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July 6

Potential energy stored in a capacitor

I'm trying to derive the equation $U=Q\cdot V={\frac {1}{2}}\cdot C\cdot V^{2}$ from what I know about electrostatics. I know that $C={\frac {Q}{V}}$ , so I tried turning it into an integral like $C={\frac {\operatorname {d} \!Q}{\operatorname {d} \!V}}\Rightarrow \operatorname {d} \!Q=C\operatorname {d} \!V\Rightarrow \int \operatorname {d} \!Q=\int C\,\operatorname {d} \!V\Rightarrow Q=C\cdot V$ , but that doesn't help me to derive the equation for energy potential. — Melab±1 ☎ 00:53, 6 July 2013 (UTC)[reply]

You need to bring energy into it. You have only related charge, voltage and capacitance. See whether you can bring in what you know about the power conveyed by an electric current. — Quondum 01:46, 6 July 2013 (UTC)[reply]

To move a differential element of charge dq, you need to add a differential amount of work, dW. If you know that the potential difference V = Q/C (from the definition of capacitance), and you know that voltage is potential-energy per charge... (all by definition)... then dW = (q/C)·dq. Integrate, and you have the work done on the charge, and therefore that is the potential energy stored in the capacitor. This derivation is Equation 2.55 in Griffiths' book, which I have handy from a question earlier this week. In his notation, lower-case q and upper-case letter Q are the differential element and the integral, respectively. Nimur (talk) 03:07, 6 July 2013 (UTC)[reply]

Ayaks, its that even possible?

Lets at first forget that that article is a huge mess (aerospaceship?)

The article says that this plane uses a "novel magneto-plasmo-chemical engine" to be able to fly in mesosphere.

And this is how the article describe the engine to me:

An plasma funnel collect air (that sounded really like Bussard ramjet collector )
It passes through an MHD generator that slows the air down
Then it passes through a plasma assisted burner fueled by "reformed fuel" from airplane skin coolant
The resulting hot gasses is funneled to a MPD thruster to accelerate it further
The plane uses power from the MHD generator to power its subsystems

My big question is, is this really possible? The article itself seems to be written by a lunatic, and it kinda implied that the craft have SSTO capability, but I'm not sure 140.0.229.26 (talk) 02:34, 6 July 2013 (UTC)[reply]

On paper, yes it would be possible -- however, in practice it would be very inefficient, the engine's thrust-to-weight ratio would be so hopelessly low that the plane would never lift off the ground, and the whole thing would be a maintenance nightmare a thousand times worse than our Valkyrie bomber. ~~And forget about the SSTO capability -- even if the plane could be made light enough to leave the ground, it would need every bit as much runway as the Tu-160, if not more.~~ 24.23.196.85 (talk) 05:50, 6 July 2013 (UTC)[reply]

I thought SSTO meant single stage to orbit, not vertical takeoff and landing. Anyhow, nowhere does the article imply that the craft can even reach orbit, let alone reach it in a single stage. The service ceiling is listed as 36 km in the Specifications section. --50.47.81.232 (talk) 06:35, 6 July 2013 (UTC)[reply]

My mistake, I thought SSTO meant "super-short takeoff". 24.23.196.85 (talk) 19:39, 6 July 2013 (UTC)[reply]

Yeah, I think it means to be a platform for an air launch to orbit system, like Pegasus. -- Finlay McWalterჷTalk 11:06, 6 July 2013 (UTC)[reply]

Yes, it does make for a rather eccentric read, but I think at least some of that is due to its being written by someone who isn't a great English speaker. "Aerospaceship" is just "spaceplane", and the thing about "particle beams" is just solar ionization of the atmosphere. -- Finlay McWalterჷTalk 11:06, 6 July 2013 (UTC)[reply]

It was probably written by a Russian-speaker, hence the incomprehensible word usage. 24.23.196.85 (talk) 19:41, 6 July 2013 (UTC)[reply]

Loss of weight after recovering from illness

Why do people who have recovered from illness lose weight? What are they losing? Fat? Water? Muscle? Clover345 (talk) 06:33, 6 July 2013 (UTC)[reply]

Is it generally true that people who have recovered from illness lose weight? What makes you say that? HiLo48 (talk) 08:33, 6 July 2013 (UTC)[reply]

Weight loss is a complex issue. Does our article Weight loss help at all? - Ka renjc 10:17, 6 July 2013 (UTC)[reply]

Some people who recover from some illnesses certainly lose weight - others do not.

The last time I had a bad cold, I weighed slightly more afterwards than I did before. :-(
This article says that unintentional weight loss is a symptom of a bunch of different things including: AIDS, Cancer (esp. if chemotherapy is required), Anorexia nervosa, Bulimia, Hyperthyroidism, Depression, Chronic diarrhea and any condition requiring thyroid medications.

The Weight_loss#Unintentional section of our Weight loss article says:

"Unintentional weight loss may be a result of loss of fat, muscle atrophy, fluid loss or a combination of these."

And also explains that:

"...it can also occur because of disease processes, changes in metabolism, hormonal changes, as an adverse effect of medication or other treatment, disease- or treatment-related dietary changes, or reduced appetite associated with a disease or treatment."

SteveBaker (talk) 13:38, 6 July 2013 (UTC)[reply]

To expand on the loss of appetite, if you didn't eat much while sick, your stomach may have shrunk, so that eating the same large meals you once did seems unpleasant.

Another possible reason is that healing requires lots of energy, and healing/replacement of damaged tissue may continue for some time after the disease has ended. StuRat (talk) 08:35, 7 July 2013 (UTC)[reply]

regarding equivalence of PG degrees.

Is M.Sc. applied chemistry equivalent to M.Sc. chemistry?

? As both are M.Sc. They are academically of the same worth. However, applied chemistry is a sub-discipline of chemistry itself. This doesn’t mean its inferior in anyway – just that it is more specialised. Can you give the reason you ask? If your asking from the point of view as a career choice, then forget learning anything that enriches mankind. Become a banker. Social parasites enjoy a financially richer life.--Aspro (talk) 16:35, 6 July 2013 (UTC)[reply]

Academically, yes. I suppose that with any one of these you could do a PhD afterwards. But, many people prefer to turn more 'applied' when they do a PG. So, maybe when it comes down to find a job the 'app. chemistry' PG is more valuable. But who knows? Do not get obsessed with degrees or what's written down on them. Choose the one were you can learn more, if you are asking for this reason. OsmanRF34 (talk) 17:37, 6 July 2013 (UTC)[reply]

Yes, I concur. If you haven't decided what specialization to focus on then don't force it. Study the broad until a specialization captures your interest. Also, don't over look the possibility that you might find general chemistry your vocation and then you might drift into to teaching. Specialization on the other-hand is always hard work as it constantly requires you to keep up with the latest research. Having worked in R&D I found that fun! It's horses for courses. Just because some of your friends might know what they want to do already doesn’t mean you shouldn’t hang back and study the larger picture. After all, new technology may develop were industry can't recruit applied chemists because it is too new but a chemical polymath might be their dream employee (remember to negotiate stock-options should you find yourself in this position). Let us know in 20 years time how you have got on and if you end up up with a big house with swimming pool, I would love to visit you for a weekend.--Aspro (talk) 19:02, 6 July 2013 (UTC)[reply]

Men and asking for directions

Is the idea that "men never ask for directions" a global thing or a local thing? If the latter, which male population or on what part of the globe do men fail to ask for directions or exhibit the tendency to do it less. Do women around the world complain about "men who fail to ask for directions"? Sneazy (talk) 17:22, 6 July 2013 (UTC) [reply]

meta-discussion

The following discussion has been closed. Please do not modify it.

Not really a science question. You might want to consider moving this to the Miscellaneous RefDesk. -- Scray (talk) 17:37, 6 July 2013 (UTC)[reply]

Apparently, it's listed under Science of the New York Times in 1992 here. From that article, I know that this phenomenon is REAL (or presumed to be real). Assuming that the article is being truthful, there may be data that have been collected on the concept that men ask for directions substantially less than women. Sneazy (talk) 17:56, 6 July 2013 (UTC)[reply]

The article to which you point is scientific. Your question is not formulated in a manner that asks for a scientific answer. If the phenomenon is local (i.e. what you're emphasizing), it's more likely to be cultural rather than inborn, though "local" could be explained by environmental or genetic influences. It's fuzzy enough to fit poorly here, IMHO. -- Scray (talk) 18:23, 6 July 2013 (UTC)[reply]

It's a hypothetical; I'm not emphasizing it. Sneazy (talk) 18:32, 6 July 2013 (UTC)[reply]

Mythbusters looked at this. In a sample of ten men and ten women from the San Francisco Bay Area that were given intentionally faulty directions, they found that nine of each stopped to ask for directions (during the 20 minutes allotted for the experiment). However, the men actually stopped an average of 20% sooner after discovering the directions were faulty. Hence in the Mythbusters' sample men were in fact somewhat more willing to ask for directions. Its a small and rather localized sample, but it does suggest that the difference between men and women in this regard probably isn't huge. Dragons flight (talk) 18:06, 6 July 2013 (UTC)[reply]

Why San Francisco? Sneazy (talk) 18:32, 6 July 2013 (UTC)[reply]

Mythbusters is based in San Francisco. Dragons flight (talk) 18:37, 6 July 2013 (UTC)[reply]

Interesting. I'd like to see a study of another thing someone claimed to me, which strikes me as kind of plausible (i.e. it seems to jibe with my observations) but I don't know whether it's true. The claim is that women, on the average, are more likely to memorize turn-by-turn directions, whereas men are more likely to keep a map of locations in their heads and work out the directions from that. Anyone know whether this has been studied? --Trovatore (talk) 18:44, 6 July 2013 (UTC)[reply]

Googling about suggests that this is quite a popular topic of study, with the general conclusion that there is a difference along these lines: men being comparatively more spatially oriented than women, and women relying on landmarks more than men do. — Quondum 19:27, 6 July 2013 (UTC)[reply]

A recent episode of the TV series Brain Games made exactly that point - that men are more likely to have a street map in their heads, while women are more likely to have a list of landmarks in their heads. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:34, 6 July 2013 (UTC)[reply]

unsourced random personal opinion

The following discussion has been closed. Please do not modify it.

As a man, I find it quite annoying when I try to get directions from a woman:

"At which corner of the intersection are you located ?"

"That depends, which direction are you coming from ?"

"No, it doesn't depend on my direction."

"Do you know where the Walmart is ?"

"No, nor do I care to know. Now run along and find a man who can give me proper directions."

"$#&%#@& !". CLICK. StuRat (talk) 07:17, 7 July 2013 (UTC)[reply]

Population studies are quite useful in estimating population tendencies, though when it comes to the individual, there may be variations within a species, and depending on how much this difference is stressed in the environment, the variation may be even more exaggerated or obliterated, or stay constant. Sneazy (talk) 19:35, 6 July 2013 (UTC)[reply]

There are certainly differences in how men and women navigate - one that's been reported frequently is the tendency for women to rotate a map such that the direction they are facing is at the top - versus men who seem to prefer north to be at the top. SteveBaker (talk) 22:24, 6 July 2013 (UTC)[reply]

(I read today a possible reason for this: Mental rotation says "males tend to be slightly faster in mental rotation tasks than females." - so it's plausible that women physically rotate the map in order to avoid having to mentally rotate it.) SteveBaker (talk) 13:36, 7 July 2013 (UTC)[reply]

Can you list a location of your observations? That other person used San Francisco. Sneazy (talk) 22:31, 6 July 2013 (UTC)[reply]

off-topic

The following discussion has been closed. Please do not modify it.

Seeing that such stuff gets researched by scientists, I wonder what topic would be too small for science. Can you get research funds to discover whether Linux users have less sex than Windows users? Or whether gay prefer to drink Pepsi and listen to Barbara Streisand? Or whether frat guys have little penises? OsmanRF34 (talk) 22:44, 6 July 2013 (UTC)[reply]

Penes, as this is the Science desk. Tevildo (talk) 23:11, 6 July 2013 (UTC)[reply]

I don't think so, unless you are a fundamental purist. [[1]] and [[2]] confirm that penises are acceptable. OsmanRF34 (talk) 23:19, 6 July 2013 (UTC) [reply]

A) Probably, B) Yes, provided you call in "market research" and get the funding from a corporation, C) Maybe though I'd think your odds would be better if "frat guys" were just one subgroup in a broader study. Dragons flight (talk) 23:54, 6 July 2013 (UTC)[reply]

Traditionally, frat guys spend a lot of their free time in broad studies. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:48, 7 July 2013 (UTC)[reply]

unsourced random guessing

The following discussion has been closed. Please do not modify it.

Women think men are less likely to ask for directions, because whenever they are in the car with men, they are going somewhere the men don't really want to go. When men are looking for somewhere they really want to get to, they have it planned out like a military campaign, and most likely their significant female other is not coming along. Gzuckier (talk) 07:05, 7 July 2013 (UTC)[reply]

Another possibility is that a man's willingness to ask for directions is reduced when a woman he knows is present, since he doesn't want to admit his navigation failures in their presence. StuRat (talk) 07:10, 7 July 2013 (UTC)[reply]

The hesitancy of men to ask for directions is just an example of their reluctance to ask for help in general. I believe the main reason for this is that men tend to view asking for help as creating a debt, whereas women are more likely to view it as creating a social bond. There are also differences in the ways that men and women navigate, but I think those are a separate issue. (To oversimplify, women tend to use route-based strategies such as "turn left at the intersection"; men tend to use map-based strategies such as "turn westward at the intersection".) Looie496 (talk) 15:52, 7 July 2013 (UTC)[reply]

I'll amplify on StuRat's last point here. All that we seem to be able to say is that there is a strong meme (probably especially amongst women) that men are averse to asking for directions, and it is not obvious how well this may have been studied. Unlike with a difference in navigational tendencies between men and women, Googling finds material relating to the perception of the male aversity (e.g. "How to get him to ask for directions"), with comparatively little reporting that doesn't come across as exploiting the perception (magazine-like articles using emotive phrasing like "26 percent [of men] wait at least half an hour before asking for directions" and "74 percent [of women] have no qualms about asking for directions", and this is evidently from a survey and will thus will be biased by social perceptions). Thus, the OP's questions relating to "the idea that" and "do women around the world complain that" seem not to be the focus of research, nor does the question about men actually being averse seem to be answered better at this point than the Mythbusters rebuttal. Perception management on the part of the men concerned may play a major role: where someone is more likely to be judged (e.g. a man when travelling with a woman who lays blame when being lost) is likely to adopt a strategy to minimize the criticism. — Quondum 16:44, 7 July 2013 (UTC)[reply]

Quote the old joke:

Wife: We are lost. Quit driving and ask for directions.

Husband: No. I don’t want to make my navigator look bad. 2600:1700:D591:5F10:51B5:288C:2F7:4B9D (talk) 16:24, 8 February 2023 (UTC)[reply]