# Tag Info

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It is an old conundrum how and why Newton's 3rd law fails for the differential form of Biot-Savart. To quote Bleaney & Bleaney:"Page and Adams {1945) have shown that there is no real violation, since the electromagnetic field of the current elements possesses momentum which is changing at a rate just equal to the difference of the two forces." Leigh Page ...

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To see if this is possible we can use a formal material selection approach of the kind presented in "Material Selection in Mechanical Design", Elsevier, M.F.Ashby. Our objective is to maximize buoyancy while keeping within the no-buckling constraint. To make things easier I suggest some simplifications. First, Poisson's Ratio does not vary much for most ...

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The force on a magnetic moment (magnet) in a magnetic field depends on the magnetic field gradient. (How fast the field is changing in space.) So you don't really want a big field, but a big field gradient. The force from a single coil has a rather complicated dependence on position. Maybe I can sell you one of these? ...

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Experimental data is given in http://journals.aps.org/pr/abstract/10.1103/PhysRev.98.889 - unfortunately I only have access to the abstract. It may be worth taking a look. The shape of the cathode does not matter. The material does. Key to solving this problem is knowing the work function of the material - that is the minimum energy that an electron needs ...

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It is very hard to keep track of all the experiments that have been done so far and the way in which they were done and under what assumptions. For instance, Newton's inverse square law is a "weak field limit" of general relativity. It works really well on a lot of scales. But on which scales was it actually precision-tested? Also, the experiment is often ...

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We do not validate theories. We fail to falsify them. The whole scientific method is about the crucial fact that we will never have all experimental facts, and that tomorrow can always yield an observation that will invalidate what we have held to be true for centuries. And so science becomes an endless process of thinking up hypotheses, statements that ...

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As far as data of particle physics goes the theory going by the name of Standard Model embeds the overwhelming majority of data from experiments and observations (astrophysics). It is validated by the data, and its predictions pan out, the recent one the discovery of the Higgs boson. Of course there are many parameters in the SM fitted from previous data. ...

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New theories don't just appear fully formed from the febrile brains of the more lunatic theorists. To convert an idea for a new approach into a construction capable of making predictions is a vast amount of work often taking years. Theorists are only willing to put in such a large amount of effort if there is a known target to aim at. For example this might ...

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There are indeed two honeycomb structures in the picture, but as suggested by the inset in the left bottom corner, the smaller one corresponds to the atoms. The graphene in the scanning tunneling microscopy (STM) picture you show is adsorbed on an Iridium surface with Miller indices (111). Since the lattice of the Iridium atoms at the surface and the ...

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Let $W_a$ and $W_w$ be the weight of the object in air and water. V be the volume of the object. As mentioned 9/10 of the object is immersed in water. $\rho$ be the density of water, Principle of Archimedes states below expression $$W_a-W_w = 9/10 * V* \rho.$$

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The density of water is 1 g/ml. If the volume of the object is 100 ml and the object weighs 90 g, it is less dense than the water (0.9 g/ml) and hence only 90 ml of the object will be submerged (depending in the shape), leaving 10 ml of the object exposed above the water level.

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There is already a number of good answers, but in addition let's compare LHC, the "useless" particle collider; with ITER, the path to the final solution of the humanity's energy hunger. They share technologies in the fields of superconductivity, vacuum, radio frequency, diagnostic instrumentation... the latter would probably not being constructed right now, ...

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Phenomena such a paramagnetism and ferromagnetism cannot be explained using classical statistical mechanics. This is called the Bohr-van Leeuwen theorem. An explanation of these phenomena need us to invoke quantum mechanical ideas such as spin.

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According to link from foregoing comment $a_i$ measurments are inderect, so errors are $$\Delta a_{i}=\sqrt{\sum_{k}\left(\frac{\partial a_{i}}{\partial w_{k}}\Delta w_{k}\right)^{2}}.$$ After calculations it yields $$\Delta a_{i}= \frac{1}{\left(\sum_{j}\frac{w_{j}}{A_{j}}\right)^{2}A_{i}}\sqrt{\sum_{k}\left( ... 4 Yes, experiments involving magnetism at the quantum level have been performed. For example, precise measurements involving the spin magnetic moment of an electron have established that the anomalous magnetic dipole moment predicted by quantum electrodynamics is correct. The experiments involved are among the most precise experiments ever performed; see the ... 1 1GHz is not NMR but ESR (unless you can find a 22T magnet...). I wouldn't try anything else than water for an NMR demonstrator experiment. It's cheap and the proton density is high. I think they are usually adding a little bit of copper sulfate or so as a quencher, but I didn't look into that. Your main worry is the magnetic field. I would try to generate ... 5 You are thinking too much physics. Instead, think about how you process the physics data that is generated from the experiments. The answer is that there are not only physicists at CERN but also - and actually quite a lot - hardware and software engineers. The detectors are one huge combination of custom built hardware. From there on it continues to custom ... 13 Just to mention the latest developments brought up from neutrino science, it seems that the useless, wimpy, weakly interacting neutrinos (and their anti-neutrino sisters) can be harnessed to detect and monitor nuclear reactors anywhere in the world that violate non-proliferation agreements I remember a discussion about a really big neutrino beam that could ... 36 Places like CERN are a huge forcing function for computer science - think high performance computing, networking, data storage, etc. If my memory is correct, Tim Berners-Lee was at CERN when he started developing the WWW... 2 It is indeed possible to make experimental realizations which are very close to the ideal infinite quantum well. The cleanest way to do this is using what are known as nanostructures / heterostructures in semiconductor joints, as well as quantum dots and quantum wires. Semiconductor nanostructures work by confining electrons to the interface between layers ... 68 The truth is we don't know. But when you think about it, how can we know? If we knew what technology would eventually come out of experiments like this, why would we not build that technology now? Large expensive machines like the CERN super-collider help us to further understand that laws of nature. And through understanding these laws, new technologies ... 34 In practice very little new technology results from experiments like those at CERN. While they are pushing the envelope on some things like the design of resonators, power klystrons and particle detector technology, the immediate technological return on those things is relatively small, even though one can argue that modern x-ray imaging (tomography) has ... 1 It is currently possible to measure gravity between the single atom and the Avogadro number of atoms. The gravitational energy corresponding to the interaction of electron and proton at the distance of Bohr radius in term of h omega corresponds to omega = 10^-23 Hz and so 1 Hz will be obtained where the second mass is the Avogadro number of protons. This ... 0 Altimeters based on barometric pressure should work equally well below the surface as above the surface. (You would either have to calibrate the altimeter based on the known local atmospheric pressure, or average the reading over a long period.) 1 If you are just looking to simulate the data produced at the LHC then the right program to use is Madgraph. It is by far the most popular Monte Carlo generator to use for simulations at the LHC and can produce events for any process you want. Madgraph will then also invoke Pythia and PGS to simulate hadronization and detector simulations if you wish. There ... 1 Geant4 is probably the closest thing you could conceivably get. It's a detector simulation software package with a steep learning curve that's heavily used in the HEP community, and, as far as I know, is available for anyone to download and build. Full disclosure - I did HEP experiment once upon a time but that was 20+ years ago. So if someone currently ... 0 You did not say that you did not have an Internet connection and a computer with a browser. If you knew the name of the underground facility and they where in USA, the guards and the staff probably have a licensed surface transmitter licensed by the American FCC. The transmitter is for surface perimeter security and staff trips to the local store for ... 5 I hear that surveyors who work underground in mines and tunnels use a gyro-theodolite. My understanding is that a gyrocompass is based on the same physical principles and will also work underground. When either device is turned on, it spins up an internal gyroscope. Then the rotation of Earth leads to torque-induced gyroscopic precession of that gyroscope, ... 26 A precise measurement of the Coriolis force will not only give you your latitude, but will also tell you which direction is true north. A compass will tell you which direction is magnetic north, and the combination of knowing your latitude and your magnetic declination will give you your longitude. Measuring the long-term average air pressure, assuming ... 8 John's answer gives some ideas for latitude and longitude. You could measure your altitude (read depth) by measuring the weight of a known mass. In a perfectly uniform, spherical Earth, the weight is proportional to your distance from the center. 16 A Foucault pendulum will tell you your latitude. The rate of rotation per day relative to the Earth is:$$ \omega = 2\pi\sin\theta $$where \theta is the latitude (positive for north and negative for south). To a first approximation determining the longitude is impossible because to a first approximation the Earth is axially symmetric. If you have an ... 19 The detector that took that image--Super Kamiokande (super-K for short)--is a water Cerenkov device. It detects neutrinos by imaging the Cerenkov cone produced by the reaction products of the neutrinos. Mostly elastic scattering off of electrons:$$ \nu + e \to \nu + e \,,$$but also quasi-elastic reactions like$$ \nu + n \to l + p \,,$$where the neutron ... 19 The neutrinos are coming straight at us. Indeed, their interactions with anything along the way are minimal at best. The reason the image is so big is that the angular resolution of the detector is rather poor (compared to, say, an optical telescope). This is not unexpected when it comes to neutrino telescopes. The details of how the detector work are ... 0 A quantum of EM radiation has energy E=hc/\lambda. For a number state, the energy is E=nhc/\lambda. To find the power this corresponds to, imagine that all of those excitations are being generated in a laser in a time \tau. The rate of energy production (the power) is then P=nhc/\lambda\tau. The average occupation number of a coherent state is ... 2 There are several ways to create Bose-Einstein condensates or systems that behave that way, there are ultracold atomic gases, solid state quasiparticles, and even photon condensates. Since you are obviously interested in ultracold atomic gases, I am going to cite Experimental methods of ultracold atomic physics by Kurn and Thywissen: The material must ... 0 The interaction is not a measurement because the probability that it will produce a measurable change in the momentum of the reflecting object is extremely small. The magnet is in a mixed state in which its momentum has a range of values that is large compared to the change in momentum produced by the force exerted by the electron. So the shift in the ... 12 My answer to this is that the LHC costs were of the same order of magnitude as one aircraft carrier. The total cost of construction for each ship was around 4.5 billion Of which several are around The cost of the LHC was With a budget of 7.5 billion euros (approx. 9bn or £6.19bn as of June 2010), So we have one country, the US spending same ... 1 One could probably measure the light pressure of a photon gas on a pair of parallel mirrors. Experimentally that's on the order of 1e20+ particles in a relatively small setup with two dielectric mirrors and a laser. The resulting force should be around 1e-7N, which is easily measurable. Would you accept that as an implementation, or are you looking for an ... 2 This is actually more subtle than you would think it would be. First, remember that a fourier transform is defined, for some time-dependent signal F(t), as{}^{1}:$$F(\omega) = \frac{1}{\sqrt{2\pi}}\int_{-\infty}^{+\infty} dt\, e^{i\omega\,t} F(t) Well, this is great in special relativity, but in general relativity, what time do we actually use? ...

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You will generally have three types of trajectories, periodic, quasiperiodic and chaotic. Plot the $\theta_1, \theta_2$ and these three will manifest as A Lisajouss-like curve, i.e. a curve which closes after a finite amount of time. This would be a periodic trajectory. A "box curve" shifting every once in a while, filling regularly a certain area and ...

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As a general rule of thumb, you can often assess the importance of air resistance by considering the mass of the air swept out by an object compared to the mass of the object itself. Though if you are being a little more accurate, you should estimate the ratio of the drag force to a relevant force for your problem. Air Drag To start, let's first try to ...

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The forces which a fluid through which a solid body is moving can be separated on the basis of their direction: the force along the body's direction of motion is a drag. The force perpendicular to the direction of motion (assuming for simplicity the body to be rotationally symmetric with respect to the velocity axis) is called lift. The drag comprises ...

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The drag force [1] is proportional to the square of the velocity, the density of the surrounding medium and the product of the cross section of the projectile and the drag coefficient [2] of your projectile. You need to compare this force to other forces involved to determine if you can omit it in your calculations. ...

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There's an old theory called "tired light" where the momentum is lost due to waves hands some other reason, but as far as I'm aware this has been pretty much discounted these days. The background behind the current-best-theory is this: When you look at light from a star it's not a smooth spectrum, it has a series of dark lines in it, an "emission ...

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As far as I understand, it has something to do with Hubble's Law. Essentially, based on looking back at energy density of a distant star at one point, and then looking at it again, and determining that it has diminished, or something along those lines. I assume it's a far fancier version of looking at a light you just passed as you drive down the road. If ...

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The middle magnet is spinning, so it attracts and repulses the other two magnets once per rotation. It is spinning "super fast" - that is so fast that the attraction and repulsion phases are super short. The other magnets are just too heavy to even start moving visibly in one or the other direction, before the direction of the force changes again. We ...

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Vacuum magnetic birefringence basically involves the same loop diagram as light-light elastic scattering except that two of the four photons come from a magnet. Detecting this effect is the aim of the PVLAS experiment in Ferrara, Italy. See arXiv:1406.6518 and references within. The experiment is running at the moment but the sensitivity is not good enough ...

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Misaligning one of the end mirrors will produce a set of vertical or horizontal fringes at the detector plane (depending on the misalignment of the mirror). The number of fringes is proportional to the misalignment angle of the mirror and inversely proportional to the wavelength of the light. When first setting up the alignment of the interferometer, this ...

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The easiest method is to use the transfer matrix: http://en.wikipedia.org/wiki/Transfer-matrix_method_(optics) Your question is actually related to a recent Science paper: http://dx.doi.org/10.1126/science.1249799

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In general Allen variance is not a good way to characterize non-harmonic processes and processes which modulate the phase, frequency or amplitude of the oscillator in a non-stochastic manner for the same reason that the conventional variance is not a good measure for processes that do not, at least approximately, follow a normal distribution. For practical ...

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