question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Let's consider the following situation. We put a body of mass $m$ at a distance $A$ from the center of Earth. We let the Earth attract the body and analyze the situation at a point $B$, closer to the Earth.</p>
<p>Now, the work done by the gravitational force (a conservative force, which seems to be important) is g... | 2,997 |
<p>An electron is ejected from the surface of a long thick straight conductor carying a current, initially in direction perpendicular to the conductor. The electron will:
a) ultimately return to the conductor
b) move in a circular path around the conductor
c) gradually move away from the conductor along a spiral
d) mov... | 2,998 |
<p><strong>Chern bands or Chern insulators</strong> in 2 spatial dimensional(2D) are a way to construct the bulk insulating gap, but with edge or surfaces with <strong>gapless fermions</strong>. Such gapless fermions are emergent, and which seems to be different than the <strong>High Energy Physics Lattice Fermions app... | 2,999 |
<p>In <a href="http://web.physics.ucsb.edu/~mark/qft.html" rel="nofollow">Srednicki's QFT book</a>, eq. $14.27$ is a result used over and over again for computing loop correction. It is the following integral evaluated in terms of gamma functions:</p>
<p>$$
\int d^dq \frac{(q^2)^a}{(q^2+D)^b} =
\frac {\Gamma (b-a-\fr... | 3,000 |
<p>Under a Galilean transformation, the coordinates and momenta of any system transform as:
$$ t \rightarrow t',\\ \vec r\:' = \vec r + \vec vt,\\ \vec p\:' = \vec p + m\vec v $$
where $\vec v$ is velocity of frame moving w.r.t it. Now, what will be unitary transformation that can that will carry out this transformat... | 3,001 |
<p>Both are feebly attracted by a magnetic field. I know the difference between these substances(on why these get attracted to magnetic field) but as both get feebly attracted how to find out whether a given substance is ferri-magnetic or para-magnetic?</p>
<p>Is it that all ferri-magnetic materials are compounds of d... | 3,002 |
<p>When we do a transformation (norm preserving one) for a given quantity, from what I have understood it seems like there is a representation of the group element for each quantity depending how they transform (eg : scalar, vector, rank 2 tensor spinor.. ).</p>
<p>Considering a normal rotation in 2-D plane (associate... | 3,003 |
<p>If a golf club strikes the ball out of the centre of the club face with the club path on the target line through impact, and the face square to target, the ball will move towards the target with no side-spin.</p>
<p>If the same shot is played but the impact is towards the toe of the club, the club face will open sl... | 3,004 |
<p>OK, this question is not your usual one: Last night while hiking solo from the mountains back to my car at the mountain/desert interface (Lone Pine, CA), I had a rather bizarre -- and downright spooky -- experience.</p>
<p>The last half-mile of my return was in total darkness, which wasn't a problem since I had pre... | 3,005 |
<p>Simulations of the Bak-Sneppen Model of Species Evolution (introduced in <a href="http://link.aps.org/doi/10.1103/PhysRevLett.71.4083" rel="nofollow">http://link.aps.org/doi/10.1103/PhysRevLett.71.4083</a>) show that it exhibits Self-Organized Criticality where after a transient only mutation through barriers of hei... | 3,006 |
<p>There has been recent activity by astrophysicists to determine whether a fourth flavor of neutrino, a sterile neutrino, exists. It would likely be more massive than electron, muon or tau neutrinos. However, it wouldn't be affected by the weak force, only by gravity. It would therefore have similar characteristics to... | 3,007 |
<p>I recently saw cm^3/g as a unit for amount adsorbed. Usually, you see either kg adsorbate/kg adsorbent or mole adsorbate/kg adsorbent. Does anyone know the meaning of this unit?</p> | 3,008 |
<p>Electromagnetic waves travel in straight lines but do all waves travel in straight lines?</p> | 3,009 |
<p>How do you obtain the spectral function for advection equation in one dimension?
2.How about 2D?
thanks a lot</p> | 3,010 |
<p>Let $B$ be the magnetic field.
If </p>
<p>$$\nabla \times B = 0$$ and of course $$\nabla \cdot B= 0$$</p>
<p>Can we conclude that $B=0$?</p>
<p>For a general field it is wrong because every constant vector will satisfy those conditions.</p>
<p>But for the magnetic field is it enough?</p> | 3,011 |
<p>Electron-phonon and electron-defect scattering clearly contributes to resistance, but pure electron-electron scattering conserves the total momentum (and energy) of all the electrons. Then, how is it possible for electron-electron interactions to contribute to electrical resistance?</p> | 3,012 |
<p>I am trying to understand and find a way to distinguish two same sounds of different people by some physics formula, so could you guys help me? </p>
<p><p>OK I'll try to explain my question in this way that, for example, there are two people A and B are reading this sentence aloud. <em>"Crackers are Cracking for Cr... | 3,013 |
<p>So the <a href="http://en.wikipedia.org/wiki/Geodesic_deviation_equation" rel="nofollow">geodesic deviation equation</a> gives the relative acceleration between two geodesics in motion. But given a pair of geodesic (let's say on the two sphere) that start at the equator, separated by some distance. Is there a way to... | 3,014 |
<p>I have the following equations</p>
<p>$$\ x′′(t)=−\frac km x′(t)$$</p>
<p>$$\ y′′(t)=−\frac km y′(t) - g$$</p>
<p>where $k$ is the drag, $m$ is the mass of the object and $t$ is the time. $g$ is the gravity constant.</p>
<p>After integrating the functions twice, I end up with the following equations</p>
<p>$$... | 3,015 |
<p>In the systems like photon gas in a cavity and phonon gas in a solid number of particles is not conserved and chamical potential is zero. Is this a general rule? If yes, how zero chemical potential is obtained from number non-conservation? </p> | 3,016 |
<p><strong>Question:</strong></p>
<p>What isotope has the shortest half life?</p> | 3,017 |
<p>Let's assume that we build a giant steel hull in a shape of cube with open top (2km long edge) and lift it to the top of stratosphere and then pump air out of it. Would it float on the outer layer of stratosphere like a ship floats on the surface of water?</p> | 3,018 |
<p>A class 1 lever and a class 2 lever are connected in series, on the resistance end of the class one lever is a 500g weight. On the 2nd class lever sits a weight of an unknown mass. From the end of the 1st class lever to the center of the known mass is 46cm, from center of the known mass to fulcrum is 4cm. On the lef... | 3,019 |
<p>There is a block of wood on a plank, with friction, and the block is moving down with <strong>uniform speed</strong>. They are asking what is the <strong>torque acting through the center of the block</strong>. </p>
<p><img src="http://i.stack.imgur.com/RicWP.jpg" alt="Force diagram of block on plank"></p>
<p>My d... | 3,020 |
<p>I am a novice on this topic. However, I wonder if we use nuclear bombs against the tsunami, will it reduce the speed and impact of the tsunami. Is it possible to break the massive wall of waves using nuclear bombs? In other words, is it possible to create another opposite force which can neutralise/reduce the energy... | 66 |
<p>If the Universe has two 'end points', one being the Big Bang, and the other being heat death, is there anything in the laws of physics which forbid a random fluctuation in the heat death state from being the reason for the Big Bang? My thinking is this: we know that moving along the time axis from the Big Bang to H... | 3,021 |
<p>I am currently reading this <a href="http://journals.aps.org/pr/pdf/10.1103/PhysRev.104.563" rel="nofollow">Phys Rev paper</a> by H C Torrey. In this paper, he derives the Bloch equations with an additional diffusion term. He says that the current density is given by
$$\mathbf j_{\pm} = n_{\pm} \mathbf V_{\pm} - D ... | 3,022 |
<p>The strain energy density is defined as
$$dU = \int_0^{\epsilon_{ij}} \sigma_{ij} d \epsilon_{ij}$$
(see Reddy "Energy Principles and Variational Methods in Applied Mechanics", 2nd Ed, 4.11). Assuming a linear stress-strain relationship, I get
$$U = \frac12 \sigma_{ij} \epsilon_{ij}$$
which is consistent with the ... | 3,023 |
<p>Here's a question I got in my final exam this morning. "If in a Young's double slit experiment setup, the ratio of intensity of the bright spot to the dark spot is 25:9, what is the ratio of the width of the slits?"</p>
<p>Here's what I did. Since the ratio of intensity at the bright and dark spots is 25:9, the rat... | 3,024 |
<p>We can describe (some of) the dynamics of many systems using fluid mechanics. Of course these include classical fluids like water, more exotic fluids like photon gases and the universe as a whole and even solid(ish) things over long times, like glasses and ice. Further still we can treat general classical systems in... | 3,025 |
<p>Can a electrostatic field $\vec E=\vec E(x,y,z)$ (time-independent) or electrostatic potential $\phi=\phi(x,y,z)$ be quantized? If yes, will these quanta be photons again? But we don't have an electromagnetic field here.</p> | 3,026 |
<p>I once saw a demonstration where an electric current caused a drop of mercury to spin. The drop contained bits of iron, which could be seen flowing around in a circular pattern. As soon as the current was turned off, the spinning slowed fairly quickly. What caused the circular motion within the drop to slow? It ... | 3,027 |
<p>I just broke a 120mm computer fan in name of science and now I'm pissed; can anyone explain why this doesn't work? :</p>
<p><img src="http://i.stack.imgur.com/rfwqo.jpg" alt="enter image description here"></p>
<p>The battery should create a potential difference across the motor, causing the fan to spin up, right?<... | 3,028 |
<p>I am in search of a simplified version of the derivation of Newton-Euler equations of motion (both translational and rotational) for a rigid body (3D block) that has a body fixed frame and where the center of mass of the body is not at the center of gravity. I can find elementary derivations for the same system whe... | 843 |
<p>A recent article, <a href="http://www.sciencenews.org/view/generic/id/350088/description/Counting_cracks_in_glass_gives_speed_of_projectile" rel="nofollow">Counting cracks in glass gives speed of projectile</a> (Andrew Grant, <em>Science News</em>, May 1 2013) indicates that the number of cracks in a broken glass ca... | 3,029 |
<p>As far as I have read so far,
proper time is the time measured on the clock of an inertial frame moving uniformly with respect to another inertial frame. The concept and the mathematical expression for proper time is originated from the concepts of relativity of simultaneity and time dilation, both of which are evid... | 3,030 |
<p>I thought that I understand the "Bragg's Law" understanding of crystal diffraction, but recently I read something that made me confused. I understand that if the planes in the crystal have sufficiently small spacing relative to wavelength (more specifically, such that $sin \theta$ in Bragg's Law >1 even for lowest o... | 3,031 |
<p>Is it possible to create matter? In a recent discussion I had, it was suggested that with enough energy in the future, "particles" could be created. </p>
<p>It seems like this shouldn't be possible due to conservation but perhaps I could be wrong. Would any of you Physics masters care to elaborate?</p>
<p>(Note...... | 67 |
<p>So I'm not OK with how some people derive this equation.</p>
<p>These people consider a pipe whose endings have cross-sectional areas and heights which are different. They then use the conservation of energy principle by saying $dW = dK + dU$ (Where $W$ is work, $K$ is kinetic energy, and $U$ is potential energy)... | 3,032 |
<p><strong>Disclaimer.</strong> I am a graduate student in pure mathematics, so my knowledge of physics more advanced than basic 1st/2nd year undergraduate physics is very limited. I welcome corrections on any misconceptions present in my question.</p>
<hr>
<p><strong>Background.</strong>
From readings I have done on... | 3,033 |
<p>I recently read that:</p>
<blockquote>
<p>"A drop of water landing on a hot plate at $150^o C \:(300 F)$ evaporates in a few seconds.
A drop of water landing on a hot plate at $200^o C \:(400 F)$ survives a whole minute."</p>
</blockquote>
<p>How would you explain this observation using physics principles?</p... | 3,034 |
<p>So here is my question: Say we have measured something to be 15,67 mm and the <a href="http://en.wikipedia.org/wiki/Significant_figures" rel="nofollow">significant</a> error is $\pm 0,01$mm. then we convert the measurement to meter to be 0,01567m would the significant error then be $\pm 0.00001$m?</p> | 3,035 |
<p>In <a href="http://www.phys.ubbcluj.ro/~emil.vinteler/nanofotonica/PWM/pwmmanual_Guo.pdf" rel="nofollow">this document</a>, what does the line "Write $\vec{G}_i + \vec{G}_i' \rightarrow \vec{G}_i'$" after equation (25) actually mean?</p> | 3,036 |
<p>In the following I will give some arguments that will indicate that the gravitational coupling "constant" actually depends on the scale (space and time) of the interacting systems. The question is:</p>
<p>Question 1. Which of the following arguments are invalid?</p>
<p>The following arguments are inspired by the f... | 3,037 |
<p>As a mathematics student with almost no modern physics background (just an introduction to relativity when I was in secondary school) I find Leonard Susskind's lectures videos (freely available in Youtube) very interesting but I am wondering, in which order should I watch them? Which courses first? These are the one... | 3,038 |
<p>Each person exists as an unchanging 4D worldtube in the block universe. At each slice of the worldtube there is a present, past and future.</p>
<p>However, there is a black box* which appears to exist in only one slice of the block universe at a time. How could this be explained?</p>
<p>I am not trying to attack t... | 3,039 |
<p>I assume that for a Lorentzian manifold (i.e. with Minkowski signature), the analog of an open ball is the interior of a light cone. My question is motivated by the observation that whereas any point on the boundary of an open ball on a Rimannian manifold (i.e. with Euclidean signature) can be considered to be simul... | 3,040 |
<p>Two balls, first with the mass $m_1$ and the second with the mass $m_2$ are falling from the heigh $h$. Suppose all the collisions are perfectly elastic and do not consider the size of the balls. $m_1 < m_2$ and ball with the mass $m_1$ is on the top.</p>
<p><img src="http://i.stack.imgur.com/463dY.png" alt="ent... | 928 |
<p>why airplanes are banned with use of cellphones? What were the impacts while we answer an call or make an call ,what was the <strong>physical</strong> reason behind the ban of using cellphone inside airplanes ?</p>
<p>I expect answer related to physics here</p> | 3,041 |
<p><img src="http://i.stack.imgur.com/Pik0X.jpg" alt="enter image description here"><img src="http://i.stack.imgur.com/LL2TD.jpg" alt="enter image description here"></p>
<p>I got confused about the difference between the last term of both pictures. In the first one, we have w x r, but in the second we have w x r under... | 3,042 |
<p>Electromagnetism implies special relativity and then the universal constant "c". And if we set c=1, the coupling constant has units of angular momentum (so in relativistic quantum mechanics we divide by $\hbar$ and we get the adimensional coupling $\alpha$).</p>
<p>Question, loose, is: In which explicit ways does t... | 3,043 |
<p>A familiar trope within science-fiction is that of a large relativistic object hitting a planet such as the earth. This is normally an interstellar spacecraft or a kinetic weapon with a mass in the range 10<sup>3</sup> - 10<sup>6</sup> kg. But what would actually happen?</p>
<p>The two scenarios seem to be: (a) the... | 3,044 |
<p>Does anybody know the Fermi wavelength of graphene? I searched the Internet for a while without success. I found, by inspection with the Fourier transform of an S.T.M. image
$$
3.84e^{-10} \mathrm{m}.
$$
Is this value of the right order of magnitude?</p> | 3,045 |
<p>Is the Oort cloud blocking a substantial amount of light in the visual spectra, making it harder for observers seeing outside the solar system? </p> | 3,046 |
<p>Assume this question:
In a simple model of a monovalent metal consisting of point positive ion cores embedded in a uniform jellium of electrons, a value for the average energy for electron is:
$$E = \frac{9}{10} \frac{e^{2}}{r} + \frac{3\hbar^{2}}{10mr^{2}}\left(\frac{9}{4\pi}\right)^{2/3}$$
where r is the radius of... | 3,047 |
<p>I know that it is dust blocking the light. But what is this dust made of, gases or more heavy materials. If it is gas why is it not already drawn together in nebulas? </p> | 3,048 |
<p>From studying waves I find that I can visualise longitudinal waves where the wave propagates in the direction of the displacement. However I don't understand what causes the propagation perpendicular to the displacement in transverse waves. How is a perpendicular displacement caused in adjacent particles?</p> | 3,049 |
<p>$$F = \frac{\pi^2 EI}{(KL)^2}$$</p>
<p>Is Euler's buckling formula applicable for impact calculations, considering speeds relevant for a car or aircraft crash? </p>
<p>If there is a level where the formula becomes inapplicable or inappropriate in impact calculations, what determines this, and what behavior (and he... | 3,050 |
<p>In the context of producing a pulling force perpendicular to the 'spinning plane' of a propeller/fan, <br>
is it correct to say that a <strong>propeller</strong> mainly achieves it's force by being aerofoils producing lift and a <strong>fan</strong> mainly achieves it's force by utilizing Newtons third law?</p> | 3,051 |
<p>States of matter in physics are the distinct forms that different phases of matter take on. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma.
What is physics behind States of matter?</p>
<p><strong>For Example:</strong></p>
<p>I found a Trick to freeze water in about half a sec... | 3,052 |
<p>What sense can be made of the natural logarithm, When appearing in a physical process?</p>
<p>For example, This integral in the thermodynamic $\int_i^f \frac {dV}{V}=Ln\frac {V_f}{V_i}$ when $V$ denotes Volume.
in general $Ln\frac {Q_f}{Q_i}$ when the $Q$ denotes Physical quantities.</p>
<p>or this one
$S=k_BLn\O... | 3,053 |
<p>How does Einstein got equivalent mass- energy equation E=mc2 ?</p> | 68 |
<p>I'm reading about uncertainty principle, and something has been bothering me for quite a while. There is the formula: </p>
<p>$$\sigma_x \sigma_p \ge \frac{\hbar}{2}$$</p>
<p>I know what this means: <em>the more you know about the position, the less you know about the momentum, and vice-versa.</em> </p>
<p>As an ... | 3,054 |
<p>A <a href="http://www.cnn.com/2013/02/15/world/europe/russia-meteor-shower">report</a> on the Chelyabinsk meteor event earlier this year states </p>
<blockquote>
<p>Russian meteor blast injures at least 1,000 people, authorities say</p>
</blockquote>
<p>My question is </p>
<ul>
<li>Why do meteors explode? </li>... | 3,055 |
<p>In Kaluza-Klein theories I often see that the compact space is assumed to be an Einstein manifold, that is, its Ricci tensor is proportional to its metric. </p>
<p>So, why is this done?</p> | 3,056 |
<p>From the <a href="http://en.wikipedia.org/wiki/Closed_timelike_curve" rel="nofollow">Wikipedia article</a>, it seems that physicists tend to view closed timelike curves as an undesirable attribute of a solution to the Einstein Field Equations. Hawking formulated the <a href="http://en.wikipedia.org/wiki/Chronology_p... | 3,057 |
<p>Under the Lorentz transformations, quantities are classed as four-vectors, Lorentz scalars etc depending upon how their measurement in one coordinate system transforms as a measurement in another coordinate system.</p>
<p>The proper length and proper time measured in one coordinate system will be a calculated, but ... | 3,058 |
<p>I've seen the claim made several placed; Terning's "Modern Supersymmetry" p. 5 on N=1 SUSY algebra states it as well as anyone:</p>
<blockquote>
<p>The SUSY algebra is invariant under a multiplication of $Q_\alpha$ by a phase, so in general there is one linear combination of $U(1)$ charges, called the $R$-charge,... | 3,059 |
<p>In the definition (in one spatial dimension) of $\Delta \tau$ there is the relation:</p>
<p>$(\Delta \tau)^2 = (\Delta t)^2 - (\Delta x)^2$ which is invariant. If $(\Delta x)^2 > (\Delta t)^2$ then there is the characterization "spacelike."</p>
<p>In this case $\Delta \tau$ will be an imaginary number.</p>
<p>... | 3,060 |
<p>In the <a href="http://en.wikipedia.org/wiki/Quantum_eraser_experiment" rel="nofollow">quantum eraser double slit experiment</a>, does the photon (or wavefunction) pass through one slit or both slits when different polarizers are placed over the slits?</p> | 3,061 |
<p><img src="http://i.stack.imgur.com/XvaWP.gif" alt="enter image description here"></p>
<p>Imagine the sliding part of the mirror is controlled by computer and opens on intervals.</p>
<p>Is it possible to increase the power of the beam by making it bounce between the mirrors thus going through the lens and then rele... | 3,062 |
<p>The largest Mercury mirror telescope is the Large Zenith Telescope in Vancouver, Canada. When spinning the Mercury is spread out in a layer that is about 2 milimeter thick at every point on the dish.
<br>
<br>
<br>
I want to examine the following simple case: a Mercury mirror located on the equator, spinning counte... | 3,063 |
<p>I just read about a team of physicists at the University of Darmstadt, Germany, that managed to completely slow down a beam of light that traveled through an opaque crystal (article <a href="http://www.newscientist.com/article/dn23925-light-completely-stopped-for-a-recordbreaking-minute#.UfG1bG1ZTJt" rel="nofollow">... | 3,064 |
<p>I was reading a webpage on <a href="http://www.astro.umd.edu/~miller/nstar.html" rel="nofollow">neutron stars</a>, and it mentioned that a neutron star's gravitational mass is about 20% lower than its baryonic mass due to gravitational redshift. I understand the basics of what the terms mean, but I do not see why gr... | 3,065 |
<p>There is a charge q at a perpendicular distance z = d from an infinite conducting plate z=0. We use the image method and place -q on the other side of the plate and calculate the field. This field points outwards from the charge q and inwards towards the -q and the field at z = 0 on the x-y conducting plane is $E_{x... | 3,066 |
<p>This question is about the Hamiltonian for more than one particle (non-relativistic).</p>
<p>Griffiths (Introduction to Quantum Mechanics, 2e) seems to imply that it is $\displaystyle H=-\frac{\hbar^2}{2}\left(\sum_{n=1}^N\frac{1}{m_n}\nabla_{\mathbf{r}_n}^2\right)+V(\mathbf{r}_1,\dots,\mathbf{r}_N,t)$, but wikiped... | 3,067 |
<p>Can I create a device that moves in one direction with a design like Figure 1? I suspect that the forces cancel each other by the recirculation. It is a simple exercise of action and reaction, but I can not figure out the math to explain. </p>
<p>Maybe my problem is of type <a href="http://meta.stackexchange.com/qu... | 3,068 |
<p>For instance, this image: </p>
<p><img src="http://i.stack.imgur.com/6uN1dm.jpg" alt="enter image description here"></p>
<p>shows human eyelashes close up. </p>
<p>The lashes look green, in fact the whole surface area has a strange tint of green Why is this?</p> | 3,069 |
<p>I've seen numerous examples where the De Broglie wavelengths of macroscopic objects such as bullets and baseballs have been calculated. However, in each case, the objects are moving fast and the corresponding momentums are large, resulting in tiny De Broglie wavelengths. What happens if you slow the bullet down to... | 3,070 |
<p>I was watching a <a href="http://www.youtube.com/watch?v=P8ZOf8xp1no" rel="nofollow">video</a> and when the car did blow up I asked to me... what happens with the atoms and their bonds when an object blows up of this way? what is the behavior of the atoms and their bonds when an object is on fire? what is the atomic... | 3,071 |
<p>The simplest magnetic field is that of an infinitely long wire with uniform current. It does enjoy radial symmetry about the wire and has the variation as 1/r.</p>
<p>To find the direction of the resulting magnetic field you use the right hand grip rule (for conventional current). This rule repeats the experimental... | 3,072 |
<p>So I was reading this: <a href="http://physics.stackexchange.com/questions/11885/invariance-of-lagrange-on-addition-of-total-time-derivative-of-a-function-of-coo?newreg=6fd794fac6bd4ee7beaa30633f9484f5">Invariance of Lagrange on addition of total time derivative of a function of coordiantes and time</a> and while th... | 3,073 |
<p>I have to calculate<br>
$$ i_\rho \times i_\phi $$ it should be $$ i_\theta $$ but in my notes I have $$ - i _\theta $$</p>
<p>Which one is correct? How can I do this kind of operations without mistakes?</p> | 3,074 |
<p>Most quantum mechanics texts include a phrase such as 'any ket can be written as a sum of eigenkets of a given observable'.</p>
<p>I have problems with the generalities of <em>any</em> ket.</p>
<p>Does this literally mean <em>any</em> ket, or does it mean any ket of the same observable? It seems odd that any ket, ... | 3,075 |
<p>Plenty of material on the web will tell you what to expect when you run a 50/60Hz 3-phase induction motor at 60-80Hz, but what if you would like to run it at 140Hz? or 250Hz? Or at any frequency?</p>
<p>Currently we have a 50Hz motor which drives a conveyor via a chain arrangement that gears up by a factor of 2.8 (... | 3,076 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/1639/whats-the-difference-between-running-up-a-hill-and-running-up-an-inclined-tread">What's the difference between running up a hill and running up an inclined treadmill?</a> </p>
</blockquote>
<p>I... | 69 |
<p>I have a book saying,</p>
<blockquote>
<p>$\int \delta(x-x')\psi(x)dx = \psi(x')$ where $\psi(x) = \langle x\lvert\psi\rangle$, so our definition of delta function would be $\langle x'\lvert x\rangle = \delta(x-x')$.</p>
</blockquote>
<p>However I could find some documents (<a href="http://hitoshi.berkeley.edu/2... | 3,077 |
<p>In a question <a href="http://physics.stackexchange.com/questions/30524/does-a-interstellar-spacecraft-traveling-at-relativistic-velocity-require-contin">here</a> Ron Maimon comments that "relativistic mass makes gravity, not rest mass."</p>
<p>If so, does that mean that the faster that stars orbit the galaxy the l... | 3,078 |
<p>Some of the distant galaxies appear to be receding from us faster than the speed of light due to stretch of the space between us and those galaxies.</p>
<p>By an analogy with the <a href="http://en.wikipedia.org/wiki/Ant_on_a_rubber_rope" rel="nofollow">ant on a rope</a> paradox, the light emitted from those galaxi... | 3,079 |
<p>$\newcommand{\ket}[1]{\left|#1\right>}$
I have the next protocol:</p>
<ol>
<li><p>$A$ tosses a fair coin $a\in \{0,1\}$, if $a=0$, $A$ sends to $B$ $\ket{\psi_0}=\ket0$, if $a=1$ $A$ sends to $B$, $\ket{\psi_1}=\ket{+}$.</p></li>
<li><p>$B$ now picks randomly $b\in \{0,1\}$.</p></li>
<li><p>$A$ sends to $B$, the... | 3,080 |
<p>I'm new here, loving this website and I'm having some difficulty with the wilson-loop operator in kitaev's honeycomb model.</p>
<p><strong>problem statement</strong>
The Kitaev model (<a href="http://arxiv.org/abs/cond-mat/0506438" rel="nofollow">Kitaev, 2006</a> is the original paper) consists of spins residing at... | 3,081 |
<p>Suppose I have two triangles relatively close together (so they probably shouldn't really be treated as point masses). I want to calculate the gravitational force (and potentially torque?) generated between the two bodies in the 2D plane.</p>
<p>For spheres/circles you can just treat them as point masses and go fr... | 3,082 |
<p>The stature and design of the human body. Is it possible that the best physical structure belongs to a human being? If not. What are the flaws in it and what improvements could be done?
Is there actually a perfect physical design in terms of strength and agility?</p> | 3,083 |
<blockquote>
<p>If a projectile is launched at a speed $u$ from a height $H$ above
the horizontal axis, and air resistance is ignored, the <strong>maximum</strong>
range of the projectile is $R_{max}=\frac ug\sqrt{u^2+2gH}$, where $g$ is the
acceleration due to gravity.</p>
<p>The angle of projection to ac... | 3,084 |
<p>When we measure a physical quantity multiple times, we can calculate several values which should help us understand the whole measurement better: Standard deviation, variance, median, average, and so on.
What Im interested in: How many measurements should I take to get a representative number?
Clearly it depends on ... | 3,085 |
<p>On the Wikipedia page on <a href="http://en.wikipedia.org/wiki/Superfluidity" rel="nofollow">superfluidity</a> one can find the sentence</p>
<blockquote>
<p>not all Bose-Einstein condensates can be regarded as superfluids, and not all superfluids are Bose–Einstein condensates.</p>
</blockquote>
<p>So I was wonde... | 3,086 |
<p>This one has been in my mind for years, but I simply can not find any reason for this event.</p>
<p><strong>The Situation</strong></p>
<p>Imagine yourself sitting in the living room while watching television. It's 9 p.m and the news are on. Suddenly the news presenter announce of an event and contacts a field repo... | 3,087 |
<p><a href="http://en.wikipedia.org/wiki/Ostwald_ripening">Ostwald's Ripening</a> is a phenomenon where the surface area to volume ratio of droplets causes small particles to shrink until they disappear and for droplets above a certain volume to continuously grow. This is due to mechanisms of evaporation and condensat... | 3,088 |
<p>Let's say it's a laptop charger not connected to a laptop, and it is frayed near the tip. I am guessing about 20Volts runs through that area. Now if a person touches a bit of plastic below the frayed area, and they receive a painful shock in the finger but not enough to throw them back, about how much percentage of ... | 3,089 |
<p>I don't have any physics background (except the material we did in high school-long time ago).<br>
I was watching a documentary with Stephen Hawking about whether God created the Universe and I could not follow one of the arguments.<br>
<strong>Note:</strong> This is <strong>not</strong> a theological question. I am... | 3,090 |
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