Wikipedia:Reference desk/Archives/Science/2020 August 13

= August 13 =

Wash inside out
Why do laundry labels tell you to wash clothes inside out? Thanks, DuncanHill (talk) 14:30, 13 August 2020 (UTC)
 * So that the extra abrasiveness of being tossed around in your washing machine doesn't cause extra wear on the outward-facing parts of your clothes. Things like screen printing on T-shirts can fade or become damaged.  -- Jayron 32 15:00, 13 August 2020 (UTC)
 * Additionally, when the textile surface rubs against other clothes, fibres of the thread strands break. This makes the textile surface more fuzzy, so that it will capture and hold minute pieces of broken fibre floating around in the wash water. This in turn will make its colour look faded (especially if dark clothing is washed together with light-colored textiles) or not quite clean (for white clothing washed with dark textiles). Better to have this off-colour appearance on the inward facing side of your clothes. --Lambiam 17:58, 13 August 2020 (UTC)
 * Thanks both, so nothing to do with cleaning as such. Hmm. Well I don't have any screen-printed clothes, and I prefer what I wear to look lived-in rather than new, so I'll continue to save time by not turning things inside out only to turn them outside out again afterwards. DuncanHill (talk) 20:42, 13 August 2020 (UTC)
 * In the case of undergarments it could also help with cleaning, since it is mostly the inside that will need cleaning and turning them inside out will expose the inside to more water.--Shantavira|feed me 08:06, 14 August 2020 (UTC)
 * the fuzzying Lambiam described is called pilling and that's what I always understood the purpose of the instruction to wash stuff inside-out as meaning to prevent delay, too. Aecho6Ee (talk) 12:31, 19 August 2020 (UTC)
 * Our article specifically mentions "Textile authorities say consumers can prevent or postpone pilling ... by turning clothes inside out before washing them." --Lambiam 13:02, 19 August 2020 (UTC)
 * Is what we see here an instance of red pilling? --Lambiam 13:02, 19 August 2020 (UTC)

Inverted flight
I recently recently discovered that the explanation I have always heard for how wings work, is wrong. According to this article, the actual mechanism is this:

As air flows over the curved upper surface, its natural inclination is to move in a straight line, but the curve of the wing pulls it around and back down. For this reason, the air is effectively stretched out into a bigger volume—the same number of air molecules forced to occupy more space—and this is what lowers its pressure. For exactly the opposite reason, the pressure of the air under the wing increases: the advancing wing squashes the air molecules in front of it into a smaller space. The difference in air pressure between the upper and lower surfaces causes a big difference in air speed (not the other way around, as in the traditional theory of a wing). The difference in speed (observed in actual wind tunnel experiments) is much bigger than you'd predict from the simple (equal transit) theory. So if our two air molecules separate at the front, the one going over the top arrives at the tail end of the wing much faster than the one going under the bottom. No matter when they arrive, both of those molecules will be speeding downward—and this helps to produce lift in a second important way.

However, I don't see how this explanation resolves the issue of how aircraft fly inverted. In my unsophisticated view (I'm not a physicist, this is just my intuition), any explanation for how a wing works both ways has to involve gravity, or else there would be no way for the wing to "know" which way is down. -- Puzzledvegetable Is it teatime already?  18:59, 13 August 2020 (UTC)
 * You assume that there is only one way of a wing to generate lift. That assumption is wrong. A wing can generate lift by its shape, but also via its angle of attack. An aircraft that is flying "upside down" for extended periods of time does not have the plane of its wing perpendicular to the force of gravity, but rather angled upwards. This directs air down, providing lift via Newton's famous actio est reactio. --Stephan Schulz (talk) 19:21, 13 August 2020 (UTC)
 * The article in question shows the wing angled upwards slightly. I assumed that was always part of it. What I don't understand is how the same wing on the same plane can do both. The article says this is possible because of the lift caused by downdraft, but I'm not sure why that should be enough to cancel out the downward 'lift' from the inverted wing. -- Puzzledvegetable Is it teatime already?  19:51, 13 August 2020 (UTC)
 * The wings shown in the article are all asymmetric airfoils (i.e. top and bottom is not the same). These wings generate lift even when their chord is horizontal. If you want to fly upside down with these wings,you will need to angle them, otherwise they would not create lift but downforce (like the wings on an F1 car). There exist also foils that are symmetrical, but these can still fly when put at an angle. Even without an angle, having ailerons will allow such wings to generate lift up or down depending on the angle of the aileron. Such symmetric foils are still used in Acrobatic airplane I believe. Rmvandijk (talk) 11:47, 14 August 2020 (UTC)
 * Prof Mike Merrifield gives a nice explanation of the surprisingly complicated way in which wings work (including inverted flight) which you can find on YouTube by googling "sixty symbols lift and wings" — Preceding unsigned comment added by 37.175.69.231 (talk) 07:08, 14 August 2020 (UTC)
 * I think lift (force) does a good job of explaining if you read it all the way through, though it's a bit on the verbose side. The really really short version, to try to help with an intuitive grasp of it, is wings produce lift by pushing against the air. All the stuff about angle of attack, wing shape, etc., is just about the factors involved in getting a wing to push sufficiently to support the craft. A stall is what happens when the wing stops pushing sufficiently. And lighter-than-air flight works by getting the atmosphere to "do the pushing" itself due to the density difference, same as with buoyancy in water. --47.146.63.87 (talk) 00:11, 15 August 2020 (UTC)
 * User:Puzzledvegetable has found one of numerous popular science articles that attempt to be sensational about debunking classical science. They contain a little bit of truth and that is what makes them plausibe to general audiences. You can read about another example at Talk:Lift (force). Dolphin ( t ) 07:58, 15 August 2020 (UTC)

Terror Crocodile’ the Dimensions of a Bus Fed on Dinosaurs, Examine Says - New English?
What is HAVEERU ONLINE? AboutFace 22 (talk) 20:50, 13 August 2020 (UTC)
 * I don't think the science reference desk can help answer your question on what a random website it. As for what the website is, we have an article that may help. Do you have a specific question relating to the content of that website? --OuroborosCobra (talk) 21:08, 13 August 2020 (UTC)

My question is about the broken English in the article. Sometimes it seems to obscure the meaning. I am curious what it is? AboutFace 22 (talk) 22:17, 13 August 2020 (UTC)


 * .mv is the domain name for the Maldives. From a quick look at the website, I suspect it's a news aggregator reproducing content from elsewhere. --174.89.49.204 (talk) 02:11, 14 August 2020 (UTC)


 * See Haveeru Daily. --Lambiam 04:00, 14 August 2020 (UTC)


 * Very likely some machine translation, or automatic manipulation to avoid copyright infringement. Graeme Bartlett (talk) 05:13, 14 August 2020 (UTC)


 * The uncredited New York Times article of which this is a paraphrase is written in English. A forth-and-back translation then? BTW, Dhivehi is not on the list of languages Google translate knows to handle. Most of the changes consists of substitutions by synonyms (sometimes bizarrely inappropriate ones), so by the looks of it this may indeed have been produced by a not very sophisticated app for confounding plagiarism detectors. --Lambiam 10:38, 14 August 2020 (UTC)

I've kept thinking about it after I posted. I think it is a scam to avoid copyright infringement lawsuits, as @Graeme Bartlett said, for the sake of shameful advertisements which is on the right margin of the page. I wonder what the NYT thinks about it? AboutFace 22 (talk) 14:06, 14 August 2020 (UTC)