Wikipedia:Reference desk/Archives/Science/2014 March 25

= March 25 =

Heart disease
Can heart disease cause a rash on the patient's chest (and in particular, a red mark shaped like the letter "A")? Note: this is NOT medical advice (as you can hopefully see from the link). 24.5.122.13 (talk) 01:39, 25 March 2014 (UTC)


 * Why would you think that it could ? StuRat (talk) 03:21, 25 March 2014 (UTC)


 * See for more relevant inspiration. Wnt (talk) 04:15, 25 March 2014 (UTC)


 * True enough -- but do you suppose the Reverend branded himself as a form of penance? 24.5.122.13 (talk) 06:25, 25 March 2014 (UTC)


 * It's a long blathery tale told from a mad perspective, which doesn't even say exactly what was there, if anything - for all I know he could have imagined it, it might have been supposed to be a divine manifestation, he scratched it into his flesh over and over again with his fingernails, who knows? What I do know is that there's a sternum, a not inconsiderable mass of bone, separating the heart from the skin except in certain cases of congenital malformation.  Any relation with heart disease would have to be an incredible Rube Goldberg biological mechanism. Wnt (talk) 15:31, 25 March 2014 (UTC)


 * Thanks for the answers, everyone! The reason why I asked is because the Reverend's physical symptoms (weakness, unhealthy pallor, chest pains) are unmistakably those of heart disease.  However, considering what you told me, and what the book says, the most likely explanation is that his remorse for his transgression (and not just for the act itself, but for seeing Hester suffer public ostracism while himself being unfairly spared from it), and the stress caused by the need to hide it from the public, both exacerbated his heart disease and also drove him to brand himself as an act of penance (among other things such as rigorous fasting, nighttime vigils, self-flagellation, etc.) 24.5.122.13 (talk) 22:53, 26 March 2014 (UTC)

What might happen in a wall wart if connected across a battery?
I made my own dynamo-powered bike light with a very simple circuit which charges some NiCad cells to keep the light on when I stop at traffic lights. Due to a disconnected wire, I used it without input which of course drained the cells. I tried to the charge them in a manner I did once before - by connecting via crocodile jumper leads to a variable wall wart power supply. Now I'm trying to do the same thing but the light on the power supply turns off whenever connected across my cells. What might be happening inside that power supply? Does it short the batteries? I imagine it was never designed for this purpose but it did work once before set at 6 V and at 7.5 V (I have five cells connected to form a ~6 V battery) --129.215.47.59 (talk) 12:04, 25 March 2014 (UTC)
 * I'd guess the cells are fried. If you lucky one is fried and the others are OK. If you had a multi-meter you could test to see if there is any juice left in them, normal discharged cells will still read 0.1V–1V. If you lucky the power supply has some short circuit protection and its detecting a short and switching off, if your unlucky you have fried the power supply as well. Normally when charging the current is limited to prevent the batteries over heating or over charging, connecting them straight across the power supply  didn't have such protection. See Rechargable batteries--Salix alba (talk): 15:06, 25 March 2014 (UTC)


 * I think a miscommunication occurred. The battery has open circuit voltage 5.9 V and the charger, still set to 6 V is at 6.02 V (plus or minus whatever), according to my multimeter. I didn't leave them charging and come back. I attempted to initiate charge and no current would flow (and the light on the power supply would go out) whereupon I left everything disconnected and posted here. 129.215.47.59 (talk) 17:09, 25 March 2014 (UTC)


 * It sounds as if your power supply has a current limiter and switches off because it thinks it is being short-circuited. Try putting a small resistance in series with the circuit to limit the current that is drawn.  Why not just recharge the cells with your bike dynamo (with the lights turned off)?    D b f i r s   17:33, 25 March 2014 (UTC)

....Wall wart? ( link added at 22:58, March 25, 2014‎ by Medeis. )
 * Yes, thanks for the helpful link, Medeis. I'd never heard them called that until I started reading Wikipedia Reference Desk a few years ago.  I don't actually have any of mine plugged into walls, but it's an amusing analogy.    D b f i r s   13:32, 27 March 2014 (UTC)

Magnet motor
Hi, on WP Their is a redirection on Magnet motor to Perpetual motion. Don't magnets lose there magnetism over the years? What do you think of those videos. --YB ✍ 14:32, 25 March 2014 (UTC)


 * All videos showing free energy from magnets are fake. There is no exception to this. Magnets can indeed loose their magnetism.217.158.236.14 (talk) 15:07, 25 March 2014 (UTC)


 * As a general rule, nearly all "science" videos on YouTube are fakes. Sure, there are a few honest people making nice videos of real effects - but they are BY FAR outnumbered by the pathetic fakes and camera tricks.  When you see an amazing effect on a YouTube video, it's about 90% certain that it's a fake.


 * The confusion that nearly everyone who proposes these things has is that they confuse the physics concept of a "Force" with the concept of "Energy" or "Work". Something can exert a force without consuming any energy.  If you hang a weight on the end of a chain, the chain is exerting a force on the object (in this case, it's equal and opposite to the gravitational pull of the earth).  But nobody thinks the chain is going to lose it's ability to support weight because it somehow "runs down" like a dead battery.  Magnets are the exact same deal - they can support a weight against gravity without consuming energy in the process.


 * However, as soon as you get something moving as a result of a force, some energy had to be expended to make that happen - and once it's gone into moving the object, the energy is lost to whatever set it in motion. Magnets don't contain any special energy source - so they can't be used to "power" a machine.  That's why 100% of "magnet motor" videos are faked.  These machines cannot possibly work - but it's not because the magnet might "run down" - that's a complete red herring.


 * Sure, you can use a magnet to pick up (say) a steel ball-bearing from a table...but that's a one-time thing. Once the ball-bearing is stuck to the magnet, you've got to use some energy to pull it away again - and the amount you need is more than the energy that was required to put the ball-bearing there in the first place.  So you can't use this to make perpetual motion.


 * It's just the same as using gravity to do the same job. You can roll a ball down a hill - but to do that a second time, you have to expend some energy to raise the ball back to the top again.  You can't make a perpetual motion machine from gravity either.


 * SteveBaker (talk) 21:30, 25 March 2014 (UTC)
 * The above lecture contains almost only correct usages of the contraction "it's" meaning "it is". 84.209.89.214 (talk) 00:12, 26 March 2014 (UTC)
 * Now don't be sad, ’cause six out of seven ain't bad. —Tamfang (talk) 05:30, 26 March 2014 (UTC)


 * As to how the fakery is done in this case, notice in the first video that the device the magnetic gizmo is attached to is supposed to be a generator, but that isn't what it is. The metal cylinder is suggestive of a generator housing, but it's a plain cylinder of metal, without any heat sink fins or at least air holes to help cool off the windings that one would expect on a real generator of that size.  Also, in addition to the expected wires that carry the power from the back end of the "generator", there's also an extra small pair of wires coming out of the rotor end of the "generator", which wouldn't make any sense if that device was really a generator.  The other end of that pair of wires, which go to the magnetic gizmo, would also make no sense if the "generator" was really a generator.  The magnetic gizmo is supposedly a purely mechanical device (it doesn't contain any windings or other visible circuitry) that produces its own energy, so why would it need power supplied to it from the generator?  I think the paper with "challenge to all the engineers" written on it a bunch of times that's wrapped around the top of the "generator" is there to help with the illusion by helping to hide the fact that that metal cylinder really doesn't look all that realistically like a generator.  I think the "generator housing" is what contains the batteries that are really powering everything, as well as the motor that keeps the useless but impressive magnetic gizmo in motion.  The small pair of wires that don't make sense if you assume the setup isn't fake make total sense if you assume that in reality, those wires are attached to a switch connected to the gizmo housing such that shutting the gizmo housing is what switches on the motor and external circuit.


 * Hopefully this "explanation" will be adequate for me to get my payment from the free energy suppression conspiracy consortium. Red Act (talk) 05:46, 26 March 2014 (UTC)


 * Actually, a buried power cable into the base of the fan would also work as the power source, instead of batteries in the motor housing. The fan is never lifted, it's always plugged in while the device is running, and it's sitting on a patch of dirt next to the patio instead of being on the patio like everything else is. Red Act (talk) 06:16, 26 March 2014 (UTC)
 * The point is that magnet motor should not be called a perpetual movement machine because magnets lose their magnetism after a while.--YB ✍ 14:56, 26 March 2014 (UTC)
 * I think the amount of energy stored in a permanent magnet must be small, but how do you calculate it? I'm thinking the magnetic field necessarily contains some energy, but that doesn't speak of the magnet itself.  Another way I look at it gets a different result: take two strong magnets sitting on a table at rest.  They snap to each other, liberating a small amount of extractable energy in the process.  Now in order to demagnetize them, you need to put that energy back in, so when stuck together they actually have less energy than demagnetized magnets... right?  But... if you chop up and randomize a magnet into itty bitty pieces, letting them all reassort to neutralize each other, doesn't that get the most energy out of them?  Oh phooey, I confused myself this time.  But looking at a paper from 1953 there seems to be a formula, based on the idea that a material usually adopts a magnetization state that minimizes its free energy as one would expect; it still needs some unpacking to get to a number though. Wnt (talk) 15:07, 26 March 2014 (UTC)


 * No, magnets losing their magnetism over time is irrelevant. The phrase "perpetual motion machines" isn't used to describe a set of devices which are actually capable of running literally forever.  Instead, it's used to describe a set of devices which are intended by their inventor to be capable of violating the first and/or second laws of thermodynamics.  All "perpetual motion machines" would stop functioning eventually due to wearing out in one way or another.  But the more important problem that makes such devices be called a "perpetual motion machine" is that they are incapable of violating the laws of thermodynamics as intended even initially, long before wearing out would ever become an issue.


 * Besides, magnets can hold their magnetism for centuries. A perpetual motion machine that uses magnets would fail due to wear on its bearings long before demagnetization would be the expected failure mode.  Red Act (talk) 17:40, 26 March 2014 (UTC)


 * I think there's some confusion here. Magnets do not contain energy.217.158.236.14 (talk) 16:15, 26 March 2014 (UTC)


 * E = MC2. Which implies that Wnt's two magnets will have a (very slightly) greater mass when separated than they do when they come together. (See also this old ref desk discussion on the increase in mass of an alarm clock spring resulting from it being wound up ). AndyTheGrump (talk) 16:25, 26 March 2014 (UTC)
 * And it takes a certain amount of energy to unstick two magnets. But it's not the point.--YB ✍ 16:39, 26 March 2014 (UTC)
 * Wow, it would be easy to miss that you tweaked "point" to link to magnetic bearing. However, magnetic bearings would be inadequate to keep a device rotating without energy input until demagnetization became an issue.  Magnetic bearings use permanent magnets to provide the bias field, but usually require active control coils for stability purposes, due to Earnshaw's theorem.  Those active control coils consume energy due to resistance in the coils resulting in Joule heating.  A homopolar electrodynamic bearing doesn't require control coils, but it works due to induced eddy currents.  Those eddy currents again cause energy loss due to Joule heating, causing the rotor to slow down until it ultimately stops.  Red Act (talk) 03:43, 27 March 2014 (UTC)


 * Even an electron, which really does spin forever, is not a perpetual motion machine, because a "perpetual motion machine" is a device that violates the first or second law of thermodynamics and not, despite the name, one that moves forever. All this discussion of whether a device made of magnets will eventually spin down seems irrelevant. Getting back to the original question of whether "magnet motor" should link to "perpetual motion", I think it probably shouldn't because the phrase could just as well refer to an ordinary electric motor. -- BenRG (talk) 07:50, 27 March 2014 (UTC)
 * Except electrons don't actually spin at all, they just have a property called spin. DMacks (talk) 04:11, 28 March 2014 (UTC)

Amber-colored vertical displays


What are these vertical, amber-colored displays? What do they do? Why don't they just use normal LCD monitors? -- Toytoy (talk) 16:41, 25 March 2014 (UTC)


 * The look like old Monochrome monitors from the 1980s. As to why they use them, perhaps they are connected to a system that uses them and has not been upgraded.  The principle "if it ain't broke, don't fix it" may apply here.  -- Jayron  32  16:51, 25 March 2014 (UTC)


 * And it looks like it's only used to display text data, where color isn't all that useful. Also, you don't have to worry about picking colors so the colorblind can still read it properly (unless they do something really stupid, like green text on a red background). StuRat (talk) 16:55, 25 March 2014 (UTC)


 * Very first Ghit for mission control amber suggests they show the console DVIS panel (Digital Voice Intercom System).--Shantavira|feed me 17:00, 25 March 2014 (UTC)


 * Yes, they're the DVIS keysets which allow controllers to connect into different voice channels (like a phone conferencing system, where the conferences are on all the time). info. DVIS is the second generation system, consisting of an amber aviation-grade touchscreen; the first generation was VIS, which had a physical button for each channel, and DVIS was replaced with DVICE, which is a more modern LCD touchscreen. Photos of all three are here. -- Finlay McWalterჷTalk 17:16, 25 March 2014 (UTC)


 * A little bit more about DVIS operation is here. -- Finlay McWalterჷTalk 17:33, 25 March 2014 (UTC)


 * The display looks a lot like the "plasma panel" invented at the University of Illinois in 1964, later marketed by IBM, which used a flat neon based panel which could both store a display and was touch sensitive. It may be a precursor of today's plasma TV displays( which don't have the touch sensitive feature). Edison (talk) 16:51, 26 March 2014 (UTC)