question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>The space-time interval equation is this:</p>
<p>$$\Delta s^2=\Delta x^2+\Delta y^2+\Delta z^2-(c\Delta t)^2$$</p>
<p>Where, $\Delta x, \Delta y, \Delta z$ and $\Delta t$ represent the distances along various coordinates according to an observer, and $\Delta s$ is the space-time interval. All observers agree on th... | 3,815 |
<p>I am doing some <a href="http://physics.stackexchange.com/questions/28563/hours-of-light-per-day-based-on-latitude-longitude-formula">calculations</a> to see how many hours of light does a specific location (identified by latitude and longitude) has in a specific day of the year.
Contrary to my expectations I get a ... | 3,816 |
<p>$s$ is <em>sharp</em>, $p$ for <em>principal</em>, $d$ for <em>diffuse</em>, $f$ for <em>fundamental</em>.</p>
<p>Where do all those term come from? I do not see any link with the corresponding shapes.</p> | 3,817 |
<p>I've recently been learning about Fourier optics, specifically, that a thin lens can produce the Fourier transform of an object on a screen located in the focal plane.</p>
<p>With this in mind, does the lens in a human eye produce a Fourier transform on the retina?</p>
<p>Any help appreciated</p> | 3,818 |
<p>I'm studying fluid mechanics and I have the following doubt: on the book, the author first deduces the differential form of the equation of balance of momentum. First he argues that if the fluid is ideal and is contained in a region $D\subset \mathbb{R}^3$ and if the pressure is $p : D\times \mathbb{R}\to \mathbb{R}... | 3,819 |
<p>I went to a restaurant yesterday and while I was eating dessert, I saw a <strong>standard stainless steel spoon (note the alliteration!</strong>) balancing on a plate. It was balancing on its handle, and I started wondering, </p>
<p>Why is that particular point the center of gravity for the spoon?
Thanks.</p> | 3,820 |
<p>Do all the planets in our solar system have the same angular speed? Physics teacher says yes, my research is not crystal clear. I want to make sure I have the right information for future reference.</p> | 3,821 |
<p>In regular quantum mechanics of particles, I have the Schrodinger evolution picture for a <strong>general state</strong></p>
<p>$$ i\hbar \frac{d}{dt} \left|\psi(t)\right> = \hat H \left|\psi(t)\right> $$</p>
<p>then we take the inner product with respect to $ \left< x\right| $ to obtain the equation in ... | 3,822 |
<p>Why is there a size limitation on human/animal growth? Assuming the technology exists for man to grow to 200 feet high, it's pretty much a given that the stress on the skeletal structure and joints wouldn't be possible to support the mass or move...but WHY is this? if our current skeletal structures and joints can s... | 3,823 |
<p>I - and others - observe that when a musical performance ends, the echo of the last chord appears to rise in pitch by up to a quarter tone while the echo decays. This effect appears to be independent of the type of performance - orchestral or choral. I am tempted to assume that this is related to what is known in el... | 3,824 |
<p>Would the excess charge on a conductor move to surface until the electric field inside become zero if the Coulomb law was for example $\frac{1}{r^3}$? If yes, would the distribution $\sigma(x,y)$ be different from when it is $\frac{1}{r^2}$?</p> | 3,825 |
<p>Let's say I have a law like this,
$$D=\frac{c}{r}$$
where $c$ is a constant, $r$ a distance in meter. my measures of $r$ are [$0.02m$, $0.01m$], then $<r>=0.015m$ and $\delta r = \pm 0.005m$. So now if I want to calculate $D+\delta D$ should I use $+\delta r$ or $- \delta r$ in my equation?</p>
<p>because if ... | 3,826 |
<p>I recently read about the <a href="http://en.wikipedia.org/wiki/Kessler_syndrome" rel="nofollow">Kessler Syndrome</a> and am thinking about writing a story set in a world suffering from it. In the interest of realism, I am curious about the secondary effects which would be produced by this kind of scenario.</p>
<ul... | 3,827 |
<p>The <a href="http://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation">Schrödinger equation</a> describes the quantum mechanics of a single massive non-relativistic particle. The <a href="http://en.wikipedia.org/wiki/Dirac_equation">Dirac equation</a> governs a single massive relativistic spin-½ particle. The photon i... | 3,828 |
<p>In interferometry (specifically, in the domain of <a href="http://en.wikipedia.org/wiki/Fabry_Perot" rel="nofollow">Fabry-Perot cavities</a>), the function $$f(\phi) = \frac{1}{1 + F \sin^2 \phi}$$ , which describes the shape of the resonant structure of the cavity, is often called the "Airy function" (for instance,... | 3,829 |
<p>Within the context of Einstein space-times, we know that the contraction of the Weyl tensor across a set of indices always vanishes, like so :</p>
<p>$$C{^{\alpha }}_{\mu \alpha \nu }=0$$</p>
<p>From a purely mathematical standpoint this should be straightforward ( but perhaps tedious ) enough to prove from the de... | 3,830 |
<p>Both energy and mass gives has gravity. If an object receives energy, it will appear heavier and space will curve slightly more around that object.</p>
<p>That energy could be potential energy, or static energy.</p>
<p>If an object A is accelerated toward a black hole B, it gains velocity and thus energy. It will ... | 112 |
<p>Does anyone know where I can find a pedagogical explanation of large-N factorization in SU(N) gauge theories or nonlinear O(N) sigma models (in the latter case the trace corresponds to a dot product).</p>
<p>The reference I am using is Polyakov's gauge fields and strings. However, I find the explanation of large-N ... | 3,831 |
<p>In the second edition of <em>Classical dynamics of particles and systems</em> by Jerry B. Marion, it is said that the van der Pol equation
$$\ddot{x}-\mu\left({x_0}^2-x^2\right)\dot{x}+{\omega_0}^2x=0$$
where $\mu$ is a positive parameter of small value, has a limit cycle with amplitude $|x_0|$ (I'm paraphrasing thi... | 3,832 |
<p>Assuming we have a plane with a propeller driven by an engine like <a href="http://selair.selkirk.bc.ca/training/aerodynamics/graphics/piston-turn-propeller.gif" rel="nofollow">this one</a> .
How would the torque reaction be generated if the piston is aligned with the plane center of mass? What I mean is, where are ... | 3,833 |
<p>This question seems a lot like one of those "Phylosoraptor" memes all over the Internet, and it might be very silly, but I've been thinking about this for a while.</p>
<p><strong>Is it possible that space is not actually expanding but rather, the speed of light is decreasing throughout the entire Universe?</strong>... | 113 |
<p>Let </p>
<p>$$\mathbf{H} = H_x \mathbf{u}_x + H_y \mathbf{u}_y + H_z \mathbf{u}_z$$</p>
<p>be a vector field whose components are defined with respect to the unit vectors $\mathbf{u}_x$, $\mathbf{u}_y$ and $\mathbf{u}_z$, so in the $(x,y,z)$ system of coordinates.</p>
<p><strong>Question 1</strong>: If we compute... | 3,834 |
<p>I have came to understand that humid air will help prevent electrostatic forces that can propel dust and cause it to cling to surfaces.</p>
<p>My first question: is this above statement true?</p>
<p>If the answer to the first question is true, then please continue: I have attempted to find designs for the various ... | 3,835 |
<p>In a question: </p>
<blockquote>
<p>To construct a solenoid, you wrap insulated wire uniformly around a plastic tube 12cm in diameter and 50cm in length. You would like a 2.2 A current to produce a 2.6 kG magnetic field inside your solenoid.</p>
<p>What is the total length of wire you will need to meet these... | 3,836 |
<p>my question is about how photons travel from a light source and hit an object.</p>
<p>When you look at an object being hit by light the whole surface becomes brighter.</p>
<p>What i'm trying to understand is why the entire surface lights up.</p>
<p>When the photons leave the light source they scatter out to hit o... | 3,837 |
<p>The heuristic argument for Hawking Radiation is, that a virtual pair-production happens just at the event horizon. One particle goes into the black hole, while the other can be observed as radiation.</p>
<p>I never quite understood this explanation. Say, a virtual pair is created. From the point of view of the "rad... | 3,838 |
<p>I have two 4,000V, 2.5mA, DC power supplies and am attempting to use them in such a way to cause a 6x4x1-inch ABS plastic object to repel dust from the ambient air and prevent this dust from settling on the object.</p>
<p>I understand that two points that have opposite electrical charges will attract each other and... | 3,839 |
<p>In AdS/CFT a charged Black hole is probably someway equivalent to introducing a chemical potential (<a href="http://physics.stackexchange.com/questions/7470/chemical-potential">Chemical potential</a>) at the boundary theory. Is there a quick way to see how it is or how does this correspondence work? </p>
<p>I am su... | 3,840 |
<p>The hall conductivity $\sigma_{xy}$ seems to reflect to some extent the response of a system in direction $\hat{y}$ to certain perturbation (electric field for example) restricted in $\hat{x}$ direction. </p>
<p>My question is, does a nonzero $\sigma_{xy}$ imply anything about the the physics of edge response, i.e... | 3,841 |
<p>A small ball of radius $r$ performes small oscillations within a hollow cylinder of radius $R$. What would be the angular frequency of the oscillations given that the rolling is without slipping?
The angle between the radius connecting the center of the hollow cylinder to the ground (my $y$ axis) and the line connec... | 3,842 |
<p>This question is metallurgical engineering, but I had a similar doubt regarding density of liquids and what causing it.</p>
<p>Forged parts refines defects, dislocations will be moved strengthening the metal. But will the density of forged metal change?</p>
<p>My earlier question was, what causes liquids to have d... | 3,843 |
<p>What unexplored areas (known unknowns) are there in atomic layer deposition (ALD)? What unexplored applications of ALD are there? It seems like people use it a lot for coatings of either insulators or sometimes transparent conducting contacts. What else could you do with it?</p> | 3,844 |
<p>When I was in some physics -lesson, probably something to do with Quantum Physics -- the teacher said that certain Maxwell equations would change if the Higg's boson is found. It is also possible that I have mixed something, he may have meant magnetic monotones. Anyway does there exist any change to Maxwell equation... | 3,845 |
<p>Could anybody suggest a reference for the present stellar models? <em>In particular</em>, I would appreciate references containing the core temperatures and pressures of neutron stars...</p> | 3,846 |
<p>Victor Stenger argues that the apparent randomness in quantum mechanics is a result of the randomness in the macroscopic detectors (similar to the randomness in the laws of thermodynamics) and is not something that is inherent to quantum mechanics (this is my interpretation of Stenger). This would imply that QM is u... | 3,847 |
<p>I am reading Zee's <em>Quantum field theory in a nutshell.</em> On time reversal he has</p>
<blockquote>
<p>Consider the transformation $t\rightarrow t'= -t$. We want to find $\Psi'(t')$ such that $i(\partial/\partial t′)\Psi′( t′) = H\Psi'(t′)$. Write $\Psi′(t′) = T\Psi(t)$, where $T$ is some operator to be det... | 3,848 |
<p>Say a canon is where the circle is, and it shoots two different canonballs at different angles, but at the same speed, which angle would make the cannonball hit the ground first?</p>
<p><img src="http://i.stack.imgur.com/6LZic.png" alt="enter image description here"></p>
<p>Intuitively I'd think they'd hit at the ... | 3,849 |
<p>Sorry if this is a silly question (engineer here), but I was wondering if the math in particle physics assumes that unitarity applies even between measurements. In other words, I take it that the evolution of quantum states is governed by an operator that ensures the probability of all possible events adds up to 1 ... | 3,850 |
<p>Two clocks are located at either end of a two light-hour long pole and motionless relative to the pole. Each clock transmits its time and notes that the other clock shows a reading two hours behind its own. That is, the clocks can be considered synchronised with each other.
There is a flashbulb at the midpoint of... | 3,851 |
<p>Consider a uniform disk rolling without slipping with a certain constant angular velocity.Firstly it is moving in sufficiently rough surface.What will happen if it crosses the rough surface and just enters the smooth frictionless surface in its way?Will it be in the state of pure rotation or attains translatory moti... | 3,852 |
<p>As I understand, the CIExy graphic maps "greenness", or rather middle-wavelengthness, to the Y axis and "redness", or rather long-wavelengtsness, to the X axis. The trapping used to reduce the 3d gamut of the human eye to 2d is that the gamut is specified for a certain constant luminosity, and long-wavelength + midd... | 3,853 |
<p>What is the difference between <a href="http://en.wikipedia.org/wiki/Stress_%28mechanics%29" rel="nofollow">stress</a> and <a href="http://en.wikipedia.org/wiki/Pressure" rel="nofollow">pressure</a>? Are there any intuitive examples that explain the difference between the two? How about an example of when pressure ... | 3,854 |
<p>That's all there is to it. Well... I was daydreaming about making gloves that had the ability to shock people when you punched them. I thought how it would be better if they didn't need a battery and I thought I wonder if you could put two repelling magnets on the knuckle that when forced to come together (by a punc... | 3,855 |
<p>The <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/uncer.html" rel="nofollow">Uncertainty Principle</a> is a relationship between measurements of pairs of attributes, position and momentum, as well as energy and time. Perfect precision of one attribute's measurement leads to a full lack of knowledge about the o... | 3,856 |
<p>Special Relativity (<a href="http://en.wikipedia.org/wiki/Special_relativity" rel="nofollow">SR</a>) paradoxes are old-hat. But as I read explanations, they tend to resolve issues of simultaneity by applying the appropriate math... but that seems to me to be proving the theory by positing the theory. Just because t... | 3,857 |
<p>Why did scientists study black body radiations from something as complicated as a hollow container rather than the radiation from something simple like a thin solid cylinder?</p> | 3,858 |
<p>Please give your explanation in layman terms, without throwing any complex equations at me.</p>
<p>We have a 5000 liter tank dug in ground and a water pump connected to this tank that draws water from it and fills a overhead tank. We also have a tap at the opening of the pump. (A T joint is connected to the output ... | 3,859 |
<p><a href="http://en.wikipedia.org/wiki/Planck_time" rel="nofollow">Planck time</a> is really a weird topic, if we try to find out that is it time or time interval.
It is the time taken by light to travel a Planck LENGTH so it must be time interval. But we also know that Planck length is MOST FUNDAMENTAL and it can't... | 114 |
<p>I've been reading about <a href="http://en.wikipedia.org/wiki/Scalar-tensor_theory" rel="nofollow">scalar-tensor</a> theories of gravity, such as Brans-Dicke theory, and I started thinking about the scalar field. Now, I know that the Higgs field is a scalar field, and of course has a quanta, the Higgs boson. Accordi... | 3,860 |
<p>I am given the following problem:</p>
<blockquote>
<p>If an airplane propeller rotates at 2000 rev/min while the airplane flies at a speed of 480 km/h relative to the ground, what is the linear speed of a point on the tip of the propeller, at radius 1.5m, as seen by (a) the pilot and (b) an observer on the ground... | 3,861 |
<p><strong>Questions:</strong></p>
<p>Three $x$ m long rods form an equilateral triangle. Two of the rods are charged to $+q$ C and the third to $-q$ C. What is the electric field strength at the center of an equilateral triangle?</p>
<p><strong>Attempt:</strong></p>
<p>I know how to find the electric field strength... | 3,862 |
<blockquote>
<p>During an interval of time, a tennis ball is moved so that the angle between the velocity and the acceleration of the ball is kept at a constant 120º. Which statement is true about the tennis ball during this interval of time?
Choose one answer.</p>
<p>a. Its speed decreases and it is changing... | 3,863 |
<p>Is it valid to approximate the function $$ Z(t)=\sum_{n}e^{-tE_{n}} ,\ t\ge 0$$ </p>
<p>by the integral over phase space: $$ \frac{ 1}{2\sqrt \pi}\int_{0}^{\infty}dxe^{-tV(x)}?$$</p>
<p>For example, in order to evaluate the zeta function over eigenvalues</p>
<p>$ \Gamma (s) \zeta _{H} (s,q) = \int_{0}^{\infty}dt... | 3,864 |
<blockquote>
<p>An object is thrown horizontally with a velocity of 30 m/s from the top of a tower. It undergoes a constant downward acceleration of 10 m/s2. The magnitude of its instantaneous velocity after 4.0 sec, in meters per second, is:</p>
</blockquote>
<p>To approach this question I first thought to myself t... | 3,865 |
<p>Basically I have a set of vectors of unit length, $\{\nu_i\}$, describing the movement of phonons (all orthogonal to each other), $\{\omega_i\}$. Lets say I only have two atoms, $m_1$ and $m_2$. In this case with only two atoms I have $N=3\times2=6$ modes. In the following it really doesn't matter how many modes I h... | 3,866 |
<p>Following up on <a href="http://physics.stackexchange.com/questions/65838/lorentz-transformation-of-single-particle-states">this question</a>: Weinberg says </p>
<blockquote>
<p>In general, it may be possible by using suitable linear combinations of the $\psi_{p,\sigma}$ to choose the $\sigma$ labels in such a wa... | 3,867 |
<p>As in <a href="http://physics.stackexchange.com/questions/65834/why-are-non-momentum-dofs-of-single-particle-states-discretely-labeled">this question</a>, let $\psi_{p,\sigma}$ be a single-particle 4-momentum eigenstate, with $\sigma$ being a discrete label of other degrees of freedom.</p>
<p>Weinberg discusses the... | 3,868 |
<p>In evaluating the vacuum structure of quantum field theories you need to find the minima of the effective potential including perturbative and nonperturbative corrections where possible.</p>
<p>In supersymmetric theories, you often see the claim that the Kähler potential is the suitable quantity of interest (as the... | 3,869 |
<p>In a critical theory with dynamical critical exponent $z \neq 1 $, which amongst frequency, $\omega$, and dispersion, $E(\vec{k})$, may be referred to as ''energy''? I'm confused about this since in general $\omega$ and $E(\vec{k})$ can have different scaling dimensions. Some clarification would be very appreciated.... | 3,870 |
<p>My question is in reference to the action in equation 4.130 of Becker, Becker and Schwartz.
It reads as, </p>
<p>$S_{matter}= \frac{1}{2\pi}\int (2\partial X^\mu \bar{\partial}X_\mu + \frac{1}{2}\psi^\mu \bar{\partial} \psi_\mu + \frac{1}{2}\tilde{\psi}^\mu \partial \tilde{\psi}_\mu)d^2z$</p>
<ul>
<li><p>Its not ... | 3,871 |
<p>Following the treatment of Weinberg, chapter 2, we consider $\psi_{p,\sigma}$ as single-particle eigenstates of the 4-momentum. Weinberg says that $\sigma$ labels all other degrees of freedom and we take this label to be discrete for one-particle states. So what exactly is the physical implication of discrete and co... | 3,872 |
<p>I know that I can just read off the phase diagram for water (for the surface atmospheric pressure on each object). But could there possibly be some nuances that someone might miss just from viewing the diagram?</p> | 3,873 |
<p>Will the <a href="http://www.jwst.nasa.gov/" rel="nofollow">James Webb Space Telescope</a> (JWST) be able to capture, or ever be used for, anything similar to the <a href="http://en.wikipedia.org/wiki/Hubble_Ultra-Deep_Field" rel="nofollow">Hubble Ultra Deep Field</a> (HUDF)?</p> | 3,874 |
<p>Currently there is a <a href="http://astronomy.stackexchange.com/questions/914/what-is-an-approximation-of-the-average-number-of-supernovae-every-century-in-the">unique chance</a> for amateur astronomers to observe a very near <a href="http://en.wikipedia.org/wiki/Type_Ia_supernova">type Ia supernova</a>, named <a h... | 3,875 |
<p>What knowledge of computer science should I have, to be able to pursue research in quantum computing. I am a Physics undergrad and would take three core courses in QM, before the completion of my degree. SO I guess necessary QM would be done. What about computer science?</p> | 3,876 |
<p>I've studied differential geometry just enough to be confident with differential forms. Now I want to see application of this formalism in thermodynamics.</p>
<p>I'm looking for a small reference, to learn familiar concepts of (equilibrium ?) thermodynamics formulated through differential forms.</p>
<p>Once again,... | 3,877 |
<p>I am rather confused because it would seem that mathematical conclusions I have drawn here goes against my physical intuition, though both aren't too reliable to begin with.</p>
<p>We have a potential step described by $$V(x)=\begin{cases}0& x\le0\\V_0 & x>0\end{cases}$$</p>
<p>and a wavefunction $\psi(... | 3,878 |
<p>A billard ball is struck with a cue. The line of action of the applied impulse is horizontal and passes through the center of the ball. The initial velocity $v_0$ of the ball, its radius $R$, its mass $M$ and coefficient of friction $\mu_k$ between the ball and the table are all known. How far will the ball move bef... | 3,879 |
<p>I'm CS major trying to learn QFT on my own . I'm trying to make an efficient study plan .The problem is that I've never read any textbook from cover to cover and solved all the problems .What of the following is the most productive approach:</p>
<p>A-To start reading textbooks from cover to cover like reading most ... | 115 |
<p>I have a question which is inspired by considering the light field coming off an incandescent lightbulb. As a blackbody radiation field, the light is in thermal equilibrium at temperature $T$, which implies that each normal mode has a <em>mean</em> energy given by Planck's law, and a random phase. Thus, if I were to... | 3,880 |
<p>In an oscillations exercise there is a spring attached to another spring, attached to a block.</p>
<p>Long story short: I have to find the global $k$.
In the solutions it says:
"Because the springs are massless, they act similar to a rope under tension, and the same force $F$ is exerted by each spring."</p>
<p>I d... | 3,881 |
<p><a href="http://www.keelynet.com/tesla/00685958.pdf" rel="nofollow">http://www.keelynet.com/tesla/00685958.pdf</a></p>
<p>An elevated, insulated copper plate, a patented Tesla Condenser, and a voltage inverter, we've got free electricity right?</p>
<p>admittedly small, but as a proportion to potential difference i... | 3,882 |
<p>On page 135 in Srednicki he defines the functional integral </p>
<p>$$Z(J) = \int\mathcal{D}\phi\,\exp\Big[\mathrm{i}\big(S+\int\mathrm{d^4}y \,J_a\phi_a\big)\Big], \tag{A}$$ </p>
<p>where $S$ and $J_a$ are the action and sources respectively (sum over $a$). What I don't seem to get is that when he cosiders a smal... | 3,883 |
<p>I just need a confirmation on a problem that I am dealing. In my problem I have a statioary kaon which spontaenously splits into two pions which are headed in different directions.</p>
<p>Is it possible to write the energy conservation like this: </p>
<p>\begin{align}
E_1 &= E_2\\
\sqrt{{E_{01}}^2 + (p_1c)^2} ... | 3,884 |
<p>I am not quite understanding what needs to be done but I am assuming that I must combine the two equations and get rid of the variable $T$ in order to make this equation of $f$ below:</p>
<p>(Note:These formulas are in the regards to inclined planes)</p>
<p><strong>Equation of $f$:</strong>
$$f=g(m-M\sin(\theta))... | 3,885 |
<p>Let us consider a routine mechanics problem.A block of $ 10kg $ rests on another block of $ 2kg $ on a frictionless table.Let $ \mu = 0.2 $ be the coefficient of friction(let's neglect the difference between coefficients of static and kinetic friction here)between the surfaces of the two blocks.
<img src="http://i.s... | 3,886 |
<p>I worked 20years in a very high magnetic field at an Aluminum foundry. I'm now in my 50's and I don't know or am I aware of any negative effects from this. Is there anything I should be on the look out for?
I am also trying to understand Tesla's understanding of Earth's magnetic field an tapping into that power.
Can... | 116 |
<p>I don't understand how to solve this:</p>
<p>A $\pi^+$ decays into a muon and neutrino. Find the pion's energy if</p>
<ul>
<li>max $E_\nu$ / min $E_\nu$ = 100/1;</li>
<li>$m_\nu = 0$</li>
<li>$m_\pi*c^2 = 140\text{ peta-eV}$</li>
</ul> | 3,887 |
<p>Can anyone please provide an intuitive explanation of why phase shift of 180 degrees occurs in the Electric Field of a EM wave,when reflected from an optically denser medium?</p>
<p>I tried searching for it but everywhere the result is just used.The reason behind it is never specified.</p> | 358 |
<p>I read that there is an effort to define a kilogram in terms that can exactly be reproduced in a lab. Why has it taken so long to get this done? It seems this would be fairly important.</p>
<h1>Edit</h1>
<p>Today I got around to finding the references.<br>
You can see the international prototype of the kilogram IP... | 184 |
<p>In one dimension -</p>
<p>How can one prove that the Hammiltonian and the parity operator commute in the case where the potential is symmetric (an even function)?</p>
<p>i.e. that [H, P] = 0 for V(x)=V(-x)</p> | 3,888 |
<p>Say you had a very radioactive element in a confined area: could that element (hypothetically speaking) go through beta decay, then, once it has too many protons could it immediately go through electron capture to become that same radioactive element OR become another unstable element that will again go through beta... | 3,889 |
<p>I don't quite understand what a self-sustained discharge is. I figure it means that the processes involved are self supporting and generate themselves, so that I don't have to put energy into the system and generate an outside voltage at the electrodes. Can an experimental device ever by fully self-sustained? If yes... | 3,890 |
<p>In my Computer science class I was given a problem where I have to simulate a bouncing ball using "real physics". I have been trying to find a equation that will simulate the height of the bounce given a gravity and an arbitrary mass. And I will need to calculate the next bounce and it's height. A lot of the equatio... | 3,891 |
<p>I am trying to use <a href="http://archive.eso.org/cms/tools-documentation/jsky/" rel="nofollow">JSkyCat</a> to mark a set of coordinates on a FITS image, and have found the dialog for choosing a catalog file to load. However, I am having trouble finding any documentation on what format it expects (and my guesses ha... | 3,892 |
<p>I know that we now have telescopes which can capture the images of the stars and galaxies millions of light-years away from us.</p>
<p>Does the telescope capture the past image of the star, i.e. the light which it emitted centuries ago? </p>
<p>What guarantee is there that the star is still alive? </p>
<p>What ba... | 3,893 |
<p>On Earth, North is determined by the magnetic poles of our planet. Is there such a thing as "North" in outerspace? To put it another way, is there any other way for astronauts to navigate besides starcharts? For instance, if an astronauts spaceship were to be placed somewhere (outside of our solar system) in the mil... | 3,894 |
<p>On an elliptical treadmill a regular person can easily burn 1000 calories in one hour (treadmill reports calories burnt). This translates into:
$$(1\times 10^3\mathrm{cal/hr}\times 4.2\times10^3\mathrm{J/cal})/3.6\times 10^3\mathrm{s/hr} \approx 1.2 \; \mathrm{kW} \approx 1.5 \; \mathrm{hp}$$
On the other hand, <a h... | 3,895 |
<p>Why is it that neutrons evaporate from nuclei more easily than protons do? </p>
<p>Intuitively, since protons are electrostatically repelled (in addition to whatever nuclear forces they have in common with neutrons), one would expect protons to be ejected more readily than neutrons. (Maybe this is even what does ha... | 3,896 |
<p>The equation of state for a perfect fluid is that $p=\omega \rho c^{2}$, where $p$ is the pressure, $\rho$ is the density, $c$ is the vacuum speed of light, and $\omega$ is called the equation of state parameter. $\omega$ may be constant or varying in time. I'm looking for broad answers (and references if possible) ... | 3,897 |
<p>Why can't the expansion of the universe be thought as the Big Bang itself still in progress? Why do we need to introduce dark energy? The Big Bang was powerful, and that explosion itself could still be continuing right?</p> | 3,898 |
<p>In the SM with gauge group U(1)xSU(2)xSU(3), those factors are associated to the gauge bosons associated with a local symmetry and the Higgs field provides masses to the elementary fermions AND the W,Z bosons (the photon is inert) through SSB. My question is, the Higgs boson has (likely) a mass of about 127 GeV, wha... | 3,899 |
<p>I'm reading about the acousto-optic effect and on the Acousto-Optical Tunable Filters on particular and wanted to understand the physics under its working. I found this paper</p>
<p><a href="http://dx.doi.org/10.1016/S0079-6727(03)00083-1" rel="nofollow">http://dx.doi.org/10.1016/S0079-6727(03)00083-1</a></p>
<p>w... | 3,900 |
<p>I have heard my friends referring to quantity ma as the "force of acceleration" whereas my teacher told us it can't be referred as so. Is it correct to refer that quantity a force? If not, how can we better describe this quantity?</p> | 3,901 |
<p>I am trying to solve a situation, where I'd like to know how much energy would be needed to push a mass of water out of a container. Here's an image to help understand:</p>
<p><img src="http://i.stack.imgur.com/3tyr0.png" alt="enter image description here"></p>
<p>The water tank has a height of 2 meters, length of... | 3,902 |
<p>Let a two dimensional system be in the state $\phi=|0\rangle\langle0|$, for any basis $M$ spanned by the orthogonal vectors $|\psi_0\rangle,|\psi_1\rangle$, we can measure $\phi$ in basis $M$ and obtain "0" and "1" with probabilities $p_0=\mathrm{tr}(|\psi_0\rangle\langle\psi_0|\phi)$, $p_1=1-p_0$. </p>
<p>My ques... | 3,903 |
<p>Particles can be represented as <a href="http://en.wikipedia.org/wiki/Wave_packet" rel="nofollow">wave packet</a>. So how do particles get <a href="http://en.wikipedia.org/wiki/Compton_scattering" rel="nofollow">scattered</a>?
Waves superimpose on one another, they don't bounce off of on one another.</p> | 3,904 |
<p>This is a long shot, but while the 100YSS conference is going on at Houston, i haven't been able to get a grip on myself and think in other, more mundane and short-term rewards as normal people do. The main thing that has been taking up my mind is scalable ways to stabilize and store positronium in a way that the ma... | 3,905 |
<p>I find the idea of the wave function being 'just' a collection of numbers (probabilities) quite alluring, and elegant in explaining away the whole 'collapse' business (see Luboš' answer to <a href="http://physics.stackexchange.com/questions/10068/on-the-nature-of-the-collapse-of-the-wave-function">this question</a>)... | 3,906 |
<p>In "The Elegant Universe," two individuals, George and Gracie, are noted to be moving relative to one another in space and wearing clocks. They sync their clocks upon passing each other. Each observes the other's clock to be ticking more slowly. Gracie communicates with George via cell. </p>
<blockquote>
<p>Graci... | 117 |
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