Wikipedia:Reference desk/Archives/Science/2017 August 23

= August 23 =

Before a storm, do electrons turn from - to +  or  + to -  ?
}}}} — Preceding unsigned comment added by Lgklange (talk • contribs) 00:23, 23 August 2017 (UTC)


 * Electrons are always negative.Dja1979 (talk) 04:00, 23 August 2017 (UTC)


 * Dja is right, but the flow can be up or down, with hugely different effects, see lightning. μηδείς (talk) 04:45, 23 August 2017 (UTC)


 * I'm guessing that what you meant to ask is if positive or negative ions form before a storm. The answer is both.  That is, a roughly equal number of positive and negative ions form, and are physically separated.  Lightning occurs when the charge equalizes by the electrons moving from the negatively charged area back to the positive. StuRat (talk) 20:19, 23 August 2017 (UTC)

Name for optical illusion?
Hello, how is this optical illusion called? Obviously some kind of tunnel-y 3D effect :), but I am looking for a more formal descriptive name for this Commons image. Bonus question: which Commons category in Commons:Category:Optical illusions should this image be placed in? GermanJoe (talk) 10:55, 23 August 2017 (UTC)
 * Is this a Fraser spiral illusion? -- Jayron 32 10:57, 23 August 2017 (UTC)
 * No. The Fraser spiral illusion only appears to be a spiral. The illustration shown here really is a spiral. I'm not convinced it is an "illusion" of any sort.--Shantavira|feed me 11:20, 23 August 2017 (UTC)
 * This seems simply an Interference (wave propagation)-picture with no special name, as far as i am aware. Sorry if i hurt the artist who generated it by revealing his rather simple technology. The possible Interference-patterns are almost endless and only a few typical patterns have a name, usually in connection to their meaning in/for technology and science, like the better known Moiré pattern due to its broad appearence in display and image technology today. This is also the base of Interferometry which is very important and often used in science and technology, like for example as Astronomical interferometer. --Kharon (talk) 11:49, 23 August 2017 (UTC)


 * If you are referring to the fact that the pattern seems to vibrate, that's basically a type of grid illusion often generated by interference patterns. If you're referring to the fact that it gives a sense of three-dimensionality, that isn't considered an optical illusion, just an aspect of human depth perception. Looie496 (talk) 14:06, 23 August 2017 (UTC)


 * Well, it's the cover to a book on optical illusions.
 * We have articles on grid illusion and Illusory motion, which both seem to be present in this image. But I don't know that this exact image has a name. ApLundell (talk) 14:23, 23 August 2017 (UTC)
 * The illusory motion could be creating a secondary Kinetic depth effect; that is the fact that the image appears to vibrate slightly may also add to the sense of depth in it. -- Jayron 32 14:52, 23 August 2017 (UTC)
 * Hah! That article looks like it's trying to cram the whole spinning dancer article into an image caption. ApLundell (talk) 16:56, 23 August 2017 (UTC)
 * Not anymore. Good thing we have a freely-editable encyclopedia.  -- Jayron 32 18:21, 23 August 2017 (UTC)
 * Here's an illusion where the wheels of a car appear to be turning backwards . 81.151.100.122 (talk) 17:07, 24 August 2017 (UTC)
 * For many years I wondered why first - class prepaid envelopes had a silhouette of a pillar box on them.  Then one day I realised that it was the figure "1" in white on a black background. 81.151.100.122 (talk) 17:32, 24 August 2017 (UTC)
 * If you manage to look at it for one hour you get a personal Enterprise class warp drive update! --Kharon (talk) 01:35, 25 August 2017 (UTC)


 * Thanks all for the interesting information and the Amazon link. With the previous publication and the generic Youtube filename, the file's copyright is atleast unclear - nominated for deletion at Commons. GermanJoe (talk) 10:59, 26 August 2017 (UTC)

What does it mean to have a mental age of 8 or 12?
There is that Kennedy girl, Rosemarie, who has a below average IQ. The Wiki article says she has the intelligence level of an 8- year-old to 12-year-old child. What does that mean? When I was 8, I could do multiplication and division and write essays. When I was 12, I could do the order of operations and basic algebra. Though, even when I was 3 or 4, my workbooks indicated that I practiced addition. At all stages of my life, I like toys, especially stuffed animals. 140.254.70.33 (talk) 14:06, 23 August 2017 (UTC)
 * Yes, but you are one person, so you are statistically insignificant. Your singular experience means nothing at all, and cannot be used to draw conclusions about humanity as a whole.  However, if you take all people (or a representative sample of all people) and from that sample, develop an average set of capabilities, you have a benchmark by which to compare people against known expectations.  When statements like the one you note above are made, they are being made looking at an average across all humanity, not against YOU.  You, and your experiences, don't matter to such a comparison. -- Jayron 32 14:46, 23 August 2017 (UTC)


 * It basically means that her score on a standard IQ test would be near the mean for children in the 8-12 year old range. Looie496 (talk) 15:14, 23 August 2017 (UTC)


 * Mental age --AboutFace 22 (talk) 15:31, 23 August 2017 (UTC)


 * When a person is older than its mental age, see Mental Retardation. -- Hans Haase (有问题吗) 18:46, 23 August 2017 (UTC)


 * That would be substantially older than their mental age. StuRat (talk) 20:21, 23 August 2017 (UTC)
 * What about if you only look older than your mental age? All the best: Rich Farmbrough, 17:51, 25 August 2017 (UTC).


 * Progeria? Jailbait images? Yes, some look older than they are. -- Hans Haase (有问题吗) 08:58, 26 August 2017 (UTC)

Design and build construction contracts
Is it generally the case that with design and build construction contracts, the clients are more hands off and a lot of the risk and accountability is transferred to the suppliers? Compared to framework contracts where the client is very much in control and breaks contracts down into small work packages. 82.132.235.85 (talk) 16:35, 23 August 2017 (UTC)
 * Design–build says so Gem fr (talk) 09:27, 24 August 2017 (UTC)


 * This is the theory, even more so with "DBO". However it is not always clear which classes of risk are being transferred.  In particular contractors are reluctant to take on regulatory risk, especially when contracting to a government.  All the best: Rich Farmbrough, 17:56, 25 August 2017 (UTC).