The magnet is stopping due to Lenz's law. Basically, the moving magnet is creating a magnetic flux. The law states that any change in flux (in this case, it's creation through spinning) will work to counteract the change. So, the spinning magnet is creating Eddy currents which cause the magnet to stop spinning.
SixThough, That's a great idea. A spherical or cylindrical magnet should work better. SquidCaps, The north and south poles of the magnet are at the top and bottom, so aliment wouldn't make sense.
hkcute; Flux isn't the issue. Its the second time and spatial derivatives of the magnetic vector potential which induces an opposite (eddy) current density. And yes, if it was perfectly homogenious a spinning cyllinder wouldn't induce any eddy currents in a plane purpendicular to its axis, but you won't find any sufficiently perfect magnet for that to actually work. Zigi Samblak; At the (pretty bad) level of vacuum that he could generate, air resistance would be orders of magnitude weaker than the electro-magnetic losses. In other words, it would stay spinning for literally hundreds of minutes if air resistance were the ONLY loss mechanism.
Why not just hook up that little glass pipe to atmospheric pressure and have a 'vent' valve to push it? I think you could get better spinning with that.
Cody'sLab; It does increase the circularly induced eddy currents (kind of like a magnetic stirrer works). Asymmatry in the same plane as the conductor is bad news, but since you have a pretty substantial conductor in all 3 dimentions (and the entire vacuum chamber would also have a BIG effect, even though it is relatively far away - see Gauss' Law for charge screening), ANY deviation in the up-down direction would also cause quite a lot of enegy loss in those modes.
A round/disc magnet will have a axially symmetry magnetic field, if you rotate about the axis of symmetry the magnetic field doesn't change and so you can eliminate the eddy currents. To reduce the faraday disc effect you'd need to use only diamangetic levitation but i'm not sure of the relative strength of these effects. A square magnet doesn't have a axially symmetrical magnetic field. Also you could just use polycardon which has a larger diamagnetic effect than bismuth but might be difficult to get a large enough sample.
MrEvilchickens the problem I see is finding a round magnet that is accurately symmetric enough. Without that, it will spin slanted (as the square magnet in the video) and have symmetry defects, which will end up with the same result (albeit maybe a slightly longer spin duration)
you demonstrated why it won't spin forever, when you attempted to move the magnet to start it spinning. Although, there is no force of friction due to air, the bismuth's irregular shape experiences the magnetic field differently as it spins. this still acts as a type of drag. perhaps if you levitate a more perfect sphere you might see more noticeable effects.
Christopher Nah it didn't work, it wasn't strong enough as he said. I really like seeing how he sets stuff off with the laser though. I don't know what he could do without that thing.
My hypotheses for why it stopped (in order of likelihood) are: 1) Eddy currents and magnetic resistance 3) Earth's magnetic field 2) Earth's gravity 4) Not a perfect vacuum The solution: Use superconducting magnets in a perfect vacuum, in intergalactic space.
Has basicallybeen done, in the Gravity Probe B - Mission. Except they did it in an orbit around the earth, because gravity causes no friction, this difference does not matter. They levitated spheres coated in a superconductor cooled to 2K in a vacuum surrounded by superfluid helium, surrounded by a superconductor.
sandqwert the correct answer is nothing, it will outlast anything, the problem nothing is the concept of the lack of anything, this concept could better be described but human intelligence can only go thus far, nothing was before the universe nothing will be after the universe, thus nothing lasts forever
Basically it wants to line up with the Earths magnetic field like a compass. I'm wondering what if you had a magnetic track and a superconductor that you pushed around the track, that will eliminate the magnetic flux, You would then have the issue of keeping the superconductor cold but if it was in a vacuum and levitating then it should stay cold.
Wait...that makes so much sense. And even if he had a perfect magnet and a non conductive magnetic material, it would still stop because of the earth's magnetic poles.
Not sure if it is the earths magnetic field doing this or not. The question I have is why it unwinds when it stops, then rotates the opposite direction, and continues oscillating until it stops completely. Need to mark the spinning magnet and see if it stops every time in the same position relative the the earths magnetic field to be sure! Or it could be the orientation of the supporting magnetic fields. More testing needs to be done.
External magnetic field applies torque to the magnet, trying to align it's magnetic field. But there is no feedback according to magnet's spin speed, if magnet is not perfectly aligned it just always aplies some torque, until magnet crosses balance point at which torque changes direction. But magnet already got some momentum, it can't instantly stop. So it's continues to rotate after balance point until rotational force accumulates enough and it starts to spin other way. I dont think it's only earth's mangetic field, huge magnet on top must add to it. Maybe, quite a lot. So it will be resultant force.
I really LOVE these electro-magnetic experiments! You could maybe try casting the bismuth into a circular mould with many thin pieces of plastic acting as insulators (like in transformer laminations). Also, perhaps you could try a non conductive ceramic magnet (AlNiCo and Samarium Cobalt are about equally conductive, with ferrites being MUCH less conductive) as levitation device? You could theoretically even use many small pieces of Neodymium magnets (without the nickel coating of cource) and have them pin a thin insulator between themselves (mica perhaps?).
I'm so happy you did this because during my physics class in last year we were talking about efficiency of motors due to friction and it got me thinking about this exact situation, I just never had the opportunity to look into this.
Cody, I think the magnet won’t spin forever because it will always point at magnetic north. Correct me if I’m wrong but that’s also why the magnet was favoring facing one side and than swinging back and forth as earths magnetic pull eventually brings it to a stop always facing the same direction.. go get a compass and see if I’m right Cody.
Eddy currents in bismuth are probably quite low, since it his high electrical resistance for a metal. Copper Electrical resistivity is 16.78 nΩ·m (at 20 °C) or 0.00000001676 Ω·m bismuth Electrical resistivity is 1.29 µΩ·m (at 20 °C) or 0.00000129 Ω·m So if I did my math right bismuth has 76.8 times higher resistance then copper. I'm thinking about making a bismuth tube to drop my 3/4" neodymium magnet through, so i can see how much the eddy currents slow it down compared to dropping it into a copper tube.
There is not much inertia going on in this magnet. By the way, one comment out there pointed out, that if magnetic field would be very axial with center of mass, there would be no change of magnetic field in any point around magnet spinning on same axis. So, +Cody'sLab, could you please check same with spheroidal or, may be, cylindrical magnet, and, may be, huge chunk of copper above it?
Thank you for performing this experiment. I suggested it to another youtuber who plays with vacuum chambers but he totally butchered it in my eyes. This is pretty much exactly what I would have done, provided I had the stuff to try it.
Visually stunning, informative, casual and clean editing; Cody, you gorgeous gangster - this is my favourite video of yours (been a fan since Westminster bees).
you know those hand crank flashlights? You feel more resistance the faster you crank them. That resistance is a rotating magnetic field cutting a conductor and inducing current into something. This is the force that stops this magnet
i'll risk making this comment before watching to the end of the video, but at 5:30 you can see there is some asymmetry in the magnetic field from the way the magnet seems to ever so slightly lurch into a "stable spot" before climbing back out again and continuing to rotate with slightly less speed.
really ? seems like a good explanation, but i wouldnt have thought the effects of earth's magnetic field would contribute significantly enough to this system, given the much higher field strength of the magnets and bismuth Cody has set up here. Or is that still possible given that the forces from said magnets are mostly cancelled out ? Basically it seems intuitive to me that this would spin a lot smoother and lose much less energy to this fabled stable spot, if the magnet was perfectly balanced and not sagging on one side. Or would it still get stuck on magnetic north in this "perfect" case ?
I think gravity as well as earth magnetic field is just adding sinusoidal wobble to speed. It does slow magnet down half way, but also do speed it up other half.
posysajrazdwatrzy No, the earth's field is at basically 90 degrees to the rotating magnet's field. It's pulling the magnet to flip on its side, not rotate on axis.
There are a number of forces I can think of that may be causing the magnet to stop: - Air flowing in slowly when the pump is turned off - Vertical magnetic currents from the larger magnet, orthogonal to the rotation plane, causing alignment (like the moon has one face locked in position) - The Earth's magnetic field, like in a compass - Hysteresis currents
The fact that the magnet is slowly oscillating back and forth when it should be at rest, indicates to me that it's not going to spin forever. There appears to be some resistance in the magnetic field itself that the object is "bouncing" off of. It will probably sit there and oscillate for a long time but eventually stop doing that as well.
Since liquid oxygen is being attracted to a magnet and is not metallic, would it be possible to contain the oxygen in some form of container (like your glas tubes) to get rid of eddy currents and stuff? Or would you need a ridiculously huge magnet to lift the oxigen together wit its container?
If I understand this correctly, if there is a little enough amount of radiation then items in a vacuum will just get colder and colder to a certain point (I may have misunderstood), so to that end if the oxygen is frozen and placed in a vacuum then it will stay cold enough to stay solid. Alternatively you can always seal the container and if you keep it cold enough to not expand then you should be good.
Zeibentaul Unless the oxygen gave off a form of radiation, I don’t think it would decrease in temperature in the vacuum chamber. That said, it would expand into a gas, and the atoms might transfer their energy to the container walls (say, a sealed glass tube, not the walls of the vacuum chamber). So the gaseous oxygen may decrease in temperature relative to the increase in temperature of the container. Since all the energy would still be conserved within the system.
Cody when you put a microwave in your vacuum chamber it seemed to draw more power. If you put a microwave in a pressure chamber would it use less power ?
I think you would need a perfectly ballanced cube or disk to let it turn longer, because the cube doesn't look's like that. If the cube is nearly at the end of the applied force, it swing's back and forth. Which means that there is a point on the cube lower than all other on the downside, which is affected by gravity.
I'm wondering if there is a different factor here: Earth's magnetic field. That would explain a force that causes it to "rock" left and right at the end of the spin.
Thank you so much for this video Cody. Back in highschool I wanted to research this for my "thesis" but my teacher thought I wouldn't be able to finish it. Now I finally know the outcome!
I'd say that it's possible, but I doubt that it's the only reason. Earth's Magnetic field surely interracts with it, but I also think there's more factors than just that.
it's pulling in one side, you can see it choosing a fixed position, going back and forward until it finds it. so the magnet is not positioned correctly, it's pulling in several directions at the same time
Get you an MKS SRG, The MKS Spinning Rotor Gauge (SRG) line is a high-vacuum gauge that operates by measuring the amount of viscous drag on a magnetically-levitated spinning ball, which is directly related to the number of molecules in the chamber (i.e. pressure).
The magnet induces electricity in all the metal parts around it, which generates an electromagnetic field which counteracts the spin that created it. It's very much like the magnet in a copper tube experiment. Of course, with such a small magnet and such far away and not aligned metal parts the effect is nearly nonexistent, but it does waste some energy, which means that even if all forms of friction were removed the magnet will still eventually stop. Also, generally acquiring perfect steady motion (including rotation) with anything that is magnetic is impossible because of the natural electromagnetic background of the Universe which will always slightly influence it. EDIT: Oh, you've mentioned it. Well, leaving the comment for reference.
You could apply an electric field to the magnet above to get the magnet inside the chamber to spin. Eddy currents would slow the magnet eventually, however. It would spin longer than under atmospheric pressure.
Apparently these magnets (assuming you're using a neodymium magnet) are usually coated with nickel having a 1.4*10^7 S/m conductivity but the neodymium iron boride, despite being a ceramic, has a conductivity of about 1*10^6 S/m. So, probably some of the effects of the eddy currents, which would indeed be on the surface of the magnet, would be somewhat lessened if you removed that coat.
Hi, Cody. You need to use a spherical magnet instead of a cube. The magnetic field of a cube shaped magnet has components that vary with rotation angle. Rotation of the cube magnet then generates a time-varying magnetic field and this will always induce eddy currents in any metals near the magnet. These eddy currents dissipate energy thermally. This is the energy loss that is damping the rotation of the cube magnet. Since the field of a spherical magnet is unchanging with respect to rotation on its dipole axis, it eliminates the time-varying field components and thereby eliminates the eddy current losses that are damping the rotation of your cube magnet. When using a spherical magnet, the only remaining source of eddy current induction will be due to imperfections in the magnets field due to material defects, but these will be very small effects.
That it's rocking back and forth after the first attempt shows that it isn't just air resisting it spinning. Weight distribution or something else, there's a "hump" there that it has to overcome.
Replace the air with a superfluid, maybe depending on your temperature. A fundamental experiment here, I love it! Analogues of this are still "spinning" with superconducting loops.
If I recall, the viscosity of air is constant down to about a torr, which is what you pumped down to, so you're probably still seeing significant air resistance effects. You might try with a lower vacuum pressure if your system can do that.
Great video, you actually got your answer as to whether or not it would spin forever at 3;00 you can see the magnet oscillating back and forth. Which means there's some kinda force on it.
if im not wrong a magnetic field has magnetic friction acting on the bismuth , still doesnt defy the law of thermodynamics , its just losing lesser energy over a period of time as it is harder for it to disperse energy which can be seen as the most efficient way we have found to sustain motion
powdered iron is used with a binder in RF inductors for exactly the reason you need: minimize eddy currents. It won't be zero but alot better than what you've got now. Also ferrites are used. Google powdered iron toroid or ferrite toroid for example.
I think it is the magnet's "compass" behaviour that is slowing it down. As the magnet wants to point north it is periodically accelerating towards it and slowing away from it. Thats why when it is slowing down it will slow and then speed up before slowing again. I imagine doing this experiment a considerable distance away from an active planet's core would work.
Hey Cody, if you're looking for a magnetic material that's non-conductive, you should check out some ferrites. They're good insulators and they're ferrimagnetic, so if you put a piece in a strong magnetic field you can permanently magnetize it. If you get a hard ferrite (high coercivity) it might work in this experiment, though it won't be nearly as strong as the neodymium magnet you've got so I'm not entirely sure it would hover above the bismuth as well.
My best guess is that this is caused by electromagnetic resistance. The best example i can think of when you crank a hand generator no matter how hard you push it ramps up slowly because of the resistance of the fields interacting with eachother. Basically an electromagnetic form of friction
Wood doesnt burn in vaccum, and probably there would be induction on the bismuth because it isn't a superconductor replicating identically the magnetic field lines. And the superior magnet would induce a current on the bottom one due to magnetic field flux be changing. Thanks Cody, I aways wanted to see if it worked out, if I had condition I could do the same experimento that you did.
Cody, you might want to try electrostatic levitation, if you really like challenges. All you need is HV generator, concave base and very lightweight and thin insulator. Levitating disk will have some charge so it will not be perpetual motion, but charge count compared to metal will be very small. Actually base can be insulator as well, conductors might be arranged in it radially from the center, so Eddy currents will not be induced.
Hey Cody I was about to dive into this. Check this out. Pipe an air compressor into the glass to push the magnet. It has to be a very small amount of air pressure. And your decompresor would have to constantly run. But just for proof of concept in space. This could be it.
The spinning magnet is creating small electrical currents in the metal below it and these currents are causing their own magnetic fields that are counter to the small magnet and thereby slowing it's spin. Similar to dropping a magnet down the middle of a copper pipe and watching it's rate of fall slow.
The Earth's magnetic field will also be absorbing energy from the system. Magnetic remanence is another source of loss. Then there's still a little bit of air still inside the chamber. Thanks Cody. Interesting,as always.
You didn't need the blower. It started spinning because it's lob-sided (more mass on one side) so you can create a circular motion of the top magnet and induce a spin in the bottom one.
You could try embedding a superconductor in solid nitrogen using evaporative cooling. The vacuum would freeze the nitrogen and would simultaneously isolate the whole thing so as long as you keep intense light from it, it would levitate.
The field of the magnet extends throughout all space. It is necessarily going to interact with every conductor in the universe, creating eddy currents. Those conductors in general are not superconductors so have electrical resistance. That leads to heating and energy loss. So the answer is no it won't. No matter what you do eventually it will stop. (Well, down to the quantum limit of zero-point motion that is)
Please bear in mind that even the small oscillations of the magnet will cause a change in magnetic flux on the NeFeB magnet on which it levitates. As a result, eddy currents will be created to counteract this. Since these cube magnets ARE NOT perfect in the alignment of the "net magnetic dipoles", this will have a dampening effect not only on the linear oscillations, but also reducing the angular momentum. @Cody'sLab
you should pressurize a fluid then bring it room temp. so that, when it depressurizes it will be about 40 F or "ice cold". in my ap chem class we thought of a soft drink that when you open it, it will depressurize and chill the drink inside so you don't have to chill your drinks.
If you could replace the bismuth with a superconductor you might get further. The trick is getting a high-temperature superconductor ($$$, if you even can) and cooling it down evenly with liquid nitrogen without damaging the vacuum chamber.
If you cool the entire apparatus down to the point at which materials become superconductive, you could replace the top magnet with a strong electromagnet. You would have to raise the stand inside the vacuum chamber to reduce the gap between the electromagnet and the Bismuth sample. If you could make the electromagnet oscillate at controllable frequencies, you could use that to spin the metal sample (bismuth). After gaining enough speed, switch the electromagnet to a regular state with only enough power output to levitate the metal. At a high enough velocity the sample would spin for a much longer duration...Just a thought...
The magnetic force between the magnets making the levitation makes it slow down like friction. Even if it didn't unless you had a complete vacuum air would slow it down eventually
Glass is diamagnetic. Not as much as Bismuth...but when the well the magnet floats within is self-centering, the last few spins remind me of torque translation, or putting square wheels on a vehicle over flat ground. At one face especially, it looks like it's climbing a hill, then falling down the opposite side. If I look really carefully, it appears that to be pistoning (up and down) against gravity; spinning in this well looks like work.
it doesn't really matter what you use, so long as you use a diamagnetic material, as it will form resistance moving so close to the material in question, and eventually sacrifice its momentum for a proportional electric field
i think it will rotate much longer with a round magnetic form like a like a zylinder or a ball. Because the cube had a resistance to the magnetic field.
Maybe its because the magnet is not directly straight up and down. I noticed this because the magnet increased in speed when the lower part of the magnet is closer to the magnet on the bottom but also slowed back down a bit when it turned around. maybe this causes gravity to pull at one side more than the other while its turning because the lower magnet is not extremely level or even more interesting the lower magnet doesn't have the same magnetic push throughout the whole thing and it may be effecting the floating magnet on the right half only maybe causing some extra magnetic friction if that's what you call it.
The reason of the stop is lenz lawa, the magnet is inducing a current on the opposite direction hence creating a force to the other, this makes sense because if it where to go on forever you would be essentially making infinite energy
Ferrite cores used in high frequency switching transformers have magnetic properties but have low electrical conductivity, the core material is designed specifically to reduce eddy currents, not sure how well the material would work but it would be interesting to try.
At 1:01 it's already clear it won't spin forever, because when it's levitated it rotates, but then rotates back a bit. Something makes it prefer a direction... even possibly Earth's magnetic field.
I think you've made a compass. notice at the end of the spin it rocks back and forth. remember that your magnetic fields are not the only ones around. might try again marking which side is facing the front of the chamber at rest if the magnet stops with the same side facing the the front then it might be an outside magnetic field causing the magnet to stop.
it still react or lines up into the direction of magnetic poles of the earth like a compass that's why i think it will not really spin forever even if there is no air resistance.
Before and during the experiment when it stopped it would then rotated a little in the opposite direction. I also noticed that the speed once it was in a vacuum varied depending on which side it was facing. That tells me that it isn't balanced. Even though it's being levitated it is still subject to the force of gravity. I think the heavy side is a force of friction.
Non conductive magnetic , Yes, ferrite. According to this brochure, Ferrite-NiZn has a resistivity of 10^4 Ohm·m. This is better than damp wood, at least. You can trade magnetic properties for resistivity by coating and embedding ferrite pellets in an insulator, as suggested in the comment above, but fashioning your own metamaterial will probably involve quite a bit of research and experimentation.
Or it just migt try to orient itself along the Earth's magnetic lines. Sure, it's facing up/down direction. But the Earth's field is not exactly paralel to the surface either. I mean, I can stick two small magnets together with a thread in between and it readily orients itself in North/South direction. So hanging in vacuume with all the forces being equilized all it takes is a bit of extra magnetic field to stop it. The fact that it's tilted could make extra tendency to orient along the lines as well as being a consequence of that tendency.
It's actually slowing down because of one field you cannot totally evacuate even in a vacuum chamber .. and that is Earth's gravity slowly stealing the angular momentum from any object within its influence. If however you were to do this same sort of experiment in deep space and it began tumbling, in theory, it should keep doing so indefinitely for eons until some massive objected interacted with its inertial moment.
its going to slow down because magnetism is as much a physical force as actually touching something. its 'friction' because just like the surface of two objects rubbing together isnt perfect and so the forces of those imperfect ridges and valleys at a microscopic scale slamming into each other causes heat, the magnetic field - thogh invisible - also has imperfections when sliding against another field that is going to cause minut changes in the action leading up to a slowdown.