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May 18

Toyota Truck Ad off Cliff

In the Toyota Advertisement (http://youtube.com/watch?v=6HzegzpTSDI&feature=related ) where the Toyota truck pulls a cargo container up the side of a quarry, would it be possible, if the quarry was deep enough, and you were wearing a parachute, and the window was open, to, if the truck was pulled over the edge by the container: As the truck is falling, would I be able to escape through the window, push off the truck far enough to open the chute, and then survive? —Preceding unsigned comment added by 140.180.14.157 (talk) 00:30, 18 May 2008 (UTC)[reply]

If the quarry was deep enough, sure, why not. I'm not quite sure what "deep enough" would mean in this instance. I don't even know how low you could be and still make a parachute jump that would leave you alive and mostly unbroken, but at least one source indicates that the lowest parachute jump in history would be 29 meters. That's not a whole lot; it's the kind of a drop you might actually find in a quarry without looking too hard. But, of course, you would need the time to open the window (or wriggle your way through it -- or just open the door, which might be easier and faster), get in position to firmly push off and then yank that rip cord to open your parachute.

So. If we assume that you're absolutely ready to dive out, are already wearing the parachute and don't need to bother with taking off your seatbelt or anything of the sort, I would assume that it would take at least five seconds for you to get free of the truck, even if you had trained at that maneuver and got lucky with it or posses some kind of Jackie Chan-like qualities that enable you to do exit falling cars through side windows like it ain't no thang. For the sake of argument, let's say that you have and you do, and that you can pull that off even while you're in free fall.

Knowing, as we do, that ignoring air resistance, the speed of an object falling freely near the Earth's surface increases by about 9.8 meters per second every second. Because I'm lazy and absolutely can't be bothered to do the math, I do what all of us lazy bastards do and use the internet: apparently, in order to get about 5 seconds of free fall (which the ABSOLUTELY TRUE FACTS at my disposal have revealed to be the time you would need to kick free of the truck), you need to fall for about 125 meters. That in itself wouldn't be enough, though, because you would still need those 29 meters for the parachuting part. So... yes, provided that the quarry was 149 meters deep, you didn't waste any time getting out of the truck and popping the parachute, and didn't somehow screw it up, you could do it. Come to think of it, you would probably even have a little bit of extra time there, actually, since we're just ignoring air resistance here. It's not much, but hey, at this point, you'll want all the help you can get. You think you might need an extra second to get out of the truck? That'd be another 55 meters of free fall you need, then; that acceleration really is a bitch.

Personally, though, if I was in that position, I'd prefer to give myself a little more margin for error. Like, you know, a couple of kilometers. -- Captain Disdain (talk) 01:37, 18 May 2008 (UTC)[reply]

...also, I'm a little stupid, because I now notice that the 29 meter record is actually a BASE jump. That means that there's not a lot of acceleration before the jumper pops his chute. In this scenario, though, you would already have been falling for at least five seconds, which means the parachute would need more than the 29 meters to slow you down to keep you from breaking your legs or getting killed. Still, y'know, if the quarry was deep enough, sure, you could do it. -- Captain Disdain (talk) 01:41, 18 May 2008 (UTC)[reply]

Don't mean to be cynical here, but you could just turn the camera to vertical and walk away, Julia Rossi (talk) 10:15, 18 May 2008 (UTC)[reply]

Oh, Julia. Is there no adventure in your heart? -- Captain Disdain (talk) 16:43, 18 May 2008 (UTC)[reply]

You're right –– t's a wonderful thread and fully exploring. I take it all back. The real cliff it is! Ok-aay – back to the dolly then, set up the wind machine for the parachute take guys Ak-shown! ; )) Julia Rossi (talk) 23:47, 18 May 2008 (UTC)[reply]

5 seconds is a long time, I expect you could do it quicker than that if you were ready for it. You could have the door open to start with, for example, and no seat belt. You could probably get clear and pull your rip cord in 1 or 2 seconds. --Tango (talk) 16:08, 20 May 2008 (UTC)[reply]

Right, and you could do it in a third of a second if you were already hanging on the outside of the car. You're right, of course; five seconds can be a pretty long time. On the other hand, maneuvering in a confined space with a parachute strapped on your back, in free fall, in a car that might well be moving sideways as well as downwards, while freaking out at the awesomeness of what you're attempting and being simultaneously horribly aware of how much of a harsh mistress gravity can be -- that's probably more difficult than we think. But, yes, absolutely, if you can do it more quickly, the pit doesn't have to be as deep. -- Captain Disdain (talk) 08:04, 21 May 2008 (UTC)[reply]

You would struggle to drive the car while hanging outside. ;) --Tango (talk) 14:35, 21 May 2008 (UTC)[reply]

Pfft. Brick on the accelerator, one hand on the wheel. (Wait -- that's the part that strikes you as unlikely about this scenario?! ;)) -- Captain Disdain (talk) 20:29, 21 May 2008 (UTC)[reply]

Do I just suck?

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

We can't really offer you advice about your symptoms, including offering a possible diagnosis or prognosis for your condition. If you are concerned about your health, you should speak to an appropriate professional. TenOfAllTrades(talk) 01:01, 18 May 2008 (UTC)[reply]

Possible Fuel Alternatives

http://www.drivecarwithwater.com

DISCUSS. Namely, discuss whether or not this is possible, or if it's nothing more than a scam.

216.178.50.4 (talk) 01:33, 18 May 2008 (UTC)[reply]

No, it's crap. The hint is the mention of 'HHO gas'—some nonsense espoused by noted crank Ruggero Santilli. Note that it also fails the 'too good to be true' test. TenOfAllTrades(talk) 01:43, 18 May 2008 (UTC)[reply]

Took me 3 seconds to call the scam. Apart from everything else wrong with it, the question is if its that easy, why isn't everyone doing it? It would solve the worlds energy problems. Luxosus (talk) 01:51, 18 May 2008 (UTC)[reply]

It's possible, but it's still a scam. You require more electricity to split water into oxygen and hydrogen that you'd get more power out of the battery converted to motion if you used the battery to run the car directly. --Wirbelwindヴィルヴェルヴィント (talk) 02:03, 18 May 2008 (UTC)[reply]

Basically, a solely water-fueled car would be possible in a frictionless, lossless universe - but that's just silly. If the fuel starts out as water and ends up as water, no energy has been extracted, so you can't give the car any energy to accelerate or counteract drag. This sounds like a repeat of Stanley Meyer's water fuel cell. In fact, how are these guys even allowed to do this, in lieu of the precedent set by the court case against Stanley Meyer? --Bmk (talk) 02:48, 18 May 2008 (UTC)[reply]

Actually, I didn't really look at it carefully - I guess this is different - they're claiming to have a gas-water "hybrid" engine. They don't say how it might work, so I guess it's hard to comment about its validity. --Bmk (talk) 03:04, 18 May 2008 (UTC)[reply]

Just thought, this would be the same (actually theoretically worse) than running a electric car directly from the battery used in a normal car wouldn't it? Luxosus (talk) 12:55, 18 May 2008 (UTC)[reply]

It's a complete scam - and several people who tried to make money from it wound up being found guilty in court as a result. Stanley Meyer is the most notorious - he was found guilty of "gross and egregious fraud" following his efforts to con investors out of large amounts of cash. The deal is that water is already in it's lowest possible energy state. There is no energy inside a water molecule - think of it like the ash that's left over after burning a piece of wood - the ash can't be burned any further...neither can more energy be extracted from water. Hence these machines have to put energy INTO the water to split it into hydrogen and oxygen - then burn the hydrogen in the oxygen to get some energy back. But nothing in the world can run at 100% efficiency - so you lose some energy in pulling the electricity out of the battery - you lose more energy as heat when converting water to hydrogen and oxygen - more energy is lost pumping the gas into the engine - and we know for sure that the engine isn't 100% efficient because no internal combustion engine ever can be. Then the energy that the engine produces has to be used to recharge the battery - but the generator/alternator loses energy - and when you recharge a battery, you lose energy. So through all of these lossy processes there is no way for the car engine to keep the battery recharged - let alone extract energy to drive the car. So these things are ALL scams - 100% certain - there is no wiggle room for cleverness because the laws of thermodynamics are cast iron scientific laws that cannot be breached. 66.137.234.217 (talk) 14:05, 18 May 2008 (UTC)[reply]

Weight of the Universe

1) Was is the estimated weight of all the known and unknown universe, including all real and virtual matter and energy ?

2) What would the universe weigh if it was filled with milk or tomato soup ?

69.157.239.231 (talk) 13:01, 18 May 2008 (UTC)[reply]

Nobody knows the size/weight of the entire universe. What's more, in a sense nobody can ever know because it is so large that light has not had time to travel from the furthest extents to Earth since the big bang. Worse still, you can't talk about the 'weight' of something unless you know what the local gravitational field is - and that's different everywhere. Even 'size' becomes a tricky concept with curved space and the expansion of the universe. So to be able to answer this question in any way at all, I have to assume you are really asking about the mass of the known universe (the part we can theoretically see with telescopes). See Observable universe which says the diameter is 92 billion light years and the volume is 3×10⁸⁰ cubic meters with the total mass of everything within that volume being 3x10⁵³ kg. Since liquids like milk and soup are roughly as dense as water, and a cubic meter of water has a mass of 1000 kg, the mass of a ball of soup or milk the same volume as the known universe would be roughly 3x10⁸³ kg. Of course such an object would collapse under it's own gravitational field into a black hole leaving nothing but a feint smell of chicken and noodles. 66.137.234.217 (talk) 13:54, 18 May 2008 (UTC)[reply]

In response to question #2, given that most of our universe is empty space it would be alot more massive if the whole thing was filled with soup. And it would also be delicious. --Shaggorama (talk) 07:51, 19 May 2008 (UTC)[reply]

You might want to look at Orders of magnitude (mass). You definitely want to see mass instead of weight. This reminds of of a nursery rhyme about what if the oceans were filled with ink, but I can't place it... Sandman30s (talk) 14:17, 19 May 2008 (UTC)[reply]

Magnetism

How does a magnetic field exert a force? My thinking is it must be from an exchange of particles, similar to gravity and gravitons, however I've never heard of such a particle/theory. Luxosus (talk) 13:02, 18 May 2008 (UTC)[reply]

Photons transmit the electromagnetic force.--Shniken1 (talk) 13:14, 18 May 2008 (UTC)[reply]

That's just theory, however, and I don't buy it, as it requires an infinite number of photons to account for the magnetic interaction of every particle in the universe with every other particle. The same is true of gauge boson theory in general, however. StuRat (talk) 16:21, 18 May 2008 (UTC)[reply]

Well, I'm not fond of the photon-exchange picture either, and I don't think it makes sense at cosmological scales. It's probably better to think of an electromagnetic field (or a gravitational field) as something which is simply present in space and affects the motion of objects in regions where it's present. This is the usual classical picture, but it's also a correct quantum picture.

As for how the field exerts a force, here are a couple of possible answers.

It just does; we don't know why (yet). Hypothesis non fingo.
There aren't really any forces; the apparent forces are all really side effects of the geometry of spacetime, just like gravity. This is the idea behind Kaluza-Klein theory. It seems likely that something along these lines is correct, but it's too early to be sure. -- BenRG (talk) 19:17, 18 May 2008 (UTC)[reply]

The photon picture is perfectly plausible and consistent with all observations, such as small fluctuation in the electromagnetic force at small length scales. It does work across larger, even cosmological, scales and it does not require an infinite number of photons unless there are an infinate number of charged particles interacting. *Max* (talk) 21:23, 24 May 2008 (UTC).[reply]

Graviton powered cars

If physicists were able to isolate the hypothetical graviton particle, what kind of energy would it give out ? Is this the point where we would have flying cars ? Could it help solve the issue of travel at light speed ? 69.157.239.231 (talk) 14:30, 18 May 2008 (UTC)[reply]

I don't think isolating it would be enough, you would need to be able to create them artificially. If you could that, then anti-gravity would probably be possible, and that would easily allow for flying cars. It might allow faster than light travel using wormholes, or something - currently theories for the creation of wormholes require exotic matter, which the ability to manipulate gravitons would probably help with. --Tango (talk) 14:58, 18 May 2008 (UTC)[reply]

A graviton would just be a gravitational wave, in the same way that a photon is just an electromagnetic wave. Maxwell didn't anticipate things like broadcast radio when he developed his theory of electromagnetic waves, and I suppose there might be non-obvious uses of gravitational waves as well, but offhand I can't think of anything. I don't see any way to use gravitational waves to make flying cars, but I do see a way to use electromagnetic waves for that: you just fire a sufficiently powerful laser beam downward from the car, and the light pressure will push it upward. But sufficiently powerful here means on the order of 10 trillion watts for a car of a couple of tonnes, so the laser will fry anything unlucky enough to be underneath the car, not to mention guzzle gas at a rate of around 100,000 liters per second. As usual, more prosaic technologies tend to work better in practice.

One big difference between gravitational and electromagnetic waves is that everything is transparent to gravitational waves. This is the main thing that makes them so difficult to detect—imagine trying to build a telescope using nothing but transparent materials, keeping in mind that the building housing the telescope is also transparent and "night" is no darker than day because the Earth is transparent too. And everything has refractive index 1, so you can't even make a lens. Nevertheless it is possible in principle (though extremely difficult) to do gravitational-wave astronomy, and this might be one use of gravitational waves, though not gravitons as such—they would allow us to "look" directly inside things that are opaque to light, like the Sun and the big bang primordial fireball. Neutrinos share some of these properties and might be useful in a similar way. We can already detect solar neutrinos and they do help in understanding stellar structure.

One could imagine, say, using gravitons (or neutrinos) instead of photons for broadcast radio and cell phones, thereby eliminating the problem of dropout when you drive under a highway overpass. But the detection (and even generation) problem is far too difficult for this to work in the real world. That's the closest thing to an application that I can think of. -- BenRG (talk) 17:14, 18 May 2008 (UTC)[reply]

DNA base letter representations

DNA base letter representations. DNA bases can be represented by letters like A, G, T and C, but there are also other letters used to represent particular combinations of the other four (like, perhaps Y represents either G or A in a sequence). Where might I find a full list of these? ----Seans Potato Business 14:42, 18 May 2008 (UTC)[reply]

Why, you'd be looking for the list of degenerate bases. TenOfAllTrades(talk) 14:55, 18 May 2008 (UTC)[reply]

Indeed I would! Thank you, old sport! ----Seans Potato Business 16:57, 18 May 2008 (UTC)[reply]

Gearing a wind turbine?

Hi all,

I am planning on making a small wind turbine to generate 5-10V (probably a Savonius, but I don't think it matters for this question).

I have a number of used bicycle parts, such as gears and chains. I was trying to decide whether it would make any sense to have the generator separate from the turbine, connected by a chain, and had a couple of questions:

If we pretend that we have a 100% efficient, frictionless drivetrain (and a spherical cow...), would there be any advantages or disadvantages to having different gear ratios between the turbine and the generator (where the magnets and coils are)? Would any ratio deliver more volts for a given wind speed than a 1:1 would?
If there were some ratio better than 1:1, would this be enough to offset the real-world loss in efficiency caused by having a drivetrain? (I've read figures for losses of up to about 15% from using a drivetrain).

Any thoughts greatly appreciated, thanks! — Sam 15:34, 18 May 2008 (UTC)

The drive strength is proportional to the amount of wind, and the effectiveness of the turbine at converting a linear force to a torque. You want to spin the generator as fast as possible to generate the most amount of energy; and you want to maximize the turbine's ability to spin freely with a light wind. These two are conflicting desires - if you had a numerical description, you could find a maximum efficiency. I would be willing to guess that a small wind turbine will need to spin very freely in order to capture light breeze, so you may want the higher gear ratio on the turbine side, instead of the generator (e.g. 10 turns of the fan yields 1 turn of the generator). Nimur (talk) 15:55, 18 May 2008 (UTC)[reply]

I want to try to put a "finer edge" on Nimur's reply. I think what you're looking for is "maximum power coupling" between the wind and the electrical line feeding out of the generator. The gear ratio and the generator design doubtless have a big influence on that but I suspect you'll find that optimum gear rato varies depending in the wind speed, so you'll need to chose a ratio that hits some sort of "sweet spot" in the overall range of velocities. (I think the whole situation is strongly analagous to how matching the source and load electrical impedances in a circuit optimizes power transfer.) I also assume you'll actually be driving an alternator and not a direct current generator (even if you use bicycle parts). For that, you need the alternator spinning fast enough to overcome the relatively-fixed voltage drop that occurs in the rectifier diodes that convert the AC to DC. For larger alternators that use an electromagnet as their "field", you also gain another tuning parameter: by varying the current in the field winding (the "excitation"), you can vary the mechanical load that the alternator puts upon the wind turbine. And, of course, your design can't allow the wind turbine, alternator, or generator to "overspeed" (exceed its design limits) in any wind condition.

Atlant (talk) 13:37, 19 May 2008 (UTC)[reply]

(Thanks, I was having a hard time articulating my meaning!) Yes, the "optimum" gear ratio will vary based on the wind speed, so you should design based on expected wind speed. As Atlant says, it's very much like matching impedance. Nimur (talk) 03:28, 20 May 2008 (UTC)[reply]

A generator from a car with field coils (no magnets) needs to spin much too fast, use something with permanent magnets. Direct drive is good; theoretically if the voltage needs to be higher at a particular speed you can have more poles. I know a system like this that used direct drive, and then a voltage doubling electronics to charge a battery.Polypipe Wrangler (talk) 23:14, 19 May 2008 (UTC)[reply]

Optimal dishwashing efficiency

For economical dishwashing, does the reduction in efficacy of washing-up liquid necessitate re-filling of the sink once the bubbles have left the surface, or does this signify that the remaining capacity of the washing-up liquid has fallen below a certain percentage? I read that some surfactants don't even make bubbles. ----Seans Potato Business 16:28, 18 May 2008 (UTC)[reply]

Lack of bubbles means that all the soap is in the water instead of in the bubbles. It doesn't necessarily mean that all the detergent is bound up with food particles yet. If the dishes aren't coming clean, you can always just squirt a little more soap into the existiong water. Franamax (talk) 18:07, 18 May 2008 (UTC)[reply]

We are talking about manual dishwashing in a sink here, not using a machine, right ? Instead of adding dishwashing detergent to the water, I suggest you add a drop to each dish directly, so that all the detergent touches the dishes, which is better than the small portion of the detergent that the dishes touch when they are dunked in soapy water. You can then do a first rinse in the water under the dish you just washed and a second rinse in the water on the other side (I'm assuming a two-sded sink here, if you lack one, use a plastic tub for the primary rinse). If you really hate any detergent residue, you can rinse each dish a third time under the tap, but this wastes tap water. StuRat (talk) 19:12, 18 May 2008 (UTC)[reply]

Stu, the problem I see there is that the soap droplet will not disperse on the dry dish; there is no water-of-hydration to form the detergent micelles around the hydrophobic contaminants; and immersion of the dish in warm water will cause dispersal from the surface in any case. Proper consideration would also consider release of the detergent to the general environment, so excess detergent is also detrimental. Sloshing the dish around in the soapy water and using the dishcloth should give effective random contact of the "soil" and the detergent. Now that I think of it, pre-soaking of the dishes in cold water will give the best overall cleaning efficiency. Franamax (talk) 22:48, 18 May 2008 (UTC)[reply]

The best dishwashing efficiency is acheived by getting someone else to do the dishes. But, failing that, I heartily second Franamax's advice: pre-soak your dishes, preferably overnight. Most soil can then be easily removed with minimal effort, even stuff that seemed really hard-cooked-on the night before.

Atlant (talk) 13:18, 19 May 2008 (UTC)[reply]

However, I would discourage you from soaking dishes for much longer than 12 hours because all those yummy food particles will eventually promote the growth of bacteria in your dish water, which can be unhealthy. Dragons flight (talk) 14:22, 19 May 2008 (UTC)[reply]

Ahh, good point, but my thought would be to discard the "soak water" at the conclusion of the soaking period and then wash the dishes per your favorite usual method; ours is usually using a dishwasher. (And often, the "soaking" just means piling the dishes into a suitably-sized dirty pot/pan and flooding the pot/pan; almost by definition, that soak water then gets dumped prior to further washing-up.)

Atlant (talk) 17:32, 19 May 2008 (UTC)[reply]

I agree with the soaking advice. That's what I do myself, I just forgot to mention that part. Also note that a few drops of bleach can be added to the soak water to stop the nasties from growing, but don't do that if you have anything metal in there that could rust (including allegedly "stainless" steel). Wood may lighten but should be otherwise OK. Plastic is a good thing to bleach periodically. StuRat (talk) 18:56, 19 May 2008 (UTC)[reply]

First Primate

What is considered to be the first primate species that evolved? Sorry if I demonstrate no understanding of this topic. 24.77.21.240 (talk) 17:01, 18 May 2008 (UTC)[reply]

No apologies are necessary. The topic of primate evolution is still quite debatable, despite it being a topic of rather intense research. So far as I can determine, this little fellow currently qualifies as one of the earliest primate or primate-like fossils found. Cute little fella, isn't he? I don't know why they gave him such a nasty name. Matt Deres (talk) 19:04, 18 May 2008 (UTC)[reply]

Cute? Little? What happened to respect for one's elders? :) Zain Ebrahim (talk) 19:13, 18 May 2008 (UTC)[reply]

Because the type specimen came from a site called Purgatory Creek, I believe. Presumably that's somewhere hot and unpleasant. 134.96.105.72 (talk) 11:41, 19 May 2008 (UTC)[reply]

That's a primate? Looks like a rat to me! I will never understand how biologists classify animals - seems like picking names out of a hat, half the time! ;) --Tango (talk) 21:12, 18 May 2008 (UTC)[reply]

Primates are most closely related to rodents, among the other large mammalian orders. What the paleontologists mean (and classification of extinct species is quite different from classification of living species) is that ancestors of primates at the point in time in which primates began to separate from rodents (at which time, yes, they all pretty much looked like rats) were more like Purgatorius than they were like the other protorodents running around at the time. It's true, Purgatorius doesn't look much like a primate, but every other mammal alive in its time (that we know about so far) was even less primate-like. arkuat (talk) 21:25, 18 May 2008 (UTC)[reply]

Actually, this is still in question. Some believe primates are closer to bats than rodents; see Archonta (the classification that puts bats closer) versus Euarchonta (the classification that thinks rodents are closer). (There is also a proposal that bats are not monophyletic, and that the Megachiroptera are very close to, or even nested within, primates while the Microchiroptera are distantly related.) Vultur (talk) 22:05, 18 May 2008 (UTC)[reply]

It's not really still in question, I think. The association of megachiropters with primates was primarily due to similarities in visual pathways (i.e. they see in similar ways), but all the genetic studies since that theory was floated have pointed to the monophyletic system (i.e. all bats share a common ancestor). The supposed similarities are more likely due to convergent evolution, which makes sense as they developed to perform the same kind of thing. Matt Deres (talk) 02:19, 21 May 2008 (UTC)[reply]

Very interesting! I guess I should stop thinking of Chiroptera as a small mammalian order compared to Primates and Rodentia. arkuat (talk) 02:23, 19 May 2008 (UTC)[reply]

Why do large wind turbines have only a few blades and turn slowly?

What is the primary reason large wind turbines used for power generation typically have very few blades, which move slowly? Is it for power conversion efficiency? Ease of construction? Safety for the turbine itself and the humans near it? Safety for birds? --71.162.233.156 (talk) 17:51, 18 May 2008 (UTC)[reply]

Cost, I imagine. Putting too many blades on will start needing pretty heavy-duty bearings in the turbine. The blades seem to rotate quite slowly, but the tips are actually moving very fast, ~100 mph If I recall. Franamax (talk) 18:00, 18 May 2008 (UTC)[reply]

There also is aerodynamic efficiency. Rotor blades will cause turbulence. Putting to many too close together will actually be counterproductive. The same is true if you spin them too fast. As far as I know, they are constructed to spin at an approximately constant speed (which will also be the speed that the generator is optimized for), which is regulated by adjusting the load on the generator. See wind turbine for more. --Stephan Schulz (talk) 18:14, 18 May 2008 (UTC)[reply]

I'm pretty sure that rotation speed is also regulated by adjusting the pitch of the blades; at least, I've seen some that appear to have pivoting blades. ~Amatulić (talk) 21:36, 19 May 2008 (UTC)[reply]

I believe I've read that the newer, larger-but-slower designs also minimize the problem of bird mortality near the wind turbines.

Atlant (talk) 13:14, 19 May 2008 (UTC)[reply]

They don't move slowly, they are just so large that the rotation rate becomes low for a given speed of the blade tips. The tip speed is actually close to the speed of sound. (It is held below the speed of sound to avoid the messy and lossy aerodynamic effects that would kick in if they went supersonic.) --169.230.94.28 (talk) 18:54, 19 May 2008 (UTC)[reply]

Um, no, I don't think so. Here's a typical example: [1] 33m diameter, 50 rpm gives a blade tip speed of 125 m/s, far below the speed of sound in air (about 346 m/s). Still 125 m/s is pretty fast (about 280 mph). ~Amatulić (talk) 21:36, 19 May 2008 (UTC)[reply]

The slowly rotating wind generators are able to generate 60 Hz (or 50 Hz, depending on the country) power by having a great many poles in the windings, so that one rotation produces many cycles of electricity. Edison (talk) 19:59, 19 May 2008 (UTC)[reply]

Boson Bomb

How powerful would a bomb using sub-nuclear particles be ? Say, a neutrino bomb ? Or a muon bomb ? A hadron bomb ? Or even graviton bomb ? What would that look like ? 69.157.239.231 (talk) 18:18, 18 May 2008 (UTC)[reply]

I can't see any way to make a bomb out of such things. Neutrinos barely interact with anything, so you certainly can't build something with them. And I can't see how muons or gravitons would bind together, either. Hadrons include regular atomic nuclei, though, so you can just build a normal nuke. --Tango (talk) 18:31, 18 May 2008 (UTC)[reply]
(edit conflict)This question is not really well-posed. An atom bomb goes boom because certain nuclear reactions generate net energy, not because of the size of the particles. It's unclear which sub-nuclear reactions would provide energy. Neutrinos don't really interact much with anything, so a neutrino bomb is somewhat pointless. All particles made up of quarks are Hadrons, so everything from a China cracker to an antimatter bomb could be described as a hadron bomb. --Stephan Schulz (talk) 18:37, 18 May 2008 (UTC)[reply]

I think the intent of the question is this. An ordinary chemical explosion releases energy stored in chemical bonds (between atoms in a molecule). A nuclear fission explosion releases energy stored in the bonds between nucleons in an atom. What would a bomb that broke the bonds between quarks in a nucleon be like? —Preceding unsigned comment added by Vultur (talk • contribs) 22:11, 18 May 2008 (UTC)[reply]

There is the problem that this appears to be more or less impossible. See color confinement. Algebraist 22:21, 18 May 2008 (UTC)[reply]

As I understand it, bonds actually reduce the energy stored in a molecule/nucleus - a bomb exploits the energy released when new bonds form. Basically, you need to go from a high energy state to a low energy state, and the difference is what goes bang. As Algebraist points out, separate quarks is not a lower energy state than a nucleon (in fact, it's not an achievable state at all). It might be possible to convert mesons to baryons, or vice versa, and get energy that way. I'm not sure what the bind energies are for such things, or even if there are combinations that would work. --Tango (talk) 23:25, 18 May 2008 (UTC)[reply]

Take a look at Energy density—it basically tells you what sorts of things would make a good bomb (or, put another way, a good bomb is something that can release a large amount of energy in a very limited amount of space or time). The only thing that really is more impressive than nuclear fusion (in a thermonuclear weapon) are pure matter-antimatter interactions. --98.217.8.46 (talk) 15:15, 19 May 2008 (UTC)[reply]

What about using the w boson to catalyze a fission reaction via beta decay? convert a neutron to a proton which then makes the atom unstable?--75.20.225.74 (talk) 18:09, 18 January 2010 (UTC)[reply]

Home generator idea

Would it be possible to increase the efficiency of a home generator (whether gasoline, propane, natural-gas powered, etc.) by using the excess heat produced to run an extra steam-powered generator ? I'd design it to have an expandable tank so it wouldn't split if the water freezes in winter. The water tank would have a hose attachment so you could hook a regular garden hose up to it to provide the water. I'd also design it so that the cooling fins in the water would air-cool the device when the water runs dry. I realize that scale from the minerals in the water would eventually build up on the fins, but for a generator only used for emergencies, this may not happen for decades, and the fins could always be cleaned. StuRat (talk) 18:46, 18 May 2008 (UTC)[reply]

This is confusing. If it's only for emergencies, why would you care about efficiency? However, you could capture excess heat in a combined cycle, although maybe just using it as a source of hot water instead of steam would be more practical. There's also the question of how to capture the heat. If you use an enclosure to capture the heat, when the water ran dry, wouldn't you have an empty enclosure with non-circulating air, thus no cooling function whatsoever? Franamax (talk) 19:01, 18 May 2008 (UTC)[reply]

Also, beware if you're going to play around with pressurized steam, that's called a boiler, needs certification, and can burn you real good. Franamax (talk) 19:01, 18 May 2008 (UTC)[reply]

I'm no expert but I'd apply Occams Razor here (in a sense). Rather than try and power a steam generator from the excess heat, find a way to use the heat more directly. Exxolon (talk) 19:15, 18 May 2008 (UTC)[reply]

The point of the efficiency is to get more energy out of a given sized generator. You could design the pressure tank out of metal with fins so that any heated air inside would heat the tank and dissipate heat into the environment. However, to make the tank be able to withstand freezing water, I wouldn't make the tank entirely out of metal, but also include flexible materials. As for any boiler requiring certification, certainly a tea kettle doesn't require an inspection, and it's actually inside the home, so their must be some lower limit on size and pressure, below which an exemption exists. StuRat (talk) 19:24, 18 May 2008 (UTC)[reply]

As I and Exx have said, the best way to get more efficiency is probably to make hot water, not steam. Your heat dissipation plan is OK, but you are introducing an extra stage, metal->air->metal->air, whereas the generator is designed for single-stage metal-to-free air cooling. You will drastically decrease the cooling efficiency if you are dissipating heat into confined air. As for the boiler, I'll look at Ontario TSSB requirements, but basically a kettle is releasing steam into free air, you are talking about confining the steam until it is sufficiently pressurized to do meaningful work, I can pretty much guarantee you that under those circumstances an accidental release will burn you very badly. I'll look around though. Franamax (talk) 21:07, 18 May 2008 (UTC)[reply]

Per TSSA (they changed the letters), you are talking about a "low pressure boiler" since you will presumably have < 30 sq.ft. of wetted surface, or <160 psi and <10 sq.ft. surface, so go nuts. Everything else about cooling efficiency and severe burns still applies though. Good luck :) Franamax (talk) 21:21, 18 May 2008 (UTC)[reply]

The problem is that to extract useful energy you need a big temperature differential. It's quite easy to extract energy when there is a 100 degree temperature difference - but it's really hard when there is only a 1 degree difference. In this case, instead of attempting to turn your relatively low grade temperature differential first into motion, then into electricity and then into something useful - why not use the heat directly. For example, you could take a cool water feed from the bottom of your home hot water tank, run that off to the generator - wrap the hose around the hot exhaust a few times and then back up to the top of your hot water tank. Since hot water is less dense than cold, the water should flow around the loop without being pumped - and your hot water tank will gradually heat up. If you normally heat your water with electricity - then the electricity savings should be a lot more than all of that messing around with steam engines could posibly get you.

70.116.10.189 (talk) 11:42, 19 May 2008 (UTC)[reply]

Actually, StuRat, I've seen this done in other areas. For example, in my line of work I saw a demonstration of using the heat from a vehicle's exhaust to generate electrical power using a Peltier effect hot-cold plate. In another example I saw an experimental pickup truck converted by NASA to run on a stirling engine, which merely needs a heat differential, and which could run an electrical generator. I'd say (just guessing) that various thermoelectricity methods might be more efficient than a steam engine. ~Amatulić (talk) 21:45, 19 May 2008 (UTC)[reply]

A common setup is to run a battery charger from the generator as well as the usual load. Then, later, when the generator is off run some things off the battery. Especially useful with generators that require a minimum loadPolypipe Wrangler (talk) 23:20, 19 May 2008 (UTC)[reply]

I remember seeing an old a for a small gas engine for use on farms before rural electrification. The motor, progagby under 1 horsepower, could be rolled around like a wheelbarrow, and could quickly be hooked up via drive belt for various applications. First, it could be hooked up to a generator to produce 32 volts DC or so to charge up batteries to light the home. When the batteries were charged, it could be wheeled over to the pump to pump the days water up into the water tower. Then it could be wheeled out by the barn to run a conveyor belt to lift bales of hay up into the hayloft, or to run a buzzsaw to cut firewood, etc, etc. Such an engine might have a water reservoir for cooling and the water sinply boiled away, but it could have been used to heat up water for the wash, if the timing were right. Edison (talk) 14:03, 21 May 2008 (UTC)[reply]

Ok, thanks for the answers everyone. StuRat (talk) 02:41, 20 May 2008 (UTC)[reply]

Neutrinosphere

I heard there was a place in the super-galaxy called the neutrinosphere, where the surface is heavily blanketed by neutrino particles. What's the point of such a zone ? Does it hold the galaxies together ? 69.157.239.231 (talk) 18:58, 18 May 2008 (UTC)[reply]

I'm not sure whether you're talking about dark matter (or, even less likely, dark energy) or about something else entirely. I don't think a surface heavily blanketed by neutrino particles is physically possible, though, except momentarily inside stars going supernova, thermonuclear weapons exploding, and that sort of thing. Dark matter does help hold our galaxy together gravitationally, certainly: that's how it was discovered. arkuat (talk) 20:54, 18 May 2008 (UTC)[reply]

A neutrinosphere is a transient region within a supernova explosion where neutrinos exist in thermal equilibrium. It has nothing specific to do with galaxies. Dragons flight (talk) 22:15, 18 May 2008 (UTC)[reply]

Could neutrinos form a pool in a gravity field is a question I have been asking myself. However even with the very cold Cosmic neutrino background at about 1.9 K they are moving much faster than the escape velocity of the earth. How fast they move depends on their mass, which could be around 0.01 eV. Perhaps in the centre of galxies or near white dwarfs, the gravity may be strong enough to retain these neutrinos in a closed orbit. But more likely the neutrino will fall in to the gravity well, speed up and then shoot out the other side in a hyperbolic orbit and not slow down! Graeme Bartlett (talk) 22:13, 19 May 2008 (UTC)[reply]

I believe neutrinos generally travel at just short of the speed of light, so this is very similar to the question above about light in gravitational fields. You would need something close to a black hole to get neutrinos to orbit - the centre of a galaxy would qualify. Near neutron stars might work, white dwarfs probably not (but possible, I'd have to look up some figures to be sure). I'm not sure what you mean by "form a pool", though, pools form when gravity is resisted by contact with something (the ground, say), but neutrinos would pass straight through pretty much anything, so they can't form pools. --Tango (talk) 23:27, 19 May 2008 (UTC)[reply]

The resistance comes about from Pauli exclusion principle whereby fermions cannot occupy the same quantum state. A sufficient accumulation of cool neutrinos would start to resist each other's presence rather than just passing through each other. This is the same principle that keeps atoms apart. The speed of the CNB would be around 10⁷ meters per second, which is fast exceeding escape velocity of the sun or earth.

As far as I can tell, that accumulation would have appear as if by magic. Once you've got it, it can stop new neutrinos and grow, but I can't see how it can form in the first place. --Tango (talk) 11:59, 20 May 2008 (UTC)[reply]

When was Ephemeris Time adopted, exactly?

This is perhaps more of a history of science question, but I expect the people here will probably be more helpful than the good folks at the history desk. I've already read the Ephemeris Time article and several other related articles and hope to add any information I get from the answers to this question to that article. ET and TAI are offset from one another by 32.184 seconds, because that was how far ET and UT had diverged from one another at the time that TAI was defined (1958) and in turn began its own divergence from UT. I already understand about leap seconds and that UT is not and cannot be a regular scale of time, and why it can't be.

What I want to know is when was ET adopted? Using a rough estimate of 0.7 seconds per year divergence between an ET clock and a UT clock, it looks as if the divergence began around 1912 or so. (That's 32.184 s divided among the 46 years from 1912 to 1958.) Can I get some historians of science to help me pin this down more precisely, and perhaps help me find the appropriate proceedings of the IAU (or whatever the IAU's predecessor was)? --arkuat (talk) 19:29, 18 May 2008 (UTC)[reply]

The Russian version (ru:Эфемеридное время) claims the decision was made in 1952 (8th General Assembly of IAU) with the "starting point of the time" chosen to be 1900 January 0. --Martynas Patasius (talk) 23:04, 18 May 2008 (UTC)[reply]

Thanks! So sometime between 1890 (?) and 1952, ET came into use, and became well-established enough at some point to have a statable divergence from UT, which divergence was not defined and fixed by international agreement until 1952, at which point the divergence was backdated to 1900. I am reminded now of Simon Newcomb#Director of the Nautical Almanac Office, which doesn't state any of this clearly, but hints at some of it. arkuat (talk) 02:13, 19 May 2008 (UTC)[reply]

Ephemeris Time (ET) was so named because it was the independent time scale used in government ephemerides from 1900 through 1983, in the American Ephemeris and Nautical Almanac, the British Nautical Almanac and Astronomical Ephemeris, the French Connaissance des Temps, the German Astronomisches Jahrbuch, and the Spanish almanac. ET was defined (but not named) by Simon Newcomb in 1895/98 as the weighted average of mean solar time refered to the Royal Observatory, Greenwich between 1750 and 1892. It was implemented at Greenwich mean noon on 31 December 1899 (0 January 1900), meaning that from that date on the stated positions of the planets in the ephemerides would be calculated in terms of ET, not in terms of Greenwich mean solar time (named UT in 1928) which had been used before 1900. ET differs from UT quadratically, not linerally, that is, the difference is generally a parabola. See ΔT. However, this divergence was not recognized in 1895, instead its implemention included a "great emperical term", a sinusoid with a period of 257 years. — Joe Kress (talk) 08:09, 19 May 2008 (UTC)[reply]

Thanks, Joe. I hope you don't mind that I've copied your entry here to Talk:Ephemeris time, because I think several of the points you make ought to be incorporated into the text of that article. arkuat (talk) 21:32, 20 May 2008 (UTC)[reply]

Measurements

How would one convert $yd^{2}in$ to $yd^{3}$ ? Thanks, Zrs 12 (talk) 19:47, 18 May 2008 (UTC)[reply]

I have no idea what it means but does this help? Zain Ebrahim (talk) 20:04, 18 May 2008 (UTC)[reply]

Divide by 36. You might measure the amount of rainfall that lands on a rood in

yd^{2}in

, and the amount of water that this added to a cistern (via the gutters) in

yd^{3}

.-Arch dude (talk) 20:31, 18 May 2008 (UTC)[reply]

Indeed, divide by 36. All you actually need to do is convert inches to yards, the yd² can just tag along for the ride. --Tango (talk) 21:10, 18 May 2008 (UTC)[reply]

What puzzles me most about this question is why the OP asked it - given his user page. Richard Avery (talk) 06:46, 20 May 2008 (UTC)[reply]

Cut the kid some slack. Just because you are interested in complex topics doesn't necessarily mean you are great at them (no offense Zrs). According to his user page, he's a HS freshman. --Shaggorama (talk) 05:57, 21 May 2008 (UTC)[reply]

Spontaneous activation

What is Spontaneous activation? And how it works in oocytes? —Preceding unsigned comment added by 131.220.58.9 (talk) 20:23, 18 May 2008 (UTC)[reply]

Activation of the oocyte genome is mentioned in Folliculogenesis#Primary. There's not much there, but I hope this helps. arkuat (talk) 21:05, 18 May 2008 (UTC)[reply]

My computer will be shut down automatically every time I try to logon...Please help

Hi there:
Since last night, I couldn't logon my computer anymore. Every time after I typed the password,
the system will be shut down automatically and a blue screen popps up with some notes on it:

 STOP: c000021a {Fatal System Error}

 The windows Logon process system process terminated unexpectedly with a status of

 0xc0000005 (0x00000000 0x00000000).

 The system has been shut down.

It all happened after the latest automatic update of Window XP. This kind of thing never happened
before since I have been using McAfee for more than 10 years to protect our
computer. Could that be a virus? Do you expert think so? Please help me out of this.

--Wendyzh (talk) 22:10, 18 May 2008 (UTC)Wendyzh[reply]

[2] might help. I have no idea what the cause is, but that explains how to fix it (it's not easy, though - you may need to call your neighbourhood geek, every neighbourhood has one!). --Tango (talk) 22:24, 18 May 2008 (UTC)[reply]
(edit conflict): I don't know if this is the right place for this question, but a lot of people had trouble with their computers after they instralled Service Pack 3. Apparently, there is some trouble with OEM versions, drivers, and (especially) AMD processors. You might want to upgrade to Linux. If you want to stick with Windows (why?), this site might help, and has further links into the Microsphere. --Stephan Schulz (talk) 22:26, 18 May 2008 (UTC)[reply]

Try asking here :) Regards, CycloneNimrod^Talk? 22:39, 18 May 2008 (UTC)[reply]

Yup, it sounds like Service Pack 3 is the culprit, from the description and the news I've been reading. On the other hand, it could be a coincidence with a dirty cpu heat sink. I've had my computer shut down by itself when the heat sink cooling fins got too clogged. ~Amatulić (talk) 21:48, 19 May 2008 (UTC)[reply]