Science desk
< March 3	<< Feb \| March \| Apr >>	March 5 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 4

Trumpet mouthpiece discolored?

Hey everyone, this may be a chemistry-related question. So, I play a Vincent Bach 1.5C mouthpiece, and lately I've noticed the inside is beginning to turn a light shade of bronze or gold, it seems, from the normal silver. A similar incident has happened before, where the inside of another mouthpiece had actually turned blue/purple/black. What's caused this? And I've heard that something can be done about the color change by using aluminum foil, baking soda, and hot water. Someone else said to use toothpaste. Can this work? Thanks. 64.229.204.125 (talk) 00:02, 4 March 2014 (UTC)[reply]

Do you know what the metal is ? Sounds like some type of patina has formed, and the first method sounds like using electrolysis to remove it, while the toothpaste method is just using abrasion to remove it. If it really is silver, then silver polish might work (although silver tarnish is typically not that color). StuRat (talk) 01:21, 4 March 2014 (UTC)[reply]

"Silver Plated", according to Bach: 351 1.5C Trumpet Mouthpiece - Silver Plated 71.20.250.51 (talk) 05:56, 4 March 2014 (UTC) —(Also available in Gold-plate:[1])[reply]

Could be that the silver plate is wearing through, beginning to show the brass underneath - assuming you clean regularly with a brush or whatever. The bluish-black is the normal silver oxide "patina". 71.20.250.51 (talk) 06:06, 4 March 2014 (UTC)[reply]

According to our articles, silver tarnish actually consists of silver sulfide, not silver oxide. Silver sulfide is black, so I agree with 71.20.250.51 that it sounds like with your current mouthpiece, the silver plating is wearing off, exposing the underlying brass.

The Vincent Bach mouthpiece manual[2] says "If the silver plating of your mouthpiece has worn off, the mouthpiece should either be refinished or discarded. Caution: Exposure to raw brass can lead to an allergic reaction or poisoning." You'd have to use your own judgment as to whether that admonishment still applies if the only place the silver plating is wearing off is inside the mouthpiece's throat and/or backbore. Red Act (talk) 06:26, 4 March 2014 (UTC)[reply]

(WP:OR warning) I played trumpet (poorly) for years. On the rare occasion I get it out, my mouthpiece looks just like you describe. As others suggest, it's (probably) just the plating wearing off if it looks bronze-y. If it's the purple/black, it can be cleaned off with toothpaste. I've used mine (with plating worn off inside) with no problems for years. But I don't play every day (nor even every year). If you do play often, it's probably worth getting a new mouthpiece, they are not very expensive. SemanticMantis (talk) 16:28, 4 March 2014 (UTC)[reply]

Do they make stainless steel mouthpieces ? If so, they might be less expensive and require less maintenance. Hopefully they are either solid stainless steel or at least have a thicker layer than won't wear through. StuRat (talk) 19:33, 4 March 2014 (UTC)[reply]

Hmmm, would different expansion rates in the metals foul up the music? (Unless it's a stainless steel horn, that is) Wnt (talk) 05:58, 5 March 2014 (UTC)[reply]

Pro musicians will say that the choice of metal affects the timbre. 12.217.87.18 (talk) 13:01, 5 March 2014 (UTC)[reply]

DNA testing and meiosis

How does making a match in a DNA test work when one of the samples is haploid? For example, if testing sperm from a crime scene, how does one prove it matches to a suspect if the sperm is meiotic/haploid/gametic, while presumably a DNA sample obtained from a suspect is mitotic/diploid/somatic. (Pardon all the slashes there, but I'm not 100% on which is the best terminology.) Thanks in advance, 76.168.226.134 (talk) 00:47, 4 March 2014 (UTC)[reply]

An individual sperm is haploid, but a sample of multiple sperm contains all the possible choices and so tends to look a lot like diploid DNA. If you had a really small one-sperm sample you'd be missing some markers, which could happen if you lost some of the DNA of a single cell sample to degradation also. So it isn't a big practical difference. Wnt (talk) 00:59, 4 March 2014 (UTC)[reply]

The probability of a sample of m sperm cells containing both copies of all of n chromosomes is (1 - (1/2)^m-1)ⁿ. For humans, n=23, and with 10 sperm cells the probability is already more than 95%. Icek (talk) 15:05, 4 March 2014 (UTC)[reply]

Well, remember that there is chromosomal crossover in the pachytene stage of meiosis, so chromosomes aren't inherited as units. However, the same analysis still applies for n markers on your actual test, provided they are not in linkage disequilibrium (i.e. a large number of centimorgans distance between them). I assume that any forensic tests will choose fully independent markers -- unless the agents are being really overzealous and starting to look into the health or mental propensities of their suspects rather than merely trying to identify them. Wnt (talk) 15:55, 4 March 2014 (UTC)[reply]

Missile Command

Some here remember that fabulous advance in video game technology known as Missile Command, in which players stopped incoming missiles (which were slowly moving, later not slowly moving, lines) that would reach and destroy your cities unless you set off immense explosions in their path with your own missiles. The scenario is seemingly very straightforward, and somewhat documented,^[3] - by exploding nukes in space you could use them as effective anti-ballistic missiles. This led to a disastrous space test in 1962 known as Starfish Prime and others in Operation Dominic that disabled various satellites including the original Telstar. (Before the invention of intercontinental ballistic missiles around 1957 I suppose it would always have made more sense to send ordinary fighter aircraft to stop an incoming plane) On account of the unwanted side effects, the Partial Nuclear Test Ban Treaty was enacted in 1963 to ban the space tests.

Despite the lack of testing under peacetime conditions, it makes me wonder: how long was a Missile Command scenario actually possible, or even a mainstay of nuclear strategy? I would think that with the advent of multiple independently targetable reentry vehicles the time to calculate the intercept would decrease, and the number of shots required would increase (almost like the game). Perhaps more significantly, having some manner of second stage propellant on board would seem to suggest to me that these were no longer ballistic missiles, but moving targets. The MIRV article says that they were first deployed in 1970; the SALT I entry seems to suggest more like 1968; in any case, the advent of MIRVs and the agreement of arms reductions seem closely linked. So I would hypothesize that Missile Command is what caused nuclear arsenals to swell to the point of "being able to destroy the planet N times over", and that reduction in the arsenals was an almost unavoidable aspect of that no longer working. Mutual Assured Destruction may have been coined in 1960, but it would seem to be a reality once "Missile Command" becomes impossible. (But if the ABM treaty proposed in 1967 and enacted in 1972 hadn't been made, could they have gone that way? I'm not sure when SDI/BMDO/Missile Defense Agency stopped being bravado and became plausible, if they really have)

Anyway, I've tried to answer my own question, but I'll pose it to you anyway: how long was "Missile Command" a real strategy? Did the various treaties I've described emerge as the nearly inevitable consequences of advancing technology, rather than as any reflection of the political 'thaws' and 'reforms' between the then superpowers? And does it still have a place in our thinking, and an effect on the number of missiles in our arsenal, even today? Wnt (talk) 15:48, 4 March 2014 (UTC)[reply]

Well, the Stanley R. Mickelsen Safeguard Complex was active for about a year in 1976-76. The Russian A-135 anti-ballistic missile system still exists, though it's an open question how useful it really is. (I recall wasting a lot of quarters in Missile Command machines, coincidentally in the mid-1970s, so it was clearly an au courant concept at the time). Acroterion (talk) 16:15, 4 March 2014 (UTC)[reply]

Hmm. I'm thinking this is the "exception that proves the rule". Not just the exception to the ABM treaty - with coverage of 100 nuclear missiles in a small area, MIRVs wouldn't apply very much to this either, because they'd all have to go the same place more or less. Wnt (talk) 17:18, 4 March 2014 (UTC)[reply]

The US basically abandoned the "set off nukes in space" method of defense in the late 1970s when the LIM-49 Spartan was removed from service. That, plus the shorter-range Sprint were part of the Sentinel Program developed in 1963. But that program was never actually built, except for a significantly scaled-down version that became Safeguard. So it was a real strategy, but only for a few years. Treaties were part of the reason it was killed, but there were also technical, strategic, and cost issues. The current US system, Ground-Based Midcourse Defense relies on a direct impact with the target. Mr.Z-man 17:36, 4 March 2014 (UTC)[reply]

The Nike Hercules were deployed in 1958 and only deactivated in 1988 in Europe although all the nuclear variant ones were removed in the late 70s from the U.S. 75.41.109.190 (talk) 17:55, 4 March 2014 (UTC)[reply]

The Nike Hercules was intended for interception of supersonic bombers and short-range ballistic missiles -- it was never capable of intercepting an ICBM. 24.5.122.13 (talk) 07:21, 5 March 2014 (UTC)[reply]

Missile Command, the game wasn't detailed enough to tell what kind of missiles you were intercepting or at what altitude. 75.41.109.190 (talk) 18:15, 5 March 2014 (UTC)[reply]

Wasn't there a version specifically titled "Patriot Command"? 24.5.122.13 (talk) 03:15, 6 March 2014 (UTC)[reply]

Would that be the version where the missile never goes where you tell it to? --Carnildo (talk) 02:21, 8 March 2014 (UTC)[reply]

Explaining the existence of molecule with MO

Hi there,
Can somebody explain me why Ethane and Ethylene exist according to the MO theory?
Thank you — Preceding unsigned comment added by 77.125.103.142 (talk) 16:17, 4 March 2014 (UTC)[reply]

Because when you figure out the molecular orbitals of those molecules, you end up with more electrons in bonding orbitals than in antibonding orbitals. But that is why anything exists in MO theory. If you want some references that show how all of the molecular orbitals in Ethane work this page showed up using a simple Google search for "Molecular orbitals of ethane" and a similar page here for ethylene (ethene). In the future, if you try typing variations on your question into search engines like Google, you can often find web pages such as this. --Jayron32 17:17, 4 March 2014 (UTC)[reply]

Hospital evacuations

How are critical parts of hospitals such as intensive care units or operating theaters evacuated if there is an immediate fire hazard near them. Surely they can't just stop during a surgical procedure. 194.66.246.65 (talk) 17:23, 4 March 2014 (UTC)[reply]

Generally, such facilities are designed to permit a strategy of "defend in place" (Google that phrase with 'fire' and/or 'hospital' and you'll get a multitude of discussions and plans). Buildings are designed with physical firebreaks, and staff are trained in procedures, to allow critical areas to be isolated from their surroundings in the event of a fire or other incident, for long enough (fire doors are often rated for two or more hours) to allow firefighting and outside rescue. TenOfAllTrades(talk) 17:48, 4 March 2014 (UTC)[reply]

Hospitals, nursing homes and similar facilities are always subdivided by fire and smoke barriers so that the occupants of one section of the building can be evacuated into another section on the same level. Theyt're also required to have sprinklers. The next time you're in a hospital, look for the bazillion cross-corridor fire doors, usually held open with a magnetic latch until the fire alarm is activated. In ICUs and ORs there are additional requirements, but if a fire breaks out in an ICU, for instance, the patients will be evacuated. The monitors have batteries, and the beds usually have an oxygen cylinder on board for such a contingency. In an operating room it would depend on the medical procedure that's being performed to determine how feasible evacuation might be. Nearly everything in an OR has wheels and back-up power. Acroterion (talk) 04:36, 6 March 2014 (UTC)[reply]

Water bond angle, snake oil

Hi, I recently came across this charmingly over-the-top snake oil site "water cures anything" [4]. Now, let me make it clear I don't believe any of the numerous health claims, but this bit caught my eye:

“

REPURIFYING WATER 100'S OF TIMES PER GALLON to produce results many times faster, as the Hydrogen Bond Angle opens up from 104 to 114 degrees)! ANY Healing Water (Lourdes, Nordenau, Vilcabama etc) ALWAYS has a Hydrogen Bond Angle a few degrees GREATER than ordinary water (104 degrees) which allows Blood to get through a membrane into the cells more easily...hence the HEALING noted by increased Blood Flow, confirmed by Doppler Ultrasound! Ordinary distilled water (processed ONLY ONCE!), produces the WORST BLOOD FLOW (with a Hydrogen Bond angle of ONLY 101 degrees, it's WORSE THAN TAP WATER at 104 degrees)!

”

My question: is it possible to change the bond angle of a given water molecule? Or, failing that, is it possible to select from a mixture of angles, to produce a sample with a different distribution than the original? I see that water model has a table with values ranging from ~104.5 to ~109.5, but it's not clear to me if these are just different model outputs for the same water, or if the distribution of bonding angles varies that much in nature. Or does the angle of a specific molecule vary depending on its environment? Thanks! SemanticMantis (talk) 18:21, 4 March 2014 (UTC)[reply]

The answer is no. There's going to be some difference in the bonding angle from any one water molecule to another because of molecular vibration, see here for a rather easy to understand discussion of the modes of molecular vibration. However, it isn't possible to "select" water that is at any one bond angle within the normal range of vibrational motion, nor is anything written above anything except unmitigated bullshit. Pay it no mind. It is completely nonsensical, excepting that it uses sciency-sounding words. It's the chemistry equivalent of someone randomly pasting words from a foreign language together and hoping the resulting sentence fools people who don't speak it into thinking it is really French or something. --Jayron32 18:50, 4 March 2014 (UTC)[reply]

Thanks. To clarify: any samples of relatively pure water (at same temperature and pressure) will have indistinguishable distributions of bonding angles, correct? Is the 104.45 given at properties of water just a mean for standard temp and pressure? If so, does heavy water have the same mean (our article says it has a larger dipole moment than regular water)? SemanticMantis (talk) 19:03, 4 March 2014 (UTC)[reply]

Yeah, that's pretty much it. Heavy water may have slight differences in bonding angles, and probably for the reasons you note, but as Wnt's (hopefully satirical) account below shows, it still doesn't add any credence at all to the silliness above. Someone learned a few words in HS chemistry, and is hoping the consumer remembered the same words, and is banking that the consumer doesn't have any real understanding of the principles involved here. --Jayron32 21:54, 4 March 2014 (UTC)[reply]

In the VSEPR model, water has a bond angle because electron pairs more or less "push" the hydrogen atoms (and associated electron pairs) together. I'd expect that, say, the water in David Banner's superpowered urinary tract might, under harsh green gamma irradiation, have some of its electrons pushed to far, far outer shells, where they would no longer be subject to the Pauli exclusion principle with those interacting with the hydrogen atoms, or one another, and thereby all of them could more or less muddle around the nucleus symmetrically, leaving the hydrogen atoms to wander more or less opposite one another. The caveat being that outside of comics that would be a very short-lived state, and the water would return in very short order to normal (unless it reacted to form hydrogen peroxide, ionized to a hydroxide ion or something). I don't know if anyone has actually observed hydrogens moved apart in excited water molecules or not. Wnt (talk) 21:43, 4 March 2014 (UTC)[reply]

Resolved

Ok, I knew it was nonsense as a whole, but I was a little confused about whether bonding angles can ever change (outside of vibrational modes). Thanks to Wnt and Jayron, I'll call this a wrap. SemanticMantis (talk) 22:10, 4 March 2014 (UTC)[reply]

Why do people appreciate panoramic views?

Most people will consider a panoramic view to be much better and more pleasant than, say, a street scene in which nothing far away can be seen and everything is at base level. Particularly, why do humans find valleys with a view, or any sort of terrain which has different topographic elevation and provides a good view, appealing compared to flat surfaces or areas where not much can be seen in the distance?

It's also worth noting that castles and other fortified structures have often been built on hilltops, or at least on higher ground, that provide a good view around as throughout history this would have been valuable in terms of defence.

In terms of evolutionary psychology, what would the reason for this be? Would the ability to see everything from a vantage point provide a sense of comfort in that it would mean that a person would be secure from threats from other humans and dangerous animals? — Preceding unsigned comment added by Lookbackbeforeyouleavemylife (talk • contribs) 18:57, 4 March 2014 (UTC)[reply]

Yes, being able to see trouble coming is useful, but having places to hide may be even more important. A primitive man standing out on an open plain would be a sitting duck. Also, even if cornered, say by a pack of wolves, having part of the approach blocked off would limit the directions from which he could be attacked, and perhaps his spear would be able to ward off attackers from that direction.

Another consideration is protection from the elements. Even a natural windbreak would make a storm more survivable. StuRat (talk) 19:15, 4 March 2014 (UTC)[reply]

IIRC, there's a section on this in Pinker's How the Mind Works, but I seem to have mislaid my copy. --ColinFine (talk) 20:22, 4 March 2014 (UTC)[reply]

According to this research, humans prefer the view of savannahs [5].

“

Appleton’s (1975/1996, according to Han,2007) prospect-refuge theory offers an explanation of why would people prefer locations similar to the savanna grasslands in Africa, or why such settings could have been a good choice for our ancestors. It is because grasses provide easy lookouts for spotting prey and threats, and scattered trees offer hiding places from enemies and predators; thus these settings afford prospects and provide refuge; they offer the opportunity to “see without being seen”.

”

Link is to blog post, see also peer-reviewed articles cited therein. SemanticMantis (talk) 20:53, 4 March 2014 (UTC)[reply]

Was it Pinker who said we prefer wooded meadows with a gurgling stream, indicating fresh water, cover, shade, and hunting opportunities? This seemed to be a trope in evolutionary psychology in the nineties, going along with blue and green being the most popular colors. See landscape art and evolutionary aesthetics. μηδείς (talk) 18:32, 5 March 2014 (UTC)[reply]

A panoramic view of London from the London Eye, click for larger image

I think there are cultural norms involved too. Arguably England's finest views are to be found in the mountains of the Lake District National Park. Before the Picturesque movement extolled its virtues and Wordsworth wrote about the daffodils, the Lake District had been described as "very terrible" (Celia Fiennes, 1698) and "barren and frightful" (Daniel Defoe, 1727). Alansplodge (talk) 17:17, 6 March 2014 (UTC)[reply]

As far as the strict definition of 'panoramic view' I think it's appealing because human eyes have a wide peripheral vision, thus your brain is taking in more information that whatever you're focused on. But i'm not sure of the connection to topography or distance. El duderino ^(abides) 07:04, 7 March 2014 (UTC)[reply]

Laser hair removal

A few years back, I was told that laser hair removal works, but that it only works for hair that is dark in color (and not white or gray or blonde hair). Has any more modern technology changed that? Or is that still the case? Does anyone know anything about this? I will appreciate any info. — Preceding unsigned comment added by 75.44.113.200 (talk) 19:34, 4 March 2014 (UTC)[reply]

For a start, laser hair removal says "Coarse dark hair on light skin is easiest to treat," and "At this time, [ electrolysis ] is the only permanent option for permanent removal of all types of hair, including very fine and light-colored hair." So... according to our article, laser removal is less effective on light or fine hair, but it doesn't say that it is ineffective. SemanticMantis (talk) 21:00, 4 March 2014 (UTC)[reply]

One obvious thing to try is first dying the hair black, then laser treating it. However, I suspect that the dye doesn't make it's way down to the roots. And the object is to heat the roots to kill them, without heating the surrounding skin enough to cause burns.

Another solution would be if there is a frequency of light that is absorbed by even light-colored hair roots, and not skin, but I suspect there isn't such a frequency, or it would be widely used by now. StuRat (talk) 21:25, 4 March 2014 (UTC)[reply]

Shrink-fitting

Hi, You might think I should know this, as I'm an engineering student, but I just can't figure it out. We haven't learnt it in my university syllabus, and lecturers are useless. I am making a wheel assembly for a Formula Student car and I am trying to get a shaft into a bearing. The bearing is a 3207RS bearing (http://simplybearings.co.uk/shop/Bearings-Angular+Contact+Ball+Bearings/c3_6/p500893/32072RS+Budget+Rubber+Sealed+Double+Row+Angular+Contact+Ball+Bearing+35x72x27mm/product_info.html - this gives dimensions in the 'Technical' tab), and the shaft is made of mild steel. I want to shrink fit the shaft with liquid nitrogen, to give a really tight fit so it doesn't fall out of the bearing as that will mean that the wheel will fall off.

So, I am trying to find out how much bigger the diameter of the shaft should be than the hole in the bearing, when at room temperature. I don't know how to calculate that, so I'm using this website: http://www.amesweb.info/InterferenceFit/InterferenceFit.aspx It can't be too small, otherwise the shaft will slip out under force, and not too big otherwise there will be too much interference force and the bearing might break or something.

For the website...

For the First Part

The torque transmitted is maximum 1100 Nm. I calculate axial load to be 1400Nm, using how this guy did it: http://www.physicsforums.com/showthread.php?t=655431 -- the car will be maximum 300kg, travelling at max 31.3m/s, with a steering angle of 30 degrees.

Coefficient of friction, I don't know, because I don't know what metal the bearing uses. This (http://hypertextbook.com/facts/2005/steel.shtml) has varying figures for steel on steel. I'm guessing 0.15 is right. Operation temperature is 21 degrees (room temp) And maximum rpm is 2000, I'm estimating. Engagement length is 27mm.

For the Second Part

The outer diameter of the bearing is 72mm; I don't know why that matters, but we seem to need it. The inner diameter of the bearing is 35mm. I don't know what the deviations are - let's guess 0.05mm.

I don't know what to put for stress concentration factor. Could you help? The website auto-provides 2, so that seems fine to me I can't get another value.

As I don't know the metal of the bearing, I'll guess it's also steel (but it's probably not). According to Wikipedia, "The density of mild steel is approximately 7.85 g/cm3 (7850 kg/m3 or 0.284 lb/in3) and the Young's modulus is 210GPa (30,000,000 psi)." Wiki also gives Yield strength as ~250MPa and Poisson's ratio as 0.27. Coefficient of thermal expansion is approximately 0.0000117m/mC (from here:http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html).

For the Third Part

The shaft is 35mm diameter when cooled with liquid nitrogen, and a little bigger when at 21 Celsius so that there is a tight fitting. (how much that little bit needs to be is what I'm trying to figure out) There is no inner diameter for the shaft as it is not hollow.

Then the exact same as before: "I don't know what the deviations are - let's guess 0.05mm. I don't know what to put for stress concentration factor. Could you help? The website auto-provides 2, so that seems fine to me I can't get another value. As I don't know the metal of the bearing, I'll guess it's also steel (but it's probably not). According to Wikipedia, "The density of mild steel is approximately 7.85 g/cm3 (7850 kg/m3 or 0.284 lb/in3) and the Young's modulus is 210 GPa (30,000,000 psi)." Wiki also gives Yield strength as ~250MPa and Poisson's ratio as 0.27. Coefficient of thermal expansion is approximately 0.0000117m/mC (from here:http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html)."

For the Fourth Part

I don't think we want a clearance.

For the Fifth Part

I don't know what this is. The website gives 6 for everything, so I'll go with that.

Could you please help with this? I realise it's a lot, but I just don't know how to do it. I don't know if I'm putting the right numbers in, and I don't really understand the numbers that come out. I just need to know what diameter the shaft needs to be manufactured to.

Thanks so much for any help that you can provide!! 143.210.123.79 (talk) 20:29, 4 March 2014 (UTC)[reply]

3) I suggest you do a test with liquid nitrogen and calipers, to determine the exact diameter at both temperatures. (Use leather gloves and safety goggles when pouring liquid nitrogen.) StuRat (talk) 21:32, 4 March 2014 (UTC)[reply]

Does your project have faculty advisers (it should...) Ask them about it, if you can. Or, if you don't get any other responses here in a day or two, try again next week. Lacking that, take the empirical route, as Stu suggests. SemanticMantis (talk) 00:06, 5 March 2014 (UTC)[reply]

My university does have advisors, but they are useless. My supervisor is an electrical engineer, so he knows nothing about mechanical engineering, even though my whole project is mechanical. I was told that last year someone used +0.03mm and it worked, so I'll just do the same. Thanks! 143.210.123.80 (talk) 11:57, 5 March 2014 (UTC)[reply]

Ah, well, in that case, perhaps you could ask an unaffiliated mech.Eng professor, or look for specific Mech.Eng forums to post on. The only other advice I have is to make a few prototypes for that part before you settle on the final. You don't want the competition part to also be a test case! SemanticMantis (talk) 15:10, 5 March 2014 (UTC)[reply]

Or they can try to make the competition part right off, but, if something goes wrong in manufacturing or testing, consider that to have been a prototype, evaluate what went wrong, make adjustments, and try again. Of course, this requires allowing time for several tries. StuRat (talk) 19:12, 5 March 2014 (UTC)[reply]

There is no time (Easter holidays in 4 weeks after which there are exams, which is ablout the time it takes machinists to get things made) and the Department won't provide much money, so there's no room for making prototypes. I'm just going to cross my fingers and hope for the best! 143.210.123.60 (talk) 20:57, 5 March 2014 (UTC)[reply]

Ah, the spirit of studenthood! Good luck, sorry we (apparently) have no MechE types to weigh in at this time. SemanticMantis (talk) 21:25, 5 March 2014 (UTC)[reply]

That's OK, thanks for trying :). I found out that ISO tables will give the value I need, but I still don't understand, so I'm sticking with my guess 143.210.123.106 (talk) 22:38, 7 March 2014 (UTC)[reply]

Future power supplies

Sir/Madam, As an example solar power & wind power & other renewables processes will not generate electricity 24/7, at the present time coal fired power stations are used as a back up, what do you see as a viable way to replace these Coal fired power stations? — Preceding unsigned comment added by Discspray (talk • contribs) 22:19, 4 March 2014 (UTC)[reply]

We don't really do opinion and speculation on the reference desk, but you might be interested to read our articles on Nuclear power and Tidal power. This combination, with seawater pumped up to a reservoir at off-peak times to generate extra power at peak times should provide a viable alternative to coal, but see also Combined cycle#Fuel for combined cycle power plants Dbfirs 22:43, 4 March 2014 (UTC)[reply]

Why just seawater ? Fresh water can be pumped up to higher reservoirs, too, and that has several advantages:

1) Less corrosive on the pipes and less sediment will accumulate.

2) Available many places where seawater is not.

3) Can also be used as drinking water, with the higher reservoir providing better water pressure. In places where pumps must be used to deliver fresh water anyway, this makes even more sense.

4) Seawater can contaminate the nearby soil with salt, killing any plants that live there (or replacing them with salt-tolerant plants).

5) Many "freshwater reservoirs" already exist, along with generation capacity. For example, water could be pumped back up behind Hoover Dam when demand is low, or back up Niagara Falls (beyond the generators).

6) If the average generation capacity is more than is needed, this excess fresh water can help to replenish lakes and reservoirs at low levels as a result of drought and overuse. StuRat (talk) 19:06, 5 March 2014 (UTC)[reply]

You are correct, of course, but I specifically mentioned seawater because of the tide factor. By pumping up at high tide and generating at low tide, an apparent storage efficiency of more than 100% can be achieved, though that would be possible only with appropriate timing of demand, and distribution of power between areas with different tide times. I was thinking specifically of the UK with a good spread of tide times over a relatively small area. In non-coastal America, freshwater pumping makes more sense. Dbfirs 07:02, 6 March 2014 (UTC)[reply]

Also, note that we currently do not generate all our power exactly as when it is used -- that would be very difficult! See energy storage for more information on how we can balance supply and demand for power. Many of those methods are fairly sustainable and have low environmental impact. SemanticMantis (talk) 23:29, 4 March 2014 (UTC)[reply]

Supposedly a Tesla project and competing efforts promise cheap batteries in the future that will equalize power usage day and night.[6][7] But I don't trust these PR-like news stories, and after a few decades of disappointments I don't trust any battery until many years after it is in mass production... Wnt (talk) 01:33, 5 March 2014 (UTC)[reply]

There are some radically different approaches to the problem:

Nuclear fusion is unfortunately not available yet, but once it is, it would make a great backup. As of now, the only kind of fusion we can use is the natural kind, and modern nukes for some very special purposes.
Mixing several methods. When there's no wind, maybe the sky is clear and photovoltaics are useful. Hydro and tidal power mix quite well, too. You can use tidal energy when the tides allow, and keep the hydro plants as a reserve for times when the tidal power generators can't provide any power. Where photovoltaics are not profitable (read: almost everywhere), biofuel is a potential application.
If you have a surplus, there are literally dozens of ideas on how to use them. The most practical one right now is simple, too: using the power to pump more water into the reservoirs of hydro plants. Other energy storage ideas work on a smaller scale, for example, flywheels.
Use fission and coal if you really need.

Of course, these methods aren't mutually exclusive either. - ¡Ouch! (^{hurt me} / _{more pain}) 06:44, 5 March 2014 (UTC)[reply]

I lived in Denver, Colorado, USA until late last year, a place where soi-disant "progressive" politics has made it the law that wind and solar ("renewable") energy are to be the preferred source of electric power in the state's power generating grid. This, in my humble opinion, has MUCH less to do with the economics and physics of power generation or the ecology of Colorado than it does with the political patronage of wind power investors, and finding something to do with millions of dollars' worth of solar cell parts now being expensively stored in and around Denver.

However, Denver's almost ideally suited to be a test site of at least one storage technology. A huge reservoir, the Cherry Creek reservoir, is located on a bluff overlooking much lower land in suburban southeast Denver. A lower reservoir could be dug on that land, the idea being to use Denver's spare water as a gravitational storage battery -- in times of peak demand, let the water flow down to the lower reservoir through hydroelectric turbines, then in the daytime or during high winds, use surplus power to pump water back up to the higher reservoir. That solves one pressing issue with wind and solar power - they somehow never seem to be present exactly when needed. However, it fails to address the other pressing issue (ignored by the Colorado Democratic Party) - the dismal cost inefficiency of solar and wind power - one of several issues that precipitated referendums in Northern Colorado counties on secession from the autocratic central government in Denver. loupgarous (talk) 19:08, 6 March 2014 (UTC)[reply]

Colorado could also benefit from oil shale-based synthetic fuel technology (having a veritable cornucopia of the stuff in the Green River formation); however, pollution control could be a problem. 24.5.122.13 (talk) 07:26, 7 March 2014 (UTC)[reply]

Please note that pumped-storage hydroelectricity is not something that needs a test site, but a well-proven technology that has been in use since circa 1930. As a current example, Denmark (with a lot of wind, but flat as a pancake) is cooperating with Norway (many steep mountains) to store Danish wind energy in Norwegian reservoirs. --Stephan Schulz (talk) 18:45, 7 March 2014 (UTC)[reply]