Wikipedia:Reference desk/Archives/Science/2006 December 4

= December 4 =

Docking in orbit
How do 2 spacecraft in the same planetary orbit achieve docking when they are initialy far apart?--Light current 00:43, 4 December 2006 (UTC)


 * I'm not sure if it's the only way, but the simplest at least is for one of the spacecraft (call it A) to make a retro burn to slow itself down, which will raise its orbital altitude and increase its orbital period. The other spacecraft (B) will eventually 'catch up' with A, at which point A can make a positive burn to increase its speed again, lowering its altitude back to the original level and matching the speed of B to achieve rendezvous. This may seem a bit counterintuitive, and is one reason why it's really difficult to perform a rendezvous manually. --YFB ¿  01:18, 4 December 2006 (UTC)


 * You have retrograde and posigrade reversed here. The first burn should be a posigrade to increase velocity, raise apoapsis and increase the period. The second burn is retrograde to decrease velocity, lower apoapsis and decrease the period back to match B. Other than that, it's about right. Of course all of this assumes that the two spacecraft are initially in the same orbit, with A ahead of B. If B is ahead of A, reverse the procedure. Also note that both burns have to occur at the same point (periapsis for the burn described) in order to return to the same orbit. Finally, if the two orbits are not the same initially, this all gets a lot hairier, and phenominally complicated. --anonymous6494 06:39, 4 December 2006 (UTC)


 * Apoapsis? Ah I was just interested in circular orbits. Forgot to say that.--Light current 08:17, 5 December 2006 (UTC)


 * I thought if you made a positive burn it would increase your 'altitude' . Is that wrong?--Light current 08:26, 5 December 2006 (UTC)


 * Correct. A posigrade burn will raise your orbital altitude, but one of the fundamentals of astrodynamics is that if you perform a transfer between any two orbits, the two orbits must coincide at the point where you made the transfer (assume an implusive (instant) transfer). So your altitude is the same at the point where you made the posigrade burn, and greater than before everywhere else. The same principle applies to the transfer you initially asked about. The initial orbit is circular, but A's transfer orbit (between the two burns) is elliptical. The burns occur at periapsis of the elliptical transfer orbit.--anonymous6494 23:25, 5 December 2006 (UTC)


 * Hmm I think I understand and I think it makes sense to me. If Im behind you, I put the brakes on to catch up distance then accelerate to regain height. Right? --Light current 23:48, 5 December 2006 (UTC)


 * Bullseye. -anonymous6494 16:04, 6 December 2006 (UTC)

Advanced Motion
I need something advanced about motion (not that advaned, but medium-ly advanced, not basic) that I can explain in 2 minutes or less. Thanks for any ideas. Cbrown1023 01:04, 4 December 2006 (UTC)


 * How about Newton's three laws of motion? If you're good at explanations you should be able to do this at a reasonable level of detail in two minutes. Or isn't that 'advanced' enough? --YFB ¿  01:20, 4 December 2006 (UTC)
 * It is a good idea, but we already are studying those... I've been thinking for a while and can't seem to come up with a good idea... Cbrown1023 01:22, 4 December 2006 (UTC)
 * I think I'm going to do Motion capture. Cbrown1023 01:45, 4 December 2006 (UTC)
 * Sounds like a good choice - best of luck :-) --YFB ¿  02:02, 4 December 2006 (UTC)

Dots in eye w/o glasses - explaination/image?
Hi! I remember that a while ago I had seen an image and a short explaination on why people with Myopia see small moving dots and lines when looking at a bright light without glasses, but searching, I cannot find it. Does anyone who is familiar with the phenomenon know where to find such an explaination? Thanks! 69.253.41.139 01:26, 4 December 2006 (UTC)
 * Do you mean Floaters? risk 03:20, 4 December 2006 (UTC)


 * Under the right conditions, you can also see the red blood cells circulating in the capillaries of your retina. The effect is most pronounced if you're staring into a deep blue, featureless field (such as a cloudless sky). The Exploratorium in San Francisco has a device that demonstrates this effect very clearly; other science museums may also have copies of this gadget.


 * Atlant 14:17, 4 December 2006 (UTC)


 * (Blue field entoptic phenomenon)

Speed in space
I'm having trouble understanding the concept of speed in outer space. I mean, if you're in a spacecraft in interstellar space on the other side of the galaxy, is there any way to measure what speed you're traveling at? I know that speed is defined relative to points of reference, which makes me wonder if speed has much meaning here. But on the other hand, the speed of light is (usually, I think) a kind of definite limit on how fast you can go...so I was thinking, could you (theoretically) measure your speed against a beam of light that you shine forward? If you could (somehow) measure that the light you project is traveling away from you at 539,626,424.4 km/h, then could say that you're traveling at .5c, wherever in space you're located? Or if the light is traveling away from you at 1,079,252,848.8 km/h, could you say that you are "stopped"? Or is this just all nonsense? Thanks for any help you could offer. --Lazar Taxon 01:28, 4 December 2006 (UTC)
 * Well, I don't think so - light always travels at C relatve to the observer - so that may not work. However, a pulse of light "launched" - for lack of a better term - at a stationary object can easily calculate distance, then repeating that after a set amount of time can calculate speed. 69.253.41.139 01:31, 4 December 2006 (UTC)
 * You do have a good point. I'm just having trouble reconciling the fact that all speed is relative, with the fact there is an absolute speed of light. --Lazar Taxon 02:14, 4 December 2006 (UTC)
 * Great, now I've gotten a headache :P As you said in your first post, speed may not have much point in outer space, except when relative to sometihng - such as the international space station or the moon, both of which are "moving" relative to the earth and to the sun. I think that the best way to do that, would be similar to sonar, shoot something at your target and use time to measure distance. 69.253.41.139 02:34, 4 December 2006 (UTC)
 * Light as a sonar would not work. Speed of light has some interesting reading. The hardest concept to grasp is that light does not really have an analogous physical thing that makes it easier for us to imagine, you have to really use all your conceptual power to even begin to grasp it. Light has constant speed for ALL frames of reference, it doesn't matter if you are travelling at 0.5c and you fly past someone and turn on your headlights, to you it will look like the light will shoot away from you at the speed of light, and to the 'stationary' observer it will look like the light will shoot away from you at the speed of light too!!! It's crazy. If you are travelling forward at half the speed of light and the light is shooting out in front of you, in one time unit according to the frame of reference the light has travelled one and a half distance units, but according to the 'stationary observer' the light is shooting out in front of you STILL at the speed of light even from their point of view. So in one time unit it has only travelled one distance unit according to them?!?? wait for your mind to melt. We know the speed of light is constant, what is speed? It is V = d/t (distance over time). In normal observable physics, what we see day to day, time and distance are constant for all frames of reference, and SPEED is variable, if you change either t or d you simply change V, but with light V is the constant! Therefore, if you change d, like we did in the above example, the only other variable you can alter to balance the equation is TIME it self, time changes depending on your frame of reference! crazy business! Vespine 03:03, 4 December 2006 (UTC)
 * Another interesting concept is if you are traveling in your car and pass someone near the speed of light, and turn on your headlights, you will completely fry him with the brand new X ray emitters you used to call headlights. --Tbeatty 03:12, 4 December 2006 (UTC)


 * You've basically touched upon the crux of the (special) theory of relativity, which states that even though all speed is relative, the speed of light is not relative. So if I'm on a space ship speeding away from earth, and you're on earth, and we both measure the speed of the same beam of light, we we'll both find c. You might think, well, then if I'm traveling at some speed v relative to the earth, near the speed of light, and someone else is traveling at speed v relative to me, then isn't he traveling at v + v relative to the earth? The thing is that simply adding speeds together like that isn't allowed in the theory of relativity. The actual equation makes sure that as you go faster, you approach the speed of light, but you never reach it. If I'm traveling 0.5c relative to the earth, and somebody is traveling 0.5c relative to me, he's actually traveling 0.75c relative to the earth (NB: these are probably not the actual numbers, but that's the idea). The article on the special theory of relativity has more info. risk 03:02, 4 December 2006 (UTC)


 * Instead of a flashlight, pick a star and a known hydrogen emission. Speed of light is constant so the difference in kinetic energy between the star and observer is translated into frequency.  This is how astronomers have determined that the universe is expanding and everything is moving away from us.  --Tbeatty 03:08, 4 December 2006 (UTC)

Phenotypic ratio
What is a phenotypic ratio? --  T H  L  R CCD 01:54, 4 December 2006 (UTC)
 * In biology a phenotypic ratio is the ratio between two or more phenotypes. A phenotype is the result of a certain gere - blue eyes, or brown hair. This is similar to, but seperate from, a genotypic ratio. If I have 4 offspring with the genes of Bb Bb bb BB for eyes - b means blue and is not dominate, B is brown and is dominant - my genotypic ratio is BB:Bb:bb = 1:2:1, however my phenotypic ratio is Brown:blue 3:1, since a Bb is Brown eyes, not blue. ST47 Talk 02:04, 4 December 2006 (UTC)

Chemistry Molar Question
What does 6M HCl mean? Like I know you say it 6 molar HCl, but what does the molar mean, and how high can the xM (replace x with a number) go? —Preceding unsigned comment added by Darkleg (talk • contribs)
 * In this case, "mole" refers to Mole (chemistry), specifically Molar concentration. -Fsotrain09 02:26, 4 December 2006 (UTC)
 * See also Concentration. --David Iberri (talk) 02:30, 4 December 2006 (UTC)


 * The concentration can go fairly high; it depends on the substance and how soluble it is. 6M is fairly concentrated. Normally in chemistry classes you deal with concentrations between 0.01M and about 6M. BenC7 02:47, 4 December 2006 (UTC)


 * For the specific case of hydrochloric acid, the limit is about 12M or 13M, because that's "fuming" hydrochloric acid, which means hydrogen chloride gas is constantly coming out of solution. Although we usually don't talk about the "concentrations" of pure solids or liquids (because they don't effect chemical equilibrium), they're still defined, and the concentration of pure iron is 140 mol/L. —Keenan Pepper 06:06, 4 December 2006 (UTC)

Anatomical name for "weenis"
I've heard that the skin on your elbow is know as a "weenis". Is this the real name or is just a neologism? Imaninjapirate 03:54, 4 December 2006 (UTC)


 * neologism. --⁪froth T C  05:38, 4 December 2006 (UTC)


 * A quick Google for "elbow skin" brings me to a Google Answers question with a surprisingly large price. No answer was ever accepted, but I like the suggestion of "olecranal skin" or "olecranon skin".  -- Plutor talk 13:49, 4 December 2006 (UTC)

Fastest Piston Powered Aircraft
What was the fastest *piston* powered aircraft ever built? Include prototypes and xplanes if that helps Spencer McGrew


 * A modified F8F Bearcat called the Rare Bear (528.33 mph or 850.26 kph), according to the article. Clarityfiend 05:34, 4 December 2006 (UTC)

Really quick question
How do you pronounce the name of the antibiotic coformycin? Is it /'koh-fuhr-,mii-s^n/ or perhaps /'koh-,fawr-'mii-s^n/ (pardon the idiosyncratic phonemic transcription? Thanks, anon. —Preceding unsigned comment added by 162.83.150.164 (talk • contribs)
 * With a midwest accent (or lack thereof) I would say Ko-for-mysin with the accent on the first syllable, and the "for" pronouned as in "go-for-broke" but suspect the exact sound of the middle syllable would vary by the speaker's accent. alteripse 05:11, 4 December 2006 (UTC)
 * Since it's found in Nocardia interforma it's reasonable to assume the pronunciation is derived from the organism, making the for- part of the word form or forma --13:54, 4 December 2006 (UTC)172.145.44.11

I would say k'form-a-sin (conform to sin). Theavatar3 18:14, 5 December 2006 (UTC)

No of Universe
Are there exactly 10^50 number of atoms in the universe??Any idea on how to get to that conclusion?? And what about the probable number of universes that could have been formed with that many atoms??


 * Bit of a lame answer to the last question: one. The universe is all there is, so there can only be one. DirkvdM 09:39, 4 December 2006 (UTC)
 * Atom suggests there are about 1080 atoms in the universe. This is a ballpark guesstimate only; google for number of atoms in the universe for different estimates and methods of estimation. Nobody really knows; but if you estimate the number of galaxies, average number of stars in each, average size of stars, you end within a factor of 10 from that number. Weregerbil 12:48, 4 December 2006 (UTC)

Magnetism
We know that we are having a net velocity as we are travelling across the universe.So why not any charged particle emit magnetism  if it is kept stationary on earth??


 * Because it's all relative! In this case, it's important to remember that magnetic fields are only detectable from the relative motion of charged particles. If, from your point of view, a charged particle isn't moving, then you won't detect a magnetic field (though you will detect an electric field). But if you were elsewhere in the universe, moving relative to the Earth, then you would detect a magnetic field coming from that particle. Confusing Manifestation 11:16, 4 December 2006 (UTC)

Coeper pair
Any idea if a photon forms a positron/anti positron coeper pair??
 * Did you mean cooper pair?87.102.32.183 09:29, 4 December 2006 (UTC)
 * And by "anti positron" do you mean, um, an electron? Anyway, from looking at Cooper pair, it seems to me that you can't have them with an electron and positron, because they depend on the polarization of the ion lattice attracting another negative charge.  Electrons and positrons already attract one another, but you certainly couldn't have positrons in a normal-matter superconductor.  Perhaps you want to look at pair production?  --Tardis 17:53, 4 December 2006 (UTC)

tritium
Since tritium is a non-gamma ray beta emmitter when used in the place of hydrogen to make sulphuric acid does it give the acid a negative charge and if so is this charge sufficeint to charge a lead acid cell? Adaptron 10:45, 4 December 2006 (UTC)


 * There is no creation of charge in this reaction. The opposit charge is also present and will lead to neutralisation. With a half life of 11 years the recharging would take some time. —The preceding unsigned comment was added by 134.76.234.75 (talk • contribs).


 * Would "neutralisation" result in a thermal increase? 71.100.6.152 08:33, 5 December 2006 (UTC)


 * There are power sources which use the beta decay of tritium to generate electricity (see Betavoltaics), but not in the way you suggest, which would be grossly inefficient. —Keenan Pepper 16:20, 4 December 2006 (UTC)

Oxygen Generation
I heard somewhere that the great grasslands of the World contribute more oxygen to the Planet than all the forests, is this true?


 * I would think the relative land areas of each would be the most important factor. Perhaps, if there are now more grasslands than forest due to human deforestation, that might now be true. StuRat 12:43, 4 December 2006 (UTC)

decomposition of phosphene
Dear Sir/Madame, I would be most obliged if you could give the chemical equation for the following reaction:

Phosphene when decomposed gives phosphorous and hydrogen

Sincerely, Sruthi


 * assuming white phosphorus as product:

4PH3 --> P4 + 6H2

Cambrian Man - ?
Evidence of a fully fossilized 500 million year old fully formed Human Being, unearthed in modern day Ethiopia. This 'Pre Cambrian Man' as he's been called is a fully developed homo sapien, and predates any human remains yet known. How do you explain this discovery without conflicting evolution theory? - User:CC clamb


 * Useful answer: This thing is called a Australopithecus afarensis, not a homo sapiens. Friday (talk) 01:25, 6 December 2006 (UTC)


 * May we conflict any other theory (in physics, for example)? –m y s i d ☎ 13:59, 4 December 2006 (UTC)


 * Can you please provide us with a link so we know whether this "evidence" is from some rabidly anti-science creationists or from legit scientists ? StuRat 14:13, 4 December 2006 (UTC)
 * I find zero relevant hits from Google for "Pre Cambrian Man", nor for Google's suggested "PreCambrian Man". The few hits which do exist for the term seem to be using it to mean "prehistoric man", which is certainly not the same thing.  User:Zoe|(talk) 19:41, 4 December 2006 (UTC)

Does not exist. --Zeizmic 15:07, 4 December 2006 (UTC)
 * You may not understand the word "theory". "Evolution theory" is not a set of immutable facts.  See Theory.  Friday (talk) 15:26, 4 December 2006 (UTC)

Do you guys remember what existed before the Cambrian? All the life forms were lower than trilobites. This is nonsense. alteripse 22:12, 4 December 2006 (UTC)


 * The sensible answer to the crazy question is of course: time travel. Some far future human goes sight seeing in the distance past and gets his face sucked off by Opabinia regalis.  Then 500 million years later the fossil is discovered, but fearing a creationist nightmare and/or a temporal paradox, scientists tell no one save for a single posting on Wikipedia that no one will believe.  Dragons flight 22:28, 4 December 2006 (UTC)


 * A Wikipedian sucked off someone's face?  bibliomaniac 1  5  02:54, 5 December 2006 (UTC)


 * . User:Zoe|(talk) 03:03, 5 December 2006 (UTC)


 * And what, pray tell, my dear Zoe, does the discovery of a mechanical device from the time of Eratosthenes, who accurately determined both the size of the Earth and the distance to the Moon, have to do with the subject at hand? B00P 23:41, 5 December 2006 (UTC)
 * It's evidence of time travel, of course. :)  User:Zoe|(talk) 03:44, 6 December 2006 (UTC)

social psychology
Social Psychology cannot explain all our social problems. Discuss


 * Some students cannot figure out the meaning of the sentence at the top of this page that states Do your own homework. Discuss. --Kainaw (talk) 15:54, 4 December 2006 (UTC)

Reference Desk in Wikipedia would not do your homework for you. Discuss 202.168.50.40 23:00, 4 December 2006 (UTC)

I majored in psychology. I found that social psychology was the most useless, tautological course of all. Which, of course, is the most useful thing of all to learn, for someone studying psychology.

Psychology teaches you beautifully how one person will act. Try to extraopolate that to a group of people, and you're left high and dry. As we live in a world of considerably more than one person, studying psychology to begin with means you are already high and dry.

That said, Nietzsche did not err when he said something to the effect of 'psychology is the mistress of all other disciplines'. It coherently answers questions like, 'why study botany at all?' Theavatar3 18:18, 5 December 2006 (UTC)

Fastest piston warplane
What was the fastest piston powered aircraft in millitary service? Spencer


 * Scroll up - this question as asked and answered. --Kainaw (talk) 16:11, 4 December 2006 (UTC)
 * The de Havilland Mosquito is also a noteworthy fast piston aircraft, in that it did extensive service as a reconnaisance, plane, fast bomber, and night fighter. It cold do 415 mph at 28,000 ft (668 km/h at 8,535 m) It could have theoretically completed 2 round trip bombing runs while the slower heavily armed bombers were doing one. Its variant the de Havilland Hornet would do 472 mph. Edison 18:34, 4 December 2006 (UTC)


 * This second question is a little different. The Rare Bear was privately owned. According to Dornier Flugzeugwerke, the fastest fighter in WWII was the Do-335 (474 mph, 763 kph). Clarityfiend 19:49, 4 December 2006 (UTC)


 * Hmmm...according to de Havilland Hornet, its prototype topped out at 485 mph. Clarityfiend 03:37, 5 December 2006 (UTC)


 * Not that the question said "in military service." Perhaps the prototype did not have to carry equipment which was necessary for military service (giuns and ammo? long range vacuum tube radio and power supply? Navigation equipment? life raft?). In modern military planes, they are hotrods capable of fast climbing until the avionics and weapons are added. Most planes can also go very fast in a dive, but that doesn't count. Edison 16:50, 6 December 2006 (UTC)

plants
what is the worlds slowest growing plant


 * Petrified wood. But Bristlecone pine is right up there. Atlant 16:54, 4 December 2006 (UTC)


 * Huh, how can you consider petrified wood, a type of fossil, to be a "growing plant"? -- AJR | Talk 17:54, 4 December 2006 (UTC)


 * That was a joke, the second answer is the serious one. StuRat 18:01, 4 December 2006 (UTC)


 * And, of course, I offered an answer that actually describes "the world's oldest multicellular, non-cloned plant", which isn't exactly what was asked, but as I said, definitely rates "up there". But it's entirely possible that the real answer is some sort of cryptobacteria (bacteria in a cryptobiotic state).


 * Atlant 18:23, 4 December 2006 (UTC)


 * Yes, and some seeds can stay dormant for many years before growing at all; that certainly qualifies as slow growth. StuRat 19:50, 4 December 2006 (UTC)

My guess would be the trees that live in the pygmy forests on the west coast of CA near Mendicino. They grow in nutrient poor soil, due to leaching. Some are over one hundred years old and as small as a few feet tall with trunks as small as 3cm diameter. Another candidate might be the bristle cone pines. Some live to 4000 years old and they have very very hard wood. This means their annual rigns are very close together and thus have very slow growth. Use google to get more info. David D. (Talk) 21:52, 4 December 2006 (UTC)

Electricity Efficiency
Why do power stations transfer electricity at 50hz to achieve the highest efficiency and how does this frequency maintain that? I would also find it extremely useful if a table with voltage (in and out of transformer), current(in and out of transformer), power in (to transformer), power out (of transformer) depending on frequency of electricity could also be supllied. thank you.
 * They don't all transfer power at 50 HZ, some transfer power at 60 HZ, a few countries even use a mixture of the 2 frequencies --172.147.216.150 16:57, 4 December 2006 (UTC)


 * 50 or 60 Hertz was a reasonably "comfortable" frequency representing a good compromise between several competing needs:


 * the efficiency of transformers (which, for crummy, low-tech materials tends to improve at lower frequencies)
 * the size of transformers (which get a lot smaller with higher frequencies)
 * Reactive losses on power lines (which rise with frequency)
 * The ability to build practical induction and universal electric motors.
 * Various industrial processes (such as electric arc furnaces, electroplating, etc.) that would prefer DC but could use low-frequency AC


 * Nowadays, in the high-tech world, the operating frequencies of devices are becoming completely decoupled from the mains frequencies, though, and you can see the result:


 * Long-distance transmission is going to DC (see High-voltage direct current)
 * While transformation goes to ever-higher frequencies (with hundreds of kilohertz now common in switched-mode power supplies
 * While motors now generate their own frequencies (see Brushless DC electric motor)


 * By the way, there's no good reason to choose 50 versus 60 Hz; that difference is just an artifact of competing equipment vendors trying to lock each other out of various markets.


 * Atlant 17:10, 4 December 2006 (UTC)

As to how the frequency is maintained, think of the electrical utility system as a car going at a certain speed, in which the gas pedal must be pressed harder to maintain that speed when the car goes up a hill. The steam from the boilers spins the turbines driving the generators. If load is added, as by customers turning on lights, ovens, and air conditioners, all things being equal, the frequency would decrease because of the imbalance between generation and load. The governors or speed controls at the generating station sense the added load and frequency drop, and open the steam valves to allow more steam to the turbine to maintain the frequency, just as in a car the driver (or the cruise control) sends more gas to the engine to maintain the desired speed. If the generator and turbine system are maxed out, or if several generators trip off the system, then the frequency will continue to drop. Low frequencies can destroy the generator at certain resonant frequencies, and will destroy motors. Ovespeed will also destroy a generator. There are protective relays to trip it offline if either condition occurs. In historic cases in the 1940's utility frequencies dropped from 60 to 45 hz, destroying all large connected motors. In the 1965 New York power blackout, during the progressive collapse there was ultimately a huge overload on the few remaining generators in the city, causing a frequency drop from 60 hz to (if I recall correctly) 55 hz before underfrequency relays on that generator tripped it offline. To avoid recurrences of this, utilities have installed underfrequency relaying systems to detect such a progressive decline in frequency and automatically shed load to restore a balance between load and generation, and to maintain the frequency to acceptible levels. This reduces the human element from hesitating when a decision to drop load has to be made within a few seconds. The actual system frequency often drops (less than 1 Hz) during periods of heavy load, causing a synchronous clock to fall as far as 30 seconds behind the correct time. When the load drops, or more generation is put on line, the frequency is set slightly above nominal to catch up the synchronous clocks. The powerline frequency is a far less accurate frequency standard than a quartz clock. Edison 18:51, 4 December 2006 (UTC)

50Hz or 60Hz was chosen not because of efficiency but because of the lightbulb. If the frequency is too low then the light from the lightbulb would flicker or rather the flicker would be noticed by humans. 202.168.50.40 20:40, 4 December 2006 (UTC)


 * Incandescent light bulbs do not flicker at line frequency. Melchoir 01:15, 5 December 2006 (UTC)


 * Which was the previous poster's point. On 25 Hz power, say, they would.  (Incidentally, there is still some 25 Hz generation at Niagara Falls -- see utility frequency.  This dates from way-back-when and is now only for industrial use, big motors that nobody wants to convert, but it was in residential use until around 1960.) --Anonymous, 08:00 UTC, December 5.

GSM interference with speakers/amplifiers
I've noticed that GSM (and AMPS) phones sometimes cause a sporadic humming interference with amplifiers and computer speakers (especially when transmitting). Since they transmit in the 800-1900MHz range, how are they producing interference in the 20Hz-20kHz range? Oh, no need to dumb down the answer for me. --Dgies 18:16, 4 December 2006 (UTC)


 * Rectification, most likely. You're probably hearing the envelope of the carrier wave.


 * Atlant 18:18, 4 December 2006 (UTC)


 * Signals trapped inside a metal case can cause humming at different frequencies, but I've found the common culprit to be cheap speakers. My wife had a pair that, even if they had no power to them and weren't plugged in, would pick up transmissions from the shrimp boats off shore.  I threw them away and got better speakers and the problem went away. --Kainaw (talk) 18:20, 4 December 2006 (UTC)
 * So a higher quality design would have a low-pass filter before the amplifier I guess... --Dgies 18:39, 4 December 2006 (UTC)


 * The first range of frequencies you mentioned is the frequency of electromagnetic radiation (in this case radio waves) while the second is the frequency range of sound waves (vibrations). the two are completely distinct.. there's no reason why electromagnetic waves interfering with your speekers should produce sound waves of the same frequency.


 * No, Atlant explained it correctly. 1.8GHz radio waves induce voltage in the amplifier, which is fed into a rectifier.  Rectification (either full or half-wave) has the effect of mixing the cell phone signal with a square wave at the frequency of its carrier.  Therefore the original modulation of the radio signal has been mixed down to baseband and when fed into the speaker's voice coil, will produce audible sound.  So in an ideal amplifier, you need a bandpass filter on voltages being fed into the rectifier unless you want to get mixer effects. --Dgies 22:08, 4 December 2006 (UTC)
 * I've examined the waveform of the interference, and the "1" squares of the square wave last exactly for the duration of one TDMA timeslot; the "0" phase lasts for seven slots (the TDMA frame in GSM has a total of 8 timeslots). It made me think the interference is mostly due to TDMA; the mobile phone switches the transmitter on and off at a frequency which is in the audible frequency band. –m y s i d ☎ 11:58, 5 December 2006 (UTC)

Global Warming
Would it be a good (or feasible) idea to combat global warming by collecting large amounts of carbon dioxide (and other Greenhouse gases) from factories and such like, putting them in containers, taking them into space and releasing the gas there instead of on Earth?81.158.81.209 20:42, 4 December 2006 (UTC)


 * No, the pollution caused by the rocket would far outweigh that removed by the rocket. And, carbon dioxide isn't bad, so long as it's not in the air in excessive quantities.  A better approach is to use plants (like algae) to convert it to carbon and oxygen. StuRat 21:37, 4 December 2006 (UTC)


 * Acoording to [| Popular Science], that wouldn't be a good idea either. They say that increasing the levels of algae and plankton enough to stop global warming would completely through off the underwater ecosystem and could potentially kill off every living thing underwater. On the plus side, it wouldn't cost too much money and could be started immediatly if the UN decided to do it. They say that the best combination of feasibilty, price, and risk to our health is actually like 81.158.81.209's... take all of our CO2 emmissions and storing it underground. Paragon12321 22:39, 4 December 2006 (UTC)


 * A better approach would be to lock it up in rocks (like limestone) See Carbon cycle 8-(--Light current 23:00, 4 December 2006 (UTC)
 * More specifically, see carbon sequestration. --Tardis 23:27, 4 December 2006 (UTC)


 * Well.. to be honest I was thinking more of the LONG term carbon cycle that involves absorption into rocks (maybe by sea shells etc), submerging of the rocks by the sea, subduction of the rocks, melting of the rocks and finally spewing of molten rock from volcanoes along with Gt of CO2. But apart from that, carbon sequestration probably has a minor role 8-)--Light current 01:19, 5 December 2006 (UTC)

CO2 concentrations in the atmosphere is a tiny component. Build lots of nuclear power plants to turn it into diamonds and oxygen. --Tbeatty 23:37, 4 December 2006 (UTC)


 * Man (or woman) cannot live by diamonds alone! 8-)--Light current 01:14, 5 December 2006 (UTC)

Grow trees, cut them down and throw them in the sea or somesuch place! Where will we need to put them to prevent their locked-up carbon from getting into the atmosphere? Maybe making more of our funiture out of wood since it's gonna end up in a land-fill anyway... --Username132 (talk) 02:07, 5 December 2006 (UTC)
 * We have an excellent discussion on carbon sequestration going on at physicsforums right now. I highly recommend it for the inquirer, and readers. X [' Mac Davis '] ( DESK | How's my driving? ) 02:57, 5 December 2006 (UTC)

Mass, Volume, or Charge Times Distance
Is there any measurement that is "mass times distance", "volume times distance", or "electrical charge times distance"?The Anonymous One 23:29, 4 December 2006 (UTC)


 * Do you mean moment? --Tbeatty 23:39, 4 December 2006 (UTC)

No. Moment is force times distance, not mass, volume, or charge times distance.The Anonymous One 00:30, 6 December 2006 (UTC)


 * You would simply call it gram meters or litre miters etc.

Fluorescent light with motion sensor
I have a fluorescent light that worked fine. I put a motion sensor on it and now, instead of lighting properly, it flickers. The instructions for the motion sensor say that I need a balast for it. The fluorescent light has a balast in it - or it wouldn't work in the first place. Does anyone know why this problem occurs and the proper way to fix it? --Kainaw (talk) 23:48, 4 December 2006 (UTC)
 * You perhaps already thought of this and it's an unlikely solution but is the motion detector sensing the flicker of the light? What happens if you put your hand over the sensor so it can't detect the flicker? (Can't offer any electrical advice, sorry) --Username132 (talk) 00:14, 5 December 2006 (UTC)


 * The motion sensor probably has a thyristor or triac switch in the output. These are not intended to operate fluorescent lights. Presumably you are not using any sort of ballast for the motion sensor? I dont know why it would need one but there you go. Are you reading the instructions properly? Also, you cant use dimmers on fluorescents for the same reason--Light current 00:26, 5 December 2006 (UTC)


 * Sorry, but it can't be done. Most timers can now handle fluorescents, but the in-switch motion detectors can't...I've tried. :(  One day they might be able to do it, but I would then expect to see a big advertising splash.  --Zeizmic 01:04, 5 December 2006 (UTC)


 * I don't know if I'm thinking of the same thing, but at university, when we walked along the hallway in halls of residence, the strip lights (fluorescent, right?) would come on (albeit with an annoying delay). --Username132 (talk) 01:19, 5 December 2006 (UTC)


 * Maybe but I bet they were relay activated. --Light current 01:21, 5 December 2006 (UTC)


 * Then can Kainaw use a relay or is that impractical? --Username132 (talk) 01:38, 5 December 2006 (UTC)


 * I was rather stupid. I should have mentioned that it flickers when it should be off, but lights up when it should be on.  Looking at these answers, I think that the sensor is letting enough electricity through in the "off" position to get a blink of light every few seconds. --Kainaw (talk) 02:10, 5 December 2006 (UTC)


 * Well really, fluorescents shouldnt be switched on and off like that! They take some time (depending on the starting circuit) to strike anyway.--Light current 02:15, 5 December 2006 (UTC)

As mentioned, there are very expensive motion detectors designed specifically for fluorescents, but the cheap in-switch types can't handle it, since they must maintain a small current through the system to keep active. --Zeizmic 13:11, 5 December 2006 (UTC)


 * Lots of "intelligent switches" of various types (motion detectors, darkness detectors, X-10 remote control devices, and the like) all have a function whereby they detect when you flip the manual switch on the external load and they then apply full power. That is, if they're controlling, say, a table lamp, you can turn the table lamp on from the lamp's switch no matter whether the intelligent gadget was thinking that the lamp should be "on" or "off". The way they do this is to attempt to pass a trivial amount of current through the load at all times. When you close the switch on the table lamp, this "test current" can pass through the load, the intelligent device detects that, and turn on the full current.


 * This worked great for incandescent light bulbs where the test current caused no visible effect. But for some modern devices, the test current is enough to actuate the lamp, either continuously (for LED lamps) or sporadically (for your flourescent lamp with an electronic ballast). For some LED Christmas lights that I was playing with on an X-10 controller, they were nearly as bright with the controller "off" as they were with the controller "on".


 * There are several solutions, none great:


 * Modify the intelligent device to remove the "test current" feature. This voids the warranty on the device, risks electrocution for you and the burning down of your house unless you know what you're doing, etc.


 * Use an intelligent device that doesn't include this feature


 * Use a relay as an intermediate control device. Same caveats as for modifying the intelligent device.


 * Atlant 14:14, 5 December 2006 (UTC)