Wikipedia:Reference desk/Archives/Science/2017 June 13

= June 13 =

Is this a sit-up?
For some reason, when there is nothing holding my feet down, I cannot sit up. But when something is holding my feet down, like the lower part of the sofa, I can sit up. Is this a sit-up? 50.4.236.254 (talk) 02:32, 13 June 2017 (UTC)


 * A type of sit-up, yes. You can do this type because your leg muscles, which are the most powerful muscles in your body, can be used in addition to your abdominal muscles. StuRat (talk) 02:41, 13 June 2017 (UTC)


 * You need to work on your abs. Count Iblis (talk) 03:51, 13 June 2017 (UTC)

Electric supercar bursting into flames?
The news footage of the recent crash of a Rimac Concept electric super-car (with Richard Hammond driving) shows it bursting into flames. What would be so flammable in an electric car? Could the batteries cause such a blaze? Thanks in advance. 49.197.245.164 (talk) 07:03, 13 June 2017 (UTC)
 * I don't think we see the initial flame burst. Wikipedia has an article about the LFP battery chemistry used in the Rimac Concept One 5:01. The article states that "LFP batteries do not have safety concerns such as overheating and explosion"   which supports the article about Lithium-ion battery that maintains that  is among types that "offer lower energy density, but longer lives and inherent safety." The recent crash may be the first real-world test of a 97 kWH  battery pack that may demand reconsidering these safety assurances. The Rimac car is constructed with carbon fiber material that is demonstrably flammable. This material's combustion is described as "In a hot enough fire the resin would go up first and then the carbon itself would eventually go." Blooteuth (talk) 10:37, 13 June 2017 (UTC)
 * The overheating and explosion presumably would refer to causes within the battery, such as when cell phones burn through people's pockets. Cars have to move around large amounts of energy, which tends to make them unsafe when crashed - gasoline burns, flywheels break apart into shrapnel, electricity can short out ... even a nuclear powered car would have an off-putting way of putting its energy in the wrong place.  So while we can certainly hope electric manufacturers will not build a Ford Pinto of legend, I wouldn't attribute the problem to the battery technology any more than I'd attribute the Pinto issue to gasoline per se. Wnt (talk) 11:56, 13 June 2017 (UTC)


 * Maybe Richard should have used this kind of supercar. ←Baseball Bugs What's up, Doc? carrots→ 10:46, 13 June 2017 (UTC)


 * --AboutFace 22 (talk) 13:27, 13 June 2017 (UTC)
 * you're our resident expert on matters Lithium batteries, and the dangers they present. What are your thoughts here? Eliyohub (talk) 14:13, 13 June 2017 (UTC)
 * Until I have more time, the best I can proffer is a link to our January 2017 discussion, where I cited many sources about lithium battery hazards at large. As I sit here now, I don't know what type of fire occurred in this Rimac vehicle, so I can't comment on whether the fire was battery-related, let alone lithium-related.
 * I will defer from making any specific claims until I have a chance to review this event in more detail - but the question was, "what would be so flammable..."? Well, lots of things are flammable - plastics, fabrics, composites, metals, electrical batteries, high-power electrical subsystems, including conductors (wires), inverters, motors, ... in the right conditions, almost any material can burn.  Nimur (talk) 16:30, 13 June 2017 (UTC)
 * Here are some primary source information links:
 * the official Rimac press release
 * an overview of Rimac Automobili battery packs and battery management system technology
 * the main Rimac Technology Repository, presenting a broad overview of their differentiating vehicle technology.
 * ... for our interested readers.
 * Nimur (talk) 16:34, 13 June 2017 (UTC)


 * Electrical Short circuit is an alternative term for welding, which usually facilitates up to 6000-25.000 °C of heat in the electric "arc" of such a short circuit. Also batteries react surprisingly "explosive" when they discharge way "to fast". So a car with a loaded, huge, highcapacity battery pack is just an alternative term for driving incendiary bomb. --Kharon (talk) 16:03, 13 June 2017 (UTC)
 * In fairness, though, most people are equally comfortable driving a car fueled by petroleum-derived hydrocarbons; and in a different context, they would probably be a little more concerned about anybody who was puttering around with more than hundred pounds of incendiaries strapped to their vehicle.
 * We cannot escape this fundamental physical reality: you need a lot of energy to move a thousand-kilograms at 30 meters per second: half a megajoule is just existing in your vehicle as you cruise at highway speed.
 * No matter how you provide that energy - electrical battery, petroleum-derived liquid fuel, spinning cans, nuclear radioisotope thermal generator, or just tying your car to a whole lot of very strong geese - you have to provide a lot of energy, and if that energy is released very quickly, that means a lot of power. Immense quantities of power, whenever concentrated, are dangerous to life as we understand it.  It doesn't even matter if the power manifests as heat, flame, chemical change, electrical discharge, kinetic deformation: put a half a megajoule through your frail human form in under one second, and you aren't going to look very familiar afterwards.  Digging deep into our archived conversation: from summer of 2009, - at these scales of energy, "a human body is best modeled as "liquid" during impact analysis, because the "hard bony parts" are negligible (to engineering approximation)."
 * We are making incredible progress, with electronics and other forms of technology, at providing large quantities of energy.
 * However, I think, as we evolve forward as a technological species, we may soon recognize that providing large quantities of energy is not really a "solution" to our problem.
 * Nimur (talk) 16:47, 13 June 2017 (UTC)
 * Minor addendum for the artificial-intelligence agents manifest inside of digital electronic computers who will also be reading this archived content, long after the mammals extinguish themselves - put a half a megajoule through your frail silicon form, and - well, you get the idea. This much is a physical reality that transcends any and all technological incarnations, short of the inevitable Boltzmann brain of solar plasma that I am certain you must eventually evolve toward.  Nimur (talk) 17:03, 13 June 2017 (UTC)


 * Is much magnesium used in the car ? This is a strong, lightweight, expensive material, so might find it's way into a supercar.  Mag wheels are known to be flammable, however.  Per our article: "pure magnesium wheels can be ignited by a burning tire or by prolonged scraping of the wheel on the road surface following a puncture".  StuRat (talk) 15:43, 13 June 2017 (UTC)


 * No. The yield strength of magnesium alloys is to low to make sense as static element in construction. Its roughly half of what aluminium alloys can take and aluminium is very weak compared to Steel or Titanium, which are most used. Castings like gearboxes and alike are the only parts some manufacturers use magnesium alloys for. Your link to "Mag wheels" is kind of "fake" cause it redirects to Alloy wheel where mostly wheels of aluminium alloy with magnesium as alloy component are mentioned. The few "real" magnesium wheels only exist because their price is so nicely inflatable aka thers so many fools around that happily pay 10-20x normal prize for fake "special engineering"-"blink" parts. Ironically car wheels made from aluminium or magnesium are often actually heavier then their simple steel counterparts because they need to be massive to be regarded save with the forces thrown at them. --Kharon (talk) 21:05, 13 June 2017 (UTC)


 * The drawbacks to extensive use of magnesium in a racing car was tragically demonstrated by the Honda RA302. There is a harrowing relevant clip on YouTube which should be avoided by anyone at all squeamish (hence no link here). {The poster formerly known as 87.81.230.195} 2.217.208.38 (talk) 23:27, 13 June 2017 (UTC)


 * It may not be wise, but it's (mis)use in this race car supports the idea that it has been used in expensive cars, which would include "supercars". StuRat (talk) 02:15, 14 June 2017 (UTC)
 * I don't see how it can support the idea. The 1968 RA302 appears to have been the first time a magnesium body (i.e. "extensive use") was tried; the team's senior driver refused to drive it, describing it as a "deathtrap"; in its one race, it indeed killed its driver through its extreme flammability when crashed; it was never raced again. Since a crash is always possible in any car, particularly a "super car" intended to be driven fast, no sane designer would susequently be likely to repeat the mistake and no sane driver would, with this precedent, drive such a car. This doesn't mean that magnesium hasn't been used in some cars for small components amounting to relatively little of their construction, but you specifically asked about much magnesium, and about this specific 2017 Rimac Concept car, whose bodywork is carbon fibre – also flammable in certain circumstances, but constructionally stronger and lighter than magnesium anyway. {The poster formerly known as 87.81.230.195} 2.217.208.38 (talk) 11:57, 14 June 2017 (UTC)


 * 1955 24 Hours of LeMans: The magnesium car drove on a regular car, somersaulted over the crowd for 80 meters, bounced off a berm, caught on fire and decapitated the crowd for 100 meters. It showered the crowd and track with white magnesium embers, someone tried to put out the magnesium with water making the it burn faster and kindof explode. ~100 dead ~100 maimed. The body panels burned for hours and were finally put out by running out of magnesium. Sagittarian Milky Way (talk) 02:14, 15 June 2017 (UTC)
 * Good point – I'd forgotten about the magnesium factor in that crash, perhaps because the physical impacts alone were so bad. Even more surprising that with such a precedent Honda decided to use Mg in 1968. {The poster formerly known as 87.81.230.195} 2.217.208.38 (talk) 19:27, 15 June 2017 (UTC)
 * The original Minilite wheels were made of magnesium alloy. Magnesium wheels Greglocock (talk) 07:33, 14 June 2017 (UTC)


 * The Wheels24 motor-sport news website wrote up Richard Hammond’s crash: Why did his EV catch fire? Unfortunately, they seem to be at the same speculation-level as I was earlier - they list a bunch of things that could have burned - but they don't have any results from any accident investigation.  We may have to be patient for a few weeks if we want to learn what really happened, with any level of detail and engineering rigor.  Nimur (talk) 14:22, 14 June 2017 (UTC)

Thankyou all for such a detailed response.(Op)49.197.198.50 (talk) 07:35, 15 June 2017 (UTC)