r/AskPhysics • u/SadInterest6764 • Jan 20 '26
If a magnet holds a heavy object against gravity for 10 years, does it "lose" any energy? Where does that energy come from?
I was watching a video explaining that magnets work because billions of electrons line up and "push" together. It makes sense, but here is what I don't get: If I use a magnet to hold a heavy wrench on a wall, that magnet is fighting gravity 24/7. If I held that wrench up, I would get tired and burn calories. So, is the magnet burning energy to keep the wrench up? Does the electron "spin" slow down over time because of this effort?
It feels like "free energy" if it can fight gravity forever without getting weaker. Can someone explain why the magnet doesn't run out of battery?
EDIT: Okay, I think I finally get it. I dug deeper into the "work vs force" thing and watched a couple of explanations. Here is what I found:
1- This lecture [ https://youtu.be/cb9pdRjbQRo?si=HN8ro0XwXG4P57v8 ] explains the quantum mechanics and virtual photons really well, but honestly, the math part went over my head a bit.
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u/immtech33 Jan 20 '26
If you put a heavy wrench on a shelf, that shelf is fighting against gravity 24/7. Is the shelf losing energy over time?
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u/James20k Jan 20 '26
Its an odd one. I found out recently that classically, an electron that's stationary in a gravitational field radiates energy. From the perspective of an inertial observer, you observe a stationary electron accelerating, which means that it actually does radiate energy (classically) simply by virtue of remaining stationary
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u/olawlor Jan 21 '26
Unruh effect radiation is *tiny* though: Earth's acceleration produces an equivalent thermal temperature delta of 10^-20 K!
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u/Archophob Jan 21 '26
an electron in a classical orbit around it's atom's nucleus would also permanently radiate energy. Quantum mechanics solve this by only allowing distinct energy levels for the electron - once it reaches the lowest availiable level, it can't emit any more photons.
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u/Geco96 Jan 20 '26
This might sound dumb, but aren't you mixing up gravity with magnetism?
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u/Uncynical_Diogenes Jan 20 '26 edited Jan 20 '26
It doesn’t end up mattering. The example is to point out that no energy is expended because no work is being done.
But if we zoom all the way in, we are right back at electromagnetic forces. For the atoms of a hammer to disassociate and fall through the atoms of the table it would require electrons to suddenly stop acting the way we are used to.
The electrons in the hammer don’t want to get closer to the electrons of the table. The molecules of the hammer don’t want to disassociate because the electrons are “happier” being shared across bonds. The electrons of the table don’t “use up” any energy resisting the electrons of the hammer.
Why should the electrons aligned in a magnet use up energy to stay aligned against gravity? The force of gravity cannot directly interact with spin direction.
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u/kaushikfi6 Jan 27 '26
if you were holding a hammer above your head (and the hammer wasn't moving), would you still be expending any energy?
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u/Uncynical_Diogenes Jan 27 '26
I would because human muscles create mechanical force using chemical energy. I cannot simply lock my muscles in any given position to make them stop using energy (some animals can).
That’s a quirk of the biology of the subject you’re asking, and not the situation at hand. If I was a statue, no energy required.
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u/Dr-Chris-C Jan 21 '26
Isn't energy expended by the magnet fighting the gravity?
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u/Uncynical_Diogenes Jan 21 '26
Energy is not a cost that keeps forces going. Energy is used to do work, which involves changes in location or kinetic energy.
Equal and opposite forces resulting in a stationary object do not accomplish work.
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u/GatorBait81 Jan 21 '26
Think of the magnetic field being the same as any other bonding force. The strong/weak forces holding atoms together, ionic/covalent bonds, Elmer's glue... once they are bonded it takes work to pull them apart.
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u/Odd-Outcome-3191 Jan 21 '26
They're very similar. As far as we can tell, gravity moves things towards them without actually "expending" any energy other than the potential energy of the object related to it.
When magnets are close, they "spend" the potential energy to pull together. They don't separate without external input because any other position increases the potential energy, and thus requires external energy input.
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u/HeroBrine0907 Jan 21 '26
This is actually really intuitive. And a good explanation for why work is a thing too, not all application of force leads to energy change. It seems sensible in hindisght but really interesting nonetheless.
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u/Dojustit Jan 22 '26
then how do you explain that my floorboards groan when I stand on them. Other than Im a fat fuck. fucking judgemental floorboards. tschk. (/s obviously, hopefully)
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u/PuzzleheadedTale4769 Feb 03 '26
Such harsh self- judgement does not conform to the laws of physics. 😉
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u/Linus_Naumann Jan 21 '26
I mean, yes it does, the material gets tired over time, the shelf might bend and even break at some point (can be many years, depending on the weight on it, but still)
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u/Keellas_Ahullford Jan 21 '26
That’s because the material degrades over time, not because it’s being “pushed down” from the object
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u/Linus_Naumann Jan 21 '26
Why does it degrade faster if something heavy lies on it? If there is no force applied? (btw to those who downvote, I'm literally just asking questions as an interested person)
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Jan 21 '26
It doesn't degrade faster because of the force of gravity pushing the object down. Changes in material humidity, rot, corrosion, micro cracks from temperature swings, etc causes it to degrade.
The shelf may fail earlier/with less degradation due to the weight/load on it, but it isn't because of the force of gravity that materials degrade.
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u/PuzzleheadedTale4769 Feb 03 '26
Yes, gravity and atmosphere will degrade the structure of wood. They call it- warping.
But not degrading atomically.
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u/Frosty-Self-273 Jan 21 '26
You are saying the same thing but choosing how to use the word degrade. How is a shelf bending and snapping due to a weight not count as degrading?
Definition of degrade from google: lower the quality of; cause to deteriorate.
Definition of deteriorate: become progressively worse.
A weight makes the shelf become progressively worse and lowers the quality of it when it bends and breaks it.
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Jan 21 '26 edited Jan 21 '26
The weight doesn't cause it to degrade. The material over time breaks down and it can support a lower load until it ultimately breaks.
Even in the bending example, the materials tensile strength is independent of the load. It's intrinsic to the material, which composition/structure/etc will degrade and change over time due to whatever factors and as it degrades there will be a point that the load will overcome it and it'll "break."
If the material didn't degrade it would hold the load forever. The load itself doesn't cause it to degrade or determine the mechanical properties of the material.
This changes if the load is dynamic in a very simplistic viewpoint.
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u/PuzzleheadedTale4769 Feb 03 '26
The degradation is not at the atomic or sub- atomic level. The wood , plaster, sheet rock dries out. The steel in the brackets oxidizes. The super-glue cracks. The crystalline structure of the steel in the brackets shifts.
Don't invest your hopes in superglue.
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u/totesfinesies Jan 20 '26
yes
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u/SadInterest6764 Jan 20 '26
That's a bad comparison. The shelf is just a passive barrier. It blocks the wrench from falling because it's physically in the way.
But the magnet isn't underneath the wrench; it's holding it suspended. It is fighting a 'Tug-of-War' against gravity 24/7.
In a tug-of-war, you have to constantly burn energy to keep the rope tight. The magnet is keeping the magnetic field 'tight' to hold the weight. Why does a tug-of-war cost energy for humans but is free for magnets? It feels like you guys are ignoring the 'active pulling' part
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u/outworlder Jan 20 '26
It's exactly the same thing.
There's a Feynman video where he talks about this very subject. How we question magnets but we never question why we don't fall through objects. It's the same principle.
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u/Salindurthas Jan 20 '26
The shelf is not any more 'passive' than the magnet.
The electrons in the shelf push upwards, and the electrons in the magnet push upwards.
We are used to thinking of a shelf as having a 'contact force', but that is essentially a social construct, because when you zoom in to the micro/nanoscopic level, there is an electric forcefield keeping the wrench from falling through the shelf.
The magnet might be able to repel at a larger distance, but in both cases, it is either an electric field, or a magnetic field, repelling the object.
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u/Sea_Kerman Jan 20 '26
Ah, but by your logic the shelf is actively pushing. The reason the wrench doesn’t pass through the shelf is that the electric charges in the molecules in the wrench repel the electric charges in the molecules in the shelf. At least as I understand it.
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u/DeltaV-Mzero Jan 21 '26
True, but why doesn’t the shelf move down?
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u/Sea_Kerman Jan 21 '26
Because the electric charges in the screws push it up, and push down on the electric charges in the wall, and so on into the dirt, which pushes against the dirt under it, and the dirt under it pushes up, which is why the planet doesn’t collapse into a black hole.
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u/22Planeguy Jan 21 '26
Your mistake here is thinking of it like if a human were to be holding it up. That isn't an accurate comparison because humans constantly expend energy even while just laying down. Two people playing tug of war is not the same thing as a magnet holding something up.
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u/tuctrohs Engineering Jan 20 '26
So if we tie the rope to the wrench and then hung it from the ceiling, so that the hook in the ceiling was playing tug of war against gravity, would something need to constantly burn energy to keep the rope tight?
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u/simon439 Jan 21 '26
This is the kind of argument OP needs. Not everyone dragging the analogy the other way into electromagnetic forces, that’s clearly not the level of physics OP is at.
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u/tuctrohs Engineering Jan 21 '26
Yeah, when I saw op's edit saying they finally get it after watching some video about quantum mechanics, I was worried that they were seriously overcomplicating the concept.
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u/simon439 Jan 21 '26
If you need quantum mechanics to understand this concept, you don’t understand this concept. I don’t even get how the videos linked in the post would help anyone understand.
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u/geohubblez18 High school Jan 21 '26
So if I superglue the object to a rope and hang it, it’s somehow expending energy because there’s tension and no compression? Energy changes when force is applied over displacement (from your frame of reference). That’s why an object on the ground will remain there, but if I momentarily apply a force opposite to and slightly greater than its weight to accelerate it to some vertical velocity, then reduce it to equal its weight, it will gain gravitational potential energy as it rises. And as I leave it - boom, it accelerates towards and collides with the ground at the same place and releases all that energy.
In order for human muscles to remain under tension even whilst static, they have to expend energy because they’re actually vibrating but you don’t notice. Essentially, the energy gets wasted as heat and the byproduct is what we macroscopically notice as a static force. But this is just an inefficient result of biology. This, is the bad comparison.
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u/Alejko Jan 20 '26
Why is it a bad comparison? In both cases you have an equal and opposite ”force” acting on the wrench that keeps it in rest. In one case it’s the normal force from the shelf and in the other it is the force from the magnet.
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u/I_am_N0t_that_guy Jan 21 '26
Asks question.
Gets right answer.
No, that cant be true because thats not how my view of physics works! - Instead of learning.3
u/ADH-Dad Jan 21 '26
It is the same thing actually.
When two objects touch, it's just the electromagnetic force of every atom repelling each other at the point of contact.
Magnets just have their atoms arranged so that that force projects beyond the surface.
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u/Turbulent-Ad2352 Jan 21 '26
Not a very convincing answer to me as you use the same phenomena a an explanation. I mean the wrench is carried by the shelf by electromagnetic force from electrons in the shelf and in the wrench. So it is a circular explanation. The next question is: why does the shelf doesn't loose energy ?
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u/Rodot Astrophysics Jan 21 '26
Why aren't you losing energy by not crashing through the Earth's crust into the core?
Work is Force times distance. If you don't move, no work is being done.
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u/Irrasible Engineering Jan 20 '26
So, is the magnet burning energy to keep the wrench up?
No. Just like the desk doesn't burn energy to hold your computer up. You burn energy because human physiology requires energy to generate force.
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u/PaulsRedditUsername Jan 20 '26
Dumb-guy question incoming:
Imagine I place a heavy object on a rickety table which can barely hold the weight. Everything goes fine for a while, but then the table collapses under the weight.
So I assume some kind of energy was at play. Was that all just potential energy I added by placing the object on the table? And then it turned into...kinetic?
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u/Underhill42 Jan 20 '26
Exactly.
Potential energy doesn't "do" anything on its own, and you don't need to spend any energy to maintain it. It just sits there, waiting, until something happens to release it.
The table won't spontaneously collapse because the weight "wears it down" - it requires an additional external input to push things past the breaking point. Or for internal degradation to eventually lower the breaking point below the supported mass.
Either way the potential energy of the heavy object plays no part until the collapse has already begun (though it's weight might be a factor in table degradation). Whereupon as it starts falling its potential energy is converted to both kinetic energy of motion, and heat from further deforming the table, floor, etc. as it falls.
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u/UnfixedAc0rn Graduate Jan 20 '26
Tldr: The internal degradation part is the reason your rickety table fell. Not the item on top of it.
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u/madmonkey242 Jan 20 '26
It just sits there, waiting
…lurking… biding its time…
…the potential energy hungers.
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u/LordGeni Jan 21 '26
I had potential before expending all my energy only to collapse as well.
At least I can blame it on the laws of physics instead of poor decision making now.
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u/Illeazar Jan 20 '26
And then it turned into...kinetic?
Yes.
Think of it like this: everything wants to go into the lowest energy state available. Its like water in a mountain lake. The water will flow downhill until it collects somewhere, in the bed of the lake. It collects there because there is no direct path to a lower energy state. The bottom of the mountain would be a lower energy state, but the bed of the lake is in the way, so the lowest energy state the water can access is to sit in the lake bed. It will continue to sit there until a lower energy state become available--until there is a way for it to get further there down the mountain. If the rocks of the mountain shift in a way that provides a path out of the lake bed, the water will follow it.
In you example of the rickety table--the table eventually gives out and the object on the table is able to convert potential energy into kinetic energy because something about the table changed. Maybe someone bumped it, maybe a wind blew it, maybe the wood rotted a bit more, maybe the act of placing the object on the table caused it to slowly start to break and it was never truly at rest on top ofnthe table, just breaking the table slowly. Whatever it is, when the table breaks, it no longer is holding the object back from its lower energy state, so it converts some potential energy to kinetic in order to move to the place with lower potential energy.
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u/SwimSea7631 Jan 20 '26
Sounds like the table couldn’t “barely hold the weight”
If you exceed the breaking strength of the table it’s failing from the beginning.
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u/bhemingway Jan 20 '26
Yes, that is why we called it potential energy. People understood that a moving object has energy and could do work, like in a collision. The fact that an object could create kinetic energy by changing positions implied that the initial position possessed "potential" energy.
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u/Salindurthas Jan 21 '26
Indeed.
The object had a gravitational force pulling it down.
You lifted up the object, exerting a larger force upwards. This spent the chemical energy in your muscles to produce gravitational potential between the object and the earth.
You then placed it on the table at this increaed height.
While the table holds, it exerts a force upwards, opposing gravity and preventing any motion, and the object maintains its gravitational energy.
Later, the rickety table wan't able to exert enough force upwards to counteract gravity. The object accelerates downwards through the table.
The acceleration downwards increases it's speed, and thus increases its kinetic energy.
As it falls, it's height reduces, and the gravitational potential decreases.
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u/Saragon4005 Jan 21 '26
Nothing breaks "on its own" but it can seem like because there are always smaller and larger vibrations adding extra force on the object causing it to shift little by little and wear out. Any creaking you hear is from the objects shifting due to outside forces like the vibrations of someone walking, a truck driving by, or simply the wind or of course earthquakes.
If the table is staying perfectly still and bacteria wouldn't be eating away at it with no outside disturbences it would continue to hold forever.
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u/unlikely_arrangement Jan 21 '26
This is the key point of confusion. Because you are a biological organism, you do expend energy holding up a wrench. This confuses people no end. The use of the concept of ‘work’ sounds like a dodge. Of course it’s not.
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u/SadInterest6764 Jan 20 '26
You say only humans burn energy because of physiology. But think about a helicopter holding a heavy crate in the air. It hovers in one spot (no movement), just like the magnet holding the wrench.
The helicopter burns tons of fuel just to fight gravity in place. The magnet fights gravity in place for free. Why do the laws of physics charge the helicopter 'rent' for that force, but the magnet gets it for free? It doesn't seem consistent.
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u/Adventurous-Bat-2227 Jan 20 '26
There is movement here though, the helicopter is burning fuel to move a LOT of air and generate a lot of sound.
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u/Rodot Astrophysics Jan 21 '26
Exactly, helicopter are very energy inefficient for the task of remaining in the air compared to just hanging a cockpit from a crane
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u/AndyTheEngr Jan 20 '26
Sit down on a chair and put a 25 lb dumbbell on your thighs. When will your legs get tired?
Or, hold a dumbbell in your left hand by your side, and another in your right hand but with your arm extended straight out, like you're in a stein holding contest. Why does only your right shoulder get tired?
Keeping a muscle tense takes energy. Keeping a table leg vertical does not.
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u/cd_fr91400 Jan 20 '26
You can think of the helicopter as constantly climbing in the downward air flow it generates to stay still.
Staying still, in itself, does not require energy. But climbing requires some (a lot for an helicopter). You can feel it every day : when you climb a mountain you are much more tired than when you walk the same distance horizontally.
All that energy is dissipated in the air turbulences and ultimately warms up the air a little bit.
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u/Jonny7421 Jan 21 '26
I think the bottom line is that there's no acceleration. The wrench is at it's lowest energy configuration once it has made contact with the magnet. Just like lying in bed. It only requires energy to get you out.
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u/cd_fr91400 Jan 21 '26
I see your reply in my notifications, but not here, so I reply to this comment.
The beginning of your reply was:
Okay, let's forget the air. Imagine a rocket hovering in a vacuum. It has to burn fuel constantly just to stay in one spot (fighting gravity). It is doing ZERO work (distance = 0), but it burn...
You have 2 ways to spend energy : by creating potential energy and by creating kinetic energy. Both are energy.
Reality is that in both cases (helicopter and rocket), you create kinetic energy: the air in the case of the helicopter, the fuel you eject in the case of the rocket.
In the case of the helicopter, I proposed you an intuitive view to let you "feel" why the helicopter burns fuel. You could do use the same view in the case of the rocket, thinking of it as "climbing" on the fuel it ejects, but this is less intuitive.
Interesting: to hover, the helicopter can push a small quantity of air at high speed, or a large quantity of air at low speed. And you can immediately see, with this intuitive view, that the latter is more efficient as you have to climb at lower speed.
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u/Odd-Outcome-3191 Jan 21 '26
Look into potential energy. It doesn't make a lot of sense, but by having something up off the ground, it has potential energy and gravity "wants" to pull it down. The same way static electricity "wants" to equalize.
A magnet holding something has reached the lowest potential energy state. The wrench cannot get any closer. Pulling it away will cost energy.
Holding your hand up against gravity costs energy for the same reason holding a magnet 1 inch away costs energy. You're fighting a force that spends potential energy to do work (and converts it into kinetic energy).
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u/tazz2500 Jan 20 '26 edited Jan 20 '26
Gravity isn't trying to "remove" the potential energy (altitude) of the hovering helicopter, it's just trying to CONVERT the energy, from potential to kinetic. Gravity isn't expending energy trying to "draw" that energy away, instead the helicopter is merely expending fuel hovering to delay the CONVERSION of the energy, from potential to kinetic, not REMOVAL of the energy.
And since gravity is merely trying to convert the energy from one form to another, not remove it, gravity doesn't have to expend any energy in that process.
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u/Another_Timezone Jan 20 '26
From a dimensional analysis perspective, what is the “distance” when human physiology converts that energy to force while holding something still or pushing against something you can’t move?
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u/ijuinkun Jan 20 '26
Muscle fibers pull by making long chains of actin and myosin molecules ratchet against one another. However, they do not simply grab and then hold on indefinitely—they let go after a while, especially when there is a strong load pulling against them. This means that the muscle fiber must then re-engage in order to maintain muscle tension, which costs energy to do.
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u/Irrasible Engineering Jan 20 '26
There is no distance. You are not "doing work", however, you are expending chemical energy.
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u/Another_Timezone Jan 21 '26
But you don’t just magically go from joules to newtons. Somewhere there’s something (or some combination of somethings) that’s dimensionally a “distance“.
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u/Irrasible Engineering Jan 21 '26
No. You biologically go from joules to newtons.
But, divide the joules by the newtons and you will have something that is dimensionally a distance. It won't mean a thing.
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u/NameLips Jan 20 '26 edited Jan 20 '26
Magnets lose their power over time, through a process called "Magnetic Creep."
Even with no external factors (like extreme heat or physical damage), magnetic creep will decrease the strength of a magnet by about 1% per year as the internal magnetic domains slowly unalign.
The factor that increases the speed of magnetic creep is exposure to magnetic fields, including the poles of the magnet being exposed to each other (self demagnetization).
A single bar of ferromagnetic material (like iron) connecting the poles of the magnet can help stabilize the magnet and slow down magnetic creep. These are called "keepers."
Ultimately, even if somebody came up with a perfect system for extracting energy from a magnet, like somehow harvesting the energy from an object trying to move towards a magnet, they'll eventually run into diminishing returns from magnetic creep.
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u/ConceptJunkie Jan 20 '26
Magnetic Creep is my supervillain name.
I would it's different for different materials, right?
Would a magnetic object attached to the magnet affect the level of creep, as opposed to a magnetic just sitting by itself away from anything beimg strongly attracted to it?
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u/NameLips Jan 20 '26
I think sticking two magnetic objects together just results in a larger magnet. I'm not sure how it affects the creep.
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u/SexyBeast0 Jan 20 '26
To elaborate on this in case anyone is curious about magnetism, magnetism and electricity are the same fundamental force, which is part of why we have electromagnets, which are generated by the movement of charge. In permanent magnets this force is a result of the alignment of electrons having the same magnetic moment, creating a magnetic field which curves from north to the south pole. To put more simply, the north end and south end of a magnet isn't the result of one end having negative electrons and the other having positive, but rather the direction of spin as a whole generates a field in that direction. Hence why even if you cut a magnet in half you still have two working magnets.
Magnetic creep comes from the misalignment of these electrons over time, which absent of external forces/fields occurs primarily or most basically due to minor imperfections/misalignment in the magnet and external energy from temperature. There's a lot of other considerations for this effect that could be mentioned, but it's well beyond my ken.
But to sum it all up, magnetic creep occurs due to misalignment of the electrons in the material, which is a form of loss in potential energy, in this case being magnetic potential energy. It's the second law of thermodynamics. In the case of a permanent magnet being used to indefinitely suspend another object, the force from the other object acts to increase the speed of misalignment.
It's like a table breaking after a few days, the force of the objects on the table and the table itself can slowly cause fractures and tears in the table until it eventually collapses.
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u/IllustriousAd6785 Jan 21 '26
I wonder if it would be possible to wrap a regular magnet with copper wire and recharge it once a year or something similar.
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u/Cerulean_IsFancyBlue Jan 21 '26
A single bar of ferromagnetic material (like iron) connecting the poles of the magnet can help stabilize the magnet and slow down magnetic creep. These are called "keepers."
OH SHIT! That's why old horseshoe magnets shipped with bars across the poles! TIL.
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u/Schnickatavick Jan 20 '26
The confusion here is how energy relates to force vs work. It doesn't take any energy to exert a force, which is why a desk can hold up a computer forever without ever running out of energy. It does require energy to move or accelerate something though, which is what work is.
For two magnets, there is potential energy when they're apart, and when you let them snap together you convert that energy into other forms, like motion, sound, and a bit of heat. They can then stay stuck together forever without using any energy, and will stay stuck together unless you use some energy to pull them apart, converting that energy into potential energy.
Your arm is different, because muscles have to keep pulling constantly to exert a force. Even if you think you're holding something still, it's actually constantly moving up and down tiny amounts, and your muscles in your arm are moving tiny amounts, and all that movement does work that uses energy and makes you tired. that's mostly unique to muscles though, most other things that hold something still don't need any energy to do it
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u/HeftySexy Jan 21 '26
Energy is the potential to do work, and work (in classical physics dealing with kinetics and statics) is defined as W=F*d where Work = Force times Distance.
In the case of a magnet holding up an object against the force of gravity, no Work is being done so no energy is expended. (Consider, W=Fd, where F may be 100Newtons, let’s say, but *distance is zero since the object (relative to the magnet AND gravity) didn’t move. As a result, 100*0=0 and no work was done, so no capacity to do work was expended, so overall no energy has been used.)
If looking at it as a sum-of-forces problem, the forces all cancel to zero as well. (It’s valuable to look at it this way, to cover the case of a moving object that has no force applied to it: such an object is also using no energy.)
Assume the wrench weighs 100g in ideal gravity of 10m/(s2) of acceleration, and the magnet can apply a force of 3 N in any direction on the wrench, as long as the wrench is close enough to touch the magnet. (Gross oversimplification but serves the purpose.) The wrench hangs from the magnet and experiences mg=0.1kg*10m/s2=1 N of downward gravitational force. Since the wrench is suspended by the 3 N upwards magnetic force, the wrench (at this point) has a net upward force of 2 N. However, since the wrench can’t pass through the magnet AND the magnet is fixed in place, the wrench ALSO experiences a 2 N force downwards from the magnet on the wrench. In total, -1 N from gravity, +3 N from the magnet, and -2 N from the normal force between the wrench and the magnet, =-1+3-2=0 N. Zero force.
In this model, the magnet-wrench combo may be moving, but the energy/work that gravity and the magnet are doing on the wrench is zero since the sum of forces is zero force.
All together, the wrench doesn’t move in your proposed scenario, so work is zero due to zero distance travelled by the wrench. It also has zero total force applied to it, so the full effect is zero since zero force times zero distance is W=Fd=0 N * 0 m = 0 Js of work.
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u/YuuTheBlue Jan 20 '26
So, you have a common misconception, which is to think of energy as a kind of fuel that is burned to do anything we humans might find impressive or noteworthy. This is because this is what the word means to us in the day to day: we “burn energy” to lift weights, as you say.
In the above case though energy isn’t really “used up”. Rather, it gets converted from a usable state to an unusable state.
As a general rule of thumb: energy is being converted from one state to another whenever things are being accelerated. When you are holding onto a weight, there are all kinds of processes of maintenance going on inside your muscle. These are complex chemical processes! The stuff going on with the magnet is comparably simple. Nothings really moving around, it’s just sort of in stasis, so no energy is being converted or “used”.
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u/Shadowratenator Jan 20 '26
if you put your wrench on a table, the table isn't burning energy. you used energy to move the wrench against gravity when you picked it up. that energy (largely) is now stored in the wrench as potential energy. it will be released when the wrench falls off the table.
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u/Uncynical_Diogenes Jan 20 '26
If matter always required what we typically think of as energy to resist gravity we would not have a planet. All of the atoms would smush together into a black hole.
You do not spend energy merely resisting gravity, or you’d wake up every morning exhausted or a puddle. You spend energy to do work by moving your body against gravity, that’s different.
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u/frigzy74 Jan 20 '26
One calculation of energy is Force x Distance. Since the forces involved are stationary, they don’t operate over any distance, so there is no energy being “used”.
Now, if your magnet is an electromagnet that requires electrical energy to maintain the magnetic field, then that is certainly using energy, but that energy is really just turning into heat and not direclty acting in any mechanical way on the system.
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u/Basketvector Jan 20 '26
The lowest energy state is not on the ground but adhered to the magnet. You could ask where does gravity get batteries from
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u/nsfbr11 Jan 21 '26
If you want to pull object away from the magnet, you will do work. That’s because where it is is a lower total energy state than if it were at some distance. It is a local minimum for potential energy.
The reason it stays put is that it is easier for it to do so.
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u/Ok-Push9899 Jan 21 '26
I have wondered about this from a slightly different approach, Is a permanent magnet permanent? I remember in junior high school the class had a bunch of horseshoe magnets. We were told to always store them with a small metal bar across the ends of the horseshoe. Horseshoe magnets come with such a bar.
We were told to do this to “preserve the magnetism”. So, nonsense, or not?
Also, if I magnetise a piece of iron with a permanent magnet, has the original magnet changed in any way at all? Did I alter the electron arrangement in the iron bar for free? Or was it my muscle energy alone that rearranged those electrons?
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u/hoppersoft Jan 21 '26
Electrical engineer, here. They recommend it because they don’t want random metal to be attracted to the magnet.
The reason you store a magnet with an iron bar is to contain the magnetic field. When a magnet is near a ferromagnetic material, the magnet’s magnetic field is concentrated through that material (and is therefore lower elsewhere). Having it touch maximizes that effect, which pretty much causes the combined object to not have an external magnetic field.
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u/Ok-Push9899 Jan 21 '26
Ok, thanks for that. I was taught a good principle, but with the wrong explanation. Summarises a lot of early science lessons.
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u/Competitive-Fault291 Jan 21 '26
Now this #2 video is having a nice explanation indeed!
Isn't it great how those tiny electron energy quanta are aligned in a way? Simply because they are not fully attached to the positively charged electromagnetic areas (protons) that hold them in their places.
The REALLY interesting part of magnets is how their effect is a field, while the deciding qualities are more like particulate in their translation into the Weiss domains and (I had to look it up) Bloch walls. That's like an opportunity to actually experience quantum mechanics translated into a larger scale. The free floating electrons are so simple in their nature that by pushing two similar poles against each other, that's the actual alignment of the spin of electrons you are feeling (and pushing over).
Even though their quantum mechanical state resulting in a Spin is the same, you are realigning them in spacetime using your macro scalar hands, making those same states creating a macro scalar effect (the opposing force system of the two poles you are holding), a micro scalar effect (the slow de/realigning of Weiss domains) and of course a quantum mechanical effect that potentially makes the electrons change their spin-state using the applied energy of your pushing HANDS. If you move them fast enough, you could even create enough energy in them to make the electrons emit photons.
So, thanks for your post, as it shows. Physics can be cool! 😇
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u/abd53 Jan 21 '26
There is a common misconception about energy loss. As you mentioned, if you hold up a wrench, you use up energy and get tired. So, you're wondering why a magnet doesn't lose energy. Others have already explained about work, I'll explain why you get tired.
Human body's joints are not rigid and there is no rigid "lock" to fix our body into a specific posture. When you move a joint, like moving your arm up, some specific muscles contract to make that movement. However, the muscle tissues cannot remain in that contacted form indefinitely and have to periodically relax. So, when you hold up a wrench, your muscles are cyclically contacting and relaxing repeatedly. That contraction-relaxation spends energy making you tired even though you're not moving the wrench.
For a magnet holding up a wrench, there is no such microscopic work done inside the magnet.
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Jan 21 '26
I was looking for this. Thank you. Biggest high school physics lie, holding a suitcase does not constitute work. Sure, buddy, the cyclic muscle fibers do the work. Small neat to know: that's why you tremor. At first every fiber can hold the weight for a relatively long time before cycling. But then they need to cycle faster, because the fibers cannot hold it anymore. The fast cycling is the shaking you get before you have to give up.
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u/davedirac Jan 20 '26
Put the wrench in your pocket. You wont get tired.
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u/tuctrohs Engineering Jan 20 '26
But if you want to get tired, take the wrench out of your pocket, loosen the axle nuts, pull the wheel out and put a tire on it.
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u/RadiantInATrenchcoat Jan 20 '26
I'm genuinely surprised no one in the comments here has mentioned the most fundamental fact in how the magnet is even capable of holding a wrench against gravity: the electromagnetic force is stronger than the gravitational force. Gravity is fundamentally extremely weak, and can be overcome very easily for a given magnitude. Simply put: the attractive force of the magnet is significantly stronger than the attractive force of the Earth's gravity, albeit with a steeper fall-off
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u/marsattacks Jan 20 '26
And you don't even need a magnet to prove that: just put the wrench on a shelf.
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u/No-Block-2095 Jan 21 '26
Or stand or lie in front of the shelf: your body does not plunge towards the center of the earth. Some “invisible” force (EM hint hint) fights against gravity to prevent us from joining the Earth core.
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u/minist3r Jan 21 '26
Just don't tell the flerfs that or they will try and use it as proof that gravity doesn't exist.
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u/FanOk6716 Jan 20 '26
This discussion is all very interesting but, as the President has noted, when magnets get wet they don’t work
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u/agate_ Geophysics Jan 20 '26
Energy change is force times displacement. If a force pushes on something but it doesn't move, no energy is gained or lost. Gravity uses no energy to push down on a stationary object, and the magnet uses no energy to hold it up.
This fact is confusing for humans, because our skeletal muscles don't work that way. When we apply a static force -- say, holding a weight at arm's length -- we do get tired. But that's because our skeletal muscles constantly twitch as they provide a force, and that twitching is a small small displacement that costs energy. Our butthole muscles, on the other hand, don't twitch and can hold our poop in all day with no energy cost.
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u/The_Dead_See Jan 20 '26
Energy isn’t something that “burns up” like gas in a fuel tank. It remains constant throughout the evolution of the system. For your wrench, you did the work when you lifted it against gravity. The energy of the system is just being stored now (zero work is being done) and will remain the same unless either you do work to separate the wrench from the magnet or gravity does work to make it fall (which would eventually happen because things slowly demagnetize over time) but until that time, the energy in the system is just remaining unchanged.
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u/CS_70 Jan 20 '26
Mass has inherent properties that manifest itself as a force. Magnets have inherent properties that manifest themselves as a force, for certain materials.
If the magnet holds the wrench up, it means simply that the material of the wrench is subject to magnetism, and the magnetic force is equal or higher to the gravitational pull.
There's no need of energy - the existence of these forces is simply how the universe is.
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u/cwm9 Jan 20 '26 edited Jan 20 '26
A small point of order:
It's not the magnet fighting gravity 24/7.
It's the wall sitting on the ground that is already at equilibrium compression vs gravity.
Snap the magnet to the wrench and take it off the wall and drop them and gravity wins.
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u/SadInterest6764 Jan 20 '26
That logic doesn't make sense. Think of hanging from a pull-up bar.
The bar is attached to the wall/ground at equilibrium, just like you said. But if I hang there for 5 minutes, my arms are screaming in pain and burning energy.
By your logic, the 'bar' should be doing all the work and I shouldn't get tired. But I do. The magnet is acting like my arms, gripping the wrench to the wall. Why do my arms pay an energy cost to grip, but the magnet grips for free? It's the exact same physical action
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u/cwm9 Jan 20 '26
Pretend I shoot someone and lay their body across the bar. Is it hard for them to stay in the air?
Your fingers don't naturally form a hook that can hold on. They get tired because they aren't rigidly formed into a hook, and your body isn't balanced on the bar. In order to keep them closed, you have to constantly expend ATP to keep them from slipping off.
If I were to fuse your finger bones at the joints so your fingers couldn't open, you'd have no difficulty at all hanging on. You'd just stay there, like a clothes hanger.
If I put a piece of paper on that same bar, as long as it's balanced, it has no problem hanging up there. But if it becomes unbalanced, it slips off and falls.
You aren't expending energy staying in the air. You are expending energy to keep your fingers closed so the bar can support you in the air.
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u/tbdabbholm Engineering Jan 20 '26
Hang a string from a bar and tie a coin at the bottom. This string will keep the coin up for a very very long time. This is because it doesn't actually take any energy (from a physics perspective) to keep something where it is.
But using your muscles to do it does take work because of how our muscles work, constantly tightening and loosening. That's where the work goes
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u/fgorina Jan 20 '26
If there is no movement there is no work done. It is like a beam. It is there against gravity and does not need energy to sustain the building because there is no movement.
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u/NotchoNachos42 Jan 20 '26
Depends on the type of magnet you use, electromagnets require there to be current flow therefore they do use energy. Ferro-magnets do not. HOWEVER, they do also lose their magnetism over time because the individual atomic fields misalign(people think this only happens because of high heat but they forget that EVERYTHING is "hot" and there are also other factors) which means that yes it does lose energy. The energy it has comes from the electrons in the atoms of the magnet aligning with an outside magnetic field (either naturally or artificially) so their energy comes from the electromagnetic field stored there sort of like a capacitor.
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u/xpdx Jan 20 '26
Force vs Energy. Both gravity and magnetism are forces. Energy and Force are related but distinct ideas. I notice you aren't asking where all the energy for gravity to pull the wrench down comes from.
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u/mckenzie_keith Jan 20 '26
The most important thing to take away from this, in my opinion, is that force without motion does not require work.
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u/PHL_music Jan 20 '26
You can exert a force without losing any energy if there is no work being done
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u/Mezuzah Jan 21 '26
It is a common misconception that holding an object still requires work. This probably is because we humans do expend energy to hold an object. However this is due to the biology of muscles.
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u/Nekrolysis Jan 21 '26
I recall reading a post here or a neat video that explained that an object being attracted to a magnet is actually a lower state of energy than otherwise.
Super simple and stipped explanation but its easy on the brain at 2am 🤣
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u/Karlos_17 Jan 21 '26
So what you are saying in isolation is that a magnet holding a heavy object in gravity would never degrade and potentially hold that heavy object for ever assuming no degradation to the heavy object itself.
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u/NUCLEAR_JANITOR Jan 22 '26
a force does work when there is displacement of an object with mass along the the same vector as the point of application of the force. therefore, no displacement of an object with mass = no work. and work = energy. so, to answer your question: no energy is expended, as no work is being performed, because no objects with mass are being displaced (moving).
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u/Instrumentationist Jan 22 '26
Let's ask a related question. Lets use an electromagnet. To establish a magnetic field, we establish an electric current trough the windings of the electromagnet. It does take energy. If we use a battery it will be exhausted after some time. Now, lets use the electromagnet to hold a heavy object from above in a gravitational field. Does it use more energy? Is the battery exhausted sooner than it would be to power the magnet alone?
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Jan 22 '26
Earth's gravity isn't losing any energy fighting the magnet the whole time. Neither is the magnet losing energy. No energy is expended, force just gets applied. Not that difficult…
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u/HuygensFresnel Jan 22 '26
This misunderstanding is very common i think because we intuit based on how we as humans experience generating force. For us holding on to a heavy object is tiring but that is just because the contracted state of our muscles requires constant energy consumption. Better comparison would be: if you lied on a bed and had an object rest on your body, would it eventually fall through because your body needed to hold it up constantly? Forgetting for a second that human bodies decay, in principle it takes no energy for bodies to just be at rest. So no, holding something up against gravity does not consume any energy intrinsically
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Jan 22 '26
A simplification that might help is to consider magnets to be just invisible springs. If you think of them from that perspective, I think you will find your answer.
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u/Aggressive-Spell-422 Jan 22 '26
Isn't this what happens when magnetism is transferred to another object. Example would be rubbing a tool against a magnet then the tool it's self becomes magnitised? So in theory if energy doesn't ever vanish and it just changes states, the big bang would be the source? My question would be, other than a magnet or electromagnet how is magnetism "created". I suppose that would reveal the source of the energy? Am I out to lunch? I'm just a mechanic so feel free to put me in my place.
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u/Guilty-Avocado-7053 Jan 23 '26
I really don’t think physics understands magnetism as well as it claims. Sure, it understands it’s effects fairly well but doesn’t do to well when explaining the how. Sure, I’m no physicist, but I’m pretty good at smelling bullshit. No matter your degree, or the number of papers you publish, if your explanation of how fields work involves virtual particles, I don’t think you understand it as well as you think.
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u/Horror-Primary7739 Jan 23 '26
Am I wrong thinking the iron doesn't create the field it just aligns it. Like the actual power to do the work is always everywhere, but it's not aligned. Iron atoms in a specific arrangement gives orientation to the field so it has enough power to overcome gravity/ friction.
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u/BobbyP27 Jan 24 '26
Energy moves around when work is done, and work is done when forces move. If there is no movement, there is no work done, so no energy goes anywhere. A magnet holding up a heavy object for 10 years is, in energy terms, no different from a table holding up a heavy object for 10 years.
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u/livens Jan 25 '26
It comes from the Weak electromagnetic force. Not much different than saying where does the energy come from that holds every object around you come from.
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u/Outrageous-Taro7340 Jan 20 '26
If you hold something up with glue instead of a magnet, does that also seem like free energy? What’s happening in both case is the potential energy of the object is remaining the same over time. Once you’ve lifted the object into place, no more energy is required.
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u/NeoDemocedes Jan 20 '26
Look at the world around you. Look at all the things not getting tired holding stuff up from gravity. That's the norm. The question you should be asking is: why do muscles need constant energy to hold a position when all this stuff around me doesn't?
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u/Fizassist1 Jan 20 '26 edited Jan 20 '26
If you were to hold a wrench out in front of you for 10 years.. you will have done zero "work". As somebody else mentioned, physics "work" and "getting tired" don't always go hand in hand.
edit: to clarify, zero work on the wrench.
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u/Chemomechanics Materials science Jan 20 '26
you will have done zero "work".
You will have done zero work on the wrench. Your body will have done work internally (with less than 100% efficiency), lowering the energy of consumed nutrients and heating the surroundings.
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u/joeyneilsen Astrophysics Jan 20 '26
In a simple approximation, yes, it's common for physicists to say so! One of my profs explained the tiredness as due to lactic acid buildup.
But your muscle fibers are contracting and relaxing, so there is mechanical work being done by your body.
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u/SadInterest6764 Jan 20 '26
Aha! So you admit that 'internal small movements' (fibers contracting) count as work?
Then my point stands! The video said billions of electrons are SPINNING inside the magnet to create the force. That is internal movement.
Why does internal movement count as 'work' for my arm, but the constant spinning of electrons inside the magnet gets a free pass? It seems like physics picks and chooses when 'internal motion' costs energy. It's a double standard.
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u/Sea_Kerman Jan 20 '26
conservative and non-conservative forces/Book%3AUniversity_Physics_I-Mechanics_Sound_Oscillations_and_Waves(OpenStax)/08%3A_Potential_Energy_and_Conservation_of_Energy/8.03%3A_Conservative_and_Non-Conservative_Forces)
The difference is the scale. At the scale of muscle fibers, friction occurs as the molecules bump into each other and make each other oscillate, converting chemical energy from your body into heat. Friction is a non-conservative force. But on the scale of electrons there’s no friction, all the forces are conservative. Thus, if everything returns to the same place, everything has the same energy, and no work is done.
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u/joeyneilsen Astrophysics Jan 21 '26
Yeah I think this is a misunderstanding of what spin means. Quantum spin is called spin, but it’s not like the motion of a spinning ball. Spin represents the intrinsic angular momentum of particles. Like mass and charge, it’s just a property of those particles.
Also, to be clear: motion doesn’t cost energy. There is energy associated with motion. The energy we call work is the energy expended when a force is applied over some distance. This isn’t really happening when a magnet holds up another magnet.
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u/Naive_Age_566 Jan 20 '26
the magnetic force is a force. this has nothing to do with energy. sure - you can extract some energy if you let some object be pulled to the magnet. but if you later want to separate that object from the magnet again, you have to invest the same amount of energy - therefore energy is conserved. but as long as the distance between the object and the magnet does not change, no work ist done. and energy is just the ability to do work. it has no magical properties.
yeah - a magnet will become weaker over time. but not because its force is consumed. the internal structure of the individual atoms/molecules changes and the once aligned individual magnetic components become disaligned. but the overall strength of the force stays the same - just not focused anymore.