_id stringlengths 1 6 | title stringlengths 15 150 | text stringlengths 30 20.1k | instruction_seed stringlengths 58 1.47k | __original_row_idx int64 0 38.3k | _source stringclasses 1
value |
|---|---|---|---|---|---|
15199 | What is a nonlinear field? | I have read two possible definitions. A nonlinear field is 1. A field taking values on a manifold. 2. A field whose equation is nonlinear. What do you understand by a nonlinear field or a nonlinear theory? | What are the key distinctions between a nonlinear field defined on a manifold and a nonlinear field characterized by a nonlinear equation? | 31,207 | cqadupstack-physics |
81142 | Second order degenerate perturbation theory | What is a good resource to learn about higher degree **degenerate** perturbation theory \- one that involves mathematics that isn't much more advanced than first order perturbation theory? I've looked around and I've only found Sakurai talk about it but he uses projections operators and other fancy mathematics. Also, d... | What are the conditions under which degenerate perturbation theory can be applied to a quantum system, and can you provide a specific example illustrating its use in calculating energy shifts? | 29,862 | cqadupstack-physics |
45387 | Why can't missing mass be photons? | After a star lives and dies, I assume virtually all of it's mass would be photons. If enough stars have already lived and died, couldn't there be enough photon energy out there to account for all the "missing mass" (=dark matter) in the universe? And if there were enough photons to account for all the missing mass, wha... | If a dying star transforms most of its mass into photons, calculate the total energy produced by a star with a mass of 2 solar masses at the end of its life, and determine whether this energy could account for the estimated amount of dark matter in the universe, which is approximately 27% of its total mass-energy conte... | 20,562 | cqadupstack-physics |
133941 | A Variation on Laplace's equation (context: Yang-Mills N-Instantons, Rajaraman's book) | **Statement of the problem** I need to solve the equation \begin{align} 0 = \frac{1}{\phi} \partial_{\sigma}\partial_{\sigma} \phi \hspace{20mm} (1) \end{align} where $\phi$ is a scalar field and we're working in Euclidean 4-space. More specific questions are asked below. Basic advice on this would also be appreciated.... | What is the general solution for the scalar field \(\phi\) in the equation \(0 = \frac{1}{\phi} \partial_{\sigma}\partial_{\sigma} \phi\) when \(\phi\) is allowed to be singular, and can you verify if \(\phi = \frac{1}{|x|^2}\) satisfies this equation for all \(x \neq 0\)? | 21,077 | cqadupstack-physics |
32553 | What should I call an n>4 dimensional Minkowski metric? | I am manipulating an $nxn$ metric where $n$ is often $> 4$, depending on the model. The $00$ component is always tau*constant, as in the Minkowski metric, but the signs on all components might be + or - , depending on the model. (I am not trying to describe physics with this metric). Can I call this metric a Minkowski ... | Given an \( n \times n \) metric with the \( 00 \) component equal to \( \tau \cdot \text{constant} \) and the possibility of varying signs for other components, how does the signature of the metric (i.e., the number of positive and negative eigenvalues) determine whether it can be classified as a Minkowski metric when... | 36,634 | cqadupstack-physics |
54259 | Could a universe with purely Newtonian mechanics exist? | I've heard about the fine-tuning principle and how if the fundamental constants of the Universe were changed even a slight bit, life could not exist as we know it. However, study on this subject seems to only have really started after the discovery of relativity (or at least study based on any real empirical inferences... | If the fundamental constants of the universe were to align perfectly with those described by Newtonian mechanics, what conditions would need to be met for complex life, similar to that on Earth, to emerge and thrive? Please provide a quantitative analysis or example to illustrate your answer. | 25,696 | cqadupstack-physics |
123103 | Cooling induction current generation | We know that conducting materials can be heated by electromagnetic induction. Is it possible to generate current using a cooling process? | Is it possible to generate electric current in a conductor through a cooling process, and if so, what principles govern this phenomenon? | 2,532 | cqadupstack-physics |
31831 | Is my electric kettle collecting old water during the week? | I have an electric kettle at work. On Monday, it's empty and I pour in about 1.5 liters of water. I usually end up drinking about 1 liter per day and refilling 1 liter each morning. At the end of the week, I rinse it out because in my mind, there is .5 liters of "old" water from the beginning of the week on the bottom.... | If I start with 1.5 liters of water in an electric kettle and drink 1 liter per day while refilling it with 1 liter each morning, how much "old" water remains in the kettle at the end of the week if the water is consistently mixed? | 15,869 | cqadupstack-physics |
118772 | Throwing ball against oily/slippery wall | I would like to know whether a ball bounces back normally if you throw it against an oily wall. Like a wall watered down with oil. Basically I want to know if it will actually slip before bouncing back or not? | What is the coefficient of restitution for a ball thrown against a wall coated with oil compared to a dry wall, and how does this affect the ball's ability to bounce back versus slip before bouncing? | 17,667 | cqadupstack-physics |
135302 | Strange definition of microcanonical partition function | I always thought that the microcanonical partition function would measure the number of states that correspond to some fixed energy. Despite, I found in this paper (equation 3.4) that we integrate over all configurations that have an equal or lower energy than some fixed number $E$. Does this make sense to you? See eq.... | In statistical mechanics, how does the microcanonical partition function relate to the number of accessible states for a system with fixed energy \( E \), and what is the significance of integrating over all configurations with energy equal to or less than \( E \)? Provide a mathematical expression for the microcanonic... | 6,295 | cqadupstack-physics |
18874 | Could someone remind me what this means again? $\nabla U = \pm F$ | You know that for a potential function (conservative force/fields) that $\nabla U = \pm \vec{F}$ In math, we don't have that minus sign, we have only the plus one. What does it mean if you get rid of the plus sign? I remember the minus signs tells us that the force is always in the opposite direction of the increasing ... | Is it possible to construct a potential function \( U(x) \) for which the corresponding force \( \vec{F} = -\nabla U \) increases in magnitude as the potential \( U(x) \) increases, and if so, provide an example or a mathematical formulation that demonstrates this concept? | 1,443 | cqadupstack-physics |
108992 | Is there work done when two current carrying wires are attracted? | When a current carrying wire attracts(or repels) another wire, the wire moves under the action of a force. Also, it is obvious that the work done is due to force of "magnetic field" on "moving electrons". Now, from the equation $$\overrightarrow F=q[\overrightarrow v,\overrightarrow B] $$, where $[\overrightarrow a,\ov... | Explain why the work done on a current-carrying wire moving in a magnetic field is not necessarily zero, despite the force being perpendicular to the velocity. In your answer, consider the role of the magnetic field and the interactions with the charge carriers in the wire. Additionally, what implications does this hav... | 28,775 | cqadupstack-physics |
62650 | Supersymmetry and non-compact $R$-symmetry group? | The $R$-symmetry for $N$ supercharges is $U(N)$. Is it possible to generalize $R$-symmetry [let's take $U(4)$) to be something like $U(2,2)$ (maybe analogous to Wick rotation of $SO(3,1)$ to $SO(4)$?)]? | Given the $R$-symmetry for $N$ supercharges is $U(N)$, can you derive the implications of generalizing $R$-symmetry from $U(4)$ to $U(2,2)$ in the context of supersymmetry, and what would be the resulting transformations of the supercharges under this new symmetry? | 30,550 | cqadupstack-physics |
133556 | How can light travel at speed of light? | I am well aware that the speed of light is a universal constant at which nothing but light can travel. But why? Why can even light travel at such a speed? Our maths tell us that anything with rest mass takes infinite energy to reach speed of light, so do we just mean that light is the lightest of all things and it can ... | Why is the speed of light considered a universal constant, and what is the physical mechanism that allows massless particles like photons to travel at this speed, while particles with rest mass cannot reach it? | 5,310 | cqadupstack-physics |
8094 | what about there is no time, only space | what about a theory where no time exists, only discrete space, steady states and occasion chains. what would speak against this? ;-) | In a theoretical framework that proposes a universe consisting solely of discrete spatial points with no temporal dimension, how would you quantitatively assess the implications for the principles of thermodynamics, particularly regarding the second law? | 37,466 | cqadupstack-physics |
53653 | Pauli matrix rotations | When doing physics with two-level systems and introducing rotations, a term that appears quite often is the rotation of a pauli matrix by another one: $e^{- i \sigma_i \theta/2} \sigma_k e^{i \sigma_i \theta/2}$ The way I know to evaluate this is by using $\exp(i \sigma_i \theta/2) = I \cos \frac{\theta}{2} + i \sigma_... | What is the result of the operation \(e^{- i \sigma_x \theta/2} \sigma_z e^{i \sigma_x \theta/2}\) when evaluated using the exponential form of the Pauli matrix, and how can this be simplified without tedious calculations? | 32,689 | cqadupstack-physics |
134501 | Is the image formed at the retina messy? | The following passage has been extracted from Newton's book Opticks: > ...So if PR [in Fig.at the top] represent any Object without Doors, and AB > be a Lens placed at a hole in the Window-shut of a dark Chamber, whereby the > Rays that come from any Point Q of that Object are made to converge and meet > again in the P... | How does the size of the eye lens relative to the objects we observe affect the quality of the image formed on the retina, and can you explain the relationship between the convergence of light rays and the clarity of the resulting image? | 34,306 | cqadupstack-physics |
59212 | Deriving torque from Euler-Lagrange equation | How could you derive an equation for the torque on a rotating (but not translating) rigid body from the Euler-Lagrange equation? As far as I know from my first class in Classical Mechanics, there is no potential defined for a rotating body, so the only term I see in the Lagrangian is the $\frac{1}{2}I\omega^2$. Since t... | How can you demonstrate that the torque on a rotating rigid body can be derived from the Euler-Lagrange equation, given that the Lagrangian is expressed as \( \mathcal{L} = \frac{1}{2}I\omega^2 \) and there is no potential term or angular displacement variable (\(\theta\)) in the Lagrangian? | 13,890 | cqadupstack-physics |
4994 | Pedagogical explanations of critical dimensions of string theories | Once you understand the formalism, I think it's clearest to say the critical dimension of the space-time arises because we need to cancel the central charge of the (super)conformal ghosts on the worldsheet. But suppose I need to explain this to a person who only knows very basic QFT. How would you explain the concept o... | What is the critical dimension of space-time required to cancel the central charge of (super)conformal ghosts on the worldsheet in string theory? | 28,779 | cqadupstack-physics |
60811 | Problem solving moments in equilibrium | > _Two straight ladders, AC and BC, have equal weights $W$. They stand in > equilibrium with their feet, A and B, on rough horizontal ground and their > tops freely hinged at C. Angle CAB = 60$ ^o$, angle CBA = 30$^o$ and AB = > $l$ (see diagram). Find the vertical reactions at A and B._ ![illustration of mechanical pr... | Given two straight ladders, AC and BC, each of weight \( W \), with their feet A and B on rough horizontal ground and their tops hinged at point C. The angles formed are CAB = 60° and CBA = 30°, and the distance between A and B is \( l \). If the vertical reactions at A and B are \( N = \frac{3W}{4} \) and \( R = \frac... | 31,714 | cqadupstack-physics |
35806 | Why does it take until the middle of summer before lakes have warm water, but desert sand heats up in hours? | My sister asked me this question and I keep thinking that water would conduct heat much faster than sand. Hence the energy transfer of heat across the lake does not allow it to heat up soon. Sand on the other hand is probably a bad conductor of heat and hence more heat energy is held up by each grain of sand. But then ... | What is the thermal conductivity of water compared to that of sand, and how do convection currents in water affect its ability to transfer heat compared to sand in a controlled environment? | 1,232 | cqadupstack-physics |
52865 | Indicators on how even the heat is distributed? | I'm wondering if there are any good indicators on how even the heat is distributed on an object (for simplicity, a flat object maybe)? What are the possibly reasonable ways to maximize the evenness if varying the shape of the object is allowed. | If a flat object with a uniform material is heated at one edge, what is the optimal shape of the object to ensure maximum evenness in heat distribution across its surface, and how would you mathematically model this distribution? | 34,571 | cqadupstack-physics |
17720 | Modeling galactic colonization | I found a really cool sounding order-of-magnitude modeling question but am a bit at a loss on how to approach this: > The Milky Way contains 100 billion stars and has a radius of 250,000 light > years. Suppose that humans set a long term goal to colonize every > inhabitable star system in the Milky Way and that 10% of ... | Assuming that 10% of the 100 billion stars in the Milky Way are suitable for colonization, and considering an average distance of 5 light years between these suitable star systems and a travel time of 5000 years for a settler ship, calculate the total time required to colonize all suitable star systems in the galaxy gi... | 19,020 | cqadupstack-physics |
125913 | How to calculate launch angle for tangentially launched satellites? | What is the value of theta for a satellite not falling back to the Earth if it is launched from the direction tangent to the surface of the Earth? I have found the escape velocity which is 11.18km/s, and initial speed for the satellite which ensure it doesn't fall back to Earth, which is 7.4km/s. Shall I solve the ques... | What is the angle \( \theta \) at which a satellite must be launched tangentially from the Earth's surface to maintain a stable elliptical orbit, given its initial speed is 7.4 km/s? | 15,717 | cqadupstack-physics |
65915 | Clarification of Landauer approach | I am trying to understand the Landauer approach. Consider the setup: (left contact)-(conductor)-(right contact). For simplicity, the conductor is a 1d wire (the transverse part is not relevant for this question). The eigenstates of the conductor are $$\psi_n(x)=\sin(k_nx), \qquad k_n=\frac{n\pi}{L}$$ ($L$ length of con... | In the Landauer approach, if we assume a one-dimensional conductor of length \( L \) with eigenstates described by \( \psi_n(x) = \sin(k_n x) \) where \( k_n = \frac{n\pi}{L} \), calculate the conductance \( G \) of the conductor if the right contact is populating states with wave numbers \( k_n = \frac{2\pi}{L} \) for... | 31,387 | cqadupstack-physics |
22544 | What really is the future about the Standard Model | The fact that the bosons of the weak force have mass is something that I think technically poses many problems. To avoid this and other problems with the masses of the particles devised a mechanism within the standart model $SM$ of particle physics $"smpf"$ called "the Higgs field." This field is transmitted by a boson... | What are the expected mass ranges for the Higgs boson and how might the discovery of its superpartners, if they exist, influence our understanding of the Standard Model of particle physics? | 8,007 | cqadupstack-physics |
71377 | 1D Ising Model with different boundary conditions | The Hamiltonian for one-dimensional Ising model is given by, \begin{equation} \mathcal{H} = -J\sum_{<ij>} S_iS_j; \quad i,j=1,2,...,N+1 \end{equation} where $<ij>$ denotes that there is nearest neighbor approximation. The partition function is given by, \begin{equation} \mathcal{Z}=\sum_{\\{S_i\\}} e^{-\beta \mathcal{H... | What are the expressions for the partition function \(\mathcal{Z}\) of the one-dimensional Ising model when the boundary spin \(S_{N+1}=+1\) and when \(S_{N+1}=-1\), considering that the spins \(S_i\) (for \(i=1,2,...,N\)) can take values of \(+1\) or \(-1\)? | 31,040 | cqadupstack-physics |
127820 | Ghosts in theories of gravity and holographic theories | I want to understand when a theory leads to ghosts in gravity. Is there any relation between ghosts and non-linear higher order theories? Ghost is a clasical or quantum field concept? | In the context of non-linear higher order theories in gravity, how do the presence of ghost fields affect the stability of the theory, and can you quantify this effect by determining the conditions under which ghost instabilities arise? | 15,420 | cqadupstack-physics |
5141 | Aside from carbon, what materials change structure under intense pressure? | I was thinking the other day about what sort of exotic materials one would find in the depths of a planet. I have heard theories about how an enormous diamond might be found in the centre of gas giants. Current theories have a ball of iron at Earth's core - would that be like the iron up here on the surface or does the... | What are some examples of materials that undergo structural changes under high pressure, and how do these changes affect their physical properties? | 17,222 | cqadupstack-physics |
101482 | Realistic interpretations of quantum entanglement: Are there alternatives to the "Transactional Interpretation"? | Quantum entanglement bridges space and time: entangled particles show correlations independently of where and when they are measured. This is most evident in "delayed choice quantum eraser" experiments, where the outcome of single measurments _now_ depends on which measurements are done _in the future_ (though there is... | What are the key differences between John Cramer’s "Transactional Interpretation" and Bohmian mechanics in explaining quantum entanglement and delayed choice quantum eraser experiments, and can you provide examples of their implications for our understanding of spacetime correlations? | 17,253 | cqadupstack-physics |
86150 | Partition Function for Two Level System | I have a system with $N_s$ sites and $N$ particles, such that $N_s >> N >> 1$. If a site has no particle, then there is zero energy associated with that site. The $N$ particles occupy the $N_s$ sites and can be in energies $E_1$ or $E_0$, where $E_1 > E_0$. We also know $m$ particles have energy $E_1$ and $N-m$ have pa... | Given a system with \( N_s \) sites and \( N \) particles, where \( N_s \gg N \gg 1 \) and the particles can occupy two energy states \( E_1 \) and \( E_0 \) (with \( E_1 > E_0 \)), derive the correct expression for the partition function \( Z \).
Assuming that \( m \) particles are in the state \( E_1 \) and \( N - ... | 35,879 | cqadupstack-physics |
63157 | EM Waves Energy Loss | Where does the energy go when two photons interfere destructively at a point on a screen in Young's double slit experiment ? | In Young's double slit experiment, if two photons interfere destructively at a point on the screen, what happens to the energy of those photons at that specific point? | 27,232 | cqadupstack-physics |
101920 | Differentiating between mass number (A) and activity (A) in a nomenclature/glossary | I'm not sure if this is the best place to ask this question, but as it's related to the terminology of nuclear physics I thought it would probably be a logical place to start. I'm currently writing my thesis, and in the section on radioactive decay I talk about the mass number and activity of radionuclides. The problem... | What symbols are commonly used to represent the mass number and activity of radionuclides in nuclear physics to avoid confusion when both are denoted as _A_? | 22,597 | cqadupstack-physics |
105518 | Why is the water on one side of a bridge choppy? | My daily commute take me across the Evergreen Point Floating Bridge on Lake Washington. I have noticed on several occasions that the water on the southern side of the bridge will be quite choppy while the water on the northern side is relatively still (not completely still but there is a noticeable difference from the ... | What factors contribute to the difference in water surface conditions, such as chop and stillness, observed between the southern and northern sides of floating bridges, specifically on the Evergreen Point Floating Bridge over Lake Washington? | 1,729 | cqadupstack-physics |
30675 | What exactly are super WIMPs? | I recently got confused (and slightly annoyed by the lack of technical details) when reading a popular article (authored by Jonathan Feng and Mark Trodden) introducing the concept of super WIMPs. The article characterized super WIMPs (without giving more detailed explanations) as follows: * WIMPs could probably decay... | What are the theoretical foundations of super WIMPs in particle physics, and how do they relate to supersymmetric models like the MSSM? Specifically, could you explain the interactions of super WIMPs, particularly in terms of their potential gravitational and dark force interactions? | 13,036 | cqadupstack-physics |
63155 | Sign crazyness on the stress energy tensor? | I would like to know on what depends the sign of the stress energy tensor in the following formula : $T_{\mu\nu}=\pm(\rho c^2+P)u_{\mu}u_{\nu} \pm P g_{\mu\nu}$ In my case the metric is equal to $g_{\mu\nu}=\pmatrix{-c^2 & 0 & 0 & 0\\\0 & 1 & 0 & 0\\\0 & 0 & 1 & 0\\\0 & 0 & 0 & 1}$ and $\rho$ is the mass density. The p... | What determines the sign of the components of the stress-energy tensor \( T_{\mu\nu} \) for a perfect fluid in a given metric, and how can this affect the interpretation of mass density \( \rho \) and pressure \( P \) in a specific context such as cosmology? | 544 | cqadupstack-physics |
132072 | Is light so important in special relativity? | I'm an amateur physics enthusiast with no formal university education in Physics. So my question might sound very naive, so forgive me. I had this question in the back of my mind since the wrong discovery of neutrinos travelling faster than light. My understanding of special relativity is as following. You can measure ... | If a hypothetical particle could travel faster than light and maintain a constant speed relative to an inertial frame of reference, what implications would this have for the principles of time dilation and length contraction as described by special relativity? Can you provide a quantitative example demonstrating how me... | 37,575 | cqadupstack-physics |
52262 | What is the maximum time dilation between two objects, if one is standing still and the other is moving at $c$? | What is the maximum ratio in the rate of change in time in reference to object $A$ which is standing still and object $B$ which is moving at the speed of light? | What is the ratio of the rate of change in time experienced by object $B$, moving at the speed of light, compared to object $A$, which is at rest, according to the principles of special relativity? | 24,149 | cqadupstack-physics |
17787 | Would a solution to the Navier-Stokes Millennium Problem have any practical consequences? | I know the problem is especially of interest to mathematicians, but I was wondering if a solution to the problem would have any practical consequences. Upon request: this is the official problem description of the aforementioned problem. | What are the practical implications of solving the specified mathematical problem in terms of its application to real-world scenarios in biology, physics, or chemistry? | 34,817 | cqadupstack-physics |
8999 | 115 GeV, 170 GeV, and the noncommutative standard model | Several years ago, noncommutative geometry was used to describe the standard model, somehow yielding a prediction of 170 GeV for the mass of the Higgs boson, a prediction which was falsified a few years later. Meanwhile, for a long time there have been indications of a Higgs boson at 115 GeV. As it happens, 115 GeV and... | What value of the coupling constant \(\lambda\) would need to be set in order for the Higgs boson mass \(m_H\) to be approximately 115 GeV, given that \(\lambda = \pi\alpha\) and using the relations from equation 5.15 of hep-th/0610241? | 8,642 | cqadupstack-physics |
48128 | Surface UV exposure with cooler star | If the sun's surface was ~ 4000K (and earth closer to compensate), the UV component of the radiation would be less. However, UV makes ozone via photolysis of oxygen. Also, the stratosphere would probably start up higher (and contain less mass) because UV heating is what's responsible for the inversion. So what is the r... | What is the expected relationship between the temperature of a star in Kelvin and the level of DNA damage due to UV exposure on a planet orbiting that star, considering factors such as ozone generation and stratospheric heating? | 3,267 | cqadupstack-physics |
77299 | Simple rope tension problem | I have this really simple rope tension problem that can be solved for seconds using simple logic. I know what the answer is, I know why it is, but I cannot write it down and explain it mathematically. The problem is the following: An object with mass 6 kg hangs from a rope. The rope is pulled with acceleration of 1 m/s... | An object with a mass of 6 kg is hanging from a rope, and the rope is accelerating upward with an acceleration of 1 m/s². What is the tension in the rope? | 26,099 | cqadupstack-physics |
26374 | Sky-Watcher Skyhawk 1145P SynScan AZ GOTO | What is the experience using the Sky-Watcher Skyhawk 1145P SynScan AZ GOTO telescope and can it be recommended for a new astronomer? Is it any good? | What are the primary optical specifications (aperture, focal length, and magnification) of the Sky-Watcher Skyhawk 1145P SynScan AZ GOTO telescope, and how do these characteristics affect its suitability for beginners in astronomy? | 19,861 | cqadupstack-physics |
77802 | Geodesic in general relativity aproaching ellipse | In the gravity well-like 2d surfaces that are used in documentaries to illustrate the fact Earth orbits the Sun, I don't seem to find any kind of geodesic that will at least resemble an ellipse... What am I doing wrong? Is spacetime curved entirely different from what the animators show us? Any mathematical argument is... | Can you explain how the curvature of spacetime affects the shape of orbits, particularly why elliptical orbits occur in gravity wells, and provide a mathematical demonstration of this concept? | 22,978 | cqadupstack-physics |
11706 | How to apply Andreev reflection formalism to ferromagnet ,normal metal interface? | The traditional formalism for andreev reflection deals with what happens at normal metal, super conductor interface.http://en.wikipedia.org/wiki/Andreev_reflection (i.e when an electron from normal metal is incident on the super conductor interface, a hole is generated in the normal metal which lets the formation of a ... | How does the reflection of an up-spin electron incident from a normal metal onto a half-metal interface differ from Andreev reflection at a superconductor interface, particularly when the spin polarization of the electron is at an angle to the interface? Additionally, what is the quantitative expression for the probabi... | 25,600 | cqadupstack-physics |
83625 | Formula for the energy per site in the triangular Ising model | I'd like to check the correctness of a simulation I ran on the Ising model on a triangular by verifying if I get the good value of the mean energy per site. I found a formula giving it for high temperatures on a square lattice but nothing on the triangular case. My simulation focuses on the critical point so I guess th... | What is the expression for the mean energy per site in the Ising model on a triangular lattice at high temperatures, and how does it compare to the mean energy per site at the critical point? | 5,311 | cqadupstack-physics |
68564 | Why is the stress-energy tensor symmetric? | The relativistic stress-energy tensor $T$ is important in both special and general relativity. Why is it symmetric, with $T_{\mu\nu}=T_{\nu\mu}$? As a secondary question, how does this relate to the symmetry of the nonrelativistic Cauchy stress tensor of a material? This is apparently interpreted as being due to conser... | Derive the condition that leads to the symmetry of the relativistic stress-energy tensor \( T_{\mu\nu} \) in the context of special relativity. Additionally, explain how this condition correlates with the symmetry of the nonrelativistic Cauchy stress tensor, particularly in terms of conservation laws such as angular mo... | 20,360 | cqadupstack-physics |
86409 | Commercial large scale production of graphene | I am a third year undergraduate Physics student, and for my solid state physics course I am asked to give a short (10 minute) qualitative presentation on the current standings of graphene production, about what can be done right now, what is expected to be doable in the near future, what the current problems are that h... | What are the main current methods for producing graphene, and what are their respective outputs (e.g., single-layer vs. multilayer graphene), along with the challenges faced in these production techniques? Additionally, what advancements or techniques for graphene production are anticipated in the next five years? | 21,947 | cqadupstack-physics |
35041 | supressing certain decay paths and enhancing others with interference | In a scattering reaction, there are many possible final states for the products, each with different production rates. > **Question:** Is there a way in which we could in general supress certain > rates of products of the reaction and enhance others? can we use coherence > and interference of the initial states to modu... | In a scattering reaction leading to the production of antihydrogen, how much could the production rate of antihydrogen be theoretically enhanced by using coherence and interference of initial states, expressed in orders of magnitude? | 20,545 | cqadupstack-physics |
18330 | Difference between Clausius-Clapeyron and Van't Hoff equation | I was wondering what is the difference between the Clausius-Clapeyron equation and the Van't Hoff equation. They appear to have the exact same physical meaning and are often used interchangeably. | What are the specific conditions under which the Clausius-Clapeyron equation and the Van't Hoff equation yield similar or different results, and can you provide an example of a scenario where one is preferred over the other? | 21,113 | cqadupstack-physics |
30726 | failing to see the conundrum in the Einstein hole argument | I've been reading about the Einstein hole argument, and i fail to understand what makes active diffeomorphisms "special" compared to passive diffeomorphismsm also known as good old coordinate transformations. Supposedly this article is a good overview of the problem. I've read this, but i feel that i must be missing so... | In the context of general relativity, how does the relationship between active diffeomorphisms and the physical reality of a gravitational field manifest, particularly in terms of observable quantities? Can you provide an example involving a specific metric where such differences would affect the interpretation of phys... | 12,536 | cqadupstack-physics |
106262 | Is the Hilbert-Felber model of repulsive gravity correct? | This theory states that at relative velocities exceeding 3^-0.5 c, gravitational repulsion ensues. The relevant papers are on arXiv by Franklin Felber. Here's one of them http://arxiv.org/abs/0910.1084 I have seen two interesting critiques thus far. The first is that the effect is an artifact of the choice of coordinat... | What is the threshold relative velocity (as a fraction of the speed of light, c) at which gravitational repulsion is proposed to occur according to the theory mentioned by Franklin Felber? | 6,309 | cqadupstack-physics |
30154 | extracting energy from cosmological expansion | This question is a more concrete reincarnation of an old question about energy conservation in GR. Are there mechanisms to extract energy from the cosmic rate of expansion? putting some extremely long ropes across the universe and extract work from their increase of separation? assuming this is possible ( i don't see w... | If it were possible to harness energy from the cosmic expansion of the universe using extremely long ropes, what would be the equivalent force exerted back on the system if we extracted a specific amount of energy, say 1 joule? Additionally, could this process theoretically lead to a measurable reduction in the rate of... | 18,153 | cqadupstack-physics |
103274 | Learning about group velocity, phase velocity and particle velocity | I am studying quantum physics and I would like to know a bit more in detail about group velocity, particle velocity and phase velocity. Can you guys suggest some books/online resources where I can learn the same. | What is the relationship between phase velocity, group velocity, and particle velocity in wave mechanics, and how can these concepts be mathematically expressed? | 18,497 | cqadupstack-physics |
98424 | phospholipid bilayer | I'm a high school student. The head is hydrophilic, the tail is fatty acid,in other words hydrophobic. Here is the thing I don't understand, all textbooks state that water is repelled by hydrophobic tail, why? The hydrophilic head is composed of polar molecule,and water is polar,so they will attract each other. But why... | Why do hydrophobic tails, composed of nonpolar molecules, repel water molecules despite the presence of hydrophilic heads that attract water due to their polar nature? | 1,463 | cqadupstack-physics |
77662 | Waves produced by a mass of water on the calm sea surface | Suppose we have a parallelepiped shaped box full of water on the surface of the sea. Suddenly the box disappears. What is the shape of the waves vs. time caused by the fall of the water contained in the box? | If a parallelepiped-shaped box full of water suddenly disappears while sitting on the surface of the sea, what is the height of the water waves produced in the surrounding sea after 1 second, assuming the box contained 100 liters of water? | 26,979 | cqadupstack-physics |
78894 | Pendulum Hits a Mass and Spring | I think this problem’s solution is on the web but after a few days of searching, I can not find it. Can anyone give me a reference? Thanks in advance. A mass and spring are resting on a frictionless table. A pendulum is pulled back, released, and hits the mass. The spring coils, recoils, and propels the pendulum. One o... | How can the energy transfer and motion between a pendulum, a mass, and a spring on a frictionless surface be quantitatively modeled when the pendulum strikes the mass and compresses the spring? Please provide the relevant equations and describe how the system behaves over time. | 10,505 | cqadupstack-physics |
90196 | Quantum barrier for photons | In quantum mechanics, a particle may tunnel through a barrier it would not be able to surmount in a classical sense. My question is this: **What are all the factors that may prevent a photon from propagating (thus it would need quantum tunneling to do so), and can they be described in a general way for any given materi... | What are the key factors that determine whether a photon can propagate through a given material, and how can these factors be quantitatively described for different materials with respect to their refractive index and absorption coefficient? | 958 | cqadupstack-physics |
16142 | Is QFT mathematically self-consistent? | After recently going through a short program of self-study in quantum mechanics, I was surprised to find a quote attributed to Feynman essentially saying he was extremely bothered by the computational process of renormalization. It's "dippy" that anyone should have to subtract one infinity by another in order to arrive... | What is the concept of renormalization in quantum mechanics, and how does it relate to the concept of dealing with infinities in calculations? Additionally, what recent developments or approaches are being explored to address the challenges associated with renormalization in theoretical physics? | 21,735 | cqadupstack-physics |
81731 | Sign in the time-independent Schrödinger's equation | In the time-independent Schrödinger's equation: $$ -\frac{\hbar^2}{2m} \frac{d^2} {dx^2} u + Vu ~= Eu, $$ why there is a minus sign before the first term? | Explain the significance of the negative sign in front of the kinetic energy term in the time-independent Schrödinger's equation, and provide a mathematical derivation showing how it arises from the classical kinetic energy expression. | 2,320 | cqadupstack-physics |
32260 | Does a celestial system exhibit a collective magnetic field? | Sol exhibits a magnetic field, most of the planets in orbit around Sol exhibit a magnetic field - strong and weak both. Does the solar system as a whole exhibit a magnetic field? Does the paradigm scale upwards to larger celestial systems such as a cluster or galaxy? | What is the net magnetic field strength of the solar system when considering the contribution of Sol and the magnetic fields of each planet, and how does this compare to the magnetic field strength observed in a galaxy cluster? | 18,598 | cqadupstack-physics |
114341 | What is wrong with the Bohr model? | What is wrong about the Bohr model? Many books say it is wrong but doesn't say why and I don't know why. | What are three major limitations of the Bohr model of the atom, and how do these limitations affect its accuracy in predicting atomic behavior? | 25,051 | cqadupstack-physics |
70326 | Where does additional heat energy come from in isothermal step of Carnot cycle | According to widipedia: > During step 1 (isothermal heat addition or absorption) the gas is allowed to > expand and it does work on the surroundings. The temperature of the gas does > not change during the process, and thus the expansion is isothermal. The gas > expansion is propelled by absorption of heat energy Q1. T... | If the gas undergoes isothermal expansion and absorbs heat energy \( Q_1 \) from a reservoir without a temperature gradient, what is the source of this heat energy, and how can it be absorbed if there is no difference in temperature? | 19,372 | cqadupstack-physics |
63372 | Temperature of a small system | What is wrong if I define temperature of a small system (I mean, a system which has not a large number of particles) by $$1/T = dS/dE$$ ? | What is the derived temperature expression for a small system, defined by the relation \( \frac{1}{T} = \frac{dS}{dE} \), when applying the concepts of thermodynamics, and how does this expression behave as the number of particles in the system changes? | 37,413 | cqadupstack-physics |
105614 | At which point of the universe $R_{\mu \nu}=0$ if there is a source of gravitation (point mass) | Schwarschild found his solution to Einstein's field equations for vacuum ($T_{\mu \nu}=0$) by placing a point-mass in the center of origin. Since the Ricci tensor $R_{\mu \nu}$ and the Einstein tensor $G_{\mu \nu}$ are trace-reversed, meaning they vanish identically: **Which point of a universe with a mass in it would ... | In the context of Schwarzschild’s solution to Einstein's field equations, can you determine the distance from a point mass at which the Ricci tensor $R_{\mu \nu}$ becomes zero, given a specific mass $M$ and the formula for gravitational potential $V(r) = -\frac{GM}{r}$? | 33,454 | cqadupstack-physics |
67396 | Stability and lifetime of soap bubbles formed with light gases like helium or hydrogen? | A friend asked me if it would be possible to make soap bubbles out of a gas like hydrogen and if you did, would they float higher, faster. Due to the lower mass of light gases (compared to the air) I know they will float up faster (buoyancy). I wonder how stable they would be though. **My question is, will bubbles fill... | How does the stability of soap bubbles filled with light gases like helium or hydrogen compare to those filled with air in terms of longevity, and what factors might influence this stability? | 36,639 | cqadupstack-physics |
100137 | Sterile Neutrinos and Supersymmetry | Just read a Scientific American review of a recent article which suggests evidence for sterile neutrinos: http://www.nature.com/news/cosmic-mismatch-hints-at-the-existence-of-a- sterile-neutrino-1.14752 The article is a little unclear about exactly what evidence, but my question is more general. A sterile neutrino woul... | What is the minimum number of supersymmetric (SUSY) particles required to incorporate a sterile neutrino into the minimal supersymmetric standard model (MSSM), and can sterile neutrinos exist outside the framework of supersymmetry? | 15,577 | cqadupstack-physics |
93332 | How the mass loss rate by stellar wind is calculated for massive stars? | I have been searching for some examples about the different rates at which massive stars lose their mass by stellar wind, but I haven't been able to get anything other for the sun. To be more specific, I want to find a example for a known star with mass between 20-40 solar masses. | What is the typical mass loss rate due to stellar wind for a massive star with a mass between 20-40 solar masses, and can you provide an example of such a star along with its estimated mass loss rate? | 35,784 | cqadupstack-physics |
61295 | What energy changes take place when you operate a jet-ski? | What energy changes take place when you operate a jet-ski? | When operating a jet-ski, what is the approximate conversion efficiency of chemical energy from fuel into kinetic energy, and what energy losses occur during this process? | 12,992 | cqadupstack-physics |
24267 | eigenvalue staircase and hamiltonians | Let two Hamiltonians $H_{1}$ and $H_{2}$ be defined in such a manner that their eigenvalue staircases satisfy $ N_{1} (E) = N_{2} (E)+A +O(E^{-1})$ What can we say about their potentials $ V_{1} (x) $ and $ V_{2} (x)$ ?? Are they the same at least for $ x \rightarrow \infty$ ?? If we consider that the energy function $... | Given the Hamiltonians \( H_{1} \) and \( H_{2} \) with eigenvalue staircases satisfying \( N_{1}(E) = N_{2}(E) + A + O(E^{-1}) \), are the potentials \( V_{1}(x) \) and \( V_{2}(x) \) asymptotically equivalent as \( x \rightarrow \infty \)? Additionally, if we represent the energy levels as \( E_{n}^{i} = f^{i}(n) \) ... | 24,291 | cqadupstack-physics |
87467 | Number of 2-electron integrals | Consider 2-electron integrals over real basis functions of the form $$ (μν|λσ)=∫dr⃗_1dr⃗_2ϕ_μ(r⃗_1)ϕ_ν(r⃗_1)r^{−1}_{12}ϕ_λ(r⃗_2)ϕ_σ(r⃗_2) $$ I am told that for a basis set of size $K=100$, there are $12,753,775$ unique 2-electron integrals of this form. Symmetry considerations mean that we have less than $K^4$ unique i... | Given a basis set size of \( K = 100 \) and using the formula for the number of unique 2-electron integrals, which is
\[
\frac{1}{8} n(n+1)(n^2+n+2),
\]
calculate the total number of unique 2-electron integrals. Can you show the detailed steps in arriving at the final answer of \( 12,753,775 \) integrals? | 3,171 | cqadupstack-physics |
99314 | Is energy lost in an elastic tunneling process? | Suppose we had two metal plates separated by an Angstrom. Now, apply a voltage $V$ between the two metal plates. There will be a tunneling current $I$ between the metal plates. Since $P=IV$, does that imply power is being dissipated by the system, even if the tunneling is elastic? Some additional thoughts: Perhaps this... | If two metal plates are separated by an Angstrom and subjected to a voltage \( V \) resulting in a tunneling current \( I \), calculate the power dissipated in the system using the formula \( P = IV \). Discuss how the existence of a tunneling current might affect the system's resistance, particularly in relation to ba... | 12,968 | cqadupstack-physics |
82267 | Dark Energy Explanation Found | It's my sincere request to this Physics forum that if i am wrong (which has the least possibility atleast from my side) just reply "wrong" so that i can move on futher. I know personal theories are not allowed but i am not finding any place to get it checked. thanks DARK ENERGY The theory described below does not conta... | How does the potential energy associated with curved space change when a particle of unit mass is evaporated, and what implications might this have on the motion of galaxies? | 27,685 | cqadupstack-physics |
62319 | Rotational Dynamics | In studying rotational dynamics of a rigid body , I can't seem to understand why you can solve the problem correctly only using certain points in a body and not all ? Means angular momentum and torque leads to correct answer only in some cases | In the analysis of rotational dynamics, why is it that the angular momentum and torque calculations yield correct results only when considering specific points in a rigid body, rather than applying these calculations to all points uniformly? Can you provide a quantitative example to illustrate this concept? | 18,681 | cqadupstack-physics |
31354 | 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 $\dim(X) \times > \dim(Y)$, while the vector pr... | What is the dimension of the result when performing a vector product on two vectors \(X\) and \(Y\) each having a dimension of 10, and how does this compare to the dimension of their tensor product? | 16,333 | cqadupstack-physics |
11905 | When is the Hamiltonian of a system not equal to its total energy? | I thought the Hamiltonian was always equal to the total energy of a system but have read that this isn't always true. Is there an example of this and does the Hamiltonian have a physical interpretation in such a case? | Can you provide an example of a physical system where the Hamiltonian does not equal the total energy, and explain the physical interpretation of the Hamiltonian in that context? | 12,340 | cqadupstack-physics |
10120 | Confusion between the de Broglie wavelength of a particle and wave packets | So I learned that the de Broglie wavelength of a particle, $\lambda = \frac{h}{p}$, where h is Planck's constant and p is the momentum of the particle. I also learned that a quantum mechanics description of a particle is a wave packet. I learned that a wave packet is a summation of different basis functions overlapped ... | If a particle is represented by a wave packet that is highly localized in position space, leading to a spread of possible momenta, how can you calculate its de Broglie wavelength? Specifically, do you use the average momentum of the wave packet, calculated as $\lambda = \frac{h}{\langle p \rangle}$, to determine the wa... | 18,167 | cqadupstack-physics |
91548 | What software do publishing companies use to create drawings for text books? | What software is used to create free body diagrams, inclines, springs and so on in the introductory physics textbooks ? I know Adobe, Luxology, and many others could, but I am more interested in software with ready made objects, that could still create good looking diagrams with less effort. Most of the textbooks have ... | What is the average time it takes to create a free body diagram using specialized physics software compared to general graphic design software? | 17,880 | cqadupstack-physics |
51631 | Could one argue that h (Planck constant) and $\hbar$/2 (Dirac constant) are in fact independant constants? | My question is very naive and could sound strange but it seems to me natural in so far as the Planck constant is related to the first quantization (of newtonian particle mechanics/galilean relativity) while the Dirac one shows up in the second quantization (of fields theory/special relativity)... Anyway I think the con... | What is the relationship between the Planck constant and the Dirac constant in terms of their roles in quantum mechanics, and how do they impact the transition from first quantization to second quantization? | 16,085 | cqadupstack-physics |
118995 | Why is number of collisions equal to number of scattered particles times number of scatterers? | In Landau, Lifshitz "The Classical Theory of Fields" $\S12$ "Invariant cross- section" the following is said1: > ... according to the usual definition of the cross-section $\sigma$, the > number of collisions occuring in volume $dV$ in time $dt$ is $$d\nu=\sigma > v_{\text{rel}}n_1n_2dVdt,$$ where $v_{\text{rel}}$ is t... | Can you explain the relationship between the cross-section $\sigma$, the number of collisions, and the parameters $v_{\text{rel}}$, $n_1$, $n_2$, and $dV$ in the context of particle interactions? Specifically, how does the formula $d\nu = \sigma v_{\text{rel}}n_1n_2dVdt$ account for multiple collisions and what does it... | 4,729 | cqadupstack-physics |
121930 | "Weakness" of gravitational force | I often hear that gravitational force is much "weaker" than electroweak and strong forces. But how can you compare the strength of interactions without the parameters like mass, charge on which it depends? Surely the gravitational force can be made as (practically) strong as one wants by increasing the mass? | Compare the gravitational force between two objects with masses \( m_1 \) and \( m_2 \) at a distance \( r \) using the formula \( F_g = \frac{G m_1 m_2}{r^2} \), where \( G \) is the gravitational constant. What mass values would be required to generate a gravitational force equal to the electrostatic force between tw... | 15,359 | cqadupstack-physics |
114069 | Can one assign an equivalence principle of some kind to the EM field? | Introduction: Consider the EM field. There was a time when the field was defined in a similar manner to that of the gravitational field. This changed when the view on gravitation evolved to this new idea which suggested it was a consequence of space-time curvature. Now consider the equivalence principle, it was due t... | Assuming an equivalence principle similar to that of general relativity could be assigned to the electromagnetic field, what would be the implications for the energy-momentum tensor of the electromagnetic field in terms of its geometric interpretation, and how might this differ from the existing formulations in classic... | 22,638 | cqadupstack-physics |
100825 | Electric Potential Energy | When work is done on a positive test charge by an external force to move it from one location to another, does the potential energy increases or decreases, and does the electric potential increases or decreases? | If a positive test charge is moved against the direction of the electric field by an external force, how does the electric potential energy change, and what happens to the electric potential at the final location relative to the initial position? | 9,877 | cqadupstack-physics |
88493 | Question about liquid / gaseous insulators | I'm looking for information about liquid / gaseous insulators, but I can't find any, is there any website (because I can't find on Wikipedia) where I can get this information? Also, can I get a list of examples of liquid / gaseous insulators? Any kind of help is appreciated. | What are five examples of liquid or gaseous insulators, and what are their key properties that make them effective as insulators? | 3,312 | cqadupstack-physics |
101036 | Calculating Dynamics of a Thick Sheet of Material | So I'm working on a computational neuroscience problem, and I'm attempting to model skin dynamics for use in some perception models. The problem is as follows: Imagine you had a two dimensional sheet with some thickness. Imagine stimulating it with a probe with negligible spatial extent (i.e. a point source of stimulat... | In a two-dimensional sheet being stimulated by a sine wave from a point probe, the displacement at the probe's location is given by \( z(0,t) = A \cos(2\pi f t) \). It has been experimentally determined that the displacement at a distance \( r \) from the probe decays according to the formula \( z(r,t) = \frac{1}{r^{\g... | 8,994 | cqadupstack-physics |
109199 | Why is $\vert I=1,I_3=1\rangle = -p\bar n$ | My book doesn't explain well how to build a doublet of antiparticles that transforms the same way the particle doublet $(p,n)^T$ (proton neutron) does. They claim $$\tag 1 \vert I=1,I_3=1\rangle = -p\bar n$$ for a composite nucleon-antinucleon system. **Why is $(1)$ true?** Perhaps it's just bad notation in the book? I... | Can you explain why the state \(\vert I=1,I_3=1\rangle\) can be expressed as \(-p\bar{n}\) for a composite nucleon-antinucleon system, and clarify the role of the negative sign in this context compared to the Clebsch-Gordan coefficients? | 24,009 | cqadupstack-physics |
38720 | Riddle: can you swim faster upstream than downstream (with respect to the water)? | A friend of mine posed a riddle to me: A man swims upstream in a river, which is flowing at an unknown rate. He is wearing swimming goggles. At a certain point he loses his goggles. 10 minutes later he realizes he lost them, so he immediately turns around and swims back downstream to get them. When he finds his goggles... | If a man swimming upstream in a river loses his goggles and, after realizing they're missing 10 minutes later, swims back downstream to find them, ending up 500 meters downstream from the original loss point, what is the speed of the river in km/h? Additionally, if the man swims at a speed of 4 km/h relative to the wat... | 4,726 | cqadupstack-physics |
23222 | Videos of changing the orientation of an astronaut in space | Kane, Headrick and Yatteau describe in their paper "Experimental investigation of an astronaut maneuvering scheme" possible maneuvers to change the orientation in space without external torque. Is there any video (best available in the web) which shows real astronauts doing such motions? | What are the key principles of maneuvering in space without external torque as demonstrated by astronauts, and can you provide a specific video example of these maneuvers in action? | 1,681 | cqadupstack-physics |
5114 | Gravitational and gauge-gravitational anomalies in N=1 D=4 supergravity coupled to a SUSY gauge theory with chiral matter | When people talk about the first superstring revolution they often mention the miraculous cancellation of anomalies via the Green Schwarz mechanism. My question is whether such a string-theoretic mechanism is also at work when the 4D gravitational and gauge-gravitational anomalies are tackled? In this context, would it... | What are the specific types of higher-order stringy couplings in the Lagrangian that are necessary for canceling gravitational and gauge-gravitational anomalies in the context of N=1 D=4 supergravity? | 36,153 | cqadupstack-physics |
64846 | Optical depth in astrophysics | How can be the exponential decay of the intensity $I$ via the optical depth $\tau$ be derived? $$I(\tau)=I(0)e^{-\tau} $$ | What is the intensity of light $I(\tau)$ after it has passed through an optical depth of $\tau = 3$ if the initial intensity is $I(0) = 100 \, \text{units}$? | 21,187 | cqadupstack-physics |
92430 | does a rocking kettle cause the water to boil more slowly? | When I boil water in the kettle on my electric stove, sometimes it rocks back and forth making an annoying sound at a frequency of about 6Hz. When that happens, I move the kettle slightly to make it stop rocking. It occurred to me that although my motivation is to stop the annoying sound, it might also make the water b... | What is the impact of kettle vibration on the time it takes to boil a specific volume of water, and how can I design an experiment to statistically analyze this effect while controlling for variables such as ambient temperature and the initial temperature of the water? | 18,165 | cqadupstack-physics |
131663 | Hugh Everett's MWI | According to Hugh Everett's many worlds interpretation, all the possibilities of one action can happen at the same time in other parallel universes, so how come we can't see these worlds? now I bumped into something called the quantum decoherence but I can't seem to get how this decoherence work? | In the context of quantum decoherence, how does the interaction of a quantum system with its environment lead to the suppression of interference effects, and can you quantify the timescale over which significant decoherence occurs for a simple quantum system such as a spin-1/2 particle? | 36,227 | cqadupstack-physics |
133732 | Why does a wave actually diffract? | I know that waves diffract around a slit and this is due to the Huygens- Fresnel principle. But I never understand this in an intuitive wave that why does a wave become a spherical wave front at the slit? Huygens principle gives all the math behind this but does not actually explain that why does a wave bend round the ... | How does the wavelength of a wave relative to the width of a slit affect the degree of diffraction observed, and can you quantify this relationship using the diffraction pattern created in a single-slit experiment? | 1,623 | cqadupstack-physics |
9800 | Why is the steam from cooling towers not used? | If I see the steam coming out of cooling towers at an altitude of 200 meters, I cannot help but think that this energy is wasted. My question is: Why isn't this steam cooled enough to become water and used to create hydroelectric power due to the drop from 200 meters? | What is the potential energy available from 1 kg of steam released from a cooling tower at an altitude of 200 meters, and how could this energy be converted into hydroelectric power? | 35,265 | cqadupstack-physics |
39424 | Work Done by an Adiabatic Expansion | I am given the information that a parcel of air expands adiabatically (no exchange of heat between parcel and its surroundings) to five times its original volume, and its initial temperature is 20° C. Using this information, how can I determine the amount of work done by the parcel on its surroundings? I know that $dq ... | Given a parcel of air that expands adiabatically to five times its original volume starting at an initial temperature of 20° C, how can I calculate the amount of work done by the parcel on its surroundings during this expansion? Please provide the necessary equations and steps involved in the calculation. | 1,195 | cqadupstack-physics |
23426 | Maximum speed of a water skier | Water skiing is a sport where an individual is pulled behind a boat or a cable ski installation on a body of water, skimming the surface. Consider an idealized case where the boat is moving at a constant velocity $\overrightarrow v_0=\text{const}$ (relative to the water), independently of the skier. The boat and skier ... | What is the maximum possible instantaneous speed of a skier, $v_\text{max}$, relative to the water when being pulled by a boat moving at a constant velocity $v_0$, given that the skier's velocity can vary and the connection is made with a massless, unstretchable rope? | 5,519 | cqadupstack-physics |
15022 | Stochastic processes and wavefunction collapse | Some time ago I had an idea that, as the unitary evolution of the wavefunction is described by a deterministic equation (PDE, simply), could be the collapse of it be described by some kind of a stochastic differential equation? Was this question posed before (I suppose yes...), and what kind of an SDE could it be? | What type of stochastic differential equation could potentially describe the collapse of a wavefunction in quantum mechanics, and is there any existing research or models that explore this concept? | 27,861 | cqadupstack-physics |
106418 | Thermal noise from capacitor; circuit analysis | I'm trying to model the thermal noise from a capacitor. The capacitor is connected directly into an amplifier with resistance $R_{A}$ and capacitance $C_{A}$. A noisy capacitor is modelled as a thermal noise source $V_{J}$ due to a frequency-dependent resistor $R_{J}= 1/\omega C_{J} \tan \delta$ ($\tan \delta$ is the l... | Given the thermal noise voltage \( V_{J} = \sqrt{4k_{B} T R_{J} \Delta f} \), where \( R_{J} = \frac{1}{\omega C_{J} \tan \delta} \), and the transfer function for voltage \( |V_{A}| \) from the noisy capacitor connected to an amplifier, derive the expression for the ratio \( \left| \frac{V_{A}}{V_{J}} \right| \) and e... | 3,741 | cqadupstack-physics |
130374 | Changes in planetary orbit? | Forgive a novice and her naive curiosity, but I was wondering about planetary orbit and the aging of planets. As a **planet ages** , does its transit around its sun/star **decrease** or **increase** in **speed**? ## Does the speed and proximity of a planet's orbit around the star, have more to do with the age and type ... | As a planet ages, how does the speed of its orbit around its star change, and what factors primarily influence this change: the characteristics of the star, or the planet's own properties and its distance from the star? Additionally, under what conditions could a planet's orbit be altered significantly by external forc... | 37,479 | cqadupstack-physics |
117255 | Is there a theoretical physics masters that accepts mathematics graduates? | I plan to graduate with an honours (four year) degree in philosophy and a general (three year) degree in mathematics. Are there any physics graduate programs that might admit me if I were to apply? For context: My plan-A is to work in academic philosophy. A physics education might not appear on the resume of most philo... | What are the admission requirements for physics graduate programs, and how would a background in philosophy and mathematics affect my eligibility for these programs? | 15,772 | cqadupstack-physics |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.