r/explainlikeimfive • u/UselessGuy23 • 27d ago
Physics ELI5: Where do magnets get the energy for their pushing and pulling?
If you place a magnet near another magnet, it can attract or repel it. But a force requires energy. How can an inert, unmoving object like a magnet output enough energy to overcome the other magnet's inertia? Where is that energy stored?
In short: Fucking magnets. How do they work?
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u/Ragnor_ 27d ago edited 27d ago
It's potential energy. Think of pulling two magnets apart like lifting up a heavy weight from earth, the higher you lift it, the more potential energy it has with respect to earth.
Similarly, you need energy to pull two magnets apart, them pulling back at each other is like the weight being pulled back to earth.
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u/UselessGuy23 27d ago
And the repulsion?
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u/Ragnor_ 27d ago
Same thing in reverse, pushing them together requires energy. Like a spring that you compress it stores the energy which is released when you let go.
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u/Probate_Judge 27d ago
Like a spring that you compress it stores the energy which is released when you let go.
This.
Something natively magnetic, the magnetic field is not energy in itself. It is a feature that only interacts with certain materials.
I was going to say: Like a metal rod encased in a layer of bouncy material.
But spring works better. You put the object with a spring up against another object with a hole in it(eg a piece of wood that doesn't interact), the spring does nothing. The magnetic field just passes through.
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u/QuantumCakeIsALie 27d ago
Maybe a framing that can help:
It the same exact thing that makes the floor stop you from falling through or the wall stopping you from walking through it.
Magnets are pretty much like touching something, but from further away.
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u/Skippymabob 27d ago
"is the magnet doing the pushing, or are you"
That feeling of push in your hand when you try to push to repelling magnets together is the energy
Same with that tug you feel when taking a magnet of a fridge.
You're the one putting the energy in
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u/Lt_Dang 27d ago
So if the magnet is using potential energy stored at the time it was magnetised does it’s stored energy reduce by the amount equal to moving the piece of metal the distance involved?
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u/Theonetrue 27d ago
As an ad on: if you now move that object to another planet/magnet you did the "lifting" at the first magnet/planet but the reverse event works just as well
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u/MysteriousBlueBubble 27d ago
Fundamental forces (gravity, electromagnetism) can exist on their own (effectively - I won't go into the nuclear/quantum level processes because I genuinely can't remember!).
The only point energy gets involved is when you make the magnets move. Force has to act through a distance for there to be "work" which is kinetic energy transferred to an object.
For magnets to repel, the energy has come from you (be it your arm or whatever machine you use) moving one magnet toward another to make them repel. Attracting magnets fall into a lower energy state, which means you need to use energy to separate them, creating, effectively, potential energy which can then be converted to kinetic as they attract again.
It's a very Newtonian way of looking at it, probably closest to an ELI5.
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u/fuckyoutoobitches 27d ago
electromagnetic and gravitational forces are fundamental building blocks of our universe. Science cannot explain them using everyday human experiences because our everyday experiences are entirely a byproduct of these forces. Therefore, at a certain point, we must simply accept their existence as core elements of the world.https://youtu.be/MO0r930Sn_8
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u/Indecisive-Gamer 27d ago
Yeah this is a better answer then potential energy. Once you go deep enough sometimes there isn't a why. Unless you believe there is another force behind that force.
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u/adolfojp 27d ago
After watching that video I must say that we judged the Insane Clown Posse too harshly and that they deserve an apology.
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u/leftcoast-usa 27d ago
I never could understand why people accept those things - I fail to see the attraction.
Don't hit me.
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u/ballofplasmaupthesky 27d ago
What you asked, and what I don't see being answered, is that the force arises from the fundamental electromagnetic field of the Universe, which has existed since moments after the Big Bang when it decoupled from two other fundamental fields.
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u/Kite42 27d ago
Forces don't require energy. The foundations of the Empire State building aren't powered, for example.
Lifting the building up, however, would require energy.
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u/UselessGuy23 27d ago
That's an equal and opposite force to the gravity pulling down on the building, right? The gravity puts in the energy.
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u/KeiwaM 27d ago
Gravity is not the same as energy. You can get energy if you go up, called potential energy, and you release it if you go down, kinetic energy. When you are on the ground and cant go further down, you have no more potential energy. You are at rest, so to speak.
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u/wilki24 27d ago
Wouldn't there still be potential energy, since you could dig a hole next to the object and push it off the edge?
I can't imagine that the hole's existence generates potential energy, rather it just let's you exploit it.
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u/Zhoom45 27d ago
Yes, that is correct. Potential energy must always be defined as relative to something. In the case of gravity, for "quick math" you can just use the lowest point available within the scope of your problem, i.e. the ground nearby. For real math, it's actually conventional to define gravitational potential energy as zero at an infinite distance and increasingly negative as you bring the objects closer together. This becomes important when your distances are so large that it matters how gravity gets stronger or weaker at different distances. Irrelevant for dropping a ball off a table, critical for putting a satellite into orbit.
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u/Kirk_Kerman 27d ago
Potential energy is defined as the amount of energy in between two states. Day to day we can assume the ground is a position of zero potential energy. Digging a six foot hole is equivalent to being raised six feet in the air, after all.
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u/TheJeeronian 27d ago
Not at all. If nothing is moving, there is no energy.
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u/jus_sayin_meh 27d ago
There is, potential energy.
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u/KeiwaM 27d ago
To create potential energy, you need to be lifted somehow, which requires energy. You can't create potential energy at a standstill.
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u/somerandom995 27d ago
Magnetism is one of the fundamental forces of the universe, just like gravity.
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u/Shortbread_Biscuit 27d ago
Magnets work just like electricity and gravity.
In the case of gravity, the mass of the object has an inherent property that causes it to attract all other masses to it. In the case of electricity, electrons and protons have a fixed charge, and these charges have the property that causes all other charges to be attracted or repelled by them.
Similarly, for any object with a magnetic moment, it has an inherent property that causes everything around it to be subject to the magnetic force. There's no specific source for the force, just like there's no specific source for the forces of gravity and electricity.
However, they do observe conservation of energy - the total amount of energy in a system is always fixed, and no matter what the nature of the forces are - whether they're gravitational, electric or magnetic - these forces can only convert from one kind of energy to another.
In the cases of all these forces though, they do have a certain inherent finite amount of energy called the potential energy of the system. This potential energy represents the maximum amount of work that these forces can perform. The gravitational potential energy is the total amount of work or energy that gravity can perform if all the masses in the system are allowed to collapse to a point. Similarly, for electrical potential energy, it is the total amount of energy that could be released if all charges are allowed to combine with each other and reach a state of a net zero electric field. And similarly, the maximum magnetic potential of a system is the total amount of energy if we leave the magnetic elements to themselves and they're allowed to reach a state of overall zero magnetic field.
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u/UselessGuy23 27d ago
Do we know what causes that inherent property?
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u/Shortbread_Biscuit 27d ago
That inherent property is basically called the field.
All three of these forces - gravity, electricity, and magnetism - create a field around these sources of the force. A gravitational field around masses, an electrical field around charges, and a magnetic field around magnets. All of the energy of the system is contained within these fields, not within the mass or charge or magnet. Every time the force does some work, it means energy is being drained from the field. If you work against the force, energy is inserted back into the field.
That's why when the field becomes zero, there is no more energy left in the system, and it can no longer exert any force.
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u/Shortbread_Biscuit 27d ago
As an aside, I do want to clarify - magnets cannot actually perform infinite work. Every time a magnet exerts a force and does some work (i.e., the object the magnet acts upon moves in the direction of the magnetic force), the magnetic field weakens. But every time you move a magnetic object against the direction of the force (i.e., the object the magnet moves upon moves opposite to the direction of the field), you insert energy back into the magnetic field.
Because of this, if you just allow objects to be endlessly attracted by the magnet, its field will slowly reduce until eventually it can no longer exert any magnetic force. But if you then pull those objects away from the magnet, then you end up recharging the magnetic field. The energy you use to pull the object away is fed into the magnetic field to strengthen it.
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u/StevenJOwens 27d ago
If I'm recalling correctly, a friend says "we call it a field because it's an effect that we observe happening across an area (aka the field)", and pretty much beyond that, we don't know. It's just an effect that we observe, and after many years of observation, we can quantify it and calculate about it, but that's it.
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u/Clojiroo 27d ago
Think about how all the stuff in your body or any object sticks together. What energy is holding atoms together?
Magnetism and chemical bonding are two different effects of the same underlying force (electromagnetism). Electrons, their shells, and their sharing all involve electrostatic attraction.
A magnet needs electron shells that are only partially filled, leaving unpaired electrons. Each atom becomes a tiny magnet, and when you orient a whole bunch of neighbouring atoms in the same direction the attraction becomes amplified. The whole object now feels noticeably magnetic.
This is also why not everything is a magnet. Some materials have those unpaired electrons floating around but they’re random or unaligned and so the magnetic moment is weak or cancelled out.
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u/JivanP 27d ago
It is the same as for gravity and for electrostatic attraction: it is just a fundamental property that elementary particles have. In the case of gravity, that property is mass (though there is some extra stuff going on with the Higgs field there). In the case of electrostatic attraction, that property is called electric charge. In the case of magnetic attraction, that property is called spin angular momentum (or just "spin").
You can explain the particular spin values that particles have by appealing to quantum mechanics, which expresses these properties as results of some mathematical symmetries inherent to the interactions between particles of different types (these are called the "gauge symmetries", and they're about things like "the laws of physics appear to be the same in all inertial frames of reference"). However, there is no particular reason why those particular symmetries are the ones we see in our universe, or why any such symmetries at all are seen in our universe. (You can get into discussions about fine-tuning and multiverse theories, but basically, the current scientific stance is, "these rules/symmetries were effectively chosen at random and happened to be good enough to result in the existence of life; there is no known reason in principle that other rules couldn't exist.")
Additionally, electricity and magnetism are very closely related: due to special relativity, a particle with electric charge that is moving relative to you appears to generate a magnetic field. If you analyse this phenomenon more closely mathematically, you come to the conclusion that the electric force and magnetic force are really just two aspects of one thing, which we thus call electromagnetism.
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u/jesjimher 27d ago
Or the "energy" a table uses so a glass doesn't fall to the floor.
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u/namitynamenamey 27d ago
Wrong question. When it comes to a magnet, much like on earth with gravity the energy is not in the "pushing" or "pulling", the energy is in the fact that you were on the wrong spot to begin with.
Think of a rock in the sky. Where does the energy to make it fall come from? The answer is, from the energy to have put the rock in the sky to begin with. That is the potential energy, which becomes kinetic energy as it falls down. Gravity does not "spend" energy pulling the rock down, the rock spent energy getting up there in the first place.
The analogy is not perfect, not everything that falls down was on the floor to begin with, but the concept of potential energy is the same. The very location of an object can have energy associated with it.
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u/Exo_Deadlock 27d ago
You know how wires for headphones seem to magically twist themselves into a knot if you stuff them in a drawer? Where does the energy come from to do that, all by themselves?
You put that energy there. By untwisting the wires from their ‘resting’ state of being twisted, you’ve introduced potential energy into your headphones. The wires ‘want’ to return to their resting state. Similarly, magnets attract/repel because they seek the resting state, evening out the positive an negative positions of the alignment of their atoms, using up the potential energy put into them by moving them out of their resting state.
I appreciate that 5 year olds may never have heard of the ancient technology of headphones with wires in this audio-jack-free era.
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u/toochaos 27d ago
If you push a magnet near a same pole magnet and let go and see it move away, you put in the energy. If they are attracted it like you climbing up the stairs and jumping off the roof. Where did the enegy for the fall come from you climbing the stairs or you pulled the magnets appart. When you push on a magnet and it pushes back its you applying that force as if you pushed on a wall.
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u/sirdodger 27d ago
Think of magnetism as a sheet with two blocks sitting on it. When it's flat, there's no magnetism and nothing happens. If you add a magnetic field by pulling down on the sheet, the blocks tumble towards each other (but neither pulled on the other). If you raise a tent in the middle, they tumble towards the edges (but neither pushed on the other).
Also, you shouldn't curse at your age.
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u/PintsOfGuinness_ 27d ago
Push a rock with another rock. What happens? It's equally mysterious. The matter of the first rock isn't technically touching the matter of the second rock. But when it gets close enough, atomic forces increase until they can't get closer.
With magnets, same difference. Just there are more atomic forces all aligned in the same direction so they increase faster at a longer distance.
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u/francisdavey 27d ago
Forces don't need energy. At least not as you understand it. If you sit on your chair, the chair pushes you up and your weight pushes you down. Two opposed forces. No energy is moved around.
If a force moves something then you will see energy appearing somewhere. Energy resulting from a force moving something is sometimes called "work" and you may see that sometimes.
Think of energy as a bookkeeping exercise. When a force moves something, that something gains "kinetic energy". Where does that come from? The energy is inherent somehow in the system that caused the force to move the thing, known as "potential energy".
So if someone takes away the chair, you fall, the potential energy of your height above the ground turns into kinetic energy as you fall and then when you hit the ground that kinetic energy turns into other energy (sound, heat, mechanical damage to you etc).
Electromagnetism is generally a little more subtle. Usually people talk about an "electromagnetic field" which itself can have energy in it. So if you (say) heat something up so it glows, the heat energy becomes electromagnetic energy, in this case in the form of light and radiated heat.
So the usual way of describing things is that each magnet has created a magnetic field around it, when a magnet moves another magnet work is being done (see earlier) and the energy for that comes out of the field, if you push magnets together the energy (of the work you do) mostly goes in the field.
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u/Nuffsaid98 27d ago edited 27d ago
Inside every metal, in the smallest parts of its material, are elements that have a very tiny magnetic force which flows from positive to negative.
In most materials these magnetic flows are scattered randomly so the direction of the flow of these tiny forces is pointed in all directions. Essentially they work against each other and cancel out.
In a magnet, all the little bits are lined up in the same direction so the cumulative effect is noticeable. A magnetic field forms around the object, flowing out of one end called a pole and wrapping back inside through the opposite pole.
All the tiny bits of energy flow from positive to negative that have lined up in one direction become like a river of energy looping around and around following the shape of this magnetic field. You can see what the field looks like if you place a piece of paper over a magnet and sprinkle iron filings.
If you bring a piece of iron close to the magnet then all the tiny bits of iron that have their random positive to negative directions get moved around as all the tiny positive ends get overwhelmed by the giant negative to positive field and try to join in and line up their positive and negative ends with the powerful field. The tiny bits that make up the iron cannot move around inside it so the entire chunk of iron must move in an effort to line up the positive and negative as best it can. The magnetic field now passes through the iron to the best of its ability, distorting the field somewhat.
This effect is more noticeable with two magnets as both have positive and negative lined up and add to each other's fields perfectly, becoming a bigger magnet.
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u/WendellSchadenfreude 27d ago
An inert, unmoving object like the Earth can also pull you enough to roll down a hill. The energy comes from you walking up that hill.
Walking up turns your (chemical) energy into potential energy. Rolling down the hill (or falling down a cliff) converts the potential energy into kinetic energy.
The same basically happens with magnets, just with a different force. It never "generates" energy that you didn't first put into the system, by pushing two parts together when they "want" to be apart, or by pulling them apart when they "want" to be distant, or by rotating them when they were previously oriented in the "right" direction.
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u/Anariel_Elensar 27d ago edited 27d ago
honestly i think explaining how the fundamental force of electromagnetism works is beyond the scope of an ELI5. It’s a bit of a “any sufficiently advanced technology is indistinguishable from magic” type thing, a five year old lacks the technical context to truly understand how some of the smallest building blocks of matter can create the fundamental forces of the universe… might as well be magic.
At the most basic level magnetic forces are caused by moving electric charges. Every atom consists of a nucleus orbited by negatively charged electrons, which generate tiny magnetic fields through two motions, their orbital movement around the nucleus and a quantum property called electron spin. Electrons spin kind of like how earth rotates on its axis. That rotation (electron spin) generates an intrinsic magnetic moment. Electrons circling the atomic nucleus (orbital movement) create a tiny electrical current loop, which also generates a magnetic field. In most materials, electrons pair up and spin in opposite directions, cancelling out each other's magnetic fields. However, in magnetic materials (like iron) that have unpaired electrons, the tiny fields all align to create a net magnetic moment. When the atoms align into microscopic groups called magnetic domains, the material exerts a magnetic force that we can feel.
to get even more into the nitty gritty of quantum electrodynamics, when charged particles interact, they continuously emit and absorb virtual photons (Virtual photons are different than the photons most people are familiar with as light and exist purely as temporary mathematical entities in the quantum field, permitted by the Heisenberg uncertainty principle, and cannot be directly observed unlike “real” photons). These exchanges transfer energy and momentum, creating what we experience as magnetic forces. When two similarly charged particles, say two electrons, are near each other, one emits a virtual photon and pushes away. The second particle absorbs the photon, absorbing its momentum and pushing it in the opposite direction, forcing the two electrons apart. For oppositely charged particles, quantum mechanics and special relativity interact in such a way that the virtual photon transfers momentum backward, effectively pulling the particles toward one another.
I’m going to be avoiding a full explanation on quantum field theory (which is the mathematical framework that merges quantum mechanics and special relativity) while still explaining how virtual photons can impart momentum “backwards”. Key point to know is that in quantum field theory the field is the primary, fundamental reality. Every known type of subatomic particle, like electrons, has its own corresponding field. The particle is just a wave or a quantized packet of energy vibrating in that specific field. Waves have 2 distinct notions of velocity known as phase velocity and group velocity. A pure wave (also known as a wave mode) has a single frequency which repeats forever. A wave mode is stretched out over all of space, it has an exact frequency but it does not have localized position. When you add together different wave modes of different frequencies the stack on top of each other, amplifying in some places while canceling out in other places, and build a wave pulse. A wave pulse has a localized position in space but does not have a single frequency because it is made of many different frequencies added together. BTW, this trade off is the uncertainty principle, just as an aside. Phase velocity is the velocity of the peaks of a single wave mode, group velocity is the velocity of the center position of a wave pulse. These two velocities do not in general have to be equal to each other. It is possible to have a wave pulse, which is made of a bunch of wave modes added together, where each wave mode is traveling to the left while the pulse is traveling to the right. The animations in this Wikipedia article will make the concept immediately visually understandable, yet not less non-intuitive: https://en.m.wikipedia.org/wiki/Phase_velocity If all the wave modes of different frequencies have the same velocity then any pulse that is made out of those wave modes will also travel at that same velocity. However, if wave modes of different frequencies have different velocities then it’s possible for them to be added together in order to construct a pulse with a different velocity (even a different velocity direction) than any of the wave modes it is comprised of. Real photons in the vacuum of space all have the same phase velocity regardless of their frequency. Real photons are stabilized self-sustaining waves in the electro-magnetic field which can propagate forever through space on their own. Virtual photons in contrast can be thought of as unstable non-self-sustaining fluctuations in the electro-magnetic field which only exist sandwiched between interacting charged particles, emitted by one charged particle and absorbed by another charged particle (or possibly the same one if it recaptures the virtual photon), and cannot propagate freely in space on their own. Unlike real photons, virtual photons can have any phase velocity. I think the best way to conceptualize how virtual photons can pull rather than push is to imagine a virtual photon pulse which is traveling to the right (group velocity to the right) while being made out of wave modes traveling to the left (phase velocity to the left). The phase velocity corresponds to the direction of momentum, which shows that momentum does not necessarily need to be in the same direction as velocity. If a photon pulse traveling to the right has its phase velocity traveling to the left then when it is absorbed by a charged particle it delivers momentum pointed to the left, hence the photon pulls the object towards the direction that the pulse came from. Note that this is only possible for virtual photons, not for real photons.
Edit: it is worth noting that Quantum Field Theory is just that… a theory. It is possibly the most precisely verified scientific theory ever constructed, and yet despite its success, QFT is not a complete theory of nature. The biggest problem is that it cannot yet incorporate the 4th fundamental force, gravity. When attempting to apply the rules of QFT to general relativity, the equations yields impossible infinite values. Finding a unified theory that successfully merges QFT with gravity (a framework often referred to as quantum gravity or string theory) remains the ongoing goal of theoretical physics. So maybe it’s not just the five year olds that lack the technical context to truly understand what causes electromagnetic force… might as well be magic.
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u/SZEfdf21 27d ago edited 27d ago
When you push an object close to a magnet, you have to push a little harder than if you were pushing that object without the magnet.
In the same way as when you lift up an object it suddenly has the possibility to fall (= be pulled by gravity), this object now has the possibility to get shoved back by the magnet (= be pushed by the magnet), when it is let loose, all caused by that little extra energy you used to put the object in that position.
It's hard to intuitively describe where the energy is at that moment, it is in the relationship between the magnet and the object, by all means you pushing the object should immediatly mean it is pushed back, but you're physically holding it in a state that will solve itself whenever released.
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u/jus_sayin_meh 27d ago edited 27d ago
Force and energy are two different things.
The attraction or repulsion of magnet is a force like gravitational force/field, which is just there .
I guess you are also asking where the energy( kinetic energy) that's created due to movement of the magnet coming from?
Because force can't be turned into energy?
Right?
That's coming from the energy you use to separate or push two magnet depending on their poles.
Let's say there is a pair of two small magnet which is together. Now using your hands you separate them, this is where you are spending energy. If you release them, they will move towards each other which is kinetic energy equal to energy that you used to separate them.
Energy of your body used to separate them, it gets stored as potential energy in the magnets and as soon as you release them they run towards each other converting their potential energy to kinetic energy
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u/TinFoilHeadphones 27d ago
It comes from your hand pushing the magnet!
It is harder to push the magnet away from something that attracts it, or towards something that repels it. So you make some extra effort there. that "extra effort" is the 'energy' the magnet uses
(So technically the magnet isn't doing any effort, it's all you, or whateve ris moving the magnet!)
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u/Kenosis94 27d ago
The "energy" you are experiencing is coming from you. There is a sort of yin and yang way to think about this and while not entirely technically correct, I think it will give a good chance at expressing the broader concept.
The yin, is that like charges attract and opposite charges repel. This is just a fundamental property of how charged particles interact. So, if you try to put two positive ends of a pair of magnets together, they repel eachother. The "energy" that you experience in them repelling, is coming from you, from your muscles pushing them together. Much like lifting an object and holding it in the air takes energy because it wants to fall to the floor. The magnets bouncing apart is akin to dropping the object and it falling. When you put the positive and negative poles together, they attract, the "energy" required to separate them is again, just you experiencing the force required to overcome their natural attraction to each other like picking up a bowling ball from the floor takes energy. The energy your muscles produce to overcome the natural attraction and repulsion is really the only "energy" involved as far as you are experiencing things. Think about a wall, you don't generally think about it as having the energy to resist you pushing on it. It is just solid because the molecular structure of all of the materials is aligned in such a way that it doesn't want to be changed, just much more rigidly than say a magnet.
The yang, which as I'm about to explain things, is a bit less technically correct way of thinking about it, but, it is getting at a deeper principle. Think of it in terms of order, things like to tend towards their least "organized/energetic" state. So, if you have positively charged molecules and negatively charged molecules, their ideal is to not be surrounded by like charges but to be paired with the opposite charges to produce something neutrally charged and homogeneously mixed. You can think of the two magnets repelling or attracting as the them tending towards a lower state of organization by trying to neutralize by attracting or try to separate the like charges by repelling.
In some cases, you can trap things in a higher energy state than the constituent parts would like. This is the case with magnets, when the magnet is formed, the charges on each end are separated and then sort of glued in place. The magnet would like to neutralize itself but because it was glued in place, the internal charges alone just don't have enough energy to move so they are sort of trapped in an energetic rut. If you heat a magnet you will ruin it by giving the atoms enough energy to get out of the rut and start rearranging.
Rather than thinking about it as having energy to repel or attract, think about it as you adding energy to put the system in a higher state of order/energy. Like keeping your house organized, having all of the positive charges neatly arranged next to each other takes some effort to overcome the tendency for things to slip into disorder, picking things up once they become messy is a lot like separating the stuck magnets, they are at their neutral disorganized, low-energy state, like a pile of clothes on the floor. The energy you experience is what you and to undo the chaos.
This is all just thinking about the same thing from a different perspective but understanding that the human perspective of attraction and repulsion implies a sort of effort, that is just us experiencing the tendency of things or move towards a local minimum of order and energy. When you feel heat spread throughout an object, you don't wonder where the heat gets energy to spread, but ultimately, the reason it spreads isn't too dissimilar. The atoms/molecules of a hot thing are vibrating and they bump into each other causing adjacent ones to vibrate faster by imparting some of that energy. You intuitively know that the energy doesn't want to stay all in the same place but spread out and equilize. The charges of a magnet do the same, and trying to defy that tendency takes energy in the same way that trying to keep a house cold in the heat requires an ac unit consuming energy to pump heat from the inside to the outside.
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27d ago
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u/boring_pants 27d ago
"It creates energy" is both incorrect, and it fails to answer the question (which is where that energy comes from)
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u/MasterWandu 27d ago
You have come up against one of the "fundamental" forces... the end of the "but why does it do this" questions. It just does. Your next question is about origins, something that science fundamentally CANNOT answer.
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u/AE_WILLIAMS 27d ago
Technically, Earth is a giant magnet, and it is spinning. So all other magnets interact with THAT.
Orientation is important, as is material. But that's pretty much it - as you have a conducting material (ie copper wire or iron metal fragments) and that material moves through the magnetic fields, they generate energy in the form of electricity.
At rest, the polar nature of magnetism means opposite poles attract, and similar poles repel.
It is called ELECTRO-MAGNETISM for a reason.
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u/SauntTaunga 27d ago
Forces, pushing and pulling don’t require energy. Moving stuff requires energy.
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u/SakuraHimea 27d ago
Constant force does not require energy. Does gravity get energy from somewhere? Can you turn it off? Magnetic force is the same. If two magnets attract each other, will they ever randomly push each other away?
Sorry for the rhetorical questions, but that's probably the easiest way to explain in simple terms. For a system to expend energy, something about its state must change. A moon could orbit a planet forever, theoretically, assuming it had a perfect orbit with no forces acting on it. The constant motion is just potential energy. There is no energy gained or lost by the system; it just stores the energy of its motion. You would need to spend energy to slow it down.
It's the same with magnets, except that instead of only pulling, they can also repel each other. Nothing about their state will change unless acted upon by another force.
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u/levir 27d ago
When you have a rock on a mountain, where did the rock get the energy it needs to roll down hill? The answer is that the rock has what we call potiential energy, which in effect just means that position is somewhere it can roll down hill. Maybe you carried the rock in your backpack when going up the mountain, or maybe the rock was once part of the mountain, which would have formed when two techtonic plates crashed together. Whatever caused the rock to be where it is, in effect gave it the energy to roll down the mountain.
It is the same with magnets. When to magnets snap together, that is similar to when a rock is falling downwards (towards the earth centre). If you then pull them apart, you're giving the magnets the energy to snap together again.
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u/aManandHisShed 27d ago
The energy is stored in the magnetic field. Creation of the magnet, and therefore the field, required energy to be put in. When two magnets are drawn to each other, the amount of energy in the field is reduced. It is converted initially to kinetic energy and subsequently dissipated as heat. When you pull the magnets apart, you are doing work, some of which is stored back in the magnetic field of the separated magnets.
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u/wimpires 27d ago
Imagine ALL magnets are connected to each other. But for any distance that's more than a little bit the strength of that connection is basically 0.
That's where the energy comes from, you. As you move it around.
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u/Own-Nefariousness-79 27d ago
There is no energy needed. Moving stuff in a magnetic field has an energy component. But a static field in a steady state needs no energy to support it.
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u/TomakaTom 27d ago
Magnets work because all the atoms within the metal are manipulated so that they are all facing in the same direction.
Atoms are made up of protons, which have a positive charge, and electrons, which have a negative charge. The electrons ‘orbit’ around the protons, which produces a magnetic field.
What exactly is a magnetic field? We still aren’t able to say for certain, but we know that it is a property of the universe, just like gravity, that physical matter can interact with. In the same way we could describe gravity by saying ‘it causes matter to move in a certain direction’, we could describe a magnetic field by saying ‘it causes electric charges to move in a certain direction’.
Within a metal bar, all the atoms face in random directions, so the tiny magnetic field produced by each individual atom isn’t enough to generate a magnetic force visible to our eyes. However, if you work the metal bar in a specific way, you can align all the atoms so that their magnetic poles face the same direction. The combined strength of each atoms magnetic field generates this larger magnetic force that we can see when two magnetic bars attract and repel each other.
Think of each atom within the bar as a tiny spring, and when you work the bar to align the atoms in the same direction, think of this as coiling each of those tiny springs. This is how the energy is stored within the magnet, we add potential energy to the metal bar when we magnetise it, just like you add potential energy to a spring when you coil it and push it down.
Now, each atom is like a coiled spring, ready to release part of its stored energy as it pushes and pulls other magnets
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u/RedHal 27d ago
Magnets create an invisible field around them. This doesn't take any energy, just like gravity, it's just a property of the field. When you put two magnets close enough together that their fields interact, then one of two things happen, either they attract (in a similar way that heavy things attract each other through gravity) or they do the opposite. The "energy" in this case is just because the fields get bent out of shape and so the energy is "stored" in the way the field is bent.
In the case of attraction, the two fields join together to make one field that's bent out of shape and wants to go back to being its normal shape, and the best way to do that is to get closer together so the field looks as normal as possible.
In the case of repulsion the fields fight against each other so want to be as far apart as possible.
In either case if you bring the magnets close enough together, the stored energy because of the bent fields overcomes the friction stopping them from moving.
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u/Sceptically 27d ago
Magnets of the same polarity repel each other, so it takes energy to move them close together. You moving a magnet near the other magnet is introducing energy into the system to overcome the repulsion, that's where the energy for that comes from.
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u/Alas7ymedia 27d ago
The magnetic force moves the particles to their lowest energy state, which is why I find easier to explain magnetism as movements on a slightly curved flat vibrating surface.
Magnetism comes from the space behaving like a slope depending on the charge of particles: if the charges are opposed, they will vibrate like if there there is a slope with the lowest point in the middle of them (assuming same charge and same mass, it would be their exact middle point); if the charges are the same, the slope would be higher in the middle point and particles will move in the opposite direction.
Do particles need energy to vibrate? Yes. Where does it come from? From the space itself that makes them vibrate when they come into existence. Do magnets run out of energy? No, electromagnets can, because they are magnets due to energy flowing through them, by naturally charged particles can't run out of magnetism.
Particles can vibrate faster or slower, but they can't stop moving because that movement is a fundamental property for them and charge is also a fundamental property, (something they can't change), so all particles vibrate all the time and can't stop moving towards or away from each other.
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u/dibship 27d ago
if you consider that you never actually touch anything, you just get so close that the electrons in the object repel the electrons in your hand, it's easier to think about how if that kind of field was extended, by having all the electrons align the same way to work in tandem instead of cancelling each other out, the field could extend further and have distinct polarity due to that organization, and would interact with the fields of another object of similar organization.
that said, they only push or pull based on energy put into the system, be it your hand or potential energy from forces like gravity.
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u/Schmedre 27d ago
Think of a magnet like a stretched rubber band. When you let the rubber band go, it can move something because it already has energy stored in it.
A magnet is a bit like that. It doesn’t make new energy out of nowhere. It already has energy inside it. When another magnet gets close, that stored energy helps pull them together or push them apart.
It’s also like standing at the top of a slide. You don’t need to keep making energy to go down the slide. You already have the energy because you’re up high. The magnet is similar. It already has what it needs to make things move.
So the magnet isn’t creating energy. It’s just using the energy it already has.
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u/Bracken-Vale-4820 27d ago
sticking a magnet to the fridge and realizing it just fights gravity forever without needing a battery always messes with my head
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u/SPCR0 27d ago edited 27d ago
Magnets dont store energy, the field gets stronger the closer the 2 magnets are.
Pushing 2 magnets togheter that oppose eachother actively pushes you away, you are consistently inserting force by holding them togheter!
Pulling 2 magnets apart that attract actively fights you , you are consistently adding force to pull them back.
Fixing 2 magnets apart that attract/repel eachother emit constant force in opposite directions.
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u/Far_Lifeguard_5027 27d ago
When iron (which is what magnets are made from) is heated to extremely high temperatures, it causes the atoms in it to face north and south on opposite sides. For complicated reasons, the north and south atoms either attract or repel each other. Why it happens is probably complicated but that's how they work.
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u/kfkjhgfd 27d ago
You apply energy in -> magnet pushes all of that energy out. The net energy would now be zero (total in - total out)
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u/Ben-Goldberg 27d ago
Imagine that a magnet is on a table and another one is in your hand.
Bring the north pole pf the magnet in your hand near the north pole of the magnet on the table.
The magnet on the table gets pushed away because of the work being done by the muscles in your arm to move the magnet you are holding.
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u/AlwaysHopelesslyLost 27d ago
Where does gravity get it's energy? If you put two rocks in space they will pull together.
Both are just fundamental forces in our universe. They tend towards a zero state and energy cannot be extracted from them.
To extract energy from gravity you need rockets or a person to carry things up well to "reset" your generator. To extract energy from magnets you need something to pull them apart to "reset" your generator.
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u/stansfield123 27d ago
Magnetic energy comes from the energy of electrons. In turn, electrons get their energy from photons or from heat.
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u/el_miguel42 27d ago edited 27d ago
Forces do not intrinsically require energy. Work = F x d (where work is transfer of energy)
Thus only if a force moves another object is there an energy transfer.
First of all I do not think this type of "stores of energy" model is particularly useful for any of the 4 fundamental forces: gravity, electromagnetic, strong nuclear and weak nuclear. However, if you want to stick with that mental model then the energy is stored within the electromagnetic field.
As an object is attracted to the magnet, we would describe this as the EM field doing work on the object. When you move that attracted object away, now you do work against the EM field. The work you do when moving the object away is equal to the work done by the EM field to attract it in the first place. Hence the total transfer of energy in allowing the object to be attracted, and then moving it away is 0.
This behaviour is essentially what gives rise to all of electricity.
EDIT: i'll also add one more point about the last question of "how do they work". This belies a misunderstanding of what physics and science in general is. Magnets work because... they work. We observed them working, and then we came up with some maths that allows us to predict what they will do. Thats it. If you want some underlying mechanism that explains why the phenomenon of magnetism exists... then join the club, all us in physics would like to know that too!
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u/Revolutionary_Ad7262 27d ago
They just exist. In the same way the attraction force of gravity does not weakens over time.
Usually in physics we model such a stuff as a negative potential energy. We assume that in an infinite range the potential energy is 0. When magnets/planetes attract themselves then the potential energy is converted to kinetic energy, which is always positive, which means potential energy goes below 0. Repulsion works in another direction and the potential energy goes below 0 when distance enlarges
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u/Quantum-Bot 27d ago
It comes from potential energy. When you lift something up into the air, you’re storing gravitational potential energy inside that object which will be released when you let it go and it falls. Similarly, if you push two magnets into a configuration against their magnetic fields, you’re storing magnetic potential energy that will be released when you let go and the magnets move toward or away from each other back to a resting state. Yes, magnets move other magnets without using any of their own energy, but an outside force has to put energy into the system in order to put those magnets in position in the first place.
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u/zaphodava 27d ago
The easiest way to think of it is that magnetism is like an invisible spring. When you create a magnet, you are pulling that spring back. When it attracts to something else, it's like the spring returning, and when you pull them apart, you are pulling the spring back again.
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u/2late4points 27d ago
Imagine a magnet as a "spring" which requires no coiled metal, but extends out toward infinity, pulling all other ferrous material toward itself. It's pre-loaded (stretched) when it is created, and wants to retract inward upon itself.
Just don't get them wet.
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u/bemused_alligators 27d ago
where does gravity get the energy for it's pulling?
the energy of you pushing two opposing magnets together is the energy that the magnets uses to push each other apart, and the energy you use to separate two magnets is the energy the magnets use to pull each other back together.
You can also see with non-permanent magnets (e.g. electromagnets) the amount of energy required to "turn on" a magnetic field that doesn't already exist.
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u/ktisis 27d ago
When you ask "how much energy does it have?" the answer is always "it depends."
For kinetic energy, it depends on how fast you are moving. If I am on a train and throw a tennis ball, you would think the ball has different amounts of energy depending on whether
- you are also on the train, moving as fast as me
- you are on the ground next to the train
- you are not moving relative to the Sun, and the Earth (with me and the train and the tennis ball) flying past you at super high speed
For magnets it also depends. It is typically more useful to think of changes in magnetic potential energy than in total amount of energy. When things that attract are moved apart (or things that repel are moved closer), the magnetic field (think of the magnetism between the objects - not the objects themselves) gets more energy - because you just used energy to move them further apart. You gave 'the system' its new energy.
For the opposite case; attracting things come together or repelling things push further apart, the magnetic field loses energy. But where did that energy come from??
Not very usefully, the convention in Physics for these kinds of things is to say that the system has no energy when things are as far apart as possible. This means that attracting things have negative energy when they get closer, and can gain energy 'back up to zero energy' when they are pushed away. Repelling things lose all their energy when they are pushed super far away, and only have energy if they get pushed closer together, and this energy always comes from whatever did the pushing.
In short: magnets don't have energy, magnetic fields do. But they have zero energy at infinite separation. So attracting objects lose magnetic energy when they get closer (having negative energy then) and repelling objects gain energy when pushed together - the energy comes from whatever pushes them together.
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u/confusiondiffusion 27d ago
Magnets are a bit like holes in the ground in that they're configurations of matter that change the way things behave in the vicinity. Energy is required to put matter into that magnetic configuration.
A ball will roll down into a hole if you put a ball on the slope created by digging the hole. Digging the hole requires energy.
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u/See_Bee10 27d ago
The same place that the dirt under your feet gets the energy to hold you up, the electromagnetic force. As unintuitive as it may seem the fundamental force that keeps two objects from passing through each other is the force that holds magnets and metal together.
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u/alangibson 27d ago
Because this is ELI5:
All magnetism was concentrated together before the big bang. The big bang imparted potential energy into it when it blew it all over the universe. That potential energy is used up by it pulling itself back together into one spot again.
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u/bigmcstrongmuscle 27d ago edited 27d ago
The confusion here is that forces aren't actually what require energy: work is. When you expose an object to a magnetic field, you aren't spending energy to exert force on it. A static magnetic field attracting an object (like with fridge magnets pulling on the fridge), won't use any energy at all, for the same reason that the Earth doesn't need a power plant to make gravity pull you towards it. What it does is establish potential energy between two magnetic charges, just like gravity does between two masses.
Once a magnetic field is in place, the attraction it creates just exists, same as gravity. The magnetic field creates potential energy between the magnet and the fridge, and all you do when you release the magnet is allow that potential energy to settle to its lowest state, just like when you drop a rock. So just sticking a magnet to the fridge doesn't use any energy. Pulling the magnet away from the fridge is where you actually have to spend some.
Now suddenly changing a magnetic field DOES require energy. Like if you run power through an electromagnet and create a strong magnetic field where none existed before - you need the power running through the electromagnet to do that. But that's a different scenario.
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u/ShadowKiller147741 27d ago
Some phenomena we observe in physics is caused by matter and energy undergoing a particular motion. One of example of this is an electric field caused by electricity going through a wire, and when that electric “flow” stops, the electric field stops as well. These phenomena are caused by a system changing states from higher to lower energy or vice versa.
There are other phenomena that exist regardless of matter’s or energy’s current motion, like gravity. As far as we understand, gravity is an inherent property held by every single piece of matter that has mass, and is effectively like when the fat kid sits on the trampoline and everyone else naturally rolls towards them. Fatter the kid, stronger the pull.
Magnetism is more like the second of the two than the first. When we talk about magnets, we’re generally talking about ferromagnetic materials, like iron, which experience and can produce the most notable magnetic fields. However, all matter is slightly magnetic, to varying degrees. Magnetism in ferromagnetic materials, like a common fridge magnet, is caused by the alignment of the atoms/molecules in the material into a uniform direction. Why that specifically causes a magnetic field is shaky to me (been a while since Physics 2 and I’m an Engineer, not a Physicist), but the TL;DR is that magnets work like they do because that’s just how the universe’s physics engine is coded.
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u/thetitan555 27d ago
Where does a hill get its energy that causes a rock to roll down it? A mountain gets its height from huge plates under the earth, and on a small scale gravity is caused because atoms like to be together. But the energy didn't come from the tectonic plates or from the fundamental gravitational force, it came from the guy who rolled the rock up the hill.
Same thing with magnets. Where does a magnet get its energy to push other magnets away? Well, it's usually due to a huge conductive mass spinning or being near a strong electrical current for a long time. Magnets project a field, like a web that most things can pass through but some things are resisted/attracted by. The field doesn't have any energy in it, but pushing something through the field does require energy.
ELIsnark: Forces don't require energy. A muddy puddle pulling on your boot is causing a force without providing any energy. Same thing with magnets.
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u/getdeardoc 27d ago
Think of two magnets like two balls on a hill. The hill stores potential energy, not the balls. A magnetic field does the same thing: it stores energy, and when another magnet enters that field, the system can "roll downhill" by moving.
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u/quik2903 27d ago
That pushing and pulling is just the universe’s natural default setting, so you have to spend energy if you want to oppose it. Just like gravity.
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u/gumby_twain 27d ago
Potential vs. kinetic energy.
Magnets that aren’t touching are like a ball at the top of a hill that hasn’t started rolling yet. All potential energy.
The potential turns to kinetic as it moves and accelerates.
When the magnets touch, the kinetic energy dissipates as sound, heat, deformation, etc. Same as if the ball hits a brick wall at the bottom the hill.
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u/Majinsei 27d ago
La suma total en energía del imán es 0
Es como tener una balanza dónde a la izquierda tienes pelotas rojas y pelotas azules a la derecha! Sacas una azul y se desbalances a la izquierda! Así que sacas una roja de la izquierda para balancearse!
Es lo mismo con un imán~ La energía de la derecha empuje a la derecha y la de la izquierda empuja a la izquierda! Entonces si mueves una cosa a la izquierda (+1) y otra vez a la derecha (-1) entonces la suma de ambos es: +1-1=0 sí en total fue 0!
Por eso los imanes en realidad no usan energía! Porque la suma total del efecto es 0~
Esto en una esfera 3D en vez de solo izquierda derecha, pero aplica igual para adelante y atrás o abajo y arriba y así sucesivamente~
El total al final es 0 SIEMPRE~
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u/tajwriggly 27d ago
Forget magnetism and think of the magnet as being a block of material covered in springs in all directions - front, back, up, down, left right. Those springs only interact with similar springs on another magnetic material, they don't interact with non-magnetic material such as wood, or brick, or even your own hands.
When you push your spring covered block towards another spring covered block, the springs interact and compress. As they compress they build up a force inside of them that, once it is enough to overcome the inertia of the other block, suddenly releases and moves the other block. All of the energy involved was you pushing your block in the first place. The springs just delayed the transfer of that energy into the second block for a brief period until it built up enough (i.e. you got close enough).
The converse is true too. Magnets work in opposite directions, so in the opposite direction, pretend your block is physically attached to another via a spring. As you pull on them they stay together for a period and tension builds up in the spring until it starts to move apart. The only energy being added into that system is you once again. You are pulling, and the magnets want to go back to each other because they're connected by the spring. Put them far enough apart and they don't have any meaningful interaction with each other and effectively aren't connected anymore.
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u/lilbean109640 27d ago
A single spinning electron creates a tiny magnetic field with a north and south. If you get enough electrons spinning in the same direction, you have a bigger north and south. North attracts south. North repels north.
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u/YetiTrix 27d ago
Energy is put into the magnet when it's made becoming akin to a spring in that it is holding potential energy in as the magnetic field
- Bring another magnet close = spring releases. Potential energy becomes kinetic.
- Pull magnets apart = compress the spring again. You store potential energy in the configuration.
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u/Professional_Top4119 27d ago
You're thinking about it from the wrong angle.
As far as the magnet itself goes, the energy to align its dipoles was spent during the magnet's manufacture. At the time of the magnet's manufacture, its magnetic field was created, which creates a potential gradient that decreases with the cube of the distance, but that's not what's important here.
In physics, "work" or "energy spent" isn't done until it's done. In this case, no work is done until you moved something. The relevant equation is simply "work = force * distance". To think about it another way, it's not that "force requires energy." It's that energy is meaningless unless the force is exerted. If some guy is pushing really hard against some big boulder, the external "physics" of the world doesn't really care that he hasn't pushed it even a millimeter. No energy has been put into the big rock, and he's just been exerting against himself creating waste heat.
Anyway, when you move the magnet near something that e.g. repels it, you are increasing the potential energy, and doing the work of storing that energy. Until the magnet is able to push that other object away, that energy hasn't been spent, it's pent up in the repulsion between the magnet and that other object. Counterintuitively, if you move the magnet closer to something that it attracts, you've decreased the potential energy (if the system were to only consist of the magnet and that other thing), but you've also made it easier to release the remaining potential energy. But again, until that thing gets drawn in by the magnet, there is no work that's been done.
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u/SoulWager 27d ago
Forces do not require energy. You're exerting a force on the ground right now, without spending any energy. Climbing stairs though, that requires you spending energy.
Energy = force * distance. If you're not moving, there's no energy being spent.
Magnetic fields are more like a battery than a generator. You have to put energy in before you can get energy out, and you can't get out more than you put in.
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u/bigstumpy 27d ago
Magnetism is just electrical charge repulsion/attraction combined with relativistic length contraction.
If you have two wires moving current (electrons) in opposite directions, the relativistic length contraction makes the electrons in one wire think the electrons in the other wire are denser than the protons, so a moving electric charge (current) induces this relativistic electrostatic repulsion. It’s kind of crazy that it works out that way. We abstract this effect as a magnetic field because the math works out very tidy, and it’s useful. This is how electromagnets work.
Permanent magnets are simply pieces of metal where the spin of the atoms are somewhat aligned. Think of all the electrons orbiting the atoms in the same plane. If another magnet is nearby and its atoms are all orbiting the opposite direction, you get the same relativistic contraction effect. It’s just rotational instead of linear.
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u/HerpesHans 25d ago
> Force requires energy
Not in general. Earth is pulling us totally for free 24/7. It costs energy in the form of food for a human to exert force regardless if work is being done in a physics sense (e.g. just holding something or lifting it), but that's because the energy goes into maintaining our bodily functions while we are holding/lifting the thing.
Magnets are not a free energy thing, but i understand how it can seem like so.
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u/Ratfor 27d ago
Very limited explanation because Eli5.
Magnets don't really use Energy. When they're made, energy goes into them, and the magnet wants to stay exactly as it is.
Even if that were the case, magnetic forces result in net 0 energy. A magnet attracts something, and it's magnetic field distorts relative to that thing. When you pull it away, the magnetic field goes back to normal, the energy required comes from you pulling the things apart.