Wikipedia:Reference desk/Archives/Science/2017 January 27

= January 27 =

Microwave oven radiation and computer storage media
Does microwave oven electromagnetic radiation cause any harm (file corruption, data loss, etc.) to computer storage media (such as magnetic hard drives, floppy disks, optical discs, USB flash drives, solid-state drives, memory cards, etc.) that are right outside (not inside) the oven? If one were to stack five hard drives, USB flash drives, memory cards, etc., on top (outside) of a microwave oven, would it do anything? —Lowellian (reply) 04:50, 27 January 2017 (UTC)
 * Prob'ly not -- these things are very well-shielded (although with floppies, I'm not so sure). 2601:646:8E01:7E0B:7D41:3D:E6CE:B1EE (talk) 05:14, 27 January 2017 (UTC)
 * I agree, probably not, but if I had to store media right next to a microwave oven, I'd try to fit a sheet of steel, or perhaps just some aluminium foil between the media and the microwave, just in case any stray surges escaped the shielding. If the microwave has vents on top, then these shouldn't be obstructed.  Perhaps you could build a shelf to give a couple of inches separation just to be sure.    D b f i r s   08:19, 27 January 2017 (UTC)
 * Somewhat related:
 * https://www.youtube.com/watch?v=Fgm0FRN0KbU
 * https://www.youtube.com/watch?v=eZRK0Y8_VBc
 * https://www.youtube.com/watch?v=lKd92oU9ivs
 * --Guy Macon (talk) 14:09, 27 January 2017 (UTC)

Is this an approved method in other spacecraft?
. Have any spacecraft carried spare atmosphere(s) in tanks in case they need to depressurize? Are the insides designed to survive depressurization? (no lubricating oils boiling off and whatnot) Sagittarian Milky Way (talk) 09:47, 27 January 2017 (UTC)
 * Define "spare atmosphere". Any incident like this is almost certainly a mission-ending incident (it's not meant to happen, so the mere fact that it did happen shows that things were already out of control at that point, let alone any damage caused by the fire). So incident planning for this is likely to be of the "immediate return" basis. In that case, it's time for a switch to suit air, needing less volume to be provided. Even if the cabin is pressurised, it may not be pressurised with anything breathable. Also a suit is more flexible without a pressure differential to the outside.
 * As to depressurisation, then cabin equipment will work OK in a vacuum. It's designed to be largely vacuum tolerant by its choice of materials. When this is done very carefully for satellites, that's because they're facing a long period under vacuum and also there are only low forces involved. Welding or galling of metal-metal surfaces is a big problem for satellites, especially when a bearing is only moved by a low torque motor. In the capsule in an emergency though, such problems don't have time to develop and there's a hulking great cosmonaut hauling on the valve handle if it's a bit sticky.
 * Years ago I worked around the edges of comsat operations. We had satellites that could switch their transmitters to different antennae, with different coverage patterns. My team wanted to use these switches, maybe once a year. Operations vetoed this, as their satellite wasn't broken and they were terrified of any change, even throwing a remote switch that was designed to be used, in case something broke, owing to these vacuum welding effects. Andy Dingley (talk) 10:32, 27 January 2017 (UTC)
 * Wasn't the Gemini spacecraft designed to fully depressurize and repressurize for EVA's? 2601:646:8E01:7E0B:F868:9F8D:812:676B (talk) 11:26, 27 January 2017 (UTC)
 * Yes - see . Also the Apollo Lunar Module did not have an airlock, and was completely depressurised during moon walks, then repressurised again when the astronauts returned - see . Gandalf61 (talk) 11:45, 27 January 2017 (UTC)
 * Yes, that made the Gemini spacewalks much simpler to achieve, but both astronauts needed to suit up. See Leonov's problems in re-entering the Voskhod capsule through the temporary airlock. The Soviets used a collapsible airlock design that was stowed during launch and deployed externally. As Leonov's suit expanded in the vacuum, he had a lot of trouble fitting back in through it. Apollo used the same system to Gemini, even for the lander. Venting the cabin atmosphere was one of the constraints on mission duration though.
 * Although the Soviets were first to spacewalk (and almost died), the early US walks achieved a bit more, earlier on. The Soviets though then regained an advantage later, with Salyut, as they had already gained more early experience in operating airlocks, particularly in suits that were workable for them. Andy Dingley (talk) 12:13, 27 January 2017 (UTC)


 * To be pedantic, that is not quite right about equipment will still work in a vacuum. Alexey Leonov required an external fabric air-lock for his space EVA as the space capsule itself needed to maintain an atmosphere to convect away all the heat from thermionic valves (tubes). Where as, the Gemini craft that Edward White exited from, was a different creature. In a vacuum (think vacuum food flasks) electronic equipment can only loose heat by radiation and conduction. So it is not right that 'any' electronic equipment will work regardless of ambient gaseous pressure  conditions.--Aspro (talk) 15:41, 27 January 2017 (UTC)
 * Most low power valves run perfectly well in an external vacuum. They don't need to be cooled by airflow (and this wasn't what needed cooling in the Russian craft anyway). Most valves are already cooling themselves by radiation anyway, as their own internal pressure is so low. They will run a higher envelope temperature in vacuum, but that's rarely a problem.
 * High power valves use metallic anode caps to conduct heat out through the envelope. It's easy to arrange these with metal or liquid-cooled heatsinks, as a replacement for forced air cooling. Andy Dingley (talk) 15:50, 27 January 2017 (UTC)


 * Thought it was well understood that the metal alloy of the the thermionic pins and the glass enveloper have to have their coefficient of expansion closely matched to maintain a gas-tight  seal between the glass an metal - under 'normal' operating temperatures. Grab hold of a (say) a PL 105 thyratron used in the old 405 standard TV sets and you will discover how hot it gets. In vacuum, the temperature will rise well  beyond its design limits. Thus, was the reason that many an early 1950's American satellite failed immediately. The British boffins solved it with the successful deployment of Telstar. Space capsule avionics need incorporate things like transformers which  don't work  on DC  so the capsule needs a ruddy great inverter or two, which equals =  lots of heat. Metal heat sinks still need gaseous convection. Liquid coolants depended on ionic water and pipe work – look at a ground based water cooled radio transmitter valves and it should become obvious. Both would have added unnecessary mass.  Maintaining an atmosphere in Voskhod was the best compromise. The airlock was necessary for two reasons: first, the capsule's avionics used vacuum tubes, which required a constant atmosphere for air cooling. As Michael Caine might say: Not a lot of people know that!  But now -you do! --Aspro (talk) 22:16, 27 January 2017 (UTC)
 * Typo: 1960s Sagittarian Milky Way (talk) 23:57, 27 January 2017 (UTC)
 * While British boffins contributed in their ground station, the Telstar satellite was built by a team at Bell Telephone Laboratories that included John Robinson Pierce, an American who created the project; Rudy Kompfner, an Austrian who invented the traveling-wave tube transponder that the satellite used; and American James M. Early, who designed its transistors and solar panels. Telstar 1 and 2 are still orbiting after half a century and might work again if someone would pop up there and replace some transistors. Blooteuth (talk) 01:24, 29 January 2017 (UTC)
 * That paper is interesting... it suggests that ionization damage to transistors can actually repair itself. And the damage was because Telstar was nuked - many high energy particles striking were from Starfish Prime.  Which makes me wonder... has anyone tried to communicate with the satellite lately?  Would be really funny if it worked! Wnt (talk) 14:47, 29 January 2017 (UTC)
 * Telstar was preceded by the first Echo communications satellites, actually just gasbags that burned up after a few years. Much as I would like to tinker with an early Telstar it would involve a legal question of whether the maritime Law of salvage extends to Space debris that I cannot answer. Blooteuth (talk) 18:17, 29 January 2017 (UTC)
 * Well, if you can round up a big radio dish and get an answer from it, I don't think the legalities really matter. It would be a cool geek thing to do, and ... who's going to sue you? Wnt (talk) 02:29, 30 January 2017 (UTC)

Counteracting force
Say, a tiger is closing its jaws in a bite. Tigers reportedly generate around 4,450 newtons of bite force. How many newtons would be required to counteract this by holding its jaws steady? Generally, how do I calculate a force required to counteract another force either by balancing it out or progressively overcoming? Brandmeistertalk  15:13, 27 January 2017 (UTC)
 * About 4,450 Newtons ought to do it.
 * There's a different matter with crocodilians (and maybe tigers, I don't know). They have much stronger jaw closing muscles than opening them, so it's possible to hold them shut relatively easily (hand pressure), thus making them useless for the whole snapping and biting thing. Andy Dingley (talk) 15:25, 27 January 2017 (UTC)


 * The force needed to counterbalance a force of X is -X (so, an equal number of newtons going in the opposite direction), per Newton's first law.
 * Now, it might be easier to keep the tiger's jaw closed than to keep it open, and depending on how the force is applied maybe a balance of torque is a better way to approach the problem.
 * Needless to say, neither I nor Wikipedia condones a live trial, for obvious reasons of wellbeing of both parties (experimentalist and tiger). Tigraan Click here to contact me 15:35, 27 January 2017 (UTC)


 * OP where does that number come from? The word "newton" does not appear at your link, nor does the string '4,450'. The paper (I think) being referenced is freely accessible here, and the word 'newton' does not occur there. The study is based on muscle dissections, and "values reported here reflect FL [fiber length] and PCSA [cross-sectional area] at near-minimum gape". Table 4 gives forces at different locations, and Table 8 gives a total bite force of 703.74 kg for P. tigris, which seems to be 6,900 newtons or 1551 pounds.  SemanticMantis (talk) 16:50, 27 January 2017 (UTC)
 * Note that 4,450 newtons is 1,000 pounds of force. Wherever this number came from, it was obviously converted from pounds with excessive precision. --76.71.6.254 (talk) 02:09, 28 January 2017 (UTC)
 * The actual force will vary considerably, of course, depending on which tiger, which teeth (back teeth will exert more force than front teeth), how it holds its jaw, and whether it is feeling strong that day. Giving four or five significant figures seems spurious accuracy.    D b f i r s   17:16, 27 January 2017 (UTC)
 * You are welcome to complain about spurious accuracy to the editors of The Anotomical Record. I am not an anatomy expert, I only wanted to share the reference to the peer-reviewed literature. If you read the paper or even just skim the tables, you will see there are scads of results showing forces for different parts of the mouth, discussion of how the estimates relate to real world, etc. The reported force figures are an estimate, not an observation, and they are based off of methodology from a long chain of prior work devoted to deriving force from muscle observations. I cannot begin to evaluate that entire of body of work going back to the 1970s, but I can extend a basic trust in the reliability of a reputable journal, its editors, and peer reviewers. SemanticMantis (talk) 17:33, 27 January 2017 (UTC)
 * Yes, the authors do make it clear that they calculated the estimate using a simplified lever method over an average of eight tigers and that the accuracy is kept for the purpose of establishing correlation with body mass over a number of species of felids. My criticism was not of the authors, but of our selection of one piece of data to represent all tigers and all bites.  You did round the newtons appropriately.  I'd rather take their calculation as a good estimate than try field experiments for myself!  Thank you for sharing the interesting paper.    D b f i r s   19:01, 27 January 2017 (UTC)
 * Wikipedia has an article on tiger versus lion, and as our article makes abundantly clear, more expert scientists readily admit that tiger is stronger, faster, bigger, jumps farther, and weighs more than lion, and if matched, tiger would win. The strongest tiger is the Amur tiger or (snow tiger) and its bite force is compared to lion in this YouTube video.  Some scientists, who compile giant lists of rankings of animal bite-force, use bite force quotient to give Lion and other small animals an advantage in the rankings, by normalizing bite-force with weight; but even then, tiger still wins.   Nimur (talk) 17:35, 27 January 2017 (UTC) (نمر)


 * Note that it's not just about total force. The pressure also matters. For example, if you wanted to use some type of a pressurized bag in the mouth to hold it open, it would need to be able to resist the pressure at the teeth points, or it would rupture. StuRat (talk) 17:38, 27 January 2017 (UTC)


 * While we're at it, a funny point is that force can be in series or in parallel. For example, if you put two jacks side by side and started trying to open the tiger's jaws with them, then each might exert roughly half the force.  But if you and a friend put them back to back and each worked on opening a jaw, you'd each need to apply the full force with your jack.  Because the jack pushes from A against B - with each action there is an opposite reaction - so the bottom of each jack would be fighting the "reaction" from the other.  In the same way, if you have a piece of string under tension, each and every little subsection along the string is under the same tension. Wnt (talk) 14:54, 29 January 2017 (UTC)

Releasing pressurized gas near absolute zero
Say you were to place a pressurize gas inside a container, inside a large room, then lower the room and it's contents to near absolute zero, then evacuate all the air from the room (as near as you can get). The container then releases the gas, so that the pressure drops. This would normally cause cooling of the gas, but it can't go below absolute zero, so what happens ? StuRat (talk) 17:46, 27 January 2017 (UTC)


 * See Free expansion and the Joule–Thomson effect. This is basic physical chemistry stuff; I remember doing these sort of calculations like 20something years ago.  The math gets messy and calculusy, but if you get down to basic terms, temperature change is assymptotic the closer you get to absolute zero.  -- Jayron 32 18:27, 27 January 2017 (UTC)


 * There are two simple thought experiments that help understand your hypothetical experiment. I hope these are helpful and not too elementary. First, you assume that as you freeze the room, the container will cool as well. It logically should. As you lower the temperature of the compressed gas, what happens to the pressure of the gas? Pressure is caused by the little atoms/molecules bouncing around. As the gas cools, the little atoms/molecules move slower, bounce less, and reduce the pressure. As you approach absolute zero, the pressure drops to the point that you won't get a quick expansion of the gas. An interesting topic: Does gas at absolute zero expand? Second, you assume that the gas is as cool as the room. If the room is an absolute vaccuum at absolute zero, the gas is the only source of heat for the room. The gas will be relatively warmer. Since we can't yet get gas to absolute zero, it will always be more than absolute zero and have the ability to cool as it expands. 209.149.113.5 (talk) 18:58, 27 January 2017 (UTC)


 * No (zero) Thermodynamic energy simply is just that. What you ask is like asking how long a tree falls if you cut it off from a chopped down tree. It has already fallen and therefor cannot fall any more. --Kharon (talk) 21:03, 27 January 2017 (UTC)


 * A real gas would turn solid or liquid when you got close to absolute zero. When you open your container it would fall to the bottom of the room and get some energy that way. But as everyone above is saying, no expansion will happen. So you may ask why in cold outer space doesn't the hydrogen condense to solid hydrogen? Graeme Bartlett (talk) 21:33, 27 January 2017 (UTC)


 * Because in deep space, pressure is too low. State of matter is a complex dance between pressure, volume, and temperature, and while temperature is indeed low enough in deep space, the other two factors (volume and pressure) are respectively far too high and far too low to cause hydrogen to condense into a liquid or a solid.  In simple terms, in order to form a condensed phase (solid/liquid) a material needs 1) sufficient intermolecular forces 2) low enough temperature and 3) close enough proximity to other molecules to "grab" on to them (high pressure/low volume).  For hydrogen in deep space, it only has the one (low temperature).  IMF in a tiny molecule like hydrogen is such that extremely close proximity between molecules is necessary to get them to "grab" on to each other enough to overcome even a miniscule amount of kinetic energy; that's why metallic hydrogen requires such extreme pressures to form; even at near absolute zero, hydrogen molecules need to be crammed very close to each other for the extremely tiny london forces between them to form a condensed phase.  -- Jayron 32 05:18, 28 January 2017 (UTC)


 * Note too that even in the openest of open space the temperature will not fall below the temperature of the cosmic background radiation, which is around 3 degrees Kelvin. This is not high enough to melt hydrogen, but it is high enough to drive sublimation. Looie496 (talk) 15:03, 28 January 2017 (UTC)


 * How would you open the container without adding some heat to the setup? Richerman    (talk) 15:22, 28 January 2017 (UTC)


 * Use a plug that will sublimate away into space, leaving a hole behind ? StuRat (talk) 16:57, 28 January 2017 (UTC)
 * Use a solid plug that shrinks as it approaches absolute zero? Use lasers to form a virtual container that you can shut off? There are many ways to have a "container" open without adding heat to a closed system. 209.149.113.5 (talk) 14:30, 30 January 2017 (UTC)