Wikipedia:Reference desk/Archives/Science/2018 November 26

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November 26

If I have hundreds of balls of different sizes but the same weight would the bigger ones settle on top or bottom? And why?

If I have hundreds of balls of different sizes but the same weight would the bigger ones settle on top or bottom? And why? 105.235.193.238 (talk) 13:03, 26 November 2018 (UTC)

See Granular convection. --Wrongfilter (talk) 13:17, 26 November 2018 (UTC)

Friction hinders free movement of balls packed together. If friction is sufficiently reduced e.g. by lubrication and/or applying vibration (shaking), the smaller balls fall below the bigger ones which settle on top. This is because the larger balls have lower Density and exhibit Buoyancy in the "fluid" represented collectively by the balls. DroneB (talk) 14:03, 26 November 2018 (UTC)

I'm not sure it has much to do with density, heavy rocks can be brought to the surface of fields by the same effect. Dmcq (talk) 14:33, 26 November 2018 (UTC)

The "larger rises" effect beats the "heavier sinks" effect every time when we are talking about solid objects mixed together and shaken. put a large lead ball in a tub of small styrofoam beads, shake it for a long enough time, and the lead ball rises to the surface. The only constraint is that you have to shake it hard enough that the lead ball "hops" at least a little bit and the styrofoam beads fall into the hole where the lead ball used to be. --Guy Macon (talk) 15:45, 26 November 2018 (UTC)

The science field of Rheology contains the center rules for "flow", which is the base for any sorting of loose masses but they only allow reliable predictions for extended "flow" events. An avalanche that is already stopped after just 500 m likely has no "flow time" long enough to allow any sorting of its masses worth mentioning.

If you put 1000 of your different balls in a big box and rattle it for an half hour, they are likely perfectly sorted like the rules of Gravity determine. --Kharon (talk) 22:33, 26 November 2018 (UTC)

Multiple editors have mentioned (and linked to our cited article) that density or mass is not the most significant factor. "Like the rules of gravity determine"? You should probably stop contradicting our articles and their peer-reviewed cited sources. DMacks (talk) 06:09, 27 November 2018 (UTC)

That's why i pointed to Rheology and tried to explain with samples (Avalanch, Box) that a sufficient combination of movement, flow event, time and physics is needed. --Kharon (talk) 22:46, 27 November 2018 (UTC)

How did they discover that a photon was the smallest unit of light, and how did they fabricate an instrument that could shoot individual photons?

How did they discover that a photon was the smallest unit of light, and how did they fabricate an instrument that could shoot individual photons? 202.79.53.210 (talk) 13:19, 26 November 2018 (UTC)

A beam splitter can be made that lets very few photons through. "very few" as in one photon per minute or per hour. Beam splitters were well known in 1850; see Fizeau experiment. --Guy Macon (talk) 15:52, 26 November 2018 (UTC)

For the development of the photon model, see Photon#Historical development. The short version is that the existing models to explain blackbody radiation, the Rayleigh–Jeans law and Wien's law had serious flaws that did not match experimental results. To fix this problem, Max Planck created a "fudge" in the mathematics that presumed that energy was not continuous (see Planck's law), but only existed in discrete "chunks" (or quanta). Planck wasn't particularly happy about this little fudge, he didn't think it represented anything in reality, but when you put it into the equations, you ended up with a near-perfect match to experimental data. Independent of this, Einstein in the first of his Annus Mirabilis papers established that Planck's proposed "quanta" actually explained a phenomenon known as the photoelectric effect, a process known about for some time, but which no one could adequately explain. The short, short version is that Max Planck proposed the existence of the photon, and Einstein proved it with his paper on the photoelectric effect. You can read about single-photon sources at the Wikipedia article titled Single-photon source. The first true single-photon source was developed in the 1970s. --Jayron32 16:12, 26 November 2018 (UTC)

It should be noted, although Einstein today tends to be more associated with relativity, that his paper on the photoelectric effect is what won Einstein his Nobel Prize, so yeah, it was kind of a big deal. --47.146.63.87 (talk) 21:43, 26 November 2018 (UTC)

As noted, a "true" single-photon source didn't exist until not that long ago. You don't need one to demonstrate most of the crazy behavior of quantum mechanics. The famous double-slit experiment shows that light behaves as both a particle and a wave. --47.146.63.87 (talk) 21:43, 26 November 2018 (UTC)

This question is a copyvio from Reddit Dbfirs 19:03, 28 November 2018 (UTC)

How are mineral deficiencies even possible in adults? Minerals dont degrade or break down in enzymatic reactions (unlike many molecules) so cant the body completely stop excreting them if intake is low?

How are mineral deficiencies even possible in adults? Minerals dont degrade or break down in enzymatic reactions (unlike many molecules) so cant the body completely stop excreting them if intake is low? 45.251.43.162 (talk) 14:32, 26 November 2018 (UTC)

Firstly because it may be difficult/inefficient to extract or recycle minerals that are part of enzyme complexes, secondly because removing 100% of free minerals from a liquid costs a lot of energy. So for example, in order to preserve all potassium, the membranes would need to overcome a very high osmotic pressure in order to separate the potassium ions from the urine it excretes. Apart from the energy it requires, such large pressures can also cause physical damage to biological tissue. - Lindert (talk) 15:07, 26 November 2018 (UTC)

No, the body cannot completely stop excreting them if intake is low. Why would you think that it can? --Guy Macon (talk) 15:55, 26 November 2018 (UTC)

This is a good question. No, the body can't stop all electrolyte excretion. The reason is the physiology of the kidneys. The kidneys make extensive use of countercurrent exchange based on ion gradients between the blood and filtrate. Ions get pulled into the filtrate by osmosis; pumping them back into the body against their concentration gradient takes energy. Here's a good video about kidney physiology. And, based on my layman's understanding, human kidneys "sacrifice" potassium in favor of sodium. Blood sodium level is more acutely important because it's the major extracellular electrolyte, whereas most potassium in the body is found inside cells, so the body has a large "reservoir". Thus, the kidneys preferentially excrete potassium in order to use the resulting concentration gradient to pump sodium back into the body. This is why when intravenous hydration is needed, normal saline is typically used: just sodium, no potassium, because blood potassium levels aren't as critical.

Remember that evolution is a "blind watchmaker". Biological systems don't have to be perfect, just "good enough". Human kidneys are "good enough" for humans. Animals adapted to arid climates have kidneys that are very good at limiting water and electrolyte loss, but with the attendant costs, which are worth it in their environment. For example, camel urine is a thick syrup, and camels can meet all their water needs simply from consuming food. --47.146.63.87 (talk) 21:34, 26 November 2018 (UTC)

The body cannot stop completely loss of minerals through excretion, as has been noted above, and so deficiency will result over time if there is insufficient of the mineral in the diet.

Consider the essential mineral copper. We have articles on copper in health and on the consequences of copper deficiency. There are diseases like Menkes disease, which results from an inability to properly absorb copper, and Wilson's disease, which leads to copper toxicity due to an inability to properly excrete excess copper. More generally, essential minerals tend to demonstrate a similar pattern on health – a range of concentrations which lead to good health, with poorer health as levels present rise too high and also when concentrations are too low. This has been demonstrated nicely using copper where plants were grown in solutions with increasing copper concentrations. I can't find the original paper, but the plant heights (and also dry weight) follow the patterns shown here (from this webpage) and here (from the journal article doi:10.1007/s11356-015-4496-5). EdChem (talk) 22:40, 26 November 2018 (UTC)

Another copyvio from Reddit. Is someone trying to find out who gives the best answers? Dbfirs 19:06, 28 November 2018 (UTC)