Wikipedia:Reference desk/Archives/Science/2011 December 1

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December 1

Electrical generation via the urban heat island - mesometeorology

Hi. Over the atmosphere of major cities, the urban heat island effect often makes the air up to 8-10°C warmer than areas surrounding. Vast thermals rise to higher regions of the troposphere, and there appear to be some similarities between this urban thermal plume and the much smaller stack effect that occurs in chimney-shaped thermal solar updraft towers and solar power towers. Since both the heat and uplifting air contain large amounts of energy, it would potentially be possible to generate electricity from this. Some possible sources of the electricity include:

• Turbines and rotating devices to convert thermals to electric current, similar to current concept designs for high-altitude wind power
• Circulation of air masses between the high-temperature air "dome" and surrounding cooler air in balloon-like systems that feed on turbulence
• Solar panels that would capture more sunlight and for a longer time than near the surface in the polluted city
• Direct energy generation via condensed water vapor (certainly there are small-scale battery-size devices that already do this)
• Materials that generate large amounts of static electricity from opposing air masses of different densities and vapor content that converts to electric current
• Airborne vehicles that rise given the temperature gradient and pull on ground-based generators via tethers that yank and spin turbines
• Reflector dishes that concentrate and focus waste energy such as waste heat, light pollution and light domes, noise pollution that might be trapped by air masses, or transparent materials that "steal" from the greenhouse effect at infrared wavelengths
• Electromagnetic propulsion

Of course, this type of power generation would be quite different from high-altitude jet stream power, as it uses large moving masses of stable air rather than narrowly-focused stratospheric air that moves at 400 km/h. The energy could potentially be used for various purposes, with unknown efficiency:

• Feeding directly to the city's electrical grid
• Providing cooling of the city during the summer or heating during the winter via electricity or other direct air circulation methods
• Blocking incident radiation from entering the city
• Using the higher carbon dioxide levels of the city and rising water vapor (which is both a greenhouse gas and contributes to higher summer Humidex) and synthesizing oxygen or converting to synthetic fuels or Synthetic biodegradable polymers
• Minimizing stress and heat/energy waste on electrical grid during peak hours
• Scrubbing pollutants and unwanted tropospheric chemicals
• Direct carbon dioxide air capture from the atmosphere at high altitude
• Sending signals to off-course artificial satellites
• Electrolysis and hydroponics
• Floating platforms could potentially be useful for transportation.

I came up with the initial idea for this less than a year ago while researching alternative energy. My question is: is such a mode of energy production feasible, or will the required size of such a device make it so heavy that it crashes onto the city below and poses a danger to its inhabitants? Has there been any current or former scientific research done on a similar such concept? Thanks. ~AH1 ^(discuss!) 00:52, 1 December 2011 (UTC)

For one thing, people wouldn't appreciate being cast in shadows by it on most days (maybe during heat waves they would). I'd urge you to think small scale. How about a series of tiny but strong wind turbines hanging over the edges of a tall buildings to capture the updrafts ? They could be plugged right into regular electrical outlets to provide some of the electricity needed for the buildings. Solar panels can also be placed on roofs.

I think your 8-10°C temp difference is more than typical, and, in any case, the problem with using that to generate energy is that there are many kilometers between that air and the air at the normal temperature. StuRat (talk) 01:16, 1 December 2011 (UTC)

Seems you'd be better off going in the opposite direction, and getting geothermal electricity.  Card Zero  (talk) 09:21, 1 December 2011 (UTC)

The idea is valid (it's not altogether that dissimilar from wind energy); but the engineering is implausible. You can do some back-of-the-envelope calculations to determine the total energy that is possible to extract from such a thermal. The answer will be "not much," and "it will require building a huge, probably-expensive contraption that would test the limits of 21st century engineering." You might start out by reading about carnot efficiency to learn why a 10-degree temperature difference above ambient atmospheric conditions can never be very efficient at performing useful work. So, if it's not efficient, you're relying on massive scale to extract large quantities of energy from a very inefficient process. You might read about some of the topics linked from energy economics to see why that is impractical in today's economy. Nimur (talk) 16:51, 1 December 2011 (UTC)

The UHI effect is not persistent -- depending on the causative factors in a given place it may be appreciable only under certain conditions such as night, calm days, or clear skies. It's unlikely that building the infrastructure for a power source of such an unreliable and intermittent nature would be economically practical. Interesting to think about, though. Short Brigade Harvester Boris (talk) 01:02, 2 December 2011 (UTC)

Range of a liquid fired from a hose related to pressure

According to Fire hose they have pretty high pressures, 290 psi. If you were to constantly increase the pressure, would the range of the stream produced continue to go up or would it drop off eventually? If so, why? ScienceApe (talk) 01:18, 1 December 2011 (UTC)

Assuming you keep the diameter of the hose constant btw. ScienceApe (talk) 01:20, 1 December 2011 (UTC)

It would approach a maximum limit asymptotically, because air resistance would increase and break the stream up into finer particles and eventually water vapor. In other words, you would end up using energy to accelerate more and more air at higher speeds. In a vacuum, however, the speed might very well go up proportionately. StuRat (talk) 01:23, 1 December 2011 (UTC)

This would occur with all liquids? ScienceApe (talk) 01:33, 1 December 2011 (UTC)

Yes, to some extent, although oils would tend to stick together better at moderate speeds and evaporate less. Mercury has an even more minimal tendency to evaporate in air at room temperature, so that would be less of a problem with it (although the portion that did would be toxic) and it's higher density might allow it to travel farther before air resistance stops it. StuRat (talk) 01:45, 1 December 2011 (UTC)

So the liquid encounters enough air resistance to the point of where it boils and turns into a gas? Changing the boiling point of the liquid could extend range then? ScienceApe (talk) 01:48, 1 December 2011 (UTC)

A liquid with a higher boiling point might well travel farther before turning into vapor, yes, and that would reduce the effect of air resistance somewhat. However, at high speeds the liquid will be heated to thousands of degrees by the air resistance, so you might not find anything that stays liquid at those temps. After all, small meteors manage to evaporate when they strike the atmosphere. Also note that even if it did stay liquid, it would still be broken into tiny droplets and encounter huge amounts of air resistance. StuRat (talk) 01:54, 1 December 2011 (UTC)

Does this imply that you could use ultra high pressure water as a "fan", to move large amounts of air without blades or turbines while consuming a negligible quantity of water doing so? Wnt (talk) 01:49, 1 December 2011 (UTC)

I wouldn't think it would be very efficient at that, as the turbulent air movements it would create would mostly be dissipated as heat. So, the energy would ultimately go to warming and increasing the humidity in a large quantity of air. StuRat (talk) 01:56, 1 December 2011 (UTC)

However, it can be (and often IS) used as a vacuum pump. 67.169.177.176 (talk) 03:08, 1 December 2011 (UTC)

What about a Magnetorheological fluid? Should have better range if a current is run through it yes? ScienceApe (talk) 04:46, 1 December 2011 (UTC)

You'd need to have a strong magnetic field over the entire course of the fluid. If you're going to do that, you might as well fire it in a vacuum. StuRat (talk) 04:49, 1 December 2011 (UTC)

What about a Electrorheological fluid? Can't you just run an electric current through it? ScienceApe (talk) 05:21, 1 December 2011 (UTC)

Don't they sometimes use electrified water for riot suppression? 67.169.177.176 (talk) 05:25, 1 December 2011 (UTC)

Do you mean Electrified water cannon (linked from Water cannon#Electrified water cannon)? If so the answer appears to be no Nil Einne (talk) 09:16, 1 December 2011 (UTC)

No regarding what though? Electrified water cannon demonstrates that you can run an electric current through a fluid fired from a cannon, but it's not a electroheological fluid. ScienceApe (talk) 13:55, 1 December 2011 (UTC)

As should be clear from the indenting, I replied to 67 so of course I meant no to what 67 said. It should also be obvious from the refs I provided that the answer to 67's question appears to be no. Nil Einne (talk) 21:17, 1 December 2011 (UTC)

Can't be too careful. Sometimes people just indent for consistency sake. ScienceApe (talk) 21:45, 1 December 2011 (UTC)

Well I don't really see how my answer could be intepreted as a reply to your comment even if we ignore the indenting, but I guess it doesn't matter. Nil Einne (talk) 08:00, 2 December 2011 (UTC)

North-South flying jet lag?

Is there any sleep disturbance associated with long distance North-South flies? You won't be changing time zones, but seasons, and that within one day, so, I thought that maybe that's too much for us humans to handle, since during evolution we didn't flied around. Quest09 (talk) 01:28, 1 December 2011 (UTC)

I wouldn't think it would cause sleep disturbances, but other health problems might result, if you end up wearing inappropriate clothing for the season. StuRat (talk) 01:47, 1 December 2011 (UTC)

The solar angle may be different, meaning differing times of sunrise/sunset and potential for hypersensitivity for example given seasonal affective disorder. ~AH1 ^(discuss!) 02:55, 1 December 2011 (UTC)

When I fly long distances in the same, or neighboring, time zones, such that so-called "jet lag" caused by crossing many timezones, shouldn't be a problem, I still feel wiped out for a day or so just from the experience of sitting in a tiny seat in a little metal tube breathing recycled air all day. The physical and psychological effects of boredom and confinement are probably something which affects people to a small degree. --Jayron32 05:09, 1 December 2011 (UTC)

Another factor of spending a long time on an airplane is cabin pressurization, which is often the equivalent of spending time at 8,000 feet (2,400 m) or so. Not everyone is equally effected by this, but having spent a lot of time in Colorado at altitudes that high I know I am. It tends to make me feel generally exhausted and headachey--much like I do after spending a few hours on a jet plane. I'm hoping the newer airplanes, like the Boeing 787, might make this factor of air travel more bearable. Pfly (talk) 23:59, 1 December 2011 (UTC)

Maybe you'd be happier if they brought back the Connie -- that plane was AFAIK pressurized to sea level, and the seats had more legroom as well. But then of course the flights took 2 to 3 times as long, and the cabin was also noisier than in today's jets. 67.169.177.176 (talk) 06:28, 2 December 2011 (UTC)

Add the fact that inside the plane you won't get much exposure to sun light and you get your North-South jet-lag effect. The effect would probably be the same if you stayed at home under the same conditions. — Preceding unsigned comment added by 80.58.205.34 (talk) 18:06, 2 December 2011 (UTC)

Current limits in different thicknesses of wire

Can 6mm² wire be used to supply a sustained 25A current at 13.7V or do I need to upgrade to 10mm² wire? It is ordinary PVC insulated multi-strand copper wire. The length is about 1.5m. Roger (talk) 09:16, 1 December 2011 (UTC)

I assume your cable is made of copper. With a length of 1.5 m there will be no problem with 6mm^2. It wont even get warm. Heat is in fact the only limiting factor in the current carrying capacity of a wire although a rule of thumb in elec eng is a max current density of 1000A/cm^2.(or 10A/mm^2).So using this current density your cable could carry 60A and still be within the (IMO arbitrary) limit. I never did find out who made up this rule.--78.148.138.159 (talk) 14:19, 1 December 2011 (UTC)

The length and voltage are not relevant to the question (as long as the wire is not looped around itself. The rule is not arbitrary. Too much current will melt the wire potentially causing a fire. Dauto (talk) 16:58, 1 December 2011 (UTC)

Thanks! Roger (talk) 17:11, 1 December 2011 (UTC)

Length is significant only if there might be a problem with voltage drop over the total resistance in the length of the wire, but that is very unlikely to be a problem in a 1.5 metre length. Heat might possibly be a problem if the wire is in a restricted space with exceptionally good heat insulation, but overheating is unlikely at 25 amps. (I have taken the liberty of correcting "c" to "m" in 78.148's helpful reply which applies to unbunched wire with reasonable heat conduction.) Dbfirs 17:11, 1 December 2011 (UTC)

American wire gauge has a nice chart of the "official regulations" for current-carrying capacity of various wire sizes. DMacks (talk) 17:15, 1 December 2011 (UTC)

As Dbfirs noted, voltage drop needs to be considered in addition to carrying capacity, and as acceptable voltage drop is usually given as a percentage of the nominal voltage, voltage and length are important in wire size calculations. In general, carrying capacity is the limiting factor for higher voltage circuits and shorter runs, and voltage drop is the limiting factor for lower voltage circuits and longer runs, but both must be satisfied. (That is, you don't want your wire to get too hot and you don't want your application to be undervoltaged due to drops in the wire, and either problem can happen independently of the other.) As your example is short and low voltage, both limitations need to be considered. Using this online voltage drop calculator (which includes carrying capacity tables -- a search should yield one in metric units), a 5ft (1-way) run of 10AWG (5mm²) copper in a 12vdc circuit carrying 25amps will drop 0.257volts or 2.14%. This is acceptable for either critical circuits (3% limit) or non-critical (e.g. general lighting) circuits (10% limit), so your 1.5m 6mm² run should be fine. Note that if your run was twice as long, while the previous arguments about carrying capacity would still hold, your 6mm² wire would exceed the critical circuit voltage drop limit. -- 203.82.66.201 (talk) 01:47, 2 December 2011 (UTC)

Reply to User:Dauto, When i said there would be no problem with the length, i was of course referring to the voltage drop due to the resistance of such a short length. I reiterate that there is no fundamental limit to the current density in a conductor as long as the heat is removed and that therfore 1000A/cm^2 is indeed arbitrary and you could easily start a fire at that current density if you pushed it through a high enough resistance.92.25.106.108 (talk) 13:39, 2 December 2011 (UTC)

The point is that a 1 mm^2 of copper gives a resistance low enough that a 10A won't start a fire. Dauto (talk) 14:46, 2 December 2011 (UTC)

Depends how long it is, whether its coiled tightly and how good the heat transfer to the heatsink is.--92.25.106.108 (talk) 15:16, 2 December 2011 (UTC)

Yes, the recommended maximum current is for unbunched and unenclosed wire (except for normal electrical insulation). British regulations quote different figures when cables are run together in conduit or other enclosed space. Tightly coiled wire or heat-insulated wire can reach a very high temperature after some time at a much lower current. I've seen 1mm^2 copper wire carrying a 10A current smoking dangerously from the heat produced in an extension lead where the small amount of heat was not being conducted away from the wire. Dbfirs 09:11, 5 December 2011 (UTC)

Jupiter's role on changing uranus axis

can we find any role for jupiter on changing uranus axis 97 degrees?Akbar mohammadzade--78.38.28.3 (talk) 09:37, 1 December 2011 (UTC)

No, there is none. The tilt is a result of angular momentum transfered from a passing or colliding body, possibly a consequence of the Tyche (hypothetical planet) incident. A fifth gas giant hypothesised to have been disrupted from its orbit between Jupiter and Saturn, may have made a close pass with Uranus, trading angular momentum in the process. Plasmic Physics (talk) 11:20, 1 December 2011 (UTC)

modeling of system (for the effect of solar wind) shows that any effect simlar to wind tunnel created by two giant planets had made uranus to turn 97 degrees in self rotation --81.12.40.120 (talk) 08:46, 2 December 2011 (UTC)

That definitely sounds surprising to me. Do you have any reliable source for that claim? --Stephan Schulz (talk) 09:50, 2 December 2011 (UTC)

Trichloroethylene residue

I bought a aerosol container containing trichloroethylene. It was a cleaner and was advertised as leaving no residue, designed for things like degreasing metal etc. The thing is is that it appears to be leaving a residue. For example when I get it on my hands even after I rinsed them off it still leaves a minty smelling residue that is very drying to the skin. The fact that it's difficult to wash off and drying to skin makes me think that it might be cutting fluid? Is it possible that there is cutting fluid left over from the manufacturing process on the inside of the metal aerosol can? Or is it that trichloroethylene does in fact leave a residue? --Jrbsays (talk) 09:50, 1 December 2011 (UTC)

It is de-greasing the dead layer of skin (epidermis) on the surface which makes it look dry. The smell is from the trichloroethylene that the dead skin adsorbed and is now slowly evaporating. It can be detected by smell down to a few parts per million in air. Therefore, its not surprising you can still smell it for a time afterwards. You ought not get this stuff on your hands, as the natural skin oils are part of the body's bio-defence. Spray it on a clean piece of glass, wipe with a clean tissue and spay again. Look for any residue on that. Do this in a well ventilated area.--Aspro (talk) 11:31, 1 December 2011 (UTC)

Spay whom??? 67.169.177.176 (talk) 07:13, 2 December 2011 (UTC)

When my skin is dried out by cleaning fluids, I find moisturizer helps to replace the oils. StuRat (talk) 16:28, 1 December 2011 (UTC)

I regularly work with other solvents such as mineral spirits, toluene, and acetone and I have not experienced any residue on my hands with these products. That's one of the reasons why I think that something in this cleaner is leaving a residue. Is this possible? For example cutting fluid --Jrbsays (talk) 05:17, 2 December 2011 (UTC)

I haven't worked specifically with trichloroethylene, but I've worked with other halocarbons and once spilled a beaker of methylene chloride all over myself. Well, let me tell you, my hands smelled of that stuff till next morning (and AFAIR they felt kinda sticky-wet, too, even after I rinsed off all the solvent and wiped my hands off). And that was chemically-pure methylene chloride from the stock bottle, not the aerosol variety, so there couldn't have been any cutting fluid in it. 67.169.177.176 (talk) 07:12, 2 December 2011 (UTC)

drywall mud

I Was looking at the MSDS sheet for a powdered drywall mud that you mix with water and hardens in 20 min. what was strange to me is that it has formaldehyde in it, presumably as a biocide. I don't see any functional purpose for this as it's a powder and it dries in 20 min. can anyone shed some light on this? The link to it is below --Jrbsays (talk) 11:26, 1 December 2011 (UTC)

http://www.usg.com/rc/msds/joint-compounds/sheetrock/durabond/sheetrock-durabond-20-joint-compond-msds-en-61205014.pdf

I'm certainly not an expert on building materials, but the the text above the carcigenicity table in that data sheet says, "All substances listed are associated with the nature of the raw materials used in the manufacture of this product and are not independent components of the product formulation," which clearly implies that they're not intentionally using formaldehyde as an ingredient in the product. My guess is that both acetaldehyde and formaldehyde may be given off by the "vinyl alcohol polymer" that is an ingredient in the product. Deor (talk) 13:13, 1 December 2011 (UTC)

It's not the EVA, I don't think, otherwise the MSDS would mention the formaldehyde as a decomposition product, no? --jpgordon^{::==( o )} 15:11, 1 December 2011 (UTC)

It might get damp from time to time from condensation, especially on an exterior wall, such as when it's cold outside and you've just taken a shower nearby or boiled water on the stove. A roof leak or window left open during rain could also dampen it occasionally. StuRat (talk) 16:26, 1 December 2011 (UTC)

"BGC Multipurpose Joint Compound Data Sheet" says "trace amounts of residual vinyl acetate monomers, acetaldehyde and formaldehyde may be associated with the production of the emulsion polymer". So it's a by-product of the manufacture. --Heron (talk) 19:20, 1 December 2011 (UTC)

I don't think it's a leftover product, because other MSDS sheets from the same company on a different type of drywall mud do not list formaldehyde as an ingredient. That MSDS sheet can be found below

http://www.usg.com/rc/msds/joint-compounds/sheetrock/sheetrock-all-purpose-joint-compound-msds-en-61320001.pdf

In addition other brands of drywall mud such as "dap" brand do not list formaldehyde on their MSDS sheet.--Jrbsays (talk) 05:25, 2 December 2011 (UTC)

Was Ernst Haekel really that ridiculous?

An early version of part of Haeckel's "tree of life"

Could someone with access to the full article in ref 17 in our article neanderthal see if it really does say that Ernst Haekel wanted to call it homo sapiens stupidus, or (as the most recent version of the article says) homo stupidus. Either is ridiculous, and it seems to have appeared in an edit by User:Dave Sousa at 19:19 on 24th May this year. I'd give the diff, but pasting doesn't seem to work in the edit box at the moment. It's diff 430719602 in the edit history.

And if it really is true, I'd be interested in any background information. 86.164.60.202 (talk) 15:17, 1 December 2011 (UTC)

A quick check on Google Scholar seems to confirm this, though I can't access the relevant journal: [1]. AndyTheGrump (talk) 15:33, 1 December 2011 (UTC)

The paper you link to Andy only confirms the existence of "Homo 'stupidus'" as a proposed designation, it attributes it to an 1899 book in German by Haekel, but doesn't clarify if he originated the name or provide enough information to link that proposal to Neanderthals. Dragons flight (talk) 16:06, 1 December 2011 (UTC)

I'm not ordinarily one for spelling flames, but let's spell his name right, please: it is Ernst Haeckel. I don't know specifically what he wrote about "homo stupidus", but he did write extensively about suboptimal design in biology, which he called dysteleology, so that would fit with his basic themes. (See also argument from poor design.) Looie496 (talk) 17:21, 1 December 2011 (UTC)

Let me give a bit of follow-up info. Haeckel was actually writing before any Neanderthal fossils had been discovered. One of the things he is noted for is being the first to visualize evolution as a tree -- the tree of life. In his tree-drawing from 1868, he attached a label "homo stupidus" to a point in the tree underneath homo sapiens -- it was intended to represent a hypothetical but as-yet-undiscovered ancestor. I have attached a picture of a drawing he made in the 1860s -- you can clearly see the label "homo stupidus" near the top. Looie496 (talk) 18:01, 1 December 2011 (UTC)

The same tree was published in Haeckel's later Last Words on Evolution (1906). The journal article cited in the Neanderthal article does not discuss this, but the TalkOrigins page cited does. I think it only looks "ridiculous" to you because you don't realize that stupidus is a real Latin word — it is not faux Latin. It is also worth noting that the associations with words shift over time. "Moron" was originally a technical term; now it is not, for example. --Mr.98 (talk) 18:08, 1 December 2011 (UTC)

Also I think the OP means User:Dave souza Nil Einne (talk) 21:13, 1 December 2011 (UTC)

It was better than his first choice, Biggus Diccus. --Jayron32 18:33, 1 December 2011 (UTC)

The wiktionary link is not very comprehensive. One, and obviously the relevant English synonym of the Latin stupidus is "speechless". Hurriquake (talk) 03:30, 2 December 2011 (UTC)

Using stupid to mean incapable of speech ? That's just plain dumb. StuRat (talk) 05:30, 3 December 2011 (UTC)

Thanks all: that was both helpful and informative. It makes more sense (if a little presumptious on his part) that he was giving it a name meaning "speechless". From our article, it sounded like he'd discovered a specimen, but later than the first, and so was too late to pick a name. The explanation above is clearer, and pretty interesting :) Thanks. 86.164.60.202 (talk) 08:48, 3 December 2011 (UTC)

Thanks everyone, the TalkOrigins page clearly shows Haeckel as having coined the term in 1866, after the discovery and naming of Neanderthalensis. It gives the alternatives "Homo stupidus! (Or, even stranger, Homo sapiens stupidus: "stupid wise man".)" From other sources, the shorter version seems to be right, and the sketch diagram above was apparently published in 1866. Archaeology: the key concepts By Colin Renfrew, Paul G. Bahn, p. 71 is one of the sources describing it as a hypothetical evolutionary sequence, from Pithecanthropus allalus (speechless ape man) via Homo stupidus (some other sources suggest this means not very clever rather than "stupid" in the modern sense) to modern humans. So, if it was coined as a hypothetical ancestor after Neanderthalensis had been discovered, this suggests that wasn't actually intended to apply to Neanderthals. However, we really need another source to confirm this and replace the current source which also covers some other points. . dave souza, talk 17:29, 3 December 2011 (UTC)

Cluelessness (battery life)

If I have a battery (12v, 100 ampere) and a LED TV (45 watt, 12v) how long can I provide power to the TV? 45 watt divided by 12 volt is 3,75 ampere. 100 ampere divided by 3,75 is 26.6667 hours. Is my calculation correct? Wasbeer 16:11, 1 December 2011 (UTC)

Unfortunately, it is not that simple. First, you've made a unit-error, dividing 100 amps by 3.75 amps and mysteriously obtaining "hours." This is incorrect, and provides a clue to the error: you're missing a critical piece of information. A battery can only provide 100 amps for a limited period of time. For this reason, you will often see a battery rated in amp-hours - in other words, this is the rated period of time that the battery will deliver 100 amps at 12 volts.

Such a battery is typically used for short bursts of high current - things like driving an automotive starter motor - which only lasts a few seconds. So it's very unlikely that you'll get several dozen hours out of the battery, even though you aren't using its full rated current capability - you're using the battery in an unintended way.

As a last comment, dealing with such batteries can be dangerous. Even though the voltage is low, the current drive is quite high, and there's a lot of stored chemical energy in such a battery that can rapidly convert to electrical or thermal energy. Even if you don't get a zap, you may be risking a fire. Consider using a lower current battery intended for long duration use. Nimur (talk) 16:20, 1 December 2011 (UTC)

No. The voltage and amperage describe how quickly electricity flows from the battery, but says nothing about how much energy is stored in it. You would need a rating for watt-hours or kilowatt-hours (kwh) to answer the question. Also, most types of battery will have a voltage drop that makes them unusable before they are fully discharged. If you can tell us what battery type it is, perhaps we can research it. I added to your title to make it more useful. StuRat (talk) 16:17, 1 December 2011 (UTC)

(E.C.) Your calculation would be roughly correct if by "100 ampere" you meant to say "100 ampere-hours" (or amp-hours for short), a measure of the battery's capacity. If instead, your "100 ampere" was its cranking amps (CA) or cold cranking amps (CCA), then no, your calculation is not correct. Our articles dimensional analysis and especially units conversion by factor-label may also be of interest to you. -- 203.82.66.201 (talk) 16:42, 1 December 2011 (UTC)

If your battery is a lead-acid battery designed for use in a motor vehicle, then it is not designed for deep discharge. The recommendation is that you should not discharge it much more than about half-way before recharging, if you want it to have a long life. Batteries of a similar capacity, but designed for low-currents and deep discharge can be obtained from marine and other suppliers. If you need to use a 100 ampere-hour car battery, then I would recommend that you recharge it after about 12 hours of use at just under 4 amps. Dbfirs 17:01, 1 December 2011 (UTC)

Wow, thanks a lot for all the help everyone! Wasbeer 04:16, 2 December 2011 (UTC)

Color of flame

According to flame, "The spectrum of a premixed (complete combustion) butane flame on the right shows that the blue color arises specifically due to emission of excited molecular radicals in the flame, which emit most of their light well below ~565 nanometers in the blue and green regions of the visible spectrum."

I'm not sure if I understand this. Let's say you are burning propane. Some of the valence electrons in propane move from a higher energy state, to a lower energy state and give off photons in the blue visible light spectrum as a result of changing to a lower energy state. This is what produces the blue flame, is this correct? 198.151.130.148 (talk) 16:12, 1 December 2011 (UTC)

Also is hydrogen a radical? 198.151.130.148 (talk) 16:19, 1 December 2011 (UTC)

Flame color is a complicated mix of incandescence (that is, light due to the blackbody radiation of the gas); and spectral emission related to the combustion chemistry; and a variety of other spectral emissions due to the various constituents and impurities in the air around the flame. In the case of burning propane, I have always been led to believe that the blue flame is due to the much higher temperature that results when the correct fuel-air ratio is used (providing a lot of oxygen, effectively raising the flame temperature).

We have a chart for the butane flame spectrum, linked from Fourier transform spectroscopy. If that data is credible, there's a strong C-H line that is prominent in the blue part of the spectrum. Nimur (talk) 16:28, 1 December 2011 (UTC)

But is the statement I'm saying regarding electrons moving into lower energy states correct though? 198.151.130.148 (talk) 16:53, 1 December 2011 (UTC)

Right; it's an atomic spectral line, and we call the whole process "spontaneous emission." I never liked this term, because the "emission" is only half the story: to emit energy, the electron first had to absorb energy. Of course, the electron took that energy from the heat of the fire.

Individual electrons gain thermal energy because they're part of molecules that bumped into other molecules (the exact mechanisms are inter-molecular collisions governed by statistical mechanics; and individual collisions are described by some type of scattering or collision, (the "correct" type of physical model to use depends on whether you're an atomic physicist or a molecular physicist or a chemist). Now, an individual molecule can't just "have" excess thermal or kinetic energy: one individual molecule is small enough to be governed by quantum mechanical rules, so after undergoing a collision and gaining energy, one or more electrons have been placed in an excited state. Other possible ways to store the excess energy are far less likely. But, we can't rule out any other excited quantum states - nuclear reactions, and so on. In fact, a quantum-mechanical treatment of an intermolecular collision deals with all of these details by "solving the wave function" for both molecules prior to, and after, the interaction; the result is a probabilistic set of quantum states that satisfy the collision.

In plain English, we can say that the kinetic energy of a molecule was converted in to an increase in the electron's energy-level. We skip over this entire process in high school chemistry classes, mostly because nobody actually enjoys solving molecular quantum mechanics problems - not even high school chemistry teachers. The details of "absorbing" energy through molecular collision are actually quite difficult compared to emitting a photon (which can be described using high school algebra).

After some period of time, the excited electron will spontaneously decay back to a lower state. This releases a photon. For the most common C-H excited state transition, the photon appears blue. Nimur (talk) 17:26, 1 December 2011 (UTC)

Is it possible for a reaction to produce green or violet photons, and thus produce green or violet flames? 198.151.130.148 (talk) 18:34, 1 December 2011 (UTC)

If copper, iron, sulfur, chromium, or a few other elements are present, the flames can be very colorful. We used to create "rainbow flames" by mixing in a small amount of various metal salts into a beaker of ethanol, for part of our "Chemistry Magic Show" outreach program. It's been a while, but I recall chromium as a deep blue, copper as a solid green, iron as a very deep red, and I do recall a purple flame (potassium chloride, maybe?) Unfortunately the most interesting colors were produced by the more noxious chemicals. You can also read about coloration in fireworks and pyrotechnics. Nimur (talk) 18:42, 1 December 2011 (UTC)

The article Flame test contains a good list of colors associated with burning various elements. --Jayron32 18:47, 1 December 2011 (UTC)

Phalanx versus Tercio

I hope I did not chose the wrong category, and "military science" belongs here...

Would one of the sides have a decisive advantage if a classical greek/macedonian phalanx would fight with an equal number of tercio pikemen? Let us assume it would not be a complete surprise so they would have at least a short moment to learn the capabilities of the equipment of the other side.

Steel is superior to the bronze used in classical antiquity, but would it matter that much? And would it make a great difference if they were only phalanx pikemen vs. tercio pikemen, or both sides could bring their auxiliaries (javelin throwers for the phalanx and a 10% - 20% of matchlock arquebusiers as used in early tercios) --91.23.196.250 (talk) 17:59, 1 December 2011 (UTC)

Something that armchair archaeologist forget/ignore, is that whilst steel is far superior to bronze weapons, it was only once the importance of steel production was recognised by the governing forces (in this case the Romans) that steel weapons could be made in greater quantities, due to to the greater abundance of known and workable deposits of iron ore; compared to that of copper and tin. A good steel weapon (swords etc.) that would not shatter during mortal combat - needed a lot of skilled art in its making. Yet labour, was cheaper than the raw material. It was both the greater organised industrial base taking advantage of this common metal and the ability to mobilise larger bodies of military force, that fought in disciplined units, that enabled Romans win out over the Gauls etc.. The average Roman solder however, didn't have it easy. A bronze sword, strong enough to be to be worthy of such a name, was very heavy and could ruin your whole day if you only used your little Roman sword to fend it off -instead of your shield. Roman swords were only good for stabbing a close range. --Aspro (talk) 22:09, 1 December 2011 (UTC)

OK, let's make some things clear here...

First of all, the word "tercio" was completely unknown in ancient Rome -- this term denotes a type of infantry unit in the armies of Renaissance Spain and Portugal. The Spanish (not Roman!) tercio was built around a pike square, with musketeers deployed at each corner, and sometimes also lightly armed swordsmen deployed as skirmishers and/or to protect the musketeers against enemy cavalry; the Portuguese tercio had a similar composition. Note that the use of the term pretty much implies that the auxiliaries are present on the battlefield -- if not, then the unit is no longer a tercio, but a simple pike square.

Second of all, when you use the term "phalanx", you have to be specific about what type of phalanx you're talking about: i.e. whether you mean a phalanx of hoplites armed with short spears and shields, or a phalanx of sarissiers armed with extra-long pikes, but no shields. (The outcome of this hypothetical battle may be affected by this.)

Third of all, is this supposed to be an all-infantry battle, or can the cavalry also deploy with the infantry (Companion cavalry with the phalanx, and dragoons with the tercio)? This can also be a decisive factor in this engagement.

That said, here's how I see the three different scenarios:

(1) Pikemen only, no auxiliaries: This would be a close match, especially if the phalanx consists of sarissiers. Essentially, in this scenario two forces of pikemen would clash together and stab at one another with their spears, trying to grind each other down in terms of casualties. The "tercio" would have a little bit of an advantage because of its better ability to maneuver, but not decisively so. In short, this engagement would boil down to which force has better discipline. If the phalanx consists of hoplites, on the other hand, the battle would be not so much a draw as a non-engagement of the Monitor-versus-Merrimac type -- the hoplites' short spears wouldn't reach the "tercio"'s front ranks, while the "tercio"'s long spears would be stopped by the hoplites' shields. Now that I look at this scenario for the second time, the "tercio" should win here too: if the Spanish commander is smart, he'd deliberately leave gaps between adjacent pike squares (as in Scenario #2) -- then, just as in Scenario #2, the pike squares stop the phalanx to their immediate front, the phalanx advances into the gap, and the "tercio" pikemen face outward and cut down the hoplites (or sarissiers) from their unprotected flanks. (Incidentally, AFAIK this is exactly how the Roman legionaries defeated the Greek hoplites.) No musketeers or swordsmen necessary to achieve victory (though they really help the tercio win with fewer casualties).

(2) Infantry with auxiliaries, no cavalry: In this scenario, the tercio would most likely mop up the street with the phalanx -- the tercio's musketeers would easily drive off the shorter-range peltasts, and then pour their fire into the phalanx, while the swordsmen dive under the phalanx's pikes (using their bucklers to ward off the spear thrusts) and cut down the nearly defenseless sarisseers. This would allow the tercios to cut into the phalanx, allowing it to partly (or completely) envelop the tercio formations (via the gaps deliberately left between adjacent tercios), at which point the pike squares join in the fray, facing their pikemen outward and thrusting at the sarisseers' or hoplites' unprotected sides and rear. If the phalanx was made up of hoplites, this could allow them to defeat the tercio's swordsmen, but the end result would still be the same.

(3) Infantry and cavalry: This one really depends. On one hand, the tercio's dragoons can add their fire to that of the musketeers, and/or charge the phalanx's flanks, where they can then proceed to cut down the hoplites (or sarisseers). On the other hand, the phalanx's Companion cavalry could charge the tercio and drive off the musketeers, at which point the peltasts could reenter the fray and inflict casualties on the tercio's pikemen and swordsmen, perhaps to the point where the pike squares could no longer hold off a determined charge by the phalanx. On the other other hand, the dragoons could form up again to the rear of the tercios and start firing through the gaps, once again putting the peltasts to flight. In other words, this scenario's outcome depends on a lot of things: (a) whether the phalanx's Companions or the tercio's dragoons win the cavalry skirmish; (b) if the dragoons are defeated, whether they're able to re-form and continue fighting; (c) once again assuming that the Companions win the cavalry engagement, whether the tercio's swordsmen are able to stop them from attacking the musketeers; and (d) if the musketeers are put to rout, whether the phalanx has enough peltasts left to keep up the harassing fire against the tercio's pikemen. (Am I forgetting any other factors?)

In short: The forces' respective composition makes an enormous difference regarding the outcome of the battle.

67.169.177.176 (talk) 00:37, 2 December 2011 (UTC)

Note that the Arquebus is a slow, heavy, short-range weapon. It's main advantages are ease of use and logistics, not tactical strength. If the phalanx is accompanied by auxiliary slingers, they may well have comparable or better ranged weapon support. --Stephan Schulz (talk) 10:07, 2 December 2011 (UTC)

The arquebus had a shorter tactical (not extreme) range than the slingshot, but had many times more stopping power, especially if both sides were wearing armor. And both these weapons had a much greater range than the throwing javelins of the Greek peltasts. Anyway, if you insist on adding auxiliaries that were not normally part of the unit (such as your example using mercenary slingers to reinforce the phalanx), you might as well also hire crossbowmen from the nearest town's militia to augment the tercio, in keeping with your spirit of using all the weapons available at the time rather than only those normally part of the unit. And of course the crossbow has a longer range than the sling, so there! 67.169.177.176 (talk) 21:09, 2 December 2011 (UTC)