in a harmonic trap (or a bending cantilever) that is undergoing thermal kicks from Brownian motion. The strength of these fluctuations depends on temperature; if the t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28425",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Is energy "destroyed" when walking? Conservation of energy states energy can't be destroyed, but isn't energy used up when walking in a straight line? If your not walking up a slope, kinetic energy isn't converted to gravitational potential energy, so what is it converted to?
| In case of walking on horizontal plane chemical energy is turned into heat. (Muscles are constantly contracting and expanding and in this way your body's temperature increases.)
Moving your limbs is not very efficient way of moving, this is why there is a room for improvement. E.g. if you are cycling (or skating...),... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28501",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Hours of light per day based on latitude/longitude formula I'm looking for a formula that will return the number of hours per day given a specific location. I was thinking that can be calculated as a difference of sunrise and sunset, but I see that there are some other ways, like in this topic.
What is the best, fast a... | \begin{align}T_{0} &=\frac{T}{\pi}\arccos\left(\frac{\tan\varphi\sin\theta}{\sqrt{\tan^{2}\alpha+\cos^{2}\theta}}\right) \\ \textrm{daylength} &=\begin{cases}
T-T_{0} & \frac{\pi}{2}\le\alpha\le3\frac{\pi}{2}\\
T_{0} & \textrm{otherwise}
\end{cases}\end{align}
where $T=24\ \textrm{hours}$, $\varphi$ is latitude, $θ = 2... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28563",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 5,
"answer_id": 4
} |
The Faddeev-Popov Lagrangian This is a non-abelian continuation of this QED question.
The Lagrangian for a non-abelian gauge theory with gauge group $G$, and with fermion fields and ghost fields included is given by
$$
\mathcal{L}=\overline{\psi}(i\gamma ^\mu D_\mu -m)\psi+\sum _{k=1}^{\dim (G)}\left[ \frac{-1}{4}F_{\m... | The third term is a gauge fixing term. At this point in time, the Wikipedia article on gauge fixing has has a nice section on it, here: https://en.wikipedia.org/wiki/Gauge_fixing#R.CE.BE_gauges These express the so-called $R_ξ$ gauges - with $\xi=1$ called the Feynman–'t Hooft gauge, and the $\lim\xi\to0$ being the Lan... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28629",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 3,
"answer_id": 2
} |
Linking two balls together I have a physics simulator that simulates a bunch of balls moving and colliding with each other, and I would like to be able to "link" two balls together so they stick to each other (are always tangent to each other), i.e. I want to be able to make a chain of balls. What is the general approa... | If you can simulate pendulums, you could make Newton's cradle.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28683",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
One-Plaquette Action and SU(2)'s Irreducible Representations I have a typical single-plaquette partition function for a gauge-field
$$ Z=\int [d U_{\text{link}}] \exp[-\sum_{p} S_{p}(U,a)]$$
with $U$ as the product of the the $U$'s assigned to each link around a plaquette. Now the $U$'s are irreducible representations... | I'm not completely sure what OP is asking(v1). However here is my interpretation.
OP asks:
How do I know which group elements [...] to assign to each link?
The group element $U_{\ell}\in SU(2)$ affiliated with a link $\ell\in L$ is not fixed. One is supposed to integrate over all possible group values of $U_{\ell}\in... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28741",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Optical Tunneling Is there light tunneling taking place in optically transparent mediums like glass? wherein light travels a larger path in these mediums without interacting with atoms and without any change in velocity, frequency, wavelength or momentum? but just getting affected by the field of atom and following the... | I'm not sure what you mean by light tunneling through an optically transparent medium without interacting. When light propagates through a medium, it does interact with the medium. You can think of a transparent medium to be composed of a lot of tiny dipoles which are driven to oscillate due to the electric field of th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28815",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
What is a "Center Of Mass" issue of a Gorillapod? I read somewhere that a Gorillapod may have "Center Of Mass" issues when used with the long lenses.
So, I wish to understand what is a "Center Of Mass" issue?
I have to clarify that I am NOT a physics student nor I ever intend to be. Answers in a layman's language woul... | Continuing from Pygmalion's answer a graphical explaination can be as below
(Warning! - Representation may be a bit wierd and out of proportion)
Initially without the camera this is the case
After camera with long lenses is placed the COM (centre of mass) shifts upwards and outwards as below
This might be the "Cent... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28882",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 1
} |
Introduction to string theory I am in the last year of MSc. and would like to read string theory. I have the Zwiebach Book, but along with it what other advanced book can be followed, which can be a complimentary to Zwiebach. I would like a more mathematically rigorous book or lecture notes along with Zwiebach.
Specif... | There's always David Tong's notes on string theory. If you really want to get the ideas and move forward then it's the place to go. If you really want to take a stroll through string theory (and not in a hurry) then Polchinski is something you should definitely look.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29007",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "33",
"answer_count": 8,
"answer_id": 7
} |
How can there be a quantum field theory that predicts all particle masses? Say I have a theory with only one (energy) scale, e.g. one given by the fundamental constants
$$\epsilon=\sqrt{\dfrac{\hbar c^5}{G}}.$$
In this case, where I can't compare to something else, is there a way to argue that
$$\epsilon<\epsilon^2<\e... | Theories don't predict units unless you put units in. A theory which predicts the masses of the fundamental particles would actually only predict the mass ratios $a_\phi$. Presumably they would emerge as eigenvalues of some operator, or perhaps as the zeros of some complicated function.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29058",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 4,
"answer_id": 2
} |
Does the Breit Wigner formula apply to intermediate virtual particles? Breit Wigner Formula describes the cross section for interactions that proceed dominantly via a intermediate particle (O*) A+B → O* → C + D:
$$σ = \frac{2\Pi}{k^{2}}\frac{Γ_{i}Γ_{f}}{(E-E_{o})^{2} + (Γ/2)^{2}}$$
A short question: Does the formula ap... | The Breit Wigner Formula in the cross-section reveals a pole in the scattering amplitude living in the upper half-plane of complex values of energy if you do a analytic continuation.
The state of the system have this form: (We are free to choose the $\pm$)
$$
\psi^{(\pm)}_g(t)=\int d\alpha\, e^{-iE_\alpha t} g^{(\pm)}(... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29101",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 2
} |
What is behind recoherence? I am quite familiar with the concept of decoherence, and I heard that a system that has decohered could recohere after that, I was wondering what could cause the the coherences that have leaked into the environment to come back to the system. I heard about thermal fluctuations for example, w... | If you consider the thermal fluctuations that arise from coupling the system to a heat bath, then if the dynamics of the open system is non-Markovian then you can have recoherence and if the dynamics of the open system is Markovian (Lindblad master equation) then you will only have decoherence.
Non-Markovian means that... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29147",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 2,
"answer_id": 0
} |
Rotational speed of a discus I was wondering whether the rotational speed of a discus has any influence on the flight of the discus. Would slowing the rotation or speeding it up change the trajectory in any way or would the flight simply become unstable when slowing down?
| Allegedly the rotation has two effects. I say "allegedly" because although I was told this in physics lectures at university I'm not sure if anyone has ever rigorously proved it.
Anyhow, with the disclaimer behind me, the first effect is that the angular momentum stabilises the angle of the discus as it travels through... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29285",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 0
} |
Light interference maximum and minimum intensity points This is a very basic question, but I just forgot how to solve this. It's classical physics question.
Suppose that there are two light sources. And some place away exists a screen. How do I find maximum light intensity points and minimum light intensity points?
And... | Suppose your sources are at points $A$ and $B$ and you're calculating the intensity at point $C$. Calculate the two distances $AC$ and $AB$. If the difference between these two distances is an integral number of wavelengths the two waves will be in phase at the point $C$ and will add to each other so you get a bright s... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29324",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Adding 3 electron spins I've learned how to add two 1/2-spins, which you can do with C-G-coefficients. There are 4 states (one singlet, three triplet states). States are symmetric or antisymmetric and the quantum numbers needed are total spin and total z-component.
But how do you add three 1/2-spins? It should yield 8 ... | Reading over the previous answers, perhaps the answer is simple. We know, in atoms, for example, that it is impossible to have three electrons with the same orbital state. You're question is essentially asking if we have one orbital and we put three electrons into it what state will it be in?
The answer is that, due to... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29443",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "42",
"answer_count": 6,
"answer_id": 4
} |
Electrostatic Pressure Concept There was a Question bothering me.
I tried solving it But couldn't So I finally went up to my teacher asked him for help . He told me that there was a formula for Electrostatic pressure $\rightarrow$
$$\mbox{Pressure}= \frac{\sigma^2}{2\epsilon_0}$$
And we had just to multiply it to the ... | I haven't seen the term electrostatic pressure used explicitly before, but I can explain how to think about the problem.
You need to consider the total force on each hemisphere, which is of course the integral over the sphere of the (vector) force per unit area. Take, then, a surface element $dA$, with charge $\sigma d... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29504",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 6,
"answer_id": 1
} |
how to measure activation energy of fission? i heard that fission activation energy of (235)U is less than of neutron separation energy of (236)U so this must the reason that (235)U is fission able
$$E_s+(236)U\to (235)U+n$$
in this interaction $E_s$ is neutron separation energy ( energy required to separate neutron )... | Anna gives an excellent description of fission by neutron capture, and I'd guess that is what you were asking about. However I thought it worth adding that nuclei can also undergo spontaneous fission, though only very heavy nuclei do this. In principle uranium (235 and 238) can undergo spontaneous fission but it's very... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29555",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
How does Lunar Orbit Injection (LOI) work? Just what the title states.
I read that LOI was used by the Apollo program (and possibly others) to achieve escape velocity. How does it work? Is it merely a matter of centrifugal/centripetal force?
| The typical Apollo TLI burn results in an Earth orbit with an apogee approximately twice the lunar mean distance. It is targeted close enough to the Moon that at some point the Moon's gravity has more influence on the Apollo's path and pulls the spacecraft toward it [the Moon]. The velocity of Apollo once it reaches th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29810",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Determine the acceleration and angular acceleration of a disc The question is:
A 90kg disc is floating in a frictionless vacuum. A 150N force is
applied to the outer rim of the disc. The disc has a radius of 0.25m
and a radius of gyration of 0.16m. What is the acceleration and
angular acceleration of this disc?... | First, it's important to properly understand the equations of rotational motion. Rather than $F = ma,$ the operative equation of motion is $\tau = I \alpha$, where $\tau$ is the torque, $I$ is the moment of inertia and $\alpha$ is the angular acceleration. This problem also requires you to know the definition of the ra... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29924",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
What is the optical power level of common fiber optics lasers? In the book Nonlinear Optics, it is stated that the nonlinear effects start to become a problem in WDM systems (around 1550 nm) after about 1 mW of optical power. However, I measured the optical power at transmission of a transmitting laser of a 10GBASE-ZR ... | The common optical power on a 4km link is about 1mW, with ~2dB/km loss.
with a good-quality single-mod fiber, the non-linear effects are negligible.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29983",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 1,
"answer_id": 0
} |
Enhance a home build spectrometer I would like to build a home made spectrometer like it's describing here:
http://coolcosmos.ipac.caltech.edu/cosmic_games/spectra/makeGrating.htm
How can I improve this spectrometer? A prism from an old binocular?
How would I enhance this spectrometer to improve accuracy and clarity?
| Tip:
Since you will be looking at light sources, try for a even smaller slit, using razor blades. Smaller slit increases resolution, but decreases intensity of lines.
Prism:
The DVD has 1350 lines per mm, that's gives a good dispersion. Prism will spread the spectra more,and stand alone emission lines will be more spac... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30031",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 1
} |
what is difference between these two expectation values? what is difference between these two expectation values $\langle \hat A \hat B\rangle$ and $\langle \hat B \hat A\rangle$?
where the $\hat B$ and $\hat A$ are two operators.
| $$\langle \hat{A}\hat{B} \rangle -\langle \hat{B}\hat{A} \rangle = \langle \hat{A}\hat{B}-\hat{B}\hat{A} \rangle$$
So it is simply the expectation of the commutator.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30155",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Formation of the overlap in metal electron bands I understand that metals have overlapping of valence and conduction bands. But is this because there exists a partial conduction band within the top part of a metal valence band, or because the conduction band exists, but periodically in the valence region? Is this enabl... | I'm not sure that "overlapping of valence and conduction bands" is a particularly helpful way to think about metals. Band structure doesn't come with a set of labels saying "this is the valence band, this is the conduction band". As a first approximation we can think of the band structure as determined by the potential... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30214",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What exactly are right movers and left movers in string theory? In string theory , What exactly are right movers and left movers ?Are they waves propagating along the string to the right and to the left respectively ?
Can some-one please show me how to derive in details the general solution of the equation of motion f... | The solutions to the classical string equations of motion are given by the embedding functions as functions of the string world sheet parameters $(\sigma, \tau)$. The solutions are given in terms of arbitrary vector functions of $\sigma \pm \tau$. The positive sign are called right movers and the negative sign left mov... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30258",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Topology needed for Differential Geometry I am a physics undergrad, and need to study differential geometry ASAP to supplement my studies on solitons and instantons. How much topology do I need to know. I know some basic concepts reading from the Internet on topological spaces, connectedness, compactness, metric, quoti... | As for algebraic topology you start with Armstrong's Basic topology or the last portion of Munkre'sTopology then move to Hatcher's AT [http://www.math.cornell.edu/~hatcher/AT/ATpage.html].if want to learn differential geometry online see Zaitsev D. Differential Geometry: Lecture Notes (FREE DOWNLOAD) and Hicks N.J. Not... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30295",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 2
} |
Collision of a black hole & a white hole A black hole and white hole experience a direct collision.
What happens? What shall be the result of such a collision?
| This question has a somewhat faulty premise that a white hole and a black hole (or anything else for that matter) could collide. In fact a white hole is defined as an area of spacetime where nothing could enter from the outside, or, mathematically speaking, it is a maximal extension of a black hole (part of an eternal ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30406",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 8,
"answer_id": 0
} |
Could a Class A Stellar Engine Use A Brown Dwarf Could a class A stellar engine (or maybe a class C one) be built using a brown dwarf (for argument's sake, a T-dwarf like Gliese 229B)? Would it be capable of enough thrust to move itself any appreciable distance over a long enough period of time? (Let's say over a perio... | The basis for a stellar engine (according to the Wikipedia link) is that the radiation pressure from the star is used to create thrust, so the question reduces to "Do brown dwarfs emit enough radiation"? Stars like the Sun do emit radiation, and lots of it - in the Sun's case, $3.846 \times 10^{26}$ watts. That's a lot... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30453",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
What is spontaneous symmetry breaking in QUANTUM GAUGE systems? Wen's question What is spontaneous symmetry breaking in QUANTUM systems? is cute, but here's an even cuter question. What is spontaneous symmetry breaking in QUANTUM GAUGE systems?
There are some gauge models where the Higgs phase and the confinement phase... | It's all about RELATIVE symmetry breaking in QUANTUM GAUGE theories. RELATIVE to the Higgs field direction, symmetry is broken. This is a novel concept of RELATIVE symmetry breaking. A spin-0 helium atom quantum state might not break rotational symmetry, but RELATIVE to the direction of one of the electrons relative to... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30613",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 4,
"answer_id": 3
} |
Pressures Necessary for Carbon Detonation Carbon detonation is a characteristic event of Type 1a Supernova, where an accreting white dwarf near the Chandrashankar limit of 1.4 solar masses explodes, which is an extremely important standard candle for cosmology. An area of active research is designing computer simulatio... | In stars, carbon-carbon fusion gets going around $5\times10^8\,\text{K}$. From a quick glance at a relevant stellar model I have lying around, it looks like the relevant pressure in the core of a $12M_\odot$ star is on the order of $10^{22}\,\text{dyne.cm}^{-2}$ or $10^{21}\,\text{Pa}$. But the densities are also very ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30755",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Why isn't it allowed to use a flash when taking pictures in a certain place? When I go to, for example, a museum I try to take some pictures.
Sometimes the museum staffs forbid me to use a flash. Do you know the reason? I don't think it is related to photo-electric effect, right?
| My local museum prohibits flash photography because other people in the museum find it annoying. It's nothing to do with any effect, real or imagined, that the flash may have on the exhibits.
Many organic pigments are slowly destroyed by light, so colours fade if exposed to light. I suppose in some special cases museum... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30835",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 6,
"answer_id": 1
} |
How do we know that Earth is not perfect sphere? I've just read here that:
Equatorial radius = 6378.16 kilometers. Polar radius = 6356.78
kilometers, so the difference in circumference is 71.1 kilometers. It
is not a perfect sphere, but kind of pear-shaped.
How correct is that information and what exactly are Equ... | As to, how do we know?
Originally we sent teams of (mostly French) madmen to measure the distance on the ground between two distant mountain tops near the equator, in the jungles of south America, and then the same thing between places in the arctic.
They then measured the angular distance between the points by making ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30920",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 4,
"answer_id": 3
} |
How to calculate speed difference between objects close to the speed of light? If two different objects (for example two rockets) move in opposite direction at close to the speed of light (for example 0.8c and 0.9c), how do I calculate the difference in speed between the two (which in classical physics would be 0.8c + ... | First, let's be clear on the physical setup here. Suppose that, in the reference frame of the Earth, there is a rocket moving in one direction at 0.8 c and another rocket moving in the opposite direction at 0.9 c. In this reference frame, the distance between the two rockets is increasing at a rate of 1.7 c. That's ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31042",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
What does spin 0 mean exactly? I heard two definitions:
*
*Spin 0 means that the particle has spherical symmetry, without any preferred axis.
*The spin value tells after which angle of rotation the wave function returns to itself: $2\pi$ / spin = angle. Therefore, spin 1/2 returns to itself after $4\pi$, spin 1 aft... | There is no contradiction, though your statement (2) for spin 0 is incorrect. The wavefunction of a particle of spin $j$, when rotated by $2\pi$ radians, is multiplied by a phase $(-1)^{2j}$, so that integer spins return to themselves after $2\pi$ rotations but half-integer spins need $4\pi$. Thus for spin $j=0$, the w... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31119",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "22",
"answer_count": 4,
"answer_id": 2
} |
Coriolis Effect and the Space Shuttle The Coriolis effect is a well-known phenomenum, important in meteorology and ocean current forecasting. In addition to location (latitude), it depends on velocity and duration. I assume that commercial aircraft autopilot inertial guidence systems have the ability to compensate for ... | I am not particularly an expert either, but my understanding is that shuttle flight is a very active process compared to ballistic motion, so any effects the Coriolis effect might have can just as well be considered as additional errors in the trajectory, which is being adjusted. There's an active feedback loop at wor... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31161",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 1
} |
What is the winding number of a magnetic monopole, and why is it conserved? I had asked a similar question about a calculation involving the winding number here. But i haven't got a satisfactory response. So, I am rephrasing this question in a slightly different manner. What is the winding number of a magnetic monopole... | Winding number of a magnetic monopole is 7 in 4D. It is conserved both in SU(2) gauge and in SU(3) gauge, where is colour-dependent. It excludes an algorithmic character both for gamma_mu and gamma_nu in Dirac equation. "Both connections are "left-handed".
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31232",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Dimension of vector resulting from tensorial product I'm quoting what I found in a book about quantum computation:
Individual state spaces of $n$ particles combine quantum mechanically through the tensor product. If $X$ and $Y$ are vectors, then their tensor product $X\otimes Y$ is also a vector, but its dimension is ... | There's no wonder you're confused - the author obviously was as well.
First, the operations he's talking about are direct sum $U\oplus V$ and tensor product $U\otimes V$ of vector spaces. This has nothing to do with the vector product (an ambiguous term which most often denotes the cross product you probably know from ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31354",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 0
} |
What is the difference of the two stable states of a Flip-flop?
In electronics, a flip-flop or latch is a circuit that has two stable
states and can be used to store state information. [...] Flip-flops and latches are used as data storage elements. Such data storage can be used for storage of state, and such a circu... | A flip-flop (bistable multivibrator) is, in simple terms, two transistors wired together in such a way that there are two stable conditions: (1) one transistor is full "on", while the other if full "off" (2) vice versa
If the circuit happens to be in a state "in-between" these two states, it will, due to positive feedb... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31527",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
How is energy transferred from one incompressible fluid to another? When you apply pressure to an incompressible fluid the pressure is transferred. If you stop applying the pressure there is no motion. Volume and density are integral parts of calculating how much energy is required to achieve certain useful motion lik... | Browse on Pascal's Principle.
The incompressibility of a fluid (liquid or gas) depends on the structure of its molecules. Thus, gases have higher compressibilities compared to liquids. This is because gases have more dispersed particles than liquids. This is analogous to a big soccer field with a lot of people standing... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31587",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
What equations govern the formation of droplets on a surface? When some smooth surface (like that of a steel or glass plate) is brought in contact with steam (over e.g. boiling milk) then water is usually seen to condense on that surface not uniformly but as droplets. What are the equations which govern the formation ... | I would suggest you the following well written review articles, by Jens Eggers, who is one of the most renowed and acknowledged researchers on this field:
Drop formation – an overview
Nonlinear dynamics and breakup of free-surface flows
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31638",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 0
} |
Sound frequency of dropping bomb Everyone has seen cartoons of bombs being dropped, accompanied by a whistling sound as they drop. This sound gets lower in frequency as the bomb nears the ground.
I've been lucky enough to not be near falling bombs, but I assume this sound is based on reality.
Why does the frequency dro... | My father was a radio operator on B-17 bombers during WWII. As we were watching an old war film together when I was young, we listened to the sound effects of bombs as they neared the point of impact on the ground. I remember my father's comment that the sounds in the movie were wrong, adding "As a bomb moves closer ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31709",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 6,
"answer_id": 2
} |
Glass - paper: Stevin's Law In my understanding the well-known experiment of the glass full of water in equilibrium with a piece of paper, the atmospheric pressure acts on a small layer inside the glass (on the top) and under the paper (outside the glass), the hydrostatic pressure (basically the weight of the water) ac... | You expect that the paper will bend downwards due to the decreased pressure applied to the air gap causing an increase in its volume, but your observation is that instead the paper is bent upwards.
I think that this is probably caused by water leakage. Try the experiment again with a plastic seal over the glass, I expe... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31759",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
formula for transparency of very thin film of metal Is there formula that gives transparency of very thin film of given metal (tens of nanometers) to the visible light/light of given wavelength ? Which properties of metals are needed for the formula ?
I need to know which thickness of aluminium has 40% transparency to... | Have a look at my answer to Make a semi transparent mirror with copper
Although the question is about a different metal the principle is the same. Note however that 40% transmission requires a very thin film, and at those thicknesses the film has a tendancy to form islands of metal with voids between them. This causes ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31830",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 2
} |
Flow of freezing liquid or a melting solid If a liquid is freezing, is equation of continuity violated? As the liquid flows, some portion of it is getting frozen. The mass of the fluid thus keeps dropping. Similarly, when a molten fluid flows over a solid, its mass may increase because the solid over which it flows als... | The continuity equation is not violated in either of the situations you describe above. The generic continuity equation for some scalar quantity (such as density) can be written as
$\frac{\partial \psi}{\partial t} + \nabla . \psi\mathbf{u} = \sigma$, (1)
where here $\psi$ is the some conseverd scalar quant... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31888",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Electromagnetic field of unpolarized light I need help in finding an expression for the instantaneous electric and magnetic field of unpolarized light in order to write down and evaluate the time-averaged norm of the Poynting vector (i.e. the intensity of unpolarized light). I expect this to be a superposition of some ... | Unpolarized light is not a superposition of polarized light (which would again be polarized) but a mixture of polarizations in all directions.
It cannot be described by a single solution of the Maxwell equations. Instead one needs for proper modeling the statistical version of electrodynamics. See the book on quantum ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31971",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 1,
"answer_id": 0
} |
What is a tensor? I have a pretty good knowledge of physics, but couldn't deeply understand what a tensor is and why it is so fundamental.
| My very simple answer is really just one of many situations where a tensor is handy when describing the forces on a body...they are used almost everywhere in physics however...this just one SIMPLE example.
A cubic body is moving through air and is feeling the resistance to motion orthogonal to it's trajectory. This nor... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32011",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "68",
"answer_count": 12,
"answer_id": 9
} |
Phase shift of 180 degrees of transversal wave on reflection from denser medium Can anyone please provide an intuitive explanation of why phase shift of 180 degrees occurs in the Electric Field of a EM wave, when reflected from an optically denser medium?
I tried searching for it but everywhere the result is just used.... | Since this has just been asked again, let me attempt an intuitive explanation. The real explanation is of course to match $\vec{E}$ and $\vec{B}$ at the interface and the direction of the reflected wave drops out, but this isn't especially intuitive.
Let's calculate the ratio $E_r/E_i$ as a function of the ratio $n_t/n... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32122",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "54",
"answer_count": 6,
"answer_id": 3
} |
Liquid crystal polarizes light reflection question I was hoping someone could help me with understanding why a row of polarizes reflects a light wave when the whole row is the same length as the wavelength of the light.
I pretty much get the physics behind the rest, just don't understand this little part. Why only the... | The question is somewhat mixed so I will try to restate it as I understood it and you should correct me if I got it wrong.
As I see, the question here is: why does a thin film of liquid crystals changes its color as it gets colder or warmer?.
The answer to this question is interference. The light is reflected from both... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32178",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Can you use PCR to make a standard kg? While reading this question: Why do we still not have an exact (constants-based) definition for a kilogram? , I had a crazy thought.
Using PCR, you make a known number of copies of a DNA strand where the length and composition is exactly known for all the copies. The number of cop... | According to http://en.wikipedia.org/wiki/Taq_polymerase the error rate in the PCR reaction is about 1 error for every 9000 nucleotides replicated. I suspect this makes PCR too unreliable to use as a standard even if you have isotopically pure feedstuffs.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32215",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
What controls whether a ball will skid or roll? A billard ball is struck with a cue. The line of action of the applied impulse is horizontal and passes through the center of the ball. The initial velocity $v_0$ of the ball, its radius $R$, its mass $M$ and coefficient of friction $\mu_k$ between the ball and the table ... | Start by finding the force that is trying to spin the ball. Actually it is a torque. Then try to find out for how long this torque needs to be applied such that the rotational speed matches the transnational speed and there is no slip at the contact.
Depending on your convention (what is positive or negative) you need ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32292",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why does laser light not affect glowing materials? I have this childrens rubber ball which glows in the dark after it's exposed to light. I "charge" it with a flash light then play with my dogs at night. I thought to try a very intense green laser, and see how the ball reacted.
The laser light had no effect on the ball... | Luminescence happens when the atoms of the material have the property of absorbing light at some frequencies, which means some electrons are kicked to an excited orbit, which happens to be stable enough, i.e. decays with a long enough lifetime to be observed as luminescence.
As a follower of this forum you must know t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32402",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "40",
"answer_count": 2,
"answer_id": 1
} |
Why does vibration loosen screws? I am trying to figure out why vibrations (say, from an engine) loosen screws. It seems to me that there is evident symmetry between loosening and tightening a screw. I am wondering what breaks this symmetry.
| The forces on the screw are not symmetric. Once the screw is no longer turning loosely in the hole tightening the screw compresses the two materials held together (i.e. increases the stress on the material, i.e. stores energy in the material), while loosening reduced the compression (i.e. releases the stress).
So a ran... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32481",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
"answer_count": 2,
"answer_id": 0
} |
particle accelerators and Heisenberg uncertainty principle In accelerators we shoot very high momentum particles at each other to probe their structure at very small length scales. Has that anything to do with the HUP that addresses the spread of momentum and space?
Related, when we accelerate a proton at exactly, say,... | Notice that the Heisenberg uncertainty relationship involves only the precision with which the two quantities are known, not their magnitude. In
$$ \Delta p \Delta x \ge \frac{\hbar}{2} $$
we see $\Delta p$ but not $p$.
That means that the magnitude of the momentum makes no difference at all as far as the uncertainty ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32576",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 4,
"answer_id": 3
} |
Motion in the body-fixed frame? This is really basic, I'm sure: For rigid body motion, Euler's equations refer to $L_i$ and $\omega_i$ as measured in the fixed-body frame. But that frame is just that: fixed in the body. So how could such an observer ever measure non-zero $L$ or $\omega$?
| You must remember that the 'body-frame' (which is the frame 'inside' the rotating body) is a frame and that OTHER bodies (which may, for example, be rotating about the same point with a different speed) will appear in the 'body-frame' to have an angular speed less than if observed in an inertial (stationary) frame.
To ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/32787",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 6,
"answer_id": 3
} |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.