What is Digg?55 Comments
- ItsGus, on 10/12/2007, -3/+74It is actually misleading to say that a Superconducter cannot be penetrated by a magnetic field. What is actually happening is that the magnetic field from the magnet is causing the electrons to move in the superconductor (superconductive means electrons can flow with NO friction, so there is no resistance at all). The moving electrons in the superconductor generate a magnetic field much the same way as an electromagnet. The magnetic field generated exactly mirrors the magnet's own field, so it floats!!
- readme, on 10/12/2007, -8/+43Was I the only one expecting a game physics demo? *embarrassed*
- gregmo, on 10/12/2007, -3/+35cuz hes a real man and real men dont feel cold
- frascellyboy273, on 10/12/2007, -1/+32ive gotta get me some liquid nitrogen
- iDealL, on 10/12/2007, -4/+29That's cool as hell. From the comments:
"The bottom piece is cooled down so it gets superconductive. The one on the top is a magnet. Superconductor cannot be penetrated by magnetic fields. So the magnet kind of floats on his field." - doig007, on 10/12/2007, -3/+24The defining property of superconductors is the Meissner effect, i.e. the very small penetrative distances of magnetic fields into the material, so the comment was correct.
Superconductivity should not be confused with perfect conductors, where, as you say, there is zero resistivity. - steelmaverick, on 10/12/2007, -2/+18Pffft. I always put my hands into liquid nitrogen. Watch:
*puts hands into bucket of liquid nitrogen*
See? *Hands shatter like glass*.
Aww crap. - xyqxyq, on 10/12/2007, -4/+16Nope.
- cmansley, on 10/12/2007, -0/+12I believe that the commenters meant Meissner effect.
http://en.wikipedia.org/wiki/Meissner_effect - trogdor282, on 10/12/2007, -0/+11Actually you've got a point kinda, could people please bother to write a frickin' summary?
- middleman, on 10/12/2007, -13/+24I think everyone wants there own liqued nitrogen.
- jcims, on 10/12/2007, -0/+10http://en.wikipedia.org/wiki/Leidenfrost_effect
- Arramol, on 10/12/2007, -1/+11You mean that wasn't running on a PhysX card? Just when I thought I finally had a reason to buy one...
- directedition, on 10/12/2007, -0/+9If the experiment doesn't cost much to do, there's always someone on digg who "did in high school." Because it was done, doesn't mean it isn't cool.
- itsmekirby, on 10/12/2007, -1/+9@Gryfft
Yes, resistivity is the measure of resistance which has accounted for the thickness and length of a wire. p=RA/l where A is the cross sectional area and l is the length of wire, and R is the resistance of that thing. Unlike resistance, resistivity is constant for any given material and temperature independent of dimensions. - jakeblat, on 10/12/2007, -0/+8Post your spam elsewhere!!!
- candiru, on 10/12/2007, -0/+6Liquid Nitrogen isn't all too dangerous against bare skin, as their will usually be a thin layer of space between any contact of nitrogen and the skin due to the large temperature difference and the resulting rapid evaporation of the liquid.
- magicmarc, on 10/12/2007, -0/+7That looks really awesome. Perhaps there's a real world use? I guess its hard to get something down to a cool level like that.
Also, if its cooled down to make it superconductive, why isn't he wearing a glove or something? His bare hand into freezing temperatures? - pritch, on 10/12/2007, -0/+6He's not wearing a glove because he's not handling anything that's actually been cooled. The magnet isn't touched by the liquid nitrogen, and that's all that gets handled in the video.
Sure, the air above a pool of liquid nitrogen is a bit chilly, but it's alright provided you don't do anything stupid like dunk your fingers into the liquid for any significant length of time. - achoo5000, on 10/12/2007, -0/+6@flameboy
The most common superconductor that people use for these kinds of demonstrations is called Yttrium Barium Copper Oxide (YBCO). It's a kind of ceramic. You'll also need liquid Nitrogen in order to cool it. I'm not sure how much it costs but that should get you started. http://en.wikipedia.org/wiki/YBCO . - h2d2, on 10/12/2007, -1/+6so that's how UFOs fly...
- ZetaEta, on 10/12/2007, -0/+4http://en.wikipedia.org/wiki/Barium#Precautions
Quote: "All water or acid soluble barium compounds are extremely poisonous."
http://en.wikipedia.org/wiki/Yttrium#Precautions
Quote: ". . .should be considered to be highly toxic even though many compounds pose little risk. Yttrium salts may be carcinogenic."
http://en.wikipedia.org/wiki/Copper#Toxicity
Quote: "All copper compounds, unless otherwise known, should be treated as if they were toxic. Thirty grams of copper sulfate is potentially lethal in humans."
Hell, even the oxygen might be too much, since stomach acid is mostly HCl. http://en.wikipedia.org/wiki/Perchlorate
So, yeah, don't eat YBCO. - Fafnir43, on 10/12/2007, -1/+5Resistivity is a measure of the resistance of a material. Basically, resistance of an object is affected by its length and cross-sectional area, and resistivity is independent of physical dimesions. It's calculated by multiplying resistance by length and dividing by cross-sectional area.
In other words, for a block of foo with resistance X and resistivity Y:
"This block of foo has resistance X." - True.
"All foo has resistance X." - False.
"This block of foo has resistivity Y." - True, but needlessly specific.
"All foo has resistivity Y." -True. - ynggrsshppr, on 10/12/2007, -0/+4Those sexy, sexy magnets.
- devin_mm, on 10/12/2007, -1/+4Particle accelerators make extensive use of superconductors. The issue with superconductors is the excessive cost involved in making and keeping something that cold.
- Keloran, on 10/12/2007, -1/+4because that would be a very boring end to the film !!
- pexor, on 10/12/2007, -0/+3"hax omfg hax"
Love the YouTube comments. So simple yet elegant, and hilarious. - DASK, on 10/12/2007, -0/+2** What's it made of??""
Seeing as it's being cooled by liquid nitrogen into superconductivity, it is almost certainly a YCBO ceramic..
http://en.wikipedia.org/wiki/High-temperature_superconductor - Murdats, on 10/12/2007, -1/+3Ive seen this before in real life, played with it myself, under supervision of the phsyics students of course, oh and has for the liquid nitrogen, ive poured a cup of it onto my hand, it just feels like air from a freezer or something (as previously stated, evaporates before it can do harm)
- simoncoul, on 10/12/2007, -0/+2I just learned this in Crystallography, it has a Pyroelectic electric crystal structure, and a change in temperture causes and material to become polarized.
- chicken101, on 10/12/2007, -1/+3It became a super conducter at low temps.
"Superconductivity is a phenomenon occurring in certain materials at extremely low temperatures (on the order of negative 200 degrees Celsius), characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field (the Meissner effect)." - Brewdaddy, on 10/12/2007, -1/+3Just a little bit won't cause much of a burn, if any. A buddy of mind dipped his fingertip in it pretty quickly the other day and it boiled away before burning him.
- brbubba, on 10/12/2007, -0/+2Anyone wanting to repeat this age old effect should start here, http://www.wondermagnet.com/. They actually sell a full kit, you just supply the liquid nitrogen, which you can probably obtain locally.
If you want to do it yourself you just need a small Neodymium magnet and a YBCO (Yttrium-Barium-Copper-Oxide) disk or other high temp superconducting material. I have no clue where to buy YBCO disks though. And BTW don't swallow the disk, apparently it reacts with stomach acid producing a poisonous chemical. - Otto, on 10/12/2007, -0/+2You can actually dunk your hand into liquid nitrogen in the right conditions, for a few seconds or so. The nitrogen evaporates as it gets close to your hand, and forms a vapor barrier between your hand and the liquid nitrogen. This prevents your hand from freezing for a while.
My physics professor used to do the rubber ball trick for new classes, where he drops rubber balls into the nitrogen to freeze them, then he reaches in, pulls them out (with tongs) and breaks them on the ground. However, the tongs he used were to protect him from the rubber balls, not the nitrogen. He'd explain this and demonstrate after busting all the rubber balls. - inactive, on 10/12/2007, -0/+1I remember when my Chemistry teacher did that. On a much smaller scale though...
- shreveyboy, on 10/12/2007, -1/+2What exactly is being used in this experiment? I would like to replicate something like this.
- ZetaEta, on 10/12/2007, -0/+1@bitbytebit
http://en.wikipedia.org/wiki/Pyroelectricity - generates energy when its temperature changes. It's related to piezoelectricity, but not the same. - flameboy, on 10/12/2007, -6/+7Okay so can someone tell me exactly what that "superconductor" is made of? Is it available for someone to buy?
- bitbytebit, on 10/12/2007, -0/+1umm piezoelectric?
- zefram12, on 10/12/2007, -1/+2There is an easier way to make a floating bed:
http://digg.com/design/Magnetic_Floating_Bed_2 - inactive, on 10/12/2007, -1/+2Actually, I just happened to have one before I watched it.
- rossinio, on 10/12/2007, -4/+5Because gloves are also really dangerous, any liquid N trapped against your skin is going to cause a lot more damage than as explained above with bare hands.. I think there is something to do with the sweat (fat) on your skin as well but cant remember..
- danep, on 10/12/2007, -1/+1In my experience it's actually not terribly dangerous... I think the heat of your skin boils off the liquid nitrogen closest to it and forms a protective insulative layer, or somesuch. There's a name for the effect but I can't recall it at the moment.
Edit: Ahh, jcims beat me to it! - piko_soft, on 10/12/2007, -1/+1HOW DO YOU DO THIS?? PLEASE REPLY ASAP!! i want to do this!! what materials do we need... all i know (from comments) is that we need Liquid Nitrogen and a small Neodymium magnet and a YBCO (Yttrium-Barium-Copper-Oxide) disk... so where do I get this?? and what is the cost!!?
- da_bradler, on 10/12/2007, -2/+1I think we now know whos been behind all those crop circles
- asherp, on 10/12/2007, -3/+1Danep's right. I played with liquid nitrogen a little too much in college when I worked in a physics demo room. My boss got pretty good at dipping his hand into a dewer and pulling it out without burning himself. You can also slosh it around in your hand and toss it back and forth, but that takes practice. With regard to magnetic flux pinning (where the superconductor is lifted by the magnet), they say part of the magnet's field gets "caught" inside the superconductor when you force it like that, and this allows you to pick it up somehow....
- dicerandom, on 10/12/2007, -4/+0Assuming that he became superconductive at LNO2 temperatures you wouldn't be able to lift him with an overhead magnetic crane, it would only push him downwards. You would need to get the magnet under him in order to actually lift him.
- alpinem5, on 10/12/2007, -5/+0so when the t1000 in terminator 2 got drenched in liq N, why didnt they use a magnetic crane to hoist him up and dip him into the molten metal (where he eventually ended up after multiple shotgun blasts and a grenade launcher shot)
- tjmasco, on 10/12/2007, -9/+4Did anyone else think it was risky to put your fingers so close to liquid nitrogen?
- vogelzang, on 10/12/2007, -10/+4Count Chocula
-
Show 51 - 55 of 55 discussions
© Digg Inc. 2009
— Content created and posted by Digg users is