11 ms·

Dropping a Magnet Through a Copper Pipe

569 points by jashmenn 15y ago

digitalsushi 15y ago
Admit you're doing the right hand rule right now. And that you just googled what was going on, and for 2 minutes you felt like the young geek that forged your path here, whatever the discipline. (Ok, the physicists are not doing the right hand rule, they are rolling their eyes)
tzs 15y ago
"I could do this all day. It's so cool". Am I correct in assuming that if he did it all day, it would not actually be so cool, as the copper tube would be heated up by the induced currents?
- digitalsushi 15y ago
  Without using any math, I believe it would be a safe assumption that between the pause of reloading the magnet manually and the heat his hand would absorb by grabbing the pipe, heat would never accumulate beyond the ambient temperature in the pipe. However, it would be delightful to hear why I am wrong, since it would be very interesting.
  - CognitiveLens 15y ago
    You are correct - there's really not that much energy being converted to electric current, much less being converted from current into heat through the resistance of copper. I would be interested in hearing what would happen if the pipe was a superconductor, though - would the induced current be so strong that the magnet wouldn't drop at all?
    - duskwuff 15y ago
      Superconductors have some special-case behavior with regard to magnetic fields: http://en.wikipedia.org/wiki/Superdiamagnetism http://en.wikipedia.org/wiki/Superdiamagnetism
    - MaggieL 15y ago
      You mean...somewhat like this? http://www.physorg.com/news/2011-10-quantum-levitating-video-viral.html http://www.physorg.com/news/2011-10-quantum-levitating-video... Only somewhat; it's a different set-up, of course.
    - alan 15y ago
      Yes. It would hang there. That was one of the demonstrations of why superconductors are so cool back in the day. I remember seeing those nitrogen(I think) liquid cooled super conductors holding a magnet above them.
      - billswift 15y ago
        I don't think so. If I remember the explanation, superconductors "block" magnetism, rather like having another magnet with the same pole opposed. In that case, the magnet would probably just fall as though the tube was made of plastic or other non-conductor. (Just speculation, it has been several years since I read about superconductivity).
        dedward 15y ago
        They are diamagnetic i believe (so is water' very weakly so. - google for levitating frogs for a laugh.) Diamagnetic materials create an equal field to what they are exposed to... Causing repulsion. In the case of superconducting, the field generated is very strong and why we can levitate any old magnet over a superconductor. Levitating a frog (mostly water right?) takes some incredibly strong fields..... Liquid cooled bitter magnets etc.... Side note - rare earth supermagets are toxic. When they shatter, you dont want to ingest any of the bits/dust
  - deleted 15y ago
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- einhverfr 15y ago
  Now, if only there were a way to capture that energy as electricity ;-)
  - baddox 15y ago
    Of course, all the energy is coming from his arm lifting the magnet from the bottom of the pipe to the top.
    - jarek 15y ago
      Perhaps we could set up a water mill or maybe even an internal combustion engine to do the lifting?
      - baddox 15y ago
        But we can already get energy directly from water mills and engines, and I doubt the magnet-pipe system would be as efficient.
        einhverfr 15y ago
        Right. Even if we replace the pipe with a coil, it's much more efficient to just use the mechanical force directly!
        jarek 15y ago
        I must have misinterpreted the ";-)" in your original post.
  - AceJohnny2 15y ago
    Quick, inform Tesla!
- twp 15y ago
  Quick math. We don't see the tube, but assume that it is 1m long. The experimenter picks drops the 100g magnet into the tube once per second and that it has zero velocity at the tube exit. i.e. initial and final kinetic energy is zero, but the experimenter keeps inputting gravitational potential energy, all of which gets converted to heat. Power = m * g * h / t = 0.1 * 10 * 1 / 1 = 1 W. So, dropping a magnet every second generates 1 W of heat, which is virtually nothing. This result is logical. The only energy input is the experimenter repeatedly moving the magnet from the bottom to the top of the pipe, and this simple movement probably won't tire him out. He could, indeed, do it all day.
presidentender 15y ago
It is not often that something runs so strongly against my intuition. Today, I am reminded just how little I know.
- goodspeller 15y ago
  who fucking talks like that?
  - deleted 15y ago
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  - jtreminio 15y ago
    Someone with a bit of education and an expanded vocabulary.
    - deleted 15y ago
      [deleted]
      - jacquesm 15y ago
        Rather the opposite.
  - noonespecial 15y ago
    That would be someone who needs to say "fucking" a great deal less than you.
    - deleted 15y ago
      [deleted]
- vacri 15y ago
  You know plenty; there is simply even more to know.
CognitiveLens 15y ago
I was fascinated by this demonstration in my high school physics class. The teacher went further and dropped the same magnet through another copper pipe of the same diameter that had a slit cut along its length - the magnet dropped straight through the slit pipe without slowing down. This provided an important "counterexample" demonstrating that the induced currents were circular around the circumference of the solid pipe - breaking the circle eliminated the braking force.
- jules 15y ago
  That's not true. A slit will cause it to fall faster, but not as fast as with a non conductive pipe. I did this experiment a couple of years ago to answer that question. Unfortunately I can't find the exact timing data. If you do the thinking and figure out how the currents should flow due to the moving magnet, this makes sense.
  - CognitiveLens 15y ago
    I do remember the demonstration clearly, and I have done the thinking to figure out how the currents should flow, but I would be interested in your explanation of why there would still be significant braking force in a slit cylinder. Essentially, the eddy currents have to be moving perpendicular to the direction of the magnet's travel, using the right hand rule as mentioned in other comments. At any point along the surface of the cylinder, the current moves along the circumference, creating a magnetic field that pushes upward. Currents in any other direction would spin the magnet, which doesn't happen, so the slit effectively limits the eddy currents, except for some negligible, localized loops along the length of the cylinder.
    - biot 15y ago
      The braking force might be insignificant in a slit cylinder, however you did originally say that the slit eliminated the braking force.
    - jules 15y ago
      I was thinking that the currents are like this: http://dl.dropbox.com/u/388822/magnet%2Bpipe.png http://dl.dropbox.com/u/388822/magnet%2Bpipe.png (apologies for the crappy picture). The green lines are the magnetic field lines. These lines go through the copper pipe at the top, and at the bottom in opposite directions. Since the magnet is falling, just above the point where a line penetrates, the flux is decreasing. Just below, the flux is increasing. Hence there should be two opposite currents. When there is a slit, the currents get rerouted like in the right picture. Another way to think about it is that every field line creates a circular current around it. When you connect all these circular currents you get what's in the picture (if I did it correctly).
jurre 15y ago
So tempted to go and buy a magnet and copper pipe now!
- VMG 15y ago
  I have a bunch of strong magnets from old hard drives and I am thinking hard how this could finally be a good use of them. But the tube is opaque, so I can't see how I can make a toy out of it. I guess I have to buy a copper tube to find out.
  - DanBC 15y ago
    Put strong magnet in small tupperware box. Put box on beach, collect fines of magnetic material. Transfer many fines to a clear pot, mix with mineral oil. Tape strong magnet to outside of clear pot, see magnetic field in 3D.
    - ramidarigaz 15y ago
      That sounds ridiculously fun. I may have to go do that. I just need a beach...
      - deleted 15y ago
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      - b_emery 15y ago
        about any old sand box will also do (the real kind).
      - DanBC 15y ago
        Or you can buy fine wire wool and snip it into tiny bits.
      - HeyLaughingBoy 15y ago
        You can just buy iron filings cheap from these guys: http://www.scientificsonline.com/catalogsearch/result/?q=iron+filings http://www.scientificsonline.com/catalogsearch/result/?q=iro...
untog 15y ago
I cannot shake my perception that this video was, in fact, created and narrated by Zack Galifianakis. "Just weird stuff. Eddy currents."
MaggieL 15y ago
At the Franklin Institute Science Museum years ago, they had a huge (2 foot diameter? More?) copper disk attached to a crank suspended in the gap of a big-ass electromagnet. The idea was you spun the crank, and then operated a foot pedal that applied current to the electromagnet, which braked the wheel with eddy currents. The disk had slotted sectors, so you could tell that the braking effect was less when those sectors were in the gap. I don't know if the exhibit survived the themparkification of fi.edu... I hope so but somehow I doubt it.
- wgrover 15y ago
  There's a similar demo at the Exploratorium in San Francisco - you can drop disks of different materials (and with different cutouts) through the electromagnet and see the different rates at which they drop. I recall it also had a thoughtful warning sign instructing folks to keep their (magnetic stripe) BART cards away from the electromagnet!
jtreminio 15y ago
This is amazing to me as I've never seen or heard of it before. Question: If this same thing were to be done in a circular copper pipe that feeds into itself (ie a hoola hoop made of copper), and that hoop were rotated at the correct speed, would the magnet in effect never actually move and just hover in mid air?
- herdrick 15y ago
  Yes. You could expect it to bounce off the walls of the pipe, though.
  - jacquesm 15y ago
    The opposing fields will center the magnet.
    - bermanoid 15y ago
      Wouldn't that imply that the (presumably static, making a steady-state assumption) fields had non-zero divergence at the stability point, though?
      - jacquesm 15y ago
        No, what you get (assuming a constant diameter of the tube without dents or shape changes) is that the magnet will induce a stronger magnetic field in the wall that is closer which will push the magnet towards the middle. It will overshoot a bit (but not as much as the original deviation) and so on until it goes smoothly down the center of the tube surrounding it without touching the walls. Likely there will always be a slight wobble but eventually that should become too small to detect.
- gus_massa 15y ago
  Yes, the force between the magnet and the cooper pipe is proportional to the relative speed, so you can leave the magnet still and move the pipe and get a force that cancels the gravity. But in a real experiment, I think that it will be very difficult to keep the magnet in the right position, it will rotate and bounce against the walls, and the force will vary, so the average force has to be equal to the gravity. So your experiment is ideally possible, but I think that it will be very difficult to implement. (In the original experiment, after a few moments, the magnet falls at an almost constant speed. This is the same speed that the pipe should have in alternative experiment.)
petercooper 15y ago
At the time of writing, the linked site is down, but I found what I suspect is a similar demonstration at http://www.bbc.co.uk/bang/handson/magneticcopper.shtml http://www.bbc.co.uk/bang/handson/magneticcopper.shtml
- nik_0_0 15y ago
  Not available in my area :( (I presume that would be true for anyone non-uk)
- hesselink 15y ago
  "Not available in your area."
- marquis 15y ago
  Not available to viewers outside of the UK, it seems. Here's another demo on Youtube: http://www.youtube.com/watch?v=30oPZO_z7-4 http://www.youtube.com/watch?v=30oPZO_z7-4
- Florin_Andrei 15y ago
  Here's the YouTube video that was linked on the Makezine page: http://www.youtube.com/watch?v=G7ysnXH53Wo http://www.youtube.com/watch?v=G7ysnXH53Wo
deleted 15y ago
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jacquesm 15y ago
I've played around with some pretty bad ass magnets during the time that I was building wind turbines and one of the more interesting effects was that if you dropped one near anything made of steel you were actually in danger of getting shrapnel embedded in your body. They move so fast it is scary, sometimes they explode on impact. This makes you pretty nervous about dropping them. Then, one day one got dropped over a chunk of solid aluminum. It floated gently to the metal landing with a soft 'click'. Besides the initial surprise (I realized the eddy currents induced a magnet field of opposing polarity in the aluminum) what struck me most was the force of that opposing magnet. If you tried to force the magnet close to the aluminum at speed it would resist so strongly that you never managed to smash it into it with any kind of effectiveness. Always just that soft 'click'. I still have a bunch of 3"x2"x1" neos waiting for some project, and whenever someone visits that's interested in technology I show them what those things can do, if you have tried to pry one of those from a chunk of solid steel (or if you're unlucky, another magnet) you know what I mean when I say I have a lot of respect for those little golden blocks.
- artursapek 15y ago
  There's a story floating around my school of a student a few years ago who wanted to make a sort of hovercraft by fixing in position two opposing large supermagnets (I go to an art school). He couldn't build it when his supermagnets arrived in the mail because it was deemed too dangerous, supposedly they could have snapped or crushed someone's arm/leg easily had they come undone, and that was assuming he even survived the construction himself.
  - jacquesm 15y ago
    Let me give you one example of just how dangerous these things are from my own experience. I was assembling the rotor/stator assembly of my windmill, to be safe I'd bolted the stator to the welding table and was lowering the the rotor around it using a chainfall. Suddenly and to my complete surprise the welding table leapt up to the rotor just to hang there suspended by the magnetic field. The table surface was a 3/8" thick 8x4 sheet with a fairly sturdy steel frame under it. You'd be hard pressed to move it, let alone lift it. Fortunately I didn't have any fingers in the airgap or I would probably be typing this a whole lot slower.
felipemnoa 15y ago
So in a nutshell what seems to be happening is that the moving magnetic field is causing the electrons in the copper to move, this electrons then give rise to a magnetic field which repulses the original magnetic field which is why the magnet slows down.
- jacquesm 15y ago
  What about the part of the tube where the magnet has just past half-way (the magnet length, not the tube), wouldn't you get an opposite effect right past that point where the magnet is slowed down due to an attraction from above? After all, a magnet has two poles, the leading end I'd imagine would be repelled while the trailing part would be attracted. If that were not the case not then the forces would cancel out and the magnet would fall at its normal speed. (I'm assuming the magnet has 'top' and 'bottom' as the poles).
  - deleted 15y ago
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  - mpyne 15y ago
    No, it's still be going slow. The very short story is "Lenz's Law" (IIRC), but basically this of it like this: top | |N |S | As the south pole falls down, it induces currents in the part of the pipe below it which tend to form a south pole to inhibit the movement (a north pole is also formed, above the south pole which also adds to the effect) As the north pole falls down, it also induces currents, in the part of the pipe above, which tends to form a south pole above it and a north pole below it, and both of those effects act to retard the acceleration of the magnet. Perhaps easiest to visualize as: s s N n | n n | n S s s where the lowercase letters are the poles in the piping formed from the eddy currents as the magnet falls.
    - jacquesm 15y ago
      > As the north pole falls down, it also induces currents, in the part of the pipe above, which tends to form a south pole above it and a north pole below it, and both of those effects act to retard the acceleration of the magnet. Yes, that was exactly my point. So it is not just a 'repelling' force, there is attraction involved as well. The 'root' comment just mentioned 'repels' as if that was the whole story, but it clearly isn't.
jtchang 15y ago
Imagine an amusement park ride where they put you in a suit full of magnets and then drop you down a copper tube. That would be one hell of an experience.
- deleted 15y ago
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- noonespecial 15y ago
  The braking phase of this ride is mostly that. This way there is no active component of the brake that can fail. Its just a big magnet and a big hunk of aluminum. http://en.wikipedia.org/wiki/Drop_tower_%28ride%29 http://en.wikipedia.org/wiki/Drop_tower_%28ride%29
  - gcb 15y ago
    mind have been blow that this is how this breaks... but the magnet armor would still be cooler
  - jtchang 15y ago
    Imagine certain parts of the shaft are copper. It would feel crazy to be free falling, then abruptly slow then, then speed up again all the way to the bottom. Okay. No more nightmare fuel.
zafka 15y ago
This is pretty funny. I just did this demo two weeks ago at work. We had two motors that were neck and neck for a project, then when we put them both in am aluminum housing, one drew 50% more current at full speed idle. I found both this demo, and the demo of dropping a big magnet on to an aluminum sheet. I for sure need to play more with magnets, In fact I am lusting for the big magnet that jacquesm talked about.
swombat 15y ago
Most of the other "zen magnet" videos linked as "related videos" are pretty damn awesome. I strongly recommend watching them all, right now. Really, there's nothing more important for you to do at this point in time. Exploding zen magnet: http://www.youtube.com/watch?feature=player_embedded&v=q7bFLchsPyM http://www.youtube.com/watch?feature=player_embedded&v=q... 140-sided zen magnet: http://www.youtube.com/watch?v=eRiMexbocBI&feature=relmfu http://www.youtube.com/watch?v=eRiMexbocBI&feature=relmf... Interlaced dodecahedron: http://www.youtube.com/watch?v=P2qfCn3gclQ&feature=relmfu http://www.youtube.com/watch?v=P2qfCn3gclQ&feature=relmf... "Hell's Diamond": http://www.youtube.com/watch?v=OF2i8eG7KhA&feature=relmfu http://www.youtube.com/watch?v=OF2i8eG7KhA&feature=relmf...
ineedtogroove 15y ago
Have you guys ever seen a magnetic vortex? http://www.youtube.com/watch?v=SAl1LVPbYhY http://www.youtube.com/watch?v=SAl1LVPbYhY http://www.youtube.com/watch?v=rLlm8UWDNe4 http://www.youtube.com/watch?v=rLlm8UWDNe4 Please explain to me how this works, I will buy you a donut
- noonespecial 15y ago
  Those are both examples of homopolar motors. http://en.wikipedia.org/wiki/Homopolar_motor http://en.wikipedia.org/wiki/Homopolar_motor In the first example, the water is acting as the "wire" as the electrolysis current flows through it. The water rotates just like the wire and drags the generated browns gas along with it.
  - ineedtogroove 15y ago
    OK, so how is a non-ferrous material (water) being moved by a magnet? Clearly in the video of the water vortex there is a proof showing that the water does not move with an iron slug, but does move with the magnet. I might buy you a donut
    - ars 15y ago
      The same way non-ferrous copper is moved by a magnet if it has current flowing through it.
    - noonespecial 15y ago
      The catch is that anything you run current through becomes magnetic, even though its not ferrous. Copper wire, water, ionized air, whatever. Take this unexpected effect, sprinkle in a little crazy and you've got your "new theory of physics that will give us all free energy if the government doesn't suppress it yada-yada."
- darklajid 15y ago
  Cool video, but nutjob submitter? "I have always wanted to show that there are many different "types" of "Magnetic fields" as the standard science says that there is only one "type"... THIS IS JUST VERY WRONG !!" "Magnetism is the primery force and electricity is the product of that effect, science says that is not so.. THEY ARE WRONG again.." "When a potential is applied a vortex is formed around the magnet and a spin of water takes place show through the gas bubbles.. This is very IMPORTANT as this will allow scientist to develop better, faster and more powerful machines to help the human condition.." Uhm... clicks button to collapse video information again - well, I have to admit that the video is nice. Without sound. And text.
joejohnson 15y ago
Here is a really easy to understand explanation of eddy currents and Lenz's Law http://www.youtube.com/watch?NR=1&feature=endscreen&v=kU6NSh7hr7Q http://www.youtube.com/watch?NR=1&feature=endscreen&...
- po 15y ago
  What is the "special green paper" that shows the magnetic field they are using?
  - carey 15y ago
    Searching for "magnetic field paper" leads me to http://www.grand-illusions.com/acatalog/Magnetic_Field_Paper.html http://www.grand-illusions.com/acatalog/Magnetic_Field_Paper... .
jamgraham 15y ago
I need a magnet suit and a big pipe
michaelf 15y ago
This video made me curious about what a magnet factory would look like and I found a really great video that goes step by step through the process at a neodymium magnet manufacturer in Shanghai: http://www.youtube.com/watch?v=BHuWloNGo6c http://www.youtube.com/watch?v=BHuWloNGo6c I was sort of hoping that the factory would look like that plexiglass prison in the X-Men movie that was designed to prevent Magneto from using his powers. Alas, it's nothing like that, but it's an interesting video nonetheless.
- robododo 15y ago
  Hrm, I think I have to refuse to watch the video then. The idea of a plexiglass factory is enticing enough that I choose the fantasy over reality.
mrb 15y ago
I accidentally discovered eddy currents not too long ago, while mindlessly playing with a copper CPU heatsink and an HDD magnet (geeky, right?) I expected copper to be ferromagnetic, but was surprised when I felt this dragging force that neither repulsed nor attracted the magnet. Curious about this discovery, it took me a few minutes of googling to eventually learn about eddy currents... I am surprised I never learned about them at school.
- acgourley 15y ago
  should have been in any "AP Physics" highschool class or college level classical physics class.
  - georgieporgie 15y ago
    It wasn't mentioned in my non-AP HS physics class, nor in my normal college physics class. :-(
- yread 15y ago
  They told us about it when mentioning why cores of inductors are made of layered steel and not a single piece. That apparently keeps the eddy currents at bay.
wicknicks 15y ago
I've read about eddy currents in textbooks. But seeing them work is simply fascinating. Maybe one day space rockets can land on planets using this principle.
testuser113 15y ago
We have weird gravity here in Rockford Illinois. The neodymium magnets are super powerful and even though they are not attracted to the copper, they still produce eddy currents that buffer the fall as seen in the video. Lenz's Law make a great experiment for kids to adult. Also, great at parties when conversation goes stale.
nyellin 15y ago
Back in high school, I lost 1st place in the Weizmann Safe Cracking Physics Contest over this. You had to build a safe that anyone with a sufficiently advanced knowledge of physics could open. The winning team had placed a magnetic switch in the middle of a long tube inside their safe. You could toggle the switch if a magnet fell down the tube slowly enough, but it never worked no matter how you dropped it. The solution was to first insert a roll of tinfoil inside the tube. They also used a gauss cannon: http://en.wikipedia.org/wiki/Coilgun http://en.wikipedia.org/wiki/Coilgun http://wis-wander.weizmann.ac.il/14th-safe-cracking-contest http://wis-wander.weizmann.ac.il/14th-safe-cracking-contest http://www.weizmann.ac.il/zemed/upload/13(3).pdf http://www.weizmann.ac.il/zemed/upload/13(3).pdf
Jun8 15y ago
Couldn't resist this Hitchhiker's Guide quote on the subject of eddies: "I have detected," he said, "disturbances in the wash." … "The wash?" said Arthur. "The space-time wash," said Ford. … Arthur nodded, and then cleared his throat. "Are we talking about," he asked cautiously, "some sort of Vogon laundromat, or what are we talking about?" "Eddies," said Ford, "in the space-time continuum." "Ah," nodded Arthur, "is he? Is he?" He pushed his hands into the pocket of his dressing gown and looked knowledgeably into the distance. "What?" said Ford. "Er, who," said Arthur, "is Eddy, then, exactly, then?"
drstrangevibes 15y ago
i wonder what would happen if you had strips of steel interlaced with copper , youd create a push-me pull-me effect i would expect.

569 points by jashmenn 15y ago

Admit you're doing the right hand rule right now. And that you just googled what was going on, and for 2 minutes you felt like the young geek that forged your path here, whatever the discipline. (Ok, the physicists are not doing the right hand rule, they are rolling their eyes)

tzs 15y ago

"I could do this all day. It's so cool". Am I correct in assuming that if he did it all day, it would not actually be so cool, as the copper tube would be heated up by the induced currents?

digitalsushi 15y ago
Without using any math, I believe it would be a safe assumption that between the pause of reloading the magnet manually and the heat his hand would absorb by grabbing the pipe, heat would never accumulate beyond the ambient temperature in the pipe. However, it would be delightful to hear why I am wrong, since it would be very interesting.
- CognitiveLens 15y ago
  You are correct - there's really not that much energy being converted to electric current, much less being converted from current into heat through the resistance of copper. I would be interested in hearing what would happen if the pipe was a superconductor, though - would the induced current be so strong that the magnet wouldn't drop at all?
  - duskwuff 15y ago
    Superconductors have some special-case behavior with regard to magnetic fields: http://en.wikipedia.org/wiki/Superdiamagnetism http://en.wikipedia.org/wiki/Superdiamagnetism
  - MaggieL 15y ago
    You mean...somewhat like this? http://www.physorg.com/news/2011-10-quantum-levitating-video-viral.html http://www.physorg.com/news/2011-10-quantum-levitating-video... Only somewhat; it's a different set-up, of course.
  - alan 15y ago
    Yes. It would hang there. That was one of the demonstrations of why superconductors are so cool back in the day. I remember seeing those nitrogen(I think) liquid cooled super conductors holding a magnet above them.
    - billswift 15y ago
      I don't think so. If I remember the explanation, superconductors "block" magnetism, rather like having another magnet with the same pole opposed. In that case, the magnet would probably just fall as though the tube was made of plastic or other non-conductor. (Just speculation, it has been several years since I read about superconductivity).
      - dedward 15y ago
        They are diamagnetic i believe (so is water' very weakly so. - google for levitating frogs for a laugh.) Diamagnetic materials create an equal field to what they are exposed to... Causing repulsion. In the case of superconducting, the field generated is very strong and why we can levitate any old magnet over a superconductor. Levitating a frog (mostly water right?) takes some incredibly strong fields..... Liquid cooled bitter magnets etc.... Side note - rare earth supermagets are toxic. When they shatter, you dont want to ingest any of the bits/dust
- deleted 15y ago
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einhverfr 15y ago
Now, if only there were a way to capture that energy as electricity ;-)
- baddox 15y ago
  Of course, all the energy is coming from his arm lifting the magnet from the bottom of the pipe to the top.
  - jarek 15y ago
    Perhaps we could set up a water mill or maybe even an internal combustion engine to do the lifting?
    - baddox 15y ago
      But we can already get energy directly from water mills and engines, and I doubt the magnet-pipe system would be as efficient.
      - einhverfr 15y ago
        Right. Even if we replace the pipe with a coil, it's much more efficient to just use the mechanical force directly!
        jarek 15y ago
        I must have misinterpreted the ";-)" in your original post.
- AceJohnny2 15y ago
  Quick, inform Tesla!
twp 15y ago
Quick math. We don't see the tube, but assume that it is 1m long. The experimenter picks drops the 100g magnet into the tube once per second and that it has zero velocity at the tube exit. i.e. initial and final kinetic energy is zero, but the experimenter keeps inputting gravitational potential energy, all of which gets converted to heat. Power = m * g * h / t = 0.1 * 10 * 1 / 1 = 1 W. So, dropping a magnet every second generates 1 W of heat, which is virtually nothing. This result is logical. The only energy input is the experimenter repeatedly moving the magnet from the bottom to the top of the pipe, and this simple movement probably won't tire him out. He could, indeed, do it all day.

presidentender 15y ago

It is not often that something runs so strongly against my intuition. Today, I am reminded just how little I know.

goodspeller 15y ago
who fucking talks like that?
- deleted 15y ago
  [deleted]
- jtreminio 15y ago
  Someone with a bit of education and an expanded vocabulary.
  - deleted 15y ago
    [deleted]
    - jacquesm 15y ago
      Rather the opposite.
- noonespecial 15y ago
  That would be someone who needs to say "fucking" a great deal less than you.
  - deleted 15y ago
    [deleted]
vacri 15y ago
You know plenty; there is simply even more to know.

CognitiveLens 15y ago

I was fascinated by this demonstration in my high school physics class. The teacher went further and dropped the same magnet through another copper pipe of the same diameter that had a slit cut along its length - the magnet dropped straight through the slit pipe without slowing down. This provided an important "counterexample" demonstrating that the induced currents were circular around the circumference of the solid pipe - breaking the circle eliminated the braking force.

jules 15y ago
That's not true. A slit will cause it to fall faster, but not as fast as with a non conductive pipe. I did this experiment a couple of years ago to answer that question. Unfortunately I can't find the exact timing data. If you do the thinking and figure out how the currents should flow due to the moving magnet, this makes sense.
- CognitiveLens 15y ago
  I do remember the demonstration clearly, and I have done the thinking to figure out how the currents should flow, but I would be interested in your explanation of why there would still be significant braking force in a slit cylinder. Essentially, the eddy currents have to be moving perpendicular to the direction of the magnet's travel, using the right hand rule as mentioned in other comments. At any point along the surface of the cylinder, the current moves along the circumference, creating a magnetic field that pushes upward. Currents in any other direction would spin the magnet, which doesn't happen, so the slit effectively limits the eddy currents, except for some negligible, localized loops along the length of the cylinder.
  - biot 15y ago
    The braking force might be insignificant in a slit cylinder, however you did originally say that the slit eliminated the braking force.
  - jules 15y ago
    I was thinking that the currents are like this: http://dl.dropbox.com/u/388822/magnet%2Bpipe.png http://dl.dropbox.com/u/388822/magnet%2Bpipe.png (apologies for the crappy picture). The green lines are the magnetic field lines. These lines go through the copper pipe at the top, and at the bottom in opposite directions. Since the magnet is falling, just above the point where a line penetrates, the flux is decreasing. Just below, the flux is increasing. Hence there should be two opposite currents. When there is a slit, the currents get rerouted like in the right picture. Another way to think about it is that every field line creates a circular current around it. When you connect all these circular currents you get what's in the picture (if I did it correctly).

jurre 15y ago

So tempted to go and buy a magnet and copper pipe now!

VMG 15y ago
I have a bunch of strong magnets from old hard drives and I am thinking hard how this could finally be a good use of them. But the tube is opaque, so I can't see how I can make a toy out of it. I guess I have to buy a copper tube to find out.
- DanBC 15y ago
  Put strong magnet in small tupperware box. Put box on beach, collect fines of magnetic material. Transfer many fines to a clear pot, mix with mineral oil. Tape strong magnet to outside of clear pot, see magnetic field in 3D.
  - ramidarigaz 15y ago
    That sounds ridiculously fun. I may have to go do that. I just need a beach...
    - deleted 15y ago
      [deleted]
    - b_emery 15y ago
      about any old sand box will also do (the real kind).
    - DanBC 15y ago
      Or you can buy fine wire wool and snip it into tiny bits.
    - HeyLaughingBoy 15y ago
      You can just buy iron filings cheap from these guys: http://www.scientificsonline.com/catalogsearch/result/?q=iron+filings http://www.scientificsonline.com/catalogsearch/result/?q=iro...

untog 15y ago

I cannot shake my perception that this video was, in fact, created and narrated by Zack Galifianakis. "Just weird stuff. Eddy currents."

MaggieL 15y ago

At the Franklin Institute Science Museum years ago, they had a huge (2 foot diameter? More?) copper disk attached to a crank suspended in the gap of a big-ass electromagnet. The idea was you spun the crank, and then operated a foot pedal that applied current to the electromagnet, which braked the wheel with eddy currents. The disk had slotted sectors, so you could tell that the braking effect was less when those sectors were in the gap. I don't know if the exhibit survived the themparkification of fi.edu... I hope so but somehow I doubt it.

wgrover 15y ago
There's a similar demo at the Exploratorium in San Francisco - you can drop disks of different materials (and with different cutouts) through the electromagnet and see the different rates at which they drop. I recall it also had a thoughtful warning sign instructing folks to keep their (magnetic stripe) BART cards away from the electromagnet!

jtreminio 15y ago

This is amazing to me as I've never seen or heard of it before. Question: If this same thing were to be done in a circular copper pipe that feeds into itself (ie a hoola hoop made of copper), and that hoop were rotated at the correct speed, would the magnet in effect never actually move and just hover in mid air?

herdrick 15y ago
Yes. You could expect it to bounce off the walls of the pipe, though.
- jacquesm 15y ago
  The opposing fields will center the magnet.
  - bermanoid 15y ago
    Wouldn't that imply that the (presumably static, making a steady-state assumption) fields had non-zero divergence at the stability point, though?
    - jacquesm 15y ago
      No, what you get (assuming a constant diameter of the tube without dents or shape changes) is that the magnet will induce a stronger magnetic field in the wall that is closer which will push the magnet towards the middle. It will overshoot a bit (but not as much as the original deviation) and so on until it goes smoothly down the center of the tube surrounding it without touching the walls. Likely there will always be a slight wobble but eventually that should become too small to detect.
gus_massa 15y ago
Yes, the force between the magnet and the cooper pipe is proportional to the relative speed, so you can leave the magnet still and move the pipe and get a force that cancels the gravity. But in a real experiment, I think that it will be very difficult to keep the magnet in the right position, it will rotate and bounce against the walls, and the force will vary, so the average force has to be equal to the gravity. So your experiment is ideally possible, but I think that it will be very difficult to implement. (In the original experiment, after a few moments, the magnet falls at an almost constant speed. This is the same speed that the pipe should have in alternative experiment.)

petercooper 15y ago

At the time of writing, the linked site is down, but I found what I suspect is a similar demonstration at http://www.bbc.co.uk/bang/handson/magneticcopper.shtml http://www.bbc.co.uk/bang/handson/magneticcopper.shtml

nik_0_0 15y ago
Not available in my area :( (I presume that would be true for anyone non-uk)
hesselink 15y ago
"Not available in your area."
marquis 15y ago
Not available to viewers outside of the UK, it seems. Here's another demo on Youtube: http://www.youtube.com/watch?v=30oPZO_z7-4 http://www.youtube.com/watch?v=30oPZO_z7-4
Florin_Andrei 15y ago
Here's the YouTube video that was linked on the Makezine page: http://www.youtube.com/watch?v=G7ysnXH53Wo http://www.youtube.com/watch?v=G7ysnXH53Wo

deleted 15y ago

[deleted]

jacquesm 15y ago

I've played around with some pretty bad ass magnets during the time that I was building wind turbines and one of the more interesting effects was that if you dropped one near anything made of steel you were actually in danger of getting shrapnel embedded in your body. They move so fast it is scary, sometimes they explode on impact. This makes you pretty nervous about dropping them. Then, one day one got dropped over a chunk of solid aluminum. It floated gently to the metal landing with a soft 'click'. Besides the initial surprise (I realized the eddy currents induced a magnet field of opposing polarity in the aluminum) what struck me most was the force of that opposing magnet. If you tried to force the magnet close to the aluminum at speed it would resist so strongly that you never managed to smash it into it with any kind of effectiveness. Always just that soft 'click'. I still have a bunch of 3"x2"x1" neos waiting for some project, and whenever someone visits that's interested in technology I show them what those things can do, if you have tried to pry one of those from a chunk of solid steel (or if you're unlucky, another magnet) you know what I mean when I say I have a lot of respect for those little golden blocks.

artursapek 15y ago
There's a story floating around my school of a student a few years ago who wanted to make a sort of hovercraft by fixing in position two opposing large supermagnets (I go to an art school). He couldn't build it when his supermagnets arrived in the mail because it was deemed too dangerous, supposedly they could have snapped or crushed someone's arm/leg easily had they come undone, and that was assuming he even survived the construction himself.
- jacquesm 15y ago
  Let me give you one example of just how dangerous these things are from my own experience. I was assembling the rotor/stator assembly of my windmill, to be safe I'd bolted the stator to the welding table and was lowering the the rotor around it using a chainfall. Suddenly and to my complete surprise the welding table leapt up to the rotor just to hang there suspended by the magnetic field. The table surface was a 3/8" thick 8x4 sheet with a fairly sturdy steel frame under it. You'd be hard pressed to move it, let alone lift it. Fortunately I didn't have any fingers in the airgap or I would probably be typing this a whole lot slower.

felipemnoa 15y ago

So in a nutshell what seems to be happening is that the moving magnetic field is causing the electrons in the copper to move, this electrons then give rise to a magnetic field which repulses the original magnetic field which is why the magnet slows down.

jacquesm 15y ago
What about the part of the tube where the magnet has just past half-way (the magnet length, not the tube), wouldn't you get an opposite effect right past that point where the magnet is slowed down due to an attraction from above? After all, a magnet has two poles, the leading end I'd imagine would be repelled while the trailing part would be attracted. If that were not the case not then the forces would cancel out and the magnet would fall at its normal speed. (I'm assuming the magnet has 'top' and 'bottom' as the poles).
- deleted 15y ago
  [deleted]
- mpyne 15y ago
  No, it's still be going slow. The very short story is "Lenz's Law" (IIRC), but basically this of it like this: top | |N |S | As the south pole falls down, it induces currents in the part of the pipe below it which tend to form a south pole to inhibit the movement (a north pole is also formed, above the south pole which also adds to the effect) As the north pole falls down, it also induces currents, in the part of the pipe above, which tends to form a south pole above it and a north pole below it, and both of those effects act to retard the acceleration of the magnet. Perhaps easiest to visualize as: s s N n | n n | n S s s where the lowercase letters are the poles in the piping formed from the eddy currents as the magnet falls.
  - jacquesm 15y ago
    > As the north pole falls down, it also induces currents, in the part of the pipe above, which tends to form a south pole above it and a north pole below it, and both of those effects act to retard the acceleration of the magnet. Yes, that was exactly my point. So it is not just a 'repelling' force, there is attraction involved as well. The 'root' comment just mentioned 'repels' as if that was the whole story, but it clearly isn't.

jtchang 15y ago

Imagine an amusement park ride where they put you in a suit full of magnets and then drop you down a copper tube. That would be one hell of an experience.

deleted 15y ago
[deleted]
noonespecial 15y ago
The braking phase of this ride is mostly that. This way there is no active component of the brake that can fail. Its just a big magnet and a big hunk of aluminum. http://en.wikipedia.org/wiki/Drop_tower_%28ride%29 http://en.wikipedia.org/wiki/Drop_tower_%28ride%29
- gcb 15y ago
  mind have been blow that this is how this breaks... but the magnet armor would still be cooler
- jtchang 15y ago
  Imagine certain parts of the shaft are copper. It would feel crazy to be free falling, then abruptly slow then, then speed up again all the way to the bottom. Okay. No more nightmare fuel.

zafka 15y ago

This is pretty funny. I just did this demo two weeks ago at work. We had two motors that were neck and neck for a project, then when we put them both in am aluminum housing, one drew 50% more current at full speed idle. I found both this demo, and the demo of dropping a big magnet on to an aluminum sheet. I for sure need to play more with magnets, In fact I am lusting for the big magnet that jacquesm talked about.

swombat 15y ago

Most of the other "zen magnet" videos linked as "related videos" are pretty damn awesome. I strongly recommend watching them all, right now. Really, there's nothing more important for you to do at this point in time. Exploding zen magnet: http://www.youtube.com/watch?feature=player_embedded&v=q7bFLchsPyM http://www.youtube.com/watch?feature=player_embedded&v=q... 140-sided zen magnet: http://www.youtube.com/watch?v=eRiMexbocBI&feature=relmfu http://www.youtube.com/watch?v=eRiMexbocBI&feature=relmf... Interlaced dodecahedron: http://www.youtube.com/watch?v=P2qfCn3gclQ&feature=relmfu http://www.youtube.com/watch?v=P2qfCn3gclQ&feature=relmf... "Hell's Diamond": http://www.youtube.com/watch?v=OF2i8eG7KhA&feature=relmfu http://www.youtube.com/watch?v=OF2i8eG7KhA&feature=relmf...

ineedtogroove 15y ago

Have you guys ever seen a magnetic vortex? http://www.youtube.com/watch?v=SAl1LVPbYhY http://www.youtube.com/watch?v=SAl1LVPbYhY http://www.youtube.com/watch?v=rLlm8UWDNe4 http://www.youtube.com/watch?v=rLlm8UWDNe4 Please explain to me how this works, I will buy you a donut

noonespecial 15y ago
Those are both examples of homopolar motors. http://en.wikipedia.org/wiki/Homopolar_motor http://en.wikipedia.org/wiki/Homopolar_motor In the first example, the water is acting as the "wire" as the electrolysis current flows through it. The water rotates just like the wire and drags the generated browns gas along with it.
- ineedtogroove 15y ago
  OK, so how is a non-ferrous material (water) being moved by a magnet? Clearly in the video of the water vortex there is a proof showing that the water does not move with an iron slug, but does move with the magnet. I might buy you a donut
  - ars 15y ago
    The same way non-ferrous copper is moved by a magnet if it has current flowing through it.
  - noonespecial 15y ago
    The catch is that anything you run current through becomes magnetic, even though its not ferrous. Copper wire, water, ionized air, whatever. Take this unexpected effect, sprinkle in a little crazy and you've got your "new theory of physics that will give us all free energy if the government doesn't suppress it yada-yada."
darklajid 15y ago
Cool video, but nutjob submitter? "I have always wanted to show that there are many different "types" of "Magnetic fields" as the standard science says that there is only one "type"... THIS IS JUST VERY WRONG !!" "Magnetism is the primery force and electricity is the product of that effect, science says that is not so.. THEY ARE WRONG again.." "When a potential is applied a vortex is formed around the magnet and a spin of water takes place show through the gas bubbles.. This is very IMPORTANT as this will allow scientist to develop better, faster and more powerful machines to help the human condition.." Uhm... clicks button to collapse video information again - well, I have to admit that the video is nice. Without sound. And text.

joejohnson 15y ago

Here is a really easy to understand explanation of eddy currents and Lenz's Law http://www.youtube.com/watch?NR=1&feature=endscreen&v=kU6NSh7hr7Q http://www.youtube.com/watch?NR=1&feature=endscreen&...

po 15y ago
What is the "special green paper" that shows the magnetic field they are using?
- carey 15y ago
  Searching for "magnetic field paper" leads me to http://www.grand-illusions.com/acatalog/Magnetic_Field_Paper.html http://www.grand-illusions.com/acatalog/Magnetic_Field_Paper... .

jamgraham 15y ago

I need a magnet suit and a big pipe

michaelf 15y ago

This video made me curious about what a magnet factory would look like and I found a really great video that goes step by step through the process at a neodymium magnet manufacturer in Shanghai: http://www.youtube.com/watch?v=BHuWloNGo6c http://www.youtube.com/watch?v=BHuWloNGo6c I was sort of hoping that the factory would look like that plexiglass prison in the X-Men movie that was designed to prevent Magneto from using his powers. Alas, it's nothing like that, but it's an interesting video nonetheless.

robododo 15y ago
Hrm, I think I have to refuse to watch the video then. The idea of a plexiglass factory is enticing enough that I choose the fantasy over reality.

mrb 15y ago

I accidentally discovered eddy currents not too long ago, while mindlessly playing with a copper CPU heatsink and an HDD magnet (geeky, right?) I expected copper to be ferromagnetic, but was surprised when I felt this dragging force that neither repulsed nor attracted the magnet. Curious about this discovery, it took me a few minutes of googling to eventually learn about eddy currents... I am surprised I never learned about them at school.

acgourley 15y ago
should have been in any "AP Physics" highschool class or college level classical physics class.
- georgieporgie 15y ago
  It wasn't mentioned in my non-AP HS physics class, nor in my normal college physics class. :-(
yread 15y ago
They told us about it when mentioning why cores of inductors are made of layered steel and not a single piece. That apparently keeps the eddy currents at bay.

wicknicks 15y ago

I've read about eddy currents in textbooks. But seeing them work is simply fascinating. Maybe one day space rockets can land on planets using this principle.

testuser113 15y ago

We have weird gravity here in Rockford Illinois. The neodymium magnets are super powerful and even though they are not attracted to the copper, they still produce eddy currents that buffer the fall as seen in the video. Lenz's Law make a great experiment for kids to adult. Also, great at parties when conversation goes stale.

nyellin 15y ago

Back in high school, I lost 1st place in the Weizmann Safe Cracking Physics Contest over this. You had to build a safe that anyone with a sufficiently advanced knowledge of physics could open. The winning team had placed a magnetic switch in the middle of a long tube inside their safe. You could toggle the switch if a magnet fell down the tube slowly enough, but it never worked no matter how you dropped it. The solution was to first insert a roll of tinfoil inside the tube. They also used a gauss cannon: http://en.wikipedia.org/wiki/Coilgun http://en.wikipedia.org/wiki/Coilgun http://wis-wander.weizmann.ac.il/14th-safe-cracking-contest http://wis-wander.weizmann.ac.il/14th-safe-cracking-contest http://www.weizmann.ac.il/zemed/upload/13(3).pdf http://www.weizmann.ac.il/zemed/upload/13(3).pdf

Jun8 15y ago

Couldn't resist this Hitchhiker's Guide quote on the subject of eddies: "I have detected," he said, "disturbances in the wash." … "The wash?" said Arthur. "The space-time wash," said Ford. … Arthur nodded, and then cleared his throat. "Are we talking about," he asked cautiously, "some sort of Vogon laundromat, or what are we talking about?" "Eddies," said Ford, "in the space-time continuum." "Ah," nodded Arthur, "is he? Is he?" He pushed his hands into the pocket of his dressing gown and looked knowledgeably into the distance. "What?" said Ford. "Er, who," said Arthur, "is Eddy, then, exactly, then?"

drstrangevibes 15y ago

i wonder what would happen if you had strips of steel interlaced with copper , youd create a push-me pull-me effect i would expect.