Have I understood these scenarios correctly, and is it possible they might actually occur (not on our Earth but on some other planet)? [[User:JIP|<span style="color: #CC0000;">J</span><span style="color: #00CC00;">I</span><span style="color: #0000CC;">P</span>]] | [[User talk:JIP|Talk]] 10:54, 25 November 2019 (UTC)
Have I understood these scenarios correctly, and is it possible they might actually occur (not on our Earth but on some other planet)? [[User:JIP|<span style="color: #CC0000;">J</span><span style="color: #00CC00;">I</span><span style="color: #0000CC;">P</span>]] | [[User talk:JIP|Talk]] 10:54, 25 November 2019 (UTC)
:2 and 3 do not work like that due to conservation of angular momentum: The axis of rotation is fixed in space and therefore changes its direction with respect to the sun as the planet orbits around it. In the solar system, [[Uranus#Axial_tilt|Uranus]] has its axis closely within the orbital plane and it does experience seasons much more extreme than ours. Scenario 1 works; if you want to remove diurnal variation, too, you need [[tidal locking]]. --[[User:Wrongfilter|Wrongfilter]] ([[User talk:Wrongfilter|talk]]) 11:29, 25 November 2019 (UTC)
:2 and 3 do not work like that due to conservation of angular momentum: The axis of rotation is fixed in space and therefore changes its direction with respect to the sun as the planet orbits around it. In the solar system, [[Uranus#Axial_tilt|Uranus]] has its axis closely within the orbital plane and it does experience seasons much more extreme than ours. Scenario 1 works; if you want to remove diurnal variation, too, you need [[tidal locking]]. --[[User:Wrongfilter|Wrongfilter]] ([[User talk:Wrongfilter|talk]]) 11:29, 25 November 2019 (UTC)
:Some seasonal effects also result from orbits being not exactly circular, but rather [[Elliptic orbit|elliptical]] as is nearly always the case. The degree of effect is proportional to the degree of ellipticality, or [[Orbital eccentricity|eccentricity]], of the orbit in question.
:[[Earth's orbit]] is only modestly eccentric (with [[aphelion]] (furthest distance from the Sun) being in July and perihelion in January), so the resultant effects are mostly swamped by the greater ones of its axial inclination (they tend to ameliorate the Northern and intensify the Southern hemisphere's seasons, but only slightly). They are however readily observable in on rocky planets like [[Mars#Climate|Mars]] and [[Pluto#Atmosphere|Pluto]] which have greater orbital eccentricities. Similar effects are detectable, though less obvious, on the [[Gas giant|gas]] and [[ice giant]] planets of our Solar system.
:For an entertaining (and extremely well written) fictional examination of the effects on an Earth-like planet with a very eccentric orbit, see the [[Helliconia]] trilogy by my old acquaintence [[Brian Aldiss]]. {The poster formerly known as 87.81.230.195} [[Special:Contributions/2.217.209.178|2.217.209.178]] ([[User talk:2.217.209.178|talk]]) 13:38, 25 November 2019 (UTC)
Revision as of 13:38, 25 November 2019
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
[1] I looked at the abstract of this and can't make head or tail of it, even after looking at our article Cytotoxic T cell. Is the implication that very old people's cells change to make them more likely to get autoimmune disorders? Or that they have somehow already gotten autoimmune disorders that cause them to develop these cells? Or what? Thanks. 67.164.113.165 (talk) 07:13, 18 November 2019 (UTC)[reply]
Nothing about autoimmune disorders is implied. In fact, the authors explicitly have no idea what these CD4 CTLs are programmed to do. The main finding is simply that these cells (previously reported as very rare in healthy individuals) are found in very high numbers in healthy supercentenarians. They also show that these cell populations are stable over time, and to the extent testable, the cells appear to be functional cytotoxic cells, meaning that they can probably kill their target cells, whatever those are. Someguy1221 (talk) 07:46, 18 November 2019 (UTC)[reply]
I noticed that the water in my Brita filtering pitcher doesn't flow downwards until the end - there's always some water remaining in the funnel above the filter, after the rest is filtered down. Is it because of insufficient pressure to push through the filter or something else? 212.180.235.46 (talk) 19:33, 18 November 2019 (UTC)[reply]
I suspect that eventually the levels would equal out, but the tiny amount of (over)pressure exerted by the water on top isn't enough to quickly force the water through the filter. Try leaving it alone for days, and see if it doesn't even out. (Be sure to cover the top, so evaporation doesn't become a factor.) SinisterLefty (talk) 19:38, 18 November 2019 (UTC)[reply]
Sorry, put it wrong a bit: the water that doesn't seep through is stuck at the bottom of the funnel below the filter. Flushing it out and filling again doesn't help, as the issue persists. 212.180.235.46 (talk) 22:59, 18 November 2019 (UTC)[reply]
It sounds like capillary action is holding it back butI can't see the difference between the water that has filtered down into the lower chamber and a small amount left in the filter chamber. I mean, the filter is not toxic and that water will be flushed down when you next fill the pitcher - ?later in the day or the next day. Richard Avery (talk) 22:43, 20 November 2019 (UTC)[reply]
November 20
A horizontal force is applied to the top of a stationary ball on a frictionless horizontal surface
F=ma so the ball will move horizontally with acceleration a, but since the force is applied parallel to a line through the ball's center of mass, wouldn't it confer a moment and thus start the ball rolling? But I thought balls only roll with static friction? 104.162.197.70 (talk) 01:25, 20 November 2019 (UTC)[reply]
The force would start the ball moving and would start it rotating in the same direction as it would if it was rolling; but as you say, with no friction it wouldn't actually be rolling. It might be rotating faster or slower; I don't know how to determine that. --76.69.116.4 (talk) 02:44, 20 November 2019 (UTC)[reply]
Why would the ball rotate if the force is straight through the center and the surface is frictionless? How would it even know which direction to rotate in? 173.228.123.207 (talk) 03:06, 20 November 2019 (UTC)[reply]
If there is a net force acting on an object, it will accelerate. If there is a net torque on an object, it will rotationally accelerate. A line of force passing straight through the center of mass would not lead to acceleration, but the OP had specified a line of force parallel to the center of mass. The first answer contains an error, though - the ball could be rotating in either direction. At least when I was learning physics, this was referred to as "slipping" to distinguish it from rolling. Someguy1221 (talk) 03:15, 20 November 2019 (UTC)[reply]
The force isn't straight through the center as 173.228 says; it's on one edge. The ball could not rotate in either direction as Someguy says, because the force determines which way it moves. --76.69.116.4 (talk) 08:05, 20 November 2019 (UTC)[reply]
"the" force is inaccurate. I guess we consider the force of cohesion will keep the ball solid instead of breaking apart, but the main thing to NOT forget is the force of reaction (to weight and all other forces) that provide for the vertical compensation to keep the ball on the surface. Without the latter, the ball would go through the surface (just like, when hit on the right side, it jerks to the left side).
The standard analysis of the hitting force F is to decompose it into a pair of forces, one normal Fn to the surface and straight to the center of the ball (so: no torque) and the other Fs parallel to the surface (so : torque). You need to know the moment of inertia of the ball to calculate the spin (as accurately stated by Greglocock below, rolling being a special case of spin, and without friction we don't know if the ball will overspin, underspin, or spin exactly as needed to have it roll).
Absent friction, we have a relaxed constraint - the linear velocity is not constrained to any specific relation with respect to the rotational velocity.
I think the OP's question is a variation on the theme of Example 7.8 (offset pulleys) or 7.9 (rolling disk) in Marion & Thornton's Classical Dynamics. One can solve these problems in many ways, but the easiest way is to write out the lagrangian. With friction present, we can relate the two velocities (linear and angular) with an equation of constraint, and solve by a relaxation method. Without friction, we can eliminate the constraint, and λ is trivially zero, yielding a trivially directly soluble system of equations.
If you're unfamiliar or unwilling to use these methods, you can try to directly compute the net torque and the net force. It ought to go without saying: when we suspend disbelief to permit the frictionless idealized system, we equally suspend disbelief to allow the set-up to impart an arbitrary force vector at an arbitrary location. How this is accomplished isn't important: we're dealing with idealizations. So, we can have a net torque due to the application of a single applied force that is applied to the object at a location offset from its center of mass. In other words, in this idealization, the ball can roll even without considering a second effective force due to friction. This problem, by construction, calls for a simplified and idealized model. If we want a more realistic model, then we're going to be solving a different problem.
Idealized models of balls will rotate any time they have angular velocity, which can be imparted by applying a net torque over time. Friction plays no specific role, except that friction could be a contributing factor to the net torque. Any other method of generating a net torque is equally acceptable, in this idealization.
It'll spin rather than roll. The angular acceleration will be some proportion of the forward acceleration, which could be worked out by considering the moment of inertia of the sphere. This is known as English when playing billiards, I vaguely remember. Greglocock (talk) 07:50, 20 November 2019 (UTC)[reply]
Any force can be broken down into two components, and for the sake of analysis, we can set up our reference frame in whatever way is most convenient, so for our purposes, you would set up your origin for your coordinate plane at the point of impact, with one axis pointed at the center of the ball (radial), and the other axis tangent to the sphere at the point of impact. You would then take the force vector and break it into component vectors along those two axes. Any part of the force that applies to the tangent will spin the ball, and part of the force that applies to the radial axis will move the ball. --Jayron3213:55, 20 November 2019 (UTC)[reply]
The terms "hit" and "impact" that have been used in responses above suggest a scenario where something external transfers its Momentum to the ball but the question title states only that "A horizontal force is applied to the top of a stationary ball..". In Jayron32's reference frame we see a finite tangential component force and zero radial force. In a solid ball of a real-world material a shear wave spreads at the Speed of sound from the top. Answering what happens? is answering how the shear wave will dissipate. In a FDM analysis there is a distribution of momentums to the particles of the ball during the first time step. In subsequent time steps Spherical harmonic oscillations decay within the ball, constrained only by reflection of any radial extension at the ball-to-surface contact point and by the material's plasticity. To prolong the incidence of "horizontal force is applied to the top" is difficult because when the ball starts moving the location of its top changes, and we no longer have a "stationary ball". DroneB (talk) 18:40, 20 November 2019 (UTC)[reply]
but since the force is applied parallel to a line through the ball's center of mass ... Any line is parallel to some line through any given point (in a geometry that's not positively curved). —Tamfang (talk) 21:14, 22 November 2019 (UTC)[reply]
A late afterthought: a similar situation applies if you imagine a skater standing still on the ice, and someone else skates up, intending so glide past very close to her, but brushes against her left side, just hard enough to set her moving. Until she reacts, she's going to start rotating clockwise and also moving in something like the direction the second skater was going. Hope this helps. --76.69.116.4 (talk) 07:07, 24 November 2019 (UTC)[reply]
a hot engine will have parts that are this hot, though. Which is why engine fires are not that infrequent, you just need some pipe leaking fuel at a wrong place. But a fire is not an explosion, you just need more than fire, you need first a fuel mix with air at a proper ratio, filling some space, then (and only then) an ignition. Vapor pressure is involved (I don't know enough to explain more), but the fact is this very seldom occurs (Not sure it can even occurs, in usual condition of enough air around: far less spectacular ignition will occur before) Gem fr (talk) 15:31, 20 November 2019 (UTC)[reply]
FYI it is not possible to light petrol with a cigarette. As a teenager we used to buy 2l (empty coke bottles) of petrol to start braais (don't try this at home) to the regret of many eyebrows. Despite our most foolish attempts no one was ever able to ignite the fire with a cigarette. Thanks Anton 81.131.40.58 (talk) 15:41, 20 November 2019 (UTC)[reply]
It's relatively safe to start a braai with petrol (but don't). How people get hurt is almost always when they start one without, then it doesn't burn fast enough, and then they pour petrol onto it. If you pour petrol onto an ignition source, you're pretty much guaranteed an explosion. You don't know where, but somewhere between the petrol and the braai, there will be just the right mixture to ignite. Andy Dingley (talk) 15:45, 20 November 2019 (UTC)[reply]
[2], [3], [4], [5]. The long-and-short of it is, under a highly controlled set-up, it is just barely possible to ignite a container or fuel tank of gasoline with a lit cigarette, and only slightly more possible to do so with an open puddle of gasoline, but basically, no. If you simply drop a lit cigarette into liquid gasoline, it does not ignite. --Jayron3218:36, 20 November 2019 (UTC)[reply]
It is my experience, too, that a lit cigarette thrown into gasoline puddle does not ignite it, but I don't know how. By the color a cigarette burns at 700 degrees celsius. The fuel is there, there is plenty of oxygen in the air - and yet no ignition. Weird. אילן שמעוני (talk) 20:18, 20 November 2019 (UTC)[reply]
Not that weird. You need heat, not just temperature. A 700 C lit cigarette tip may have heat enough to rise the temperature of contacted gasoline by, say, 70 C or less (because the mass of gasoline is so much higher). And the geometry is bad, far worse than the geometry of a candle or oil lamp mesh. Gem fr (talk) 21:40, 20 November 2019 (UTC)[reply]
Burning fuel needs an oxidiser to go with it - just oxygen in the air is enough. It won't burn or explode on its own, however you light it.
There are exceptions - things called monopropellants don't need a separate oxidiser. This also makes them quite hazardous, so they're really limited to just rocket propellants, and one called AVPIN which was used for starting jet engines. They also sold it as Thermolene for dragsters!
To ignite a fuel, you not only need to supply a heat source, so as to reach the ignition temperature - that's quite easy - but you also need to have a flammable mixture of fuel vapour and air. A small quantity of these fuels will easily reach the LEL (Lower explosive limit), where there's enough fuel to combust (if ignited). It needs to be warm enough to be above its flash point to do so. This is a commonly used term, nearly always used incorrectly - it's the lowest temperature at which it can make a flammable vapour. Not the point at which that flammable vapour will ignite (that's the autoignition temperature). The flash point for petrol (gasoline) is anything more than "cold day in Moscow", so it will light with an applied flame pretty much anywhere. However the flash point for diesel is more like "Summer day in Rome", so it's hard to set fire to diesel (a flame will do it, but a spark has trouble).
However as well as the LEL there's also a UEL or upper explosive limit (and a UFL or flammability limit too). This is the point when there's too much fuel vapour (and not enough oxygen) to make it either explode or burn. For petrol, this is easily reached inside the fuel tank. That's why some cars can have fuel pumps mounted inside the petrol tank (with sparks too) without exploding. Even inside a jerrycan of petrol with the cap off, it's over the limit.
A good example of this is backdraught in building fires. The closed room is full of flammable fumes, but doesn't burn until a door is opened, air rushes in and the mixture is diluted enough to drop below the UEL.
So if there's an accident and the tank splits, it doesn't explode. But if there are sparks nearby, or a hot exhaust catalyst, it can catch fire, and it will usually do so around the edges of the petrol spill, not from the centre. Diesel is vastly safer for that, which is why the military switched to using all-diesel some years ago. Andy Dingley (talk) 15:40, 20 November 2019 (UTC)[reply]
I'm interested in DIYing some battery heated clothing using carbon fiber tape and this may be a stupid question but does it matter at all what carbon fiber tape I use as long as the resistance is right? One supplier said their tape is not suitable for this application but it was advertised as 100% carbon in which case I don't see a problem and I'm wondering whether they're just taking a precautionary stance or whether product selection is more complicated than I figured. There's a guy in Russia selling what he claims is suitable but I think the price is unreasonable so thought I could source it myself. Of course I want it thin enough to be able to sew. 3K and 240 gsm I suppose.
If you need a second opinion, it isn't suitable for this application.
While the question itself is not stupid, it is stupid to continue following through after experts and vendors tell you that your approach isn't suitable.
What you are proposing carries serious risks for fire, burning, electrocution, and other hazards.
Talk to more experts; consider taking some time to formally study textile engineering; and don't do something that can cause serious harm to yourself and to others. If you still don't "see the problem," you need to do some more homework before you go any farther.
Per Nimur, electricity is ALWAYS more complicated than you will figure; it's why an electrician is so expensive to hire, and why they require years of training and licensure and carry lots of insurance in case they screw up. Resistance heaters (which is what you're basically building) are not the sort of thing you should homebrew, especially in clothing (which can catch fire) and your body (which can be burned if things go badly). Please don't. --Jayron3216:28, 20 November 2019 (UTC)[reply]
Yeah, super easy. Just web search. Personally I'd probably buy gloves, as heated inner gloves are cheap anyway and gloves are a PITA to sew. Most people make their own by taking a pair of either thin cotton gloves, or loose-weave Kevlar work gloves (for higher powers), lightly tacking the tape to the outside of those and then wearing them inside a loose-fitting pair of bike gloves. The tape needs to be the right stuff (conductive, not structural) but eBay's full of it. Generally don't try to heat any area which will be compressed - you don't want the tape to be getting wear and you don't want to have it pressed into your skin directly - a bit of distance through fabric avoids hot spots. About 5W-10W per glove is about right, depending on personal taste. For the 15mm tape, about 3-4 feet of tape is needed for each glove, depending on how far you wrap the fingers. Most designs go full length, from back to front of the finger, looping over the ends, but you might prefer to skip the last joint for more dexterity - depends how good your circulation is.
For this length of tape, 7.4V from a double LiPo pack is a reasonable supply, but (IMHO) it's worth adding a modern switched-mode power supply as a regulator. These are a few bucks now (eBay again), have voltage and current displays and are settable by pushbutton. Use a battery pack protector circuit (eBay again) and flat cell packs. 18650s are junk and their claimed ratings are all lies by a factor of 10×! Connectors are a PITA. Small ones break, big ones are lumpy. You don't want screw or latching contacts. I use the ubiquitous 5.5mm × 2.1mm barrel connectors. You have to decide if you use serial or parallel connection for your garments. Two matching gloves is easy, but gloves and jacket / trousers as well are a bit more awkward. Jackets probably need four cells and about 15V (or bike 12V), so you can run jacket, trousers, and a pair of series-connected gloves in parallel. Or wire the whole lot in series, go high voltage, and use a constant current circuit with a self-regulating output voltage.
As fractures used to be such a problem, I wouldn't use wire for heating for any of it any more. But I might use flex PCB element heaters in the back of gloves (I have good circulation and like dexterous fingers).
For joining wires to tape, some use silver-loaded paint. I just strip the (stranded) wire, fold it into a zig-zag, sandwich it between two layers of the tape and then oversew with metallic conductive thread (CPC).
There are commercially available examples of electrically heated gloves, jackets, pants, socks and insoles that draw power from a motorcycle's 12 volt battery. Instead of DIY, seek a reputable supplier [7][8][9] and Caveat emptor. DroneB (talk) 19:11, 20 November 2019 (UTC)[reply]
Why not use flat resistors and avoid the entire problem? Flat resistors are cheap. It is a common practice among amateur astronomers to DIY heating for the secondary mirror in Newtonian telescope, and it works flawlessly. אילן שמעוני (talk) 20:25, 20 November 2019 (UTC)[reply]
Humans aren't flat. Also a resistor isn't long enough to go all the way round. As noted, flexible PCB resistive elements are easily available now and they'd do for backs of gloves or for kidney patches in a jacket. But otherwise, the flexible carbon tape is the way to go. Andy Dingley (talk) 20:39, 20 November 2019 (UTC)[reply]
Are you sure humans are not flat? Anyhow, the circumference of the mirror is not flat either. You use small enough resistors. The same approach, I think, will work with gloves. However an issue I didn't think before of is that the wires will be bent to and fro constantly. I don't think it will hold, so my suggestion goes down the drain either way. אילן שמעוני (talk) 20:52, 20 November 2019 (UTC)[reply]
There are supposedly 4 charts for the surveys of South Georgia and South Shetland Islands[12], but for some reason records of the 74th Congress are there instead.—eric16:26, 21 November 2019 (UTC)[reply]
Paint colors for extreme conditions.
I have been working this week on a jobsite where I see a lot of container ships go by. I have noticed that a lot of the containers are a rust red, perhaps based on iron oxide or cuprous oxide. Others look suspiciously like the green of Basic copper carbonate. I don't see a lot of bright primary red, though. I also have seen the same brownish red paint used other places, such a steel bridges.
This got me to thinking; are there some paint colors that are more suitable for a marine environment or are otherwise longer lasting? Do we have an article that covers this? --Guy Macon (talk) 16:29, 21 November 2019 (UTC)[reply]
A number of years ago I researched a similar question about the historic use of green paint (or enamel) on locomotives and stationary steam engines. We were restoring a cast iron mount that had red lead primer and a green topcoat which was a mixture of chrome yellow (also a lead paint) and Prussian blue.[13] I couldn't find any mention that a specific color was preferred but I did find some references to weather proofing exposed metal and commonly used pigments.[14][15][16] I'd be interested if anyone had additional info about historic weatherproof paint. --mikeutalk18:18, 21 November 2019 (UTC)[reply]
I found something related: Lightfastness. Still looking for info on longevity as opposed to fading. I also found a list of container colors here.[17] Note the same lack of bright primary colors that I had noticed. --Guy Macon (talk) 20:20, 21 November 2019 (UTC)[reply]
Certainly different companies use different colors (Maersk is almost always gray, Evergreen is almost always green) but that does not explain why no shipping containers are bright primary red, electric blue or neon green. I have to assume that there are some colors that don't last as long. --Guy Macon (talk) 22:41, 21 November 2019 (UTC)[reply]
From mikeu's link:
Container shipping lines tend to brand their owned equipment with their corporate logo and colors, as they typically intend to keep the container for its entire useful life. This reason alone is why there are orange containers once owned by Hapag Lloyd, light green containers once owned by China Shipping, or red containers owned by K-Line or Hamburg Sud.
Indeed some of the examples like Container HAMBURG SÜD 01.jpg Container HAMBURG SÜD 01.jpg and File:Hamburg Süd Container Stack.jpg don't seem that far off bright primary red to me. And Hapag-Lloyd container stack train.jpeg Hapag-Lloyd container stack train.jpeg or File:Hapag Lloyd Container 01.jpg seems somewhat bright. As for pink, a quick search find there is Japan's Ocean Network Express/ONE [18]BEAGLE & ONE CYGNUS (48941565386).jpg BEAGLE & ONE CYGNUS (48941565386).jpg. Interesting RAL 4003[19][20] doesn't seem to be available as a colour from Hempel [21]. Maybe it's too expensive or too difficult to make, but it's also easily possible there is just too little demand. Edit: I see pink was never mentioned. For some reason I thought it was. Nil Einne (talk) 08:32, 22 November 2019 (UTC)[reply]
I see the OP also linked to the BSL RAL colour chart. However I wonder if they are confused about what it is. AFAICT, the RAL standard has nothing to do with containers per se. It's just a colour matching system originating in Germany that in the RAL Classic form which is applied to varnish and powder coatings, seems to have become something of a defacto standard. I don't think it has an special connection with containers other than apparently being used to specify the colour for some manufacturers but I get the feeling that also applies in other areas. While I don't see any super bright blues, per List of RAL colors, RAL 6037 and 6038 do exist for green. I'm not sure why they don't show in the BSL link but I'm somewhat confused by their list since they suggest they use Hempel. But Hempel doesn't seem to make all colours they list as options e.g. the RAL 4003 I mentioned earlier. (budgetshippingcontainers.co.uk do have BSL 6037 and 6038, but it sounds like they're targeting the non shipping market.)
It's possible RAL 6037 and 6038 are recent additions. While our article and [22] seems to imply no revision since 1961, both our article and [23] provides info on how new colours may be added which make me think it's probably been at least complemented since 1961. (By new I don't mean very recent, even if it came in the 1990s I wouldn't be surprised if it still hadn't filtered through to many things.)
Also if I look at the article history, it was created in 2013 from the German Wikipedia [24] and for those 2 colours said "Verwendung in der Schifffahrt zur Verkehrssicherung (Schifffahrtszeichen)" which machine translate suggests "Use in shipping for traffic safety (shipping signs)". Which makes me wonder if possible newness aside, it would be considered unsuitable for a shipping container, perhaps why BSL didn't list it.
Actually this brings up another point which occurred to me. Extremely bright colours can be distracting or used for attention in certain scenarios, potentially discouraging their usage in ordinary situations like shipping container.
P.S. I also think we shouldn't downplay the significance of my "demand" point earlier which also plays into Bus stop's point below. RAL for example requires "overriding public interest and not be subject to passing fashion". If few are demanding the colour because it's seen as bright, garish and distracting, and so not something you'd want to use in many scenarios, even if it can be produced the cost is likely to be significantly higher. It may not be that it has to be expensive, but just that it is. But then even those who may consider it may be put off by the cost and the difficulty of obtained the colour. I can't help wondering if this applied in part to ONE's magenta, but they went ahead anyway because they decided the added cost was worth it for their marketing goals.
Expense may be a consideration. Pigments vary in cost. It is the coatings industry that is of especial relevance. "The coatings industry is one of the most heavily regulated industries in the world, so producers have been forced to adopt low-solvent and solventless technologies in the past 40 years, and will continue to do so."[25] There are many factors involved in choice of industrial coating. "In general, environmental regulations are becoming more stringent in all regions to limit emissions of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs), not only in the industrialized world, but also in developing countries like China. Energy conservation and rising solvent and raw material costs are also contributing factors; raw material costs account for 50–60% of the total production costs for coatings. The coatings industry is one of the larger consumers of solvents, which are mostly derived from petrochemical feedstocks and refinery operations. The coatings industry also uses a considerable quantity of nonpetrochemical feedstocks, such as pigments and additives, which are not very dependent on crude oil and gas prices. The nonpetrochemical portion of the feedstocks is approximately one-third, on a volume basis."[26]Here is some information about considerations that may favor one color shipping container over another. Unrelated but interesting. (16 minute YouTube video)Bus stop (talk) 04:24, 22 November 2019 (UTC)[reply]
November 22
Fat burning
If a person is predominantly burning fat in his/her body, rather than carbs, due to a low carb diet, does he/she smell any different from other people who are predominantly eating more carbs?
If so, how does it smell. Is it pleasant or unpleasant.?
86.8.200.208 (talk) 01:41, 22 November 2019 (UTC)[reply]
Define "pleasant" and "unpleasant". -- Baseball Bugs 01:47, 22 November 2019 (UTC)
Is it 'deemed' pleasant or not by the general mass of people, during the normal working or relaxing day/evening in the bar or at home or on the train etc,who are smelling it?
86.8.200.208 (talk) 02:13, 22 November 2019 (UTC)
Ok. If you want to be awkward, just what does it smell like?[reply]
What the mechanism by which vinegar has a cooling effect while eating it?
"The effect of vinegar was astringent, but it was also used frequently because of its soothing and cooling effects". It states that Ruth was bidden to dip her bread into vinegar (Ruth ii. 14). See here. Is it scientific true that vinegar can cool a body by eating it? What the mechanism by which vinegar has a cooling effect while eating it? ThePupil (talk) 02:56, 22 November 2019 (UTC)[reply]
Surely vinegar mentioned here not as a cooling food, but, still, it is still mainly water, and as such WILL cool by ingesting. The energy of acetic acid can be used inside the body, releasing 875 kJ mol−1 / 14,58 kJ g−1, but this is too low to offset the cooling effect of water. So, it IS scientific truth that vinegar can cool a body by eating it, the mechanism by which vinegar has a cooling effect while eating it is just the same as water's. Gem fr (talk) 08:22, 22 November 2019 (UTC)[reply]
Does it mean that the they have the same level of effect? If so, why did they use vinegar for this purpose, while water is cheaper and tastier?ThePupil (talk) 20:52, 22 November 2019 (UTC)[reply]
Water (and food!) was a killer at the time (and remained so, well, pretty much until 20th century, AFAIK) , unless you are very sure of its purity, or disinfect it in some way. Physical mean like boiling it would do. Chemical mean such like adding vinegar also would, and could be more practical and cheaper, especially when you don't want heat; it seems that this was pretty common in the space-time you are interested in. Gem fr (talk) 22:58, 22 November 2019 (UTC)[reply]
Water always was a source of infections, and it's still. But it didn't avoid people to consume water ever. So the explanation you suggested doesn't make sense not only because the bible is full of descriptions of people who drunk water as an habit, but mainly because a few verses above in the same chapter (which describes that they dipped the bread in the vinegar (not drunk it!) there is a verse which mentions that they drunk of that which they have pumped (from the well, i.e. water). ThePupil (talk) 00:02, 23 November 2019 (UTC)[reply]
It could also be perceptive effects. After all, mint doesn't lower the temperature of your mouth, but it activates sensors in your mouth to make you perceive a sensation of coolness. That may be what they are talking about. --Jayron3213:13, 22 November 2019 (UTC)[reply]
water cools you mainly through evaporation, taking away (more or less; not exact because starting temperature, different pressure, etc.)2257 kJ/kg of evaporated water, so you need to turn ~155g of acetic acid entirely into heat to offset that. Common vinegar would have, like, 3x or more less acetic acid, AFAIK, so, too low to offset the cooling effect of water. Gem fr (talk) 17:47, 22 November 2019 (UTC)[reply]
You are simultaneously addressing energy released from ingestion and energy used for evaporation. Ingested substances do not seem likely to under go evaporation. DMacks (talk) 18:01, 22 November 2019 (UTC)[reply]
ingested water IS likely to undergo evaporation when cooling is needed (less so when cooling is not required, of course). Now, if you claim that ingested water won't cool you, well, you crossed my limit. Gem fr (talk) 18:25, 22 November 2019 (UTC)[reply]
OK, not even wrong then. The calculation (enthalpy of combustion of acetic acid) - (latent heat of water) may well yield a negative number, but drinking an amount X of water will not increase body evaporative cooling proportionally to X (see Homeostasis#Fluid_balance, Thermoregulation, etc.).
I was thinking of the calculation (enthalpy of combustion of acetic acid) - (heat capacity of water × temperature difference between ingested water and body) which yields almost surely a positive number (which makes the argument "wrong"); it probably is not too wrong for the heat capacity part, but physiology considerations would still apply to the combustion part (ingested organic matter is not entirely released as a mix of CO2, H2O and nitrates, so you cannot assume the combustion is close to complete). TigraanClick here to contact me13:24, 25 November 2019 (UTC)[reply]
The article about vinegar which I cited earlier also points out that cool water also helps relieve the sting of sunburn. So it might indeed be the water in vinegar which is doing the job, equal to or more so than the pungent parts. ←Baseball BugsWhat's up, Doc?carrots→ 18:40, 22 November 2019 (UTC)[reply]
Here is a group of interpretators of the bible that say: vinegar consumption has a cooling and refreshing effect. I'd like to ascertain it scientifically. ThePupil (talk) 20:46, 22 November 2019 (UTC)[reply]
Original Research, but I have personally observed that adding a small quantity of vinegar to tap water (which by law is of potable quality in my country) makes the water more palatable and "refreshing", masks any harmless but unappealing tastes resulting from water treatment, etc., and therefore encourages one to drink more of it.
In a Biblical context, I would observe that the alcohol in wine (and other alcoholic beverages like beer) exposed to the air turns partially to vinegar (the word literally means "sour wine") which was likely how most vinegar was anciently manufactured, and partly soured wine has been claimed to have been called vinegar, and commonly drunk, by Roman soldiers. {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 13:24, 23 November 2019 (UTC)[reply]
I don't like the smell of vinegar (and so dislike most things with enough vinegar that you can smell/taste it e.g. vinegar chips). So adding it to water is unlikely to make me drink more water. I've never had a problem drinking most tap water, even in Malaysia where it can sometimes be quite chlorinated although the norm there is to boil water and so there is a standing period which reduces it somewhat. OTOH, I do find even during winter I actually prefer ~4 degrees C water from the fridge compared to 10-20 degrees water from the tap and it probably makes me drink more. Nil Einne (talk) 15:53, 23 November 2019 (UTC)[reply]
The amount of vinegar I employ is a few drops in, say, 1/3 of a pint of water, nowhere near enough to smell, or to actually taste of vinegar. {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 22:03, 23 November 2019 (UTC)[reply]
As heavier elements sink to the core of a white dwarf, does enough uranium, radium, etc, become concentrated to start a chain reaction and explode? In a bomb on Earth made by humans, the material needs to be concentrated very rapidly to prevent the chain reaction from pushing itself apart too soon. But the might not be needed inside the pressure and gravity of a white dwarf, and any sinking of heavy elements might happen very fast, fast enough to make a bomb. If such a bomb went off, the debris might be stifled by pressure and gravity, causing sudden extreme compression and maybe a nova?Rich (talk) 15:53, 23 November 2019 (UTC)[reply]
Nuclear reactions in ordinary stars, including white dwarfs, never create anything heavier than iron. But the heavy metals could have been present in the material that the star formed from in the first place: the same reason that they exist in our solar system. See nucleosynthesis. The question is whether they could be present in sufficient quantity to react in this way, and what would happen if so. I have no information about that. --76.69.116.4 (talk) 20:11, 23 November 2019 (UTC)[reply]
The heavy elements will eventually concentrate in the center of the white dwarf. However their mass is very low - about a few thousandth parts of percent, So, any fissile explosion will have negligible influence on the white dwarf (or more likely the black dwarf). Ruslik_Zero20:54, 23 November 2019 (UTC)[reply]
No, to make a fission bomb you need weapons grade uranium or plutonium, which is made by removing unwanted isotopes which spoil the prompt critical reaction. A star will have these isotopes present. (Stars are where they're all made in the first place.) For an implosion-type bomb, you also need the core to be compressed extremely rapidly, or you just get a "fizzle". I don't think this would happen outside of a stellar core collapse, which already makes a really big boom. --47.146.63.87 (talk) 01:56, 24 November 2019 (UTC)[reply]
All fissile materials would have probably decayed long before there had concentrated in the center as there life-times are rather short. Ruslik_Zero13:53, 24 November 2019 (UTC)[reply]
How vinegar can be salt substitute?
According to this article: "vinegar is kick ass salt substitute you should be using". Now, logically when I think about it, it's difficult for me to understand the mechanism of it, since the feeling of saltiness is caused by tongue sensors of salts (or maybe NaCl only). Now, vinegar is acidic, and it should cause a sourness rather than saltiness. Isn't it? ThePupil (talk) 20:23, 23 November 2019 (UTC)[reply]
The article is talking about using salt (or vinegar) in sufficiently small quantities that it doesn't make the food taste actually salty (or saltier). Used at such low concentrations it instead has the effect of enhancing the other tastes present in the food, a usage called seasoning.
As the Wikipedia article Seasoning suggests, vinegar used for seasoning does not give a result identical to that of salt, but it does enhance other food tastes in a broadly similar way. Quite how either of them do this is beyond my ken, though I suspect that it has something to do with modifying sensory threshold processes (see also the links in that article's 'See also' section). {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 22:22, 23 November 2019 (UTC)[reply]
I doubt it would be widely effective. One of the reasons why salt enhances other flavors is that many of the receptors involved in flavor make use of sodium co-transport. Vinegar won't make up for the lack of sodium ions for co-transport. Sodium acetate would. --OuroborosCobra (talk) 23:33, 23 November 2019 (UTC)[reply]
Thank you all for the answers. 05:49, 25 November 2019 (UTC)
November 24
Memory foam for sleeping - real science or marketing gimmick?
I came here from a now-defunct conversation in Talk:Memory foam#Steady-state behavior which was less about improving the article and more about science.
Is there any actual research showing a benefit of memory foam mattresses over regular open-cell foam? In a steady state, any open-cell foam ("memory" or not) doesn't compress like a spring; it exerts a fairly constant force that is nearly independent of displacement, over a range of displacement.[28][29]
Why would it matter if the mattress is viscoelastic open-cell foam or just regular open-cell polymer foam? Each point on the foam still exerts a constant force on the object laying on it, if the foam is compressed within its constant-force range. In fact, memory foam seems less desirable because it resists changing shape, making it hard to change position or roll over during the night.
The "memory" feature of retaining a deformity for a short period seems, to me, to be nothing more than a marketing gimmick. It makes for nice photographs of impressions left by pressing a hand into it. So what? What is the advantage?
Any search I do for gets muddled by results that take it for granted that a benefit exists. Even the patent on memory foam mattresses relies on speculation and uncited tests for its claims of being a benefit to sleeping. Where are the comparisons to open-cell foam that isn't viscoelastic?
My sleep therapist suggested I look into getting a mattress pad, and in my search, knowing the compression characteristics of open-cell foam, I got stuck on this question: why not just a pad of open-cell foam? What is better about memory foam? ~Anachronist (talk) 17:51, 24 November 2019 (UTC)[reply]
" Sleep specialist Donna L. Arand, PhD, says that objective studies supporting the claimed benefits of memory foam -- or the effects of any particular type of sleeping surface -- are lacking." -- [30]
We know that element 119 is currently being worked on testing. The article (currently titled ununennium) says that +1 and +3 compounds of this element are going to be equally stable. This would mean all of the following:
Penultimium fluoride (PnF)
Dipenultimium oxide (Pn2O)
Penultimium trifluoride (PnF3)
Dipenultimium trioxide (Pn2O3)
Also, let's add the same info on element 120 (the article is currently at unbinillium.) It says +2 and +4 compounds are the most stable, which means these compounds are valid:
Ultimium difluoride (UlF2)
Ultimium oxide (UlO)
Ultimium tetrafluoride (UlF4)
Ultimium dioxide (UlO2)
Any info on what compounds of these elements are most likely besides the above?? (Please note that the terms I'm using for these elements are intended to be interpreted as meaning that I feel sure that these are the last 2 chemical elements that will ever get an official name; elements 121 and up will always have their systematic names.) Georgia guy (talk) 19:34, 24 November 2019 (UTC)[reply]
Have these compounds been shown to exist and be stable (I doubt that, given that the elements haven't been synthesized), or are you assuming that from the proposed stable oxidation states? Also, what does "I feel" mean and why do you think heavier elements 121 and beyond will always have systematic names? What source do you have for the name "penultimium," since the official IUPAC designation is still the temporary "ununennium"? What do you mean by "element 119 is currently being worked on testing?" Currently all work is on basic synthesis of the element, and so it isn't being "worked on" as there is none to "work on". --OuroborosCobra (talk) 21:28, 24 November 2019 (UTC)[reply]
Currently, all work is on basic synthesis of the element. This means we're in the early part of working on the elements. The source of the 2 names I'm using is simply my enthusiasm. Georgia guy (talk) 21:49, 24 November 2019 (UTC)[reply]
No work is being performed upon this element as this element does not exist. You also said they were doing tests. They cannot be doing tests on something that does not exist. Please see WP:OR. Basically, no one here is likely to be in any position to even begin to speculate on your questions, and your use of a name that you've made up also makes your question difficult to answer. Your question itself isn't based on real science, but your imagination (fun as that may be). --OuroborosCobra (talk) 01:50, 25 November 2019 (UTC)[reply]
Flexible Hydraulic Arm
Would a flexible arm that can have a huge range of motion utilizing hydraulic power be possible? Maybe it would be made of rubber and use hydraulics on the inside? I don't know much about hydraulics.173.119.71.63 (talk) 21:07, 24 November 2019 (UTC)[reply]
Yes, this is a topic of considerable current development. See soft robotics. One question is whether such an arm would have a rigid internal skeleton, even a "spine" of many short "vertebrae", or else would it be entirely soft? Worms, such as annelid worms, have provided a model for how this could be achieved. Andy Dingley (talk) 21:53, 24 November 2019 (UTC)[reply]
I can't remember if I have asked this before or not, but I was curious anyway.
We all know the change of seasons on the Earth happens because the axis is tilted in relation to the orbit. So I thought of three alternate configurations for a planet:
Axis is exactly perpendicular to the orbit, pointing "up" and "down" on the orbit plane: No annual change in seasons. Temperature depends only on latitude and time of day.
Axis is parallel to the orbit: No seasons. Temperature depends only on time of day.
Axis points towards and away from the sun: No seasons. One side experiences permanent sunlight and the other experiences permanent darkness.
I know there might be local weather changes that might affect the temperature and sunlight but I'm ignoring these here for the sake of simplicity.
Have I understood these scenarios correctly, and is it possible they might actually occur (not on our Earth but on some other planet)? JIP | Talk10:54, 25 November 2019 (UTC)[reply]
2 and 3 do not work like that due to conservation of angular momentum: The axis of rotation is fixed in space and therefore changes its direction with respect to the sun as the planet orbits around it. In the solar system, Uranus has its axis closely within the orbital plane and it does experience seasons much more extreme than ours. Scenario 1 works; if you want to remove diurnal variation, too, you need tidal locking. --Wrongfilter (talk) 11:29, 25 November 2019 (UTC)[reply]
Some seasonal effects also result from orbits being not exactly circular, but rather elliptical as is nearly always the case. The degree of effect is proportional to the degree of ellipticality, or eccentricity, of the orbit in question.
Earth's orbit is only modestly eccentric (with aphelion (furthest distance from the Sun) being in July and perihelion in January), so the resultant effects are mostly swamped by the greater ones of its axial inclination (they tend to ameliorate the Northern and intensify the Southern hemisphere's seasons, but only slightly). They are however readily observable in on rocky planets like Mars and Pluto which have greater orbital eccentricities. Similar effects are detectable, though less obvious, on the gas and ice giant planets of our Solar system.
For an entertaining (and extremely well written) fictional examination of the effects on an Earth-like planet with a very eccentric orbit, see the Helliconia trilogy by my old acquaintence Brian Aldiss. {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 13:38, 25 November 2019 (UTC)[reply]
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