Wikipedia:Reference desk/Archives/Science/2016 April 8

= April 8 =

Bread slice missing middle
I was nearing the end of a bag of sliced bread (branded, factory-made, bought at a major supermarket), and found that the second last piece (the piece before the end) consisted only of three edges edges (i.e. it was missing the middle and one edge) - more than just the crust, but most of the middle was gone. It looked torn, definitely not cut by a blade. The bag was closed with the original plastic clip, and there were no holes in the bag. I can't guarantee that the clip 100% securely closed the bag, but as far as I remember it was closed. The previous day I had taken two slices that sat above the odd slice in question, and they were fine. I think I would have noticed if the next slice was odd, but can't be sure. The last piece in the bag (the end) was intact.

What could have caused this? Some possibilities I thought of are: (i) at some point previously I had left the bag open and a mouse had gotten in and out, but then it would be odd for it to dig down to the second piece before last, eat it, and not disturb any of the others; (ii) there was some manufacturing error and that piece came like this; (iii) the bag was not securely closed the previous day, and a very nimble mouse or something smaller had gotten in during the night and eaten the bread; (iv) bread eating mould of some kind? The bread was a few days past its "best before" date. --PalaceGuard008 (Talk) 08:55, 8 April 2016 (UTC)


 * Possibly a damaged blade in the slicing machine. 217.44.50.87 (talk) 08:57, 8 April 2016 (UTC)


 * (ii) is definitely your answer. The bread could have been torn while slicing for some reason, or it could have been baked that way I suppose (an air bubble in the dough). shoy (reactions) 13:51, 8 April 2016 (UTC)


 * Perhaps the original Loaf had an oversize void due to uneven Leavening caused by inadequate mixing of the Bread dough. Mouse infiltration leaves tooth marks, crumbs or stools. AllBestFaith (talk) 13:54, 8 April 2016 (UTC)


 * I had a squirrel come down my chimney and attack a loaf of bread. It was fascinating what he did with it.  He formed it into mouth sized balls, presumably planning to transport it back out by mouth.  Then I showed up and ruined his plans by evicting him from my house and getting a chimney cap. StuRat (talk) 19:18, 8 April 2016 (UTC)


 * Thanks all, that must be it (faulty manufacturing, not squirrel - though that's fascinating as well)! --PalaceGuard008 (Talk) 09:11, 11 April 2016 (UTC)


 * Have we completely ruled out the possibility that Squirrel Girl was involved? :) --Guy Macon (talk) 12:24, 11 April 2016 (UTC)

"Engagement length"
What does the "engagement length" indicate in ISO 965? There are many standard screws and nuts that go above and below this range, so what happens when you use such a combination? Let's say I try to seat a M2 screw 4 mm into a threaded hole, exceeding the "engagement length" range of 1 to 3 mm， what happens then? Will the thread strip? Or it is likely to get stuck or something? Johnson&#38;Johnson&#38;Son (talk) 10:25, 8 April 2016 (UTC)
 * Google "engagement length of bolt" and take your pick of the explanations on offer e.g. "One of the main guidelines in designing fastener joints is that the length of thread engagement should be long enough so that the bolt will break rather than strip the threads in the tapped hole".  Richerman    (talk) 10:47, 8 April 2016 (UTC)
 * ISO 965 is used for pass/fail Acceptance testing of ISO threaded fasteners so it is desirable to set both minimum and maximum values for the engagement length that can be difficult to establish exactly but is critical for testing breaking strength. However the quoted maximum engagement length does not bear on usage and nothing bad happens if it is exceeded, as routinely happens with the long nut illustrated. AllBestFaith (talk) 13:37, 8 April 2016 (UTC)
 * Far as i know the minimum engagement length is defined as factor (usually 1.25x) of the screw diameter. Im irritated by this too, given that the list seems wrong in its "from"-row for minimum Engagement length. --Kharon (talk) 05:39, 9 April 2016 (UTC)

Psychology study that involves perception of pain of another person
I remember that there was this psychology study that involved a person tapping on something. If the person heard another person in the room answering the question wrong, then the other person seemed to be shocked literally. What was this study? 140.254.77.187 (talk) 17:36, 8 April 2016 (UTC)


 * Perhaps the Milgram experiment.  Sean.hoyland  - talk 17:39, 8 April 2016 (UTC)


 * The Milgram experiment.--TMCk (talk) 17:41, 8 April 2016 (UTC)


 * Damn, you both got it right, now I don't get to shock you. Aw, what the heck, BZZZZT ! BZZZZT ! StuRat (talk) 19:22, 8 April 2016 (UTC)
 * Arrgh, now I am dying! --69.159.61.172 (talk) 05:23, 9 April 2016 (UTC)

Engineering Physics
Light from a broad source source is obliquely incident on a thin transparent plate. Find the expression for the effective path difference between part of a ray reflected from upper surface and part that suffers reflection over surface internally. — Preceding unsigned comment added by 1.39.15.220 (talk) 19:28, 8 April 2016 (UTC)
 * Okay, I did it. Now you do it...seems like it's your homework not mine. DMacks (talk) 20:27, 8 April 2016 (UTC)
 * Depends on the thickness of the plate and the angle of incidence I would say. Any help?--178.101.224.162 (talk) 01:57, 9 April 2016 (UTC)
 * Just draw the path of the internally reflected ray. It forms two symmetrical right triangles.  You can calculate the angle and hence the length of the hypoteneuses (don't forget to use Snell's law to take refraction into account - within the glass, the angle of the ray is different from outside the glass).  You know the length of one side.  The rest is sine and cosine applied repeatedly, I think. Wnt (talk) 16:57, 9 April 2016 (UTC)
 * On second consideration I realize I don't know... it's a matter of philosophy. :) The thing is, not only does the refracted light bend differently; it also moves more slowly than the light in vacuum.  For most interesting measures of the path difference, like the spreading of a pulse laser when it bounces off the thing, you're measuring the time of transit, not the distance in glass + distance outside of glass.  But that would be wrong since it's not truly the length... or is it?  As I understand (the problem being, I don't), there are grand unified theories, M theory etc. that present electric fields as being a curvature of space, and the light is not really slowed, it just appears slowed as it wends and weaves through the fields of atoms.  And so its squiggly path is exactly what the time suggests, and so the "length" of the path in glass should be multiplied by this time factor.  But is curvature in space actually a part of distance? Wnt (talk) 17:10, 9 April 2016 (UTC)

Do hens ever reach a point where they are passed their egg-laying days?
Or do they lay eggs as long as they live? 140.254.70.33 (talk) 21:35, 8 April 2016 (UTC)


 * Are you talking about commercial egg laying birds or non-commercial birds? Commercial egg layers in the UK are usually kept for only 62 weeks as their egg production then starts to decrease.  In some countries, including the US, the birds are force moulted (deprived of food and water for many days) which stimulates the hens to increase their egg laying again.  This may happen several times.  Let's not forget, these commercial birds lay approx 300 eggs per year whereas a non-commercial hen might lay only one clutch (e.g. 6) of eggs each year. DrChrissy (talk) 21:44, 8 April 2016 (UTC)


 * And in Britain, where there is a Royal Society for the Prevention of Cruelty to Animals, but merely a National Society for the Prevention of Cruelty to Children, there is the British Hen Welfare Trust, which enables members of the public to re-house hens past their laying days. "They are approximately 17 months old when we collect them from farms, and are off to slaughter because they are deemed no longer commercially viable as they may be laying fewer eggs." Carbon Caryatid (talk) 22:00, 8 April 2016 (UTC)


 * Yes, I should have mentioned that. When the commercial hens start to decrease their egg laying, the producer makes a financial decision to get rid of them.  These are often called "spent hens".  If people get spent hens, these often initially stop laying (probably because of the stress of the change of habitat) but very, very often start laying again at the usual pattern (they lay an egg each day for 7 days then miss a day). DrChrissy (talk) 22:12, 8 April 2016 (UTC)


 * "Spent hen"! Should I ever feel the need to insult a mother of eight, I am now armed. :) Wnt (talk) 17:14, 9 April 2016 (UTC)


 * Your mention of the National Society for the Prevention of Cruelty to Children baffles me. How is that relevant ? StuRat (talk) 15:28, 9 April 2016 (UTC)


 * I meant that, in some ways, British sensibilities afford more value to animals than to children, and therefore it isn't surprising that there is a specific organisation to enable well-wishers to be kind to chickens. Carbon Caryatid (talk) 16:13, 9 April 2016 (UTC)


 * So it being a "National" society versus a "Royal" one indicates it is a lower priority to the British public ? I can see why that might mean it's a lower priority to the monarchy, but that's not the same thing. StuRat (talk) 16:26, 9 April 2016 (UTC)


 * And of course if British sensibilities really did afford more value to animals than to children, we'd be slitting the throats of kiddiwinks who we decide are no longer useful to us. HenryFlower 16:35, 9 April 2016 (UTC)


 * See A Modest Proposal (yes, I do realize it's satire). StuRat (talk) 16:55, 9 April 2016 (UTC)


 * The RSPCA got its "Royal" title in 1840, thanks to Queen Victoria. The NSPCC also has a royal charter, even if it doesn't use the word in its name, and the Queen is in fact the patron of both charities. 217.44.50.87 (talk) 18:12, 9 April 2016 (UTC)
 * I'm not sure if anyone noticed but the Royal Society for the Prevention of Cruelty to Animals. It includes a very long list of controversies many of which seem to be mostly sourced to the Daily Mail. Nil Einne (talk) 19:30, 10 April 2016 (UTC)


 * Hens slow down as they age and they may stop egg production temporarily during the winter cold. They might also stop if they get sick, but otherwise no. My friend had a bird that lived and laid eggs for at least 9 years. This website mentions a hen that did so for 17 years.  Modocc (talk) 20:19, 9 April 2016 (UTC)