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What Happens When You Drop A Magnet Inside A Copper Tube [video]
- IgorPartola 13y agoYup, it's pretty cool. This was one of the most impressive demo's my physics professor did in our freshman physics class. The point is that as the magnet is falling through the copper tube it creates an electric current which then creates a magnetic field in the opposite direction of the magnet's movement. In other words, this is the practical application of the Right Hand Rule [1]. Two fun facts about it: first, if you cut a small notch along the length of the tube, this will not happen as the current cannot go around the tube. Second, imagine a superconducting tube with an extremely powerful magnet right in the center of it. Now, try to get the magnet out without cutting the tube. [1] http://en.wikipedia.org/wiki/Right-hand_rule http://en.wikipedia.org/wiki/Right-hand_rule Edit: Of course, there's nothing special about the tube being made of copper. Any conducting substance will do.
- taliesinb 13y agoYou can also think of it as magnetic flux lines encountering "drag" as they pass through conductors. The limiting behavior of this view is in type II superconductors, which entirely "pin" flux lines -- they present an effectively infinite resistance to the movement of flux lines. That's why a magnet levitates over such a superconductor. [1] You can even image these "vortices" directly [2] [1] http://en.wikipedia.org/wiki/Flux_pinning http://en.wikipedia.org/wiki/Flux_pinning [2] http://www.youtube.com/watch?v=7_ZgiumS41Q http://www.youtube.com/watch?v=7_ZgiumS41Q
- IgorPartola 13y agoThe levitation over a superconductor was the other cool demo that the professor did :).
- rbanffy 13y agoLucky kids. When I was in school, the only commercial superconductors were liquid Helium cooled Niobium-Titanium alloys, something not many classrooms could handle. ;-) Luckily, when I got to programming, we already had zeroes and ones. Imagine our predecessors who had to do it with uppercase o's and lowercase l's...
- dllthomas 13y agolOl
- Intermernet 13y agoZeroes and Ones? Luxury! In my day we couldn't afford the Ones, we had to make do with just Zeros...
- mjcohen 13y agoHa! When I was in school, we had to push the electrons around by hand! You kids had it easy!
- IgorPartola 13y agoI forget what type we used but it was cooled by liquid nitrogen. That prof. used lots of magnets and superconductors in his research, some cooled by Helium-3. Now that stuff is expensive.
- hurowits 13y agoYou might wanna take a look at this video: http://www.youtube.com/watch?v=VyOtIsnG71U http://www.youtube.com/watch?v=VyOtIsnG71U
- exhilaration 13y agoIncredible. For anyone watching, make sure you at least go past 2:20 - that's when they pull out the magnetic rail.
- smitec 13y agoAs long as it isn't a magnetizable substance like iron.
- sillysaurus2 13y agoCould this be used as a kind of elevator tech? I'd love to ride one of these down a gigantic copper tube. It'd be completely impractical, of course, but a whole lot of fun.
- Crito 13y agoYou could probably use eddy-current brakes as a safety system for elevators. Many roller coasters use eddy-current brakes. It would take a hell of a lot of magnets to strap to a person to allow them to jump down a copper pipe though.
- sbilstein 13y agoYea my hs physics teacher demoed this and talked to us about possible applications for a while. i don't remember any but thank you wikipedia: http://en.wikipedia.org/wiki/Eddy_current#Applications http://en.wikipedia.org/wiki/Eddy_current#Applications
- taliesinb 13y agoAnother fun example of braking are the electrodynamic tethers [1], in which you (a satellite) are the copper tube and the entire earth is the magnet! [1] http://en.wikipedia.org/wiki/Electrodynamic_tether http://en.wikipedia.org/wiki/Electrodynamic_tether
- e12e 13y agoBut it's possible to the same experiment with a battery and an electro-magnet, isn't it? (Not sure how the power-density of lithium-ion batteries would relate to floating 80 kgs down a tube... but seeing as people have demonstrated hover-boards, it should be doable) ? Assuming the purpose is a) float down tube, and b) SCIENCE! -- and not c) with rare earth magnets...
- whatshisface 13y agoThe inverse square law of force strength falloff would make it very hard to scale this linearly, that combined with the fact that weight increases with the cube of size means that the magnets involved would have to be incredibly strong. Not impossibly strong mind you, if magnets can hold a hundred ton train car off the ground I am sure they could slow the fall of an elevator. I'd not want to be inside that elevator with anything magnetic in my pocket, though.
- orblivion 13y agoWait so does that mean that, ironically, friction is what it allows magnets to fall through a tube that isn't superconducting?
- bjornsing 13y agoYes, pretty much, but you usually call it electrical resistance.
- sp332 13y agoI would wrap an electromagnet around the magnet in the tube, then turn on current to create a field in the opposite direction. Hm... If I pulse the field quickly, maybe it would even remove itself :)
- vecter 13y agoTechnically, this has nothing to do with the Right Hand Rule. That is just a human convention to assign a positive and negative signs to a particular direction. Electromagnetism doesn't care about our silly human notations.
- calinet6 13y agoIt does, however, exhibit the properties we use language to describe. There's a kernel of truth at the center of it.
- hnriot 13y agosemantics vs syntax - magnets don't have hands obviously, but the metaphor holds just the same. There is no "technically..." nonsense! It's not a human convention either - it's an anthropomorphic metaphor.
- robotresearcher 13y agoName another animal that uses that convention.
- nrivadeneira 13y agoThe point is that it's not a convention - it's a metaphor, as hnriot pointed out.
- robotresearcher 13y agoIt's not a metaphor. http://en.wikipedia.org/wiki/Metaphor http://en.wikipedia.org/wiki/Metaphor No one is comparing or likening charge to some other thing. We simply give opposing charge "directions" a name. Everyone uses the name. It's a convention.
- nrivadeneira 13y agoThe comparison that is being made is the direction your thumb points when your fingers wrap in a particular direction. It's not merely giving it a name - it's specifically likening the vector to the relative orientation of your fingers. That's why the comparison is memorable. If it were merely a name with nothing that it is compared to, it would not be memorable nor helpful.
- reddog9287 13y agoYeah I'm actually pretty surprised that this made it to the front page. Pretty novel and I thought more people would know about it (being a typical physics class demonstration). Cool nonetheless.
- huhtenberg 13y ago> ... nothing special about the tube being made of copper. Any conducting substance will do. Any non-magnetic conducting substance that is. Otherwise the magnet will just stick to the tube wall.
- InclinedPlane 13y agoHere is a much more informative video: http://www.youtube.com/watch?v=NqdOyxJZj0U http://www.youtube.com/watch?v=NqdOyxJZj0U
- FollowSteph3 13y agoHe has a bunch of really good videos
- baq 13y agobe very careful when handling such powerful magnets - if you have something metalic on you, they might jump off the table and smack you really hard. bones will be broken.
- IgorPartola 13y agoFingers will also be pinched and possibly broken.
- salgernon 13y agoThe latch on our clothes dryer broke; the door would no longer snug up and maintain the seal or necessary pressure for the safety switch. I now have a 2x2x1" rare earth magnet holding the door shut against the dryer frame. Its strong enough to keep the door snug, but I can still open the dryer door with a good tug. I'm not sure why I had a 2x2x1" neodymium magnet laying around, but I'm glad I did.
- a3n 13y ago> I'm not sure why I had a 2x2x1" neodymium magnet laying around, but I'm glad I did. The same reason why there's beer in the fridge, condoms in the night stand and a guitar pick in your pocket: just in case.
- salgernon 13y agoYou live a far more exciting life than me. Although mine might be more surreal.
- itchitawa 13y agoHa. I did exactly the same thing with a dryer years ago but with a neodymium magnet from a hard drive head actuator.
- 72deluxe 13y agoIt is interesting that with the neodymium magnets being rare earth materials and apparent limits being placed on their mining/import/export etc., the price of them has sky-rocketed. There was a time when all the bass cabinets for bass players were getting smaller and smaller and lighter and lighter thanks to these magnets because it meant you could have a smaller speaker driver (hence less weight) but now they're having to resort to the heavier speakers again. A shame really! I never did buy any light cabinets but always wish I had! At least Class D amplifiers are doing the rounds and so massive wattage amplifiers are now tiny and lightweight.
- saxaholic 13y agoOoh eddy currents!
- mturmon 13y agohttp://en.wikipedia.org/wiki/Eddy_current http://en.wikipedia.org/wiki/Eddy_current
- malandrew 13y agoI can only begin to imagine how much a piece of copper tubing that thick costs. That's a lot of copper.
- aaronsnoswell 13y agoThe effect works just fine with thinner tubes and smaller magnets - I've done it using 15mm 'plumbing' copper pipes.
- e12e 13y agoShould work with a paper tube and copper wire as well? [edit: not saying that would be cheaper and/or easier, just that it should be possible...] [edit2: A stripped wire, that is - not one with insulation -- which would be more suitable for making a spool]
- marcosdumay 13y agoIf you close the wire (join the 2 points) you should get something, but certainly not as strong. You can try that with aluminium if cooper is too hard to get. You'll probably get better results.
- adsr 13y agoA kg is about $7 at the moment it seems, so suppose that's 5 kg then $35.
- malandrew 13y agoThat's it? I was under the impression that copper was far more expensive and is the reason why expresso machines are as expensive as they are.
- noir_lord 13y agoCopper compared to many metals isn't particular expensive per KG, it is just relatively expensive in the class of metals that we use a crapload of (for example aluminimum is around $1.8 per KG) it is still much cheaper than tin at ~$22. The main reason that copper is so valuable is it has so many uses and is very easily recycled(I saw an estimate that said 80% of all the copper ever mined is still in use) so holds it's value (You often get 90-95% of its commodity value for recycling).
- fnordfnordfnord 13y agoLenz's Law in action, lots of good demos online, or take any strong magnet and move it rapidly while in close proximity to any non-magnetic conductor (brass, copper, aluminum, etc.) You can feel the force exerted by the generated field. Automobile speedometers used to operate on this principle.
- deletes 13y agoWhere can you buy something like that. A magnet is around 150$, but I have no idea where to get a copper tube of that thickness.
- jules 13y agoIt also works with a small neodymium magnet which can be bought for less than $1 and a small copper plumbing tube which costs about the same.
- Loughla 13y agoNot sure where to get one at that thickness or diameter, but a specialized plumbing supply company can get you most standard size and diameter of copper piping. That one is huge, though. In theory, this should work with smaller, but powerful magnets, and thinner tubes, correct?
- deletes 13y agoI don't think you can make a permanent magnet any stronger as it is. There is a certain limit. I think the size matters in this case. I can only find thin pipes for plumbing online, but I would really like the think one.
- Loughla 13y agoYou can't make a permanent magnet stronger, I believe. I worded that weird. I meant a smaller magnet, that is powerful, and a smaller tube. My brain doesn't work so well sometimes.
- ThePhysicist 13y agoIf you think that's cool you should have a look at this frog: http://www.youtube.com/watch?v=A1vyB-O5i6E&list=PL8E7ED16454FE1C63 http://www.youtube.com/watch?v=A1vyB-O5i6E&list=PL8E7ED16454... The physics behind this are explained here: http://en.wikipedia.org/wiki/Magnetic_levitation http://en.wikipedia.org/wiki/Magnetic_levitation
- TrainedMonkey 13y agoIf magnet was not rotated when dropped through the tube, would it simply stick to one wall in case of slightest imbalance?
- blacksmith_tb 13y agoCopper isn't ferrous, magnets can't stick to it.
- martinvol 13y agoI can't clearly remember my psychics class, But I think I'd fall a bit faster, as the movement through the pipe is considerable as well.
- kylek 13y agoThey used crystal balls instead of magnets in my psychics class :)
- dfbrown 13y agoI don't think the spinning should have any effect on the speed. Only the vertical movement would create eddy currents. It could be he does it to keep the magnet stable as it falls (like spin on a football).
- shawabawa3 13y agoIn the last drop he doesn't spin it and it seems to fall at the same speed, it also wobbles and hits the side, so I think you're right
- tedsanders 13y agoNo. Because copper isn't ferromagnetic, it will not be magnetized by the magnet, and consequently the magnet and the copper will not be attracted to each other. (In fact copper is diamagnetic, so it will actually slightly repel.) Source: I am a magnet scientist.
- 13y ago
- frankus 13y agoYet another demo: https://www.youtube.com/watch?v=9s9I8OI82Ag https://www.youtube.com/watch?v=9s9I8OI82Ag
- refurb 13y agoThe interesting part is that NMR magnets often have a second magnet within them that creates an opposing force outside of the bore of the NMR (or at least they used to do it that way). If you notice on the video the yellow chain which keeps ferrous metals away from the instrument isn't really that far away. Also, when he drops the aluminum disc, it actually starts to accelerate after falling only a foot. Because of the "counter" magnetic field produced, NMRs have a much small/weaker external magnet field that you'd expect.
- bluejes 13y agoEuro- & Americ-awesome.
- jtreminio 13y agoI am impressed that Digg has gone through no less than 2 facelifts since v4.
- dublinben 13y agoOriginal link: https://www.youtube.com/watch?v=keMpUaoA3Tg https://www.youtube.com/watch?v=keMpUaoA3Tg This digg page is blogspam.
- aunty_helen 13y agoThe problem with the youtube link however is that any video with 'magnet' in the title brings you uncomfortably close to thousands of youtube nutters posting about perpetual motion machines.
- peter_l_downs 13y agos/problem/feature
- chrissyb 13y agoFantastic point.
- asteli 13y agoThis effect gets used in modern trains and roller coasters in the form of linear eddy current brakes. In practice, this looks like an electromagnet that's held just over the rail. More reading: http://en.wikipedia.org/wiki/Eddy_current_brake http://en.wikipedia.org/wiki/Eddy_current_brake
- dfox 13y agoWith electromagnet and iron rail the same effect is used for almost an century on streetcars under the name "electrodynamic brake". Idea is that single assembly combines this for small braking strengths and friction braking for complete stop (the electromagnet is on springs and can come into complete contact with rail, which is used as equivalent of parking brake).
- BorisMelnik 13y agomost impressed by the fact that someone actually got people to click on a digg link
- orblivion 13y agoIs that The Orb playing in the background? EDIT: or maybe Atomic Skunk? It sounds familiar.
- plq 13y agoAnother cool physics experiment: What happens when you wring out a wet cloth in space? Here's the answer: http://youtube.com/watch?v=KFPvdNbftOY http://youtube.com/watch?v=KFPvdNbftOY
- chrissyb 13y agoAs much as i like that video nothing will top his special version of Bowie - Space Oddity This might also pique you interest http://www.youtube.com/watch?v=_dQJBBklpQQ http://www.youtube.com/watch?v=_dQJBBklpQQ
- lxmorj 13y agoHey, would it levitate there if the tube was spinning? It falls back and forth when he rotates it...
- lutusp 13y ago> Hey, would it levitate there if the tube was spinning? If the tube were spinning, the magnet would begin spinning also, but it wouldn't levitate.
- lostlogin 13y agoFor a similar effect using an MR scanner see the link below. I have done similar with an old door stop. http://www.youtube.com/watch?v=fxC-AEC0ROk http://www.youtube.com/watch?v=fxC-AEC0ROk
- iterationx 13y agoThe slinky trick is better http://www.youtube.com/watch?v=eCMmmEEyOO0 http://www.youtube.com/watch?v=eCMmmEEyOO0
- 556790 13y agoI wonder, with a tube that is of sufficient thickness and a magnet of sufficient strength, would it be possible to levitate the magnet inside the tube?
- omegaham 13y agoThe best way to do it is with a superconducting magnet. And no, it doesn't quite levitate, but it takes a very long time for it to fall through. I think the video we watched in high school physics class had it take about fifteen seconds to go an inch and a half.
- liebfraumilch 13y agoWhat I want to know is where did he get that freaking awesome copper tube??
- JackFr 13y agoAgree. I'd love to have one of those.
- elheffe80 13y agoAll I could think of was the cost of that copper tube. Wow that is thick.
- noonespecial 13y agoHe had the large square magnet and the large round one within arms reach of each other so that he could swap them with one hand without walking away. That kind of freaks me out a little.
- abcd_f 13y agoEddy currents are also used in exercise equipment with "magnetic resistance". http://www.bicycleman.com/recumbent-exercise-bikes/images/Magnetic-recumbent-bike-ECB.jpg http://www.bicycleman.com/recumbent-exercise-bikes/images/Ma...
- ta_tatata 13y agoSo it's ok to post links to third party instead of the original content now ? here's the link to the video instead of this portal profiting from it: http://www.youtube.com/watch?v=keMpUaoA3Tg http://www.youtube.com/watch?v=keMpUaoA3Tg
- cLeEOGPw 13y agoWonder for how long the magnet needs to fall until it is completely demagnetized.
- ansgri 13y agoWhy should it. The energy is supplied by gravity.
- cLeEOGPw 13y agoAs magnet falls, it is slowed down, this drag is created because magnetic forces are resisting gravity. So after some time, magnet loses that force, I just wonder how long does it take. It can't fall slowly like that forever.
- glial 13y agoSpooky.