Wikipedia:Reference desk/Archives/Science/2014 June 20

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June 20

Attraction between charged object and stream of water - does it really show that water molecules are polar?

The water molecule is polar since it has a slight positive charge on one side and a slight negative charge on the other i.e. the dipoles do not cancel out. Its internal bonds are covalent i.e. based on sharing electron pairs between atoms. 84.209.89.214 (talk) 18:44, 20 June 2014 (UTC)

I have seen in several places (such as on this webpage: [1] ) that the deflection of a stream of water towards a charged object shows that water molecules are polar. Does it really show this? I have managed to find an example of a stream of liquid NOT being attracted to a charged rod ("Nonpolar tetrachloromethane molecules are not attracted to either charged rod." [2] ). This still does really show the reason why water IS attracted (and is not due to something like charges on surface, or conductivity of water, for example). FrankSier (talk) 15:26, 20 June 2014 (UTC)

I don't know the answer to your question - but the business of attracting (or not) flows towards nearby objects doesn't necessarily indicate polarization - it can also happen due to the Coandă effect and also to Bernoulli's principle...so it's not always easy to determine which effect is in play. SteveBaker (talk) 19:14, 20 June 2014 (UTC)

I think the OP is asking about a situation where the stream of liquid isn't actually touching the charged object, so fluid dynamics effects aren't really an important part of the problem. Red Act (talk) 20:26, 20 June 2014 (UTC)

You are correct, the deflection of a stream of liquid towards a nearby charged object is not a sufficient condition to conclude that the liquid is composed of polar molecules. For example, a stream of mercury will be deflected towards a nearby charged object because it conducts and hence can develop a nonzero free charge density, not because it develops a nonzero bound surface charge density due to the alignment of electric dipoles as in the case of a stream of pure water. Red Act (talk) 20:13, 20 June 2014 (UTC)

Also, carbon tetrachloride may just be not polarizable for a demonstratable effect. A longer-chained hydrocarbon may show more pronounced london dispersion forces than CCl4 even if it is non-polar. --Jayron32 02:27, 21 June 2014 (UTC)

The refractive index of carbon tetrachloride is not exactly 1 (article says n=1.4607), therefore the Lorentz–Lorenz equation gives a noticeably non-zero polarizability. DMacks (talk) 17:24, 21 June 2014 (UTC)

Isn't it true that the fact the water molecules are polarized has been established with X-ray crystallography? --AboutFace 22 (talk) 01:58, 22 June 2014 (UTC)

I'm sure that that is but one of the MANY pieces of evidence that water is a polar molecule. There's uncountable pieces of such evidence; no one "proves" the "fact" any more than any of the others, instead the entirety of the evidence is consistent with the idea that water is polar. Science does not provide "proof" of "facts", instead, science provides evidence which is consistent with some model, law, theory, or principle. The more evidence in support of an idea, then the more likely it is the idea is sound. But there is no one single "EUREKA" bit of evidence which conclusively "proves" an idea as a "fact". --Jayron32 20:22, 22 June 2014 (UTC)

What are the other pieces of evidence? The fact that salts dissociate in water? --AboutFace 22 (talk) 01:31, 23 June 2014 (UTC)

The gray circle for microwave toasting

Things like microwaveable pot pies that have a gray circle on the interior of the packaging that help to toast the product- what is that material? It must not be very metallic, otherwise sparks would fly. What is it?20.137.2.50 (talk) 16:22, 20 June 2014 (UTC)

I think it is metallic, but the metal bits are small and disconnected, so they don't get a chance to build up enough of a charge to arc. StuRat (talk) 16:24, 20 June 2014 (UTC)

Our article on susceptors have a bit more details - in short it's a material able to absorb electromagnetic energy and convert it to heat. WegianWarrior (talk) 16:43, 20 June 2014 (UTC)

Name of foot ailment.

(This isn't a request for diagnosis, prognosis or treatment advice for any medical condition)

I'm trying to find the name - and prevalence in the USA - of a medical condition whereby standing for too long (possibly for occupational reasons) can cause nerve damage - which in turn can result in some kind of postural problem - which goes unnoticed because of the nerve damage - ultimately result in a foot condition so bad that it may require amputation. That's basically all I know about it - I'm really just trying to find some hooks for information so I can go read up about it myself.

(There are days when I'm actually glad that I have a desk job!)

TIA SteveBaker (talk) 19:22, 20 June 2014 (UTC)

I don't think there is a separate foot related disease like this. What you are describing vaguely resembles peripheral neuropathy typically as a consequence of diabetes type II. Being overweight helps also. Vasculitis also may be a contributing factor. --AboutFace 22 (talk) 20:02, 20 June 2014 (UTC)

BTW, what nerve damage do you have in mind? Afferent, sensory nerves or efferent, motor nerves? --AboutFace 22 (talk) 20:07, 20 June 2014 (UTC)

I don't know! That's what I'm trying to find out. I'm guessing that because (I'm told) the nerve damage causes sufferers not to notice that they're somehow making matters worse - that it's probably sensor nerves that are the problem here. But I honestly don't know. SteveBaker (talk) 21:15, 20 June 2014 (UTC)

The context here is that someone wants to have me work on a gadget to help these people - and before I first go to talk to the guy, I'd like to try to appear at least a little fluent with the science - maybe know some of the words. SteveBaker (talk) 21:15, 20 June 2014 (UTC)

Steve, we have a (terribly sourced) article Long-term complications of standing, but it doesn't mention anything about nerve damage. Deor (talk) 20:43, 20 June 2014 (UTC)

Hmmm - didn't seem to illuminate much...thanks for trying. SteveBaker (talk) 21:15, 20 June 2014 (UTC)

You may be thinking of peripheral neuropathy. Standing too long on hard surfaces (e.g. concrete) can trap the sciatic nerve which can lead to neuropathy in the feet. The loss of sensation in the feet can lead to many complications, as evidenced by the number of diabetics who have it and the resulting huge number of amputations: according to one source, over half of all non-traumatic amputations in the US are caused by complications of diabetes mellitus/peripheral neuropathy.

The only other thing I can think of is plantar fasciitis. Standing too long is a risk factor for the condition, and certainly it aggravates the condition if already present. It can cause posture issues due to changing the way one walks because of the pain in the heels. What doesn't fit is the ultimate amputation - if methods such as cortisone injections don't address the problem, people with plantar fasciitis may have surgery. I suppose most surgery carries with it some possibility of nerve damage, but that would be an extremely rare event in this case (as far as I know). Julia\^talk 21:38, 20 June 2014 (UTC)

Thanks! I think that your description of peripheral neuropathy is closest to the mark...although our article on that subject didn't throw much light on the problem. I have gotten plantar faschiitis myself and it hurts like hell when you first stand up - but the pain goes away after a few minutes. My doctor didn't suggest any significant complications from it and a switch from wearing sandals to trainers (along with a $7 course of Meloxicam) fixed it up without problems - so it really doesn't seem to fit the description here.

The idea that so many amputations are caused by this condition perfectly fits what I've been told. Maybe the detail about this being mostly a problem for diabetics got left out of the very vague description that I was given.

I also suspect that a large part of the problem here (in the USA) is that the people suffering from this may not have health insurance - so the problem may get ignored for too long - preventative measures may not be taken in time and surgery may simply be too expensive. If these people also tend to ignore the doctors' advice on how to stand and keep moving (or whatever it is) - then you could easily see how it could get out of control and be the cause of all of those amputations.

Anyway, I feel a little better informed and can sound at least a little educated when I come to discuss it. Thanks! SteveBaker (talk) 14:31, 21 June 2014 (UTC)

There are many occupations where people spend their work days on the feet. Pharmacists is an example. Actually sitting behind your desk all day is unhealthy. You are not really blessed, you are cursed :-) There have been articles recently in the medical press. Standing up is much healthier if you are of a normal weight. Plantar fasciitis may be a connective tissue problem, not occupational. People with peripheral neuropathy often have other liabilities including cognitive and they can miss the onset of the problem. --AboutFace 22 (talk) 01:45, 21 June 2014 (UTC)

That's what I understand (see my post, above). (And, yes, I know that sitting behind a desk - as I mostly do - is bad!) SteveBaker (talk) 14:31, 21 June 2014 (UTC)

Standing and moving around may be healthier than sitting, but standing in one position isn't. We're not built for that. StuRat (talk) 02:34, 21 June 2014 (UTC)

Yeah - and I'm pretty sure that's the problem here. SteveBaker (talk) 14:31, 21 June 2014 (UTC)

I'm thinking aloud here and I have to go out shortly so I don't have the time to research this properly, but someone else might. Firstly, it is possible that standing for long periods of time might result in flat feet, but I don't see how that can ultimately lead to amputation. What might is a vascular problem though, in which the venal valves aren't capable of properly moving the blood upwards so the blood pools in the lower legs and feet. Varicose veins are one manifestation of this, possibly also stasis dermatitis. Possibly also a thrombosis. Apparently it's why policemen bend their legs at the knees, to encourage the blood to move upwards. (Gosh it's 30 years since I learnt this stuff and I guess that things may have changed since then!) --TammyMoet (talk) 09:07, 21 June 2014 (UTC)

Interesting...thanks! SteveBaker (talk) 14:31, 21 June 2014 (UTC)