question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>As we know the predominant theory where does the moon come from is that a Mars size planet hit the earth and took a chunk out of it which eventually materialized into moon.</p>
<p>My question is that if a Mars size object were to hit Earth, wouldn't it knock it off the orbit all together? What kind of collision is ... | 4,463 |
<p>I've been reading about black holes, and I keep coming across the fact that time runs slower near a them. My questions are: Does this mean that if you left Earth at age 30 and spent 30 years near the black hole, then you would be 45 years old? Do you get older more slowly, because if it's all the same what is the ... | 143 |
<p>Imagine a photo that is taken of someone looking straight at the camera.</p>
<p>Why when we look at the photo now <em>from any direction</em> it looks as if the person is looking straight at us?</p> | 4,464 |
<p>I apologize in advance for possible errors in my premises as I have no precise knowledge of Maxwell equations. Proposals for the correction or even abandon of my question are welcome.</p>
<p>As Maxwell equations are a full description of electromagnetic waves I suppose that they also describe the <strong>time</stro... | 4,465 |
<p>Our house has a glass sliding door to the shower. The shower has the dimensions of about 2 feet wide, 5 feet long, and 6 feet high. Above the door (and shower head) there is about 1 foot of open space before the ceiling to let the heat escape.</p>
<p>Sometimes I forget to slide the door all the way to the end of th... | 4,466 |
<p>I'm trying to find the Green's functions for time-dependent inhomogeneous Klein-Gordon equation which is :
\begin{align*}
\left[ - \nabla ^2 + \frac{1}{c^2} \dfrac{\partial ^2}{\partial t^2} + \kappa ^2 \right] \psi({\mathbf{r},t )} = \rho(\mathbf{r},t)
\end{align*}</p>
<p>It has bee... | 4,467 |
<p>when the sound barrier is broken, a series of concentric waves of sound is produced.Does it mean when the speed of light barrier is broken, a ripple of photons are created in the space-time fabric?</p> | 4,468 |
<p>I am reading Itzykson and Zuber's Quantum Field Theory book, and am unable to understand a step that is made on page 246:</p>
<p>Here, they consider the elastic scattering of particle $A$ off particle $B$:</p>
<p>$$A(q_1) + B(p_1) ~\rightarrow~ A(q_2) + B(p_2)$$</p>
<p>and proceed to write down the $S$-matrix ele... | 4,469 |
<p>Suppose a spring with spring constant 1 N m^-1 is held horizontally. If a pull of 1 N is applied to its left end and a pull of 2 N is applied to its right end, how much longer would the spring be as compared to its unstretched length?</p>
<p>I came up with this question because the spring related qurstions I've see... | 4,470 |
<p>One can no nothing about the magnetic force and yet arrive at it by taking the relativistic effects of a current and a moving charge system into account. I ask whether there exists such an inherent force in case of gravity.</p> | 4,471 |
<p>Are there any examples of common substances whose decay is not exponential?</p>
<p>We're used to thinking about radioactivity in terms of half-lives. This is a concept that makes sense only for a decay that is exponential. However, there are plenty of physics articles on the subject of non exponential decay. It see... | 4,472 |
<p>If I understand correctly, when an earthquake occurs, energy will be transferred to the water, resulting in water waves. As the waves reach seashore, because the sea depth is getting shallower and wavelength is getting shorter, the height of the wave gets push up, resulting in tsunami. In other words in deep sea, wa... | 4,473 |
<p>I know that there's no evidence at this point for "white holes" however would it even be mathematically possible for a black hole to be connected to a white hole (total opposite so everything would be expelled, after some really extreme physical conditions)? Maybe with a wormhole connecting them? If this was even po... | 4,474 |
<p>I've come upon Dr. J. Marvin Herndon's theory that the earth's magnetic field is generated by a hot nuclear reactor operating in the center of the earth. This is backed by various papers, some of them peer reviewed:</p>
<p><a href="http://www.nuclearplanet.com/Herndon%27s%20Nuclear%20Georeactor.html" rel="nofollow"... | 4,475 |
<p>How the field and interactions are changed when we assume that proton has finite radius in atom for example? What gives the finite size effect? Is it the higher moments of multipole expansion?</p> | 4,476 |
<p>I have to derive <a href="http://en.wikipedia.org/wiki/Wien%27s_displacement_law" rel="nofollow">Wien's displacement law</a> by using <a href="http://en.wikipedia.org/wiki/Planck%27s_law" rel="nofollow">Planck's law</a>. I've tried but I come to a unsolvable equation (well I can't solve it) anywhere I look online it... | 144 |
<p>This question is about terminology for <a href="http://en.wikipedia.org/wiki/Physical_quantity" rel="nofollow">physical quantities</a>. </p>
<p>When we talk about magnitude (while talking about scalars and vectors) do we refer to just number or Number along with units?</p>
<p>example: If a person weighs 120 pounds... | 4,477 |
<p>What are some "real" world applications of the particle in a box (PIB) and the finite square well (FSW) which are discussed in an intro quantum mechanics class? For instance, I know that the PIB can applied to quantum dots and the FSW to the Ramsauer-Townsend effect. How about other applications?</p> | 4,478 |
<p>Why does the Earth revolve with the Sun at one of its foci? Does the other focus do nothing? Why is there this asymmetry in our solar system? </p> | 4,479 |
<p>In the context of group theory (in my case, applications to physics), I frequently come across the phrase "the ${\bf N}$ of a group", for example "a ${\bf 24}$ of $SU(5)$" or "the ${\bf 1}$ of $SU(5)$" (the integer is usually typeset in bold).</p>
<p>My knowledge of group theory is pretty limited. I know the basics... | 345 |
<p>I just learned that strong and weak nuclear forces relate to decay/emission.
I know absorbtion depends on Energy levels(QM) and heat(thermodynamics , kinetic energy , entropy) and E = gamma mc^2 ( special relativity).
Assuming collision , are there fundamental forces associated with absorbtion ?</p>
<p>I add that I... | 4,480 |
<p>Consider a charge conjugation operator which acts on the Dirac field($\psi$) as<br>
$$\psi_{C} \equiv \mathcal{C}\psi\mathcal{C}^{-1} = C\gamma_{0}^{T}\psi^{*}$$
Just as we can operate the parity operator on the Lagrangian, and we say that a theory has a symmetry if $$\mathcal{P}\mathcal{L}(t,x^{i})\mathcal{P}^{-1} ... | 4,481 |
<p>I would like to know more about <a href="http://en.wikipedia.org/wiki/Ehresmann_connection">Ehresmann connections</a> in vector bundles and how they relate to the electromagnetic field and the electron in quantum mechanics.</p>
<p><strong>Background:</strong> The Schrödinger equation for a free electron is</p>
<p>... | 4,482 |
<p>What papers/books/reviews can you suggest to learn what <a href="http://en.wikipedia.org/wiki/Renormalization" rel="nofollow">Renormalization</a> "really" is?</p>
<p>Standard QFT textbooks are usually computation-heavy and provide little physical insight in this regard - after my QFT course, I was left with the imp... | 766 |
<p>It is well know that, using position representation</p>
<p>$$\langle r\lvert L\rvert \psi\rangle =r \times (-i\hbar\nabla\langle r|\psi\rangle )=r \times (-i\hbar\nabla\psi(r)).$$</p>
<p>However, I read from some books that if $L$ is acting on some position ket directly, then</p>
<p>$$L|r\rangle ~=~ r \time... | 4,483 |
<p>Suppose that I have a point mass attached to a massless string and I am rotating it vertically. That means The mass is in uniform circular motion and the path of its motion is vertical circle. How does the tension change with respect to the position of the mass. More specifically is the tension in the string is only... | 4,484 |
<p>Lately in my physics class (2nd-year undergraduate) we've been learning about the impulse response of systems and using Green's Functions to model the response of a system to more complicated input forces. Since it's a physics class, not a math class, some of the arguments for the math have been a bit handwavy. I've... | 4,485 |
<p>Is there any good definition of <a href="http://www.google.com/#q=many+body+localization" rel="nofollow">many body localization</a>?</p>
<p>It is the property of one state or it is the property of a Hamiltonian?</p>
<p>Why does disorder play an important role in many body localization?</p>
<p>What is the relation... | 4,486 |
<p>Given what we know about space, time and the movement of galaxies, have we or can we determine what our position is in relation to the projected location of the Big Bang? I've read some introductory papers on the superstructure and galaxy cluster movements, but none of them specifically mentioned space in terms of r... | 4,487 |
<p>My (just completed) PhD involved a considerable amount of research involved with the detection of solar UV radiation. This generated quite a bit of interest, especially when I was conducting my experiments outside.</p>
<p>A friend's 6 year old was most fascinated, but could not grasp the concept of UV radiation, p... | 4,488 |
<p>I know that the quantum circuit $\text{CNOT}\; (H \otimes I)$, where $\text{CNOT}$ is the controlled-not gate and $H$ the Hadamard gate, takes the computational basis of two qubits $|00\rangle,|01\rangle,|10\rangle,|11\rangle$ to the Bell states, which are maximally entangled.</p>
<p>Would $\text{CNOT}\;(H \otimes... | 4,489 |
<p>Is there a simple way to understand how scientists estimated/calculated the following percentages?</p>
<p><img src="http://i.stack.imgur.com/0GktV.jpg" alt="enter image description here"></p> | 4,490 |
<p>Prior to the Dirac delta function, what other distributions functions where physicists using? I find it hard to motivate the theory of generalized functions with just the delta function alone.</p> | 4,491 |
<p>I'm studying the diagrammatics for a Bose system (in the superfluid phase) developed by Gavoret and Nozieres (Annals of Physics 28 349 (1964)).</p>
<p>In this paper, they show how to solve the problem using skeleton diagrams. In other words, they give equations for the two-point, three-point and four-point function... | 4,492 |
<p>I have seen the charged pion decay $$\pi^{-}~\to~ \bar{\nu}_{\ell} +\ell^{-}$$ represented with diagrams containing a $W^-$ in the $s$-channel. The $\pi^-$ and $W^-$ have angular momentum $0$ and $1$ respectively, though. How does this process conserve angular momentum?</p>
<p>I see that this question has been ask... | 4,493 |
<p>To simulate a puck's movement, I use the following model (please restrain from discussing the model, it makes the simulation look the way I want it to) and would like to know how to calculate the total way the puck will move and how long it will take to do so.</p>
<p>My setup is: Per second, the puck looses 20% (<s... | 4,494 |
<p>Suppose we have a mass attached to the top of an ideal (linear and massless) spring oriented vertically in a uniform gravitational field, and on top of that mass there is another mass resting on it. The two masses are not attached at all, so they will lose contact with each other as the normal force is about to beco... | 4,495 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/679/learning-physics-online">Learning physics online?</a> </p>
</blockquote>
<p>I'm a high school student, and I got fives in AP Calculus, Mechanics and Electricity and Magnetism exams, and I've taken Li... | 145 |
<p>What is the definition of a <a href="https://www.google.com/#q=%22charge-neutral+operator%22" rel="nofollow">charge-neutral operator</a>? I guess it means something like: it is invariant under charge conjugation. It that correct? </p> | 4,496 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/17650/how-to-modify-the-bullet-trajectory-based-on-the-ballistic-coefficient">How to modify the bullet trajectory based on the ballistic coefficient?</a> </p>
</blockquote>
<p>I am new to the physics sur... | 146 |
<p>I imagine that the first ball would strike the rest as normal, but what would the last ball do, without gravity to swing it back? </p> | 4,497 |
<p><strong>Does Nantenna (nano antenna) violates 2nd Law of Thermodynamics ?</strong></p>
<p>Nantennas absorb infrared heat and convert it in direct current.
Quote from Wikipedia:</p>
<blockquote>
<p><a href="http://en.wikipedia.org/wiki/Nantenna#Future_research_and_goals" rel="nofollow">He did not discuss whether ... | 4,498 |
<p>In conventional conductors, the RC time constant is the time required to charge or discharge a capacitor through a resistor by ≈ 63.2 percent of the difference between the initial value and final value:</p>
<p>$$\tau = R \cdot C $$</p>
<p>However, in a superconductor, the resistance is exactly zero. </p>
<p>$$\ta... | 4,499 |
<p>I think Physics is fascinating , especially those really clever experiments one can do that demonstrate some important principle and probably don't cost a lot of money to make. Also the Thought Experiments of Galileo and Einstein and Maxwell (I think) and many others ; thought experiments that cost nothing and point... | 4,500 |
<p>What would be the requirement to learn matrix mechanics?</p>
<p>More specifically, what math do I need?</p>
<p>Can anyone recommend me a book that covers all maths needed for matrix mechanics?</p> | 4,501 |
<p>If the Higgs field gives mass to particles, and the Higgs boson itself has mass, does this mean there is some kind of self-interaction?</p>
<p>Also, does the Higgs Boson have zero rest mass and so move at light-speed?</p> | 269 |
<p>Could an 18th century or earlier scientist have come across phenomena which require quantum theories to explain them, given the apparatus available at the time?</p>
<p>I'll choose 1805 as the cut-off date, because that's when Maudslay's micrometer revolutionised precision in instruments.</p> | 4,502 |
<p>There is an event horizon where cosmic expansion leads to superluminal recession speeds for sufficiently distant objects -- the Hubble Volume.</p>
<p>1) Does matter beyond the event horizon affect us gravitationally or otherwise?</p>
<p>If the answer is no, there is a follow-up question.</p>
<p>If everything beyo... | 4,503 |
<p>I was thinking; <em>what shape does a black hole have?</em>. By 'Shape', I mean its form (e.g, circle , cylinder, sphere, torus, etc..).</p>
<p>We usually think of black holes as if they're plugholes (e.g, a flat circular object), but what if they're spherical? A spherical black hole would make much more sense.
I w... | 4,504 |
<p><br>Due to an experiment, I need a small heater (around 70 to 100 watts). I intend to use an incandescent bulb so it can act as a heater. What I wonder here is will a 70 watts Incandescent Bulb be equal to a 70 watts heater? </p> | 4,505 |
<p>If the electromagnetic field of an unpolarized plane wave is written as
$$\bar{E}(t,\bar{x})=(\bar{E}_{0x}+\bar{E}_{0y}e^{i\delta(t)})e^{i(\bar{k}\bar{x}-\omega t)}$$
$$\bar{B}(t,\bar{x})=\frac{1}{\omega}\bar{k}\times\bar{E}(t,\bar{x})$$
where $\delta(t)$ is a random phase shift, then the intensity of this light is ... | 4,506 |
<p>I haven't taken Physics in University. Lately, I've been reading about some of the branches of physics through Wikipedia. I read several times that many of the theoretical models do not explain why time only moves forward. And that the theoretical models support the ability for time to move backwards. </p>
<p>I'... | 4,507 |
<p>I want to experiment with an enclosure for my phone so the frequency response has a little more punch at the bottom end. I understand that something can't be created from nothing, but enclosures work for drivers so I can't see why not for the phone?</p>
<p>What sort of cabinet design would do the job? It would be n... | 4,508 |
<p>One of the most accepted frameworks for the relationship between the magnitude and frequency of an earthquake is that of the critical phenomena. In this framework, the magnitude of events must be distributed following a power law. </p>
<p>However the <a href="http://en.wikipedia.org/wiki/Gutenberg%E2%80%93Richter_l... | 4,509 |
<p>I read here (<a href="http://en.wikipedia.org/wiki/Proton#Quarks_and_the_mass_of_the_proton">mass of a proton</a>) that the mass of a proton is mostly (99%) due to the energy of the strong nuclear force which binds the quarks together, and not the actual mass of the quarks. My question is: if the quarks didn't have ... | 4,510 |
<p>I was reading a paper dealing with the Hilbert of quantum gravity (or more precisely what should it look like considering what we know from QM and GR) ref: <a href="http://arxiv.org/abs/1205.2675" rel="nofollow">http://arxiv.org/abs/1205.2675</a> and the author writes the following:
$${\cal{H}_M} = {\cal{H_{M,\,\tex... | 4,511 |
<p>We know that the <a href="http://en.wikipedia.org/wiki/Sound" rel="nofollow">sound</a> waves propagate through air, and it can't travel through vacuum. so the thing that help it doing that is the air's molecules pressure. So my question how can that happens? I can't understand that concept.</p> | 4,512 |
<p>What actually is 1 light year? What is the equivalent time in Earth time space?</p> | 4,513 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/47266/rolling-without-slipping-ball-on-a-moving-surface">Rolling (without slipping) ball on a moving surface</a> </p>
</blockquote>
<p>Apparently I didn't log in properly when I asked a question this mor... | 147 |
<p>Reading this PE question
<a href="http://physics.stackexchange.com/questions/5702/can-we-transport-energy-over-infinite-distances-through-vacuum-using-light">can-we-transport-energy-over-infinite-distances-through-vacuum-using-light</a>, a related question arises naturally: </p>
<p>Is <strong>energy transported</st... | 4,514 |
<p>This is a spin-off of the following question: <a href="http://physics.stackexchange.com/q/98001/">Are Thomas Breuer's subjective decoherence and Scott Aaronson's freebits with knightian freedom the same things in essence?</a></p>
<p>Given that Thomas Breuer has proven that universally valid theories either ... | 4,515 |
<p>I was reading Stephen Hawking's 'The theory of everything' when I came across a very interesting type of universe, the 'zero energy universe' since then, I've read some websites but all they used to prove the hypothesis's authenticity were observations(which was found to be very close to zero, and there would anyway... | 4,516 |
<p>I am trying to find a solid material that almost fully (since there is not a thing that can fully insulate electricity) blocks static charges from one layer to another. I know plastic is a good insulator but I want to know if there is a better insulator than plastic. I am going to use this material as a clothing for... | 4,517 |
<p>If there are no localized observables in quantum gravity, does spacetime really exist, or might spacetime really be an illusion?</p> | 4,518 |
<p>In a previous question on <a href="http://physics.stackexchange.com/questions/3773/shape-of-the-higgs-branching-ratio-to-zz">Higgs branching ratios</a>, I find this image</p>
<p><img src="http://i.stack.imgur.com/eljaD.jpg" alt="enter image description here"></p>
<p>(originally from page 15 <a href="http://arxiv.o... | 4,519 |
<p>Imagine you have a pile of snow and a pile of ice shards. You put a soda bottle which has a room temperature into both piles. Which bottle is going to cool down faster?</p> | 4,520 |
<p>let's say we pour some water to the Sun. Or boil water on 2000 degrees Celsius on Earth.</p> | 4,521 |
<p><strong>Problem/Purpose of me asking this question to you people who know more than me:</strong></p>
<p>So I'm doing a science project where I'm collimating a beam of light to a focus point in a light medium (water vapor or fog) and I want to calculate the intensity near it. I can't seem to find an equation that de... | 4,522 |
<p>In the renormalization procedure, is writing things like</p>
<p>$$\varphi=\sqrt{Z_{\varphi}}\ \varphi_R\ ,\ \ m_0^2=Z_m\ m_R^2\ ,\ \ g_0=Z_g \mu^{\epsilon}\ g_R$$
and
$$Z_i=1+\sum_{\nu=1}^\infty C_i^{(\nu)}(m_R,\mu,\Lambda\text{ or }\epsilon)·g_R^\nu\ , \ \ \ \ \ i=\varphi, m, g$$
really more than just an a... | 4,523 |
<p>Some equipment sometimes have a high pitch ringing, and I was wondering out of curiosity: can noises (not only drive you crazy but also) settle and become permanent ringing in your ear if you are exposed long enough?</p> | 4,524 |
<p>Few days ago I started making physics engine on directx. As it obvious I have encountered one problem. I can't find formula of air resistance for angular velocity. I only able to find drag force, but as I suspect it only works for linear velocity(<a href="http://en.wikipedia.org/wiki/Drag_(physics)" rel="nofollow">h... | 4,525 |
<p>In the plasma literature, noble gases—usually helium or argon—are frequently said to 'stabilize' plasmas. For instance in <a href="http://patentimages.storage.googleapis.com/pdfs/US5454903.pdf" rel="nofollow">this patent</a>, the inventor states that the plasma can be stabilized "by adding an electron-donor gas (i.... | 4,526 |
<p>I understand that the <a href="http://en.wikipedia.org/wiki/Dirac_equation" rel="nofollow">Dirac equation</a> has negative and positive sets of solutions and this contributes to its quantization by a superposition of two Fourier modes represented as creation and annihilation operators. What about a complex Dirac fie... | 4,527 |
<p>Who "invented" the concept of symmetries? This article is quite extensive, but it blurs the history with the modern understanding.
<a href="http://plato.stanford.edu/entries/symmetry-breaking/" rel="nofollow">http://plato.stanford.edu/entries/symmetry-breaking/</a></p>
<p>Some of the concepts can be traced to Galil... | 4,528 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/30268/basic-buoyancy-question-man-in-a-boat-with-a-stone">Basic buoyancy question: Man in a boat with a stone</a> </p>
</blockquote>
<p>If you have a large boulder on a boat, in a pond, and you throw the... | 148 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/45802/stiffness-tensor">Stiffness tensor</a> </p>
</blockquote>
<p>Let's have a stiffness tensor:</p>
<p>$$
a^{ijkl}: a^{ijkl} = a^{jikl} = a^{klij} = a^{ijlk}.
$$</p>
<p>It has a 21 independent compo... | 149 |
<p>Why do orbital speeds decrease further away from the focus? A simple question, but I want to make sure I am understanding this correctly: Is it ONLY a function of the gravity well? As in, the gravitational field is weaker as you move away from the massive body, so the speed decreases? What if the gravitational field... | 4,529 |
<p>Suppose I have a wave function $\psi(x)$ in position basis. I can make a density function
by simply multiplying $\psi(x)$ and its conjugate $\psi^*(x)$. If I operate the density matrix $\rho(x,y)=\psi(x)\psi^*(y)$ with Hamiltonian $\hat{H}$ I will get,
\begin{equation}
\hat{H}\rho(x,y)=\hat{H}\psi(x)\psi^*(y)=\psi^... | 4,530 |
<p>How do I find the most probable value of position of a (non-Gaussian) wave function? Is it the same value as the expectation value of the position? And is it true that the most probable value of position is equal to the mean for a Gaussian? </p> | 4,531 |
<p>I'm working on a pre-lab for my Physics 1 lab session, and I had a debate with the person I carpool with (who is taking the algebra-based Physics 1 lab). We seem to be unsure about uncertainties, and how they play out when doing calculations.</p>
<p>The given question was as follows:</p>
<blockquote>
<p>When the... | 4,532 |
<p>The <a href="http://en.wikipedia.org/wiki/Quantum_eraser_experiment" rel="nofollow">quantum eraser experiment</a> tells us that a photon shot at two slits is a wave, unless you measure which slit is taken <strong>and</strong> you do not destroy the measurement result.</p>
<p>I've found this very similar to the noti... | 4,533 |
<p>Fitness Model, Rob Riches, claims that doing bicep curls with Olympic bars is different than lifting with normal bars. </p>
<blockquote>
<p>Biceps have always been a favorite muscle group of mine to train, but
since I’ve started using the Olympic bar to curl with, I’m noticing my
arms start to thicken out, wh... | 4,534 |
<p>I heard that we must know the Weyl tensor for fully describing the curvature of the 4-dimensional space-time (in space-time with less dimensions it vanishes, so I don't interesting in cases of less dimensions). So I have the question: what is physical (or geometrical) sense of the Weyl tensor and why don't we need o... | 4,535 |
<p>Ok, so we can have conformal invariance on a string world sheet. However, it is well known that to preserve conformal symmetry we require states to be massless. So how is it that string theories incorporate CFT but allows massive states?</p>
<p>Is it because the CFT is on the worldsheet and therefore applies to the... | 4,536 |
<p>I'm reading the Wikipedia page for the <a href="http://en.wikipedia.org/wiki/Dirac_equation" rel="nofollow">Dirac equation</a>:</p>
<blockquote>
<p>$\rho=\phi^*\phi\,$</p>
<p>......</p>
<p>$J = -\frac{i\hbar}{2m}(\phi^*\nabla\phi - \phi\nabla\phi^*)$</p>
<p>with the conservation of probability curr... | 4,537 |
<p>The title says it all. If I'm standing in the wind and I'm wet, I feel much
colder than when I'm dry. This is true no matter how warm or cold the water.
Why is this?</p> | 95 |
<p>i have two sets of data. one leads to a value for the transition temperature from the A phase superlfuid to B phase. This was performed in a thin slab, which was too thin to observe the A-B transition. I also have an actual value of this temperature from another set of data where the slab was thick enough to support... | 4,538 |
<p>In the <a href="http://en.wikipedia.org/wiki/Muon">Wikipedia article of Muon</a>, it says</p>
<blockquote>
<p>...with unitary negative electric charge of <strong>roughly</strong> -1 and a spin of 1/2,</p>
</blockquote>
<p>What are they trying to convey with the "roughly"? Aren't the allowed values of charge disc... | 4,539 |
<p>I am confused about a trivial concept. Let the rotation of a rigid body, say with one point fixed, be described by the equation $\vec{x}(t)=R(t)\vec{x}(0)$, with $R(0)=I$. </p>
<p>Then, at each instant there is only one real eigenvector of $R(t)$ with eigenvalue 1 that we may call $\vec{v}(t)$ and which we may tak... | 4,540 |
<p>I know that the nuclear force is responsible for binding the protons and neutrons together in the nucleus. The force is powerfully attractive at small separations and rapidly decreases as the distance between the particles concerned increases and becomes repulsive after that.But, why does that happen? </p>
<p>I'm n... | 4,541 |
<p>In terms of spectrophotometer, we need to make the light monochromatic before passing it to sample. For that, we use diffraction grating. From the research, I found out that the grating reflects light into different wavelengths. Also, the grating moves in such a way that each wavelength has an opportunity to pass th... | 4,542 |
<p>My textbook says that to find the ket $|ψ\rangle$ in the same position basis as the ket $|ø\rangle$ we do the following: $$|ψ\rangle=\int dø|ø\rangle \langle ø|ψ\rangle$$ Firstly can $|ø\rangle$ be any ket? i.e. this expression just puts $|ψ\rangle$ in the same basis as $|ø\rangle$ regardless of the components of $|... | 4,543 |
<p>If <a href="https://en.wikipedia.org/wiki/Carbon%E2%80%93carbon_bond" rel="nofollow">carbon–carbon bonds</a> are reasonably strong and silicon and carbon are both in the same column of the periodic table meaning they have the same amount of valence electrons, also seeing as its bonding with itself electronegativity ... | 4,544 |
<p>This question is rather historical one.</p>
<p>kilometres can be defined in metres, metres in centimetres, centimetres in millimetres.</p>
<p>There must be some elementary unit (like millimetre or smth.) which cannot be defined in smaller units.</p>
<p>The question is : How does this elementary unit came into bei... | 4,545 |
<p>I have noticed that when I microwave an ice cube it appears to melt more slowly than I would expect. For example, an equal volume of water starting at 0 deg C would probably be at boiling point before an ice cube that was at -15 deg C had melted. I realize there is enthalpy of fusion to take into account in the melt... | 4,546 |
<p>I tried to understand the importance of conformal transformations in general relativity, but I failed. I didn't see that conformal transformations help to simplify the metrics, and also I didn't see that some physical metric (i.e., metric which describes geometry of some physical system) with conformal scale factor.... | 4,547 |
<p>When a rock falls from a ledge, why does it head to the surface and not up to where time runs faster?</p>
<p>If a rock, free from forces, follows a worldline of maximum aging, why would that rock approach Earth where the rate of time runs slower, and so would slow down the rocks aging? Shouldn’t the rock avoid eart... | 4,548 |
<p>I am looking for a map or plot of the gravitational strength in the solar system. In an ideal world there should be something like google earth to move around in the solar system, zoom in and out and get an visual overview over the field strength in different points in the solar system. </p>
<p>I didn't even find g... | 4,549 |
<p>I have a brief question regarding the formula for wave displacement that I've just encountered. My textbook says:</p>
<p>For a simple plane wave, we have, for a simple harmonic with displacement $u$:</p>
<p>$$u = A \cos(\kappa x - \omega t)$$</p>
<p>where $\omega$ is the angular frequency, $\kappa$ is the wavenu... | 4,550 |
<p>What are the main problems that we need to solve to prove Laplace's determinism correct and overcome the Uncertainty principle?</p> | 49 |
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