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Magnetic field resistance material: are there any? | [
"Shielding magnetic field without mu-metal\nI need to shield my device from magnetic interference, including earth magnetic field (if you move device around, it might be enough to cause slight currents i guess) and magnetic field caused by power nets, wires with large currents e.t.c . I know this could be achieved by making case out of mu-metal, but it seems that I can't find it anywhere (especially in small quantities). So, are the other, easier ways to shield magnetic field? Will multiple sheets of steel work for example?",
"How do permanent magnets manage to focus field on one side?\nThe actuator of a hard drive head consists of two very strong neodymium magnets, with an electromagnetic coil between them. If you take that apart, the magnets attract each other very strongly. There's no doubt the field between them is very strong. But if you flip them back to back, there is no repulsion force - there is pretty much nothing. While the magnets are very strong on one side, they seem completely inert on the other. I understand how a U-shape of a shaped magnet allows it to focus field near the two exposed poles, but how does a flat rectangular plate manage to keep the field over one flat, wide surface and nearly none near the other? [sorry about the heavy edit but it seems the question got totally muddled with irrelevant discussion about unipolar magnets and possibility or impossibility to remove magnetic field from one side. Only heavy rephrasing may help.] Edit: some photos: 1: The magnets stuck together. They hold really hard, I'd be unable to just pull them apart but I can slide one against the other to separate them.  The magnets in \"inert position\" - they don't act on each other at all, just like two inert pieces of metal.  The magnets seem to have two poles located on the surface off-center. Here, a normal magnet placed against the hard disk magnet, centering itself on one side, then flipped - on another.    The metal shield seems to act like completely unmagnetized ferromagnetic. I can stick the \"normal magnet\" any way I like to it, and it doesn't act on another piece of ferromagnetic (a needle) at all.  When I apply a small magnet to it, it becomes magnetic like any normal \"soft\" ferromagnetic - attracts the needle weakly. It behaves as if the (very powerful) neodymium magnet glued to the other side wasn't there at all.  Unfortunately the neodymium magnets are glued very well and so fragile I was unable to separate any without snapping it, and then the \"special properties\" seem to be gone."
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"Can an inhomogeneous magnetic field be built to slow down and catch a neutron? Neutrons have a measureable magnetic dipole momentum from their intrinsic spin. Is it possible to slow down and catch the neutron by imposing a force by an inhomogeneous magnetic field. I think the force the neutron experiences in a magnetic field is \\begin{align} \\bar{F} = \\bar{\\nabla}(\\bar{m}\\cdot\\bar{B}). \\end{align}",
"Cancel out Earth's Magnetic field Is there any tools except helmholtz coil to cancel out earth's magnetic field to calibrate magnetometers in practice.",
"Coercivity of a ferromagnetic material? I understand that coercivity is the field/force required to demagnetize/magnetize a ferromagnetic material. What if we had two opposite magnetic fields of different strengths values H acting on the same ferromagnet what would happen? **H1** = 50 Oe **H2** = 10 Oe The coercivity of the material is 0.5 Oe, what would happen? Will it stay magnetized to the stronger field(H1)? Or **magnetization = 0**?",
"Simulate the magnetic field of magnet I'd like to numerically simulate the magnetic field due to a cylindrical rare earth magnet of known dimensions at a bunch of points $\\vec{r}=(x,y,z)$ from its origin. My goal is to be as accurate as possible up to some global normalization which ultimately doesn't matter for my application. My approach is to simply assume the magnet is made of a continuum of dipoles and do the relevant integral: $$ \\frac{\\mu_0 m}{4\\pi}\\int\\int\\int \\frac{3\\left(\\hat{m}\\cdot\\frac{\\vec{r}-\\vec{r}'}{||\\vec{r}-\\vec{r}'||}\\right)\\frac{\\vec{r}-\\vec{r}'}{||\\vec{r}-\\vec{r}'||}-\\hat{m}}{||\\vec{r}-\\vec{r}'||^3}d\\vec{r}' $$ where the dipole moment norm $m=||\\vec{m}||$ is the aforementioned global normalization. Performing this integral is easy and it works etc., my question is about the physics: am I leaving anything out? Will a commercial solver include any physics that I haven't? In general, what will be my biggest source of error (except that I don't know $m$)? Thanks!",
"Magnetic monopoles in spin ice and Dirac string comparison 1. In spin ice systems magnetic monopole-like excitations are sources or sinks of $H$, not the $B$ field, why is that? Is it because the strings carries magnetic moment $M$ and not solenoidal $B$ filed like the Dirac string. 2. How is it different from Dirac construction of magnetic monopole? 3. In the Dirac case we still have incoming flux from the solenoid and out going from the monopole that will result in 0 for any sphere around the end. How he goes around this (why is it justified to not count the singularity) and why is not possible for the spin ice case?",
"Magnetism due to relativity? So I have been reading in some books that magnetism does not have to be assumed a priori, but can be obtained from the electric field + special relativity. And I have seen how this leads to the common formula for the magnetic field of a current carrying wire. Fine. What about materials that are inherently magnetic? Such as iron, or magnetite? Surely their magnetic field is not a consequence of relativity? (if yes, who's moving and with respect to whom?)",
"Heim Theory and FTL Years ago there was some hype around a theory that would supposedly allow for FTL. But I have since heard nothing of this. Is anything happening with the theory? How would a magnetic field allow us alter spacial dimensions?",
"is it possible to have magnetic flux density B not in the same direction of magnetic field intensity H? it is said that direction of magnetic flux density B in the same direction of magnetic field intensity H for isotropic media so what is isotropic media and is it possible to have B not in the same direction of H",
"How to find sensor hardware specs? I need a list of all magnetic field sensors, used in Android devices. Where can I find such a thing? Specs is not so important, I mean, I think I can just search for the name of the hardware and find it. But I need a list of magnetic field sensors' names, codes, manufacturers etc., something like this: Device: Magnetometer Name -------- ------------------ Samsung Galaxy II MF123A5 LG L5 Bosch ABC123 Any help would be much appreciated.",
"Electromagnetism Permittivity simple question Just a simple question regarding $\\epsilon$, the absolute permittivity. I read that it measures the resistance to of certain medium to 'permit' the formation of an electrical field. Does this mean that given a electrical field $E$, one needs more energy to produce it in a medium with a higher $\\epsilon$ ? Thanks in advance.",
"\"Magnetic mnemonics\" Over and over I'm getting into the same trouble, so I'd like to ask for some help. 1. I need to solve some basic electrodynamics problem, involving magnetic fields, moving charges or currents. 2. But I forgot all this rules about \"where the magnetic field should go if the current flows up\". I vaguely remember that it about hands or fingers or books or guns, and magnetic field should go somewhere along something, while current should flow along something else... But it doesn't help, because I don't remember the details. 3. I do find some very nice rule and use it. And I think \"that one I will never forget\". 4. ...time passes... 5. Go to step 1. The problem is that you have to remember one choice from a dichotomy: \"this way or that way\". And all the mnemonics I know have the same problem -- I got to remember \"left hand or right hand\", \"this finger or that finger\", \"inside the book or outside of the book\". Maybe someone knows some mnemonics, that do not have such problem? ",
"Expanding the Magnetic field? A magnetic field $B$ can apply a force $X$ on a ferromagnet when there is no gap to separate them, $r$ = 0. When that gap ($r$) is increased to 3 cm, the force drops to zero. How can that be solved? How can I expand the magnetic field so that it can be applied over larger distances? What methods are known to solve such a problem?",
"Would a $50\\: \\mathrm{Hz}$ spinning magnetic plate in front of a human generate harmful current? We know that spinning magnetic plate will generate current inside any wire. so if we stand before 50Hz spinning magnetic plate, then, does that 50Hz spinning magnetic plate in front of us (human body ) generate current inside human body which will cause harm to body? By considering the fact, human body is not bad conductor of electricity.",
"How can I find the largest fields? Right now, the Resistance holds >66M mind units. Those must be from some fairly large fields in fairly densely populated areas. But how can I find them? The Intel map isn't particularly useful for that, because it's too slow when loading fields and doesn't indicate when it's finished.",
"Which ferromagnetic material has the lowest Curie temperature? It is hard to search for materials by their properties in general and I am trying to find a material with a very low Curie temperature. At the moment I am browsing different sites but can only find a number of 'normal' ferromagnetic materials but few with a small Curie temperature. So which material has the lowest Curie of all ferromagnets? (By material I mean pure substance, e.g. NdFeB, but not a material under pressure, or nanocrystals or other special conditions which should all allow the suppression of ferromagnetism).",
"Is voltage important when creating a magnetic field? Would a DC circuit that has a high current and low voltage have a powerful magnetic field? I'm trying to create a powerful solenoid. In order to create a powerful magnetic field, I'm focusing more on the current(I). Increasing the number of turns would cause a stronger field, but at what cost?",
"How can a magnet have a greater magnetic field strength than a bigger, heavier and more powerful magnet made of the exact same material? Here are some informations I found on the magnetic field strength (also called \"magnetic flux density\" or \"magnetic induction\", commonly denoted as B and expressed in tesla or in gauss) of an average neodymium-iron-boron rare earth magnet. \"A modern neodymium-iron-boron (NIB) rare earth magnet has a strength of about 1.25 T.\" http://teslaradioconspiracy.blogspot.fr/2007/11/tesla-si-unit-of- magnetic-field.html \"1.25 T – magnetic field intensity at the surface of a neodymium magnet\" http://en.wikipedia.org/wiki/Tesla_%28unit%29#Examples \"1.25 T – strength of a modern neodymium–iron–boron (Nd2Fe14B) rare earth magnet.\" http://en.wikipedia.org/wiki/Orders_of_magnitude_%28magnetic_field%29 \"The magnetic field typically produced by rare-earth magnets can be in excess of 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla.\" http://en.wikipedia.org/wiki/Rare-earth_magnet Clearly, all of these sources agree that an average neodymium-iron-boron rare earth magnet has a magnetic field strength of about 1.25 T. But here's the problem: I searched on every single possible websites for THE most powerful magnet that can be bought. And THE most powerful magnet that can be bought is this one: http://www.kjmagnetics.com/proddetail.asp?prod=BZX0ZX0Y0-N52 It has dimensions of 4\" x 4\" x 2\", a weight of 138.8 oz (3934 g) and a pull force of 1226.5 lbs. And a magnetic field strength (surface field) of 4933 Gauss. 4933 G = 0.4933 T Far from the value of 1.25 T that is supposed to be the magnetic field strength of just an average rare-earth magnet... How is this possible? . And also, I found something else very intriguing: http://www.kjmagnetics.com/proddetail.asp?prod=BZX0Z0Y0-N52 This magnet has dimensions of 4\" x 3\" x 2\", a weight of 104.1 oz (2950 g) and a pull force of 1013 lbs. So this magnet is smaller, less heavy and less powerful than the previous magnet. But it has a magnetic field strength (surface field) of 5336 G = 0.5336 T which is greater than the previous magnet! Again, how is this possible? Note: Both magnets are made of the same material (NdFeB, grade N52). Both magnets have the same magnetization direction (thru thickness). And both magnets have the same plating/coating (Ni-Cu-Ni, Nickel).",
"Does zero change in magnetic flux always imply zero emf induced? If you have a uniform B field, with a finite piece of wire inside it. Assuming the B field spans all space and the wire cannot leave the field. Are you able to create an emf by moving the wire ? I say there is only one possible way, and that is if you rotate it so from its starting perpendicular to the field position it does parallel to the field. That would create a change in flux. But are you able to create emf if the wire stays perpendicular to the wire?",
"Superconductor general concept questions I was thinking about building an electric motor using superconductors and I have some general concept questions in regards to how the behavior might be different from ordinary wires. 1. The Meissner effect, expulsion of magnetic fields from the superconductor. If you construct a solenoid out of superconducting wire does this Meissner effect significantly change the field pattern compared to a regular wire solenoid? 2. If a solenoid is created out of superconducting wire is the current limited to the magnitude of the magnetic field it creates because if the magnetic field strength is too large it will return the superconductor to a non superconducting state? 3. If you have a superconducting wire with a current flowing through it and you expose it to a magnetic field does it still experience a force (obeying the same rules as a regular wire with current flow) or because of the Meissner effect the magnetic field never reaches the current carriers and so no force is experienced? Or is there only a fraction of the expected force experienced because the magnetic field does not penetrate through all the current carriers? 4. If you have two or more strips of superconducting tape stacked on top of each other with current flowing in the same direction through them and then you have a magnetic field strength probe and you probe the space above the stack, would the field be just the sum from each strip or would the Meissner effect in the strips closer to the top surface cause magnetic shielding of the lower strips and so the real magnetic field strength near the surface of the top strip would be less than the sum of the magnetic fields from each current carrying strip? 5. Is current flow in a superconductor only a surface effect? (i thought it was) Why did I see one company selling 3D wires? is that really isolated 2D stacks? 6. Is the only way to make a loop of superconductor run a continuous current is by induction? Thanks for reading and thanks in advance for any responses.",
"Finding the terminal velocity of a magnet dropped in a solenoid > We have to find proportionality of the terminal velocity with the factors of > the system:  > > Plot: a small dipole(mass $m$) with dipole moment $\\mu$ is dropped in a long > solenoid (radius $r$, Resistance $R\\: \\mathrm{\\Omega}$) along it's axis. The > gravity is acting downwards. I found it to be $$v\\propto \\dfrac{mR}{\\mu^2r}$$ Here is how: > The force in downward direction $F_{down}$ must be $mg$ and in upward > direction $F_{up}$ must be magnetic force. $$F_{up}\\propto \\dfrac{\\mu > I_{induced}}{r}$$ > > $$I_{induced}\\propto\\dfrac{ \\text{electric flux change}}R \\propto\\dfrac{\\mu > \\pi r^2 v}R$$ Flux change depends directly on the velocity, so added $v$ in the numerator. But the expression is not correct. The proportionality on the $r$ radius is not correct. I think there is a problem in the induced current factor.",
"Why is no EMF being induced in this ring passing through a magnetic field?  The book's logic is that there is no induced EMF because flux is constant as it passes through the magnetic field. Which makes sense, but this seems counter-intuitive to what I previously learned. If i'm not mistaken, if an electron is relatively moving perpendicular to a magnetic field, it WILL experience a force. The electrons in the ring are moving perpendicularly relative to the stationary field, so why aren't they experiencing a force?",
"What could magnetic monopoles do that electrically charged particles can't? I understand the significance to physics, but what can a magnetic monopole be used for assuming we could free them from spin ice and put them to work? What would be a magnetic version of electricity? * * * EDIT Sorry this wasn't clear. The question is mixed between the quasiparticle and the theoretical elementary particle based on some similarities between the two. I am more interested in the quasiparticle and if they have properties in some way that are similar to particle version: > There are a number of examples in condensed-matter physics where collective > behavior leads to emergent phenomena that resemble magnetic monopoles in > certain respects, including most prominently the spin ice materials. While > these should not be confused with hypothetical elementary monopoles existing > in the vacuum, they nonetheless have similar properties and can be probed > using similar techniques. > > http://www.symmetrymagazine.org/breaking/2009/01/29/making-magnetic- > monopoles-and-other-exotica-in-the-lab/ > > \"The Anomalous Hall Effect and Magnetic Monopoles in Momentum Space\". > Science 302 (5642) 92–95. > > \"Inducing a Magnetic Monopole with Topological Surface States\" > > \"Artificial Magnetic Monopoles Discovered\" and comments in articles about quasi-particles like this: > Many groups worldwide are currently researching the question of whether > magnetic whirls could be used in the production of computer components. led me to wonder what application might they have? Mixing these two concepts is probably a bad way to present this question. A true magnetic monopole would effect protons whereas the artificial ones don't. What I don't understand is what advantages an artificial magnetic monopole would have. And does this relate to some theoretical aspect of a true monopole?",
"Are magnetic hysteresis losses relevant to alternating currents flowing in a wire? Say we have an AC in a magnetically lossy material, like iron. Because of iron's relatively high permeability, skin effect will be more pronounced than it is in say, copper, so this iron wire isn't so great a conductor, practically speaking. However, skin effect arises due to eddy currents, which are themselves due to the time varying magnetic field due to the time varying current. So, this suggests there is a magnetic field at work, and there's the potential for magnetic hysteresis to be an additional source of loss in the material. Yet, I'm not sure if this is true or not, if somehow the geometry of the conductor and the fields around it make this a non-issue. I would think that if a time-varying magnetic field exists inside the iron, then there would be hysteresis losses. Is this true? Does such a field exist? To be clear: the issue is with iron _as an electric conductor_ , not as part of a magnetic circuit such as a transformer core as is the more common application.",
"Why there is electromagnetic resistivity in vacuum? I cant understand that. If there isn't a material that makes it hard to pass, why there is a resistivity in vacuum?",
"Magnetic field, alternated current and EMF If I apply an alternated current to a solenoid and insert into it a smaller solenoid, I could measure the induced EMF (electromotive force) and study how it changes in relation to the frequency of signal generator. If I increase the frequency, I think that the magnetic fiel increases and so also the EMF increases, isn't it? If I insert a metallic cylinder between the two solenoids, the cyclinder \"shields\" the magnetic field.. but what about EMF? And what about EMF if the cylinder is made by iron?",
"Puzzled by magnetized aluminum! For a school project I bought a set of magnets and an aluminum strip. The magnets are places along both sides of the aluminum strip (all in the same direction). Now the aluminum strip is exhibiting magnetization. I was under the impression that aluminum cannot be magnetized. What is the explanation? The strip seems to have opposite polarity vs the magnets near it.",
"Why can't a superconductor make a DC motor self sustaining? Superconducting wire can host a low current magnetic field. I do not know if it supports a corresponding electrical field. Can a superconducting wire that sustains a current accelerate a DC motor? Where is the resistance in a superconducting homopolar motor? Please explain if I am way off of target. What am I getting wrong?",
"Possible to generate an electromagnetic field from moving an object through a magnetic field? Is it possible to generate an electromagnetic field from a stationary rare earth magnet with a hole in it by passing an object through the hole? By definition, a Lorentz Force is the force on a particle which moves with velocity through an electric field and magnetic field. Would it be some how be possible to instead move a particle with force through a magnetic field to generate an electric field? (Where the magnetic field were not changing with time such as a stationary rare earth magnet with a hole in it)",
"What metals much harder than steel can be met in real life? Like pins in clothes security tags Once I bought a piece of clothes and forgot to remove magnetic tag in the store. I found, that it consists of two disks, connected with thin pin (of some metal). I was sure it is possible to break this pin with some instruments. But I broke all my saws, rasps and nippers I was applying to the pin. I wonder, which material it is made of?",
"Electrical properties of molten gallium arsenide I'm looking for the resistivity and magnetic permeability of molten gallium arsenide, but can only seem to find the values for the solid material at room temperature (e.g., Wikpedia). Not even temperature-dependency of these parameters seems to be available. Is this because the value just doesn't change with temperature? If it does, what's a good resource for such parameters?",
"Do magnets work in outer space? Is there any media where magnet lose its property?",
"North and south of magnetic field  The current I is flowing upward in the wire in this figure. The direction of the magnetic filed due to the current can be determined by the right hand rule. Can we determine the north and the south of the magnetic field produced by the current I by using a hand rule?",
"Flux, intensity, etc in ferromagnetic core by integral Cheng, Field and Wave Electromagnetics (newest ed.), ex 6-10, page 252 Some of the examples in this book are kind of sloppily described. Having trouble with this one. We have a toroidal core with permeability $\\mu$, mean radius $r_0$, circular cross section radius $a << r_0$ with $N$ turns and a steady current $I_o$. Also there's an an air gap of length $l_g$. > Determine magnetic flux density $\\textbf{B}_f$ in the core. Disregard flux > leakage and fringe effects near the air gap. Solution: $\\textbf{B} = B_f \\ \\hat{\\theta}$, $\\oint \\textbf{H} \\cdot \\textbf{dl} = NI_0$ $\\textbf{H}_g = (B_f/\\mu_0)\\hat{\\theta}$, integrated from $0$ to $l_g$ $\\textbf{H}_f = (B_f/\\mu)\\hat{\\theta}$, integrated from $l_g$ to $2\\pi r_0$ So far so good. But here I want to say $\\textbf{dl} = (r_0 d\\theta)\\hat{\\theta}$, which would give the integral $\\oint_c \\textbf{H} \\cdot \\textbf{dl} = \\oint_0 ^{l_g} \\frac{r_0}{\\mu_0} B_f d\\theta + \\oint_{l_g}^{2\\pi r_0} \\frac{r_0}{\\mu} B_f d\\theta = NI_0$ But the author kind of skips the $ dl = r_0 d\\theta$ step and just proclaims $\\frac{B_f}{\\mu}(2\\pi r_0 - l_g) + \\frac{B_f}{\\mu_0}l_g = NI_0$ So apparently $dl = r_0 d\\theta$ is incorrect. How come?",
"Does Hall Effect increases the resistance of a wire? If a current in a wire is flowing perpendicular to a magnetic field, the Hall effect will be observed, which is caused by the forces from magnetic fields 'pushing' the electrons to one side or the wire. So, does it increases the resistance of the wire, as there is now less area for current to flow through due to one side of the wire being occupied by these (assumed)immobile electrons?",
"Can we increase the magnetic flux for a permanent magnet? When we pass current to the permanent magnet does its magnetic flux, magnetic property of attraction and repulsion increases? if possible Is there any other way for increasing the magnetic flux?",
"Modeling magnetic field shielding I am wondering what is the best way to model magnetic and electric field shielding from a magnetic dipole in the near field? For example, let's say you have a coil of current carrying wire in the x-y plane which creates an AC magnetic field along the z-axis. I am interested in a model in which I could put in material parameters (such as $\\sigma$, $\\epsilon$, $\\mu$) for a shielding plate located distance $r$ from the source. I tried using section 5.4 of an online electromagnetic book which talks about reflection, and transmission of of EM waves. I would estimate wave impedance as $Z=\\omega\\mu_0r$ which is the equation for near field magnetic source. I determine the intrinsic impedance of the shielding material as $\\eta=\\sqrt {\\frac {j\\omega\\mu} {\\sigma + j\\omega\\epsilon}}$. I want to try good conductors as well as ferrite so I'm not making any assumptions such as good conductor or loss-less medium. I implemented this but the result was not what I expected. I would expect highest energy reflection with the ferrite because it has low reluctance to magnetic fields and would guide the flux through it and return to source. However, a good conductor (e.g aluminum) had almost 100% energy reflection, but I was expecting the shielding mechanism of conductors would be all energy lost as absorption from eddy currents. Let me know your thoughts of whether this is a legit model; I can give more info about parameters/equations used if that's helpful.",
"What's the explanation for the Giant Magnetoresistance effect? I've been reading this review on Giant Magnetoresistance, and something about it is bothering me. The basic effect is that, using a special \"stack\" of layers (alternating between ferromagnetic and not magnetic) you can cause great variations on the electrical resistance of the material by applying a small magnetic field.  The explanation given both on the review and on Wikipedia is the following. The configuration on the left will cause scattering for all spin down electrons that cross it, but will present very low resistance for the spin up electrons (thus a small resistance overall). The one on the right, will scatter all electrons and thus have very large resistance overall. **Here's my problem** (quoting the review) > These experimental results were all obtained for the ’Current In the Plane > of the layers’ (CIP) geometry. The current is then parallel to the plane of > the layers. How can this be? CIP in the above image would mean the current is horizontal, with probes positioned on the left and right of the middle layer. But, if you don't force the current to cross the ferromagnetic layers, why would there be an increase in resistance? I checked with a professor, and he confirmed that the standard method is indeed to apply the probes horizontally, but he couldn't tell why the effect still worked. One option that came up is that electrons don't follow a straight line from one probe to the other, and thus they would still \"flow\" through the other layers, but I know that's not the case. Using the resistors analogy seen in the image above, applying a CIP is equivalent to setting the resistors in parallel for each of the spin orientations, and parallel resistors _always_ have less (or equal) resistance than the weakest resistor. To be clear, my question: How can the above explanation be compatible with the CIP case? If it's not, then why does it still work?",
"Looking for lists of student difficulties with electromagnetism, circuits (DC and AC) I'm trying to help with an Instructor's Guide for an introductory calc-based physics text, and it would really help if I could locate some lists of typical student difficulties with topics like ... flux induced E and B fields Faraday's law Lenz's law DC circuits AC circuits Is there a better approach than just Googling \"student difficulties with XXX,\" as I have been trying with rather inconsistent luck? _Added--_ Thanks for the reminder! I actually found a copy of Randy Knight's book in the attic that I got from him at an AAPT meeting some years back. I can't believe I actually located it in my chaos ... great suggestion!",
"Understanding Counter - EMF? When an coil rotor is moving around a magnetic field there is -V induced to resist the input V. Let's take an example, a 12 V DC motor induces -10V, and the actual running voltage is 2V. If there we're no -V in the process, the motor would preform a lot better? What is the advantages and disadvantages of counter EMF? Is it wasting energy? I understand the concept, but I can not fathom how initially, the motor runs at 12V then drops to 2V(actual) and still preforms the same? Are all current motors today lose 70%+ of their input voltage due to counter EMF?",
"Circumference of a Magnetic Field Is it possible that a metallic object will _not_ be under the influence of a magnetic field at a certain _closeness_ to a conductor, but will then experience the effect on moving to a particular distance (and onwards)? In other words, is there a threshold radius around a conductor _within_ which the magnetic effect cannot be felt?",
"What is the medium that allows magnetic fields *or any forcefield* to exist? Magnetic fields are obvious distortions.. of.. something, but what exactly are they distortions of? Massive objects produce curvatures/gradients in space- time resulting in what we observe as gravity.. what is the equivalent explanation for magnetic/electric fields?",
"How can I calculate the relative permeability of iron? I'm a high school physics student, and part of our project requires us to make an electromagnet. We have an iron core, and it will go inside a solenoid. The problem is, we don't know what the relative permeability constant of iron is so we can calculate the magnetic field with the iron. How can we get this constant?",
"inductance value of a single turn thin circular coil the question may seem simple but I haven't found any fitting formula yet. The problem is the following: consider a single-turn, circular coil made of reasonably thin wire (diameter of the wire much smaller than diameter of the coil). What is the inductance of this coil, based on the coil radius, and the wire radius? The answer could be either an analytical solution, a good approximation, or a formula with elliptic integrals (for instance) I found the analytical formula for the magnetic vector potential of an infinitely thin coil on wikipedia (here), but I do not have a good software to integrate the elliptic integrals properly; and moreover, this formula does not cover finite wire radius. To have some first trends, I checked the value of the magnetic flux of such a single-turn coil on a physics modeling software, and the value of the integral (with sufficiently resolved mesh) seems to depend strongly (enough) on the wire diameter (going from 4cm to 2cm diameter wire increased the magnetic flux by 20% for a 2m diameter loop, although we have 4cm<<2m!). And the other thing, that actually surprised me, is that, with a constant current value (1 amp), a bigger loop shows a smaller magnetic flux, although the area is much bigger. I think this last effect is linked to the fact that I used 130kHz frequency to calculate the flux integral, so this needs to be clarified further, I will update on that. EDIT 8 May: this is an error because the program handled badly the unit conversion from 4 cm to 1 m. As one might expect, the flux, and the inductance, is actually proportional to the radius. That's all I can tell. Does anyone have more insight on this? Thank you very much!",
"Are there analogs to resistance, inductance, capacitance, and memristance connecting the weak force to electromagnetism? A question was asked over at EE.SE recently which I tried to answer, but much of my answer was speculative. I'm hoping someone here can help my ignorance. In electronics design, there are four physical quantities of interest: voltage, flux, charge, and current. If you have four things and want to pick two, order not mattering, there are 4C2 = 6 ways to do that. Two of the physical quantities are _defined_ in terms of the other two. (Current is change in charge over time. Voltage is change in flux over time.) That leaves four possible relationships: resistance, inductance, capacitance, and memristance. These are the values we use in every-day electronics design and analysis. (Well, not memristance, but one can dream.)  If you want another fundamental component, you need another physical quantity to relate to these four. And while there are many physical quantities one might measure, none seem so tightly coupled as these. I'd suppose this is because electricity and magnetism are two aspects of the same force. I'd further suppose that since electromagnetism is now understood to be part of the electroweak force, one might be able to posit some relationships between the weak nuclear interaction and our four quantities of voltage, current, charge, and flux. I haven't the first clue how this would be physically manifested, especially given the relative weakness of the weak nuclear force at anything short of intranuclear distances. Perhaps in the presence of strong magnetic or electrical fields affecting the rates of radioactive decay? Or in precipitating or preventing nuclear fusion? I'd yet further suppose (I'm on a roll) that the field strengths required would be phenomenal, which is why they're not practical for everyday engineering. But that's a lot of supposition. I am a mere engineer, and unqualified to comment intelligently on such things. Am I in the ballpark? Are there theoretical or demonstrable mathematical relationships between the weak nuclear interaction and charge, voltage, flux, and/or current which would correspond to my above suppositions? Or am I just looking for symmetry where none exists?",
"Opposite field's acting on a soft ferromagnetic material To external fields(H, - H) not equal to each other are acting on that material. **Based on the hysteresis loop** what would be the result? The hysteresis area of that materials is very narrow(i.e easy to magnetize & demagnetize) H = 1000 A/m and, - H = 500 A/m. I know they are both vectors so it would be H - H = H(total). However, the material's coercively is 0.1 A/m. The thing is I can't imagine this condition properly, because both fields are opposing each other, and that ferromagnetic material is placed in-between them both. What would be the result? The material responds based on it's hysteresis... H points on the hysteresis loop. Why is it incorrect to state magnetization = 0? I'm relating this to an object that has to forces acting on it, they are both on opposite directions. F1 = 10N F2= 5N [x]= is the object. 10N ->[x]<\\- 5N = 5N ->[x] Although it makes sense... The hysteresis loop changes everything. Magnetization depends on how the material reacts. The material could become magnetized and fully saturated at 100A/m, now we have both of those conditions... So M should = zero?! To picture what I mean, please take a look at this: http://uk.tdk- lambda.com/content/glossary/128522219667677500_Hysteresis%20Loop%20image.png The two points on the loop on the H axis are 100 A/m(that is the force needed to magnetize the material), however, the field applied H = 1000 A/m and - H = 500 A/m Hope it helps!",
"Redstone Circuitry - Resistors? Is there any way to construct a resistor within a redstone circuit? I was thinking that there might be some properties of cobblestone versus glass, dirt versus obsidian, etc. but I haven't had the opportunity to check it out. Is there any data on this? (I realize that there probably aren't resistors in Minecraft YET, but i'm really hoping i'm wrong)",
"Uniform constant magnetic field and traditional attractive force Why uniform constant magnetic fields can not exert net force on a piece of iron whatever strong it might get?",
"Faradays law for a falling magnet If experimentally it can be proven that the velocity of a falling magnet through a coil is proportional to the emf induced, has it also been proven that dB/dt is proportional to the emf induced and how so ?",
"Artificial planetary magnetic field I wonder how difficult it is to create an artificial planetary magnetic field with generators? What power they would need? The question is inspired by thinking about possible colonization of Jupiter's moons Io and Europa which are located inside the Jovian radiation belt. Is it possible to create with easy means an artificial magnetic field such that it to shield the surfaces of these moons from radiation? Or it would require astronomical amount of power? By easy means I mean a device that would not require power greater that normal industrial power plant, best of all, solar-powered or based on once-charged superconductor coils.",
"Attraction and repulsion of electron spin ups and electron spin downs Alright, we know that copper is a diamagnetic material, which has paired electrons. These paired electrons have different spin. I'm specifically interested in what is going on with the electrons in a copper coil, when creating an induced current with a magnet. 1 Question: \"Can you break the bond between an electron spin-up and electron spin-down in a diamagnetic material such as copper - using an external magnetic field?\" 2 Question: \"If yes, then could you say that a bar magnet with a north-pole would attract all the spin-ups and repulse all the spin-downs, due to the fact that spin-ups has south pole at the top, and spin-downs has north at the top. This would then create an opposing magnetic field, so that there in the copper would be a north-pole at the top, and a south-pole at the bottom.\" 3 Question: \"If further yes, could you say that the movement of the electron spin-ups and electron spin-downs is the so called induced current.\" 4 Question: \"And when the bar magnet is pulled out of the coil, the spin-ups and spin-downs will naturally find each other again, and bind and create a zero-magnetic field.\" Statement: If I make experiments with the galvanometer, I can see that the current is going different ways, depending on which pole I use, which in my mind can prove to be a valid proof that the bar magnet is attracting and repulsing at the same time. Either spin ups og spin downs, regarding which pole being used. 5 Question: \"If all this is wrong, and you cannot break the bond between spin- ups and spin-downs, then what exactly is the bar-magnet doing to the electrons?\" Many Regards",
"Resistance of aluminium rectangular wire I am working on upgrading an electromagnet design program. There are currently two types of wire used for the coil, circular and strip (read as: rectangular). The current algorithms in this program are empirically derived with lots of undocumented constants and so one of the requirements is to move it more into the realm of accepted physics. The formula I am using to calculate resistance is: $$ R = \\frac{\\rho L}{A} $$ These are aluminum wires so the value of $\\rho$ boils down to $2.82\\times10^{-8}$ at 20°C. For circular wires this works perfectly, giving near enough the same results (enough to put it down to the increased accuracy). For strip wires this doesn't work quite so well. The problem comes from a difference in the cross-sectional area of the wire. The original program is doing $h^2$ as the area, where $h$ is the height of the wire. Now is that not wrong? The cross-sectional area should be $wh$ where $w$ is the width of the wire. For example, If the strip wire is 8.4mm by 2.8mm, the original program would do: $$ 2.8 ^ 2 = 7.84 $$ but should it not be doing: $$ 8.4\\times2.8 = 23.52 $$ The entire original algorithm is: $$ R = \\frac{84.09L}{h^2} $$ Is there a reason the original engineer may have done $h^2$ as apposed to the correct cross-sectional area? I don't want to just declare his calculations as wrong as the results from this program have been used for the last 30 years and none of the magnets have gone bust or underperformed. Infact if anything they would have been over performing if this calculation is wrong.",
"Is a superconductor really a super conductor? It is known that a superconductor is a material with electrical resistance zero. My question is, it is exactly zero, a theoretical zero, or for practical realistic reasons it is effectively zero?",
"Is imperative magnetic flux the capacity of individual atoms, or the constituent valency of chemically-bonded molecules within a vacuum? If magnetic energy depends on the electron poles within two-fields within a permanent magnets void, how do invidiual atoms react within the attraction or repulsion of poles, and what incurrence does this live by in regards to molecular struction?",
"Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why? I need a full explantation for this concept. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid.",
"Is there a Transparent, Non-Magnetic Conductor? I am looking for a transparent (visual wavelength: 390 to 750 nm), non- magnetic (not attracted by a magnet) electrical conductor that could be used for a physics demonstration. Is there such a substance? If yes, is there a cheap one?",
"Why are magnetic field lines perpendicular to the surface of a ferromagnetic material? It is known that magnetic field lines become nearly perpendicular to the surface of a ferromagnetic material. The quantitative proof which uses the boundary condition requires that magnetization at the surface be zero. **Question:** _Why is magnetization at the surface of a ferromagnetic material zero? Also, can someone give a qualitative explanation for the approaching perpendicularness of magnetic field lines and the surface of a ferromagnetic material?_",
"Can the electric polarisation lead to a similar effect like the Anomalous Hall Effect The magnetisation of a material leads to an Anomalous Hall Effect in a material. Is there a similar effect that arises from the electric Polarisation of a material?",
"What are magnetic field lines? Does a magnetic field have concentrations of magnetic force lines as seen when putting iron filings over top a bar magnet or are these imaginary? I.e. are they just an artifact of the iron being a 'conductor' of the magnetic field lines making them look like they are concentrated along these path lines but are really continuum of strength around the bar magnet when there are no filings are present? Also I learned that field lines do not cross, yet there are magnet configurations who's forces are explained as the magnetic force vectors are indeed crossing and are additive such as a Halbach Magnet Array. So what is actually happening here?",
"Can a magnet magnetise an object with greater strength than it possesses? Trivial thought ... Materials may be broadly superconductive, diamagnetic, paramagnetic, ferromagnetic. An object is magnetized by repetitive motion of a magnetic field across it's surface Say a field of strength 1T were to be moved across a steel cylinder. Could the field created in the cylinder be greater than 1T? What if the same field were to be applied to a more strongly ferromagnetic material?",
"EMF in a half-ring shaped conductor around a solenoid A half-ring shaped conductor is being placed around a solenoid. This solenoid has a changing magnetic field. a) There is a current and EMF (Electromagnetic force) in the half-ring shaped conductor b) There is a current but no EMF in the half-ring shaped conductor c) There is no current but there is an EMF in the half-ring shaped conductor d) There is no current but there is no EMF in the half-ring shaped conductor My thoughts about this: First of all the field outside a solenoid isn't very big in contrast to the field inside the solenoid. But I assume that it can't be neglected. I think there won't be a current as we would need a full ring- shaped conductor for this. I do think that there will be an EMF in the conductor, and this will generate some eddy currents in the conductor. But there will be no \"full-on current\" so to speak. So I would say the answer is C. Is this correct? A Little side-question; Is it at all possible for a non-conducting material to have an induced EMF. For example when we move a non-conducting material (ring- shaped) into a magnetic field. The magnetic flux in the ring changes, but will there be an induced EMF? I know that there won't be a current in the loop, but I'm not certain about the EMF. Thank you very much!",
"Magnetic Fields If running a current through a magnet can reverse the magnetic field, then how strong does the current have to be and how would it best be run through the magnet.",
"Can a magnetic field alone be used to move a metallic object within a contained tube? Is it possible to make a metallic object move in a circular contained tube around and around in which a magnetic field is setup to cause the metallic object to move through the electric field within the tube through magnetic forces alone? If not, what other forces must be present to make the object move around and around in the circular tube?",
"How an-isotropic magneto resistance(AMR) changes as film thickness increases? As the film thickness increases, an-isotropic magneto resistance(AMR) changes in the presence of external magnetic field because of spin orbit interaction. But i don't know how it is responsible for change in AMR from starting to the end of film growth. I know this question is a bit stupid but neither my teacher nor the textbook are very helpful, and I would really appreciate any help. Many thanks!",
"Would a strong diamagnetic material exhibit inductance? Erm. This question got shot-down in electronics.stackexchange.com and somebody recommended I raise it on here, so ... Do metals with the property of strong diamagnetism also exhibit inductance? Would a fluctuating magnetic field induce a weaker current in a strongly diamagnetic metal as compared against a ferromagnetic/paramagnetic metal? I remember reading metal-detectors are based upon the property of inductance. So if a metal detector were to hover over a silver ingot/plate, would it succeed or fail?",
"Is there an equation for the magnetic field of a conductor attached to a magnet? Let's say I have a hollow conductive rod, 10mm diameter (O.D.), and I place a magnet of known strength 50mm up the shaft. What is the microTesla (mT) or Gauss (G) of the magnetic field (or flux density, or whatever it would be) **of the shaft** 50mm away from the magnet attached to it? Here's what I'm attempting to do: I want to attach a magnet to my manual transmission's shifter lever, and then use hall effect sensors to detect it's position and display the selected gear on a display. I have the Arduino code written and the display wired. I'm having a problem understanding what sensitivity Hall Effect Sensors to get, what strength and size magnet(s) to get, and how to go about figuring how they relate to each other. Essentially, I don't want the magnet too close to the 6 Hall Sensors, nor do I want a huge, expensive magnet. I have 216 neodymium buckeyballs I can encircle the shaft with, if I used them would it matter which polarity I had them arranged in? If I used a single magnet, would I place the poles alongside or perpendicular to the rod? How would I go about ball-parking the mT of the magnetic field 50mm (or whatever distance) down the rod, away from the magnet to get an idea of the sensitivity (rated in mV/mT for the hall effect sensors)? How does a magnetic field propagate through a conductor? How would I position the magnet(s) to maximize the mT down the rod of my shifter? How do I place the Hall Effect Sensors (which read mT perpendicular to their face) to maximize the readings? Ideally, I'm hoping to place the magnet(s) far enough away that what I'm reading is the transmitted 'magnetism' of the rod itself, is this an improper way to look at it (or even possible)? If it's not, is it the case that I have to bring the actual magnets near the hall effect sensors, and I can't 'transfer' it to the rod?",
"What is the difference between magic resistance and the elemental resistances? There are several kinds of resistances in Skyrim: magic resistance, flame resistance, frost resistance and shock resistance. Is the magic resistance essentially just resistance to all three elements, or are there magic damage types besides those three? And are all sources of flame, frost and shock magic damage, or are there non-magical sources of elemental damage?",
"Reluctance of torus shaped iron core with embedded wire loop **Imagine a circular wire loop** (r = 50mm), the wire has an assumed diameter of zero, **which is embedded in a torus shaped iron core with a circular cross-section** of R = 10mm. A current in that loop would cause a circular magnetic field around the wire. **Is there any possibility to calculate the reluctance of that core?** I'm looking for a solution for weeks now, without any success. A solution for harmonic currents is desired, but I would even be happy for a DC solution.  * * * # CONTEXT **to explain what this is all about.** My real geometry looks as following:  A torodial coil surrounded by a core with a cross section of a rounded rectangle. So I'm interested in the reluctance of the greyish part (and the other corners). If you put all corners together you'd get the mentioned torus. The green lines are the magnetic flux, the rectangle in the middle the torodial coil. For high frequencies and/or high conductive and/or high permeable materials the influence of the corners is negligible, for my case unfortunately not. I'd guess there is no analytic solution, but any idea which could get me close to it, would help. Thank you! * * * * * * # Attempted solution # Preface If one wants to calculate the permeance $P$ of a rectangular bar:  it is an easy task: $$P = \\frac{\\mu a b}{L} ~~~~ \\rightarrow ~~~~ P\\propto ab ~~~~and~~~~ P\\propto\\frac{1}{L}$$ where $\\mu$ is the material constant. (Permeability) But my geometry is a **torus with just a quarter of its circular cross section** and the field $V$ **passes through it parallel to the circumference** of the (full) cross section:  How can I calculate the permeance of this geometry, when there are the same proportional relations as above? * * * # Attempted solution I divide my geometry in $N$ hollow toruses with constant wall thickness $\\Delta R$ and medium length element $\\Delta L$, so the field passes an area of $\\Delta A$:  A little piece of the radius $R$ is $\\Delta R = \\frac{R}{N}$. Now one can calculate: $$\\Delta P_{n} = \\frac{\\mu \\Delta A_n}{\\Delta L_n} $$ with $$ \\Delta A_n = \\pi \\bigg( (r+(n+1) \\Delta R)^2-(r+n \\Delta R)^2\\bigg) $$ (Consider the full torus circumference, not just a quarter as displayed) and $$ \\Delta L_n = \\frac{\\pi}{2} (2n+1) \\frac{\\Delta R}{2} $$ (but quarter cross section!) follows: $$P = \\sum^{N-1}_{n=0} \\Delta P_{n} = \\mu\\sum^{N-1}_{n=0} \\frac{\\pi(2r\\Delta R+(2n+1)(\\Delta R)^2)}{\\frac{\\pi}{2}(2n+1)(\\frac{\\Delta R}{2})}~~~~~~~~~~~~~~~~~~~~~~~~~$$ $$= 4\\mu\\sum^{N-1}_{n=0} \\frac{2r\\Delta R+(2n+1)(\\Delta R)^2}{(2n+1)(\\Delta R)} $$ $$= 4\\mu\\sum^{N-1}_{n=0} \\Bigg( \\frac{2r}{(2n+1)} + \\Delta R \\Bigg)~~~~~~~~~~ $$ $$= 4\\mu \\Bigg( R + 2r \\sum^{N-1}_{n=0} \\frac{1}{(2n+1)} \\Bigg)~~~~~~~~~~ $$ **And this series does not converge for $N\\rightarrow\\infty$.** Which is physically seen not possible, so there must be a problem with the math. Do you see what I'm missing?",
"How to Generate a Strong Electromagnetic Field? I'm working on a project and I need help generating a strong magnetic field over an air gap with the lowest material weight that could be achieved. I have tried to use permanent magnets but its not effective so I need to know the best way to generate a strong fixed electromagnetic field with the lightest material. The attached image is a simple drawing shows the direction I need to generate the field in the boxes are the field source. ",
"Magnetic field distrotion Does one exist, or do you think it would be possible to design a tracking magnetic field distortion detector to detect fast moving magnetic anomalies in our air space. ie; track a stealth aircraft or unidentified flying object at some distance by detecting the disturbance of the ambient magnetic fields?",
"Power and magnetism If we have a solenoid and a magnetic field passes through it, a DC voltage will be produced in the wire. If we want to calculate the power, we find out the current using Ohm's law. I know there is power loss due to the resistance (joule effect). But what about the magnetic field due to current (lenz's law), does it contribute in the power loss?",
"Electromagnet, ideal turns depending on ohm More turns -> stronger field more turns -> longer copper wire longer copper wire -> more resistance(ohm) at what turn does the resistance make the electromagnet weaker? - I want to make an ideal electromagnet. (Sorry for being vague but I'm looking for some kind of formula or an example)",
"How can Superconductivity materials levitate permanent magnet? I have thought that by eddy current. But how eddy current in superconductivity materials can be generated by using permanent magnet?",
"What is the weakest magnetic field that can practically be measured? I would like to be able to measure magnetic fields that are generated by nerve impulses in extremities like in fingers. I know that they are very weak: about 100 mV electric potential would give us about current 10 mA if resistance = 1/10 Ohm, but interested in measuring magnetic fields. **How many rounds should you have in a coil to measure 10 mA current?** The jumping of electrons from one level to another may become a problem in this case. However, I am not sure where and how. Assume that there is a steady current in the situation so Biot-Savart law. The radius of the nerve is r = 0.003m.",
"What is the magnetic susceptibility of NdFeB? NdFeB is one of the most popular materials used for making permanent magnets. Yet I could find no link or reference reporting a decent value for the magnetic susceptibility of NdFeB. Magnetic susceptibilities of some common materials has been listed at the following link: http://en.wikipedia.org/wiki/Magnetic_susceptibility#Examples A scientific paper or application notes of a good company involved in magnetism would be really helpful.",
"Magnetic Permeability & Reluctance on old exam question This is a past exam question from one of our lectures, and we have an issue with (i), I believe I need to use the equation $\\rho=\\frac{RA}{l}$, but I am not sure - could someone enlighten me on the issue? > A mild steel ring of magnetic permeability 380, having a cross sectional > area of $500mm^2$ and a mean circumference of $400mm$, has a coil of $200$ > turns wound uniformly around it. > > Given that the magnetic permeability of free space is $400 nH/m$ determine: > > > * (i) The reluctance of the ring. > > * (ii) The current required to produce a flux of $800\\mu$ Wb in the ring. > >",
"Why my simple electromagnetic experiment does not work? I make a setup (see attached picture). * ONE coil (1\" diameter x ~120 turns), which is separated with a gap, is mount on two sides. Each side has an iron rod (1\" diameter x 6\" long) to increase the focus of the magnetic wave.The wire for the core is 14 gauge motor wire (5.9 amp power rating max). * Two super strong magnets (1\" diameter x 0.5\" thick each) are mount at the middle block (plastic) under Duck tape. Each of them is rated ~40 lbs holding force. Each side of the block has one magnet. * I use 6 power resistors in series to create 50 ohm resistance. I connect the circuit to wall power 120VAC. Since the impedance of the coil is small, I think I give 2.4 amp @ 60 HZ to the circuit. * Everything for holding is by very smooth plastic (Acetal Resin). * Before I connect the power, I put the system at rest. The magnet is so strong that, they make the middle piece to go to either one of the iron. I thought the MIDDLE PIECE would swing to the left and right with 60Hz. However, the system does NOT move at all. Any idea?  ",
"Ferromagnetism and electrical conductivity Are ferromagnetic materials good conductors of electricity? If yes, please explain with proper examples.",
"Superconductors and magnetic field I am working on a project, and I have a question: Concerning superconductors considered as diamagnetic material, what is the equation that describes the repulsive force to a diamagnetic material in a magnetic field?",
"Can mu-metal reduce the negative effect of metal close to low frequency RFID antennas? I have an 134.2 khz RFID antenna for sport events which is basically a 1x1 meter square sheet of rubber with 3 loops of antenna cable embedded. The problem is that the transponder recognition range is drastically reduced when the ground below the antenna contains metal (e.g. reinforced concrete). Would it be possible to solve this problem by attaching a layer of mu-metal or permalloy to the lower side of the antenna? I read that mu-metal draws magnetic field lines into itself and thus redirects them around what's behind (in this case the metal in the ground). Would this make sure that the magnetic field on the upper side of the antenna is the same as if there was no metal in the ground? (and that the transponder recognition range is as good as without the metal) What thickness of the material would be required, would a foil be sufficient?",
"Question regarding inverse relation of resistance with area of cross section It is said that resistance is inversely proportional to area of cross section. But greater area will have greater electric flux, and greater electric flux will have greater magnetic flux, and greater the magnetic flux will have greater eddy current, which is opposite to the current flowing. So this will oppose the current hence resistance increases. Am I right?",
"Magnetic Induction  Consider the figure above in which there is an electric current (constant) in R1 (consider it to be made of a conductor). Obviously there will be a magnetic field induced in R2 (consider it to be made of a ferromagnetic material) due to the electric current in R1. (http://hyperphysics.phy- astr.gsu.edu/hbase/magnetic/curloo.html) R3 (consider it to be made of a conductor) is an open loop as shown in the figure. Will there be any induced voltage across AB in R3 due to the magnetic field in R2?",
"Which metals can cause magnetic interference (passively)? I am developing an application that uses the magnetometer inside smart-phones to detect orientation w.r.t. the Earth's magnetic field. I have noticed that when the phone is held close to a metal structure, such as Iron/Steel railings, there is a huge deflection in the magnetometer reading. There is no externally-induced current flowing through the structure; it has ~~induced~~ warped the magnetic field by its own. My question is, which types of metals can show this effect? Or more generally which type of elements can show this effect? I suppose Ferromagnetic materials do show this effect. And paramagnetic materials (like Aluminium) will show a very weak effect. What about diamagnetic substances such as copper? **Update** Changed the title to mention _passively_. I understand that a copper coil forced to carry current would induce a magnetic field that interferes with the Earth's magnetic field. But does the coil distort the Earth's magnetic field when _no_ EMF is applied?",
"Two magnets with Iron truncated cone or pyramid. How low inclination can the truncated cone or pyramid be made? Two magnets with Iron truncated cone or pyramid: Frustrum **How much low inclination can the truncated cone or pyramid: Frustrum be made, without non homogeneous lines of magnetic field coming out from the sides ?????????**  Two magnets with Iron truncated cone and Yoke  Link_to_Example_1 Two magnets with Iron truncated pyramid and Yoke in a different set up.  Link_to_Example_2 Knowing the magnetic flux at the larger base of the truncated cone or Frustrum, the area of the smaller base will be the one in which you get the magnetic saturation of the Iron. But, ... **How much low inclination can the truncated cone or Frustrum be made, without non homogeneous lines of magnetic field coming out from the sides ?????????**  Also in the image of Link_to_Example_2 the gray rectangular number 2 is a block between the iron pieces to keep the distance between the two parts. It must also be a non ferromagnetic material like brass, wood, stainless steel, etc. **But what's the best material to hold strong compression and not catch magnetic field drawing it away from the main gap (number 4) ???** Help please. Thank you in advance.",
"Strength of Magnetic Field Around a Superconductor I recently learned that the strength of a Magnetic field around a conductor is proportional to the current flowing in it. So if we have a Mercury wire at absolute zero and pass a current through it (Resistance = 0) and then toss some iron filings at it, will the filings cylindrically float around the conductor (along the Magnetic field lines) due to the extreme strength of the field or just behave the way they do for an ordinary conductor (like Copper), in which case we must rest the filings on cardboard and then give it a jerk to align it along the lines.",
"Magnetic Shielding? Can magnetic fields be \"blocked\"? For example, in the game, TitanFall, a robot stop bullets with ( presumably ) a magnetic shield. I wish to calculate the magnetic force required to stop a bullet within a few microseconds. But the problem I have is that my entire electronic system or the vehicle ( most likely even a building ) will be subjected to massive fields most likely destroying it as well. Does any know of a way to \"block\" or divert the field around my vehicle? Is it even possible? My knowledge in magnetic fields are quite limited at this time.",
"Magnetic field insulators I was wondering if there is any way to stop the magnetic field, without having the insulator turned into magnet. Let me present this as a simple case, there is a magnet to the left and a piece of iron to the right, is there anything that I can put in between to stop the magnet from attracting the iron piece, provided that the insulator won't turn into a magnet as well? I am open to all possibilities, any materials, electric fields or anything that can stop the magnet field without harming the magnet or the iron piece are welcome.",
"Magnetic fields and friction If I was to pass a metal object through a magnetic field would there be any friction?",
"can I tune a magnetic field to conduct heat from a rotating object? Is there a way to transfer heat from a rotating object made of iron into a suitable heat sink using a magnetic field as a transfer medium?",
"Need an intermediate resistivity part/material I need a part or material for a planned experiment (the experiment is similar to those described in my articles http://arxiv.org/abs/1208.0066 and http://arxiv.org/abs/1109.1626 ). The problem is that the required resistivity (about 0.3 Ohm-cm or of the same order of magnitude) is much higher than that of metals and much lower than that of dielectrics. Eventually, I need a long cylindrical part, about 1.5 mm diameter and about 1 m length. So far I have considered semiconductors, conducting polymers, and absorbing materials of http://www.eccosorb.com/Collateral/Documents/English- US/Electrical%20Parameters/ls%20parameters.pdf . The latter materials seem good, but they are essentially foams, and the required part cannot be machined from them. As for semiconductors and conductive polymers, I don't have a clear idea how to get (to order) a material with the required resistivity and how to make (to order) the required part. I need the above resistivity at a frequency of about 25 GHz, so, in principle, I could use a nonconductive, but absorbing (at the required frequency) material, but I would prefer a material that is conducting for direct current as well, to be able to measure the absorbed power. I would prefer a material with decent mechanical properties, so that I could, e.g., strain (tighten) the cylindrical part. Any advice? EDIT (02/02/2014): I have finally obtained the required parts. They are made of doped polysilicon. I am grateful for the answers.",
"How may the magnetic resistance for a magnet moving through a copper pipe be calculated? When a magnet moves past non-magnetic, electrically conducting material such as copper, the changing magnetic field induces electric eddy currents in the copper, which create their own magnetic field that repels the magnet's movement past the copper. A magnet dropped through a copper pipe will descend slower than free-fall. If the magnet is strong enough the descent may be very gradual. How may the magnetic resistance of a magnet moving through a copper pipe be calculated? [Bonus] What would happen if the copper pipe were cut lenghtwise so as to make a nearly closed C instead of an O? Would the eddy currents still form and repel the magnet?",
"Electric generators? When a magnet passes through a copper coil and electricity is induced into the coil, is there a magnetic resistance on the magnet as it passes through the coil?",
"Flux through a Mobius strip I was sent here from mathoverflow, hoping for a complete answer to this: === A friend of mine asked me what is the flux of the electric field (or any vector field like $$ \\vec r=(x,y,z)\\mapsto \\frac{\\vec r}{|r|^3} $$ where $|r|=(x^2+y^2+z^2)^{1/2}$) through a Mobius strip. It seems to me there are no way to compute it in the \"standard\" way because the strip is not orientable, but if I think about the fact that such a strip _can_ indeed be built (for example using a thin metal layer), I also think that an answer _must_ be mathematically expressible. Searching on wikipedia I found that http://en.wikipedia.org/wiki/Mobius_resistor A Möbius resistor is an electrical component made up of two conductive surfaces separated by a dielectric material, twisted 180° and connected to form a Möbius strip. _It provides a resistor which has no residual self- inductance, meaning that it can resist the flow of electricity without causing magnetic interference at the same time._ How can I relate the highlighted phrase to some known differential geometry (physics, analysis?) theorem? Thanks a lot! === Now, I'm convinced that there are no way to apply Gauss law since there are no ways to bound a portion of space with a Mobius strip. Nonetheless I would like to \"see\" some equations showing me that \"[the mobius resistor] can resist the flow of electricity without causing magnetic interference at the same time\".",
"Does a material exist that reduces a magnetic field without being affected by the magnetic field itself? Consider a common bar magnet, `magnet 1` resting on a surface with its `North` pole facing up. Suspended distance $y$ above it (supported side-to-side by a plastic tube) is a second, smaller bar magnet, `magnet 2`, with its `North` pole facing down. The magnetic forces between them exceed the force of gravity, and keep `magnet 2` suspended. Consider some material, `material-X` that is moving towards the gap between the two magnets at an initial velocity $v$. Does a material, `material-X` exist that would reduce the distance $y$ between the two magnets, and pass through the gap without changing velocity $v$? ",
"low magnetic permeability, low coercivity compounds? First question: Does anyone know of any low permeability, low coercivity magnetic compounds? A physics professor told me that I should dig deep in the literature, but that I should look for materials with a Curie temperature ~100K and that I should avoid cubic structures. I haven't had much luck finding anything though. In terms of compounds with low permeability, I have found Gd75Co25, and TcC, but I haven't found any permeability information about them. Thanks for anyone who gives this question a second thought.",
"is there any relation between resistance and magnetism? i was holding a resistance wire( **insulated** ) coiled up and both of its ends were connected to a Ohm-meter it was showing 18 ohms while the circuit was on i pulled the coil from both ends and made that a straight wire with barely a knot in between and observed that the reading of Ohm meter **dropped** to 16.5 Ohms. Is there any relationship between resistance and magnetic field? or was it just because the ohm-meter is having errors?",
"What happens when you pass a current through a coil made of a ferromagnetic substance? I know when you pass a current through a length of copper coil or a solenoid, there is the induction of a magnetic flux. But what of the coil made of the ferromagnetic material, the permanent type magnetic material? Is there superposition? Is there Interference thus resulting in the cancellation of the overall field?"
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Why is gravitation force always attractive? | [
"Repulsive gravity\nIANAP, so feel free to berate me for thinking apocryphal thoughts! Just as magnetism has two charges, in which particles of like-charge repulse and particles of dissimilar charge attract, might gravity have two charges in which particles of like-charge attract and particles of dissimilar charge repulse? In practice, the state of magnetism means that there is no system composed of many particles in which all particles attract. Rather, there is a net 0 charge if there are equal numbers of each particle type. My silly theory regarding gravity would mean in practice that there would be two (or more) \"clumps\" (or universes) in existence, which are racing away from each other. So in our clump (universe) we see only attracting particles, because all the opposing particles have long since separated out and are racing away beyond the boundary of the observable universe. Just like the alien who lands in China and assumes that all humans have slanted eyes, we only observe the attracting particles (or \"charge\") and disregard the other, unobservable, \"charge\". Is there any way to disprove this idea, or like string theory can I go one believing it as it can never be disproved? Thanks.",
"Attractiveness of spin 2 gauge theories\n> **Possible Duplicate:** > Why is gravitation force always attractive? I have heard that the attractiveness of gravitation is due to the fact that it is a spin 2 gauge theory. Why is this so? I find this very interesting and would love to understand this fact.",
"Why gravity is an attractive force?\nWhy gravity is an attractive force? * * * One may say that it is because of space time curvature but General Relativity is built on this law: $\\displaystyle G \\frac{m_1 \\times m_2}{r^2}$ (To be more precise, it is derived from it's potentiel form known as Gauss's law for gravity that can be written like this: $\\nabla \\cdot g = - 4\\pi Gp $). So GR can't explain why gravity is attractive. General Relativity only explains how gravity occurs in terms of space time. * * * Another may stick with the Quantum theory stating that gravitons are responsible for the force of gravity, but why a massless particle with spin 2 will exchange positive momentum?",
"Gravitational Force (conceptual)\n1. Why is gravitational force always an attractive force? 2. And is the Newtonian formula of gravitational force applicable for very small particles like electrons and protons etc.? From **Formula of Gravitational Force** , I'm referring to: $$F_G = \\cfrac{GMm}{R^2}, $$ where $M$ and $m$ are the masses of objects. A logical explanation will be much appreciated."
] | [
"Is Galilei's reasoning on free fall valid? Galileo Galilei discovered by experiments that all bodies tend to fall with the same rapidity (I use it in an intuitive sense, you can replace it by 'acceleration' used in today's physics language), independently of their weight. He also provided the following rationale, based on the proof by contradiction (I do not have the original wording at hand, but I believe I can paraphrase the idea, which I am interested in.) Let's imagine one heavy body and one light body. Suppose that heavy bodies fall faster than light bodies, as almost everybody believes. Connect the two bodies so that they form another body. This resulting body is heavier than the original heavy body, so according to the assumption it should fall faster. But on the other hand, the original heavy body is being inhibited in its fall by the connected light body, since this \"wants\" to fall with less rapidity. Due to this inhibition, the heavy body part should fall with less rapidity than it falls normally alone. So we arrive at contradiction, and the only way to resolve it is to reject the assumption. Instead, all bodies fall with the same rapidity (acceleration). What do you think of this argument - is it valid, or no? For what reasons? It is very compelling at first, but on the other hand, should not the law of free fall be experimental law, rather than logical necessity? If so, where is the problem with the reasoning?",
"Calculating Gravitational Attraction Involving Massless Objects Using the formula $F=G\\frac{m_1m_2}{d^2}$ where $m_1$and $m_2$ are the masses of two objects, $G$ is the gravitational constant, and $d$ is the distance between the objects, it is possible to calculate the force of the gravitational attraction between the objects in Newtons. However, since light is affected by black holes, the property required to interact gravitationally is energy, not mass. How can I calculate the gravitational attraction between objects using their energies instead of their masses?",
"Inertia and Rocket Propulsion We were taught in school that the law of inertia indicates that an object tend to stay the way it is, so if you throw something in space it will tend to go on forever and ever. The reason an object falls down when you throw it on Earth is because of gravity and air resistance. If that's the case, why don't rockets and spaceships need just enough fuel to escape the atmosphere plus the single thrust to push the craft in the right direction and let inertia drift it away?",
"Why point mass leaves it's own gravitational well? I suppose that point mass has its own gravitational well. Why this point mass is still attracted by other gravitational waves. I expect that this point mass is surrounded by \"gravitational hills\". Why it is not blind to other weaker gravitational waves? If we think about gravity in terms of shape of spacetime. I mean that point mass (left chart) creates \"sharp\" gravity potential. Lowest gravity potential is exactly where point mass is located. Point stays in place (?). When mass is spread across spacetime (right chart) this is different. Lowest gravity potential is moved from the centre of the object. Object accelerates. Does point mass exist in real world? ",
"When a ball is tossed straight up, does it experience momentary equilibrium at top of its path? This question has been asked many times all over the Internet and answers can be found on places such as yahoo and ask.com, but I'm not satisfied with those answers and I don't trust the validity of those places. This seems like a more appropriate place to ask. So, here's my train of thought and I would like to ask you if you think I'm right or wrong. Even though most of the answers point to the fact that the ball does not achieve equilibrium because the force of gravity is constantly acting upon it, thus causing an acceleration, I still think there's a moment of equilibrium and here's why: When the ball is traveling up, it's accelerating towards the ground and eventually reaches a point at which its speed reaches 0. At this moment, isn't the reason the speed is 0 is due to the fact that net force is 0? The force that made the ball travel in the upward direction was canceled out by the gravitational force. So, the sum of forces at that brief moment is equal to 0, otherwise the ball would be moving. I don't think gravity is the only force acting on the ball at that moment, since the throwing force was acting on it as well, until both canceled each other out for that brief moment. Am I right or wrong?",
"How Come gravity doesn't affect itself? If gravity is this \"unexplainable force\" that pulls everything to the center of a planet or stellar remnant you stand upon, why doesn't gravity pull itself? If gravity effects anything with energy, why doesn't gravity effect itself? Gravity is energy, right?",
"Staying in orbit - but doesn't any perturbation start a positive feedback? I am not a physicist; I am a software engineer. While trying to fall asleep recently, I started thinking about the following. There are many explanations online of how any object stays in orbit. The explanation boil down to a _balance_ of the object's tangential force with centripetal force. But suppose something upsets this balance by a miniscule amount -- say, a meteorite or a spaceship crashing into Earth. Doesn't this start a **positive feedback** process to break Earth out of orbit? Suppose the meteorite crashes such that the Earth is briefly forced toward the sun. (The meteorite contributes to the centripetal force.) Now Earth is just a smidgen closer to the sun. Due to the equation $F=G \\frac{m_1 m_2}{d^2}$ that everyone learns in high school physics, the sun's centripetal force acting on Earth in turn increases! That pulls Earth even closer to the sun, increasing centripetal force yet more, and so on. A similar argument applies to briefly forcing Earth _away_ from the sun. Empirically, I want to say that there's a buffer, such that if the balance of forces is disrupted by less than X%, we remain in orbit. But I cannot justify any buffer from the equation above. So, what am I missing? How can objects in orbit suffer minor perturbations in the balance of tangential and centripetal force and yet remain in orbit, when it appears to me that any perturbation starts a positive feedback loop?",
"Normal reaction - force without acceleration When a body lies on the surface of the Earth it is under the influence of gravity. The force on the body due to gravity causes it to exert a force on the ground and the normal reaction acts in the opposite direction causing the resultant force on the body to be zero. However, how can the body exert a force on the ground when it does not have any acceleration? Since force equals mass times acceleration how does a body without acceleration experience a force?",
"Electrical force vs gravitational force Given that the electrical force is so much stronger than gravitational force at atomic levels, why is it that it's the gravitational force between you and the earth that keeps you on the ground rather than the electrical force between you and the earth?",
"Is Gravity a part of the Strong Nuclear Force? In episode 7 season 5 of Through the Wormhole, they say that gravity could just be a manifestation of the strong nuclear force and that the force carrier are a pair of Gluons. Is this valid in anyway?",
"Vacuum energy and perpetual motion The part of the Einstein equations of general relativity referred to vacuum energy, introduce a repulsive term in gravity. This means that as the space become bigger and bigger, vacuum part become more and more important, leading to an undefined accelerated growth of the universe. Why vacuum energy does not violate the principles of thermodynamic? This is a sort of perpetual motion, isn't it?",
"A force opposing Gravity _Every Action Has An Equal and Opposite Reaction_ (Newton's Third Law.) If this is the case, does gravity have an equal-opposing force? From asking around I still haven't got a very clear answer; those who I've talked to seem to believe there isn't one - that gravity is actually a singularity [a one way force] which somehow \"just works\", others think it differently - believing there **is** an opposing force of which prevents gravity from compressing masses more than it already does. So which one is the right answer? (if either!)",
"Statements about gravitational potential energy contradicting intuition? So in my textbook I am told: two masses have gravitational potential energy because work had to be done in order to move one the masses form a position very far away (lets say infinity) to the position near the other mass. Additionally, I found on a physics forum: \"zero potential energy is at an infinite distance from the centre of a spherical object.\" I am lost. My intuition suggests that you have zero gravitational potential energy when the two masses are right next to each other! As gravity is attractive, you need to do work in fact get away, not to get closer! So when you are \"infinitely\" far away from another mass m (there exists nothing else other than m and you), you actually have very high gravitational potential energy (I know I am over-simplifying). What am I getting wrong?",
"Gravity - What happens when two objects of unequal masses fall freely towards the ground? (Revisited) The common perception regarding what happens when two objects of equal sizes but unequal mass are allowed to fall freely towards the ground is that - both the objects make contact with the ground at the same instant. This is attributed to the fact that the acceleration of both the objects towards the earth are the same for a given height. This was the reason for Galileo's expirement. But the above fact ignores the fact that each of the three objects are attracting each other. In particular, the heavier object also attracts the lighter object, thus decreasing the distance between the lighter object and earth. Note : I am ignoring the fact that the lighter object would also attract the heavier object (but to a lesser extent) and since the earth moves approximately in the same direction as a result of the attraction from the other two spheres, that is also ignored. Otherwise the earth can be said to move diagonally towards the heavier object (again to a small extent). * * * I have included an illustration showing the movement of the lighter object towards the heavier one.  * * * **As such the lighter object should fall first is it not?** Note : Generally, the two objects are placed close to each other (the distance-d between the objects is lesser than the height-h from the ground - 'd < h' ). Continuing with the same logic, I have the following understanding : When two spheres of equal size but unequal masses are allowed to fall freely towards the ground - 1.) From a height greater than the distance between the two spheres, the lighter sphere makes contact with the ground first. 2.) From same height as the distance between the two spheres, both the spheres make contact with the ground at the same time. 3.) From a height lesser than the distance between the two spheres, the heavier sphere makes contact with the ground first. Note : a.) The ground is also a sphere. b.) The distance between the spheres are measured from their centers. **Is my understanding correct?** I also found this Phys.SE post. Which speaks of a scenario where in only two objects are involved. My question is similar to it. PS: I have blogged about it before as well, saying it is so and also elaborated on two other cases ($d=h$ and $d>h$).",
"How do objects even move due to gravity? I am an newbie general relativistic learner and I learnt that gravity is bending of space-time and since objects move in straight-lines but since its curved they follow curved movement through space thus creating the effect we know as gravity. That said, what if an object has velocity of 0 and since its not moving at all, (except in Time) why does the object fall or move in curved space-time (geodesics)? Is there external force that also pulls the object if so why and how does it work? If the object moves in an curved space-time, why does an object just move in an normal space-time (not curved) rather than stay at velocity 0? Is there any reason why this happens?",
"How do we end up with a gravity-dominant macroscopic universe from a quantum world having weakest gravity? At quantum scale, gravity is the weakest force. Its even negligible in front of weak force, electromagnetic force, strong force. At macroscopic scale, we see gravity everywhere. Its actually ruling the universe. Electromagnetic force is also everywhere, but its at rank 2 when it comes to controlling motion of macroscopic bodies. And, there's no luck finding strong force and weak force. How can that be? Is that because gravity only adds up but others cancelled out too? I am unable to understand how resultant of weakest force can be so big. Can you please show it with calculation?",
"Inelastic collision and impulse Suppose I have some cart moving horizontally in a straight line and with a constant velocity, and there is no friction between the surface and the cart. Now, I throw a plasticine on the cart at some angle with the path (not right angle).  The net momentum before the hit was at some angle with the path. After the hit it changed its direction to the direction of the moving cart. So the momentum is not preserved in this case which means there is some external impulse acting on the system which alters the direction of the net momentum as described before. Now, this impulse must be canceling out the vertical component of the net momentum before the collision. Therefore its direction must be upwards. Now, I'm told that this happens because of the normal force acting on the cart: before the collision it was \"canceling out\" the gravitation, which made equilibrium in the vertical axis possible, but **during the collision** it has grown so the net force has become some non- zero value at that direction, and it was the source of the impulse which \"canceled out\" the vertical component of the net momentum. My question is - how could it be? Is it because the plasticine, during this short period of time of the collision is pushing harder and harder the cart, so it pushes the ground and the ground pushes the cart with the same force (according to Newton's third law), but somehow the gravitation is not still balancing the normal force, maybe because the cart and the plasticine can't be considered one uniform object at that short period of time? And another related question - in the example described above, how can I tell whether the speed of the cart will increase or decrease (no values, just that) after the collision, knowing the angle, and using only Newton's laws (no momentum considerations)?",
"How exactly does gravity work? The electromagnetic force and strong and weak forces require particles like photons and gluons. But in case of gravity there is no such particle found. Every _mass_ bearing object creates a gravitational field around it, and whenever another mass bearing object enters its field the gravitational force comes into operation. If all other forces of nature have some particles associated with them why should gravity be an exception? And if there is no such particle, what exactly is the gravitational field and how does it spread over an infinite distance and cause the gravitational force to operate? * * * **Note:** I am a high school student and have not studied quantum mechanics.",
"How forces are in this shape? I consider friction at zero. No gravity here. It's a theoretical problem. I placed some compressible balls in a volume like this:  The volume is fixed. Balls can't escape. Balls are considered like perfect for transmit pressure. Balls have different diameters like atoms can have (Hydrogen/Uranium). I press all balls but in other plan (side view) with a fixed external force (spring for example).  Is the pressure always the same in this volume ? If the reply is yes, the curved shape give red forces, this increase pressure at \"top (of the screen)\", like pressure is the same everywhere, the pressure everywhere increase, so red force increase too, this would say the pressure increase to infinite value if balls are perfect and no friction. See the loop.  It's possible to change layer at left and at right, like that all pressure can return to each layer:  What's wrong with forces I drawn ? Or maybe I forget a force. Or maybe pressure is not the same everywhere, but in this case how explain this with forces ?",
"Forces: Worth worrying anything? I am a general physics student, I had a question in my text-book and according to it two students having gravitational attraction between them = ($6.67\\cdot10^-8\\ \\mathrm{Nm}^2/\\mathrm{kg}^2$) is not worth worrying about. My question is Why? How much force between two objects is worth anything?",
"Two hanging masses connected by springs I had this problem for a candidacy exam, but wasn't able to get the complete answer. Their spring constants and masses are not the same, find the equilibrium position and frequencies of the system. Apparently once you find their equilibrium position, i.e. when gravity and the spring forces cancel out, you can transform to about that position and ignore gravity. Why do you get to ignore gravity? This is a normal modes problem, but I couldn't justify why gravity just disappears, but it does. Anyone have a simple reason why?",
"Torque on object I would like to understand why the torque on white object is 0. I know gravitational forces are very low. But the torque must be at 0. I drawn all the study in first image. Blue color is a torus of liquid helium. The white object is vacuum (or gas at very low pressure). I drawn gravitational forces from atoms of helium to atoms of helium in second image, red forces showing gravitational forces on atoms. I drawn details of all forces in third image. Atom attract another atom: f1 and f2 forces These forces give forces on support fs1 and fs2 Support reply and give -fs1 and -fs2 Sum1 is the sum of forces on atom 1 Sum2 is the sum of forces on atom 2 Like white object can only turn. Sum1 and fs2 are canceled if surface of white object is radial or part of circle. fs1 give a torque to white object $T1 = fs1 * r2$ and atom give a torque to helium $T2 = sum2 * r1$. Torques are not the same, why ?  * * *  * * * ",
"Does gravitation of a sphere equal gravitation of a point? Under Newtonian model of gravity, a perfect sphere creates the same gravitation field as a point mass in its center. General Relativity describes gravitation differently. How much this difference affect the above equivalence? If it does not hold, what kind of difference (qualitatively) there is?",
"Positivity of Total Gravitational Energy in GR I read the following statement in the introduction to an article: > _Over the last 30 years, one of the greatest achievements in classical > general relativity has certainly been the proof of the positivity of the > total gravitational energy, both at spatial and null infinity. It is > precisely its positivity that makes this notion not only important (because > of its theoretical significance), but also a useful tool in the everyday > practice of working relativists._ Since I haven't been involved in GR for about 30yrs, I've missed this. Could someone briefly explain how these results are stated and give some references if possible.",
"So gravity turns things round It makes sense, since gravity tends to push the surface of a body towards it's center. Unless I'm mistaken, everything with mass has it's own gravity, every atom and for instance, our own bodies should also have their own gravity. The question is: how strong is our own gravitational pull? I know it must be extremely weak, but is there actually anything at all that gets attracted to us, like maybe, bacteria or molecules? And finally (this will sound ridiculous, but I'd really want to get an answer or at least a way of calculating it myself): What size would a human body have to reach in order for it to collapse into a sphere?",
"Does gravity cause Archimedes' principle and how? Why do lighter objects float and denser sink? I understand this from the perspective that if the object can displace the equal mass of water it will float, but I wonder from the perspective of **gravity**! How does gravity cause Archimedes' principle? It must be gravity, right, because in space Archimedes' principle doesn't work! The ultimate question I need to answer is **how all this force interplay causes density stratification**. For example, how does gravity cause Earth to have a density gradient: the densest elements in the core, and the lightest in the crust? * * * Here's what I got from the comments so far. I though it should be a good starting point if someone wants to write an answer. It also can be totally wrong. There is a pressure gradient inside a body of liquid along the depth gradient. It is caused by the fact that the distance between two objects is squared and inversely proportional to the gravitational pull (see the image below). The deeper water thus is attracted to the Earth stronger, and where there is a pressure difference, there is a force, the buoyant force in this case. However, now I have even more questions than I used to: 1. If there is a pressure gradient, why there's no flow in water along the depth gradient? 2. What mechanism (or what part of the gravity equation) makes denser objects sink despite the buoyant force? Is it the mass? What about Galileo's experiment then? Doesn't it show that the effect of mass is negligible? ",
"Is Brian Cox right to claim that Gravity is a strong force for large masses, is it wrong, or is it only a matter of interpretation? I watched a program of his in which it was claimed that since mass bends space in accordance to General Relativity, then in the case of very large stars it becomes a strong force to the point of being able to crush a star to a single nucleus (Neutron Stars) or less (Black Holes). His argument is that Gravity is a force that **scales** and that it is not simply a matter of adding individual components and hence to claim it's weak, but that since space is bent in those areas, then gravity as a _fundamental force of nature_ becomes stronger. Now, I wonder not only about the claim's accuracy, but also if it's only a matter of interpretation and nobody is really wrong or right, as long as the discussion is framed properly.",
"Similarity between the Coulomb force and Newton's gravitational force Coulomb force and gravitational force has the same governing equation. So they should be same in nature. A moving electric charge creates magnetic field, so a moving mass should create some force which will be analogous to magnetic force.",
"Why is work in a constant electric field equal to the force times distance? Let's say, for example, that an infinite plate generates a constant electric field that exerts a force of 6N on a 1C charge. To move the charge from a distance of 5m to 1m from the plate, the work done is given by 6N * 4m = 24Nm. The way this has always been explained is that we apply a 6N force over the 4m distance. However, this doesn't make intuitive sense to me: * If we apply a constant 6N force to the charge in the opposite direction of the electric field, won't the charge simply remain stationary? The force generated by the field and our applied force in the opposite direction should net to zero. * If the electric field exerts a force of 6N on the charge at every single infinitesimal point along the path from 5m to 1m, when we apply an opposite force of 6N over that same distance, shouldn't the charge simply stay still? * I think what's troubling me is that I don't see how applying a 6N force can \"overcome\" the electric field's force and actually move the charge in the opposite direction. I think the intuition is the same for the force of gravity. A 1kg object that is 1m above the ground is experiencing a force downwards of 10N. If I apply a constant upwards force of 10N, the object won't fall. But how is that if I apply a 10N upwards force over 1m, I can actually move the object upwards? Gravity is exerting a downwards 10N force on the object the entire time I am exerting an upwards 10N force over that 1m. If the forces are equivalent, shouldn't the mass stay still?",
"Non-Constant Acceleration due to Gravity Recently, I had the first physics lab for my university physics course. This lab was fairly simple, as we were merely using a computer and a distance sensor to graph the position, velocity, and acceleration of a cart as it moved along a linear track. One of the situations we captured data for involved starting the cart at the bottom of an inclined ramp and giving it a push upwards. As expected, it rolled up, came to a stop, and then came back down the track to its starting position. The position-vs-time graph was essentially parabolic, the velocity- vs-time graph was essentially linear, and the acceleration-vs-time graph was essentially linear. So far, so good. At this point in the lab, the instructor pointed out that, if the data was examined closely, the acceleration of the cart was greater while the cart was traveling upwards than when the cart was traveling downwards (approximately $0.546\\frac{m}{s^2}$ and $0.486\\frac{m}{s^2}$, respectively), and asked us to determine _why_ in our lab report. Now, gravity was the only force acting upon the cart, and thus it's acceleration should be a constant, at least at the scale our experiment was conducted at, so these results are completely baffling my lab group. So far, we have proposed the following ideas, but none of them seem very plausible. * Doppler effect on the ultrasonic distance sensor * Friction * Air resistance * Human error The first seems highly improbable, and the last three are more obfuscation and hand waving than actual theories. **Why does our experimental data show the acceleration due to gravity to change based on the direction the object is moving?**",
"The ideal trampoline Suppose we have a mass attached to the top of an ideal (linear and massless) spring oriented vertically in a uniform gravitational field, and on top of that mass there is another mass resting on it. The two masses are not attached at all, so they will lose contact with each other as the normal force is about to become negative. Also suppose that once the two masses separate and collide again, they undergo perfectly elastic collisions. First of all, is there a name for systems like this? It seems like an \"ideal trampoline\" to me but searching for that doesn't yield much. Has anyone ever discussed it in a book? Second of all, is this system chaotic? For sufficiently small oscillations, of course, the masses remain in contact the whole time and you get simple harmonic oscillation, but above some threshold the free mass will keep bouncing off the spring-attached mass and it's quite nontrivial to figure out what eventually happens. Do you get interesting things like period doubling?",
"If there were fundamental forces weaker than gravity, would we know about it? We know that gravity is a very weak force compared to electromagnetic forces and the nuclear forces. We know about the other forces because they're necessary to explain atoms, and we can detect gravity easily, because unlike the other forces it is always attractive, so the weak gravitational force from every particle in a planet can add up to a measurable effect. However, is it possible that there are other fundamental forces that are much weaker than gravity, or even of a similar magnitude but with \"charges\" that attract their opposite and therefore cancel out over large scales? It seems that we wouldn't necessarily have detected such a force if it did exist, and it seems different from the kind of thing you can probe using a particle accelerator. I realise this question is kind of naïve. I know a little quantum mechanics but never studied quantum field theory or particle physics. I'm curious about whether those formalisms provide a way to rule out such additional weak forces.",
"What limits range of gravitational attraction concerning space expansion? Wikipedia says: > Metric expansion is a key feature of Big Bang cosmology and is modeled > mathematically with the FLRW metric. This model is valid in the present era > only on large scales (roughly the scale of galaxy clusters and above). At > smaller scales matter has become bound together under the influence of > gravitational attraction and such bound objects clumps do not expand at the > metric expansion rate as the universe ages, though they continue to recede > from one another. ...why? All gravity equations I know are continuous and smooth - gravity never drops to zero. Reading the above though sounds as if there was a cut-off point somewhere; bodies far enough cease to be bound entirely. It's no longer several forces overlapping and struggling, like electromagnetic and strong, struggling between binding the atom nucleus and tearing it apart. The statement makes it sound as if there was a clear-cut border between where gravity works and where metric expansion works, clusters of galaxies with their gravitational field reaching a finite distance, like free-falling snowflakes able to clump together when they meet. Is there a border limiting range of gravity? How is the separation between gravitationally bound and independent systems explained?",
"Mass distribution driven by gravitational field In a gravitational field, should the mass distributions always behave well?",
"Why would spacetime curvature cause gravity? It is fine to say that for an object flying past a massive object, the spacetime is curved by the massive object, and so the object flying past follows the curved path of the geodesic, so it \"appears\" to be experiencing gravitational acceleration. Do we also say along with it, that the object flying past in reality exeriences NO attraction force towards the massive object? Is it just following the spacetime geodesic curve while experiencing NO attractive force? Now come to the other issue: Supposing two objects are at rest relative to each other, ie they are not following any spacetime geodesic. Then why will they experience gravitational attraction towards each other? E.g. why will an apple fall to earth? Why won't it sit there in its original position high above the earth? How does the curvature of spacetime cause it to experience an attraction force towards the earth, and why would we need to exert a force in reverse direction to prevent it from falling? How does the curvature of spacetime cause this? When the apple was detatched from the branch of the tree, it was stationary, so it did not have to follow any geodesic curve. So we cannot just say that it fell to earth because its geodesic curve passed through the earth. Why did the spacetime curvature cause it to start moving in the first place?",
"A real gas with gravitation-like interaction Consider a system (a gas) of point-like particles with a gravitation-like interaction (potential) $V(r) \\sim \\frac{1}{r}$ between pairs of them. One can rule out statistically that two particles will approach each other exactly along their line, so two particles will never collide directly - thus giving rise to infinite (kinetic) energies. So the particles will always whirl around each other in one way or the other. What can be said about such a system in the framework of statistical mechanics? How does its partition function look like? What are its thermodynamical equilibrium states? What happens when cooling such a system down (e.g. from very high temperatures)?",
"Do the four fundalmental forces of physics have a constant acceleration as gravity Do the four fundalmental forces of physics have a constant acceleration as gravity?",
"What is the difference between gravitation and electromagnetism? I am currently studying electrodynamics. And when looking at Maxwell's equations, I don't see any reason, why we cannot apply them to gravity. We know that charges generate a force field that attracts opposite charges. From this and using special relativity we can deduce that there must be a magnetic field (see this nice video from minutephysics). But masses also generate a force field that attracts other masses. Then by the same reasoning, moving masses must also generate some kind of field that interacts with other moving masses. And indeed, this happens. It's called Lense-Thirring effect. So if these fields are so similar, why aren't there some kind of Maxwell's equations for gravity? **What is the difference between electromagnetism and gravity?** **EDIT:** Thanks for the comments. So it basically boils down to the question why charge is invariant under Lorentz transformations while mass is not.",
"Is Newton's Law of Gravity consistent with General Relativity? By 'Newton's Law of Gravity', I am referring to > _The magnitude of the force of gravity is proportional to the product of the > mass of the two objects and inversely proportional to their distance > squared._ Does this law of attraction still hold under General Relativity's Tensor Equations? I don't really know enough about mathematics to be able to solve any of Einstein's field equations, but does Newton's basic law of the magnitude of attraction still hold? If they are only approximations, what causes them to differ?",
"Gravitation - why is it so confusing? First, does gravity emit from all directions around a star or planet equally. Secondly, how is it that gravity pulls a planet closer, then it goes further out, without the planet changing orbit permanently?",
"Space time curvature due to electric charge or magnetic charges since we know that gravitational force is nothing but a curvature in space- time. I have a similar analogous for the electric or magnetic charges. Similarity is that both electromagnetic and gravitational forces follow the inverse square law. consequence of this can be that we can have a another interpretation of electron orbital motion causes by curvature in space due to electric charge (as mass of electron is very small so STR have no significance here). But problem is that we have two different type of charges (+ve and -ve) which gives repulsion and attraction, whereas in gravitation force mass always gives the attraction forces. Please correct me if I am wrong.",
"Why is there an escape velocity? I've been trying for days, but I just can't understand why escape velocities exist. I've searched the web and even this site, and although I've read many explanations, I haven't been able to _truly_ understand them. Most of the explanations I've seen involve calculus; I only know very little calculus. Could somebody provide a more intuitive explanation? Here's what I know & understand: * Escape velocity is the speed at which the kinetic energy equals the gravitational potential energy of an object * Escape velocity isn't the same as orbital velocity, a satellite never reaches escape velocity, escape velocity is only an initial velocity. And all the other common misconceptions. What I do not understand, is why an object that has reached escape velocity will never return back to the planet it was launched from. To help you understand where I'm stuck, here's a short \"proof\": 1. Our whole universe consists of only two bodies. A teapot of mass m, and a planet of mass M. M is many million times larger than m, so the gravitational force acting on the planet is trivial. 2. We launch the teapot from the planet, giving it an initial velocity U (relative to the planet). **U > escape velocity for that particular planet.** 3. Now, the only force acting on the body (teapot) is the gravitational force from the planet, resulting in a negative acceleration (relative to the planet). The force, and therefore the resulting deceleration, will be decreasing quadratically as distance increases. The negative acceleration will get very close to, but never quite reach, zero. 4. Therefore, the speed of the teapot will never stop decreasing. **The teapot will keep decelerating forever.** 5. We conclude that at some point, **the speed of the teapot will reach zero**. The teapot will then fall back to the planet, even though U was greater than the escape velocity. I suspect that my implication _(4) => (5)_ is false. Somebody please explain why, using as little Calculus as possible. Could this be similar to the _Achilles and the Tortoise_ paradox? Thanks in advance!",
"Nature of gravity: gravitons, curvature of space-time or both? General relativity tells us that what we perceive as gravity is curvature of space-time. On the other hand (as I understand it) gravity can be understood as a force between objects which are exchanging (hypothetical) virtual particles called gravitons, similar to the way electromagnetic forces are due to objects exchanging virtual photons? At least at first glance, the two concepts seem mutually exclusive. Is there a description of gravity which includes both, or is this contradiction one of the problems in combining GR with quantum mechanics?",
"If gravitation causes constant acceleration why moon does not fall into earth? If moon travels with constant speed in one direction and earth gravitation causes constant acceleration in perpendicular direction why moon does not eventually fall into earth? I mean if gravitation causes moon to fall faster each second (10m/s2) shouldn't after time velocity toward earth be big enough to cause it to fall ?",
"How to prove that identical particles are attracted or repelled in a given spin-s interaction theory? Let's assume that we have integer spin interaction theory (EM field, linearized gravity, arbitrary gauge spin s theory). How to prove the consequence that in interaction theory with spin $s = 2n$ two identical particles (equal spins, masses, all charges etc) are attracted (like gravity), while in $s = 2n + 1$ theory they are repelled (like in EM interactions)?",
"Einstein's Explanation for gravity vs. Newtonian I was trying to understand the Einstein's explanation for gravity (gravitational force), and while I am able to understand why two moving masses will be attracted, due to the curving of the space, I am not quite able to understand what would make an apple fall, i.e., how will Einstein model explain the gravitational force between two stationary objects? (Please correct me if I am wrong anywhere. I am a computer scientist; hence physics is not my forte! :D)",
"What's a geometric explanation for exponential-falloff fundamental forces? Gravity and electromagnetism are inverse-square laws. This makes geometric sense -- if you build a spherical shell around a lamp then a shell with twice the radius has four times the surface area and hence a quarter of the intensity per unit area. The strong interaction has a nontrivial distance-strength relation with an exponential term. Is there an intuitive geometrical explanation for this?",
"What is the effect of temperature on electrostatic-gravitational balance? We have two identical massive metal spheres at the same temperature at rest in free space. Both have an identical charge and the Coulomb force [plus the black-body radiation pressure if the temperature is non-zero] exactly counteracts the gravitational force between them, resulting in no net forces on either object. They are electrostatically levitating at rest in space. It is my understanding that the charge distribution in each sphere exists only at the surface, and should be concentrated on the side facing away from the other sphere. Now heat one of the spheres uniformly with an external energy source. What happens in the instant following? Could it be: The increased mass-energy of the hot sphere increases the gravitational force, and the cold sphere starts to fall inward. Or else: The increased temperature modifies the charge distribution on the hot sphere by giving it more variance and bringing it closer on average to the cold sphere, increasing the Coulomb force. The cold sphere starts to fall away. [Carl's answer says there is no effect on the charge distribution like I describe, but DarrenW points out that there will be an increased black-body radiation pressure between the spheres, similarly causing an outward force.] Which direction is correct, and what is the best explanation? Does it depend on the amount of temperature change or the initial conditions?",
"Gravitational force between two masses I get it that there will be a gravitational force between objects attracted towards gravity but can there be a gravitational force between two objects resting on horizontal plane? In other words, does an object experience gravitational force in all directions?",
"Why is gravity such a unique force? My knowledge on this particular field of physics is very sketchy, but I frequently hear of a theoretical \"graviton\", the quantum of the gravitational field. So I guess most physicists' assumption is that gravity can be described by a QFT? But I find this weird, because gravity seems so incredibly different from the other forces (yes, I know \"weirdness\" isn't any sort of scientific deduction principle). For relative strengths: * Strong force: $10^{38}$ * Electromagnetic force: $10^{36}$ * Weak force: $10^{25}$ * Gravity: $1$ Not only does gravity have a vastly weaker magnitude, it also has a very strange interaction with everything else. Consider the Standard Model interactions:  No particle (or field) interacts directly with all other fields. Heck, gluons only barely interact with the rest of them. So why is it then that anything that has energy (e.g. _everything that exists_ ) also has a gravitational interaction? Gravity seems unique in that all particles interact through it. Then there's the whole issue of affecting spacetime. As far as I'm aware, properties such as charge, spin, color, etc. don't affect spacetime (only the energy related to these properties).",
"Equilibrium - uniform circular motion Maybe this is a bit of a silly question, but let us pretend we have a pendulum in a ideal universe with no friction, drag, or anomalous forces there to affect it. Additionally, our pendulum is subjected to an ideal gravitation force, the force vector of which is unaffected by the position of the ball (hence the responsible gravitating body is so massive that its own spherical geometry does not affect the forces on the pendulum-ball. Now we have our pendulum spin around so that it experiences uniform circular motion and some angle theta is formed between the resultant orientation of the spinning pendulum string and its previous stationary form. My question is, is this system in equilibrium? I know that no work is being done even though there is a force. And that from a relativistic (non-Newtonian) point of view, there is no centrifugal force to cancel the centripetal. So please, could you explain the \"answer\" from a Newtonian (high-school physics) POV and a relativistic POV.",
"Is there a fundamental reason why gravitational mass is the same as inertial mass? The principle of equivalence - that, locally, you can't distinguish between a uniform gravitational field and a noninertial frame accelerating in the sense opposite to the gravitational field - is dependent on the equality of gravitational and inertial mass. Is there any deeper reason for why this equality of \"charge corresponding to gravitation\" (that is, the gravitational mass) and the inertial mass (that, in newtonian mechanics, enters the equation F=ma) should hold? While it has been observed to be true to a very high precision, is there any theoretical backing or justification for this? You could, for example (i wonder what physics would look like then, though), have the \"charge corresponding to electromagnetic theory\" equal to the the inertial mass, but that isn't seen to be the case.",
"Why does the earth have to feel a pull when something falls? Heck, I'm not even worried about the speed of a reaction. But remember that if I fall towards the earth, with a force, the earth has the same force exerted upon it in the opposite direction. I was thinking, after reading a comment on a previous gravity question, that gravity should be propagated by particles (this would explain why you instantly feel gravity, its like entering a stream of particles). This would also explain why it would take time to feel a change in the gravitational field. If the change propagates at c, that would explain how similar gravitons are to light. Anyway, if I absorb gravitons, why does the planet care? It acts as though it absorbed equal and opposite gravitons in terms of its resultant force experience. Do we state that a disturbance in the field is sensed, rather like a pressure buildup? I imagine in analogy a water buildup when I stand in the shower propagating backwards up the shower head. It seems as though disturbances in the field would explain it, implying virtual gravitons in an analogy to virtual photons perhaps. Feel free to ignore that if I'm mistreating the idea of virtual photons or whatever-I have heard them described as field disturbances though. To further clarify, an analogy: suppose I am a rotating sprinkler at high frequency. As I throw down water all about me, a post in the garden \"absorbs\" the water I throw at it. I, however, do not react at all, just the water. However, according to what we observe, a planet reacts to a person's weight, and this in my perspective can only be answered if the planet \"senses\" when its gravitons have been absorbed and tries to fill in the gap, throwing in more gravitons than before. Since more gravitons are emitted forward, this would explain why the earth feels a forward push, given that gravitons carry negative energy. (Of course they have to have negative energy, otherwise when you get hit by one it would push you away). This seems more like a fluid force if the fluid moves from regions of low to high density, filling in the gap from absorbant things, in this case all mass- containing objects. Does this sound ok, or am I totally wrong on a point of importance?",
"Will perfect black hole apply force on matter? While standing on a planet its gravitation force is noticeable and manifests only through the normal force, e.g. if jupiter had rocky surface, standing on the surface will apply about 2.5 times more force than when standing on earth. However sky diving on earth and on jupiter (without atmosphere) would apply the same amount of \"destructive\" force, that is 0. Thus gravitation force cannot really destruct matter without something for the matter to interact with. If a black hole with no matter falling into it exists, will a person with space suite die if he would \"jump\" into it? he will have nothing applying \"destructive\" force on it, just kinetic energy that cannot manifest without something to hit.",
"Gravity stronger than electromagnetic force in a black hole? Well, the question has somewhat been answered before, but there's one part missing, which - I'd think - is in conflict with the physical laws. The earlier reply says that the gravitational pull even at the event horizon is so big, that not even the other forces can overcome this. So far, so good...this part I can accept. However, what makes it possible for the black hole to appear in the first place? In this situation, the gravity between every single atom would have to fight against the electromagnetic force in order to compress the atoms sufficiently to create a singularity. Once the singularity is there, the gravitational pull becomes infinite - but how the he** does the electromagnetic force allow the gravity to create the singularity in the first place? I'd say that since the strength of gravity is directly related to the amount of mass - the more mass, the stronger the gravitational pull...but the same amount of mass generates millions of times stronger electromagnetic resistance between the atoms...or, did I misunderstand something completely here?",
"Why is there no Gravitational Magnetic Field? We think that the electric field and gravitational field operate similarly with their corresponding charges/masses. With just a difference that the electric field is sometimes attractive and sometimes repulsive. Now I have read that when a charged particle moves the electric field lines associated with it, it is distorted in one way because of the finite time required to get propagated, and this is the cause of the existence of the magnetic field (if calculus is used it can be proven mathematically). So why is it not the same with the gravitational field? Why is there nothing like a Gravitational Magnetic Field?",
"Gravity is an intrinsic property of every atoms? 1. If gravity is the force of attraction between masses, does this force is an intrinsic property of every atoms? 2. Is there any possibility of some other particles within atom which is yet to be discovered? 3. Or is it simply a result of cosmic waves which created due to big bang? 4. Does anyone have any information regarding variations in gravitational force? 5. If its not there then is it simply be \"something like plasma which entire universe in within its plume and huge masses simply accelerate the attraction\"?",
"Graviton through the horizon and force felt outside a black hole Gravitational force is mediated by graviton exchange. If I am standing outside a black hole, I can of course feel the attracting force towards the black hole. This should correspond to gravitons mediated between the matter inside the horizon and myself; but then these gravitons should cross the horizon from the inside to the outside. My question is: how is this paradox precisely solved? I guess a starting point for an answer is that these gravitons are off-shell, much like in QED where photons exchanged between electrons that feel each other are virtual. But still, this confuses me a bit - is there some references explaining this in detail?",
"Attractive higgs force and inflation Inflation was the extreme accelerating expansion of the universe, see here: http://en.wikipedia.org/wiki/Inflation_(cosmology) It worked in a similar way to dark energy but was so strong it would easily tear atoms apart (if it wasn't far to hot for atoms to form in the first place). The weird thing about inflation and dark energy is that they are under _tension_. **[Optional reading]: Explanation of how pressure works backwards in general relativity** In general relativity, pressure _itself_ is attractive. This is not because it takes energy to compress materials, the energy put in to compressing something simply shows up as extra mass. This is an _extra_ effect. Suppose you dive deep into a (non-rotating) neutron star (pretend the center is liquid) and measure the central density (as a swimmer would gauge the inertial resistance of water). You then move 1mm away from the core, release a pellet of dark matter (which goes right through everything so it has no buoyancy), and measure the acceleration towards the center (because of the shell theorem and the slow maximum speed of the pellet (~10 m/s), you can assume newtonian gravity in the local vicinity). The measured acceleration will be greater than the calculated acceleration, up to almost twice as much. This is a consequence of light bending twice as much as \"expected\" and can be derived from special relativity using a reference frame with constant acceleration. Pressure is equivalent to an exchange of fast-moving particles. These \"virtual\" particles \"bend more\" toward a mass and conversely the mass is pulled back more toward it. The inflation field was under enormous _tension_ , which is the exchange of negative mass particles, and it created a _repulsion_. Another effect is that work must have been done on the inflation energy as space expanded, just as it energy is added to a rubber band when you pull on it. This work showed up as more inflation energy, and meant that it _does not dilute_ when space expands. Eventually, the pressure/density ratio, (equation of state) went above the critical value of -1 and the field began to dissipate. The -1 \"critical value\" also causes that the fluid to be Lorentz invariant, which means there is no preferred reference frame. **The question itself** The Higgs particle is a purely attractive force, see here: http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the- known-forces-of-nature/the-strength-of-the-known-forces/ Could the Higgs force create a strong enough tension (perhaps with help from other forces?) to overwhelm the positive pressure effects of quantum degeneracy and heat and leave enough tension to cause inflation? If so you would not need GUT or TOE speculations for the mechanism of inflation. Furthermore, you could quantify it's strength and the nature of it's eventual decay.",
"Gravity and free fall In Wikipedia it's stated that _\"[..] gravity, is the natural phenomenon by which physical bodies appear to attract each other with a force proportional to their masses\"_. Then I found many examples regarding free fall and gravity, such as \" _a hammer vs feather_ \", \" _an elephant vs a mouse_ \", etc. They all say that in the absence of another external force (like air-friction/resistance), the hammer, the elephant, the mouse and even the tiny feather, will all fall freely with the same speed and at a constant acceleration (like $1g$). Ok, I think I can understand that, it makes sense. Now my question regarding these \"experiments\": * let's suppose that we have an object $E=$ Earth (with its mass ~$6 \\times 10^{24}$ $kg$) * let's suppose that I have other 3 distinct objects: $O_1=$ a planet with a mass $5.99 \\times 10^{24}$kg, $O_2=$ an elephant and $O_3=$ feather. If we imagine that the all 3 objects are situated above the Earth at a distance $d= 250$ miles, and if we suppose that there is no air-resistance or any other external force to stop their free-fall, then what will happen with ours objects? Which will fall first, second, third? My understanding is that the $O_1$'s inner force will fight to attract the Earth toward it. The Earth will do the same thing but, having a mass just \"a bit\" larger than $O_1$, the Earth will eventually win and, will eventually attract the $O_1$ toward it (\"down\" to Earth). The same thing will happen with the elephant and with the mouse/feather, except that the elephant having a larger mass than the mouse (or feather), will fight just a bit more than the others and will decelerate its fall with $0.00000...1\\%$ (let's say) comparing with the mouse/feather (which seems almost the same thing if we ignore few hundred decimals). Am I completely wrong about this story ?",
"What is Verlinde's statistical description of gravity as an entropic force? What is Verlinde's statistical description of gravity as an entropic force leads to the correct inverse square distance law of attraction between classical bodies? ",
"Why is Gravitational force proportional to the masses?. We know that two mass particles attract each other with a force $$F~=~\\frac{G M_1 M_2}{r^2}.$$ But what is the reason behind that? Why does this happen?",
"Gravitation law paradox for very close objects? We all know that gravitation force between two small (not heavenly) bodies is negligible. We give a reason that their mass is VERY small. But according to inverse square law, as $r\\to 0$, then $F\\to \\infty$. But in real life we observe that even if we bring two objects very close, no such force is seen. Why is this so?",
"Why does the force of gravity get weaker as it travels through the dimensions? Some theories predict that the graviton exists in a dimension that we of course can't see, and that is why the force of gravity is so weak. Because by the time gravity has got from the dimension in which the graviton exists to our dimension it has lost much of its strength. For a better understanding of this theory, I think this might help:  Bigger: https://lh4.googleusercontent.com/-M3Z7HBllZys/T5JT- dGobZI/AAAAAAAAFIE/I_XJUA3M0pI/randall_750.jpg?imgmax=1600 Why does the force lose strength as is travels through the other dimensions?",
"Gravity vs inertia As stated according to Newton laws of gravity, every object with mass attracts all other object with a force which produces acceleration. Basically there are several forces in the universe which affects our planet as well. My question: can an inertial frame (which has net force zero) can exist in these condition, and does this frame plays any role in producing acceleration? If two objects are many miles apart and one object has much greater mass then, will the heavier object still accelerate relative to lighter one?",
"Gravitational lensing of massless photons I recently got a more complete proof of photons having no mass. (I knew it before, but now I _really_ know it.) But now, I'm curious how gravitational lensing can occur without a mass to act on. I have heard that space is like a sheet and gravity works because the more massive an object is, the more it bends space. I heard that when I was five years old. When I got older I questioned how that would work, seeing as space is 3-dimensional. The answer I eventually cobbled together from a plethora of excellent resources was this: > Gravity is like a point light source. At the center, you have the most > intense light. As you move outward the intensity decreases with the square > of the distance. Like light, gravity radiates in all directions > simultaneously. This works well for me, and I still believe it to be accurate. However, when I was thinking about photons, I realized that you cannot apply a force to an object without mass. At least, you can't by standard Newtonian thinking. This is because $F=ma$. With no mass, you can have no force. Alternately, you could rearrange to $\\frac{F}{m}=a$. With no mass, and no force, you can have no acceleration. **_Yet gravity is able to refract light._** How is this possible? Like $E=mc^2$, does this only apply to a specific set of conditions?",
"Is it possible to accelerate a mass indefinitely using gravitational field? As a particle's velocity increases, its mass increases(gamma times). Therefore, if a particle is in a gravitational field, the gravitational force it experiences must also increase(gamma times). The net acceleration of the particle, i.e.(gamma*force)/(gamma*mass) should therefore remain constant for small distance traversed by the particle and increase as the particle travels closer and closer to the object generating the gravitational field(due to inverse square relation). Hence. is it possible to accelerate a particle indefinitely using gravitational field?",
"Why do we still need to think of gravity as a force? Firstly I think shades of this question have appeared elsewhere (like here, or here). Hopefully mine is a slightly different take on it. If I'm just being thick please correct me. We always hear about the force of gravity being the odd-one-out of the four forces. And this argument, whenever it's presented in popular science at least, always hinges on the relative strength of the forces. Or for a more in depth picture this excellent thread. But, having had a single, brief semester studying general relativity, I'm struggling to see how it is viewed as a force at all. A force, as I understand it, involves the interaction of matter particles with each other via a field. An energy quantisation of the field is the force carrying particle of the field. In the case of gravity though, particles don't interact with one another in this way. General relativity describes how space-time is distorted by energy. So what looked to everyone before Einstein like two orbiting celestial bodies, bound by some long distance force was actually two lumps of energy distorting space-time enough to make their paths through 3D space elliptical. Yet theorists are still very concerned with \"uniting the 4 forces\". Even though that pesky 4th force has been well described by distortions in space time. Is there a reason for this that is understandable to a recent physics graduate like myself? My main points of confusion: * Why is gravity still viewed as a force? * Is the interaction of particles with space time the force-like interaction? * Is space-time _the_ force field? * If particles not experiencing EM/weak/strong forces merely follow straight lines in higher-dimensional space (what I understand geodesics to be) then how can there be a 4th force acting on them? Thanks to anyone who can help shed some light on this for me!",
"Force inversely proportional to the squared distance **Newton's law of universal gravitation:** \"Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and **inversely proportional to the square of the distance** between them.\" **Coulomb's law:** \"The magnitude of the Electrostatics force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and **inversely proportional to the square of the distances** between them.\" How did Sir Isaac Newton and Sir Charles Augustine De Coulomb come to know that the force, gravitational or coulomb's, is _inversely proportional to the square of the distance between two point masses or charges_ , why didn't they just say that _the force is inversely proportional to the distance of two bodies from each other or two charges_? There must have been something that made them formulate these **inverse-square laws**.",
"Why doesn't gravity bend everything equally? If gravity is the curvature of spacetime it should bend everything equally. To clarify my point I would like you to imagine two scenarios. Think of a bird flying in the storm while the wind is blowing sideways. Because the wind is an active force and the bird is fighting against it, the amount by which it's trajectory is bent should depend on it's momentum for a given strength of wind. Qualitatively speaking, more the momentum the less it bends. Now think of a train moving on a curved track. It should always bend by a fixed degree regardless of it's velocity or mass because the path itself is bent by that precise degree. I am aware that in my examples I have only considered curvature in SPACE but the theory of relativity talks about curvature in SPACETIME and I am guessing that every object's trajectory through spacetime is indeed equally bent due to gravity. Can someone explain? **EDIT** : After reading some comments, I have realized that perhaps my choice of words wasn't that great in the original question. I know that different object will follow different geodesic trajectories based on their initial conditions. What I was interested in is the CHANGE in trajectories due to spacetime curvature. The term I should have used in the question is acceleration. For example, the gravitational acceleration an object will experience near the surface of the earth is g regardless of it's mass or initial velocity. So it's natural to expect that every object will experience the same acceleration when they are moving sideways with respect to a gravitational body. In other words the \"bending\" should be equal. Hope it's a little clearer now.",
"Attraction of a Bullet due to Gravity in a Perfect Vaccum _I realise that this might be conventially very difficult to answer because there's no KG or Newtons in space, only particles._ As far as I understand, every object creates a 'pull' due to the forces of gravity, that'll be felt noticeably by smaller objects (as well as the larger object being attracted 'less' to it). If we fire a bullet in a straight line on earth it'll curve down towards the earth and hit it because of the force of gravity. If we say had a bullet fired in a straight line in space, and an object 1km away at say 30 degrees from the main path, is there any way we can work out how massive that object would have to be for the bullet to hit it. Say the bullet is fired at 10m/s and is on Earth 20g - it's not really the figures I'd just wonder if it's possible.",
"Is Newtonian gravity consistent with an infinite universe? Let us assume that we have have an infinite Newtonian space-time and the universe is uniformly filled with matter of constant density (no fluctuations whatsoever), all of it at rest. By symmetry, the stuff in this universe should not collapse or change position in any way if gravity is the only force acting on it. Now, consider Gauss theorem. It says that within a spherical system (it says more that that but this will suffice), the gravitational force felt by any point will be the same as if all matter between the center and the point were concentrated at the center. The matter outside the sphere does not contribute any force). Thus, in such a system, the matter (stuff, I do not say gas so we can consider it continuous) will collapse towards the center of the sphere. We can apply this argument to any arbitrary point in our previous infinite homogeneous universe, and conclude that matter will collapse towards that point (plus the point is arbitrary). So, why is Gauss's theorem is not valid in this case? I was signaled that this question is a duplicate and has been answered, however: The best I could get from the redirected question is this quote: \"However, the mass can't be negative and the energy density is positive. This would force a violation of the translational symmetry in a uniform Newtonian Universe\". It still doesn't give a satisfactory answer. For instance: how is that symmetry broken if we assume that there is no noise nor small density fluctuations in the system? How can you choose then the absolute \"origin\" that will break the symmetry? Still doesn't make sense to me.",
"How does the nature of nuclear force change between attractive or repulsive based on distance? I know that the nuclear force is responsible for binding the protons and neutrons together in the nucleus. The force is powerfully attractive at small separations and rapidly decreases as the distance between the particles concerned increases and becomes repulsive after that.But, why does that happen? I'm not able to find a way to explain it in anyway.How can a force be attractive and repulsive based on the difference between the concerned particles? This might have to do with how the forces actually work which I'm not familiar with. Please explain to me how this happens. Since I'm a high school student I will be unable to understand the high level math involved(if any in the answer given) so, I would like a conceptual understanding about the situation.",
"What is the smallest particle exhibiting gravitational properties? I've long been taught that all matter having mass, possesses attractive forces somewhat akin to gravity. As such, imagine we can 'teleport' a gravitonic detection device that can accurately measure the gravitational forces regardless of strength present at each location, it can detect all gravitational forces ordered by direction of pull within a given radius of up to let say [through a range of settings/switches of 0.001 nanometer to 100,000 km. We teleport these detectors equi-distantly apart in the earth, from troposphere to molten mantle to core's center of mass. measure and plot all the forces detected. Supposedly, there is no gravity at earths center of mass...that means gravity can be concentrated and nullified. Logic tends to indicate 'no gravity=no weight. Therefore why does all reference material say massive objects have tremendously large core pressures and squeeze atoms to extremely dense masses. If gravity is nullified, what is source of this crushing, without usurping all gravitational common sense?",
"Why Gravity attracts all objects with the same speed? Why Gravity attracts all objects with the same speed? Is this question was solved? What is the exact answer?",
"What is the consequence of \"infinite\" gravitational force? ## Introduction I am a mathematically minded individual. I do not intuitively comprehend physics, and as a sophomore in high school who has only taken Intro to Physics in his freshman year, I may very well have a completely erroneous view of many concepts within physics. Recently, Einstein's model of gravity has been on my mind. I was watching the following lecture here wherein Professor Sera Cremonini explains that gravity is due to the curvature of 4 dimensional spacetime, and that this curvature is caused by the mass of objects within the universe. Furthermore, the higher the curvature (equivalently, the higher the mass of an object) the higher the force of gravity near that object. To illustrate this, she uses a stretched rubber disk and puts a large ball on it whilst smaller balls are on the disk. The large ball causes the rubber to stretch, and this curvature causes the smaller balls to be pulled toward the large ball just as gravity causes orbits of the solar system. This made me think. ## Question Theoretically, is it possible for the curvature of the universe at one particular point to be so strong that the gravitational force is infinite? If infinite is ridiculous in this context, consider the question reformulated: Is there, or can there be, a point in the universe where the curvature is greater than any other point in the universe? If so, why doesn't the strength of gravity at this point cause the entire universe to be contracted to this point? That is, isn't this just like the Big Crunch? ## P.S. Once again, I don't know if I've conveyed this using the proper terminology and I'm aware it's a very bizarre idea. I hope you all can entertain my thoughts and attempt to answer my question as best as possible, and correct my understanding and terminology as warranted. Thank you.",
"Mario Livio's book on symmetry and the relationship between gravity and acceleration In his book: _The Equation That Couldn't be Solved_ Mario Livio explains the equivalence principle in laymen's terms. I took the statement on page 209: _The force of gravity and the force resulting from acceleration are in fact the same._ to mean that since our universe is accelerating, gravity is the result. In other words, we have gravity because we have acceleration. This made a lot of sense to me and seemed to explain things (like warps in space- time due to gravity of very large objects. They 'have' gravity because they are accelerating masses. In my beginner's head I extended that conclusion to mean if the acceleration of the universe was zero we would have mass but no gravity. Based on what I've read since, this does not seem to be true...is it?",
"If 2 charges have the same sign, the coulomb force is positive but repulsive, while with 2 masses the gravitational force is positive but attractive If you have two point objects both the same positive charge and both of the same mass at a distance $r$ from each other. The force between them due to gravity is $F_g=\\frac{Gmm}{r^2}$ and $F_g$ is also positive. If the objects are not charged at all, then they will move towards each other as the force is positive. But as they are charged the force between them due to the electric charge will be: $F_e = \\frac{QQ}{4\\pi\\epsilon_0r^2}$ And $F_e$ is positive so if you take the resultant force on the objects you get $F_g + F_e$ as they are both positive they're both the same direction and the particles will attract with a greater acceleration than if they werent charged Say $|{F_e}| = |F_g| = F$ then the force between the two particle would be $2F$ Except that's not the case as the charges are both the same so $F_e$ is repulsive and as its the same magnitude as $F_g$, the particles will not move as the forces cancel each other out. Basically my question is, how can the signs be the same for both equations but the actual directions of the forces be different?",
"Is there a relation between the magnetic field force of the earth and the gravitational force between the earth and other bodies? According to Newton's Universal Law of gravitation, we can say that a huge body of mass will attract another body of mass within a short range, however, if both bodies are for instance magnetic, wouldn't there be a repelling/attracting force between the bodies? Since both the earth and the sun are known to have their own magnetic fields why isn't this represented in the universal gravitation law?",
"The Shell Theorem and A Problem Related to it The shell theorem states that: > _A uniform spherical shell of matter attracts a particle that is outside the > shell as if all the shells mass were concentrated at its center._ Now, I have to solve a problem related to this theorem. The statement of the problem is: > _A particle is to be placed, in turn, outside four objects, each of mass > $m$:_ > > _(1) a large uniform solid sphere,_ > > _(2) a large uniform spherical shell,_ > > _(3) a small uniform solid sphere, and_ > > _(4) a small uniform shell._ > > _In each situation, the distance between the particle and the center of the > object is $d$. Rank the objects according to the magnitude of the > gravitational force they exert on the particle, greatest first._ As far as I understand this problem (or maybe I've not understood it yet) I think all of the objects should be ranked first. This is because, for the large uniform solid sphere if we imagine that its entire mass $m$ is concentrated at its center which is at a distance $d$ from the particle, then it will attract the particle with the magnitude $\\frac{Gmm_0}{d^2}$ where $m_0$ is the mass of the particle. And, each of the other three objects' centers distance is $d$ from the particle, and each of their masses is $m$, so it seems to be the case that all of them gravitate the particle with the same magnitude. Do the objects gravitate the particle with different magnitudes, and hence should be ranked differently? What is the reason behind it if so is the case?",
"Why is there a search for an exchange particle for gravity? If I understand correctly, according to Einstein's General Theory of Relativity, mass results in a distortion in space-time. In turn, the motion of the mass is affected by the distortion. A result of the interplay between mass and space-time is that the 'force' of gravity may be explained away. Masses are not subject to a force, but are merely following a 4-dimensional space- time geodesic; gravity is just geometry. And yet physicists are searching for exchange particles for the force of gravity, and are trying to unify quantum mechanics with relativity, or to unify the weak/strong/electromagnetic forces with that of gravity. 1. What have I missed? Are these different communities of physicists? Does relativity explain only part of the story of masses acting under gravity? 2. Is gravity a force or not? Is it only an apparent force or not? 3. Can such an apparent force 'generate' exchange particles? Are the exchange particle and geometric models both different views of the same underlying truth? 4. A side question might be: why can't the other forces be explained away similarly? Or is that what is happening with all this talk of small extra dimensions? I'd appreciate any illumination on this matter, or suggested reading (preferably at the 'popular science' or undergraduate level).",
"Why is there a gravitational attraction between two objects at rest with respect to each other? From my understanding of relativity, gravity is not a force, but a result of the curvature of spacetime. If Object1 moves past Object2, even though it's moving in a straight line, its direction may change due to the distortion caused by Object2's mass. However, what about the situation where Object1 is not moving? How can there be an attraction between two objects that are at rest relative to each other? i.e. what makes them move towards each other?",
"How does Newtonian mechanics explain why orbiting objects do not fall to the object they are orbiting? The force of gravity is constantly being applied to an orbiting object. And therefore the object is constantly accelerating. Why doesn't gravity eventually \"win\" over the object's momentum, like a force such as friction eventually slows down a car that runs out of gas? I understand (I think) how relativity explains it, but how does Newtonian mechanics explain it?",
"Vacuum and repulsive gravity How can one show from General Relativity that gravity is attractive force, and under which conditions it becomes repulsive, also why positive energy vacuum drives repulsive gravity?",
"Can we model gravitation as a repulsive force? This question is actually related to my earlier question (\"what is motion\"). The fact that objects move a lot in the universe and that the universe is expanding, can imply that gravity is a repulsive force that increases with distance.. so the farthest objects repel us more. This can still explain several existing observations, e.g., why does the apple fall? Motion is the result of such repulsion. Two objects unlucky enough not to be moving relative to each other get squished due to the repulsion of the rest of the universe around them. The earth repels the apple less than the stars so it is pushed towards the earth. Furthermore, it can explain the expanding universe without the need for dark energy. This could be demonstrated in a thought experiment. If we take a lot of same- charge particles (with small mass) such as electrons and lock them in a large box at a low enough temperature. The mutual repulsion of the particles may cause similar motion as if due to gravitational attraction. Another experiment would be to measure the slight changes in our weight during day and night when the sun and earth align (if their masses are large enough to detect the feeble change in repulsion). [EDIT: the question in the original form may not have been clear. It is \"can we model\".. with a yes/no answer and why (not). If downvoting, please justify.",
"Why Newton's law of universal gravitation is a valid law? What causes any two bodies in the universe attract each other with a force? Why Newton's law of universal gravitation is a valid law? What causes any two bodies in the universe attract each other with a force? What causes a larger body in space to have a gravitational pull on a smaller body?",
"Basic question about law of gravitation > **Possible Duplicate:** > Radial fall in a Newtonian gravitational field This is how Wikipedia defines Newton's law of Gravitation: > Every point mass attracts every single other point mass by a force pointing > along the line intersecting both points. The force is proportional to the > product of the two masses and inversely proportional to the square of the > distance between them: > > $F=G\\frac{m1m2}{r^2}$ > > where > > * F is the force between the masses, > * G is the gravitational constant, > * m1 is the first mass, > * m2 is the second mass, and > * r is the distance between the centers of the masses. > Now, say 2 spheres, one the size of the earth and the other the size of a ping pong ball are placed say 10 km apart. There are no other forces acting on the system other than gravitation. If I've understood rightly, then _both_ the ball & the earth sized sphere will be pulled towards each other with the same huge force. My question is- how can we calculate when the 2 spheres will meet? And while calculating that shouldn't we consider the fact that the force is changing every moment because the distance between them $r$ changes every moment? How can I include this factor into my calculations? Further, since the force is changing every moment, are the spheres undergoing acceleration or _accelerated_ acceleration?? (Forgive me if my terminology is improper. I'm a beginner.) Is there any name for such forces & accelerations which change at a predictable rate as in this question?",
"Does gravitational force attract bodies with mass or with energy? On my textbook is written that gravitational force is the force that attracts bodies with mass. But I've seen on a book that It actually attracts bodies with energy. I'm having a class tomorrow and I would like to know some argumments to use with - against my professor.",
"Could the attractive force of gravity be modeled as a repulsive force? If space intrinsically contained gravitons of many different wavelengths then could gravity be model as a repulsive force simular to how casimir attraction works? or any other repulsive mechanism you can think of.",
"Why does gravity attract non-metallic objects? Why does gravity attract non-metallic objects as magnetism does? I understand why gravity, because of mass of an object, works. But earth has a magnetic field, and the moon does not. Indeed, many masses in the universe do not exhibit magnetic fields. If magnetic field plays a part, why does wood on non- metallic (magnetically charged) objects fall at the same speed, especially when we have physics that indicate when a mass (e.g. earth) in orbit should fall into the law of centrifugal force. If the earth is pulled (I say pushed by other heavenly bodies) by gravity to prevent centrifugal force onto the earth. Why should centrifugal force act on non-metallic objects. There appears to be a contradiction that is unexplainable. Help me understand.",
"Thought experiment-shell theorem  Consider a uniformly dense perfectly spherical planet. At any point inside the planet, the gravitational attraction is only due to the mass below the point. (red circle) according to shell theorem. * * * Now onto the thought experiment, as per Newtons law of gravitation, _every particle_ attracts _every other particle_ with $\\frac{G m_1 m_2}{r^2}$ By symmetry, the particles in the blue region should nullify their(net) attraction at the point. Similarly, all particles in the green region would have a component of the force along the -ve X-axis. _Even the particles in the green region **but not inside the red circle** would have a small component of attraction along -ve X-axis at the point._( **contradicting shell theorem** ) Again, their Y-axis components would nullify each other by symmetry. The same would hold true by spinning this cross-section along the X-axis to a 3d planet. * * * Now what's wrong with this explanation?",
"Law of attraction Could you please explain that since we know Newton's law of Universal Gravitation says all masses attract each other. Thus, we humans should be attracted as well or any other daily life objects. Why is it that we don't feel that attraction to be prominent?",
"Weak force: attractive or repulsive? We are always told that there are the four fundamental forces or interactions of nature: gravitation, electromagnetism, and the weak and strong forces. We know that gravitation is attractive, that electromagnetism can be attractive or repulsive depending on the electric charge of the interacting particles, and that the strong force is attractive between quarks. But when the weak force is mentioned, the description is always something such as 'responsible for radioactive decay', but there is no mention of whether this force is attractive or repulsive. So my question is: is the weak force/interaction attractive or repulsive?",
"Gravitation force- Attraction and repulsion Gravitation force is always attractive. Now assume(not a practical one): I took our Earth in my hand and started shaking up and down. This will create a disturbance in space-time warp and it moves like a wave outward direction. So when the crest part of this disturbance comes in touch with another mass, it should carry that mass with it and start moving away from Earth. It was visible because I used a very massive object like Earth. Though it is not visible it should be true with low mass objects too? So is gravitation field is always attractive?"
] | 112 |
What actually is meant by wave nature of electron or any other material particles? | ["Electrons - What is Waving?\nIf an electron is a wave, what is waving? So many answers on the inte(...TRUNCATED) | ["Wave/particle duality Apologies if this has been asked before (I did check and I believe it wasn't(...TRUNCATED) | 48 |
de Broglie relations: calculate wavelength using two different approaches | ["$\\lambda=\\frac{2h}{p}$?\nI am studying quantum physics and there is something I don't understand(...TRUNCATED) | ["What is the fringe separation in Young's double slit experiment? In the double slit experiment, a (...TRUNCATED) | 76 |
Why is the earth shaped like a sphere and not any other shape: cube, prism? | ["Why are most astronomy things spherical in the shape (like, the Sun, the Moon, the Earth, and othe(...TRUNCATED) | ["What is the scientific reason for the inclination of earth's rotation axis? This titled position o(...TRUNCATED) | 238 |
Why don't spinning tops fall over? | ["Perfectly vertical spinning top\nConsider a non-spinning top. If a top is perfectly vertical, and (...TRUNCATED) | ["why does what get pushed away when centripetal acceleration is towards the center If centripetal a(...TRUNCATED) | 77 |
"Does the scientific community consider the Loschmidt paradox resolved? If so what is the resolution(...TRUNCATED) | ["Loschmidt's paradox - really a paradox?\nIs Loschmidt's paradox a paradox even today? In other wor(...TRUNCATED) | ["Without multi-level modeling, how to handle within-study replication in a meta-analysis, where the(...TRUNCATED) | 296 |
Why does it seem like a broken magnet's poles flip? | ["Repulsion of the pieces of a broken magnet\n> **Possible Duplicate:** > Why does it seem like (...TRUNCATED) | ["Magnetic moment precession around magnetic field I have a question regarding the magnetic moment o(...TRUNCATED) | 77 |
Will an object resting on a rotating platform move in a frictionless world? | ["Dynamics of circular motion\nIf there is a disc rotating about its centre, let the surface be fric(...TRUNCATED) | ["Rotational behavior of objects in zero-g with forces I would like to know how this object would ro(...TRUNCATED) | 548 |
Is spacetime simply connected? | ["Symmetrical twin paradox\nTake the following gedankenexperiment in which two astronauts meet each (...TRUNCATED) | ["Non-stationary spacetime What is an example for a spacetime that is non-stationary that is conside(...TRUNCATED) | 567 |
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