Wikipedia:Reference desk/Archives/Science/2009 July 11

= July 11 =

Washboard effect on gravel roads
Can anyone explain to me the cause of "washboarding" on gravel roads? Thanks WSC —Preceding unsigned comment added by 98.149.228.69 (talk) 00:25, 11 July 2009 (UTC)
 * Have you read Washboarding? It seems to explain it pretty well. Regards, --— Cyclonenim | Chat 00:47, 11 July 2009 (UTC)
 * Huh? It doesn't explain the cause, just talks about whether or not it's related to the vehicles' suspensions. --Anonymous, 05:41 UTC, July 11, 2009.
 * "when vehicles move above a critical speed, that depends on the properties of the vehicles and the road surface. If all the vehicles move below their critical speed the road will remain flat, but if they move faster, ripples will slowly grow and move in the direction of the vehicles." Regards, --— Cyclonenim | Chat 09:44, 11 July 2009 (UTC)
 * Exactly. It just describes what happens, not why.  --Anon, 10:01 UTC, July 11.
 * Quote from the German wikipedia "A depression in the road causes intense ground contact (?) between the wheel of the vehicle and the road surface. When moving out of the depression the wheel moves upward like on a ramp and briefly jumps to cause a new depression."  Bei dem Herausfahren aus der Vertiefung bewegt sich das Rad wie auf einer Rampe nach oben, um nach einem kurzen Sprung eine weitere Bodenvertiefung vorzubereiten. 71.236.26.74 (talk) 11:19, 11 July 2009 (UTC)
 * Vehicle suspensions are harmonic oscillators. Each vehicle tends to resonate with the depressions and bumps left by previous vehicles. The effect over time is erosion in the road of ripples corresponding to the average resonant frequency of vehicles. Cuddlyable3 (talk) 22:55, 11 July 2009 (UTC)


 * Although the article does not say this, I am firmly of the opinion that a light rain -- enough water to partly fill the holes -- is the primary "exacerbater" of the condition once it starts for other reasons. Water gathers in the "valleys" and softens the dirt; the next vehicle along splashes the mud mixture out, usually to the sides, making the valleys even deeper. --DaHorsesMouth (talk) 22:19, 12 July 2009 (UTC)
 * Your assertion is not backed by scientific studies, or the fact that washboard conditions occur even in the driest deserts. See these articles. - Running On Brains (talk page) 22:38, 12 July 2009 (UTC)

Fire
Could someone expain this passage from the fire article? Apart from a controversial gap in the Late Devonian, charcoal is present ever since. I don't understand what gap is being referred to. And the source for that statement is a bit over my head. Thanks, Dismas |(talk) 03:23, 11 July 2009 (UTC)
 * It's fairly simple. We can tell in what time periods wildfire occurred by looking for charcoal in the fossil record. The record shows that wildfires first occurred in the Late Silurian and have occurred ever since, with the (apparently controversial, though a glance at the source doesn't indicate what the controversy is) exception of a period in the Late Devonian (the source says middle to early late) in which there is no charcoal in the fossil record, so presumably no wildfire, so presumably low atmospheric oxygen. Algebraist 03:36, 11 July 2009 (UTC)
 * I should have been more clear. What is this supposed controversy centered on?  What is disputed?  Dismas |(talk) 03:42, 11 July 2009 (UTC)
 * That is not entirely clear. The controversy is about the lack of charcoal in the Late Devonian, but whether the dispute is over whether this lack exists at all or over some more subtle point I can't tell. Algebraist 03:46, 11 July 2009 (UTC)
 * Absence of evidence is not evidence of absence. --TammyMoet (talk) 08:50, 11 July 2009 (UTC)
 * If you have looked for evidence and found none, then that is evidence of absence... Absence of evidence is only nonevidence of absence if the evidence is absent because you haven't actually looked for it. Maelin (Talk | Contribs) 11:39, 12 July 2009 (UTC)
 * Not logical Maelin. The other possibility is that your method of search is fallible. In real science, this is often the most likely possibility. alteripse (talk) 19:09, 12 July 2009 (UTC)
 * Or in photo-reconnaissance... 76.21.37.87 (talk) 02:30, 13 July 2009 (UTC)
 * It certainly is logical. If the hypothesis predicts that you make a particular observation, and you in fact make a contrary observation, that is evidence that your hypothesis is false. When I open my pantry and I look for the bread and I conclude, "I cannot see any bread in the pantry", that is good evidence that there is no bread in the pantry. Contrast this with simply not opening the pantry at all and then saying "I cannot see any bread in the pantry". Absence of evidence is evidence of absence, provided you have looked for the evidence and found it to be lacking. Maelin (Talk | Contribs) 05:40, 13 July 2009 (UTC)
 * If you're looking for something and you can't see it, it might just mean that it's really well-hidden. Conversely, if you're looking much too hard for evidence of something in particular, you might see it whether it's there or not (happens sometimes in forensics, or in foreign intelligence operations, sometimes in science too, as seen in the case of global warming)...

76.21.37.87 (talk) 00:53, 14 July 2009 (UTC)


 * Why the charcoal of the Late Devonian is really well hidden is also an interesting question. — Could you indent your sig to match your text? —Tamfang (talk) 16:24, 21 July 2009 (UTC)

Fire particles
I remember reading something a couple years ago about an old theory (1500 - 1600s perhaps?) that fire was the release of particles from a substance. And when, for instance, a piece of wood was burned, these particles were no longer present in what remained. What is the name of the particle? Does this ring a bell with anyone? I thought I read it here but I don't know if I'm mis-remembering since Google searches for things like Fire Particles hasn't turned up anything familiar. Dismas |(talk) 03:45, 11 July 2009 (UTC)
 * Phlogiston. Algebraist 03:47, 11 July 2009 (UTC)
 * That's them! Thanks!  Dismas |(talk) 03:56, 11 July 2009 (UTC)


 * The neat thing about the phlogiston idea was that the particles had negative mass - so when you light a fire with (say) some wood, the phogiston from the flames enters the wood and reduces it's mass - thereby reducing it to ashes. Similarly, when you boil water - the water level drops.  When you sweat - the water evaporates, taking with it some of the phlogiston which is why you feel cooler.  It's quite a clever idea given the very limited experimental evidence of the time...but it requires some complicated logic to explain the fact that heating mercury (which produces mercuric oxide) produces something that's actually heavier than what you started with - despite all of the phlogiston you poured into it.  SteveBaker (talk) 04:21, 11 July 2009 (UTC)
 * No, phlogiston is present in flammable materials and leaves them when they burn. That's why you end up having to assign it negative mass when you discover (for example) that burning metals gives you more mass than you started with. I'm pretty sure no-one thought it came in particles, either. It was more a fluid of some sort. Algebraist 04:25, 11 July 2009 (UTC)


 * Our article mentions it has no mass. So why should negative mass be assigned, or why would mass increase when phlogiston leaves an object ? Rkr1991 (talk) 08:52, 11 July 2009 (UTC)
 * Well, I think Algebraist just answered both of those...It has negative mass because when it leaves an object, the object becomes heavier (burning substances which become heavier after a reaction are thus explained this way). The real reason an object becomes heavier after a reaction is because it has more mass (obviously not true for all reactions); but they didn't know that at the time. Vimescarrot (talk) 09:12, 11 July 2009 (UTC)
 * You don't get it. The article says it has zero mass, not negative. That is the main theory. When contradicted, some scientists suggested that it may have negative mass so that it may explain things like the burning of Magnesium. Yet, it would not work. The way Algebraist puts it, it sounds as if the main theory itself suggested that Phlogiston has negative mass. But according to the article, that was just a view of some of its later proponents. Rkr1991 (talk) 13:05, 11 July 2009 (UTC)
 * At the time the theory was created, most things that were burned contained Hydrogen and Carbon, and those were the parts that were oxidized into H20 and CO2, i.e. into invisible and odorless gases that vanished. Thus, if you burned wood, or tallow, or lamp oil, or paper, the visible remains (the ashes) are indeed lighter than the original substance - and what you lost was the hypothetical Phlogiston. This is not true for substances that create only solid ashes, like several metals. To apply the Phlogiston theory to e.g. magnesium, you need to postulate a negative weight (and thus, I assume, different kinds of Phlogiston). --Stephan Schulz (talk) 12:55, 11 July 2009 (UTC)

Wasn't the whole phlogiston theory disproved three centuries ago? 76.21.37.87 (talk) 09:27, 11 July 2009 (UTC)
 * Two and a half. The linked article has a detailed history of it. Our whole discussion here is about the theory as it was and its correctness as far as they knew at the time. It's actually still a viable discussion topic as an example of how science makes testable hypotheses and changes or discards theories as new evidence becomes available. DMacks (talk) 09:38, 11 July 2009 (UTC)

What about photons? 93.132.152.73 (talk) 09:49, 11 July 2009 (UTC)
 * What about them? Algebraist 12:26, 11 July 2009 (UTC)

Airplane glory shadow


Hi. As I was in an airplane travelling over what was presumably north of the Beaufort Sea, I saw a glory over the sea ice. The sea ice was riveted with cracks and melt ponds, and perhaps the whole section will melt by September (about 1 million km2 of it; by the way are there any predictions for minimum Arctic sea ice extent for this year?). However, that's not the point. Now, presumably in the centre of the glory should be the plane's shadow. However, that's not quite what I saw.

Now, I didn't take a picture, but it was approximately midnight local time, but there was sunlight. It was the Arctic midnight sun. I was travelling approximately west, and the sun was near the front-right area of the plane. I was looking from the left side of the plane, and the glory was slightly behind the direction facing from the left (therefore, the Sun was to the northwest and the glory to the southeast). However, the shadow of the plane was a strange shape. It started in the centre of the glory, but then extended back almost parallel to the plane, very slightly pointing away from it. There were no wings visible in this shadow; it was faint and was basically a thin line that extended farther back on the ice than I could see. Was this the shadow of the plane, and if so, how did it form such a shape? The sun was presumably very low on the horizon (15 degrees according to Yoursky); the glory was probably only visible for about 10 minutes, while Arctic daylight on the aircraft lasted seven hours (we kept just prior to midnight local time during the whole trip).

Now, here's an aside. How does one identify the difference between cloud iridescence and irisation? Is it the type of cloud, the dominant colours, the pattern of the colours, how far away it is from the Sun, the season, etc? Thanks. ~ A H  1 (TCU) 08:01, 11 July 2009 (UTC)

About the strange shape of the shadow: since the sun was at the plane's one o'clock to two o'clock and very low on the horizon (as is always the case with midnight sun), the shadow projected onto the glory was identical in shape to the plane's view from that angle, so it's only natural that the wings would not be visible (the right wing was very likely being projected onto the fuselage and the left wing obscured by it). I'm not really sure why it was stretched out "farther back than you could see"; it could have had something to do with the curvature of the plane's window, or it could have been something else. 76.21.37.87 (talk) 08:28, 11 July 2009 (UTC)

As for your second question, I'm not really sure, but the Wikipedia articles say that cloud iridescence is usually caused by light refraction/scattering by water droplets/ice crystals/smog particles (similar to a rainbow/glory/halo), while irisation is a less common phenomenon caused by diffraction and mostly seen in stratospheric nacreous clouds. However, it appears to me that there's also some overlap between these two terms, so it wouldn't surprise me if I found out that they are interchangeable. FWiW 76.21.37.87 (talk) 09:09, 11 July 2009 (UTC)


 * The shadow of your own head (or the shadow of the part of the plane where your head is situated) will be precisely at the center of the glory...which it sounds like it was. The other parts of the plane's shadow could be anywhere...the extreme distortion of the shadow comes about because the sun was so low in the sky - and that causes very distorted shadows. SteveBaker (talk) 17:27, 11 July 2009 (UTC)

can i say so
what kind of cooling arrangments do american steel manufacturers use? They tag a high steel price.I suspect some kind of air+water mixture type cooling.Kindly let me know.

sam —Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 09:22, 11 July 2009 (UTC)

I'm not a steelmaker, but I think they quench the steel in water to give it extra strength and hardness. FWiW 76.21.37.87 (talk) 09:30, 11 July 2009 (UTC)

the process varies depending on what the steel will be used for. Generally, in the case of Canned food or sheet metal, a process called Cold Rolling Is used, in which case they deform the metal by passing it through a roller that has a temperature lower than its recrystalization process allows. Then again, another process known as Quenching Has been used which increases the durability and strength of the metal.

http://en.wikipedia.org/wiki/Cold_rolling -Heres a link to cold-rolling

http://en.wikipedia.org/wiki/Quenching - heres a link to Quenching

Hope this helps. --Blaze113 (talk) 10:14, 11 July 2009 (UTC)
 * I don't think cold rolling is actually a cooling process
 * For continuous production of steel water is sprayed onto the steel.
 * For batch production water, oil or even mercury can be used to cool the steel by plunging it into the liquid.83.100.250.79 (talk) 16:09, 12 July 2009 (UTC)

They don't use mercury because the vapors generated would be highly toxic. They do, however, use water, oil (which stinks like you wouldn't believe, but is not very harmful), and sometimes silicone-based liquids for quenching of steel. FWiW 76.21.37.87 (talk) 02:35, 13 July 2009 (UTC)
 * Yes I should have said no-one uses mercury for a a long time - though it has been used in the past, as has even molten lead.83.100.250.79 (talk) 16:44, 13 July 2009 (UTC)

Orbital Capture of Moons
Can someone explain to me how a large moon could just be flying through space and suddenly captured by a planet? (fyi, I know most moons aren't formed this way) This doesn't make sense to me as whenever spacecraft want to enter into orbit of a distant body they need to burn off excess energy at the periapsis to circularize the orbit. Spacecraft can also utilize atmospheric drag, assuming the planet has one, and I suppose the moon could skim through the atmosphere but it seems the odds of the resulting orbit being stable would be very low. So how does a planet without an atmosphere capture a moon? TheFutureAwaits (talk) 11:21, 11 July 2009 (UTC)


 * Atmospheric drag is not a possible mechanism for capture. The effect of "burning off energy at the periapsis" is to convert an open, hyperbolic orbit into a closed, elliptical one, or if the orbit is already elliptical, to lower the apoapsis.  (In a two-body situation, once you have an elliptical orbit, it always continues to pass through the point where a force was last applied, i.e. the atmosphere.)  Atmospheric drag could "capture" an object into collision with the ground, but not into an orbit above the atmosphere.  --Anonymous, 20:29 UTC, July 11, 2009.


 * Collison with an existing satellite or transfer of energy in a three-body gravitational interaction between the incoming body, the planet and an existing satellite are other possibile mechanisms. For further information see Irregular moon, Ananke group and Triton (moon). Gandalf61 (talk) 11:50, 11 July 2009 (UTC)


 * Yes, that's it. The involvement of a third body is required.  --Anon, 20:29 UTC, July 11.


 * I am no physicist, but I assume the energy is needed by a spacecraft if it wants to get into a circular orbit. Without that, it, or a potential moon, would get into an elliptical orbit. I believe that over time (very much time), that would get 'flattened' more and more until finally it approaches a circular orbit, but I'm not sure why that is. DirkvdM (talk) 13:20, 11 July 2009 (UTC)


 * Well, the conservation of momentum laws apply. If the planet were somehow nailed down and unable to move - it would indeed be impossible for a moon or a spacecraft to get 'captured' into a stable orbit.  But planets are not nailed down - so conservation of momentum allows for the COMBINED momentum of planet and moon/spacecraft to be conserved because each of them cannot be considered as a "closed system".  To envisage this, consider the planet and the moon as being roughly equal in size - it's not much of a stretch to imagine them both winding up orbitting about a point midway between them - and together moving off from the planet's starting point at about half the speed of the incoming moon. SteveBaker (talk) 17:02, 11 July 2009 (UTC)


 * This does not seem to help with "envisaging" the point that there needs to be a third body involved somehow. --Anon, 20:29 UTC, July 11.


 * If there were only the planet and the moon then you are absolutely right, you can't be captured without a rocket burn. With a many body problem, however, it is far less simple. You can get all kinds of complex interactions that can result in capture. Once you've got a periodic orbit tidal forces can circularise it. --Tango (talk) 17:40, 11 July 2009 (UTC)


 * Yes, that's it. --Anon, 20:29 UTC, July 11.


 * Aren't Mars' moons supposed to be captured asteroids? If so, there was no third body involved when the first of the two moons was captured. --Roentgenium111 (talk) 13:42, 13 July 2009 (UTC)
 * Apart from everything else in the solar system, you mean? Algebraist 13:46, 13 July 2009 (UTC)
 * See Deimos (moon) for various theories. Some theories invole other bodies which were ejected from Mars orbit by the encounter. Other theories involve non-asteroid origins. Gandalf61 (talk) 13:59, 13 July 2009 (UTC)

H and O in H2O
I was wondering, say the bond between H and O in H2O could be broken safe and economicaly, how much of each would a liter of Water contain. Using it as a fuel, would it be necassary to carry many, heavy lites of water, making it useless as a fuel for say a plane ?41.15.144.2 (talk) 11:45, 11 July 2009 (UTC)
 * The molecular weight of water is 18, hence a liter of water contains 1000/18=55.55 mol of water. This means it contains 55.55 mol of H2 and half that of O2, or, in other words, about 1300 l of H2 and 650 l of O2 at normal conditions. Unfortunately, you cannot carry this around for fuel in the compact form of water, since the energy you get from burning it is exactly the same you need to split it in the first place, and you will have losses either way. --Stephan Schulz (talk) 11:58, 11 July 2009 (UTC)
 * If you use it as fuel, of course you don't carry it in the form of water, but as hydrogen (the oxygen you get from the air, so you don't have to carry that). In a car, the large volume is a problem, so it has to be compressed, but for a plane the fact that hydrogen is light can be a huge advantage. Airships sometimes use hydrogen for lift. But as you say, you can also use that hydrogen for propulsion, so you get two for one. Of course, as you burn hydrogen, you lose lift, so you'll need more hydrogen-power to keep the plane in the air. But still. I wouldn't be surprised if this idea has already been worked out in more detail, but I have never heard of it. Hydrogen economy appears to mention planes just once, in the intro, so no help there. DirkvdM (talk) 13:04, 11 July 2009 (UTC)
 * Burning the lifting gas would require ballast to be released, reducing the range of the airship. Conversely, burning gasoline or similar fuels, as in most airships, causes the vehicle to get lighter during the cource of each flight and requires some of the lifting gas to be released, which also reduces the range (and adds to the cost).  In the airship Graf Zeppelin they avoided both problems by burning a gaseous fuel that was about the same density as air: Blau gas.  (They carried some gasoline as well, to burn in case they wanted to lighten the airship gradually.)  I presume the reason other airships did not adopt this was that the volume occupied by the Blau gas was inconveniently large.  --Anonymous, 20:42 UTC, July 11, 2009.


 * Oh, there is a Hydrogen airplane article. To my surprise, this doesn't mention the lift advantage and says the hydrogen should be pressurised. Of course, a sufficient amount of uncompressed hydrogen would make the airplane rather big, which would not be good for the aerodynamics. DirkvdM (talk) 13:13, 11 July 2009 (UTC)


 * To be VERY clear - (as Stephan points out) - the laws of thermodynamics require that it takes more energy to pull the water apart into H2 and O2 than you can possibly get back from recombining them. So you cannot use water as a "fuel"...that a flat out guaranteed: "NO!"   Some people suggest that using electricity to split the water and then burning the gasses conveys some advantage - but that too cannot be more efficient over (say) just using the electricity to drive electric motors.  Moreover, since the result of burning hydrogen with oxygen is just water again - you could capture the exhaust from such a vehicle and put it back into the water tank.  That makes water the "working fluid" - and not the "fuel".  However, thermodynamics is a harsh mistress and there is no possible way to make an energy "profit" while doing that.


 * So "water as a fuel" is quite utterly "busted". Sadly, there are a lot of people out there (like these evil bastards and these nut-jobs and these scam artists and these conmen...and many, many more) who'd very much like to take your money by selling you things like that...but please don't believe a word they say!  They are all liars, cheats and con-men - the laws of thermodynamics say so.


 * SteveBaker (talk) 16:48, 11 July 2009 (UTC)


 * I see you took a class in the Christopher Hitchens school of polite expression ;-). --Stephan Schulz (talk) 17:30, 11 July 2009 (UTC)


 * To note some possible caveats to Steve's rant, though, there's a possible rationale to using water (well, the hydrogen component, as noted above) as fuel. If you've got a clean plentiful source of grid electricity, then you may not care about the thermodynamic losses of cracking water on an industrial scale.  That hydrogen supply could then serve as a clean car fuel that's easily refilled -- while it's less efficient than an electric car, it doesn't suffer the range limitations.  Note that this is different from the scams noted above, though -- it relies on a clean power source that we don't yet have at the scale required.  "Clean" is included because we could do this now with coal plants, but the greenhouse emissions make it a non-starter.  Fix that, though, and the rest becomes pretty simple to implement. &mdash; Lomn 17:47, 11 July 2009 (UTC)
 * Steve is exactly right. There is no scenario under which the water can be used as a fuel§; any attempt to produce excess energy from breaking and reconstituting the hydrogen-oxygen bond would constitute a perpetual motion machine, whose existence is ruled out by the laws of thermodynamics and is not simply a matter of developing an advanced enough technology.
 * The scenario Lomn outlines is that of using hydrogen as a fuel, which of course is completely reasonable. The fact that water may be used as the source for hydrogen, doesn't make it a fuel though - at least, if we are using that word in the conventional sense; note that conmen often assign non-standard meanings to scientific terms in order to hoodwink lay customers/investors (see Stanley Meyer's water fuel cell for one such scientific and financial scam; ).
 * §: Here, I am specifically referring to dissociating water into hydrogen and oxygen, and then burning the released hydrogen to produce energy. Of course, falling water can be used to generate electricity, and water is used in a steam engines, but in neither of those cases do we refer to it as the fuel. In addition, there are several exothermic reactions involving water  that can in principle be used to run a generator; in such cases water could validly be called a fuel, but I don't think there are any such reactions that are of any practical importance for energy generation. Abecedare (talk) 18:28, 11 July 2009 (UTC)


 * Sure - you can make hydrogen from water (at some cost in electricity or whatever) and use THAT as a fuel. But it's (a) not an efficient process and (b) not using water as fuel.   Water is the 'ashes' you get left over after burning hydrogen..it has no energy left to release - the only way to get energy out of water - is to put more energy into it first.  Once you do that (eg by boiling it in a steam engine - or splitting it into H2 and O2 in an electrolysis cell) - you can take back some of the energy you put in...but you don't get it all back.  That doesn't make steam engines or hydrogen manufacturing plants useless - using energy in a more convenient form is valuable.  Hydrogen powered cars make a certain amount of sense.

If we somehow manage to build enough windmills or get fusion reactors working - they'll be the way forward. But we have to be very VERY clear that we aren't getting energy FROM water - we're putting energy INTO water. Which is the complete opposite of what these evil conmen are claiming. SteveBaker (talk) 18:30, 11 July 2009 (UTC)


 * To be fair to your nut jobs and conmen, the last link in particular does not make explicit claims that water is a fuel; it calls it a catalyst, and it's not thermodynamically impossible that a mixture of H2, O2, and C8H18 burns so much better than just octane and oxygen that it can make up for the energy lost in turning the water into oxyhydrogen and back. But even then it might be better to just have a tank of hydrogen to add (oxygen is already available!), and I agree with you that they are being quite shady (at least!) in phrasing it as a water-dependent benefit.  And its next step needs to be peer-reviewed chemistry research, not $10 downloadable do-it-yourself kits.  --Tardis (talk) 17:19, 16 July 2009 (UTC)

Sadly, about a year ago, Reuters got sucked into doing a story on Genepax, who had supposedly developed a water-fueled car. You’d figure a big news service like Reuters would have science editors who would know better. Red Act (talk) 20:03, 11 July 2009 (UTC)
 * Sad to see Reuters fall into the trap. Such scientific illiteracy is usually restricted to local TV news reports, which always seem to include the claim that the military (or NASA) is studying the technology. Abecedare (talk) 20:30, 11 July 2009 (UTC)
 * Well, what do you expect from Reuters? They're just reporters, how scientifically literate could they be, anyway?  You want scientific literacy, go with Scientific American or with Popular Mechanics.

76.21.37.87 (talk) 01:06, 12 July 2009 (UTC)


 * Whilst on the subject of water as fuel - there have been attempts to inject water into combustion engines along with the fuel - reason being that the water is vaporised when the fuel combusts - converting heat to 'pressure' (as steam) - note that the water is not a fuel in this case. The high heat capacity and enthaply of vaporisation of water would seem to be disadvantages here...
 * The reason to do it is to increase the energy efficiency of a combustion energy by adding a 'filler' that can convert heat to pressure (usable as work) by the engine.
 * I'm not sure if it has ever been proven to actuall increase efficiency..83.100.250.79 (talk) 16:17, 12 July 2009 (UTC)

Combined dynamo and starter motor
An electric motor can operate as a generator and vice versa. Why then do automobiles have separate dynamo and starter motor? Combining them saves many mechanical parts such as solenoid, starter gear, and pulley wheel. The current is much higher during the brief time a starter operates than in the dynamo that runs continuously, so they probably need separate windings. The Isetta article says BMW used such a combined unit in their Isetta 250 microcar. Cuddlyable3 (talk) 22:29, 11 July 2009 (UTC)


 * Possible reasons that occur to me:


 * 1) If the separate starter motor fails, you can still bump-start the car in order to drive it home/to the garage/whatever (as has happened to me); if the two are a combined unit, then such a failure might make the car undrivable.
 * 2) The reliability of a (presumably more complicated) combined unit might be appreciably less than that of two simpler separate units.
 * 3) A combined unit is likely to be more expensive than either of the two separate units, so in the long run, repair/replacement costs would likely be higher.
 * 4) A combined unit is presumably smaller and lighter overall than two separate units, and its use in the tiny Isetta 250 microcar was presumably to save space and weight; in a normally sized car the space and weight saving would probably be insignificant, so would not outweigh the disadvantages. 87.81.230.195 (talk) 23:41, 11 July 2009 (UTC)
 * The starter motor is more powerful than the alternator. "Cranking" a car consumes electrical energy faster than an alternator stores it. One rotary device could doubtless be designed to serve both roles. A rotary electrical device powerful enough to crank the engine might be inefficient when spun continuously as an alternator to provide steady state power. It is certainly something to look into. I seem to recall that General Motors was looking into using one motor/generator for this purpose, shutting down the internal combustion engine when the car stopped at a red light, then restarting it when you wanted to go, with a drive belt connecting the gas engine and the motor/generator. Edison (talk) 03:51, 12 July 2009 (UTC)
 * Parallel hybrid cars also uses single device as starter motor and alternator. -Yyy (talk) 06:27, 12 July 2009 (UTC)


 * I would say that the requirements for a high torque electric motor and a low load electrical generator are probably incompatible. However, it is possible that a combined device could be designed. But, as a previous poster says, the decision to go for separate devices is probably to do with economics and reliability.  —Preceding unsigned comment added by 79.75.92.24 (talk) 21:18, 12 July 2009 (UTC)
 * A single rotar device can have multiple windings: one for steady low level generation and one for short term high current. Some motors have starter windings as well as run windings. Some utility generatos over 100 years ago had both DC and AC generation windings, could generate AC at two frequencies at the same time, or could transform one frequency to another, DC to AC, etc. Edison (talk) 19:34, 14 July 2009 (UTC)

Swine flu versus ordinary flue
How does the mortality rate, duration, and severity, of being ill from Swine flue compare with that of being ill from ordinary flue, without any drug treatments in either case? In the UK people with swine flu are given Tamiflu, so its difficult to gain an idea of what its like untreated. I understand that in the US, most people are not being given Tamiflue. I understand that most people start getting better after two or three days - previously I would have called such a short illness a cold rather than flue. I thought flue was suppossed to last more like a fortnight (which translates as two weeks in American English). Thanks. 78.151.124.180 (talk) 23:49, 11 July 2009 (UTC)
 * It's not actually much different to ordinary seasonal flu: as our article notes. However, it is considered by some to be "unstable" and therefore more likely to mutate.  There are some reports that it is a devleoping resistant to anti-virals (such as Tamiflu).  This could, perhaps, bring some debate regarding the routine administration of Tamiflu to all sufferers, rather than restricting it to severe/problematic situations.    Gwinva (talk) 00:03, 12 July 2009 (UTC)
 * And just to be clear, flus (influenzas) and colds are not distinguished by their duration: they have different viral agents, as the articles make clear. Indeed, our cold article states that the cold typically lasts 7-10 days (up to three weeks!). Matt Deres (talk) 01:42, 12 July 2009 (UTC)
 * To give you an idea of how swine flue is viewed in the states: A few weeks back when swine flu was all over the news, the local government for my state (Vermont) was telling people who thought that they may have swine flu to stay at home. They recommended only the elderly, very young, and those with compromised immune systems to actually go see a doctor.  Otherwise healthy people were asked to just stay at home and treat themselves as though they had any other cold or flu.  Dismas |(talk) 04:28, 12 July 2009 (UTC)