question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>The title says it all: is there a table that sums up the parameters, the assumptions/symmetries, and the (most important) predictions of the <a href="http://en.wikipedia.org/wiki/Standard_Model" rel="nofollow">standard model</a>? </p> | g7876 | [
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<p>Consider air from outside at $T_0$ effusing into an evacuated and thermally isolated chamber.</p>
<p>By thermodynamic potentials, the temperature inside the tank is given by:</p>
<p>$$T_1 = \gamma T_0 = \frac{5}{3} T_0$$</p>
<p>However, by using Maxwell-Boltzmann statistics, the distribution of particles effusin... | g7877 | [
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<p>A particle is projected with velocity $u$ from the bottom of an inclined plane whose inclination with the horizontal is $\beta$. If afterwards the projectile strikes the inclined plane perpendicular to the surface, find the height of the point struck (distance from the ground). The angle made by the velocity with th... | g7878 | [
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<p>When doing integration over several variables with a constraint on the variables, one may (at least in some physics books) insert a $\delta\text{-function}$ term in the integral to account for this constraint.</p>
<p>For example, when calculating
$$\displaystyle\int f(x,y,z)\mathrm{d}x\mathrm{d}y\mathrm{d}z$$
subje... | g7879 | [
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<p>I know that $p=mv$ and (0.1kg)(15m/s)=1.5 kg m/s and the momentum at the vertex is 0, but what is the momentum halfway up?</p> | g7880 | [
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<p>I recently discovered this website <a href="http://www.quantumphil.org/" rel="nofollow">http://www.quantumphil.org/</a> and wondering whether <a href="http://www.google.com/search?as_q=quantum+philosophy" rel="nofollow">Quantum Philosophy</a> is an actual field, or just an aspect of QM?</p>
<p>Apologies if this is ... | g7881 | [
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<p>I have 1 litre of air in a sealed container at atmosphere pressure (approx 15 psi absolute).
I want to reduce pressure in the container by 1 psi ( 14 psi absolute or -1 psig). </p>
<ul>
<li>If I understand correctly that 1 psi reduction is 6.66 % reduction in pressure compared to standard atmospheric pressure, </li... | g7882 | [
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<p>Force is explained as a push or pull, feels quite intuitive at first. </p>
<p>My question is if an object accelerates over distance of $100$ meter hits a car, and another object of same mass at same acceleration over a distance of $1000$ meters hits the same car, then the force of these two objects is the same, s... | g7883 | [
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<p>Can we destroy a <a href="http://en.wikipedia.org/wiki/Black_hole" rel="nofollow">black hole</a>? I know it is pretty powerful and hardcore stuff but there should be a way even theoretically as we know know nothing is perfect in this universe as it exist due to imperfection. Then how could a black hole be so perfect... | g7884 | [
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<p>Where $\triangledown$ is the covariant derivative and we are to assume that the connection is torsion free (that is, we can exchange the lower indices of the connection coefficients), how can I prove the following identity?</p>
<p>$$
X^b\partial_bY^a-Y^b\partial_bX^a=X^b(\triangledown_{{\partial}_b}\overrightarrow{... | g7885 | [
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<p>There is a strong physics case for building and running a muon collider (primarily as a Higgs factory).</p>
<p>Currently, what is the principal technological hold-up in making the muon collider possible?</p> | g7886 | [
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<p><a href="http://en.wikipedia.org/wiki/Ballistic_conduction" rel="nofollow">Ballistic Conduction</a> is the phenomenon of an ideal conduction environment for quantum particles - for electrons the Ballistic Conduction is not infinity, but is proportional to the difference between Fermi surfaces of the leads on both si... | g7887 | [
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<p><img src="http://i.imgur.com/hXoK3PP.png" alt="question">
<img src="http://i.imgur.com/9o7hB3h.jpg?1" alt="answers"> </p>
<p>I have come up with the answers to parts a and b as shown in the image above. However in part c, I can't seem to find the answer, even though it only involves fitting numbers into Bernoulli's... | g7888 | [
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<p>I know that universe is expanding equally between every pair of points but it was a single point in it's very past... so I was wondering if we could locate this center point of universe. Now I know that we can't and read (on this site) that whatever direction would we go - it would take us closer and closer to big b... | g7889 | [
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<p>Is Wick rotation invariant under proper conformal transformations? Why or why not?</p>
<p>Does Wick rotation apply to conformal field theories? $(1-i\epsilon )T$ is not invariant under proper conformal transformations.</p> | g7890 | [
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<p>In this (schematic) equation to calculate the scattering amplitude A by integrating over all possible world sheets and lifetimes of the bound states</p>
<p>$$ A = \int\limits_{\rm{life time}} d\tau \int\limits_{\rm{surfaces}} \exp^{-iS} \Delta X^{\mu}
(\sigma,\tau)$$</p>
<p>the information about the incomi... | g7891 | [
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<p>I'm a private pilot, and I have some questions to those who have knowledge of the aeroelastic effects and flutter phenomenon. I would like to talk a little about aerodynamic flutter onset speed and flight control malfunction. It is known that freeplay, worn-out control rods or slop in flight control cables might ind... | g7892 | [
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<p>I'm aware that we can describe the time evolution of states/operators (choose your favourite picture) of non interacting quantum fields and that perturbation theory is very effective in computing S matrix elements between free states in the remote past and free states in the remote future. Clearly the non-perturbat... | g7893 | [
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<p>Would a disconnected surface, especially <a href="http://en.wikipedia.org/wiki/Aileron" rel="nofollow">aileron</a>, deflect upwards as you slow down due to increased alpha? I figure out it is more likely to deflect upwards as you increase your airspeed, thus having more airflow pressure below it and pushing it upwar... | g7894 | [
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<p>Do two resistors in parallel dissipate more heat per unit time for an applied voltage when compared to two resistors in series?</p> | g7895 | [
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<blockquote>
<p>We receive sunlight on earth surface. What type of light beams are these?</p>
<p>Random/Parallel/Converging/Diverging</p>
</blockquote>
<p>I think it should be Diverging as Sun is radiating these beams away. But in one book, answer is given as Random, in another it's Parallel.</p> | g7896 | [
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<p>I'm learning about accelerating reference frames (to eventually get grasp of general relativity too).</p>
<p>I've just read about the <a href="http://en.wikipedia.org/wiki/Rindler_coordinates#A_.22paradoxical.22_property" rel="nofollow">Rindler coordinates</a> and this one caught my eye</p>
<blockquote>
<p>Note ... | g7897 | [
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<p>Can anybody explain to me the <a href="http://en.wikipedia.org/wiki/Coand%C4%83_effect" rel="nofollow">Coandă effect</a> well? I am finding that many definitions and explanations conflict.</p>
<p>I am particularly confused about the following points regarding the Coandă effect:</p>
<ul>
<li>whether the Coandă effe... | g7898 | [
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<p>I have been planning on building a solar grill for quite a time now, and the one problem, which is also the biggest - I need to shape a mirror into a paraboloid, so it bundles solar energy efficiently.</p>
<p>My designs for the whole thing have the focal area of the paraboloid - i.e. the grillage - placed in close ... | g7899 | [
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<p>Before the question: I am working on numerical calculation of three dimension parabolic equation that based on <a href="http://en.wikipedia.org/wiki/Thermal_conduction#Fourier.27s_law" rel="nofollow">Fourier's Law</a> of which I am a little confused.</p>
<p>Here comes the law in modern mathematics language.</p>
<b... | g7900 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Weibull_distribution" rel="nofollow">Weibull distribution probability density</a> is given by:
$$f(w,k,\lambda)=\begin{cases}\frac{k}{\lambda}\left(\frac{w}{\lambda}\right)^{k-1}e^{-\left(w/\lambda\right)^k} &w\geq0 \\ 0 & w<0\end{cases}$$</p>
<p>How can I modif... | g7901 | [
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<p>In quantum field theory, the propagator $D(x-y)$ doesn't vanish for space-like separation. In Zee's book, he claims that this means a particle can leak out of the light-cone. Feynman also gives this interpretation.</p>
<p>What is wrong, then, with this thought experiment:</p>
<p>Bob and Alice synchronize their wat... | g7902 | [
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<p><img src="http://i.stack.imgur.com/qBLOQ.png" alt="enter image description here"></p>
<p>figure from <a href="http://webusers.physics.illinois.edu/~m-stone5/mma/notes/amaster.pdf" rel="nofollow">http://webusers.physics.illinois.edu/~m-stone5/mma/notes/amaster.pdf</a></p>
<p>The string has fixed ends, a mass per un... | g7903 | [
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<p>This is a repost of one of my formerly-stated questions, now with correct tags and format:</p>
<p>In reference to this problem:</p>
<blockquote>
<p>An electron is placed into a dielectric container with capacitors at each end. The side of the container is of length l. A small tunnel is hollowed out in the middle... | g7904 | [
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<p>I'm looking for a nice paper that explains the difference between three particle physics models for spin-independent dark matter interaction with nuclei: elastic, inelastic and isospin violating scattering. I've found a nice paper that is giving a nice summation of the current results in direct dark matter searches ... | g7905 | [
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<p>I am having a bit of a crisis in understanding of the physical meanings of total derivatives.</p>
<p>When a quantity $\rho$ (be it a <em>vector</em> or a <em>scalar</em>) is said to be <strong><em>conserved</em></strong>, then (mathematically) $$\frac{d\rho}{dt} = 0$$
(right??)</p>
<p>Now, if I just integrate both... | g7906 | [
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-0.03306546062231064,
-0.03564728423953056,
-0.02831714041531086,
0.029958205297589302,
-0.0... |
<p>Does sound gets faster when air bubble is suspend in water?</p>
<p>c = sqrt(K/P)</p>
<p>c = speed</p>
<p>K = bulk module</p>
<p>P = density</p>
<p>When air bubbles is homogenized into water the density is lower, so should sound gets faster? Thank you.</p> | g7907 | [
0.020680507645010948,
0.024142799898982048,
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0.0378149040043354,
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0.029743965715169907,
0.03968321159482002,
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0.0... |
<p>Most of the time, temperature evolution for incompressible flow is computed assuming the <a href="http://en.wikipedia.org/wiki/Eckert_number" rel="nofollow">Eckert number</a> is negligible, that is the viscous dissipation and work of pressure variation is negligible compared to convection and diffusion.</p>
<p>Howe... | g7908 | [
0.02886377088725567,
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0.03109399415552616,
0.03716054558753967,
0.001956541556864977,
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0.0477895550429821,
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0.0022280835546553135,
0.02... |
<p>Suppose that in the intergalactic space far from any significant gravitational attractors there is a relatively small concentration of He-4 atoms. Due to gravitational attraction fermions in this case would form a sphere (gas planet), but as bosons He-4 atoms aren't affected by exclusion prinicple, so what's holding... | g7909 | [
-0.03053978830575943,
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0.030421562492847443,
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0.014... |
<p>I know this isn't the right place for asking this question, but in other places the answers are so awfull.. I'm studying eletricity, so, I start seeing things like "charges", "electrons has negative charges",etc. But I didn't quite understand what charge is. I search a little bit on the internet and found it related... | g189 | [
0.04101395979523659,
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<p>In representing an electric circuit, we would draw the sense of the current from the positive to the negative pole and the electrons from the negative to the positive .
But as I know electrons' motion create current.
So how is this possible?</p> | g258 | [
-0.013114342465996742,
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0.01610427349805832,
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0.00899145845323801,
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0.0... |
<ol>
<li><p>What is the <a href="http://www.google.com/#q=topological+mass+generation" rel="nofollow">topological mass generation</a> mechanism? </p></li>
<li><p>And what is its relation with the Higgs mechanism? </p></li>
<li><p>Can we say that after the discovery of Higgs boson, the topological mass generation mechan... | g7910 | [
0.07011449337005615,
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0.004918953403830528,
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0.03953811898827553,
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0.02520567551255226,
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-0.04324933886528015,
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0.06502436101436615,
0.010244... |
<p>I'm currently reading Brian Greene's <strong>The Elegant Universe</strong> and have also picked up his other book - <strong>The Fabric of the Cosmos</strong>. In <strong>The elegant universe</strong> Brian makes up an interesting point that empty space is not really empty. This is according to string theory. Now I m... | g259 | [
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<p><strong>Premises:</strong></p>
<blockquote>
<ol>
<li>The radioactivity is either hastened or slowed inside a fast moving aircraft.</li>
<li>Speed of fastest aircraft: <em>3,529.6 km/h</em>.</li>
<li>The earth's revolution is: <em>107278.87 km/h</em>.</li>
<li>The earth's revolution is significantly higher... | g7911 | [
0.04578375071287155,
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0.023173438385128975,
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0.02822299860417843,
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0.03651074692606926,
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0.06889783591032028,
0.00492... |
<p>What would happen if the earth would stop spinning? How much heavier would we be? I mean absolutely stop spinning. How much does the centrifugal force affect us?</p>
<p>If you give technical answers (please do), please explain them in laymen's terms, thanks.</p>
<p><strong>Edit:</strong> I am asking what would be ... | g45 | [
0.0641423761844635,
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<p>What is the total momentum of the whole Universe in reference to the point in space where the Big Bang took place?</p>
<p>According to my reasoning (and a bit elementary knowledge) it should be exactly equal to 0 since the 'explosion' and scattering of the matter throught the space would not change the total moment... | g7912 | [
0.07480466365814209,
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0.00667115394026041,
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0.0364... |
<p>I am investigating the relationship between the fall time of a paper tray and its projected area.</p>
<p>In this investigation I have been using the following variables:</p>
<ul>
<li>Controlled Variable: The air density, the height from which we drop the tray, the shape of the tray, its mass and the material it is... | g7913 | [
0.06955980509519577,
0.04239654168486595,
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0.0008599370485171676,
0.046538159251213074,
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0... |
<p>I am struggling with calculating the exclusive semileptonic $B_c^+\rightarrow J/\psi l^+\nu_l$ decay. I learnt that the amplitude is given by a product of the leptonic current $L^{\mu}$ and the hadronic current $H^{\mu}$
$$
\mathcal{M}(B_c\rightarrow J/\psi l^+\nu_l)=\frac{G_F}{\sqrt{2}}V_{cb}L^{\mu}H_{\mu}
$$
wher... | g7914 | [
0.0017651632660999894,
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0.056510016322135925,
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... |
<ol>
<li>How much mass would a black hole need to create a Schwarzschild radius that would trap a photon, whereby the photon would (to an outside observer) be continually curved 0.004km/s at the horizon?</li>
</ol>
<p>(assume a non-spinning black hole, then contrast that with a photon traveling in either direction alo... | g7915 | [
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0.02867031842470169,
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<p>What is meant by <a href="http://en.wikipedia.org/wiki/Incompressible_flow" rel="nofollow">incompressible flow</a>?</p>
<ol>
<li><p>The density of the fluid is a constant, $\rho = constant$</p></li>
<li><p>The density of a fluid has a spatial dependence but remains constant in time, $\rho = \rho(\mathbf{r})$</p></l... | g7916 | [
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<p>I know it's probably the most stupid question there is, but why do they fly are the clouds lighter than air? What's keeping those tiny ice structures floating miles about the ground? I've been looking all over the internet and I can't find acceptable answer to this basic physical question. Can you please help me?</p... | g260 | [
0.057892944663763046,
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0.019093230366706848,
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0.02400769665837288,
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0.00082... |
<p>If, in a QFT of a scalar field $\phi$, a <a href="http://en.wikipedia.org/wiki/Fock_space" rel="nofollow">Fock space</a> $n$-particle position eigenstate $\lvert x_1\cdots x_n\rangle $ is given by
$$
\lvert x_1\cdots x_n\rangle =\hat\phi^\dagger(x_1)\cdots\hat\phi^\dagger(x_n)\lvert 0\rangle \,,
$$
where $\lvert 0\r... | g7917 | [
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0.05736255273222923,
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-0.022033728659152985,
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-0.031123826280236244,
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0.... |
<p>I have a simple question: Does gravity slow down a horizontally thrown baseball?</p>
<p>Assuming when a baseball is thrown it has a vertical velocity as well, does it slow does the ball?</p>
<p>Any help is much appreciated.</p> | g7918 | [
0.12353657931089401,
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<p>I have a question about Noether's theorem in the context of QM, which I'll state in the context of the weak interaction but the basic point could be generalized.</p>
<p>According to Noether's theorem, given an $n$-dimensional Lie group there will be $n$ conserved quantities. $SU(2)$ is 3-dimensional, so that we'd e... | g7919 | [
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<p>The problem was posed as follows. Given a pendulum of length $L$ with a mass $m$ attached to it, which forms an angle $\theta$ from the y-axis to the direction of swinging. </p>
<p>First we had to find the potential energy as a function of the angle, which was trivial enough.</p>
<p>$$U = mgL(1 - cos(\theta))$$</p... | g7920 | [
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0.0229015... |
<p>The <em>kinematic</em> state is defined as the position and orientation in space. The <em>dynamic</em> state is defined as the associated velocities.</p>
<p>What is the correct terminology for the combined kinematic and dynamic state? Can I call it the <em>kinetic</em> state?</p> | g7921 | [
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<p>Is there any theoretical limitation on the size of the diameter of an Plastic optical fiber? I would like to transmit visible sunlight through it. I see bundles of small cores available but wouldn't it be more efficient to make a very large single core?</p> | g7922 | [
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<p>Conside a contact interaction given by a delta function on their worldlines. Use a gauge fixed Lagrangian for two point particles in terms of their proper times $t$ and $t^{\prime}$. <strong>Is it possible to find proper equations of motion for this system?</strong>
For e.g.
$$
S=\int dt \; \dot {x}^{2}+\iint\! dt ... | g7923 | [
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0.001425340073183179,
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0.05094899982213974,
0.0171... |
<p>I tried many hours to understand the <a href="http://en.wikipedia.org/wiki/Principle_of_least_action" rel="nofollow">principle of least action</a>, and those hours become days... and I still didn't understand that principle/ and how it relates to Newtonian mechanics?</p>
<p>Could someone please explain it to me eas... | g7924 | [
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0.0328834094107151,
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0.04313981160521507,
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-0.04032397270202637,
-0.03107243776321411,
-0.022996284067630768,
-0.0301... |
<p>What is the name of this principle? </p>
<blockquote>
<p>If the speed of the centre of mass $\vec{v}_{CM}$ of a solid is constant ($cte$), then the sum of the exterior forces that exerts into this solid $\vec{F}_{ext}$ is zero, and the opposite is true, namely that:</p>
<p>$$\vec{v}_{CM}=cte\Leftrightarrow\s... | g7925 | [
0.0984380692243576,
0.05096668004989624,
0.0023889688309282064,
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0.0714050680398941,
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0.040944118052721024,
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0.01244354248046875,
-0.05375948175787926,
-0.01630396768450737,
-0.0484834760427475,
-0.001960... |
<p>The first Navier-Stokes equation (conservation of mass) says:
$\vec \nabla \cdot \vec v=0$</p>
<p>For a stationary flow, the l.h.s of the second equation is (conservation of momentum):
$\rho \frac{D\vec v}{Dt}=\rho (\underbrace{\frac{\partial \vec v}{\partial t}}_{=0} + (\vec v\cdot \vec \nabla) \vec v)=\rho ( \und... | g7926 | [
0.08521652221679688,
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0.002465569181367755,
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0.07487530261278152,
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-0.0082670534029603,
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0.0051... |
<p>Will I get a stronger resonance if I put multiple frequency generators around the same object?</p>
<p><a href="http://i.stack.imgur.com/bdqZW.png" rel="nofollow">example image</a></p> | g7927 | [
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-0.04780060425400734,
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-0.024332327768206596,
-0.014687001705169678,
... |
<p>The action of a free relativistic particles can be given by
$$S=\frac{1}{2}\int d\tau \left(e^{-1}(\tau)g_{\mu\nu}(X)X^\mu(\tau)X^\nu(\tau)-e(\tau)m^2\right).$$
If we then make an infinitesimal transformation of the parametrization parameter $\tau$ this would be
$$\tau\to\tau^\prime=\tau-\eta(\tau),$$
for an infinit... | g7928 | [
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0.013204377144575119,
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0.0796860009431839,
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-0.01639605686068535,
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0.053143538534641266,
0.016559217125177383,
-0.018... |
<p>I have a question related to the connection between the S-Matrix elements and the path integral formalism. In order to formulate the question, I will just work with a scalar field theory for simplicity. </p>
<p>Let us assume that we are given an action $S[\phi]$. In the path integral formalism, we can now define th... | g7929 | [
0.041424378752708435,
-0.014678244479000568,
-0.009998404420912266,
0.03901936113834381,
0.015137217938899994,
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0.04255247488617897,
0.07578059285879135,
0.008287680335342884,
0.0046618347987532616,
-0.05658134073019028,
0.05986654758453369,
-0.00020243383187334985,
0.... |
<p>Every now and then, I find myself reading papers/text talking about how this equation is a constraint but that equation is an equation of flipping which satisfies this constraint.
<img src="https://dl.dropboxusercontent.com/u/55765722/0.fawaed/flipping.gif" alt="enter image description here"></p>
<p>Indeed, This eq... | g7930 | [
0.028032774105668068,
0.013311711139976978,
-0.05040748044848442,
0.007734477519989014,
0.0635213851928711,
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0.056845296174287796,
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0.004999005701392889,
0.020263856276869774,
0.0659824013710022,
0.05061327666044235,
0.032765... |
<p>We've all seen sci-fi movies with asteroid belts that require "great skill" to fly through, but how dense is the asteroid belt really? </p>
<p>How much of the belt could you see from the surface of a given asteroid? </p>
<p>Is it uneven, with dense and sparse patches?</p> | g7931 | [
-0.050580188632011414,
0.0446869432926178,
-0.011775038205087185,
-0.0372900553047657,
0.0015517139108851552,
0.041973598301410675,
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0.03947975113987923,
0.0006410769419744611,
0.058878399431705475,
0.002692204201593995,
0.04530016705393791,
-0.0... |
<p>I'm <em>so</em> confused in the use of nuclear masses and atomic masses.
I have two questions.</p>
<p>From the book "Outline of Modern Physics" by Ronald, I understand that the <em>semiempirical mass formula</em> (<a href="http://en.wikipedia.org/wiki/Semi-empirical_mass_formula" rel="nofollow">Weizsäcker's formula... | g7932 | [
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0.035424478352069855,
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0.027929579839110374,
0.04832607880234718,
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0.0129152936860919,
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-0.03437323495745659,
0.019976861774921417,
0.0... |
<p>In life, when you talk about nuclear energy, there always happens to be a guy who says that famous Einstein's equation. "<em>Yeah, they just convert mass to energy, $E = mc^2$ ya know?</em>" </p>
<p>When I think about that, all I learned about nuclear power resembles dominoes arrangements. You <em>tonk</em> a bloc... | g7933 | [
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... |
<p>Assume the following phase diagram $T-H$ of water</p>
<p><img src="http://i.stack.imgur.com/gU12G.png" alt="enter image description here"></p>
<p>At a nuclear engineering course, I was told that in order to increase the performance of a pressurized water reactor, one has to increase the pressure.</p>
<p>How such ... | g7934 | [
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0.... |
<p>It is said in many textbooks that alpha decay involves emitting alpha particles, which are <em>very stable</em>. Indeed, the binding energy (<a href="https://www.oecd-nea.org/dbdata/data/mass-evals1995/mass_rmd_mas95.txt" rel="nofollow" title="Table of atomic masses, including binding energies; OECD Nuclear Energy A... | g378 | [
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<p>Suppose we have the two-loop integral $\int \mathrm{d} ^ 4 k _ {2} \int \mathrm{d} ^ 4 k _ {1} \, f(k _ {1}, k _ {2})$, where $k _ {1}$ and $k _ {2}$ are four-dimensional vectors in Euclidean space. In the first integration with respect to $k _ {1}$, I take $k _ {2}$ to be the z-axis. Then $k _ {2} = k _ {1} \cos \o... | g7935 | [
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<p><strong>Question:</strong></p>
<p>In principle, does a system of gravitational charges exhibit equivalent behavior to a time-reversed system of like electric charges? <em>(At a single instance in time?)</em></p>
<p><strong>Additional Notes:</strong></p>
<p>I am aware that the evolution of this system would not be... | g7936 | [
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<p>Provided that the two pipe lines are of same length, same material and in the same level, is the water pressure in both the layouts same or different?
<br><br><img src="http://i.stack.imgur.com/XVSrc.jpg" alt="enter image description here"></p>
<p>PS: In 1st pipeline the turns are not "upward-downward" turns but "s... | g7937 | [
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... |
<p>I have read in many places that one point functions, like the one below:</p>
<p>$$\langle \Omega|\phi(x) |\Omega \rangle$$</p>
<p>are equal to zero ( $|\Omega \rangle$ is the vacuum of some interacting theory, $\phi$ is the field operator - scalar, spinorial, etc...)</p>
<p>Peskin's book, for instance, says (page... | g7938 | [
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<p>In a potential which needs to be evaluated at the retarded time, is this the time which represents the actual time the "physics" occurred? So $t_{\text{ret}}=t-\frac{r}{c}$, not just because it may be that you are receiving a signal at light speed but because "causality" spreads out at the maximum speed, $c$, is thi... | g7939 | [
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<p>In the arrangement shown in the figure below, an object of mass m can
be hung from a string (linear mass density $\mu$ = 2.00 g/m) that passes over
a light (massless) pulley. The string is connected to a vibrator with
constant frequency $f$, and the length of the string between point P and the
pulley is $L = 2.00 m$... | g7940 | [
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<p>I've checked specs of Russian "Dynamic Albedo of Neutrons" module on Mars MSL rover - it can do 10^8 neutron pulses at 10 pulses per second. It works on D-T reaction in tiny linear accelerator, and power consumption is quite low (14W).</p>
<p>If you check specs for all these fusors (Farnsworth, Polywell, e.t.c) - t... | g7941 | [
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... |
<p>Anecdotal evidence has it that a bottle of soda that was heavily shaken will not bubble over if tapped at the side multiple times.</p>
<p>Yet I wonder: Has the tapping really any effect? Or could it be that the mere time that passes while tapping at the side of the bottle has the carbon dioxide not mixed with the s... | g7942 | [
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<p>I found an equation in theory about magnetic induction in a <a href="http://en.wikipedia.org/wiki/Solenoid" rel="nofollow">solenoid</a>: $B_s=\mu_0 I n$. It should be magnetic induction for infinite length solenoid. I wonder if this is anyhow useful. Where can this be used? </p>
<p>($n = \frac {N}{L} $, where $L$ i... | g7943 | [
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<p>Using the formula $F=G\frac{m_1m_2}{d^2}$ where $m_1$and $m_2$ are the masses of two objects, $G$ is the gravitational constant, and $d$ is the distance between the objects, it is possible to calculate the force of the gravitational attraction between the objects in Newtons. However, since light is affected by black... | g7944 | [
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<p>From what I hear, some modern mathematical approach quantum field theory uses the following definition</p>
<blockquote>
<p>"A $d$-dimensional $S$-structured quantum field theory $Q$ is a mathematical object, consisting of its partition function $Z_Q$, its space of states $H_Q$, and its submanifold
operators $V_... | g7945 | [
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<p>Are <a href="http://en.wikipedia.org/wiki/Soliton" rel="nofollow">solitons</a> an example of collective motion? </p> | g7946 | [
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<p>I have a simple static mechanical system, but I reach a conclusion that seems to me counter-intuitive:</p>
<p><img src="http://i.stack.imgur.com/ueJV4.png" alt="enter image description here"></p>
<p>There is a pulley fixed to the ceiling and there is a weight fixed to a rope which goes through the pulley and is fi... | g7947 | [
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<p><strong>Update:</strong> Trimok and MBN helped me solve most of my confusion. However, there is still an extra term $-(2/r)T$ in the final result. Brown doesn't write this term, and it seems physically wrong.</p>
<p><strong>Update #2:</strong> Possible resolution of the remaining issue. See comment on MBN's answer.... | g7948 | [
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<p><strong>Preface:</strong></p>
<p>I'm currently sitting at my desk on a 5th floor in a South Florida office building, as I was earlier this morning when I felt the building sway slightly. It wasn't continuous and the building swayed slightly one way and stopped. The sway was so subtle that others in the office didn'... | g7949 | [
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<p>I remember many years ago, I think at 8th grade, seeing the teacher show us a <a href="https://en.wikipedia.org/wiki/Crookes_radiometer" rel="nofollow">Crookes radiometer</a>. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it was called, but the article wasn't very c... | g7950 | [
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<p>Gamma radiation follows the inverse square law, I understand this as "double the distance, quarter the intensity"</p>
<p>So if you have a gamma source, at the source (distance = 0), the Intensity is $I_0$, and say at distance = 1, the Intensity is $\frac{I_0}{2}$ (You can't work this out just from the fact it follo... | g7951 | [
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<p>After this semester, I'll have a background up to a first course in QFT (first 5 or 6 chapters of Peskin and Schroeder). </p>
<p>The next step in QFT will be something specific to the Standard Model (Elementary particles, QCD, etc).</p>
<p>Is that needed before going to study String Theory or not?</p> | g7952 | [
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... |
<p>How is it proved to be always true? It's a fundamental principle in Physics, that is based on all of our currents observations of multiple systems in the universe, is it always true to all systems? Because we haven't tested or observed them all.
Could it possible that we discover/create a system that could lead to ... | g307 | [
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<p>I am reading about the Euler Equations of Fluid dynamics from
Leveque's numerical methods for conservation laws.</p>
<p>After introducing the mass, momentum and energy equations, some thermodynamic
concepts are discussed, to introduce an equation of state. </p>
<p>He says </p>
<pre><code>In the euler equations w... | g7953 | [
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0... |
<p>How does one get the value of acceleration of gravitation on earth accurately to 5 significant digits by experiment without electronic device?</p> | g7954 | [
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0.0... |
<p>I was shocked while reading Kittel's "Introduction to Solid State Physics", that the solid state of noble gases is a well described and makes one of the fundamental achievements of solid state physics.</p>
<p>So I wonder: is every possible element and every possible compound able to exist in any of the 3 states of ... | g7955 | [
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<p>If dark energy is everywhere around us, then why don't we get separated? For example why don't I get separated from the pen kept in front of me? Or take a similar example in free space. Is dark energy's power greater than gravitational power?</p> | g7956 | [
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<p>Undoubtedly, people use a variety of programs to draw diagrams for physics, but I am not familiar with many of them. I usually hand-draw things in <a href="http://www.gimp.org/">GIMP</a> which is powerful in some regards, but it is time consuming to do things like draw circles or arrows because I make them from mor... | g796 | [
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-... |
<p>I'm running an experiment -- for the question, it doesn't matter which one, but I'm measuring an optical intensity $I$ as a function of two parameters: reflection angle $\theta$ and wavelength $\lambda$. I have motion control in place to move the setup to an angle $\theta_0$, and then I measure $I(\theta_0, \lambda)... | g7957 | [
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0.043... |
<p>As $E=hf=\frac{hc}{\lambda}$, blue light - with a smaller wavelength - should have a higher energy. However, it is the case that blue light scatters the most. Why is it that higher energy rays scatter more?</p> | g7958 | [
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<p>I saw the question <a href="http://physics.stackexchange.com/questions/3038/what-are-field-quanta">What are field quanta?</a> but it's a bit advanced for me and probably for some people who will search for this question.</p>
<p>I learned QM but not QFT, but I still hear all the time that "particles are the quanta o... | g7959 | [
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-0.05543235316872597,
-0.01161489263176918,
0.01395043171942234,
0.0304177924990654,
-0.057... |
<p>The question is pretty clear I think.</p>
<p>I only started learning GR but the results I've seen so far and
from some lectures I saw from Leonard Susskind on YouTube I understood that for low energy densities the curvature of space-time is mainly in the time coordinate.</p>
<p>Is this true, is the gravity we feel... | g7960 | [
0.06592906266450882,
0.05619075894355774,
-0.015160704962909222,
-0.019722850993275642,
0.011003885418176651,
0.053845420479774475,
0.04750298708677292,
0.004032517317682505,
-0.07708077132701874,
-0.018050571903586388,
0.048122189939022064,
-0.018657080829143524,
0.04963599517941475,
-0.0... |
<p>Could anyone explain the following expression: Why can mass not be considered concentrated at CM (center of mass) for rotational motion?</p> | g7961 | [
0.058034542948007584,
0.024507081136107445,
0.0014667811337858438,
0.026081111282110214,
0.055486761033535004,
0.003659747773781419,
0.10398068279027939,
-0.024838240817189217,
-0.03790678083896637,
-0.039032310247421265,
-0.017224518582224846,
-0.01159043237566948,
0.012521931901574135,
-... |
<p>I have a typical single-plaquette partition function for a gauge-field
$$ Z=\int [d U_{\text{link}}] \exp[-\sum_{p} S_{p}(U,a)]$$
with $U$ as the product of the the $U$'s assigned to each link around a plaquette. Now the $U$'s are irreducible representations of my group elements, which in my case is SU(2), and lets... | g7962 | [
-0.025767512619495392,
-0.03967380151152611,
-0.03190643712878227,
-0.10055223107337952,
0.05082627385854721,
0.004002573899924755,
0.046330008655786514,
0.0635308101773262,
-0.023066958412528038,
0.018479593098163605,
-0.01704057678580284,
0.06745247542858124,
0.002295960206538439,
0.0096... |
<p>The Einstein-Hilbert action of general relativity is uniquely determined by general covariance and the requirement that only second derivatives in the metric appear. Yang-Mills theory can be motivated in a similiar way. In the original paper of Scherk, Julia, Cremer there are some arguments given from which they ded... | g7963 | [
0.006172941531985998,
0.017889894545078278,
-0.012898450717329979,
0.013148205354809761,
0.03258012607693672,
0.018804118037223816,
0.07662520557641983,
0.03739040717482567,
-0.010130207054316998,
0.002629669150337577,
0.020016703754663467,
0.012485399842262268,
0.05117710679769516,
0.0271... |
<p>I understand this topic well enough to get all the task done because they aren't very creative. But for my exam I think I should have this clear. </p>
<p>During the acceleration the force from the engine is of course bigger than air resistance and friction. This force, can we find it? And then the entire force the ... | g7964 | [
0.03591964766383171,
0.03221593797206879,
0.0012237755581736565,
0.013129879720509052,
-0.005250181537121534,
-0.036971449851989746,
0.05655042454600334,
0.04218067601323128,
-0.07791762053966522,
-0.021185044199228287,
0.026696862652897835,
-0.013622192665934563,
0.01013718731701374,
0.00... |
<p>In this <a href="http://brokenspines.wordpress.com/2010/03/12/the-golden-ratio-1-61803399/">blog post</a>, I found this picture:</p>
<p><img src="http://i.stack.imgur.com/Qi3C2.jpg" alt="enter image description here"></p>
<p>Does the water really form golden ratio spiral in such cases? Or is the photo just a provo... | g7965 | [
0.05178280174732208,
0.02110110968351364,
-0.008561203256249428,
-0.0438271164894104,
0.0377497524023056,
0.03277793526649475,
0.058586545288562775,
-0.08450869470834732,
0.04264049604535103,
-0.005899631883949041,
0.016278497874736786,
-0.01393743883818388,
0.03860287368297577,
0.02130434... |
<p>I have a charcoal smoker that uses water. My understanding is that the water serves as a buffer and as a way to add moisture to the cooking environment. Some say that using water wastes fuel because you have to heat the water. </p>
<p>If I am applying Newton's Conservation Law correctly, it seems to me that the ... | g7966 | [
0.03774261102080345,
-0.023263633251190186,
0.020066551864147186,
0.015645919367671013,
0.004347402602434158,
-0.025209559127688408,
0.022860627621412277,
0.013948218896985054,
-0.04067454859614372,
-0.010078322142362595,
0.01455567218363285,
-0.023086680099368095,
-0.019673073664307594,
0... |
<p>I don't understand a particular statement in the QFT book by Klauber. The particular page I'm having difficulty on is page 67 of chapter 3 (<a href="http://www.quantumfieldtheory.info/website_Chap03.pdf" rel="nofollow">PDF link</a>).</p>
<p>The big picture is that the author wishes to investigate what the (operator... | g7967 | [
-0.000011156400432810187,
-0.0039551821537315845,
-0.009631616063416004,
0.0055180499330163,
0.04413081333041191,
0.02082488313317299,
0.02635977417230606,
0.030624091625213623,
0.010212101973593235,
0.006749188993126154,
-0.03111168183386326,
0.011994510889053345,
0.012063530273735523,
0.... |
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