Wikipedia:Reference desk/Archives/Science/2016 July 7

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July 7

Wind strength of compressed air

Imagine an invisible field that takes the form of a sphere 1000 meters in diameter filled with air. It is shrunk to a sphere 0.1 meters in diameter. Place it at sea level and shutdown the field. What would the strength of the resulting winds be? — Melab±1 ☎ 00:27, 7 July 2016 (UTC)

During your magic step that causes the sphere to shrink and the air to become compressed, are you assuming isothermal compression or adiabatic compression or something else? This important detail changes everything - including the equation(s) you need to apply - for the resulting pressure and temperature of the gas inside the sphere. Nimur (talk) 01:37, 7 July 2016 (UTC)

Would such hypothesized compression change it into a liquid or maybe solid state? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:40, 7 July 2016 (UTC)

No way! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 07:26, 7 July 2016 (UTC)

Remind me as to what isothermal compression would do. All I had in mind was this acting like a spring with just compression. — Melab±1 ☎ 21:46, 8 July 2016 (UTC)

I want to assume isothermal compression because I am envisioning pressure change. — Melab±1 ☎ 22:02, 8 July 2016 (UTC)

The wind will almost certainly be turbulent, which doesn't help matters. Where the hyperpressurised air (which, as the IP above points out, would be above its critical point and therefore would become a supercritical fluid) meets the normal air, all sorts of weird turbulence things would start happening along the boundary, which means that to calculate how the air actually flows, you'd need to solve the nasty Navier–Stokes equations. You could try simulating it with Computational fluid dynamics - there are lots of CFD simulators available online, although many of them are very hard to use. Smurrayinchester 08:23, 7 July 2016 (UTC)

First I would point out that a compression of 1e12 is ridiculous.my approach would be to work out the potential energy of the resulting sphere,eqate it to tons of TNT,and look up the effects of a groundburst of that size of bomb. The windspeed can exceed Mach 1. Greglocock (talk) 09:46, 7 July 2016 (UTC)

Sadovsky formula is a good phrase to search for.Greglocock (talk) 10:22, 7 July 2016 (UTC)

Ridiculous in what way? Mach 1 seems too low. — Melab±1 ☎ 21:46, 8 July 2016 (UTC)

The density of the compressed air would be about 10⁹ kg/litre. This similar to white dwarf matter but below that of neutron star matter. The pressure would be very extreme. perhaps 10¹⁶ atmospheres. Heisenberg's uncertaintly principle can get a handle on the speed. Also this pressure is likely enough to trigger fusion of oxygen and nitrogen. Graeme Bartlett (talk) 13:27, 7 July 2016 (UTC)

I didn't think it would be that dense. What would oxygen-nitrogen fusion look like? Is it even a common thing in stars? — Melab±1 ☎ 21:46, 8 July 2016 (UTC)

Are you assuming adiabatic compression, isothermal compression, or both? I think you assuming isothermal compression since you don't mention temperature, but you speak of fusion which normally involves high temperature, so I am uncertain. — Melab±1 ☎ 22:04, 8 July 2016 (UTC)

How about some calculations. Original volume ≈ 524000000 cubic meters. Mass of air in this 6.68×10⁸ kg. Your compression ration is 10¹². Density in your compressed sphere 1.275×10¹² kg/m³. Air has 28.96 g/mol. mol/g of electrons is about 0.5. So electron density is 6.022×10²³×1000×0.5×1.275×10¹² = 3.839×10³⁸ electrons per cubic meter.

What is this supposed to tell me? — Melab±1 ☎ 20:02, 9 July 2016 (UTC)

Calculating further, speed of electrons is around 10¹⁰ meters per second. This is way over the speed of light, so the state is relativistic. Energy per electron is 5.251×10⁻¹¹ joules. This is extremely hot, even if you try to remove all energy. The pressure comes to about 10²⁸ Pascals which is also huge. In that volume the energy would be of the order 10²⁵ joules which compared to the most powerful bomb ever exploded: 2×10¹⁷ joules, far far exceeds it. Graeme Bartlett (talk) 10:43, 10 July 2016 (UTC)

Total solar eclipse

Maps showing the band of totality of the solar eclipse of August 21, 2017, such as this one, usually show a line at the center of the band. What does this line represent?

I know that obscuration is at least 100% everywhere in the band, increasing slightly above 100% as you move toward the center. What is the difference in the viewing experience near the inside edge of the band, as compared to that at the center, if any?

I have a brother who lives in Kansas City. I used an online tool to determine that his house will see 99.97% obscuration, being just outside the band. I assume that it will be worth the short drive to get within the band, but would it make any noticable difference to drive farther north? It would be an hour's drive to St. Joseph. ―Mandruss ☎ 08:58, 7 July 2016 (UTC)

The duration of totality. The line at the centre of the band of totality indicates where totality lasts longest. If you're just inside the band of totality, it only lasts for a few seconds. Close the the centre, it may be more than 5 minutes. On the other hand, close to the edge the effects associated with beginning and end of totality (Baily's beads) will last a bit longer. If you want to see the corona, go for the centre. If there are scattered clouds, a longer duration means more chance to see something. PiusImpavidus (talk) 09:53, 7 July 2016 (UTC)

Ah, now I see. According to this tool, totality in that area, at least, will range from about one second just inside the band to about 158 seconds at the centerline. I suspect he'll go to the center. ―Mandruss ☎ 11:35, 7 July 2016 (UTC)

It could be worse. 30 years ago there was a flash totality in the ocean that was slightly over 0.15 seconds. Sagittarian Milky Way (talk) 09:49, 8 July 2016 (UTC)

Snake ID?

This snake fell on my mother as she was walking out the front door of her house this morning. She's located in Southern Oaxaca, Mexico, right on the coast. They called it a "ratonero." Any thoughts? I apologize about the picture quality. Could it be... a fer de lance? Pics. Justin15w (talk) 15:43, 7 July 2016 (UTC)

First, always assume it's dangerous if you don't know what it is. Second, we'd probably need a much clearer shot of the head, pix, but see the first point. There is also the point that ratonero means "rat hunter", and there are many different species of "rat snake" world wide, some of which look very similar to this specimen. Finally,I do not see the term ratonero used to describe the fer de lance at Spanish wikipedia (where it has a lot of local names, mostly dealing with appearance) or elsewhere on the web. μηδείς (talk) 18:22, 7 July 2016 (UTC)

This is frustrating. The image quality is not good enough for me even to hallucinate an answer to whether there are loreal pits; clearly, identifying a pit viper would be a useful start here. The shape of the head seems suggestive, but I don't know how misleading it can be. Searching ratonero serpiente on Bing got me something with similar-ish black rings, but they become staggered into a zigzag later and there aren't clear black rings on the side of the body. [1] Worse, it's labeled merely "Vibora" (viper). So I don't think I'm beating it that way. I just don't have enough image to work with to do this any proper way. But maybe a decent naturalist will just recognize it... Come to think of it, I don't know why with all the fancy-dancy AIs out there that claim to keep track of individual people by their faces can't solve the question of which snake is on a low-res photo. Wnt (talk) 19:58, 7 July 2016 (UTC)

When AI gets to that point, think either Matrix or Terminator.

What appears, to me, to be the wider hind jaw makes the snake look more like a viper such as the fer de lance, rather than a colubrid, which includes Elaphe and the other rat snakes. (Think rattlesnake or adder for viper, and gartersnake for colubrids.) I am wondering if there' a zoo or university of Oaxaca we could contact. μηδείς (talk) 21:01, 7 July 2016 (UTC)

I think I will conclude by saying that the question is not either or. This doesn't have to be either a fer de lance or a rat snake. It could very well be an anaconda. (Well, no, not an anaconda, but I assume you get the point; we lack the data.) μηδείς (talk) 22:06, 7 July 2016 (UTC)

• @Justin15w:, do either you, your mother, or someone handy speak Spanish? I have looked at some websites re schools in Oaxaca, but they have been "under construction" or otherwise not very helpful. What I would do here in the states is call the main directory for NYU, Cornell, Rutgers, or another local school and as for the biology department, and could I email them a picture. If you (pl.) are not Spanish speakers yourselves, I can help, but I am just not sure which local school would be the best to contact. μηδείς (talk) 23:55, 7 July 2016 (UTC)

The photo is indeed blurred, but provides contradictory clues. The head is wide at the back and narrow at the front,and seems to transition to a skinny neck and its wedge shape suggests a pit viper. The tail tapers very gradually, unlike certain venomous snake I have met such as water moccasins. In the US, at leas, venomous snakes (except coral snakes) have fat bodies. I would stay the hell away from it. The Wikipedia articles on various poisonous snakes such as fer de lances (or fers de lance if you prefer) have lousy illustrations. The Wikihow article on identifying poisonous snakes might almost be a humor piece from The Onion, since it says to examine the scales on the bottom of the snake's tail, then it says to examine the bite marks on your hand. Edison (talk) 03:56, 8 July 2016 (UTC)

Railway Prince Rupert–Valemount

When was the railway line from Prince Rupert to Valemount in British Columbia built?--Kopiersperre (talk) 16:04, 7 July 2016 (UTC)

The Valemount article mentions that the station was moved there in 1927. Rojomoke (talk) 16:24, 7 July 2016 (UTC)

More information at Rails Over the Mountains: Exploring the Railway Heritage of Canada's Western Mountains by Ron Brown. A station opened at Swift Creek in 1915 and was moved (presumably the whole station building was moved) to Valemount in 1927. It was moved again to become the local museum in 1992. Alansplodge (talk) 16:55, 7 July 2016 (UTC)

See also the Valemount Museum website which gives a date of 1914 for the original building, which it says was in "a town called Swift Creek [which] was just up the creek". Alansplodge (talk) 16:55, 7 July 2016 (UTC)

SIGNIFICANT DATES IN CANADIAN RAILWAY HISTORY gives a date of April 7, 1914: "Grand Trunk Pacific Railway main line is completed between Winnipeg, Melville, Edmonton, Jasper and Prince Rupert. The last spike was driven at a location 93 miles west of Prince George, BC". Alansplodge (talk) 17:02, 7 July 2016 (UTC)

Main Battle Tanks

Are the NATO tanks armored with composite armor at the sides of the hull ? 94.249.30.80 (talk) 21:14, 7 July 2016 (UTC)

Yes. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 21:31, 7 July 2016 (UTC)

...And no. 2606:A000:4C0C:E200:650F:AAC:B91D:D63C (talk) 22:49, 7 July 2016 (UTC)

Does the "Main" modify "battle" or "tank?" Edison (talk) 03:35, 8 July 2016 (UTC)

Well it's both: of the things called "battle tanks", this is the main one. Or is this a joke I missed? Yes battle tank links to the same article, but it explains that even though there are still "light tanks" which are battle tanks, it's more of a historical distinction when there used to be light, medium, heavy and super-heavy battle tanks. Vespine (talk) 04:39, 8 July 2016 (UTC)

Ultra-heavy tank aka leviathan aka landship. Indestructible. Sinks into and gets stuck in any soil it drives on. After one passed road can't be used by anyone. Has many decks. Sagittarian Milky Way (talk) 06:16, 8 July 2016 (UTC)

Like this one? ;-) 2601:646:8E01:7E0B:ECDB:601F:4E1E:971F (talk) 06:52, 8 July 2016 (UTC)

More like this land leviathan perhaps? ;-) Dmcq (talk) 07:59, 8 July 2016 (UTC)

Pfft, all that for only 100,000 square miles? How land-starved can you be? Sagittarian Milky Way (talk) 09:24, 8 July 2016 (UTC)

Well people , thank you for your contributions , but I`m asking about : M1 Abrams , Challenger 2 , Leclerc and Leopard 2 . Also note that I`m not asking about the added external armor modules , I`m asking about the main body of the tank .149.200.213.154 (talk) 08:29, 8 July 2016 (UTC) I think you want to say : if tanks were heavily armored from sides they will be immobile .149.200.213.154 (talk) 09:21, 8 July 2016 (UTC)

One respondent to this forum thread states (without a reference): "M1's side hull protection is relatively advanced when compared to other tanks. In the frontal part over driver compartment it is spaced array made from ~70mm thick ballistic skirts + ~60-70mm thick hull sides + fuel tank compartment + internal bulkhead. Over crew/turret compartment it is ~70mm ballistics skirt + ~60-70mm thick hull side. Over engine compartment it is several mm thick non ballistic skirt + ~30-40mm thick hull side. Besides this, hull sides protection are optimized to provide adequate protection within the angles of safe manouvering, which is 60 degree frontal arc of vehicle". Alansplodge (talk) 20:42, 10 July 2016 (UTC)

Safety valve

I am currently looking for a high-pressure safety valve, but can't find one which meets all my specs -- I found one which has the right inlet size, but the maximum pressure is too low (above the working pressure for my apparatus, but far below the normal peak pressure due to water hammer, which means it will open momentarily on each and every startup), and another which has the right maximum pressure, but its inlet is too small. Out of these two evils, which is the lesser one -- or are these both completely unacceptable? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 23:17, 7 July 2016 (UTC)

The first one sounds safer, as the 2nd one may not drain off the water fast enough to prevent pressure build-up. Some suggestions:

1) Find a way to start up the system gradually, to reduce the water hammer. Do you start up a pump ? Then start it at reduced voltage (ensure that this is safe for the pump first). Do you open a valve to start the system ? Then open it more slowly. This solution may have other benefits, like reducing the wear and tear on the system.

2) Let some water be released during startup. Of course, the acceptability of this solution depends on the situation. In something like a lawn sprinkler system, losing a bit of water is probably fine, as long as it drains safely into the lawn.

3) Use more than one of the smaller safety valve, so that the max flow rate is the same as the large safety valve. Of course, this may involve cutting pipes and joining them back together. This should actually be safer than a single safety valve, especially if the safety valves are widely separated. StuRat (talk) 01:20, 8 July 2016 (UTC)

Well, of these 3 choices, (1) is not really an option -- the pump gets its power directly from the mains with no voltage regulation (other than overvoltage protection). (2) is actually OK -- I expect the blowdown volume to be small, and although the liquid is somewhat hazardous (dilute phosphoric acid with copper salts), the discharge line will drain it directly into a waste container. (3) is possible, but will add cost and complexity. So I think I'll shop around some more, but if I can't find anything, I'll go with (2) -- especially since the pressure I'm looking for actually represents the worst case, and the actual pressure spikes could be much less. 2601:646:8E01:7E0B:ECDB:601F:4E1E:971F (talk) 07:21, 8 July 2016 (UTC)

Is the problem with the inlet size merely that it doesn't match your system connections, or that it would not provide adequate flow to relieve your overpressure quickly enough? Usually pretty trivial to get or build adapters for any pipesize differences as long as the relief itself actually works well enough. StuRat makes a good point that avoiding the water-hammer itself by careful system control or (re)design might be better in the long run. Another option for that is an air tank that can act as a damper to even out the pressure (lots of residential and commercial water systems have these). DMacks (talk) 03:06, 8 July 2016 (UTC)

The maximum flow is actually pretty small, so the flow through the relief valve will in fact relieve the overpressure -- the only problem is that the connections don't match. And my apparatus does in fact include an air chamber (an improvised one -- an upward-pointing dead-end pipe with its top end capped, like in a residential system but bigger and with a high pressure rating), so the pressure spikes will definitely be smaller than my worst-case calculations predict -- the only problem is, I couldn't do any testing of the system (not without a safety valve!), so I don't know how much smaller. So, with all that in mind, would it be better to use (1) the lower-pressure valve which fits the connection (which might or might not waste the reagents upon startup), or (2) the smaller higher-pressure one with an adapter? Also, if the better choice is (2), am I correct that the set pressure will have to be adjusted downward because of the smaller diameter? 2601:646:8E01:7E0B:ECDB:601F:4E1E:971F (talk) 07:21, 8 July 2016 (UTC)

You need to get both of those right. Safety valves which opened, but were too small to reduce pressure faster than it built up, have been a historic cause of boiler explosions. I'm surprised if water hammer is bad enough to open the valve though. Normally mechanical inertia (rather than spring pressure) is enough to avoid that. Maybe a larger (and so more massive) valve would be more resistant to it? If a system has water hammer to that level, I'd be concerned that the water hammer is going to be its own problem and needs to be addressed, probably by arranging an air reservoir. Andy Dingley (talk) 09:28, 8 July 2016 (UTC)

I actually don't know whether water hammer will open the safety valve -- it would according to my worst-case calculations, but I haven't tested (or even built) my apparatus yet, so I have no way to know for sure. And the plumbing does include an air chamber -- so the water hammer will be less than what I calculated (I just don't know precisely how much less). 2601:646:8E01:7E0B:ECDB:601F:4E1E:971F (talk) 09:59, 8 July 2016 (UTC)

My suggestion is option 2, just for testing purposes. If there is leakage, then I would revisit option 1. For example, a rheostat could be installed between the mains and device, allowing you to turn a dial to turn the voltage up. However, you would need to ensure that it's safe to run the pump at reduced voltage, even though it would only be for a second during startup. This is also far less work than cutting into pipes to install an additional safety valve. Note that the rheostat may overheat if used at low voltage, due to the resistor used. (The more common type of "dimmer switch" used these days rapidly turns the power on and off, instead, but this might not be good for the pump.) StuRat (talk) 16:22, 8 July 2016 (UTC)

Take a look at the valve closest to your requirements first. It probable came in a box of some sort with a label. Phone (not email) the company on that box and ask the switchboard to put you through to their Technical Department (rather than their customer help desk – as they just go by a script and are not tech people). Explain your application. Even if the company does not offer the right valve for you, these real tech people love to help and can redirect you to maybe a different company. Have a note-pad and pencil to hand when you phone so that you can right it all down. Andy Dingley mentioned an 'air reservoir', the tech dept however, might refer to such as a nitrogen bag accumulator. So when they say anything you don't immediately understand, question for clarification and write it down. I used to work in R&D and found it helpful (essential) to learn how to negotiate my way through a switch-board and get to talk to a person that had the right technical knowledge, making sure I had a note of their names, positions, tele ext etc., in case I needed to refer back to them at a later time. It sounds like your application is too specific for us to answer with out you suppling detailed information – and that is why technical departments exists. --Aspro (talk) 20:18, 8 July 2016 (UTC)