Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.
The Earth's magnetic field is certainly strong enough to have a noticeable repulsion: all you have to do is point an opposing magnetic pole and you will be repelled. That's how a compass works: it's a lightweight magnet, and if you flip it around, you can notice it being repelled from the "wrong" way and attracted towards pointing North. Levitation is hard because most of us are on the "side" of the earth as considering it a bar magnet, so the field is relatively weak and is substantially parallel to the surface. At the poles, the field is stronger and pointed perpendicular to the surface. However, the field is still really weak (0.6 gauss according to the article) and a gauss is a pretty small field, so you'd need something pretty light to be able to levitate well. DMacks (talk) 07:28, 27 April 2009 (UTC)[reply]
As well as being quite weak, the Earth's magnetic field is approximately uniform over distances of the order of a few metres. The force that turns a compass needle is a torque, which is present even in a uniform magetic field, because the forces on the two poles of the compass needle are opposite in direction. However, to produce a net force on a magnetised object you need to have a non-uniform magnetic field, to make the forces on the two ends of the object also different in magnitude. The Earth's magnetic field is so close to uniform that the net force on any reasonably sized magnetised object will be minute.
You do get a net force on a current carrier moving through a uniform magnetic field. 0.6 gauss is 60 microteslas, so a wire that is perpendicular to this strength of field will experience a force of 6x10-5 N per metre per amp - so to get a measurable force you need either a very long wire and/or a very large current. However, stronger magnetic fields produce bigger effects - this NewScientist item says that a field of 17 teslas can levitate a frog ! Gandalf61 (talk) 12:24, 27 April 2009 (UTC)[reply]
Very small and charged items like electrons and some light ions do get trapped by Earth's magnetic fields, and can be "repelled", "trapped", "resonated", and a variety of other interesting magnetic-field related motions. Take a look at the Van Allen radiation belt article. Those electrons and ions, under gravity, would get pulled into the lower ionosphere; under thermal motion, they would blow into space pretty fast; but they get trapped in the magnetic field and pulled into an "equilibrium" distance, complete with fun bouncing helical orbits that look nothing like your classic Newtonian gravitational elliptic orbits! Nimur (talk) 15:34, 27 April 2009 (UTC)[reply]
Hi,
Can you tell me What is a steam table?.How to calculate the value of enthalpy,using steam table for a given value of pressure and temperature?.Please reply if you are having any idea about this, plz share with me.... —Preceding unsigned comment added by Smenonp (talk • contribs) 12:04, 27 April 2009 (UTC)[reply]
Steam table redirects to the Water data page steam table. If you don't understand enthalpy, there is an article on that also. Basically the idea is that the enthalpy of vaporization is not constant - it actually depends on the temperature of the source water. To really understand this, you have to realize that while the "boiling point" of water is the phase transition point, in reality there is an equilibrium reaction between water and its vapor at any temperature. The steam table will tell you the values you need to calculate the parameters of that vaporization reaction. Nimur (talk) 15:38, 27 April 2009 (UTC)[reply]
I have a question regarding our article on List of common misconceptions, specifically whether or not chameleons change their color to match their surroundings as a form of camouflage. Our article currently states:
"Chameleons do not change color to match their surroundings. They are naturally camouflaged and, although they can change their skin color into a variety of different colors, these changes are caused by temperature or interaction with predators or other Chameleons.[1]".
Another editor is disputing this here [1]. The video [2] he cites appears to be legit to my eyes, but maybe this is a video of an anole and not a chameleon.
well, the video is not a legitimate source. it could easily be photoshopped (and probably is—doesn't look natural at all). by contrast, the source against it comes from a major university. Wikipedia has long guidelines about what is a reliable source, about how "original research" is not allowed, etc. --98.217.14.211 (talk) 14:08, 27 April 2009 (UTC)[reply]
Hmm, but the chameleon article itself states, with two (possibly less credible, but still) citations:
"Recent research indicates that they do not only change their color for reasons of camouflage, but also use colour changes as a method of communication, including to make themselves more attractive to potential mates." -- Aeluwas (talk) 14:22, 27 April 2009 (UTC)[reply]
The issue here is having good citations and reading what they actually say. If it can be cited effectively, great. If not, then no. In those cases, citation #1 is about communication, not camouflage ("Overall, our results suggest that the evolution of the ability to exhibit striking changes in colour evolved as a strategy to facilitate social signalling and not, as popularly believed, camouflage."). Citation #2 specifically says it is not about camouflage ("Chameleons can produce a wide range of colors and patterns on their skin, but they do this primarily to express mood, not to blend in with different environments."). So I'd say that the distillation of these sources that claims they are camouflage PLUS expression rather than expression and NOT camouflage is incorrect (certainly not what the sources say). --98.217.14.211 (talk) 14:28, 27 April 2009 (UTC)[reply]
I knew that was going to bite me in the ass. ;) I was very close to adding a "I haven't had time to check the citations" part, but I omitted it. -- Aeluwas (talk) 16:34, 27 April 2009 (UTC)[reply]
That video looks like it was intentionally made to show off a cool match moving technique. (The super-shaky camera is common in these sorts of clips. Subtly is apparently not the goal.) APL (talk) 16:30, 27 April 2009 (UTC)[reply]
The video is not a good source, but the statement in the list of misconceptions seems to be wrong according to sources that are good, such as this recent PLOS paper. It looks like a case of confusion. Apparently there are arguments that color changes are used for more than just camouflage, and that the other functions may have been most important in driving the evolution of the capability. But there doesn't seem to be any dispute about the claim that color changes do have a camouflage ("crypsis") function. Looie496 (talk) 16:53, 27 April 2009 (UTC)[reply]
This is OR: But when I lived in Kenya as a kid in the late 1960's, I caught a baby chameleon and kept it as a pet for several months before my parents made me let it go. They certainly do change color in an effort to match their surroundings - but it takes them maybe 30 seconds to complete the change (maybe adults are faster), the range of colors they can produce isn't all that great and they certainly can't reproduce patterns in the background. However, they certainly DO change through shades of green, brown, reddish brown and grey. Obviously, if you are a kid and have one of these things as a pet - you're going to try to make it do crazy color changes - and it really can't. If you sit it on a bright red sheet of paper, then after maybe half a minute, you have a reddish-brown chameleon because that's the closest it can come. If you put it on a sheet of yellow paper - you get a kind of greenish brown because mine couldn't turn yellow at all...but if you put it on a sheet of dark green paper, it'll make a reasonably good match for it. It's not going to completely vanish - but the match is good enough in 'real world' situations that the animal might encounter. Attempts to make it match spots and stripes produced a greyish-brown chameleon no matter what. It was cool to have this thing sit on your finger so you could carry it around the room looking for flies and watch that AMAZING tongue shoot out...that's by far the most impressive thing they do. SteveBaker (talk) 18:36, 27 April 2009 (UTC)[reply]
It sounds like the claim in the article that color change does not match background as camo is bogus and original research, rather than adding that some other factors in addition to background matching/camo produce color change as well. I have certainly watched a chamelion change color to match the background, and background matching is widely accepted as a survival mechanism. If it changes color to indicate temp, that would make it a great thermometer, but would be an implausible evolutionary way to enhance survival. As a reality check, what do other encyclopedias such as Britannica say? Wiki editors often go off on a crusade as True Believers in a viewpoint not widely shared in a particular field, hanging their prejudices on one reference and ignoring many others with other conclusions. Edison (talk) 15:09, 28 April 2009 (UTC)[reply]
I added a contrary ref: "Others state that chameleons can change their color in milliseconds for camouflage as well as social signalling.[2]National Geographic quotes an expert on chameleon color change, Christopher Raxworthy, associate curator of herpetology at the American Museum of Natural History, to the effect that they match the background to survive, but they also color change as a social signalling mechanism: ""Most of the time, chameleons are behaving as highly cryptic animals trying to avoid detection from predators." So the only "misconception" would be that they 'only color change for camouflage, and that's a pretty trivial one. If scientists disagree, then it should not be on a list of "common misconceptions" at all. —Preceding unsigned comment added by Edison (talk • contribs)
They change color in MILLISECONDS! I find that hard to swallow. The pet chameleon that I owned took a good 30 seconds to do it. Perhaps adult animals are faster - perhaps there are sub-species differences - but I strongly doubt it. There are animals out there that can change color that fast (cuttlefish for example) - but I never saw my chameleon do that. It's certainly possible that they could also change color to reflect mood or mating status or something - but most of the time it's certainly camoflage. These are slow-moving animals with plenty of enemies - this is their only defense! I strongly suspect that the nay-sayers are trying to make the poor critter do something it's unable to do - like match patterns or colors that it's simply unable to do...or perhaps they are buying into the "changing in milliseconds" idea and not waiting the 30 seconds that my chameleon took...or possibly they have been looking at some particular sub-species that doesn't do it. My chameleon came from a tree outside our apartment on the outskirts of Nairobi, Kenya...who knows what chameleons from other places do? I know for 100% sure that my chameleon could match reasonable backgrounds like tree bark or leaves or reddish dirt if given time. When you're an 12 year old kid with a pet chameleon - that's pretty much their only party trick (they don't obey "sit", "down" or "roll over" - and they have a whole different take on the game of "fetch"!) - so everyone who comes to your house gets to see it! Actually - I know my mother has this on video - but unfortunately, that's 8mm cine film and it's currently on the other side of the planet - so I can't easily produce it! SteveBaker (talk) 23:17, 28 April 2009 (UTC)[reply]
If they can really change color in milliseconds I suggest making computer monitors out of chameleon leather. APL (talk) 13:02, 29 April 2009 (UTC)[reply]
Wait a second, RayBan's website, now features a Chameleon. And all the sunglasses in this video are RayBans. I'd bet money that this is a 'viral advertisement' for RayBan. (Why else would anyone just happen to own so many expensive designer sunglasses of the same model, but different colors?)APL (talk) 22:51, 2 May 2009 (UTC)[reply]
Aha. It is advertisement. You can find it on the RayBan website under "Never Hide Films". Also in that category, footage of a cow giving birth to a full-grown human wearing sunglasses. APL (talk) 22:54, 2 May 2009 (UTC)[reply]
There is something I don't quite understand about this current swine flu panic we are having right now. I'm not trying to be flippant, but I don't really get what the big deal is. Every year influenza kills hundreds of thousands of people, every year new varieties of flu start spreading. I don't get why this particular one is getting so much attention? Is it deadlier than all those other varieties? Is it much more contagious? Belisarius (talk) 14:59, 27 April 2009 (UTC)[reply]
This outbreak is getting attention because of the possibility that it could become a pandemic. See swine flu. The H1N1 strain of flu is a subtype of Influenza A that descended from the virus that caused the "Spanish" influenza pandemic of 1918-1919 that "infected one third of the world's population (or ≈500 million persons at that time) and caused ≈50 million deaths." Sounds pretty important to me. --- Medical geneticist (talk) 15:27, 27 April 2009 (UTC)[reply]
But, so, why? Why is this influenza so much more dangerous than the gazillion other types of influenza out there? You know, the diseases that hundreds of millions of people contract every year, the diseases that kill hundreds of thousands of people annually? Belisarius (talk) 15:51, 27 April 2009 (UTC)[reply]
I was going to ask the same question here. I would love to see statistics on how many people die of the flu each year in Mexico. I feel like the media just happen to be jumping on this one more than other years. -- MacAddct1984(talk • contribs)16:09, 27 April 2009 (UTC)[reply]
You are asserting that human influenza is a petty illness, and for a heathy adult it's almost always non-lethal. The problems start arising when you are dealing with a group of individuals with a weaker immune system, such as the young children, ill or elderly population. You'll notice that over 1000 cases of swine flu have been reported during this pandemic, but comparatively few deaths (about 1:10, maybe just over/under). When flu infects individuals with compromised immune systems, it can cause some serious, and potentially lethal, consequences (whether it is human, bird of swine flu). Regards, --—Cyclonenim | Chat 16:13, 27 April 2009 (UTC)[reply]
We weren't asserting that it was a petty illness, on the contrary, we were saying that it is a big deal, but did not seem any worse than any other year, when thousands die each year from influenza. But I guess the fact that it's a new illness is the problem and there is currently no easy vaccine. -- MacAddct1984(talk • contribs)16:40, 27 April 2009 (UTC)[reply]
Sorry, upon rereading (where I added the below comment) I realised I misunderstood the original question, but forgot to strike. Will do so now. Regards, --—Cyclonenim | Chat 16:45, 27 April 2009 (UTC)[reply]
I realised that I probably didn't answer the question. The reason that this has so much more attention is that it has the potential to go wildly out of control. With human influenza, we have flu jabs which we can provide to the immune-compromised individuals and hopefully keep them alive through tough times like winter. With a new strain of swine flu, one which we have essentially no vaccination for, all of those immune-compromised individuals are at risk of catching the disease, meaning it can spread much, much faster and therefore kill more people. See the Spanish flu, for example, which mutated and killed thousands and thousands of people because there was no vaccination. The same problem can occur now if we don't have a vaccination, although a vaccine may be created quicker than back then. Regards, --—Cyclonenim | Chat 16:17, 27 April 2009 (UTC)[reply]
There are two things special about this outbreak. First, the genetic structure of the strain is quite different from other flu variants. Secondly, there are reports from Mexico that many of the people most seriously affected are in the 25-45 age range, a group that normally is the least affected by flu. However, more recent reports make it unclear to what extent the original reports are correct. Looie496 (talk) 16:41, 27 April 2009 (UTC)[reply]
The picture to the right compares the death rates (per 100 000) of the spanish flu with the death rates of more common flus. Notice the 'bump' around 30 year old people. Dauto (talk) 18:05, 27 April 2009 (UTC)[reply]
It's of note that this is not the first Swine flu pandemic fear—there was one in 1976 as well that didn't turn into a pandemic. The fear is, as noted, that it is related to the 1918 strain, which was much more deadly than the normal ones floating around in "flu season." --98.217.14.211 (talk) 02:08, 28 April 2009 (UTC)[reply]
To embellish a bit upon what Looie said above: Any disease that can take a perfectly healthy adult and cripple and/or kill them is scary, and when that disease is transmitted via air with no known cure it is triply scary. Add to that the fact that, unlike with the SARS and Bird flu scares of recent years, this disease has manifested itself strongly in a large population center/transportation hub relatively early in the outbreak, leading to the cases now being reported on 3 continents. Add all that with today's Twitter-minded society (and resulting hysteria), and you get a big deal in the media.
It will probably end up being nothing bigger than SARS and the bird flu--already it seems that subsequent cases outside of Mexico are less virulent (although it might be a bit too early to draw that conclusion), and though it seems to have a death rate ~1%, there may be untold numbers more who never got sick enough to go to the hospital (and thus be counted as a suspected case). Also, lets not forget how much medical care has improved since 1918.-RunningOnBrains02:46, 28 April 2009 (UTC)[reply]
The 1918-1919 flu did not mostly kill the elderly or those with weak immune systems. It killed healthy 19 -25 year olds, since their robust immune systems overreacted and the consequences of that compromised lung function. Edison (talk) 15:05, 28 April 2009 (UTC)[reply]
I have a problem of drooling while I sleep. Usually when I wake up, I find my pillow wet from my saliva. At any normal time my mouth has excess saliva. Is there a cure for this? What basically is the problem? Thanks. —Preceding unsigned comment added by 116.71.46.207 (talk) 15:02, 27 April 2009 (UTC)[reply]
If it is really bad, you could consult your doctor on whether you have a mouth condition that might be causing excessive salivation. If it is only moderate, you could try a mild diuretic before going to sleep, such as drinking tea. Looie496 (talk) 16:37, 27 April 2009 (UTC)[reply]
[comment removed - suggesting a specific OTC drug (which I don't think it actually intended to reduce salivation but just does so as a side effect) is unquestionably medical advice and is inappropriate for the reference desk --Tango (talk) 18:22, 27 April 2009 (UTC)][reply]
Mouth breathing certainly isn't the only way you end up drooling in your sleep, but mouth breathers do tend to drool in their sleep more frequently. I'd guess everybody does it sometimes, whether they're aware of it or not. The explanation for it is pretty simple: when you're asleep, you don't swallow saliva as often as you do when you're awake, and your mouth tends to go slack. If your head is in a certain position, gravity takes care of the rest; in itself, this is a really common and everyday thing. The excessive saliva may or may not be another story; if that concerns you, OP, you should probably talk to a doctor. -- Captain Disdain (talk) 20:14, 27 April 2009 (UTC)[reply]
Try swallowing your spit during the day, and closing your mouth when you sleep. I find that by the time I'm hours into sleep my saliva tends to evaporate away anyway (leaving my mouth dry). Also, It's been found that napping causes more drooling than regular sleeping. ~AH1(TCU)00:04, 28 April 2009 (UTC)[reply]
Looking at this again, I see that I probably didn't get what you were asking. The arcuate fibers are a set of connections -- the set of nerve fibers connecting the two brain areas I mentioned. Looie496 (talk) 19:44, 27 April 2009 (UTC)[reply]
I think the original question was about the arcuate fibers, not arcuate fasciculus. Please do not confuse between the two. The original question refers to the fact that the arcuate fibers article, in its present form, contains little more than just links to the three following articles: Internal arcuate fibers, Anterior external arcuate fibers, and Posterior external arcuate fibers. Now, from what I've read, all these fibers are formed by axons of neurons in nucleus gracilis and nucleus cuneatus of medulla oblongata. While medulla oblongata is generally associated with basic autonomous functions, the two aforementioned nuclei are thought to be mainly somatosensory. Lesioning experiments in cats and rodents show mostly propioceptive and somatosensory deficits following lesions to nucleus gracilis and nucleus cuneatus. So, I would say that the overarching function is delivering somatosensory information to various brain areas. You will have to do more reading to know the details. You will also have to do some research to find out if arcuate fibers in humans are implicated in some additional functions; they very well may be. Hope this helps. --Dr Dima (talk) 19:50, 27 April 2009 (UTC)[reply]
I do not get how to use the right hand rule at all...is there a way to find direction of a field, direction of velocity of a charged particle, or direction of force without using it?
Or
Could someone help me with a sample problem so i can better understand it??
"If a negativley charged particle were moving downward along the right edge of this page, which way would the mangetic field be oriented so that the particle would initially be deflected to the left?"
and
"Three particeles are moving in a uniform magnetic field. Each initially have a velociety pointing to the right. One goes into a circle that is clockwise, two goes straight, three goes in a larger circle that is counterclockwise. One and three have the same velociety and magnitude of electric charge. What can be said about the charges and masses of these particles?"
These are obviously homework problems, but I have about 40 problems like these and help with these two would definatley help me grasp the concept that I am trying to learn. —Preceding unsigned comment added by 70.129.227.81 (talk) 18:05, 27 April 2009 (UTC)[reply]
There are two different right-hand rules in magnetism as you can see in those pictures. The first one is used to find the direction of the magnetic field produced by a current. The second one is used to find the direction of the magnetic force on a (positive) charge moving with velocity 'v' (revert direction for a negative charge). I hope these pictures help. Dauto (talk) 18:38, 27 April 2009 (UTC)[reply]
OK, for those problems you will make use of the second rule which relates the direction of three physical quantities -- Velocity, Magnetic Field and Force, as indicated on the picture. The problems always give you information about two of those directions and you use the picture to help you find the direction of the third quantity in order to answer the question. Your first problem, for instance, gives the direction of the velocity (downward the page) and the direction of the force (towards the left) and asks about the orientation of the magnetic field. Keep in mind that for a negative charge the direction of the force will be the opposite of the one shown in the picture. Put your open right hand in the air with the thumb away from the other fingers in such a way that your thumb points towards the direction of the velocity and the palm (for a positive charge) or the back of your hand (for a negative charge) points towards the direction of the force. Your mid finger will be pointing towards the direction of the magnetic field. Dauto (talk) 20:30, 27 April 2009 (UTC)[reply]
In physics or electrical engineering exams it is funny to see students moving their right hands around with orthogonal thumb and digits trying to line them up with the illustrations on the exam for particle movement and magnetic field. It looks sort of like they are throwing down Gang signal#Hand signs for the Latin Kings. The illustration attached to the response is unhelpful to the OP since it shows all the fingers held straight. See also the illustration from Right hand rule, which unfortunately also has problems. Edison (talk) 14:48, 28 April 2009 (UTC)[reply]
There seem to be many different right-hand rules. This one is closer to the rule I learned. (The hand shape is the same as in your image but the labels are permuted.) That straight-palm version is as good as any other; there are still three distinguishable axes, and it looks less silly in public. You can use a left-hand rule, for that matter, if you assign the labels appropriately. And here's yet another variation. Pick one that you like and learn it. But whatever you do, don't learn two. -- BenRG (talk) 21:32, 28 April 2009 (UTC)[reply]
That straight-palm version makes a lot of sense now that I look at it. Your fingers show the direction of the parallel field lines, your thumb shows the current in the wire, and the force is in the direction you would push with your hand. I endorse that one. -- BenRG (talk) 21:47, 28 April 2009 (UTC)[reply]
I used to have a cartoon for the magnetic field around a wire using a student reading aloud from a physics textbook: "as you face the direction of current flow (had a vector pointing forward along the spine), magnetic field moves through the book from the front front cover to the back cover" and a caption "Moral: you won't get physics if you don't look in your textbook." Well, you get the idea. I know, {{global}}. DMacks (talk) 21:41, 28 April 2009 (UTC)[reply]
Reading through the Sun article reveals a lot of information about the temperatures of various parts of the Sun. How are these temps measured? How about measure the temp of the core of the earth? Are these considered actual measurements (no one has taken a thermometer to either) or are they just theoretical calculations? Thanks. Anythingapplied (talk) 19:50, 27 April 2009 (UTC)[reply]
They are theoretical calculations. I wouldn't use the word Just. Those models (specially the one for the sun core) are very solid and thrustworthy models, and have been confirmed by indirect observations. Dauto (talk) 20:34, 27 April 2009 (UTC)[reply]
(ec)These are not direct measurements. The usual approach involves either analytic or numerical models of the star or planet interior. The models are calibrated using seismology (Earth) / helioseismology (Sun) data and - in the case of the Sun at least - the light that the Sun emits at different wavelengths. Different wavelengths (different photon energies) can escape from different depths: more energetic photons usually come from deeper within the Sun as they usually have smaller absorption and scattering cross-sections; but be warned that this is by no means always the case. Matching observed spectra to the models makes it possible to infer temperature distributions with higher reliability. So these are indirect measurements. --Dr Dima (talk) 20:43, 27 April 2009 (UTC)[reply]
It is funny now to read analyses by 19th century scientists trying to account for the high temperature of the sun and the extreme age of the sun, in terms of chemical reactions (the reactants would have been used up by then) or cooling from an initial high temperature. Early measurements of the sun's tempereature did not equal todays. In 1876, astronomers determined the sun was at 1354 to 2000 degrees Centigrade(p18).By 1907, the estimate was up to "12,000 to 15,000 Fahrenheit(6600 to 8300 C) . By 1907 the best explanation seems to be not nuclear fusion, but that the sun was contracting 220 feet per year (supposedly adequate to account for its continued constant heat output for 24 million years), although presciently they referred to the relatively newly known power of radium to continue giving off heat for a very long time, at least a baby step toward the modern nuclear explanation. The 1907 estimate was actually a bit high, if it was supposed to be the surface, today estimated at 5778K (5504C) per the Sun article. Edison (talk) 00:25, 28 April 2009 (UTC
In movies when large spotlights are turned on (e.g. at a football sports arena) there is an accompanying sound, sort of like a shutter being closed. What is the cause of this? ----SeansPotato Business22:57, 27 April 2009 (UTC)[reply]
Flood lights involve a high power electrical arc. That heats the gas inside the light and will cause it to expand, creating a sound in exactly the same way thunder is produced. (The arc continues to exist after that, but since the gas is already hot there is no further sound.) I expect, but I'm not 100% sure (this is just personal deduction, rather than something I've read in a reliable source), that that is the characteristic sound of flood lights turning on. --Tango (talk) 23:19, 27 April 2009 (UTC)[reply]
It might also be enhanced for dramatic effect. In the actual site, the sound of lights being turned on would likely be drowned out by background noise such as air handling equipment, traffic on the street outside, and airplanes flying over. See Foley (filmmaking)Edison (talk) 00:19, 28 April 2009 (UTC)[reply]
There is also a loud sound when floodlights are turned on at a movie studio sound stage. Normally, the sound is not heard in the actual movie ("Lights, camera, action.") But it can be heard in a scene in the movie "Singing In the Rain" which shows the floodlights being turned on. It is the sound of heavy duty relays, called "contactors", actuating. The moving part of each relay slaps against the electromagnet. Contactors are used so that only light wiring is needed to connect the floodlights to a control panel. Heavy wiring for the floodlights themselves goes directly from the building electrical service entrance to the floodlights. This reduces long runs of heavy wiring and the need for heavy switches in the control panel. Big electrical machinery, such as at steel plants, also uses this method. Undoubtedly it is the same at sports stadiums. – GlowWorm. —Preceding unsigned comment added by 98.21.107.234 (talk) 02:57, 28 April 2009 (UTC)[reply]
In a movie, every sound you hear is intentionally placed on the soundtrack in post-production, unless it is a low budget documentary. In more modern stage lighting, the control is electronic and is not simply relays closing in full voltage. In vintage lighting, knife switches on a lighting board were used along with banks of rheostats as dimmers, again not always with noisy relays. Movies would have the luxury of turning on the lights without distracting the audience. In sports venues the clunking of relays would not be heard over the murmer of fans (of both sorts). Edison (talk) 14:40, 28 April 2009 (UTC)[reply]
