Wikipedia:Reference desk/Archives/Science/2013 July 20

= July 20 =

Bubbles in carbonated wated
Imagine an unopened can of carbonated water. At the molecular level, what does it look like? There should be a sea of H2O molecules, with some CO2 and carbonic acid evenly dispersed within it. Now, when the can is opened bubbles will form and rise to the surface. That means that the CO2 molecules, which were previously evenly dispersed within the fluid, decide the aggregate upon the reduction in pressure. Why does this happen? 74.15.137.253 (talk) 04:20, 20 July 2013 (UTC)


 * The nucleation article covers this. -- Finlay McWalterჷTalk 11:42, 20 July 2013 (UTC)


 * And note that this is part of a wider topic, how you can get chaos from order (or vice versa). Other examples include turbulence versus laminar flow and why matter isn't evenly distributed in the universe, as it presumably was right after the Big Bang. StuRat (talk) 19:35, 22 July 2013 (UTC)

Analog retransmitting rain gauge
Following up on my sprinkler question, now that I have good advice for how much it should run, I'm curious if I can get it working with an electronic rain gauge. I can see tons of them on Amazon with self-tipping rain buckets and a wireless receiver that reports the rain on an LCD display, and they're in the $25 price range. I'm trying to find one that retransmits the rain as an analog voltage or current on terminals I can connect to, or if I can't find one like that, then something that creates a voltage or shorts some contacts when the rain for some set period goes over a specified limit. Wireless isn't a big deal. 108.194.140.240 (talk) 12:10, 20 July 2013 (UTC)
 * There are bucket rain gauge tipping bucket rain gauges that you can buy, or should not be hard to construct, that contain a Reed switch or microswitch that provides a momentary closing contact each time the bucket fills. My understanding of what you want is that a sprinkler should start when pulses (bucket tips) are absent for a given rainless time. That might be achieved by using the pulses to reset a counter. The counter (say three CMOS 4161 counters wired to divide-by-4096) is clocked (say at 1.14 Hz by a 555 timer IC in astable mode) delivers a carry pulse to start the sprinkler when rain is absent for an hour. That arrangement with the commonly available components in brackets is a purely digital way to do it, and you may use different hardware. DreadRed (talk) 19:51, 20 July 2013 (UTC)
 * The system of watering timers which keeps reappearing at Home Depot etc. under different brand names includes a pair of gadgets, one is a (wireless) transmitter that sits imbedded in the lawn, the other a receiver which ends in a cable which can plug into the fancier timers.  A little experimenting might let you figure out what's what. Gzuckier (talk) 08:22, 22 July 2013 (UTC)
 * Good point - I had been focusing on the fact that they all seem to have a nice number displayed on the end, and wanted to tap into that, but the mechanical side of things will have a simple switch in it that is where the information is being derived from in the first place. My (completely overkill) sprinkler controller is a salvaged industrial PLC, so I should have no problem getting it to convert those pulses into precipitation counts. My plan is to calculate the average sprinkler rate with some flat pans scattered around the lawn, then have it combine that knowledge with the rain gauge to aim for the lawn receiving 1"/week overall. 209.131.76.183 (talk) 11:39, 22 July 2013 (UTC)

Putting a cadaver in a morgue drawer
Do you put it head first or feet first? OsmanRF34 (talk) 14:23, 20 July 2013 (UTC)
 * You ask the corpse for his preference. -- Jayron  32  14:39, 20 July 2013 (UTC)
 * LOL. See Necromancy 217.255.159.10 (talk) 14:50, 20 July 2013 (UTC)


 * The greatest mass (weight) of a body is situated in the torso. So it makes sense to place the cadaver head first on the draw to least strain the the draw glides. Other than that, the is no tradition that I know off, other than, in a large well organised morgue, it smooths daily procedures if the  cadavers are  always in the same orientation when transferring the cadaver  off and back on the gurney. The morgue staff then can then move them  feet first (which I think is a tradition in the west) without having to think about it.  I don't think there is even any effort to orientate the draws in an East-West direction – as it is not their final resting place. Next time I walk into one I will try and remember to take a compass – unless I am entering feet first myself, when it will be too late for me to reply to you.--Aspro (talk) 15:27, 20 July 2013 (UTC)


 * No reference - but I'd say it's regulated on a per-morgue basis: either all feet first or all head first. Head first would limit the load on the drawers by some amount, but feet first would mean that you don't have to open the drawer all the way to get a good look at the head.
 * No, wait...
 * It should be head first, so you can read the toe tag (if it's not an urban legend) without moving the drawer at all. 217.255.145.227 (talk) 17:36, 20 July 2013 (UTC)
 * Agreed - I've never seen a TV morgue where the corpse didn't emerge from the drawer feet first! Of course, WP has an article; Toe tag. Alansplodge (talk) 21:12, 20 July 2013 (UTC)
 * Oh, TV is more adaptable than that... in Pushing Daisies for example, or other programs where one converses with corpses, it's feet first (again, for ease of access to the business end, though in this case "heads" takes precedence over "toes". - Nunh-huh 20:21, 21 July 2013 (UTC)
 * From an accessibility standpoint, feet first looks logical for unidentified bodies, so it is easier to look at the face, and for identified bodies with wrist tags (see toe tag). Feet last is better for identified bodies with toe tags, as IP 217.255said. And it is better for TV productions with many bodies: you don't see the head, so it's less obvious if it's the same body over and over again.
 * The load on the drawer is hardly of any concern. Space would probably be the limiting factor on obese bodies, rather than weight. Not sure about extreme cases of "lead poisoning", though. - ¡Ouch! (hurt me / more pain) 12:49, 22 July 2013 (UTC)

Do they always detonate the explosives?
In Roving Mars, Steve Squyres, principal scientific investigator for the Spirit and Opportunity Mars Rovers, writes on page 211, "It's not a topic that NASA likes to talk about, but rockets can become wild, dangerous things when something goes really wrong with one. If a rocket begins to go seriously off course, it can be necessary to 'render the vehicle nonpropulsive,' as they like to put it, before it heads for a populated area. So every rocket—even the Space Shuttle—lifts off from its launch pad laced with high explosives." He goes on to say that if the rocket strays too far from its intended path, it's the safety officer's job to detonate the rocket. But he doesn't say what happens with all of that explosive ordnance if the rocket doesn't stray off its path. These stages that fall back to the earth with all the fuel and oxidizer used up with explosives too, do they always make sure those explosives go off? I'd like to see a source. 75.75.42.89 (talk) 14:55, 20 July 2013 (UTC)


 * If the launch goes to plan, the first stage (and/or strap-on boosters) will fall into an area that's known to be empty (or very sparsely populated, like a desert or a patch of ocean). An empty rocket stage isn't terribly dangerous (it's just a light metal section) - the reason for the safety feature is they don't want a fuelled section falling on someone. An interesting case is the self-destruct mechanism for the Space Shuttle's solid rocket boosters - that's described in this paper.  That works by triggering a linear charge which splits the booster casing vertically (like you were opening a banana) down 70% of its length. If the SRB was still active, the dynamic load on the propellant would shatter it and allow the flame front to engulf it all, so it would all be safely consumed before it reached the ground (other than for low altitudes, which is why they still need several miles of evac zone around the launch facility).  Note that spent SRBs are recovered from the ocean and are reconditioned - the spent ones clearly haven't been split open like bananas, so their range safety destruct mechanisms haven't been triggered, and are robust enough to survive the full launch, splashdown, and recovery cycle without accidentally triggering. I can't find documentation of the mass of the main self-destruct charge, but given that it only has to split a thin sheet of aviation metal, it's maybe only a few kg of plastic explosive. -- Finlay McWalterჷTalk 15:27, 20 July 2013 (UTC)


 * NASA's history portal contains a free book, Moon Port, which has a whole chapter on range safety during Project Apollo. Due to administrative choices, the Air Force controlled the technology and operation of the launch vehicle autodestruct.  Kennedy Space Center also maintains a current website on present range safety practices, including details of the Flight Termination systems.  Every range has its own practices, based on the types of hazards and the potential risk; for example, here is a Range Safety Manual for Wallops Island.
 * In some cases, operators of large rockets have legal (and ethical) obligations to guarantee that under no circumstance could a hazardous quantity of energetic material ever be present near e.g. populated areas. That includes guaranteeing separation of the material within a controlled area, even in the event of unplanned accidents!  For example, NASA publishes several technical standards and adheres to federal laws and regulations, as well as defense department practices, for handling hazardous materials.  This is one reason why rocket launch facilities are so remote; surrounded by high fences and enforced exclusion-zones; trajectories are carefully planned, and so on.  And should you ever find yourself inside an ordnance facility or rocket range, you'd be wise not to go trekking over the unmarked ground!  Unknown hazards, including unexploded ordnance, is frequently a problem on such facilities.  Nimur (talk) 16:33, 20 July 2013 (UTC)

Filling a gas cigarette lighter.
At the start: an empty see-through gas lighter and a full can of refill Butane fuel. When you refill the lighter it fills with liquid Butane to about 1/2 capacity. If you disengage the lighter and the refill can and then do the refill process again more fluid flows into the lighter. During the previous fill the contents of both the lighter and the refill can were at equal pressure as there was no further flow of gas/liquid yet when you go for a follow-up 'top-up' refill there is obviously a difference in pressure as more LPG enters the lighter - Can anyone explain the phenomena please?Jason Twell (talk) 19:17, 20 July 2013 (UTC)
 * When the lighter is first filled in the factory the LPG has to over come the  pressure of  atmospheric air already present in the lighter's tank. This atmospheric air slowly dissolves into the butane, so that during use, it escapes though the valve along with the butane. Therefore, the next time its filled there is less 'back pressure' from the what little atmospheric air is  still remaining.  So more butane can then be added than before. Place said lighter in a  freezer and the butane will become below its boiling  point and then, even more butane can be added.--Aspro (talk) 23:56, 20 July 2013 (UTC)


 * In your case the lighter had been filled at the factory and emptied. I suspect that what happened was that the butane coming out of the refill canister heated as it compressed in the butane lighter chamber while the gas in the refill canister cooled as it decompressed. The result was that temporarily the butane lighter chamber was warm and the refill canister was cool at matching pressures. While you waited, the refill canister warmed up (increasing the pressure) and the butane lighter cooled down (decreasing pressure).  As a result there was an available pressure differential for an additional "top up".Doppler13 (talk) 03:37, 21 July 2013 (UTC)