question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>I am assuming that zero (rest) mass particles don't interact gravitationally with each other and other particles. Does that mean they experience a "flat" spacetime instead of a curved one? I find it a little hard to imagine that. Also, does this mean massless particles can pass through an event horizon (not the sing... | g7779 | [
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<p>I am in an introductory physics class and we have been working with Gravitational Potential Energy, Elastic Potential Energy, Kinetic Energy and the Law of Conservation of Energy in relation to bungee cords. Recently, we delved into the topic of efficiency and with it I came upon the following stumbling block. </p>
... | g7780 | [
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<p>I'm an engineering student and have a few ideas to bat at the scientific community. First premise is based upon common sense. I understand that if I am standing on a skateboard on a relatively smooth surface and a stone of significant mass is thrown to me and I catch it, the momentum of the projectile is transferred... | g7781 | [
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<p>In a question titled <a href="http://physics.stackexchange.com/questions/2041/how-are-classical-optics-phenomena-explained-in-qed-snells-law">How are classical optics phenomena explained in QED (Snell's law)?</a> Marek talked about the probability amplitude for photons of a given path. He said that it was $\exp(iKL)... | g7782 | [
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<p>I'm pretty certain that the answer to the question in the title is a no, but I don't understand why. I have some basic misunderstanding of quantum processes that I’d like clarified in the form of asking questions about a hypothetical scenario. </p>
<p>So, let’s say we have a pair of entangled photons…</p>
<p>1) ... | g7783 | [
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<p>I was digging into <a href="http://latticeqcd.blogspot.com/2005/12/nielsen-ninomiya-theorem.html" rel="nofollow">Nielson-Ninomiya Theorem</a> and doubler fermions, as well as solutions to these problems using <a href="http://arxiv.org/abs/hep-lat/9410018" rel="nofollow">Domain Wall Fermions</a> and <a href="http://a... | g7784 | [
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<p>In organic light emitting diodes, only singlet excitons contribute to the light emission (this is flouresence). Everything I read, say that triplet excitons cannot recombine on the same timescale as the singlets because spin selection rules forbid it. </p>
<p>Can anyone expand on how the spin selection rules allow ... | g7785 | [
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<blockquote>
<p>I have given one-dimensional motion of the particle directed
horizontally. A problem says: "<em>...Show that for this given motion
Conservation of Energy Law holds.</em>".</p>
</blockquote>
<p>Since Energy can intuitively be thought of an operation that changes something over time, energy being c... | g7786 | [
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<p>May be this question might have already been asked but i couldn't find it, so let me know if its already there.</p>
<p>Consider a potential, $V(x) = -\frac{1}{|x|}$ and if we apply this to a one dimensional Schrodinger's equation, I'd like to know the solution for the wave function in 1-D. Does it have a simple ana... | g7787 | [
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<p>I am currently designing a heat sink for OPA 549. Among the many considerations, for example, the choice of material, the geometry of heat sink, the design of fins and all the parameters that come into play during the modelling, I am most curious about the simple choice of material.
Copper has more conductivity than... | g7788 | [
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<p>I am just reading at the beginnin of <a href="http://backreaction.blogspot.de/2013/06/passing-through-cosmic-walls.html" rel="nofollow">this</a> nice article, that axions could be responsible for spontaneously breaking of a symmetry in the early universe.</p>
<p>Does anybody know which symmetry is alluded to and ho... | g7789 | [
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<p>So far I have only actually calculated dimensional regularization and I just know about the idea of cutoff regularization. From what I understand, as the name suggests, you just ignore momentum as from some high value and integrate the virtual momenta until this arbitrary chosen value. Depending on which value you c... | g7790 | [
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<p>I was attending my philosophy class and in the middle of student presentations, I found myself mentally wondering off and thinking about light. After a few minutes of trying to piece together how the sun works I came to ask a question I could not answer myself. Why does each individual photon have such a low amount ... | g7791 | [
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<p>I would like some <strong>super simple computational code for solving magnetohydrodynamics problems</strong>. High accuracy nor performance is not my concern. I wan't it just to visually explore qualitative behavior of plasma. Important for me is:</p>
<ul>
<li><strong>Generality</strong> - it should not be speciali... | g7792 | [
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<p>I know that we can make water solid with high pressure, so I think water will be solid in the deep ocean?</p>
<p>If that is true, the depth of the ocean would be limited because water will become ice? Anyone know that maximum depth? </p> | g7793 | [
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<p>In a gravitational field, the gravitational force acting on a body (of mass m) at a point x metres away from the attracting body (of mass M) is $\frac{GMm}{x^2}$. Integrating this force from a point at infinity to x gives $-\frac{GMm}{x}$, or the work done by the gravitational field on the mass in moving the mass fr... | g7794 | [
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<p>Would a projectile fired in space and assuming there were no stars or planets in the way, would the projectile continue on to infinity, since the x-component of the projectile's velocity never changes from it's original? </p> | g7795 | [
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<p>One page 5 in Landau & Lifshitz <em>Fluid Mechanics</em> (2nd edition), the authors pose the following problem:</p>
<blockquote>
<p>Write down the equations for one-dimensional motion of an ideal fluid in terms > of the variables $a$, $t$, where $a$ (called a <em>Lagrangian variable</em>) is the
$x$ coordin... | g7796 | [
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<p>Got two accelerometers that are measuring accelerations oriented at +/- 45 deg from horizontal. I am looking to determine the conversion of the accelerometer measured data to accelerations in the vertical and horizontal direction. Can I use coordinate system conversion below ?</p>
<p>$$F_{Vertical} = (F_1 + F_2) ... | g7797 | [
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<p><a href="http://en.wikipedia.org/wiki/Work_%28physics%29">Work</a> is defined as</p>
<p>$$W = \vec{F}\cdot\vec{s}$$</p>
<p>But what what exactly is $\vec{s}$? Is it the displacement of the body on which the force is being applied? Or is it the displacement of the point of application of the force? </p>
<p>If you ... | g7798 | [
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<p>Consider a glass of water and a glass of coffee. Their contents differ by no more than a few grams of particles coming from the roasted and ground coffee, yet the former lets almost all visible light pass through, and the latter blocks most of it.</p>
<p>I am wondering <strong>what are the most efficient ways to tu... | g7799 | [
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<p>Possibly the most useful thing anyone could tell me about particle physics:</p>
<p>Naively, one could try and make an algebra by enumerating all the types of particles and defining equivalence relationships (some rules), for example</p>
<p>Objects:</p>
<p>object type 1: photon</p>
<p>object type 2: electron</p>
... | g7800 | [
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<p>How broad is the term "String theory"?</p>
<p>Typical <a href="http://en.wikipedia.org/wiki/String_theory" rel="nofollow">brief descriptions of string theory</a> focus on the fact that it describes fundamental particles as being string-like rather than point-like, or, more generally, being at least 1-dimensional.</... | g7801 | [
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<p>Can we apply the <a href="http://en.wikipedia.org/wiki/Matter_wave#de_Broglie_relations" rel="nofollow">de Broglie relations</a> to a <a href="http://en.wikipedia.org/wiki/Sound_waves#Physics_of_sound" rel="nofollow">sound waves</a> ?
Is it possible?
if yes how do you do that?
what would be the mass(m) in the equati... | g7802 | [
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<p>How does the Gordon Decomposition of Dirac Current give rise to spin angular momentum?</p>
<p>I used the Gordon Decomposition to split the Probability Current of the Dirac Field into its orbital current and its spin current. I multiplied the currents by $mc$ to covert them into momentum and then crossed the momentu... | g7803 | [
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<p>I want to calculate the distance between two objects using an iPhone camera. </p>
<p>Suppose I'm standing with my iPhone 10 feet away from the objects. Now, I want to calculate the distance between those two objects. </p>
<p>Suppose these two objects are on a straight horizontal line. So, how can I calculate the d... | g7804 | [
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<p>Much (All?) of quantum theory can be done in separable Hilbert spaces with a countable basis.<br>
How about quantum field theory? Is it “quite happy” (mathematically consistent) if everything is countable, or does it “need” to use an uncountable, continuous space (e.g. rigged Hilbert space) for mathematical con... | g7805 | [
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<blockquote>
<p>A sphere of radius $R$ is in contact with a wedge. The point of contact is $\frac{R}{5}$ from the ground as shown in figure. Wedge is moving with velocity $20~\text{m/s}$ towards left then the velocity of the sphere at this instant will be</p>
<p><img src="http://i.stack.imgur.com/8Qubm.png" alt=... | g7806 | [
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<p>Supppose we are given a quantum state that isn't pure state, such that it is a linear combination of the eigenstates of a Hermitian operator $\hat O$.
$$|\psi\rangle=N\sum \alpha_i |i\rangle$$ where $N$ is just a normalization constant.
I just want to make something clear about measuring. If we measure the corresp... | g7807 | [
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<p>How would the interference pattern look if one source emits blue light and the other source emits red light in Young's double slit experiment?</p> | g7808 | [
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<p>When are two vectors orthogonal in curved spacetime?</p>
<p>From wikipedia:
<em>"In 2-D or higher-dimensional Euclidean space, two vectors are orthogonal if and only if their dot product is zero, i.e. they make an angle of 90°, or π/2 radians. Hence orthogonality of vectors is an extension of the concept of perpen... | g7809 | [
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<p>All of my textbooks mention, that entropy-change of all spontaneous physical, and chemical processes is positive, and that such processes need another condition to fulfill- decrease in the net internal-energy of the system, taking part in the process. </p>
<p>I just want to know that what is the reason behind this... | g7810 | [
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<p>I'm studying some materials on semiconductors, and a section on photoconductivity has left me somewhat confused.</p>
<p>In an extrinsic material, is photoconductivity the result of electrons moving from the valence band to the conduction band, or is it the result of dopant atom ionization? If it is the latter, is t... | g7811 | [
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<p>Energy can be built from Lagrangian when considering the symmetry of time $(\frac{\partial L}{\partial t}=0)$. <a href="http://en.wikipedia.org/wiki/Free_energy" rel="nofollow">Free energy</a> is a generalization of energy when the system exchanges heat with the environment. I can't find any sources that building fr... | g7812 | [
0.060609690845012665,
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<p>In Synchrotrons I think they use microwaves to accelerate the electrons bundles that fly through-how does putting a microwave through a cavity accelerate an electron? I know that the Electric and Magnetic fields could and do have an effect on the electron, but if the radiation is moving parallel to the electron, wou... | g439 | [
0.025197133421897888,
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<p>We are taught that the universe began as a singularity - an infinitely small and infinitely dense point. At the beginning of time there was a 'Big Bang' or, more accurately, 'Inflation'.</p>
<p>The main evidence for this is the observation of the red shift of all of the galaxies. This shows us that as time increase... | g7813 | [
0.06935351341962814,
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<p>What is the equation for the saddle-like 2d surface (embeded in 3d Euclidean space with cartesian coordinates x, y and z) with constant negative curvature frequently used to illustrate open universe (for example in the following image is taken from Wikipedia)?</p>
<p><img src="http://i.stack.imgur.com/WNUNI.jpg" al... | g7814 | [
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<p>In an astronomy forum that I frequent, I have been having a discussion where the state of quantum gravity research came up. I claimed that Loop Quantum Gravity theories couldn't prove GR in the continuum limit, nor could they compute Mercury's perihelion because they didn't have any matter, at this point. Another po... | g7815 | [
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<p>Why in the irradiament mulipoles of Lienard-Wiechert's potential we say that electric quadrupole give a contribute of the same order of the magnetic dipole? How can we see it from their equations? And is there a physical reason for this? Sorry for my trivial question.</p> | g7816 | [
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<p>Say that the airplane is going in 1000 km/h. On the side of the airplane, there is a 10x10 cm window. How much friction would this window cause. For the sake of the calculation, imagine that the airplane is infinitely long. The window is also perfectly level with the rest of the wall, and there is no turbulence on t... | g7817 | [
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<p>This question is posed in the context of thermodynamics/statistical mechanics. Suppose we define the correlation length as the $\xi$ in the exponential factor $e^{-r/\xi}$ that appears in the correlation function $$C(r) = \langle m(0)m(r) \rangle - \langle m \rangle^2$$ (where $m$ is some relevant order parameter).<... | g7818 | [
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<p>Consider a parallel-plate capacitor in free space. A negatively charged point particle with initial velocity $v$ passes through the space between the pair of parallel plates (with an initial path perpendicular to the normal vector of the plates). </p>
<p>The point particle accelerates towards the positively charged... | g7819 | [
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<p>Two open-car trains approach each other at fixed velocities. Each has a radar to see how quickly the other train is approaching, but apart from that the trains have no <em>a priori</em> knowledge of each other.</p>
<p>Each train has engineers on its first and last cars. Each engineer has an atomic clock and a laser... | g7820 | [
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<p>I am studying the history of Modern Physics and Yang-Lee earned their Nobel the next year after the <a href="http://en.wikipedia.org/wiki/Wu_experiment" rel="nofollow">Cobalt experiments</a>. I am familiar with the chronology, but am not clear what those findings meant to the physics community to warrant such recogn... | g7821 | [
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<p>Suppose I set up the <a href="http://en.wikipedia.org/wiki/Double-slit_experiment" rel="nofollow">double-slit experiment</a> using photons as my particle. Behind the left slit I place a <a href="http://en.wikipedia.org/wiki/Beam_splitter" rel="nofollow">beam splitter</a> that points some of the light off in the dir... | g7822 | [
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<p>I have three column data that has time-displacement-force from 1D tensile/compression test. Now I would like to get the standard mechanical properties of the material, like Young modulus, yield stress/strain, strain hardening/softening exponent, Fracture toughness, work done...</p>
<p>Is there algorithms/libraries ... | g7823 | [
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<p>I've read that all paths inside the EH lead to singularity. ALL paths. Even the ones pointing away from it, right? Because there's NO pointing away from singularity, since ALL paths point to it. </p>
<p>So how could it be at the exact center? Or am I misunderstanding "center" here?</p>
<p><a href="http://physics.s... | g7824 | [
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<p>From what I've so far understood about light, a photon is emitted somewhere and after some time it's absorbed somewhere else.</p>
<p>Have we had experiments that confirm the path taken or something akin to verifying that photon really do "travel"? If so what are they..</p> | g7825 | [
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<p>In <a href="http://youtu.be/QGxNyaXfJsA" rel="nofollow">this youtube video</a> (which is an except from a documentation I believe) a DARPA development for a high-resolution surveillance camera is presented. This question is regarding the optics that are likely to be required to make it work.</p>
<h2>Summary of the ... | g7826 | [
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<p>The potential at the surface of an insulating sphere (radius R) is given by<br>
$$V(R,\theta) = k \cos(3\theta)$$
where $k$ is a constant. Use separation of variables to find the potential inside the sphere (r $\leq$ R) and outside the sphere (r $\geq$ R), and then use your answer to determine the surface charge den... | g7827 | [
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<p>Let's say I have a projectile being thrown by a player in my 2-D game. I want to work backwards and find the initial velocity to apply to the projectile such that it passes through a target point in space given that the launch point might not be at $y=0$.</p>
<p>Some applications of this would be a basketball shot ... | g7828 | [
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<p>I once came across the strange, artificial unit "hertz per dioptre", which is dimensionally equivalent to "metres per second". Could this unit, by some stretch of the imagination, be used in some artificial situation where the usage implications of both "hertz" and "dioptre" (frequency of periodic events and refract... | g7829 | [
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<p>I just saw this "<a href="http://www.youtube.com/watch?v=7ctaA2mERzI&feature=player_embedded" rel="nofollow">trick</a>" where a cup of water is turned over onto a table without spilling (using a piece of cardboard. After removing the cardboard from underneath the cup, the person then removes the cup in a partic... | g7830 | [
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<p>What is the current <strong>record</strong> number of entagled qubits and how has this number been increased? </p>
<p>The latest result on stack exchange, which is 3 years old, reports 14 via
this post: <a href="http://physics.stackexchange.com/q/4226/">How many stabilised qubits have been achieved in Quantum Comp... | g7831 | [
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<p>Okay, here is my understanding. Please correct me if anything here is incorrect. Suppose I have a cube with a side length of ten inches. It has a surface area of 600 square inches, and at an atmospheric pressure of 14.7 pounds per square inch, we can approximate 8800 pounds of air are applied on the cube by the atmo... | g7832 | [
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<p>Currently, as described in <a href="http://physics.stackexchange.com/questions/39679/why-cant-collisions-be-elastic">this question</a>, collisions cannot be elastic. However, is there a way to make a collision more elastic?</p>
<p><strong>Background:</strong></p>
<p>We're working on a project right now involving h... | g7833 | [
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<p>The one-particle states as well as the fields in quantum field theory are regarded as representations of Poincare group, e.g. scalar, spinor, and vector representations. </p>
<p>Is there any systematical procedure that one starts from the Dynkin label for a given representation, to construct a Lagrangian of that fi... | g7834 | [
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<p>What's so special about second order equations in classical mechanics? I have a basic understanding of the Lagrangian and Hamiltonian formulations of classical mechanics, so I'm not looking for answers like 'because Newton's second law is a second order ODE' or 'because Euler-Lagrange equations act on a first time d... | g257 | [
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<p>I think this is a question about the mathematical axioms of quantum mechanics...</p>
<p>Consider the following operators $\tilde{x}$ and $\tilde{p}$ on Hilbert space $L^2(R)$, defined for fixed $\delta>0$:
$$
(\tilde{x}\psi)(x) = (n+1/2) \delta\ \psi(x)
$$
when $n\delta \leq x <(n+1)\delta$ for some integer ... | g7835 | [
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... |
<p>I am wondering if there exist closed form-expressions for the time dilation experienced by an observer in different orbits around a Schwarzschild black hole, outside the event horizon, relative to some distant observer sitting fixed relative to the black hole. </p>
<p>I am no expert in GR, but I know these quickly ... | g7836 | [
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<p>I am a beginner who is learning QFT. When I was going through the quantisation of Klein-Gordon real-field. I got confused about something:</p>
<p>The solution to Klein-Gordon equations are of the form $ \psi(x^\mu) \sim e^{ik_\mu x^\mu} $. Now the solutions in Peskin and Schroeder have no time dependence. It gives ... | g7837 | [
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<p>Basically how boiling takes place? </p>
<p><em><strong>Also like to know...</em></strong><br>
What makes boiling point alter at various altitudes?<br>
Why bubbles rise through boiling water?</p> | g7838 | [
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0.05089... |
<p>I am reading Jan Boer's <a href="http://www-library.desy.de/preparch/desy/proc/proc02-02/Proceedings/pl.6/deboer_pr.pdf" rel="nofollow">review</a> of the AdS/CFT correspondence and I quote from end of page 1, where he is talking about equivalence of (d+1)-dim gravity to d-dim field theory </p>
<p>“If true, it impli... | g7839 | [
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<p>Find the <strong>minimum value of the initial velocity</strong> $u$ of the particle such that the particle crosses the wheel of radius $R$.<br>
<img src="http://i.stack.imgur.com/hN0F9.jpg" alt="enter image description here"></p>
<p><strong>Details and assumptions</strong><br>
$R=2m$<br>
$g=9.8m/s^2$<br>
Neglect ai... | g7840 | [
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<p>Say we have a balloon, negatively charged, the voltage on it is 500 V. Can I measure the charge on it or in other words, the number of excess electrons?</p> | g7841 | [
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<p>Mixing of two different fluids is associated with an increase of entropy. Conversely, separation of two gases must be associated with a decrease of the entropy of the two fluids.</p>
<p>Is there a minimum requirement imposed by this thermodynamic constraint on the minimum energy needed to separate two fluids? </p> | g7842 | [
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<p>Do the laws of physics change anywhere in the universe?Or will they change from place to place in the universe?</p> | g7843 | [
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<p>A vector field $f^\mu$ is said to be Fermi-Walker transported along a curve $\gamma$ parametrized with $\tau$ if the following holds $$\frac{\mathrm{D}}{\mathrm{d}\tau}f^\mu = -(a^\mu v^\nu - a^\nu v^\mu) f_\nu,$$ where $v^\mu$ is the tangent vector $\gamma$ and $a^\mu$ is its derivative. The uppercase D denotes the... | g7844 | [
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<p>Why any fermion can be written as a combination of two Majorana fermions? Is there any physical meaning in it? Why Majorana fermion can be used for topological quantum computation?</p> | g7845 | [
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<p>In the case of a complex shape filiform distribution of current, are we allowed to determine the magnetic field created by sections of the distribution and then summing them up, like we do with a discrete distribution of charge when calculating the electric field?</p>
<p>Thank you</p> | g7846 | [
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<p>How can the universe become infinite in spatial extent if it started as a singularity, wouldn't it take infinite time to expand into an infinite universe?</p> | g7847 | [
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<p>Are there any examples of fermionic particles or quasiparticles for which the interaction potential is a globally smooth function? i.e. no singularities or branch points. </p>
<p>As an example, in Flügge's Practical Quantum Mechanics, problem 148 has two repulsive particles on a circle. This is supposed to model th... | g7848 | [
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<p>Is there a way of calculating the mass of a galaxy, or even a nebula from the luminosity? </p>
<p>EDIT </p>
<p>I'm deleting this, and moving the question to Astronomy Stack Exchange - thanks david</p> | g7849 | [
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<p>My <a href="http://www.cs.berkeley.edu/~vazirani/s07quantum/notes/lecture2.pdf">text shows</a> (sections 0.2 and 0.3) that the joint "state space" of a system composed of two subsystems with $k$ and $l$ "bits of information", respectively, requires $kl$ bits to fully describe it. A critical consequence of this is th... | g7850 | [
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<p>I would like to start off by saying this is not a philosophical question. I have a specific question pertaining to physics after the following explanation and background information, which I felt was necessary to properly formulate my question.</p>
<p>I have done some research on <a href="http://en.wikipedia.org/wi... | g7851 | [
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<p>As an assignment for uni I need to figure out an algorithm that explodes a particle of mass $m$, velocity $v$, into $n$ pieces.</p>
<p>For the first part of the assignment, the particle has mass $m$, velocity of $0$, the particle explodes into 6 equal pieces, and is not affected by gravity.</p>
<p>The problem I'm ... | g7852 | [
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<p>I need to calculate the initial velocity required to launch a projectile at a given angle from point A to point B. The only force acting on the projectile after launch will be gravity – zero air resistance. The projectile is launched within a simulated, virtual environment; however, I am asking for help with the phy... | g7853 | [
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<p>I've been reading 'How the Hippies saved Physics', which describes a design for a superluminal communication device, of which the crucial part was a laser which duplicated an incoming photon many times. The reason this won't work is what is now known as the no-cloning theorem - a quantum state can't be duplicated i... | g7854 | [
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<p>I have a question to ask about the operationalist view of space-time. I am a mathematician who happens to be interested in physics, so if anyone thinks that my question is a silly or vague one, please feel free to close it.</p>
<p>Many physics textbooks that discuss Special Relativity mention that one way of settin... | g7855 | [
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<p>I have a small RC-controlled toy helicopter with removable tail rotor. </p>
<p>Suppose I remove the tail rotor, hold the tail with my hand, start the rotor until it moves with constant angular velocity and then let it go. Suppose that the heli remains on the floor all the time.</p>
<p>Then the body of the helicopt... | g7856 | [
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<p>A function $f(ax)$ that satisfies
$$
f(ax)=a^\Delta f(x)\,\,\, (\Delta \in R)
$$
is said to be <em>scale invariant</em>. The most general function $f(x)$ that satisfies the previous condition is of the form
$$
f(x)=C x^{\Delta}
$$
If we consider the set of distributions, namely the set of all $f(x)$ such that ... | g7857 | [
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<p>I was looking through some conformal Ward identity related things when I noticed that this paper (<a href="http://arxiv.org/abs/1212.3788" rel="nofollow">arXiv:1212.3788</a>) writes in their equation (33), a 3-point function between a conserved current and two scalars, complex conjugate of each other and having the ... | g7858 | [
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<p>I'm currently taking a high school physics class and we're doing friction problems now. I've been doing the ones that use MKS perfectly well, but when the problems start to use the FPS system, I'm always getting a relative error of around 12%. This mostly stems from my not knowing how to deal with FPS using the $ F ... | g7859 | [
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<p>I found a really cool sounding order-of-magnitude modeling question but am a bit at a loss on how to approach this:</p>
<blockquote>
<p>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 ... | g7860 | [
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<p>I have been reading the paper <a href="http://arxiv.org/abs/0810.1545" rel="nofollow">The Incompressible Non-Relativistic Navier-Stokes Equation from Gravity</a>. In it they state, </p>
<blockquote>
<p>"An instability, if it occurs, must necessarily break a symmetry ...
that the background solution preserves."... | g7861 | [
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<p>Iron is the most stable single element (I don't know about combinations of elements, but oh well, not applicable to question). Stars go through cycles where they change the materials of their cores, culminating in iron for the longest lasting and largest stars. The cores of stars naturally have tremedous forces. My ... | g7862 | [
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<p>I'm having trouble with the following problem.</p>
<p><img src="http://i.stack.imgur.com/ed8nE.png" alt="Problem"></p>
<p><em>What I've done so far:</em></p>
<p>x-y is the usual coordinate system.</p>
<p>$a=\frac{F}{m}=\frac{800}{60}$ and the y component of this is $a_y=a\sin{60^\circ}$.</p>
<p>To figure out th... | g7863 | [
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<p>Let's consider a spring. I am a strong man(well, lets assume) and I am pulling the spring. the work I do is being stored in the spring in the form of its elastic potential energy. Then suddenly, elastic limit is crossed and the spring reaches to the yielding region. then, at that very moment, i become exhausted and ... | g7864 | [
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<p>In Mudelung's book, Introduction to Solid-State Theory, I am confused by the following statement.</p>
<blockquote>
<p>For many applications a further simplification is helpful. The concept of the hole presents us with the confusing situationthat a hole in the state $\mathbf{k},\sigma$ has a momentum $-ħ\mathbf{k}... | g7865 | [
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0.03150913864374161,
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<p>The <a href="http://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect" rel="nofollow">Aharonov–Bohm effect</a> shows the vector potential $\mathbf{A}$ is more fundamental than magnetic flux density $\mathbf{B}$. However, vector potential is introduced by
$$ \nabla \times \mathbf{A} = \mathbf{B} $$ or $$ \mathrm{d} ... | g7866 | [
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0.01689280942082405,
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0.02107592299580574,
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0.0239... |
<p>How I determine the center of mass of a semicircle using the definition of center of mass? I only know solve this using the Pappus theorem. Consider that the semicircle is centered on the origin and a homogeneous mass distribution.</p> | g7867 | [
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0.0003428806667216122,
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<p>I'm supposed to calculate the inversion pressure $p_i$ of a <a href="https://en.wikipedia.org/wiki/Van_der_Waals_gas" rel="nofollow">Van der Waals gas</a>. The state equation of the Van der Waals gas is: $$(p + \frac{a}{V^2})(V-b) = RT.$$ To get a hold of the inversion temperature, I differentiate this equation with... | g7868 | [
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-... |
<p>This is sort of a silly question because I'm a total beginner, and I debated whether it was better to ask here or on Math.SE. I decided on here because it's about how physicists use terminology, even though the terminology is intrinsically mathematical and there's not actually any physical content in the question.</... | g7869 | [
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... |
<p>The <a href="http://en.wikipedia.org/wiki/Cross_section_%28physics%29" rel="nofollow">cross section</a> is a tiny area, measured in barns ($10^{-28} \mathrm{m^2}$), which relates to the probability of a reaction.</p>
<p>But I have trouble interpreting that number.</p>
<p>For example how can I calculate, when two d... | g7870 | [
-0.00765913724899292,
0.021197309717535973,
0.003235542681068182,
-0.038196347653865814,
0.05728219076991081,
0.018749291077256203,
0.008659259416162968,
0.07544402033090591,
-0.02382880635559559,
-0.08796520531177521,
0.008121781051158905,
0.0016347089549526572,
0.050254154950380325,
-0.0... |
<p>Imagine some sort of textile (as in very light, not metallic) that is tightly rolled up, can be easily unrolled by applying some force (i.e pulling it) but when released will eventually return to it's rolled up state, over and over again.</p>
<p>Does something like this exist?</p> | g7871 | [
-0.017198676243424416,
0.021738888695836067,
0.011625906452536583,
-0.049888644367456436,
-0.043309830129146576,
-0.025394119322299957,
-0.007709290832281113,
-0.030354738235473633,
0.008295038715004921,
-0.03954940661787987,
0.018202314153313637,
-0.04881315678358078,
0.051240552216768265,
... |
<p>I thought this would be a simple question, but I'm having trouble figuring it out. Not a homework assignment btw. I am a physics student and am just genuinely interested in physics problems involving math, which would be all of them.</p>
<p>So lets say we drop an object from a height, $R+r$, it falls toward earth. ... | g999 | [
0.09016318619251251,
0.06665769219398499,
-0.009590226225554943,
-0.019923033192753792,
-0.010378753766417503,
0.06679569184780121,
0.02244936302304268,
-0.02268032170832157,
-0.08296044915914536,
-0.014569035731256008,
-0.014772743918001652,
0.04109121114015579,
0.0363612063229084,
0.0193... |
<p>In paramagnetic-to-ferromagnetic phase transitions, the symmetry spontaneously breaks down from SO(3) to the subgroup SO(2) below $T_\text{crit}$. This implies that there should be two Goldstone modes and not one because SO(3) has three generators and SO(2) has one. How do we distinguish between these two excitation... | g7872 | [
-0.005361249204725027,
0.07697548717260361,
-0.011613328941166401,
-0.019603628665208817,
0.05746160447597504,
0.0631672590970993,
0.04215414822101593,
0.03652477636933327,
-0.012234236113727093,
0.02599705383181572,
-0.08930552750825882,
-0.04270417243242264,
0.025283897295594215,
-0.0225... |
<p>When a photon is emitted from a far away source and then measured by an observer, there is a loss of energy or redshift which takes place. Why does this happen?</p>
<p>I have read <a href="http://physics.stackexchange.com/questions/4821/redshifted-photon-energy">this</a> similar post, however the confusion I'm havi... | g7873 | [
0.03719322010874748,
-0.020268751308321953,
0.0010252074571326375,
-0.0009845010936260223,
0.032705433666706085,
0.014688760042190552,
0.04325583577156067,
0.09070917963981628,
-0.04042770713567734,
-0.033243242651224136,
0.011545085348188877,
0.022764313966035843,
0.012970706447958946,
0.... |
<p>(Please bear with me.)
If the universe included multi-universes, and black holes transferred matter between them, AND yet there was a large, but FINITE amount of matter and space, How would that max-limit change our understanding/perception or theories of the universe? Would it make any difference or change current ... | g7874 | [
-0.022303679957985878,
0.04820743948221207,
0.004306381102651358,
-0.013610768131911755,
-0.022489232942461967,
0.0028585914988070726,
-0.043721575289964676,
0.05962454527616501,
0.042825594544410706,
-0.03848059102892876,
0.013887732289731503,
-0.058378830552101135,
0.057081401348114014,
... |
<p>An electron in a cathode-ray tube is traveling horizontally at 2.10×10^9 cm/s when deflection plates give it an upward acceleration of 5.30×10^17 cm/s^2 .</p>
<p>B.) What is its vertical displacement during this time?</p>
<p>My work <a href="http://i.imgur.com/AqKlTuX.jpg" rel="nofollow">http://i.imgur.com/AqKlTuX... | g7875 | [
0.08438935875892639,
0.049069423228502274,
-0.012072503566741943,
0.01589863747358322,
0.05996226146817207,
0.048183515667915344,
0.035071130841970444,
-0.018857317045331,
-0.05779656022787094,
0.01737843081355095,
-0.022538311779499054,
0.08331544697284698,
-0.0244270171970129,
-0.0145250... |
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