Wikipedia:Reference desk/Archives/Science/2006 November 17

= November 17 =

Displacement of the Universe
When an object expands, it displaces something already there. If our universe is expanding, what is it displacing?


 * Is the universe an object? Melchoir 00:27, 17 November 2006 (UTC)


 * I would suggests that as it expands - it creates space - there for it displaces nothing. (any good?)


 * The universe is by (one) definition everything, so there is nothing outside it to be displaced. The problem here is that space as we perceive it in everyday life is not the same as what is at play here. Don't ask me to explain that, because it baffles me too. DirkvdM 09:32, 17 November 2006 (UTC)


 * My view is that space does not exist without mass. 8-|--Light current 16:36, 17 November 2006 (UTC)

I thank you for your answers; however, I do suggest that the universe is an object and that, as it expands, it has to displace something that is there. Does this mean that there is another universe?


 * No, it means your beliefs are not consistent with modern physics. — Knowledge Seeker দ 03:56, 18 November 2006 (UTC)


 * Which also goes for all the great scientists, but that's no guarantee .... :) DirkvdM 06:59, 18 November 2006 (UTC)


 * Like I said, there is by definition only one universe. When physicists speak of the universe they mean 'everything there is'. The word 'object' is a bit vague. I suppose you mean 'entity', which is really a mental construct (as is 'object', in a sense, for that matter) - whichever you wish to see as one whole is therefore an entity. Aanyway, I had a similar notion, but my conclusion was that the size of the universe is by definition fixed. The expansion of the universe is sometimes illustrated with a balloon with dots on it. When you blow it up, the dots all move away from each other. In kosmology, we notice that everything around us is moving away from us (apart from local movements), so an explanation for that, the reasoning goes, would be that we're part of an expanding 'balloon' (the universe). But how do you know the balloon expands? Because you compare it to its surroundings (it may also be that the room you're in is getting smaller, but that would be too complicated an explanation). But for the universe there are no surroundings, so its size has to be given (a constant), unchangeable. This eventually led me to my alternative to the Big Bang theory, but I doubt if that will clarify things for you. :) DirkvdM 06:59, 18 November 2006 (UTC)

I appreciate all your answers. Thanks.


 * Further to the answers here, consider an analogy: a two-dimensional universe like the surface of a sphere. If the surface gets bigger - like inflating a balloon - then the universe gets bigger, and things on the surface move further away from eachother. However from the point of view of the 2D people on the surface, it's not expanding into anything. There's just more space available. The thing to realise is that it's not just stuff extending out into the cosmos when the universe expands - it's space-time and reality itself. Stuff outside the universe by definition doesn't exist. Sockatume 17:30, 20 November 2006 (UTC)

Jupiter Explosion
I was wondering when Shoemaker-levy 9 crashed into jupiter why didn't the planet Explode?


 * The short answer is that the combined mass of the parts of SL9 were insignificant compared to that of Jupiter.Bunthorne 02:03, 17 November 2006 (UTC)


 * However, if the mass of SL9 had been moving at a speed close to the speed of light relative to Jupiter, far more damage would have been done. Fortunately, such large objects seldom move at those velocities, within our solar system. StuRat 02:23, 17 November 2006 (UTC)


 * Do they outside our solar system? DirkvdM 09:37, 17 November 2006 (UTC)


 * I believe there are higher speed objects outside the solar system, like ejecta from supernovae, yes. However, these objects still only move at a small portion of the speed of light. StuRat 09:49, 17 November 2006 (UTC)


 * Nope, the fastest objects (I mean large objects) in the universe only move at a few thousand kilometres per second. This is below 1% of the speed of light.  --Bowlhover 17:23, 17 November 2006 (UTC)

Perhaps you are thinking that the large quantity of hydrogen gas in the Jovian atmosphere should have ignited. This didn't happen because there isn't much free oxygen in the Jovian atmosphere, and oxygen is needed to burn hydrogen. StuRat 02:20, 17 November 2006 (UTC)


 * Could such a mixture exist for long anywhere? Any atmosphere would at some time have some sort of discharge setting it off, wouldn't it? Put differently, if such a mixture would start to build up, it would be ignited (again and again) before it ever accumulated to anything. DirkvdM 09:37, 17 November 2006 (UTC)


 * Yes, that's one reason why you only get free oxygen or free hydrogen in a planet's atmosphere, but never large quantities of both. StuRat 09:43, 17 November 2006 (UTC)


 * To add to Bunthorne's answer, the kinetic energy of Comet Shoemaker-Levy 9 was tiny compared to the gravitational binding energy of Jupiter. Cardamon 10:59, 21 November 2006 (UTC)

Greenhouse gases
What equipments must be need in order to measure the level of carbon dioxide in the air? How can you control the level of carbon dioxide? It is for a science project, so if anyone who know the answer to this question, please answer as soon as possible. —The preceding unsigned comment was added by 68.162.145.234 (talk • contribs).
 * For many applications, you can use a CO2 sensor, however they tend to be fairly expensive (in the hundreds to thousands of dollars). This sensor works with a TI calculator CBL (calc. based lab) unit.  You may want to ask if your school has some of these which they will let you borrow (or use in the lab).  If you're working with very gross measurement (pure CO2 versus air), you could use a flame to distinguish them (a flame will not burn in CO2, since it needs O2).


 * You can raise the CO2 level of a containter by adding CO2. Dry ice is CO2, just put it hot water and vapor will come off.  The vapor is a bit heavier than air, so you can manifpulate it by pouring the vapor into a container.  This would not give you very fine control over the amount, of course.  Lowering the CO2 level is a bit harder, since it is difficult to add a gas which is the same as air (O2, N2, trace gasses) excluding the CO2.


 * This seems like a fairly difficult project. What more specifically are you thinking of doing?  --TeaDrinker 04:27, 17 November 2006 (UTC)


 * A cheap but slow and probably fairly inaccurate method might be to see how fast a plant grows in that air. Of course, you'd have to calibrate this first, measuring the growth rate in known CO2 concentrations. Or use such measurements done by others and recreate exactly the same circumstances. DirkvdM 09:49, 17 November 2006 (UTC)


 * Growth rates might be even more trouble, since there is natural variablity in plants. Thus it would be necessaary to grow multiple plants in the same environment and average their growth rate.  It is further complicated by the CO2 used by the plants, since the conccentration will change with time.  Consideration of soil type, light availablity, watering, etc. would make this a difficult measurement.  --TeaDrinker 21:38, 17 November 2006 (UTC)


 * I think it's a novel idea. But it would only work while CO2 was the limiting factor in the growth of the plant. Note also that different plants take up CO2 with different mechanisms. E.g. see C4 carbon fixation. —Pengo talk · contribs 01:42, 18 November 2006 (UTC)


 * The other nutrients have to be standardised (that's part of the calibration), but that does not necessarily mean plentiful (although that will of course help). And it would have to be a very standardised plant (preferably all seeds being 'twins'), such as a highly cultivated plant. It would also help if it were a fast growing plant. Hemp comes to mind, but that might come with some legality problems. :) I suggest a narrow tube, barely wide enough to fit a seed in. Water at the bottom, with a standardised amount of nutrients dissolved in it, and air at the top, with the seed on the border between the two, possibly floating on a bit of oil (also to prevent the CO2 from dissolving in the water?), flooded in light (again standardised, so in a container to keep any other light out) and with an airtight lid on it. If the amount of air is very limited the plant will use the CO2 up quickly and stop growing at a certain point. The lenght of the seedling at that point (which can only expand in two directions because of the narrow tube, so the length is easily measured) is an indication of the amount of CO2. Do this a few times with known concentrations of CO2 (the calibration) and you've got an indication of the amount of CO2. Like I said, not too accurate and a bit slow (takes at least one day per sample), but cheap and easy. Oh, and you'd have to add some O2 (again, a fixed amount) to avoid that running out (which would be too limiting a factor :) ) That might be a bit more difficult (but not too difficult). Another option would be a clipping from one plant, but it would have to be a standardised type of clipping, which might pose a problem. DirkvdM 07:41, 18 November 2006 (UTC)


 * If you're looking for something cheap, I wonder if you could use Lime water and measure how cloudy it got? It might be tricky, and fairly inaccurate, to measure 'cloudiness' (maybe bubble the gas through a beaker with a sequence of marks underneath, of various 'blacknesses', and see which ones are still visible after a certain quantity of gas has passed through?). It should be doable with normal school lab equipment, though. Skittle 21:50, 17 November 2006 (UTC)


 * The cloudiness might be measured by shining a standard light source through it and measuring what passes through with a light sensor at the other side. DirkvdM 07:41, 18 November 2006 (UTC)


 * A photometer is a fairly common item. If your school has a photography class, they undoubtedly have light meters which may be useful in the manner suggested.  --TeaDrinker 08:39, 18 November 2006 (UTC)

Targeted Drugs
What are some the barriers that are impeded the development of targeted drugs? Since we know a specific protein looks like, what it makes so hard to design a molecule that will interact with that protein? --Wedgeoli 03:48, 17 November 2006 (UTC)


 * Of course, there are still all the barriers that all drugs face, like extensive animal and human test trial requirements. StuRat 07:48, 17 November 2006 (UTC)


 * If you know what a protein looks like, that doesn't mean you know how it does what it does and what would stop it doing that (or whatever your goal is) and when you do know that, that doesn't mean you can make that stuff (economically). And then what StuRat said. DirkvdM 09:53, 17 November 2006 (UTC)


 * The configuration of a molecule has a huge effect on the interactions between molecules. Biologists can look at a protein and say, "It's folded this way, which produces this effect," but it's very difficult to do the reverse: "I want a molecule that does THIS, so it needs to be folded thusly." Look at Protein folding. Secondly, a single type of protein chain can do a lot of different things in an organism. If you target a "bad protein," you may also be inhibiting the protein in good functions. sthomson 16:59, 17 November 2006 (UTC)

Memory foam outgassing
Anybody know what the stink that emanates from memory foam is? Will I grow a third hand from my forehead? Clarityfiend 04:53, 17 November 2006 (UTC)


 * That might come in handy (excuse the pun) if you've got the Sun in your eyes. DirkvdM 09:55, 17 November 2006 (UTC)


 * Some ventilation might be a good idea. What is the object ?  If it's a pillow, it's not going to be easy to avoid the fumes. StuRat 07:43, 17 November 2006 (UTC)


 * I developed a horrible skin rash when I first started using a memory foam mattress, though the jury's still out as to if it was the cause. I have no idea what the chemicals involved in the creation of the foam are, but they're probably not very healthy - I doubt they have significant mutagenic power, though. Most likely would probably be some nasal or dermal irritation. VirogIt's notmy fault! 08:43, 17 November 2006 (UTC)

It might be a good idea to let it outgas for a while in a garage or storage area, before using it. However, I suspect that flexing it will cause more fumes to be released. StuRat 09:38, 17 November 2006 (UTC)

Also, can you cover the item in a vapor-proof plastic ? StuRat 09:40, 17 November 2006 (UTC)
 * All new furniture and carpet has this problem. In office buildings they go through a special high-ventilation cycle for a while before allowing occupation. I'm quite sensitive to fumes, and didn't have any problems with my new Novaform mattress.  Perhaps some manufacturers pre-ventilate?  --Zeizmic 13:14, 17 November 2006 (UTC)

Any ideas/available products for simple intercom switch over POTS?
I'd like to rig something (if necessary) that can remotely communicate with a phone plugged into a POTS. The intercom system in my apartment building is a CC phone system. Visitors punch in my apartment number and my phone line rings. The thing is, I don't have land-line service (I use my cell phone), so this CC system is the only one accessible. Thus, a solution I have in mind would, by definition, not interfere with my usual phone habits.

I would like to have a small remote control (around the size of a car's remote keyless entry device) that I can clip to my belt. One button on this remote control would pick up or hang up the line. The triggered phone would be a speaker phone so I could talk without a handset. The other button would trigger the phone to send a touch tone signal and buzz the person in. So when the phone rang, I would hit the pick-up button, chat momentarily, hit the tone button, then hit the pick-up button again to hang up.

Does anyone know of anything like this available for retail? I thought that, if necessary, I could get one of those wireless doorbell things that supports multiple doorbell signals (for multiple buttons), and rig it to the phone somehow, but I'm not quite sure where to start.

Thanks! --Silvaran 05:37, 17 November 2006 (UTC)


 * Firslty Im not clear about your use of the word POTS. What you seem to have described is purely an intercom system for the building.
 * The first requirement could be met just by wiring a relay (in series with a holding coil) in parallel with the hook switch of your phone. THe relay would be activated by the remote (infra red, radio or, ultrasonic). THe phone would then operate as a speaker phone 8-).
 * For the second requirement you would need a tone generator to tbe connected to the line but not the telephone. Also at the front door, you would need a tone detector and solenoid system (if not already in existence) to operate the lock. One big problem is not interfering with other peoples intercom systems. Without a circuit diagram of the existing system, its difficult to say what the best solution is! 8-(--Light current 14:20, 17 November 2006 (UTC)


 * An electronics technician or electrical engineer could easily design a system to satisfy your needs. Please budget one man-month for preparing the proposal, designing and debugging the device, testing, and production of a final product in an attractive case, with user support. Edison 15:26, 17 November 2006 (UTC)


 * Exactly! I am available at cheap rates.! --Light current 16:11, 17 November 2006 (UTC)
 * The math is, two such qualified persons working together could have the device in your hands in about 2 weeks. Still one man month. Edison 23:07, 17 November 2006 (UTC)


 * The reason I said POTS is because it IS a plain old telephone system, not an intercom system. The panel at the front door stores code to phone number mappings (if you have phone service, you need to tell the superintendent your phone number so he can program it into the intercom system--you can even give a cell phone number if desired, but I didn't, for various reasons).  When you punch in the code, you hear the ring-out.  My phone rings (regardless whether or not I have service with the actual phone company), and I can hit 6 on the phone, the panel at the front of the building senses the tone and temporarily unlocks the door.  So I want a speakerphone with a remote control that can pickup/hangup and hit '6'. :) --Silvaran 18:50, 17 November 2006 (UTC)
 * PS: I'm not sure exactly what gets programmed into the panel when you don't have phone service, maybe an arbitrarily-assigned extension number.


 * What you are describing is a system attached to the PSTN that rings your phone when someone presses your doorbell? So your number is programmed in and it autodials your phone number. THe front door lock somehow must also respond to you dialling 6 on your phone. Yes?
 * Ah Now slightly more complex. As I said pickup/hangup is (probably) no problem. You say the phone is tone dialling so you need a DTMF chip that will generate the dual tone for '6'. You connect the o/p of your remote control Rx to the '6' pin on the chip and send it through the phone microphone. You can do this easily if its a speaker phone. No need to wire stuff inside the phone. Tell me if I ve understood your problem correctly.--Light current 19:12, 17 November 2006 (UTC)
 * It is the "slightly more complex," that runs up the manhours to a high multiple of what you would at first expect. Edison 23:07, 17 November 2006 (UTC)


 * Yup that's pretty much it. If I get a barebones speakerphone and take it apart, is it somewhat reasonable to hook up some kind of remote control to it? (to the talk/hangup button on the speakerphone, let's say, as well as the 6 key).  IR would likely be the easiest, though for obvious reasons, RF would be more convenient.  Only thing would be choosing a simple remote control (maybe one of those pedestal fans with the remote controls), and then integrating the Rx thingy on the fan to the mechanics in the speakerphone (or PCB?  Not sure when those became popular in phones). --Silvaran 19:25, 17 November 2006 (UTC)


 * Seems reasonable technically as long as the phones has got switches you can connect to. However, there may be some FCC or telephone company rules that say you cant connect anything you like (such as modified phones) to the telephone network without approval. We have such rules in UK --Light current 19:53, 17 November 2006 (UTC)
 * Well I'm not looking to violate any laws here (presumably I'm under CRTC jurisdiction here in Canada) and at the same time, my telephone jack isn't connected to the public telephone system. For the time being I'm going to grab myself a sub-$30 speaker phone and a cheap remote-controlled fan (which seems to have a minimal remote control that functions via IR) and see what I can make from that... with the right tools and some very, very careful (*cough* solder) modifications :).  I appreciate everyone's input.  I only wish I had the funds to support a more reliable development method (right Light current? :). --Silvaran 07:37, 18 November 2006 (UTC)

This may be a silly idea but why can't you buy a cheap cordless phone and plug it in instead of your speaker phone. You could then take the cordless phone with you and answer and press 6 from where ever you are! I presume you have cordless phones in canada - you know phones where you plug a base station in and then carry the handset around.


 * Hmm doesnt seem silly to me unless Im missing something. Perhaps Silvaran doesnt want to carry a large cordless around the house?--Light current 01:05, 28 November 2006 (UTC)


 * My question is why no one questioned who has access to telco lines, who might be listening in on private conversations via the buzzer/intercom system??   Oh, yeah cordless phone seems to meet the "K.i.s.s." specification.

physics
Why weight(force) is expressed in mass units(Kg)?


 * Because mass is universal, while weight varies depending on the force of gravity in your location. StuRat 07:40, 17 November 2006 (UTC)


 * For historical reasons. The SI unit is the newton (N). --Lambiam Talk  08:28, 17 November 2006 (UTC)


 * Without acceleration, either in the form of gravity or in the form of a change in velocity, mass has no weight. Weight is a type of force. Force=mass times acceleration.  Gravity produces an acceleration of about 9.8 meters/second squared, so a 1 kilogram mass acquires a weight of 9.8 kilogram meters per second squared, which is 9.8 Newtons at rest in earth's gravity. Weight is a vector force which is proportional to gravity and to mass. On Mars, where gravity is 3.3 m/s^2, the same object would only weigh 3.3 N. Edison 15:35, 17 November 2006 (UTC)


 * Weight should be expressed in Newtons. However, it's sometimes expressed in kilograms because it's easier to imagine.  Not many people know what a newton of force feels like, but most people know how heavy a 1 kg object feels (since kg is a more well-known unit).   --Bowlhover 17:11, 17 November 2006 (UTC)


 * A Newton is approx the force exerted on you by one standard (100g) apple when placed on the top of your head!--Light current 00:51, 28 November 2006 (UTC)

Original research or not?
What strikes most people about Einstein’s equation is how much energy can be derived from such a small amount of mass. What strikes me is how little mass it takes to contain so much energy. How is this possible? What must energy and mass be doing that connects them by the velocity of light squared? Velocity is the same distance an object travels in the same interval of time while velocity squared is the acceleration or deceleration or the change in distance or direction an object travels in the same interval of time. If I hit the gas and go from 0 to 60 mph then my velocity will change at a faster and faster rate. Oddly enough if my velocity remains the same and I change my direction acceleration will also occur. Go figure! Mathematically acceleration can be represented by mass/distance traveled per unit time/distance traveled per unit time or the rate of change in velocity of unit mass. Since acceleration also occurs when the direction of travel of a mass changes a mass that is traveling at a constant velocity but say in a circle is accelerating. The directional vector of acceleration (not to be confused with the direction of travel of the mass) in the case of circular travel is at right angles to the direction of travel of the mass. Now consider that instead of the acceleration of mass we have the acceleration of energy. (is such a thing even possible?) i.e., energy/distance per unit time/distance per unit time. In other words energy traveling in a circle. According to Einstein’s equation then it would appear that matter is nothing more than energy traveling in a circle at the speed of light, i.e. energy/distance light travels per unit time/distance light travels per unit time. That is that mass is simply and profoundly energy (traveling in a circle) at the speed light. Adaptron 08:43, 17 November 2006 (UTC)


 * Technically, if you integrate velocity, you get $$1/2 * s^2$$. If you hit the gas and go from 0 to 60, your velocity shouldn't change at a faster and faster rate unless your acceleration increases. Else it's a constant rate. If you change directions, of course velocity as a vector will change, but the magnitude doesn't change. And no, energy don't accelerate, and electrons do have a mass. But wait, what's the question? --Wirbelwind ヴィルヴェルヴィント (talk) 09:11, 17 November 2006 (UTC)
 * In the above, with respect to what are you integrating velocity, and what does $$s$$ stand for? --Lambiam Talk  09:30, 17 November 2006 (UTC)
 * velocity. I think I recall learning physics using d, s, and a for distance, velocity, and acceleration, and v was used for something else. But I'm also an electrical engineer, and v was probably just replaced since it's used for voltages, just like I use "j" for imaginary instead of "i" (i is used for current). --Wirbelwind ヴィルヴェルヴィント (talk) 21:42, 17 November 2006 (UTC)


 * Let's try to clarify to avoid any possible misunderstanding here. When you integrate velocity with respect to time, you get displacement. This is not usually the same as distance travelled. However, in the special case of an object accelerating from rest with a constant acceleration a, then the displacement (or, strictly speaking, the magnitude of the displacement vector) does happen to equal distance travelled, because in this case the velocity vector and the displacement vector are always parallel. In this special case, if velocity after time t is v then


 * $$v=at$$
 * $$distance=|displacement|=\int_0^tv\,dt=\frac{at^2}{2}=\frac{vt}{2}=\frac{v^2}{2a}$$


 * (although this has become not very relevant to the original question). Gandalf61 14:08, 17 November 2006 (UTC)


 * Yes, it is original research unless you can cite a source. As far as I can tell (and I happen to know a bit about relativity) it is also a strange mix of speculation, incorrect statements, and phrases I can't parse at all.  If you want to learn about relativity, please see the Introduction to special relativity. Do you have a question other than whether the above is original research? -- SCZenz 09:38, 17 November 2006 (UTC)

Is matter simply energy that is "locked" or "trapped" into circular or spherical direction at such a high velocity (i.e., the velocity of light which is beleived to have special effects on matter BTW, i.e., expansion) that energy in this state actually acquires all of the properties attributed to mass, i.e. gravitation, etc.? 71.100.6.152 11:27, 17 November 2006 (UTC)

Meh I stopped reading when, of the first three premises he states, the second is outright false (c2 is in m2/s2 not m/s2) and the third is not necessarily true (constant-acceleration, linear velocity increase is possible too). DMacks 14:08, 17 November 2006 (UTC)


 * How then does one account for such a large amount of energy being contained in such a small space? 71.100.6.152 14:56, 17 November 2006 (UTC)

Whoever said that energy has to take up space? You're incorrectly assuming that the concepts of objects and masses and kinetic energy as you're familiar with them from experiences on a macroscopic scale are the complete and true picture on all scales and for all more precise meanings. The Mass in special relativity page might be useful. DMacks 16:32, 17 November 2006 (UTC)

Excellent - "That is that mass is simply and profoundly energy (traveling in a circle) at the speed light" - but space is three dimensional so shouldn't that be a sphere? - If you can explain the 'motion' then I will surely give you a big prize. Keep up the good work...


 * Energy propagates in a linear direction (light for instance) as an electromagnetic wave which some think may be the result of a "leap frog" effect, if you will, of magnetism and electricity. Simply replace linear propagation with spherical propagation such as in a dog chasing its tail only with an infinitesimal circumference at the speed of light. (BTW please sign you comments.) 71.100.6.152 17:19, 17 November 2006 (UTC)
 * Thanks for your reply - but - the dog chasing its tail analogy is like a spinning disc and therfore still 2 dimensional - even if the circumference is reduced to infitessimally small or zero - please try again. Hope I have explained what I am asking for87.102.13.221 17:25, 17 November 2006 (UTC)


 * Think Ferret and spherical. However, at infinitesimal spherical circumference electric and magnetic lines of force may overlap the entire diameter of the sphere and exist and interact in lock step sufficient to be what we call mass. 71.100.6.152 18:26, 17 November 2006 (UTC)
 * I didn't really understand 'ferret and spherical'.


 * Ain't you never been in a pet shop where they have Ferrets on display??? Man you are missin' somethin'!. Them raskles can sure put on a show. Why they roll and turn and whatnot in so many different directions you can't see nothin' but a ball a fur. You need to get a life man. 71.100.6.152 19:39, 17 November 2006 (UTC)


 * Doesn't changing the orbital plane require a force acting in a direction other than "towards the center"? Centripetal acceleration would seem to keeps something moving only in a single flat circular orbit, so the analogy of someting moving "all around the center" (in 3D) is mis-applied I think. Again, relativistic physics and subatomic particle interactions are not just gravitational planetary motion or electrostatics writ small. DMacks 22:53, 17 November 2006 (UTC)
 * Humm... Seems like you are the one attempting to apply Newtonian to relativistic physics at the subatomic level. However, since acceleration is a vector force the directional might certainly deviate fron center or consider this: the center might thereby be constantly redefined. 71.100.6.152 20:31, 18 November 2006 (UTC)


 * As I understand it the 3d analog of 2d rotation is chirality? - anyone here who can expand on that?87.102.21.223 23:01, 17 November 2006 (UTC)


 * See Magnetic helicity. 71.100.6.152 15:57, 19 November 2006 (UTC)

_________________

Great discussion! I believe Einstein considered matter and energy to be the same thing. You may be interested in reading another debate about this here:

http://www.physicsforums.com/showthread.php?t=157836

I'm inclined to agree with you my friend. Keep up the good work!

A quote for inspiration: "Since the theory of general relativity implies the representation of physical reality by a continuous field, the concept of particles or material points cannot play a fundamental part, nor can the concept of motion. (Albert Einstein)

Posted by V.Giles

59.100.58.235 03:15, 1 March 2007 (UTC)

Levitating pens
According to Earnshaw's theorem, it should be impossible for a an array of permanent magnets to cause stable levitation. How then does the novelty magnetically floating pen and holder system work? --Light current 12:37, 17 November 2006 (UTC)

Add quote from page: ''This theorem also states that there is no possible static configuration of ferromagnets which can stably levitate an object against gravity, even when the magnetic forces are stronger than the gravitational forces. There are, however, several exceptions to the rule's assumptions which allow magnetic levitation.'' --Light current 14:08, 17 November 2006 (UTC)


 * What floating pen? Have you been drinking?


 * WP:AGF 8-))--Light current 14:04, 17 November 2006 (UTC)


 * He probably means something like this. They are a novelty pen for businessmen. --24.147.86.187 13:40, 17 November 2006 (UTC)


 * There is also gravity involved, besides the magnetic field. --Dementios.


 * I know gravity is involved! 8-)--Light current 14:03, 17 November 2006 (UTC)


 * Yes that link does show the sort of thing. especially the horizontal version--Light current 14:03, 17 November 2006 (UTC)


 * By the looks of things the magnets used are curved into a sort of cup and ball shape (like our shoulder joints) and there might be some magnets on the side of the inner bit which are helping stabalise it. I'd bet that the pen will only stay still if it is orientated a certain way (perhaps when you put the pen into its cradle it will spin to the correct position before it has time to fall over). Doesn't Earnshaw's theorem only work for magnets in a straight line (like MagLev), not curved magnets? RevenDS 14:07, 17 November 2006 (UTC)


 * It's possible that the pen itself is magnetic too, with the effect only working with pen aligned so that it has the same polarity as the magnets. Earnshaw assumed that all the forces involved were attractive, since this would cause positive feedback and drag the pen even the nearer the edge, causing even more feedback etc due to our good friend Inverse square law. Adding repulsive forces into the mix too means that you get some negative feedback, so the pen enters equilibrium. La  ï  ka  17:12, 17 November 2006 (UTC)


 * Well yes Im pretty sure the pen has magnets in as well.--Light current 21:22, 17 November 2006 (UTC)


 * See Magnetic_levitation

These are all terrible answers. Earnshaw's theorem definitely does apply, no matter what shape the magnets are, and no matter whether they attract or repel. You can't do it. The pen in the picture isn't actually levitating, it's just standing on its point. —Keenan Pepper 05:23, 18 November 2006 (UTC)


 * Not quite true; diamagnetic materials such as Pyrolytic carbon can levitate in a constant field. La  ï  ka  11:16, 18 November 2006 (UTC)
 * What about the horizontal one?--Light current 17:31, 18 November 2006 (UTC)


 * Keenan is right, the pen is not levitated, it's tip is firmly stuck in a hollow in the base, the barrel being held upright by magnetic repulsion. While on its side ,it is lying flat, not levitated. And yes, since a diamagnetic substance is not a "classic" magnet, Earnshaw would not apply. Seejyb 22:55, 18 November 2006 (UTC)


 * You obviously have not seen one in reality! 8-|--Light current 23:28, 18 November 2006 (UTC)

Just a thought: I don't think that only magnetic and gravitational fields are at play here. There is also a mechanical stress in the body of the pen, as the magnetic forces do not apply equally to every mass element of the pen; some parts of the pen are ferromagnetic while others are not, and some parts of the pen experience stronger external magnetic field than the others. The version I saw (a toy rather than a pen, but it works the same) definitely had substantial variations of magnetic field strength across its base. Stress and strain do not obey inverse-square laws. That makes the Earnshaw's arguments inapplicable, I think. --Dr_Dima.


 * No, it doesn't. Stress and strain don't affect objects that aren't touching each other. You can't levitate something with only ferromagnets, period. —Keenan Pepper 21:35, 19 November 2006 (UTC)


 * Keenan, I said stress and strain in the body of a pen, not between the pen and something else. The pen is not touching anything else, that's the whole point. And, yes, in the version I saw the "pen" wasn't touching anything else, it was levitating proper. --Dr_Dima


 * So, if it's only in the body of the pen, how in the world does it make it levitate? What force is pushing it upward? You're not making sense. —Keenan Pepper 17:10, 20 November 2006 (UTC)


 * I've seen the kind of pens you're talking about: the pen is horizontal above a sort of valley-shaped stand. The pen only levitates when you spin it along its axis, which might have something to do with it. Sockatume 17:34, 20 November 2006 (UTC)


 * The magnetic field forces the pen up, where it would levitate according to Earnshaw's Theorem were it not for it being pushed into some kind of barrier, as happens in most of these types of pens. Thus the vibrations are countered for in the reaction force of whatever the pen is touching. --86.139.127.29 21:55, 20 November 2006 (UTC)

How do you create mass from energy?
So, how?

Collide two high energy particles together, and sometimes you get extra particles. JBKramer 13:49, 17 November 2006 (UTC)


 * Just get in your car and accelerate. Per Einstein’s Special Theory of Relativity, what we call energy and mass are two ways of measuring the same thing. Every type of energy has mass, and each mass is a form of energy. Energy = mass time the velocity of light squared. When you burn a liter of gasoline, the mass of the combustion products will be slightly less than the mass of the gasoline. The missing mass, (in an amount too small to measure with a lab balance), was converted into energy. The car, having accelerated, will have more mass than it had at rest. A truck with a 10,000 kg mass is accelerated from rest to 30 m/s. The increase in Kinetic energy=1/2 m*v^2, or 1/2(10000kg)(30m/s)^2=4500000 Joule. The amount of energy turned to extra mass in the truck is m=kinetic energy/c squared=4500000 Joule/((3*10^8 m/s)^2)=5*10^ -11 kilogram, or .00000005 gram, or .00005 microgram. That mass would be undetectable in a 10,000 kg truck, but it would be mass created from energy. Edison 16:01, 17 November 2006 (UTC)


 * Are you sayin' that by using fossile fuel we are not only making the Earth more polluted but heavier too or should we just blame the sun for sending us energy that will eventually make the Earth heavier too? 71.100.6.152 19:10, 17 November 2006 (UTC)


 * You can't make the Earth heavier without adding anything to it. That's true in relativity as well as common sense. —Keenan Pepper 05:28, 18 November 2006 (UTC)


 * Endothermic reactions? (Not sure, but seems to make sense.) DirkvdM 10:18, 18 November 2006 (UTC)
 * I wonder how many useful contributions to the reference desk this user (DirkvdM) has done. —The preceding unsigned comment was added by 85.50.46.191 (talk • contribs) 11:43, November 19, 2006 (UTC)


 * Loads, I'm sure. :) DirkvdM 09:33, 20 November 2006 (UTC)

When you use fossil fuels you are not changing the mass of the earth - the energy (aka mass) is already there, you are just converting it from potential energy to heat.

To answer the original question: mass IS energy. And vice versa. If you are asking how to convert mass into a particle: gamma rays of the right frequency will spontaneously change into electron positron pairs (and potentially right back into gamma rays). If you place the pairs in a magnetic field, you can cause them two to separate, leaving you with two particles.

The biggest difference between 'mass' and 'energy' (as they are commonly defined) is their quantum numbers (spin, charge, and various others). Energy has 0 for the numbers, while mass has a non-zero value. To get a non-zero number from a 0, you need to create two particles with opposite numbers (that add up to 0). (I'm simplifying quantum numbers a bit here.)

See the article on Pair production.

Ariel. 09:04, 20 November 2006 (UTC)

Why does spin-stabilisation work?
The article about it is so helpful it might as well not exist - Dammit 13:47, 17 November 2006 (UTC)

Gyroscopic action. See gyroscope. JBKramer 13:48, 17 November 2006 (UTC)


 * Should this article exist or be merged with gyroscope?--Light current 14:06, 17 November 2006 (UTC)


 * I assume the generic term is spin stabilisation (or is that 'gyroscopic action'?). A gyroscope uses it, so could be merged into it. But it's such a broad subject that it merits its own article. It is also used for some (most?) spacecraft and I wonder if that is meant by 'rockets', but that's a different thing. Or is it also used for rockets? Another example the stub mentions is bullets. And then there is the stabilisation of a bycicle by the rotating wheels (although I remember hearing that that is not really the reason a bike stays upright). Any more examples? DirkvdM 10:28, 18 November 2006 (UTC)

Prilosec (medical question)
I read the page on Prilosec already, but I had a question not answered there. I know I shouldn't be asking a medical question without asking a doctor and all that, this is more curiosity:

Why is it that when Prilosec was made available OTC, there are all sorts of warnings that it can only be taken for 14 days every 4 months. Does the doctor normally do some sort of liver/stomach test to see how you are doing on it? I know plenty of people pretty much take it once a day for years. Namlemez 15:22, 17 November 2006 (UTC)


 * I don't know about Prilosec specifically, but one of the usual concerns about anybody self-medicating for a long period of time is that they may be concealling or ignoring symptoms of some more-serious underlying disease (in Prilosec's case, such as an ulcer or stomach cancer).


 * Atlant 16:59, 17 November 2006 (UTC)


 * Also, increasing the pH of the stomach can allow microbiological growth. By alternating between periods of high and low acidity, gastric bacteria are less likely to grow out of control.Tuckerekcut 19:00, 17 November 2006 (UTC)

casimir like effects
Now i know that this effect is touted by any load of free energy nutballs out there that wanna make a quick buck, but have gone on the NASA site and found that they are looking into it seriously for propulsion [however they think tapping it for free energy is impossible and dangerous to even try]. According to a physics website on an article called "the casimir effect: a force from nothing" it claims that the zero-point energy field is pushing in on us all the time and that if enough of the zero-point energy field is imbalanced [so far as i understand by making the cavity between to plates unable to hold larger EM waves] the pressures on the outside of the mirrors or diveders is more than on the inside and the plates are pushed together. Apparently at micron distances apart the pressure is as much as one atmosphere [just over 1 kg per cm2] thats alot of pressure pushing in every direction, my first question is why do we not feel this pressure on us? secondly the casimir effect seems to suggest that the zero-point field acts almost like water or air pressure, [similar effect with imbalances of pressure] apparently NASA wants to create a method of propulsion that makes a certain area of the zero-point field resonate at a higher frequency thus more pressure on one side of the object, this pressure propells it. We can do the same with air and water [fans, airoplane wings, etc] What methods does anyone know of that could possible do this or are any known. The institute for advanced studies in Austin thinks that maybe a disturbance of the correct kind in the ground state of an atom would create such a resonance. Any othere ideas? Robin
 * The casimir effect has an excellent article on Wikipedia. JBKramer 16:24, 17 November 2006 (UTC)


 * You mean Wikipedia has an excellent article on the Casimir effect. :) DirkvdM 10:31, 18 November 2006 (UTC)

Indeed but while it says everything it says above in a longer and more scientific fashion it gives no hint as to other methods to cause energetic equilibrium distruptions of the kind i have mentioned and the kind that NASA are in search of. Robin


 * This is a reference desk. The article actually mentions other similar effects - waves and ships, for instance. If you want to talk about hypothetical zero-point energy generators, there are numerous message boards for such. JBKramer 18:30, 17 November 2006 (UTC)

I don't see how you could take advantage of a constant pressure to create movement. The examples you gave do not. A fan/prop uses supplied energy to move the medium. A wing converts forward thrust (provided by engines) into lift. So, in both cases, outside energy is needed, and that's what actually provides the propulsion. However, if there are waves or currents in this zero-point energy, then it may be possible to derive movement from these, like a feather blowing in the wind, water currents, or solar wind. Also, if there are differences in zero-point energy pressure from one point to another, that could possibly be used to move to the low pressure areas, but some other propulsion method would be needed to move to high pressure areas. StuRat 20:11, 17 November 2006 (UTC)

indeed there are waves in the zero-point field, the casimir effect proves this because it works on radiation pressure, that implies resonance in the field and therefore waves throughout it, what one would need to do is to make a section of the zero point field behind something resonate at a higher frequency thus imparting more pressure [like sound in the air] or reduce pressure in front of an object [like the top of an airoplanes wing] to move things, and the distribution and acting of the zero point energy field seems to be much like air pressure [though nothing like it in make up]. it is however electromagnetic so creating waves in it would be much more difficult than making waves of air etc my question was does anyone know of any methods that produce waves in normal EM fields that may work on the zero point field? sorry i did not ask that properly, i was in a rush when i made the last post Thank you Robin.

Feeling a cold coming on
I woke up this morning with the ominous sore throat associated with upcoming colds. Other than stock up on medicines, is there anything else I can do now that I know it's on its way? I won't be taking anything here as firm medical advice, but it probably isn't serious, just a little foreboding. Thanks. 70.50.103.86 16:48, 17 November 2006 (UTC)


 * Ginger is very good for cold symptoms.--Light current 16:55, 17 November 2006 (UTC)
 * I usually get a half-dozen of these feelings per year, before a real cold strikes. If you have the time, take a dose of ibuprofen, and go to bed for the day, and you should be able to fight off a half-dozen of these, before a real cold strikes... --Zeizmic 16:57, 17 November 2006 (UTC)


 * Some people recommend zinc lozenges to treat the common cold. Others feel that When left to its own devices, a cold will run a week to a week-and-a-half, but when aggressively treated, it will only last seven to ten days.


 * Atlant 16:57, 17 November 2006 (UTC)


 * No, no. Thats six of one and half a dozen of the other!--Light current 17:02, 17 November 2006 (UTC)


 * Eat,eat,eat,eat. That's the cure. Oh but if you've got a cold coming on maybe you don't feel hungry? Oh dear.


 * I second Zeizmic. The best thing you can do is help your immune system, and you can do that by sleeping (not just resting at home), eating healthy food (if you're hungry) and keeping well-hydrated. Also, I've sometimes had success with gargling with hydrogen peroxide, and flushing my nasal passages with hot(tish) salt water. Also, even though you may be already infected, practice good hygeine; wash your hands often with hot soapy water, and refrain from touching your mucous membranes. Anchoress 17:49, 17 November 2006 (UTC)

Linus Pauling advocated megadoses of Vitamin C, but I don't personally see any value in this approach. StuRat 19:35, 17 November 2006 (UTC)


 * Yeah but he died!--Light current 20:02, 17 November 2006 (UTC)


 * Yes, at age 93... --Anon, 23:30 UTC, November 17.


 * And he got two Nobel Prizes - can anybody around here top that? Btw, a person's achievements are not rendered valueless when they die.  :)  JackofOz 00:58, 21 November 2006 (UTC)
 * Raw garlic is supposed to be good for it too, since it naturally anti-bacterial / anti-fungal. In Eastern medicine, ginger helps because it has yang properties. Other Eastern beliefs include the white part of oranges, but I never found that to work. --Wirbelwind ヴィルヴェルヴィント (talk) 21:36, 17 November 2006 (UTC)


 * A friend of mine swears the cure for a sore throat is to drink a little whisky, with a drop or two of honey added to it. One time, feeling a cold coming on, I tried her remedy.  The next morning I wasn't feeling very good at all.  She said I must have overdone it (which may have been true).  I asked her what healing properties the honey added to the whisky, wondering what strange medical principle was at work... she replied "Nothing... it just makes the whisky taste better!"  192.168.1.1 3:20pm, 17 November 2006 (Hic!)


 * Honey does help allergies by introducing pollen into your system. One natural way of helping allergies is consuming locally produced honey. However, honey has to be medicinal if it never spoils (it kills most bacteria by crenation, according to honey). --Wirbelwind ヴィルヴェルヴィント (talk) 01:59, 18 November 2006 (UTC)


 * In my own experience, stress and lack of sleep were often the precursors to infections such as tonsillitus and strep. Not sure of the common cold, but drinking fluids and getting plenty of rest never hurts. Edison 23:15, 17 November 2006 (UTC)


 * OK then.

--Light current 00:34, 18 November 2006 (UTC)
 * Lots of food,
 * lots of liquid
 * painkillers
 * ginger
 * garlic
 * hot milk with whisky
 * lots of sleep
 * any more?>


 * Yes, you'll need a twist of lemon! 192.168.1.1 5:14pm, 17 November 2006 (PST)


 * A good long soak in a hot bath relieves stress, achy muscles, congested respiratory tract, and helps you get ready for sleep. -THB 05:02, 18 November 2006 (UTC)

Self induced Insanity - is it possible?
Is it possible to make yourself insane by continuously acting as if you are all the time. This was an escape plan during WW2 from Colditz castle I believe (TV series).--Light current 16:54, 17 November 2006 (UTC)
 * Can you explain - what is "acting as if you are all the time". Please.
 * It means even when you think no one is watching (they are) 8-)--Light current 18:47, 17 November 2006 (UTC)


 * Are you sure this wasn't meant to send the german guards insane - it's having that effect on me>
 * It could have had theat side effect, yes. But German guards were not sent home, they went to the russian front instead where it helped to be insane. 8-|--Light current 19:15, 17 November 2006 (UTC)


 * Does this mean 'acting as if one is insane to make oneself insane"? If so - how does this help me escape from colditz? This is a total mystery.


 * Maybe one can be brainwashed to think that he is insane. Assuming self-brainwashing is possible, self-induced insanity would be very possible. Basically, if you constantly tell yourself that you are insane, then you will subconsciously believe that you are insane, and you will start to act insane...I think. Also, if the brain believes that insanity is necessary to survival, there is a good chance that it will self-induce it...I think. Anyway, this is all speculation. Studying the works of Freud could be helpful. --Naferius 17:41, 17 November 2006 (UTC)


 * If British officers went insane the Germans would take pity on them and send them back to Britain on sick leave! Strange but true! 8-)--Light current 18:53, 17 November 2006 (UTC)


 * Studying Freud could be helpful if you want to know the answer, or if you want to become insane?
 * Anyway, this sounds very doubtful to me. In the United States, it's forbidden to execute the insane; the claim is that it's "cruel and unusual punishment" if the convict doesn't understand what's going to happen and why. (I'm against the death penalty, personally, but I've never followed the reasoning there -- seems to me that knowing what's going to happen, and why, is a major part of the cruelty of it.) Anyway, as far as I know no one has managed to make himself insane to take advantage of this. The closest thing that's happened is that prisoners on anti-psychotic meds will refuse to take them, hoping to become too insane to execute, but that doesn't work unless you need the meds in the first place. --Trovatore 17:52, 17 November 2006 (UTC)


 * Just wondering if it is possible to become a genius by brainwashing myself :-) --WikiCheng | Talk 18:12, 17 November 2006 (UTC)


 * "... and then I decided I was a lemon for a couple of  weeks.  I kept myself amused all that time jumping in and out of a gin and tonic." - Arthur cleared his throat, and then did it again. - "Where," he said, "did you ...?" - "Find a gin and tonic?" said Ford brightly. "I found  a  small  lake  that thought  it  was  a  gin and tonic, and jumped in and out of that. At least, I think it thought it was a gin and tonic." (LTAE) -- 201.48.104.76 18:17, 17 November 2006 (UTC)


 * Erm..no. That requires intelligence and education primarily. But you can make your mind more receptive to learning by self hypnosis. 9-)--Light current 18:49, 17 November 2006 (UTC)


 * I can't help but think of Hamlet. For those who haven't read it (or only scanned the notes), when he is confronted with the idea that he may be crazy (since he was talking to his father's ghost), he wonders if he is crazy or if he is just acting crazy.  If he is just acting, will it end up that he is to be crazy.  To be or not to be.  So, you can see that this is not a new question and - coming from so long ago - I doubt it is one that can be answered. --Kainaw (talk) 19:47, 17 November 2006 (UTC)


 * Hmmm! 2B or not 2B That is the question eh?--Light current 19:55, 17 November 2006 (UTC)


 * A psychology professor said that in several cases in the mid 20th century a sane person had him/herself committed to an insane asylum to do investigative reporting, to get material for a book, or to investigate conditions inside for the government. In each case, within a day or two they decided that their families, co-workers or bosses had actually had them committed for real and no one would be getting them out after a short stay as planned. The point was that if you weren't insane when you went in, you would be shortly. That was a few years back. Now mentally ill people generally get put on powerful antidepressants, antipsychotics, or other psychoactive drugs, and once they are stable they generally get discharged in a very few days. There have been novels where someone decides to pretend he is insane, but turns out to really be insane., The implication is, if one decides to act as if he is insane, well maybe he is. The counterexample would be "crazy like a fox" as when a mobster pretends to be senile to avoid being tried. Edison 23:23, 17 November 2006 (UTC)


 * The pretend to be insane and go insane was not from Colditz the prisoner of war camp but from Colditz (TV series). See how easy the reality barrier breaks down? meltBanana 23:39, 17 November 2006 (UTC)


 * Yes I know it was from the TV series. What do you think I am -- insane? 8-)--Light current 00:24, 18 November 2006 (UTC)


 * It is still a mystery if Rudolph Hess really was crazy or just pretended to be. I believe he started acting ever stranger, so it might be that it was an act that made itself true (self-fulfilling behaviour?). DirkvdM 13:16, 18 November 2006 (UTC)

Didn't the NAZI's summarily kill people they felt to be insane? Would this not have been a reason for Hess to leave Germany (if he thought himself insane) and also for his English hosts to keep him hidden (locked) away presumably in the bowls of an asylum? 71.100.6.152 16:18, 19 November 2006 (UTC)

Transmission of infrared, light and others
Does someone know why:


 * steel blocks light but not infrared,
 * vacuum blocks infrared conduction and convection.
 * glass blocks UV but not visible light

Why do some materials block specific kinds of electromagnetic radiation? Mr.K. 19:50, 17 November 2006 (UTC)
 * Steel reflects light and infrared? Infrared does not go through steel.
 * Vacuum allows infrared through - there's not convection because there are no gases in a vacuum to convect.
 * Vacuum allows infrared radiation, but not conduction or convection. Mr.K. 20:11, 17 November 2006 (UTC)


 * Third question more difficult...


 * But, this is not the point. The point is why.Mr.K. 20:12, 17 November 2006 (UTC)
 * OK first point - not true - no answer then.
 * second point - both conductance and convection depend on the matter conducting and convecting - in a vacuum there is no matter - hence no conduction or convection.
 * Still no answer to yuor third point.


 * See reflectance transmittance and absorbance--Light current 19:59, 17 November 2006 (UTC)


 * Well, it does not tell why steel absorbs light but glass do not. —The preceding unsigned comment was added by Mr.K. (talk • contribs) 20:13 18 November 2006  (UTC)


 * The article doesn't, but following some links does. In a nutshell, steel has a better absorption than glass at visible frequencies. VirogIt's notmy fault! 20:25, 17 November 2006 (UTC)

See plasmon frequency--Light current 20:30, 17 November 2006 (UTC)


 * Your example about vacuum is unrelated: conduction and convection are not forms of radiation, but rather behaviors of matter. Vacuum, not being matter, doesn't participate.  As for electromagnetic radiation, and why opacity is frequency-dependent, for metals see plasma frequency and for other solids see band theory.  In short, different varieties of light have different energies per photon and thus interact differently (or, in some cases, not much at all) with the electrons in a substance.  Alternatively, you can talk about how well the electrons can absorb energy delivered at a certain frequency, considering the incoming light to be continuous.  In a metal, below its plasma frequency, the electrons move so well with the incident light that they reflect it nearly perfectly; in many other solids, only certain energies of photons can easily be absorbed and propel an electron into a higher band.  Does that help?  --Tardis 20:50, 17 November 2006 (UTC)


 * This plasmon theory is new to me - I've been explaining reflectance and other properties of metals (as well as other solids) using band theory for a long time - plasmon theory seems little more than a extension of band theory - (just poking my nose in)


 * You should be able to find pictures taken at different wavelengths. For example, microwaves are stopped by glass (meaning if we see in the microwave spectrum, glass will look like a solid wall that lets nothing through). On the other hand, if you take pictures in the x-ray wavelengths, it goes through human flesh and takes lead to stop, and I'm sure you've seen x-ray photos. But yes, plasmon frequency is where you'd want to look. --Wirbelwind ヴィルヴェルヴィント (talk) 21:32, 17 November 2006 (UTC)


 * If microwaves are stopped by glass, how am I able to cook food in a covered glass dish in the microwave oven?Edison 23:26, 17 November 2006 (UTC)


 * Microwaves are not stopped by glass. Thats why you need the metal mesh in the door!--Light current 00:26, 18 November 2006 (UTC)


 * Oops, I must have remembered wrong, or was taught wrong. "The cooking chamber itself is a Faraday cage enclosure which prevents the microwaves from escaping into the environment. The oven door is usually a glass panel for easy viewing, but has a layer of conductive mesh to maintain the shielding. Because the size of the perforations in the mesh is much less than the wavelength of 12 cm, the microwave radiation can not pass through the door, while visible light (with a much shorter wavelength) can." --Wirbelwind ヴィルヴェルヴィント (talk) 01:52, 18 November 2006 (UTC)


 * Correct!--Light current 02:14, 18 November 2006 (UTC)

Sugar mites?
I keep finding tiny (less than 1mm width, maybe 2mm length) creatures in my sugar bowl - they're pale cream color. What are they, where are they coming from?, how do they get in the bowl? I clean it out and they're back in a few days - how do they find it - can they smell sugar? (The bowl has a lid but they still get in). Is it possible for a creature to exist entirely on white sugar?. They are very small but look a bit like a louse or tick...


 * Don't know about why they are there but they might have came back because the original mites laid eggs. I suppose you could soak the bowl in some kind of detergeant to rid the bowl of life. RevenDS 21:38, 17 November 2006 (UTC)


 * Tried that - also found them in plain flour in cupboard but not wholemeal flour, caster sugar or brown sugar - also in same cupboard and left open - maybe I should just move house.

Sounds like some type of weevils. Try the following procedure:

1) Toss out any food they've infected. Be sure to seal the garbage so they can't crawl out.  You could also flush them or burn them in a fireplace.  (This especially helps get out your frustration.)

2) Clean any containers they've infected with bleach, inside and out. Don't let the bleach sit in any metal containers, or it will cause corrosion.

3) Clean your shelves with a bleach-soaked sponge.

4) Lay borax down on the shelves. They don't like borax.  Baking soda also works.

5) Make sure everything is stored in airproof containers, such as sealed Tupperware. A container with a lid that just sits on the top, like the typical sugar bowl, is not sufficient, it needs to seal.  Unopened containers are normally, but not always, sealed.  Some pasta (spaghetti, mac & cheese, etc.) isn't sealed even when unopened, however.  Once opened, the bugs can always crawl in.  If you don't have enough sealable containers, you could also store opened cereal, sugar, baked goods, etc., in the refrigerator or freezer.

If you are wondering, the bugs probably came from something you bought that already had bugs in it. I had the same type of problem, and this method worked for me. StuRat 22:24, 17 November 2006 (UTC)
 * Thanks - they don't look like weevils though more like lice (I'm no expert). Obviously I've got rid of the infected food and cleaned. I am worried about eggs though. They definately are not wheat weevils though unless an albino form exists - the head is too small as well. Most of them were in the flour though.

I'd still be interested if anyone could pin down exactly what they were..


 * Could they be ants, for example pharaoh ants? --Lambiam Talk  07:52, 18 November 2006 (UTC)
 * Definately not ants - legs too short.

They probably have three segment - the tail (abdomen is a least half the body length) they appear flattened compared to ants and the thorax/abdomen connection is quite broad (a bit like an earwig but without the tails - also much smaller and cream coloured) The head is too small to comment on.


 * Then perhaps booklice (picture)? --Lambiam Talk  14:16, 18 November 2006 (UTC)
 * No wings as in the image on the wikipedia page - but the supplied image is very similar - mine are (or hopefully were) much paler - the image is quite close to what they looked like - still possibly with less of a waist - less fat and slightly more flattened - legs might have been shorter - possibly underneath the body. Thanks.
 * Nymphs are often light-coloured compared to adults of the same species; I wonder if what you're seeing is the nymph stage of a familiar insect? Anchoress 21:53, 18 November 2006 (UTC)
 * Quite possibly - though I've seen nothing else - the flour must have been infected for at least a week before I noticed it - long enough for a nymph to change into adult?..

Steel
This is just a request for someone to write an article on Chrome-vanadium steel. I was suprised I couldn't find one as it seems to be used in many hand tools. Obviously I haven't got the expertise to do this.


 * It's a variety of stainless steel, which we do have an article on. --Robert Merkel 22:04, 17 November 2006 (UTC)


 * It's not - chromium content is much less than 10% more like 1%, plus the article has nothing on it. Typicaly they are chrome or nickel plated to prevent corrosion - surely no neccessary for a >9%Cr steel? I'd also like to ask about S2 steel as well.


 * Looks like youve got more knowledge than we have ATM. So why not start an article on it?--Light current 22:48, 17 November 2006 (UTC)


 * What you can see above is honestly about the limit of my knowledge - other than 'Chrome vandanium steel is an alloy used in tools such as screwdrivers and spanners' I couldn't say much more. Maybe someone else will turn up.


 * We do have an article Chromoly (chromium-molybdenum steel}, which could be used as a model. Unfortunately, it does not cite any sources, which might have info on CVS. What I find on the web beyond "low-alloy steel of great hardness, tensile strength and torquability used for springs and tools such as screwdrivers and bits" is of uncertain reliability. For example, is this typical for CVS in general? A text that has an encyclopedic tone (note the authoritative ring) is this:
 * Chrome Vanadium Steel.— This steel has the maximum amount of strength with the least amount of weight. Steels of this type contain from 0.15% to 0.25% vanadium, 0.6% to 1.5% chromium, and 0.1% to 0.6% carbon. Common uses are for crankshafts, gears, axles, and other items that require high strength. This steel is also used in the manufacture of high-quality hand tools, such as wrenches and sockets.
 * --Lambiam Talk 23:54, 18 November 2006 (UTC)
 * the first one probably isn't typical for spanners etc, the second has a more typical constitution compared to what I've seen quoted for hand tools. I think there probably be numbered specifications and standards for different CrV steels but I can find little or nothing at present.

skin necrosis
How long does it take to manifest when the cause is lack of bloodflow? and what is the maximum of time after which it will not present itself? or can it develop nonths or years after the trauma that cuts veins and blood vessels that supply blood to the skin? (going progressively from pink, to red, to purple, to black?).--Cosmic girl 22:22, 17 November 2006 (UTC)


 * Did you know that one treatment is using leeches to suck the excess blood out ? StuRat 22:29, 17 November 2006 (UTC)

I thought the condition was produced by lack of bloodflow, not by an exess of blood. --Cosmic girl 22:41, 17 November 2006 (UTC)


 * As I understand it, the broken blood vessels do allow blood to flow in, because of the higher blood pressure that arterial blood has (having just come from the heart). However, the lower BP in the capillaries and the resistance due to the broken blood vessels combine to prevent the blood from moving out as fast as it moves into the area.  Thus, the blood pools, and the blood cells die.  This causes the color changes you mentioned above.  Leeches can increase the rate at which blood is removed, to match the rate at which it is supplied, giving the blood vessels time to heal. StuRat 01:25, 18 November 2006 (UTC)


 * See frostbite gangrene etc (if you must). Im not going to look! Ugh puke 8-((--Light current 22:45, 17 November 2006 (UTC)


 * Then there's also necrotizing fasciitis, don't worry, no pictures. X [' Mac Davis '] ( DESK | How's my driving? ) 01:26, 18 November 2006 (UTC)


 * The few instances of necrosis I've seen have presented after a few days from the initial insult. Not sure what all this blood flowing in business is about. Necrosis results from lack of oxygen to the cells. Lack of oxygen may be due to obstruction to blood flow or lack of oxygen in the blood. If you prevent blood flowing out you can increase the pressure in the tissues above the capillary perfusion pressure and therefore this is merely another cause of obstruction to blood flow.Mmoneypenny 16:36, 18 November 2006 (UTC)


 * Obviously, if blood isn't flowing properly, oxygen won't be delivered properly, either. If blood pools in the area, this will also impede the flow of fresh, oxygenated blood into the area. StuRat 00:34, 19 November 2006 (UTC)

let's say blood pools, or it just doesn't flow anymore...in both case scenarios...how much time does it take to see dramatic color changes? and also, is it progressive over the years? or is there a time limit when it's darkest and it won't become darker?.--Cosmic girl 14:17, 19 November 2006 (UTC)


 * If there was no flow at all, the color change would happen within seconds or minutes. If the flow rate is just slightly less than what's needed, the color change might take hours or days.  If the color change takes years, then something else is going on, like a disease. StuRat 06:31, 20 November 2006 (UTC)