question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Had physics for 2 years now on highschool, but there is a thing I am wondering about.</p>
<p>You know the in the height above the earth surface around where the satellites are (Or the ISS), I've calculated that there actually is a big amount of gravity-forces, even up there. (9.1 - 9.2 <code>m/s^2</code>) - How com... | 33 |
<p>My book about quantum mechanics states that the hamiltonian, defined as $H=i\hbar\frac{\partial}{\partial t}$ is a hermitian operator. But i don't really see how I have to interpret this. First of all: from which to which space is this operator working? They are defining a vectorspace called the "wavefunctionspace $... | 1,975 |
<p>Imagine two charges A and B separated by some distance.</p>
<p>Charge A emits a photon which is absorbed by charge B.</p>
<p>Is the recoil momentum received by charge A always equal and opposite to the momentum gained by charge B?</p>
<p>Is this true both for static Coulomb fields and radiation fields from accele... | 1,976 |
<p>Is the force which acts perpendicular to a wire due to another current wire in its vicinity consistent or it is just for a brief time? I thought it should be for a brief time because only for a moment all electrons will drift in the direction of force but after that the force will change its direction (it has to be ... | 1,977 |
<p>In Chapter II of Dirac's <em>Principles of Quantum Mechanics</em>, Dirac explains that in general it is very difficult to know whether, for a given real linear operator, that any eigenvalues/eigenvectors exist and (if they do) how to find them.</p>
<p>He then goes on to state that a special tractable case can be fo... | 1,978 |
<p>I first heard about the Tokamak in highschool 10 years ago and was wondering how far the technology has come since then. Can it sustain a reaction for more than a few seconds? Are these devices still huge or have they been made on a smaller scale?</p> | 1,979 |
<p>Does anyone know the refractive index suppliers? I've found Cargille Labs (which customer service is terrible so far but the liquids may actually be OK), but nothing else comparable. I'd like to have a set of liquids with the refractive index in the range of 1.3...1.4. Are they so hard to produce that almost nobody ... | 1,980 |
<p>As the title says, is it possible to have a Riemannian Ricci flat compact manifold with $U(1)\times{}SU(2)\times{}SU(3) $ <a href="http://en.wikipedia.org/wiki/Isometry_group" rel="nofollow">isometry group</a>?</p> | 1,981 |
<p>I've read <a href="http://en.wikipedia.org/wiki/Quantum_computer">Wikipedia</a>, I've read <a href="http://www.howstuffworks.com/quantum-computer.htm">How Stuff Works</a>, I've read <a href="http://www.singularity.com/">The Singularity is Near</a>, but I still just don't get it. How does a Quantum Computer work? It ... | 1,982 |
<p>I want to outline a solid argument (or bulletpoints) to show how weak is the idea of diff(M) being the gauge group of general relativity.</p>
<p>basically i have these points that in my view are very solid but i want to understand if there are misconceptions on my part that i'm simply not getting and if its so, i a... | 1,983 |
<p>In astrophysics, I often come across the speed of sound. I understand that, broadly, it represents the speed at which perturbations travel through a medium. But there's more than one speed of sound. The most common seem to be <em>isothermal</em> and <em>adiabatic</em>, which are defined as $c_s^2=(dp/d\rho)_T$ and $... | 1,984 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/12435/einsteins-postulates-minkowski-space-in-laymans-terms">Einstein's postulates <==> Minkowski space. (In layman's terms)</a> </p>
</blockquote>
<p>In the spirit of Einstein's arguments ... | 34 |
<p>This is not a question pertaining to interpretations, after the last one I realized I should not open Pandora's Box ;) </p>
<p>For theories to be consistent, they must reduced to known laws in the classical domains. The classical domain can be summed up as: </p>
<p>$$\hbar=0 ; c=\infty$$</p>
<p>Which is OK. I nee... | 1,985 |
<p>When the shaft of the helicopter rotates, it creates a low pressure. Because of the low pressure, the helicopter lifts. Is my understanding that this is just an application of Bernoulli's theorem?</p> | 17 |
<p>I am speaking about GR with classical fields and energy. One question, spread over three increasingly strict situations:</p>
<p>Is there an energy density limit in GR? (literally, can the energy density have an arbitrarily large value at some point in space at some point in time)</p>
<p>Is there an energy density ... | 1,986 |
<p>In 2006 the IAU deemed that Pluto was no longer a planet because it fails to "clear" the neighborhood around its Kuiper Belt orbit. Presumably, this is because Pluto (1.305E22 kg) has insufficient mass to do the job. How massive must a body in Pluto's orbit (semi-major axis 39.5 AU) be to "clear" its orbit? Would Ma... | 1,987 |
<p><a href="http://en.wikipedia.org/wiki/Hydrogen_ion" rel="nofollow">Hydrogen ion</a> doesn't have one electron which clearly mean that it has only one proton..So hydrogen ion is only a proton. Am I right, please make it clear. If hydrogen ion and proton are same that how to explain the reactivity with electron?</p> | 1,988 |
<p>Here's a question inspired by <a href="http://physics.stackexchange.com/questions/7771/is-there-an-energy-density-limit-in-gr/7773#7773">Edward's answer</a> to <a href="http://physics.stackexchange.com/questions/7771/is-there-an-energy-density-limit-in-gr">this question</a>. </p>
<p>It's my understanding that the a... | 1,989 |
<p>When an object enters water with high velocity, (like in <a href="http://physics.stackexchange.com/questions/106808/why-jumping-from-high-altitude-into-water-is-fatal">Why is jumping into water from high altitude fatal?</a>), most of it's kinetic energy will be converted, eg to accelerate water, deform the object et... | 1,990 |
<p>This post relates to <a href="http://physics.stackexchange.com/questions/71526/problems-with-putting-mass-on-yang-mills-theory-by-hand">this previous one</a>. My question is, what is the actual meaning of a theory being renormalizable?</p>
<p>There might be at-least two possibilities (correct me if I am wrong)</p>
... | 1,991 |
<p>I'm not a physicist and just making some research by the way of creating simple physics simulator, because of that, sorry if this is very dumb question, but I really need help with it.</p>
<p>Let's assume that some body (rectangle, square, N-polygon, etc.), exists in 2D world in rest (no friction, gravity, etc.) an... | 1,992 |
<p>The average kinetic energy (KE) per molecule of a gas is $\frac{3}{2}kT$. While finding this we do </p>
<p>$$ \text{ Average KE} =\frac{1}{2} M \frac{1}{N}\sum v^2=\frac{3}{2}kT$$
But why do we not add rotational kinetic energy here?</p> | 1,993 |
<p>Which is more appropriate regarding Bernoulli's principle</p>
<ul>
<li>fast moving air causes low pressure or</li>
<li>lower pressure causes fast moving air.</li>
</ul> | 1,994 |
<p>The "<a href="http://www.vacuvin.com/270/Vacuum_Wine_Saver.html" rel="nofollow">Vacuum Wine Saver</a>" comes with the following "warning":</p>
<blockquote>
<p>Not for sparkling wines</p>
</blockquote>
<p>Intuitively and naively, I imagine that the <a href="http://en.wikipedia.org/wiki/Sparkling_wine#Bubbles" rel... | 1,995 |
<p>Not sure if this is the right place to ask this but here goes.</p>
<p>If the north pole ice sheets melt, everyone agrees this would be a bad thing, however one of the reasons they state for this being a bad thing is the rise in sea level.</p>
<p>Given that the north pole is essentially a massive ice sheet floating... | 35 |
<p>I'm really interested in quantum physics and would like to learn more. However, I don't know where to start and in what order I should learn things. So, ideally I'm looking for some sort of roadmap of what to learn. What physics topics do I need to know to start learning about quantum mechanics? (In addition to the ... | 223 |
<p>I'm working on a physics problem in preparation for the MCAT and there's this particular problem that's troubling me. I don't know if it's a bad question or if I'm not understanding some sort of concept. I was hoping someone here can clarify. Here's the problem verbatim:</p>
<blockquote>
<p>A 1kg cart travels dow... | 1,996 |
<p>If we roll a normal egg and a boiled egg at the same time on a floor </p>
<p>1) with friction </p>
<p>2) without friction</p>
<p>which one will come to stop first (if they will stop at all) and why?</p>
<p>Can anyone tell me reason for this?</p> | 1,997 |
<p>My research has led me to look into the idea of bubble universes which I don't know very much about. The first thing that I am looking for is understanding or visualising how could many bubbles co-exist geometrically, assuming each bubble universe is like ours (that is, a flat euclidean geometry). Are we talking ab... | 1,998 |
<p>I've seen some discussions regarding the movement of a spinning object, say a curveball. However, all have been largely qualitative. I was wondering if anyone has seen or worked through a calculation of how far a curveball moves laterally on its way from the mound to homeplate - even in an order-of-magnitude sense... | 1,999 |
<p>Trying to determine the speed of a falling body with respect to traveled distance and initial speed. I've been provided with the following equation for acceleration as a function of distance and the grav. parameter(constant) of the attracting body :</p>
<p>$a=GM/r^2$ </p>
<p>Where:</p>
<p>$a$ - acceleration.<b... | 1,000 |
<p>I was re-studying university physics last week, I'm now in the chapter about kinematics in 2 dimensions and specifically the one treating projectile motion. In page 86 of his book (Serway - Physics for scientists and engineers) he derives the equation of the range of the projectile motion to be: $$R=\frac{{v_i}^2\si... | 2,000 |
<p>I can't understand the concept of the curl of an electromagnetic wave. </p>
<p>$$
\nabla \times E = -\frac{\partial \textbf{B}}{\partial t}
$$</p>
<p>All of the examples I find show a current through a conductor, or that paddle wheel in water which I fail to see the distinction of that with an E-M wave. What I am ... | 2,001 |
<p>There is a few questions that need to be answered in detail but in an easy way...</p>
<ol>
<li><p>What does it mean to describe the 'plane of polarisation' of electromagnetic waves?</p></li>
<li><p>Why will some antenna have rods which are horizontal and some which are vertical? What does this have to do with polar... | 2,002 |
<p>I have to calculate the total number of electric field lines through a proton. I tried using Gauss' Law, i.e, $$\phi = \oint\boldsymbol E.d\boldsymbol s = {\frac{q}{\epsilon_0}} $$ $$So, \phi = {\frac{q}{\epsilon_0}} $$</p>
<p>$$ \textrm{Therefore}, \phi = \frac{1.6\times10^{-19}}{8.854\times10^{-12}}$$, as $q=1.... | 2,003 |
<p>I wish to find an everyday situation that illustrates the following:</p>
<p>A rod is moving in a direction perpendicular to its axis. One end "gets caught" and the rod starts rotating around this end. THE SPEED OF THE OTHER END OF THE ROD WILL THEN INCREASE BY A FACTOR SQRT(3).</p>
<p>Here is an <a href="https://w... | 2,004 |
<p>I have studied about the two types of doping which result in p and n type semiconductors. I also came to know that they are neutral. But, how can it be? </p>
<p>Is it that the positive charge(holes) in p-type and negative charge in n-type are negligibly small to affect the overall neutrality of the substance? But, ... | 2,005 |
<p>In case of solar system,we can explain "Why Sun would not revolve around any other planet?",by giving the reason that Sun is heavier than any other planets. </p>
<p><a href="http://physics.stackexchange.com/questions/81648/why-heavier-bodies-produce-greater-gravitational-pull-than-the-lighter-bodies">Heavier the b... | 2,006 |
<p>I have hacked a FitDesk exercise bike to output the RPM of the pedals and the position of the resistance control within its range of travel.</p>
<p>I want to characterize the energy that is required to pedal the bike at different RPMs and resistance settings.</p>
<p>My approach is to determine the torque required ... | 2,007 |
<p><img src="http://i.stack.imgur.com/dBS2M.png" alt="This is the image of the paragraph from the book"></p>
<p>Why should an equation (<a href="http://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation" rel="nofollow">TDSE</a>) in which first time derivative is related to second space derivative have a solution that con... | 36 |
<p>If you have, say, a proton it has gluon field fluctuations around it. Those flux tubes between the quarks suppresses the gluon field fluctuations and create a true vacuum between them(correct me if I'm wrong), but how does that bind the quarks together?</p>
<p>I've read that it costs energy to clear the vacuum out,... | 2,008 |
<p>I need an inexpensive instrument to measure cryogenic temperatures (down to -200C).</p>
<p>I can build a thermistor-based thermometer using an Arduino that is accurate to under 1 degree for 0 to 100C.</p>
<p>First of all, can ordinary NTC thermistors be used at cryogenic temperatures?
Second, if I were to try to u... | 2,009 |
<p>If we have two parallel charged plates, equal and opposite in charge:</p>
<p>What is the flux felt on a Gaussian surface between them? surely it sum to 0 as each amount of flux will enter and then leave? This must be wrong as it would mean the field between the two plates is also zero?</p>
<p>Let me know what i'm ... | 2,010 |
<p>If we imagine a object made up of Hydrogen gas that is optically thick to all radiation, and is in thermal equilibrium, then, microscopically, photons will be emitted and absorbed as emission/absorption lines.</p>
<p>However, the overall object should emit radiation according to <a href="https://en.wikipedia.org/wi... | 2,011 |
<p>Current in wire + moving charge next to wire creates magnetic force in the stationary reference frame OR electric force in the moving reference frame from special relativity due to change in charge density etc.... I think I understand this and I think it's super cool. Now here's the rub...</p>
<p>Current in wire + ... | 780 |
<p>In M. Salmhofer's "Renormalization, An Introduction" Wick ordering is defined as follows:</p>
<blockquote>
<p>Let $C = C_\Gamma$ be a nonnegative symmetric operator on $\mathbb{C}^\Gamma$. For $J: \Gamma \to \mathbb{C}$, let</p>
<p>$$\mathcal{W}_\Gamma (J, \phi) = e^{i(J,\phi)_\Gamma + \frac{1}{2} (J, CJ)_\G... | 2,012 |
<p>Usually in texts about Physics that uses tensors defines them as multilinear maps. So if $V$ is a vector space over the field $F$, a tensor is a multilinear mapping:</p>
<p>$$T:V\times\cdots\times V\times V^\ast\times\cdots\times V^\ast\to F.$$</p>
<p>In texts about multilinear algebra, however, a tensor is define... | 2,013 |
<p>Suppose a particle with mass $m_1$ and speed $v_{1i}$ undergoes an elastic collision with stationary particle of mass $m_2$. After the collision, particle of mass $m_1$ moves with speed $v_{1f}$ in a direction of angle $\theta$ above the line it was moving previously. Particle with mass $m_2$ moves with speed $v_{2f... | 429 |
<p>I'm trying to help a child research a science project on refrigeration.
Refreshing my incredibly rusty thermodynamics skills....</p>
<p>The ideal gas law: $PV=nRT$. Let's take air at STP:</p>
<p>$P = 101\,kPa$
$V = 1\,L = 0.001\,m^3$
$R = 8.3\,J/mol\cdot K$
$T = 298\,K$</p>
<p>$n=PV/RT = (101000) (.001) / (8.3 \c... | 2,014 |
<p>In the following image,three cases have been mentioned. $N$ is the normal force acting on the object inside the lift and $mg$ is the force of attraction due to gravity.<br>
In case 1, $N = mg$.<br>
In case 2, $N = m(g+a)$ and<br>
in case 3, $N = m(g-a)$. Why is it so in 2nd and 3rd case?
<img src="http://i.stack.... | 2,015 |
<p>Let's say I know the size of the container, size of the hole the air leaks through, pressure the air is under and temperature of the air if that helps anything. Is it possible to calculate this only from these variables? What is the formula for how fast air leaks out of a hole?</p> | 2,016 |
<p>I read an article which tells power consumption by many devices. It say that a desktop computer (computer and monitor) use 400 to 600 watt.<br>
While when i checked my computer and monitor with meter, it was about 60 + 60 = 120 watt (computer + 17" CRT monitor) after loading windows xp and running an application. Th... | 2,017 |
<p>In the time-independent Schrödinger's equation:</p>
<p>$$ -\frac{\hbar^2}{2m} \frac{d^2} {dx^2} u + Vu ~= Eu, $$</p>
<p>why there is a minus sign before the first term?</p> | 2,018 |
<p>Mass m is connected to the end of a cord at length R above its rotational axis (the axis is parallel to the horizon, the position of the mass is perpendicular to the horizon). It is given an initial velocity, V0, at a direction parallel to the horizon. The initial state is depicted at position A in the image.</p>
<... | 2,019 |
<p>In Peskin and Schroeder's QFT book, page 189, equation 6.38, how do they get from the first line to the second line?</p>
<p>In particular, I am stuck on the transition from what I perceive to be:
$$ k'_\alpha \gamma^\alpha m \gamma^\mu + m k_\alpha \gamma^\alpha \gamma^\mu $$
into:
$$ -2m(k+k')^\mu $$</p>
<p>what ... | 2,020 |
<p>I read a lot about the classical twin paradox recently. What confuses me is that some authors claim that it can be resolved within <a href="http://en.wikipedia.org/wiki/Special_relativity">SRT</a>, others say that you need <a href="http://en.wikipedia.org/wiki/General_relativity">GRT</a>. Now, what is true (and why)... | 249 |
<p>What are the different death scenarios for a black hole? I know they can evaporate through Hawking radiation - but is there any other way? What if you just kept shoveling more and more mass and energy into the black hole?</p> | 2,021 |
<p>Imagine a circuit with a voltage source, a switch and an inductivity all connected in series.</p>
<p>First, the switch is open and there's no current and no magnetic field around. If we close the switch, the potential difference of the voltage source is instantaneously applied to the inductivity. Lenz's Law tells u... | 2,022 |
<p>Given the solution of the Von Neumann equation
$\rho(t) = e^{-i H t/\hbar} \rho(0) e^{i H t/\hbar}$</p>
<p>How can we justify if it will be stabilized as $t\rightarrow\infty$ in general?</p>
<p>For example, $H=\begin{pmatrix}0 & 1 \\ 1 & 0\end{pmatrix}, \rho(0)=\begin{pmatrix}\frac{1}{2} & \frac{1}{2}... | 2,023 |
<p><img src="http://www.a-levelphysicstutor.com/images/matter/E-r-graph.jpg" alt="potential energy vs intermolecular distance r"></p>
<p>I'm trying to understand this curve better, but I can't quite figure out what "negative potential energy" means.</p>
<p>The graph should describe a molecule oscillating between $A$ ... | 2,024 |
<p>This is a question on the synchronization of clocks. If a girl on a train has the same clock that a guy has on the platform and they synchronize their clocks at 12am together when the train and the platform are both stationary with respect to each other. Then if the train runs and some time later (a random time late... | 2,025 |
<p>Starting with the Maxwell action for a $U(1)$ vector gauge boson with a general metric and (I'm assuming) using a plane wave ansatz for the vector, is it possible to derive the action for a massless point particle?</p>
<p>EDIT: More information on what I'm trying to do. The Maxwell action and the action for a massl... | 2,026 |
<p>Common wisdom is that for a QFT to be renormalizable it must be invariant under a symmetry transformation. Why does renormalization need an unbroken symmetry? Which is the first publication that proves it?</p> | 2,027 |
<p>This brand new published result (nature):</p>
<blockquote>
<p><strong>Experimental non-classicality of an indivisible quantum system</strong><br> by
Radek Lapkiewicz, Peizhe Li, Christoph Schaeff, Nathan K. Langford, Sven Ramelow, Marcin Wieśniak & Anton Zeilinger</p>
</blockquote>
<p>(see <... | 2,028 |
<p>What is the centripetal acceleration and angular velocity of a child located 8.2 m
the center of a carousel? The speed (size of the tangential velocity) of the child is
2.1 m / s</p>
<p>A train moves in a straight path north until it turns to west.
If the road segment used to change direction is shaped like a quart... | 2,029 |
<p>I was looking for a derivation of the expression for the energy density at any point in a static magnetic field. I do know that it is $\dfrac {1}{2 \mu_0}\left|\vec{B}\right|^2$ -- I was just wondering if there was a derivation that could be built up the way one derives the energy density $\dfrac {\epsilon_0}{2}\lef... | 2,030 |
<p>If p-type semiconductor and n-type semiconductor of a diode are equally doped, and if the diode is forward biased, then holes will move toward the n-type semiconductor and electrons will move toward the p-type semiconductor and they will diffuse with each other. Then will there be any electron that will go to the po... | 2,031 |
<p>The human brain is said to produce a magnetic field resulting from the action potentials released inside the brain. What's the nature of such a field in terms of size and strength, and what is the potential for manipulation of brain functions by interfering with it by means of electromagnetic radiation?</p> | 2,032 |
<p>Hi I'm trying to solve this textbook example but I don't know where to begin;</p>
<blockquote>
<p><em>NASA has decided to send an experimental probe to Mars. Its weight on earth is $40 kg_f$. When the probe is near the planet it will be
attracted by the its gravitational field ($g_{Mars} = 3.75\ m/s^2$). Det... | 2,033 |
<p>This was another question from my son's workbook. It said:</p>
<pre><code>Ever jumped into a pool on a warm day and still felt cold, even after measuring the
temperature of the water with a thermometer and finding that it is the same temperature as
the air? Would this be conduction, convection or radiation then?
<... | 2,034 |
<p>Assuming that I calculated the electric field in a single point between a uniform charged positive sphere and an infinite long wire charged positive uniformly.
Now, I want to calculate the velocity of a given particle q+ which will be set free from the point (A) which I calculated the field at, while hitting the sur... | 2,035 |
<p>We typically say that forces cause acceleration inversely proportionate to mass. Would it be any less correct to say that acceleration causes forces proportionate to mass? Why?</p>
<p>(Note that the underlying question in my mind - essentially, what distinguishes cause from effect - is far more general. But this se... | 2,036 |
<p>From a paper on tunnel design I've been reading: (<a href="http://www.sciencedirect.com/science/article/pii/0886779887900113" rel="nofollow">http://www.sciencedirect.com/science/article/pii/0886779887900113</a>)</p>
<blockquote>
<p>In the present application, the solu-
tion corresponding to a sinusoidal load
... | 2,037 |
<p>I need to find a parachutist's displacement after a given height (nearly 37000m) and at a given latitude. I have his mass, area, parachute area, drop height, parachute deployment height, data about the atmosphere, and other assorted values. I don't have velocity and Temperature so I'm stuck. Please help.</p>
<p>My ... | 2,038 |
<p>The eigenfunctions of a Hermitian operator are real. But consider a function $\psi(x)=e^{-\kappa x}$, $x\in\mathbb{R}$, where $\kappa$ is a real constant. Then, $$\hat p \psi(x)=-i\hbar \frac{d}{dx}e^{-\kappa x}=i\kappa \hbar \psi(x).$$ This gives a pure imaginary eigenvalue. Is it not a contradiction? Or am I missi... | 2,039 |
<p>On page 160 Peskin & Schroeder, they say: </p>
<blockquote>
<p>Therefore we expect $\mathcal{M}^\mu(k)$ to be given by a matrix element of the Heisenberg field $j^\mu$: $$\mathcal{M}^\mu(k) = \int \mathrm{d^4}x \; \exp(\mathrm{i}k \cdot x)\langle f | j^\mu(x) | i\rangle.$$</p>
</blockquote>
<p>Why do they ex... | 2,040 |
<p>In quantization of scalar field theory we impose commutation relation between the field operators <strong>by hand</strong> and similarly we impose anti-commutation relation between Dirac field operators <strong>by hand</strong>. As a consequence one gets Bose-statistics (two-particle wavefuction is symmetric) in the... | 2,041 |
<p>Where can one find some concrete physical problems (with solutions) that illustrates the uselfullness and power of QFT? These must not be solvable by QM or SR alone.</p>
<p>It would be good if the problem utilizes the most central QFT concepts. I am trying to learn QFT but it looks like only some mathematical defin... | 2,042 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2175/is-it-possible-for-information-to-be-transmitted-faster-than-light-by-using-a-ri">Is it possible for information to be transmitted faster than light by using a rigid pole?</a> </p>
</blockquote>
<p>... | 4 |
<p>Considering the fact that electrons tend to take the maximum conductance path to flow from A to B. This is justified by saying that $\vec{E}$ is larger in conductors. But once similarly it was thought for gravitation, that if in a region the gravity was stronger, the mass more likely took that path, then later it wa... | 543 |
<p>Hi, I am thinking about acceleration. Let's think we have a force of $1$ N and a particle of $1$ kg, then acceleration will be $1$. So the speed gets higher every second and $c$ seconds later, <em>in Newtonian mechanics</em>, the particle will reach the speed of light. In relativity, of course, something like that ... | 37 |
<p>Is there any reason for the names of the decay chains? As shown in this chart (<a href="http://upload.wikimedia.org/wikipedia/commons/thumb/6/62/Radioactive_decay_chains_diagram.svg/2000px-Radioactive_decay_chains_diagram.svg.png" rel="nofollow">larger version here</a>):
<img src="http://i.stack.imgur.com/0LVtw.png"... | 2,043 |
<p>I have two coherent point sources of light, $A$ and $B$, separated by a distance $L$, which I focus down to the diffraction limit using a high-powered objective (e.g. a $\approx 100x$ objective). If I turn on $A$ and turn off $B$, I have an Airy disk at position $c_1$, and I turn off $A$ and I turn on $B$, I have a... | 2,044 |
<p>I read in wiki that the speed of light is 88km/s slower in air than it is in a vacuum.</p>
<p>Do neutrinos travel faster than light in air?</p> | 2,045 |
<p>A lot of textbooks and exam boards claim that light incident at exactly the critical angle is transmitted along the media boundary (i.e. at right-angles to the normal), but this seems to violate the principle of reversibility in classical physics. How would a photon or ray travelling in the reverse direction "know"... | 722 |
<p>RHIC has been the dominant player in heavy ion physics, producing tantalizing evidence in support of the entropy/viscocity formula from AdS/CFT.
What's the potential of the LHC's Pb ion collsions? What can it achieve which RHIC can't? What measurements will be improved?</p> | 2,046 |
<p>I don't know how this "paradox" can be solved. I'm given the following system: A permanent magnet with a magnetic field given by ($\hat{a}$ are unit vectors in the x and y directions)</p>
<p>$$\vec{H}=H_0\hat{a}_y$$</p>
<p>and a parallel plane capacitor with an electric field</p>
<p>$$\vec{E}=E_0\hat{a}_x$$</p>
... | 2,047 |
<p>The only explicit computation I have seen is the planar 1-loop one, but there should be a way to write the multi-loop case in terms of boundary states as well. </p> | 2,048 |
<p>I had a test on Quantum mechanics a few days ago, and there was a problem which I had no clue how to solve. Could you please explain me?</p>
<p>The problem is:</p>
<blockquote>
<p>Let's look at the $\hat H=E_0[|1 \rangle \langle 2| + |2 \rangle \langle1|]$ two-state quantum system, where $E_0$ is a constant, and... | 2,049 |
<p>A copy of <a href="http://math.stackexchange.com/questions/687534/are-continuous-mathematical-models-of-discrete-physical-phenomena-messy-because">my question on Mathematics</a>:</p>
<p>Examples from statistical mechanics and continuum mechanics abound: a discrete phenomenon (e.g. kinetic energy of molecules) is "a... | 38 |
<p>I know ice floats in water because it's crystalline structure causes $H_20$ solid to be less dense than $H_20$ liquid. Is the same true for salt because it is crystalline? If not why?</p> | 2,050 |
<p>In the popular culture the XIX-XX century competition between Thomas Edison and Nikola Tesla is well-known. The example could be the <a href="http://www.imdb.com/title/tt0482571/" rel="nofollow"><em>Prestige</em></a> movie, where there are some "Edison's agents" who sabotage Tesla's efforts. From electrical engineer... | 2,051 |
<p>The diagram in <a href="http://physics.stackexchange.com/questions/36092/why-are-l4-and-l5-lagrangian-points-stable">Why are L4 and L5 lagrangian points stable?</a> shows that the gravitational potential decreases outside the ring of Lagrange points — this image shows it even more clearly:
<img src="http://i.stack.i... | 2,052 |
<p><img src="http://i.stack.imgur.com/sUvHk.png" alt="enter image description here"></p>
<p>As you see, this is the electric field generated by a point charge moving at constant speed v. I know that when $v$ -> 0, $E$ is just the Coloumb Law. But how do you interpret $E$ when $v$ -> $c$ ? </p>
<p>Can I just interpre... | 2,053 |
<p>If while calculating a band gap, the band just below the Fermi level touches the Fermi level, can we say the material is semiconducting?</p> | 2,054 |
<p>I'm currently reading the Seiberg-Witten paper on $N=2$ supersymmetric Yang Mills pure gauge theory (i.e. no hypermultiplets). I have the following question:</p>
<p>How does one understand that the metric on the moduli space of the full quantum theory is the same as the metric obtained from the Kahler potential for... | 2,055 |
<p>I'm swimming in the ocean and there's a thunderstorm. Lightning bolts hit ships around me. Should I get out of the water?</p> | 2,056 |
<h1>Problem</h1>
<p>If you had a long bar floating in space, what would be the compressive force at the centre of the bar, due to the self-weight of both ends?</p>
<p>Diagram - what is the force at point X in the middle of the bar?:</p>
<pre><code><----------------------L--------------------->, total mass M
==... | 2,057 |
<p>The Lippmann-Schwinger equation in the first Born approximation, in the far field, is the Fourier transform of the potential. The scattering potential for an electron beam incident on a crystal is by the Coulomb potential which can be recast as crystal electron density by the Poisson equation. The scattering field i... | 2,058 |
<p>Does the nature of the assortment of virtual particles depend upon the warping of spacetime in a direct manner ?</p> | 2,059 |
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