question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>Does a surface in front of a radiator (not in contact) have a significant effect on the room's temperature or heating rate?</p>
<p>Some time ago I had a discussion about it, and despite none of us knowing anything about thermodynamics, we were pretty sure of our opposite intuitions (just like in politics, hehe).</p... | 6,012 |
<p>I have a time series of kW where each sample is measured at regular intervals (10 seconds). Could anyone explain to me how could I calculate the total power consumed (kWh) over an hour?</p>
<p>Thanks</p> | 6,013 |
<p>When an object's speed increases, its (relativistic) mass increases. Are new atoms created inside the object by its increased speed? or is its "gravitational charge" increased by its increased speed, without more atoms?</p> | 6,014 |
<p>How do I properly construct the <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations_in_curved_spacetime" rel="nofollow">electromagnetic tensor in curved space-time</a>? I have my curved spacetime metric $(+,-,-,-)$ and my magnetic vector potential $A$. I tried two ways but not sure which is right (if there i... | 6,015 |
<p>What is sector decomposition and how can it be used to 'disentangle' UV and IR divergences?</p>
<p>I have read about it in the paper <a href="http://arxiv.org/abs/1011.5493" rel="nofollow">SecDec: A general program for sector decomposition</a>,<br>
but I have no idea if, with a suitable change of variable $x=1/q$ o... | 6,016 |
<p>You may have seen the story of the <a href="http://www.cnn.com/2011/TECH/mobile/07/18/iphone.skydive/index.html?hpt=us_t2">iPhone which was dropped from perhaps 13,500</a> feet by a skydiver - it survived.</p>
<p>This made me wonder how to work out the terminal velocity for something like that. Obviously calculatin... | 6,017 |
<p>Dirac gives the relation: $\exp(iaq)f(q,p) = f(q, p - a\hbar)\exp(iaq)$ where $\hbar$ is Planck's constant. Can anybody give me the corresponding relation when the $\exp$ function is a $\ln$?</p> | 6,018 |
<p>We know that spiral galaxies spin in a way such that we have to assume that dark matter is responsible for the extra mass required to do so.</p>
<p>My question is, can Lagrangian points (L1 and L2) be used to describe a galaxy's rotation instead?</p>
<p>Can we explain that objects far away from the center of the g... | 6,019 |
<p>I am not sure about the pressure existing in fluids.If the vertical pressure acts due to gravity and the atmospheric pressure since it also changes due to height also acts due to gravity then why is there horizontal pressure in a liquid. If there is then is it also equal to the vertical pressure at the point?</p>
<... | 6,020 |
<p>Simple question: Why is charge $q$ outside symmetrically distributed?<br>
The material is a conductor.<br>
<img src="http://i.stack.imgur.com/8Tutg.png" alt="enter image description here"></p> | 6,021 |
<p>As a preface, I am not a physicist. I'm simply interested in abstract physics and fundamental principles of the universe and such. As such, if you can provide an answer for the layman (as non-academic and unjargonized as possible), it would be very, very appreciated so that I can actually understand it.</p>
<p>Ev... | 6,022 |
<p>My Question is as follows.</p>
<p>What is the effect of refractive index of an object for imaging (Photographs by high speed camera) on its size and shape information incurred from image?</p>
<p>Lets say ,</p>
<p>I keep the camera focal length, aperture, distance between camera & object, light intensity of t... | 6,023 |
<p>In order to prove the Bernoulli’s principle ($\frac{p}{\rho} + \frac{1}{2}u^2+\phi = constant$ ), I have to use the <a href="http://en.wikipedia.org/wiki/Euler_equations_%28fluid_dynamics%29" rel="nofollow">Euler equation</a>: $\frac{Du}{Dt} = -\frac{1}{\rho}\nabla p + g$.</p>
<p>I know how to prove it, but I didn'... | 6,024 |
<p>I think this is a very straightforward question but I don't see it right now. In Tong's notes on String theory (<a href="http://www.damtp.cam.ac.uk/user/tong/string/four.pdf" rel="nofollow">http://www.damtp.cam.ac.uk/user/tong/string/four.pdf</a>) section 4.2.3 he defines the weight of an operator under $\delta z=\e... | 6,025 |
<p>Suppose, I somehow happen to dig a hole diametrically through the Earth (neglecting all constraints like molten core etc ) ... and I throw an object from one side of the hole, will it reach the other end? </p> | 76 |
<p>In QM I have the state $\lvert 00 \rangle \langle 00 \rvert$. Can anyone tell me what this would look like as a matrix? I know that
$$ \lvert 00 \rangle = \begin{pmatrix} 1 & 1 \\ 0 & 0 \end{pmatrix}. $$</p> | 6,026 |
<p>For the Noether theorem for pseudoeuclidean 4-spacetime a-current $J_{a}^{\mu}$ is equal to</p>
<p>$$
J_{a}^{\mu} = \frac{\partial L}{\partial (\partial_{\mu}\Psi_{k})}Y_{k, a} - \left( \frac{\partial L}{\partial (\partial_{\mu}\Psi_{k})}\partial_{\nu}\Psi_{k} - \delta_{\nu}^{\mu}L \right) X_{a}^{\nu},
$$</p>
<p>... | 6,027 |
<p>I believe the purpose of a tuning fork is to produce a single pure frequency of vibration. How do two coupled vibrating prongs isolate a single frequency? Is it possible to produce the same effect using only 1 prong? Can a single prong not generate a pure frequency? Does the addition of more prongs produce a "mo... | 399 |
<p>Could somebody please explain something regarding the Nordstrom metric?</p>
<p>In particular, I am referring to the last part of question 3 on <a href="http://www.hep.man.ac.uk/u/pilaftsi/GR/example3.pdf" rel="nofollow">this sheet</a> -- about the freely falling massive bodies. </p>
<p>My thoughts: The gravitation... | 6,028 |
<p>Photovoltaic panels are rated under standard conditions: eg a $100\mathrm{W}$ panel if irradiated with $1000\mathrm{W}/\mathrm{m}^2$ at $25^\circ\mathrm{C}$.</p>
<p>When the cost effectiveness of photovoltaics is discussed one is often presented with daily irradiation maps averaged yearly or possibly monthly. This ... | 6,029 |
<p>A standard example of a problem involving torque is opening a door - the same force F applied far from the hinge causes a larger angular acceleration than if applied close to the hinge.</p>
<p>I always had trouble getting an intuitive explanation for this - when you're close to the hinge and you're pushing the door... | 6,030 |
<p>From Jackson, problem 10.3:</p>
<blockquote>
<p>A solid uniform sphere of radius $R$ and conductivity $\sigma$ acts as a scatterer of a plane-wave beam of unpolarized radiation of frequency $\omega$, with $\omega R /c \ll 1$. The conductivity is large enough that the skin depth $\delta$ is small compared to $R$.
... | 6,031 |
<p>Or, perhaps, the question is in which circumstances can I couple it, and of these, which are the simplest. </p>
<p>For instance, I think that you can not have a massive Dirac fermion and just couple the left part of it to the electromagnetic field: you trigger some vector-axial current and then trigger the anomaly ... | 6,032 |
<ul>
<li>particles with real-mass have time-like kinematics ($ds^2 > 0$).</li>
<li>particles with zero-mass have light-like kinematics ($ds^2 = 0$).</li>
<li>particles with imaginary-mass have space-like kinematics ($ds^2 < 0$) (tachyons).</li>
</ul>
<p>So the question is pretty simple:</p>
<p><strong>What would b... | 6,033 |
<p>In Special Relativity, the Lorentz Group is the set of matrices that preserve the metric, i.e. $\Lambda \eta \Lambda^T=\eta$.</p>
<p>Is there any equivalent in General Relativity, like: $\Lambda g \Lambda^T=g$? </p>
<p>(We could at least take locally $g\approx\eta$, so we recover the Lorentz group, but I don't kno... | 890 |
<p>Probability of interaction between two particles tends to wane with increasing energy. Technically, the cross section of most interactions falls off with increasing velocity.</p>
<p>$$\sigma(v) \propto \frac{1}{v}$$</p>
<p>This begs a fun question. Since interaction probability diminishes with increasing relativ... | 6,034 |
<p>On one hand, I think they should be equal since the external force and internal force are equal in equilibrium. On the other hand, I don't see anything related between them, the inside pressure is hold by rubber strength, while ground pressure is equal to gravity, e.g a lightweight steel wheel can hold very high int... | 6,035 |
<p>sorry if I sound little noobish. Though I have a fairly good understanding of physics, I sometimes don't understand the electrical aspects.</p>
<p>Say there is a capacitor. This capacitor is expected to act as a storage buffer. By extension, the capacitor will have a "charge" interface and a "discharge" interface. ... | 6,036 |
<p>What exactly is meant when one uses the word <a href="http://en.wikipedia.org/wiki/Sector" rel="nofollow"><em>sector</em></a> in Particle Physics?</p>
<p>As in, the <a href="http://en.wikipedia.org/wiki/Hidden_sector" rel="nofollow"><em>Hidden Sector</em></a> or the <a href="http://en.wikipedia.org/wiki/Standard_Mo... | 6,037 |
<p>To my understanding, practical resonance occurs when the amplitude is at a maximum. Is this correct? </p>
<p>Also I have looked all over for a derivation of the formula for angular frequency of practical resonance but I can't seem to find a clear one. Is anyone able to show me or provide a link? </p> | 6,038 |
<p>I've been reading Max Tegmark's book: Our Mathematical Universe. It's very interesting, but I wanted to know more about one particular thing. The book simplifies things and I know inflation theories to be varied and complex, but I will briefly describe what Max was saying and hopefully someone can pick up one what I... | 6,039 |
<p>Consider the following metric which is 5 dimensional (2-parameter) spherically symmetric Kaluza-Klein solution</p>
<p>$$-\left(\frac{1-m/r}{1+m/r}\right)^{2/\alpha}dt^2+(1+\frac{m}{r})^4\left(\frac{1-m/r}{1+m/r}\right)^{2(\alpha-\beta-1)/\alpha}(dr^2+r^2d\Omega^2)+\left(\frac{1-m/r}{1+m/r}\right)^{2\beta/\alpha}dx_... | 6,040 |
<p>I thought that I understood the centrifugal force earlier, but I can't seem to grasp how it interacts when considering that everything is relative?</p>
<p>Let's imagine that you are the only one in the entire universe, and that you are spinning with high angular velocity, with the rotation axis pointing in the same... | 6,041 |
<p><a href="http://en.wikipedia.org/wiki/Hawking_radiation" rel="nofollow">Hawking Radiation</a> is formed when particle, anti particle pairs formed by the uncertainty principle are separated by the event horizon of a black hole. It seems like an equal amount of particles and anti-particles should end up on each... | 6,042 |
<p><img src="http://i.stack.imgur.com/HrAKL.png" alt="">the red dots represent a side view of path traveled, F is downward force and the tool used here is a pen placing parallel to the coin</p>
<p>I have newly started to study mechanical physics. based on study, I conduct a simple experiment. But unfortunately I am un... | 6,043 |
<p>I've probably read it somewhere in Sakurai but I cannot recall it at the moment. So how does one really measure the proton's spin? I mean the proton's spin and not its constituents. </p>
<p>Do you measure it using a Stern-Gerlach type of setup?
How about atoms and other stuff, how is their spin measured?</p> | 211 |
<p>"In the presence of chaos, even small fluctuations
(including quantum fluctuations) can be amplified to produce large uncertainties in later
behavior"(<a href="http://arxiv.org/pdf/gr-qc/9210010v2.pdf" rel="nofollow">http://arxiv.org/pdf/gr-qc/9210010v2.pdf</a>)</p>
<p>Is there some experimental evidence for the ampli... | 6,044 |
<p>BQP is the set of problems solvable in polynomial time for a given error tolerance, and it is suspected to be larger than P (and BPP, which is probably equal to P). However, inability for the gates to act perfectly, etc would require error-checking overhead. What is the overhead cost in the algorithm? In particular,... | 6,045 |
<p>Is linear momentum conserved in any direction? More specifically, if you project all momentum vectors in a system onto another vector, will momentum be conserved?</p>
<p>I know that momentum is conserved along the $x$ and $y$ axes, so I'm expecting this to be true, but I have yet to see a rigorous proof.</p> | 6,046 |
<p>Below is a picture of Giant Water Lily. Scientific Name: Victoria Amazonica. Leaves of some of these could be as big as 3 m diameter and carry a weight of 45kg spread evenly and can support a child. Now the problem: </p>
<p>Suppose that a leaf of such flower with a child is floating freely on water. Child crawls a... | 6,047 |
<p>I want to consider conformal maps on suitable compactifications of $\mathbb{R}^{n}$. I know that a special conformal transformation: $$x_i\mapsto\frac{x_i-x^{2}b_i}{1-2b\cdot x+b^{2}x^{2}}$$ can be written as a composition of a spherical inversion, a translation (by $b$) and another inversion about the same circle. ... | 6,048 |
<p>in recent questions like "<a href="http://physics.stackexchange.com/questions/2041/how-are-classical-optics-phenomena-explained-in-qed-snells-law">How are classical optics phenomena explained in QED (Snell's law)?</a>" and "<a href="http://physics.stackexchange.com/questions/1898/do-photons-gain-mass-when-they-trave... | 6,049 |
<p>How is the following relation true</p>
<p>$$\tau = \large\frac{I}{g} \times \alpha$$</p>
<p>where $\tau$ is torque,</p>
<p>$I$ is moment of inertia,</p>
<p>$g= 9.8ms^{-2}$,</p>
<p>and $\alpha=$ angular acceleration.</p> | 6,050 |
<p>I know the ground state of hydrogen is unaffected by the Stark effect to first order. And I also know that the 1st excited state is split from 4 degenerate states to 2 distinct, and 1 degenerate state like this:</p>
<p><img src="http://i.stack.imgur.com/zO0Zt.png" alt="Hydrogen splitting"></p>
<p>But I don't quite... | 6,051 |
<p><a href="http://en.wikipedia.org/wiki/Apsis#The_perihelion_and_aphelion_of_the_Earth" rel="nofollow">Earth's perihelion</a> passed about nine hours ago. How accurately do we know the moment of closest approach of the Earth to the center of the sun? How do we make this measurement?</p> | 6,052 |
<p>Except for Mercury, the planets in the Solar System <a href="http://en.wikipedia.org/wiki/Table_of_planets_in_the_solar_system#Planets">have very small eccentricities</a>.</p>
<p>Is this property special to the Solar System? <a href="http://en.wikipedia.org/wiki/Extrasolar_planet#Orbital_parameters">Wikipedia stat... | 6,053 |
<p>The Navier-Stokes fluid dynamics equations, said that, as Sir William Thomson (or Lord Kelvin) predicted:</p>
<ol>
<li><p>When two smoke-rings are moving in the same direction, with the same speed, one behind the other, the 'leading' ring will slow down and enlarge, while the 'following' one will get smaller and sp... | 6,054 |
<p>The basic thermodynamics problem is stated as follows.</p>
<blockquote>
<p>The nebula contains a very tenuous gas of a given number density (atoms per volume) that is being heated to a given temperature. What is the gas pressure?</p>
</blockquote>
<ol>
<li><p>What are the basic assumptions that should be taken i... | 6,055 |
<p>Is it possible to create, and sustain, an electrified silicon gas vortex?<br>
If it is possible: would it produce an electromagnetic field?<br>
And how would that field affect the vortex? </p> | 6,056 |
<p>I'm interested to know the colour of starlight - particularly in rgb terms, I'm pressuming it's either white, or very close to white, but I'm interested to know how close. </p>
<p>To make it slightly more specific - I'm interested in the colour of stars as observed from the ground with the naked eye. And I'm intere... | 6,057 |
<p>I'm a bit puzzled about an excercise in which I have to find the expectation values for position and momentum. Normally this should be pretty easy but in this case I just don't get the point.
Wavefunction is: $$ \psi(x) = \frac{1}{\sqrt{w_0 \sqrt{\pi}}} e^{\frac{-(x-x_0)^2}{2(w_{0})^{2}}+ik_0 x} $$</p>
<p>In a) you... | 6,058 |
<p>To write the electromagnetic field tensor in CGS units I just have to kick off the c-s from the SI tensor right?
I know this is a stupid question but I need a reliable answer.</p> | 6,059 |
<p>I try to simulate a solar system with planets (with random mass) placed randomly around a sun with a mass $X \times \text{solar mass}$.</p>
<p>The simulation is going well when I use real data (sun,earth,moon for instance), but now I'd like to simulate randomly generated system.</p>
<p>My problem is that I didn't ... | 6,060 |
<p>Are there any examples in the history of physics where a phenomenon was considered by the physics community to be not explainable by classical physics and needed a quantum explanation whereas some time later it was noticed that this claim was wrong (perhaps because for instance one "over-idealized" the system, negle... | 6,061 |
<p>It seems there is a new theorem that changes the rules of the game in the interpretational debate on QM:</p>
<p><a href="http://www.nature.com/news/quantum-theorem-shakes-foundations-1.9392">http://www.nature.com/news/quantum-theorem-shakes-foundations-1.9392</a></p>
<p>Does this only leave Bohm,Everett and GRW as... | 6,062 |
<p>Suppose, we know the length of the shadow of an object at some known time.</p>
<p>Can we use the this information to find position of the object (the longitude )? </p> | 6,063 |
<p>I've noticed that ads for postdoctoral positions emphasize the skill set that one must have for a particular position. That said, what are the areas of research to avoid because they give you few transferable skills and hence limit your range of possible postdoctoral positions?</p>
<p>For example, String Theory mig... | 6,064 |
<p>This question is inspired by this question/answer pair: <a href="http://physics.stackexchange.com/questions/22789/is-this-formula-for-the-energy-of-a-configuration-of-3-fluids-physically-reasona/22823#22823">Is this formula for the energy of a configuration of 3 fluids physically reasonable?</a></p>
<p>Consider thr... | 6,065 |
<p>What processes occur when a meteor enters earth's atmosphere and then what will be speed of meteor when it encounters air resistance?</p> | 6,066 |
<p>As history of thermodynamics say, it was a mystery that what is the required condition for a given energy conversion to take place? Like there are two possible events each conserving energy but only one is chosen. So, in order to resolve this Clausius introduced a quantity called <a href="http://en.wikipedia.org/wik... | 6,067 |
<p>I have the following minus sign problem: </p>
<p>Consider an infinitesimal Lorentz transformation for which $\Lambda^{\mu}_{\nu}=\delta^{\mu}_{\nu}+\lambda^{\mu}_{\nu}$, where $\lambda^{\mu}_{\nu}$ is infinitesimal small. Define the vector fields $M_{\mu\nu}=x_{\mu}\partial_{\nu}-x_{\nu}\partial_{\mu}$. Show that a... | 6,068 |
<p>There are a number of <a href="http://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations#Exact_solutions_of_the_Navier.E2.80.93Stokes_equations" rel="nofollow">exact solutions</a> to the <a href="http://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations" rel="nofollow">Navier-Stokes equations</a>. How many exa... | 1,027 |
<p>Apparently it is to be shown that for electrons under an external magnetic field, in the limit as $B\to 0 $
$$
\chi = \frac{dM}{dB} \approx \frac{n\,\mu^{*^2}}{k\,T}\,\frac{f_{1/2}(z)}{f_{3/2}(z)}
$$</p>
<p>So this is the Pauli paramagnetism problem and I understand the effect and the physics, but cannot seem to g... | 6,069 |
<p>The cross section of a nuclear interaction is a measurement of the probability of that interaction occuring. These probabilities are typically presented in terms of barns ($10^{-28}$ m$^2$) as a function of incident particle energy. You can look up values <a href="http://atom.kaeri.re.kr/ton/index.html" rel="nofol... | 6,070 |
<p>There have already been a lot of questions on this site on diffraction but I still believe this one might be slightly different. In electromagnetic waves, diffraction and any other phenomenon of wave propagation can be solved by Huygen's principle, a geometric construction that asks us to consider all points on a wa... | 6,071 |
<p>I have a monochromatic ribbon beam with $E(x)e^{i(kz-\omega t)}$ being the electric field's amplitude. I want to show that the lowest order approximation in terms of plane waves is</p>
<p>$\mathbf{E}(x,z,t)=\mathbf{\epsilon} \int{d\kappa A(\kappa) e^{i(\kappa x+kz-\omega t)}}$</p>
<p>where $\mathbf{\epsilon}$ is t... | 6,072 |
<p>I have been playing around with <a href="http://earth.nullschool.net/#current/wind/isobaric/10hPa/orthographic=-1.45,54.02,482" rel="nofollow">this nice visualisation</a> and noticed that in the mid-stratosphere (P=10hPa), the airflow around the equator and south of it is in the opposite direction to the earth's rot... | 6,073 |
<p>As I've been taught lately in my mechanics course: </p>
<blockquote>
<p>the wheel has a unique property: at every moment of motion, the
touching point between the wheel and the ground is not in movement and
therefore no work is done by the friction force.</p>
</blockquote>
<p>Now, many of those problems are ... | 6,074 |
<p>I understand the derivation and calculation of de Broglie wavelengths, but what exactly does the wave of a particle represent? What does the wavelength of a particle mean? I'm assuming it's not the wavelength of its probability wave because then there would be no uncertainty in momentum, unless it represents the ave... | 6,075 |
<p>This is a very simple question, which will most likely yield a prompt response from someone who knows more than I. The reason I ask:The quarks that we can detect (as they interact electromagnetically) are much lighter than the particles that they make up. From what I know, we say that gluons augment the energy level... | 6,076 |
<p>I will be a grad student in condensed matter theory starting this fall. As an undergrad, I did the basic physics and math courses as well as a few grad classes (qft, analysis, solid state physics etc.) </p>
<p>When I start reading research papers, I often feel overwhelmed because there is so much that I don't know ... | 115 |
<p>Here's a puzzle I have been pondering over.</p>
<p>If we have two extremal black holes with the same charge, the electrostatic repulsion between them ought to cancel the gravitational attraction between them. Without any net attraction or repulsion between them, how close can we bring these two black holes to each ... | 6,077 |
<p>Why do only big rocks (planets) have satellites, and not small ones? Why doesn't cosmic dust orbit rocks that are many times heavier than the dust grains? If dust is still too heavy then what about molecules, atoms, or any particle for that matter? The mass difference should be millions of millions times; isn't it e... | 6,078 |
<p>Is the Lorentz Force acting on a wire, that has current $I$ in a magnetic field $B$ <a href="http://en.wikipedia.org/wiki/Conservative_force" rel="nofollow">conservative</a>? Or non-conservative? I understand that all the fundamental forces are conservative, am I correct? </p> | 212 |
<p>This was just a random thought that crossed my mind, and I'm sure there is a simple physics explanation. Say we have a leaky faucet 20 feet above the ground that lets out the exact same amount of water every few seconds or so. Why is it that the splash pattern for every drop is never the same as any other drop? Now ... | 6,079 |
<p>I'm trying to calculate two 2d disks' collision with rotational motion.
The collision is perfectly elastic: the sum of translational and rotational energy is conserved. In the instant of the collision the contact of disks' surface is without slipping. Could you give me hint for this calculation?</p>
<p>Thanks.</p> | 6,080 |
<p>I'm trying to relate them, I'm trying to find the key relation that would show how the <a href="http://en.wikipedia.org/wiki/Conservative_force" rel="nofollow">conservative forces</a> serve <a href="http://en.wikipedia.org/wiki/Conservation_of_energy" rel="nofollow">conservation of energy</a>.
How would they relate?... | 6,081 |
<p>I've read this question and answer: <a href="http://physics.stackexchange.com/questions/1493/how-efficient-is-an-electric-heater">How efficient is an electric heater?</a>
, but still don't understand.</p>
<p>If I have an electric radiator it heats the room with 1000 Watts of power. And I feel the room's getting war... | 6,082 |
<p>Metallic strings exist in different kinds but I would like to measure for a metallic string:</p>
<ul>
<li><p>the section/geometry along its length, to a precision of 1/100 mm</p></li>
<li><p>its elongation when a tension is exerted on it on a measuring system I would construct to apply forces of the order of 1 to 1... | 6,083 |
<p>What is the difference between conduction of electric wave in conductor and propagation of electromagnetic wave in dielectric?</p>
<p>Why propagation term is used for dielectric and conduction for conductor?.</p>
<p>Somehow why propagation of electromagnetic wave (is it energy wave) is not possible in conductor, b... | 174 |
<p>In our undergraduate E&MWaves class, we learned about a rectangular waveguide, and how to calculate the electric and magnetic field distribution throughout the waveguide using finite element analysis. Out of curiosity, I am interested in how you would go about solving the boundary conditions of a funnel wave gui... | 6,084 |
<p>Can we make a jacket using an electronic circuit that uses electric force to cancel the effect of gravity so that we get lifted in air.</p> | 6,085 |
<p>I was doing <a href="http://www.ocr.org.uk/Images/62267-question-paper-unit-g485-fields-particles-and-frontiers-of-physics.pdf" rel="nofollow">this</a> past paper and am a little confused by question 5) part c)ii)</p>
<p><img src="http://i.stack.imgur.com/3MBvP.png" alt="Diagram from past paper"></p>
<p><img src="... | 6,086 |
<p>If we put earth like planet made up of antimatter (same mass of earth, same diameter etc..) with same distance from moon as current distance between earth and moon then center of gravity of moon and earth will change or not? Why?</p> | 6,087 |
<p>Can anyone resolve this contradiction:</p>
<p>$$\vec{r}\cdot\dot{\vec{r}}=\frac{1}{2}\frac{d}{dt}\left(\vec{r}^2\right)=\frac{1}{2}\frac{d}{dt}\left(\left|\vec{r}\right|^2\right)\equiv\frac{1}{2}\frac{d}{dt}\left(r^2\right)=r\dot{r}, \qquad r=|\vec{r}|.$$</p>
<p>But the velocity $\vec{v}=\dot{\vec{r}}$ has not to ... | 6,088 |
<p>I've seen the following formula for the potential energy of a body in a gravitational field ($\rho$ is the density, $g$ is the gravitational acceleration):</p>
<p>$$ \rho g \int_E z dV $$</p>
<p>Can you please explain to me how this formula is deduced? Thank you.</p> | 6,089 |
<p>In physics, the word entropy has important physical implications as the amount of "disorder" of a system. In mathematics, a more abstract definition is used. The (Shannon) entropy of a variable $X$ is defined as</p>
<p>$$H(X)=-\Sigma_x P(x)log_2 [P(x)]$$</p>
<p>bits, where $P(x)$ is the probability that $X$ is in ... | 6,090 |
<p>Considering all of the appliances that the average home uses--microwaves, light bulbs, dishwashers, refrigerators--is it safe to say that all of the electrical energy in a home will be converted to thermal energy inside the home?</p>
<p>If you think about the resistance going through wires, that is converted to hea... | 6,091 |
<p>Suppose we have 2 fixed end connected with a wire and now we insert a vibrator <strong>in the middle</strong> of the wire, and resonance occur. How would the fundamental frequency looks like?</p>
<p>I know the case when the vibrator is at one ends and another ends are fixed while in this case, there are 2 fixed poi... | 6,092 |
<p>As I know, the working fuel of choice is Hydrogen because of its low molecular mass. When it comes to escape velocity, the estimate vary too much, from $8$km/s to $50$km/s (gas core reactor).</p>
<p>Wouldn't it be better to use water as a fuel since it's so much easier to store? </p>
<p>If we used water as a fuel... | 6,093 |
<p>If you take the homogenous wave equation:</p>
<p>$$-\Delta_x u(x,t) + \frac{1}{c^2} \frac{\partial^2 u}{\partial^2 t} (x,t) \ = \ 0 \ \ \mathrm{in} \ \Omega \times (0, \infty),$$</p>
<p>with some proper initial- and boundary conditions and make the ansatz:</p>
<p>$$u(x,t):= e^{-i \omega t} v(x),$$</p>
<p>i.e. we... | 6,094 |
<p>I fear that I have a fundamental misconception about the "wave particle duality" of light, but in a related question, the answerer said, in some sense, that a light wave propagates until it hits something, at which point in time it (can) act(s) like a photon. Which is fine to me, but there are a finite number of pho... | 6,095 |
<p>My textbook presents an idealization of a conductor as made up of infinitesimal units of charge and derives results. I was not convinced, so I started thinking of how electric fields are in real metals. Here is what I think now:</p>
<p>i) My description of a "static" situation - There are electric fields inside a c... | 6,096 |
<p>During a very short time after the big bang, the universe must have had an edge of space-time which is very close to all the matter in the universe. The particles which are close to or on the edge must also have gravity and other forces. How did those forces interact with the space-time boundary? And, if the range o... | 6,097 |
<p>In an effort to destabilize hurricanes by burning the necessary cold zones it has been proposed that planes drop various <a href="http://www.dailygalaxy.com/my_weblog/2007/10/can-man-control.html" rel="nofollow">carbon trash</a> on them. That seems like a minor amount of heat change over a large area. What not just ... | 6,098 |
<p>The philosopher of physics Laura Reutsche argues in her book Interpreting Quantum Theories (review/summary here: <a href="http://philsci-archive.pitt.edu/9493/1/ruetsche-review.pdf" rel="nofollow">http://philsci-archive.pitt.edu/9493/1/ruetsche-review.pdf</a> ) that a "pristine" interpretation (1-1 correspondence be... | 6,099 |
<p>Volcanic eruptions sometimes cool the earth. How many eruptions of what magnitude, locality and type would be required per year to neutralize Global Warming?</p> | 6,100 |
<p>How to find the intrinsic covariant derivative component?</p>
<p>In general relativity the elements of the acceleration four-vector are related to the elements of the four-velocity through a covariant derivative with respect to proper time.
where the covariant derivative is broken into two parts, the extrinsic norm... | 6,101 |
<blockquote>
<p>A nonuniform horizontal bar of mass $m$ is supported by two massless wires against gravity. The left wire makes an angle $ϕ_1$ with the horizontal, and the right wire makes an angle $ϕ_2$. The bar has length $L$.</p>
</blockquote>
<p><img src="http://i.stack.imgur.com/LB8VB.png" alt="enter image desc... | 6,102 |
<p><a href="http://i.stack.imgur.com/ph7zc.png" rel="nofollow">click to view the image</a> <br/></p>
<p>Before I start, I want to say that this is not a duplicate of "Is it possible for information to be transmitted faster than light by using a rigid pole?", Since point A is not a real object, it is possible for A to... | 4 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.