Wikipedia:Reference desk/Archives/Science/2011 November 24

= November 24 =

Creature in brinicle ice video
Hi all. Does anyone know what the white snake-like creature is that you see moving in the bottom left of this video from 0:42 to 0:43? Akamad (talk) 01:59, 24 November 2011 (UTC)
 * My best guess after some wikisearching and g**gling would be a nermertine or 'ribbon worm' (which funnily enough was also my first guess before researching), but I suspect it's going to take a genuine expert to give anything like a reliable answer. Hopefully one will come along. You might like to explore this page of a website about Arctic ocean diversity. {The poster formerly known as 87.81.230.195} 90.197.66.23 (talk) 02:55, 24 November 2011 (UTC)


 * . Note that the documentary is speeded up drastically (i.e. they do not move that fast in real life). They are nemertean worms. Most likely Parborlasia corrugatus.--  Obsidi ♠ n   Soul   03:00, 24 November 2011 (UTC)


 * Interesting! Thanks. - Akamad (talk) 21:04, 24 November 2011 (UTC)

The usefulness of the Washington Accord (or how to become licensed in the US)
Are there any engineers here who can tell me how the licensure process in the United States works for foreign engineers? Is it sufficient to have a degree accredited by a signatory of the Washington accord? More generally, how does a foreign engineer become licensed in the United States? Widener (talk) 03:24, 24 November 2011 (UTC)


 * There are two issues: getting permission from the Citizenship and Immigration Service to work in the US, and getting a license. See the Professional Engineer article. The accredited degree will take care of the education requirement, although you may have to pay for an evaluation to demonstrate the degree is equivalent. Most states require 4 years of experience after the bachelor's degree, and will count a master's degree as one year of experience. Sometimes states insist the experience be under a licensed engineer, so getting them to recognize your foreign experience might be difficult. Finally, a fairly difficult nationwide exam is required. Jc3s5h (talk) 03:32, 24 November 2011 (UTC)
 * What do you mean by "The accredited degree will take care of the education requirement, although you may have to pay for an evaluation to demonstrate the degree is equivalent."? Do you mean that the accreditation itself is sufficient to demonstrate satisfaction of the education requirement? Or is it that the accredited degree will probably meet the education requirement but not automatically (and hence why you may still need an evaluation)? Widener (talk) 04:16, 24 November 2011 (UTC)
 * Also, that seems like a lot you have to do. Do you have to do all that even if you have met all the engineering requirements and are a fully practicing engineer in your home country? i.e. Is it not possible to have the professional status transferred? Widener (talk) 04:22, 24 November 2011 (UTC)
 * I think it's clear from the articles the OP Jc3s5h is saying that an accredited degree is enough to satisfy the education requirement, however recognition may not be automatic i.e. someone with a degree may still have to pay some other party to evaluate and certify you satisfy the requirement (but provided the person really has an accredited degree there's no real way they the other party can find the person don't satisfy the requirement). I don't know if it's possible to transfer the professional status but it seems clear from reading both articles the only thing the Washington Accord is for is to ensure the degree is recognised and that in most or all US states the normal process to become a professional engineer requires experience and passing additional exams in addition to a degree. Nil Einne (talk) 06:43, 24 November 2011 (UTC)

Hopefully the above have covered it. The technical term is comity. The Washington Accord merely helps with your first degree. Engineering licenses are a state matter, not federal. As such if you wish to practice as a PE in a given state, contact that state's licensing body. The rules do differ from state to state. The chances are that you will have to take both exams, but with any luck they'll waive the experience requirement. The exams seem to cause fear and trepidation, I tried some questions from the structures one and found them rather banal, but then I'm a mechie and don't design to code in my real job. Your other options would be to work for a PE, or work in an exempt field. Greglocock (talk) 00:56, 25 November 2011 (UTC)


 * The issue with the experience requirement is that some states, like New York accept experience statements from whoever your supervisor was, whether the supervisor had a license or not. Some states specify the supervisor must have an engineering license. Those states might or might not accept experience under a supervisor who is licensed in another country. In states that require licensed supervisors, you might have a problem if your home country does not require licenses for engineers. Jc3s5h (talk) 01:15, 25 November 2011 (UTC)

Water and heating device temperatures.
Good afternoon,

I wonder from which temperature water drops rebound on a [kitchen] stove (the temperature of the stove). --213.213.234.54 (talk) 14:07, 24 November 2011 (UTC)
 * Complement. A video from the Universidade Federal de Santa Catarina shows the phenomen: http://www.youtube.com/watch?v=XtlgI34y3Wc --213.213.234.54 (talk) 14:10, 24 November 2011 (UTC)


 * If I understand your question correctly, that would be the boiling point of water, which is nominally 100°C.--Shantavira|feed me 16:25, 24 November 2011 (UTC)


 * I think the OP may be interested in the Leidenfrost effect... -- Jayron  32  17:22, 24 November 2011 (UTC)


 * I stand corrected. So it seems we're talking about the Leidenfrost Point, which is somewhere around 193°C.--Shantavira|feed me 17:52, 24 November 2011 (UTC)


 * The OP presumably means cold water dropped on a hot kitchen stove. The Leidenfrost effect of drops skittering on cushions of superheated steam occurs at surface temperatures that are not definable more precisely than about 200°C. The body of the drop heats only gradually. On the concave underside of the drop, water boils off at 100°C very slowly, just enough to replace the steam that escapes sideways. Hence the long life of the levitating drop. The video posted by IP User 213.213.234.54 does not show the Leidenfrost phenomenon. It shows instead a drop that falls on to a liquid surface with which it coalesces in a series of collapses of surface tension with no boiling involved. Cuddlyable3 (talk) 00:03, 25 November 2011 (UTC)


 * Thank you for the Leidenfrost effect article link. The OP.

Relative speeds
Okay, so the Millennium Falcon is travelling at .9 c in one direction, and the Enterprise is travelling at .7 c in the opposite direction (both speeds relative to an at-rest third observer). As they approach each other, what will each ship measure the other ship's speed as, and how is this determined? --Goodbye Galaxy (talk) 17:38, 24 November 2011 (UTC)
 * This does not appear to be addressed by our present understanding of physics (or at least by my understanding). Presumably they are travelling in "hyperspace" and not our normal space, so at superluminal speeds their relative speed might be undefined. Edison (talk) 19:45, 24 November 2011 (UTC)
 * Uh, no. The ship names were just for flavour. No hyperspace or sci-fi-physics involved. Goodbye Galaxy (talk) 19:52, 24 November 2011 (UTC)
 * It is addressed perfectly well under our understanding of physics. The Lorentz transformation allows one to calculate such velocities as measured in other frames of reference.  Both Han Solo and Captain Kirk will still measure each other's speed as less than c.  The specific speed is beyond me (mathematically), but anyone with sufficient training could probably pick the correct equation out of the Lorentz transformation article and spit out the correct answer quickly.  -- Jayron  32  19:59, 24 November 2011 (UTC)
 * See also Velocity-addition formula. WikiDao    &#9775;  20:02, 24 November 2011 (UTC)


 * The correct answer is that they'll determine the speed by whatever sci-fi means they have available, and record it in whatever form is convenient for them. The most convenient form would presumably be relative to a nearby planet or space station or to the fixed stars that they use to get their bearings. It's much easier to keep track of everything if you pick a particular reference frame (such as the frame of the fixed stars) and stick to it. The only time you might care about the relative speed of two vessels is if they're on a collision course.


 * If you detect an enemy ship on radar and want to determine its course and speed on your charts, in a Newtonian world, it's a vector subtraction: the other ship's velocity relative to you (as determined from radar) minus your velocity relative to your reference coordinates equals the other ship's velocity relative to your reference coordinates. In relativistic physics, it's a more complicated formula which is misleadingly called "the velocity subtraction formula" even though it's not a subtraction. It's really a velocity transformation formula. The Enterprise "sensors" might work like radar, or they might use some hyperspace magic, or they might track ships against visible reference points, and there would be correspondingly different ways of converting the raw sensor data into something useful to the bridge crew. -- BenRG (talk) 20:50, 24 November 2011 (UTC)
 * Lawl. Everyone's getting hung up on the spaceships. Let's change it to two rocks with no other visible reference points. Jaryon's answer was what I expected, just without the math. Anyone got the math? Goodbye Galaxy (talk) 21:20, 24 November 2011 (UTC)
 * Rocks don't measure each other's speeds. If you want to know about the velocity-addition formula then you can read the article that WikiDao linked, but if you think it's relevant here then you're misunderstanding what it's about. -- BenRG (talk) 21:55, 24 November 2011 (UTC)
 * I think time dilation is what throws the spanner in the works and makes this very counter intuitive. The ships traveling at close to the speed of light will experience TIME it self differently which completely changes how they perceive velocity, their own and that of any observed objects. Vespine (talk) 22:22, 24 November 2011 (UTC)
 * No, whatever the speed, each ship experiences time perfectly normally. Nothing actually happens to local time as a ship approaches the speed of light.  It's when they start observing objects not moving at the same speed that they notice the other objects seem to have a peculiar time frame.    D b f i r s   22:37, 24 November 2011 (UTC)
 * Read the article that WikiDao linked. This section in particular. --130.216.55.200 (talk) 23:00, 24 November 2011 (UTC)


 * I'm disappointed at the awful quality of (most of) these responses. The answer is 0.982c, and this is calculated using the velocity-addition formula linked to by WikiDao and 130.216.55.200.  --140.180.13.218 (talk) 09:03, 25 November 2011 (UTC)
 * Well, no, the answer is the one I gave, unless you're taking a test in an undergraduate special relativity course, in which case the formula they are expecting you to plug the numbers into is that one, yes. But the ability to pass those tests is not useful in later life, even if you become a physicist. -- BenRG (talk) 09:32, 25 November 2011 (UTC)
 * Yes, I calculated the relative velocity as 0.981595c and was about to post this yesterday, but had an edit conflict with Ben (who does know what he is writing about), so I didn't post it, since I agreed that my answer was meaningless for rocks. The formula gives the rate of decrease in separation between the rocks or spaceships (as would be observed from either ship), but that is not what was asked.    D b f i r s   10:19, 25 November 2011 (UTC)


 * How is it not what was asked? The question was "what will each ship measure the other ship's speed as, and how is this determined?"  Each ship will measure the other's speed as 0.982c, period.  There is no way around that answer.  If the ship measures d/t, it will get 0.982c.  If it measures the blueshift of the other ship's light, it will also get 0.982c.  If it uses radar and measures the frequency change of the reflection, it will get 0.982c.  If it measures its own speed against an external observer, then the other ship's speed against an external observer, and computes the relative speed, it will get 0.982c.  If it looks inside the other ship, calculates its time dilation or length contraction, and uses that to find speed, it will get 0.982c.  Every correct physical measurement will give the same answer because special relativity is valid in all inertial reference frames.


 * Also, I know that Ben knows what he's talking about, but I think he misunderstood the question. I doubt it was supposed to be about sci-fi, considering that the OP said "no hyperspace or sci-fi involved" and "Everyone's getting hung up on the spaceships. Let's change it to two rocks with no other visible reference points."  It was quite clearly a question about science, and about why 0.9 + 0.7 c is not 1.6c.  --140.180.13.218 (talk) 15:39, 25 November 2011 (UTC)


 * Ah! Suddenly the responses of several editors make more sense. On my monitor I could not see the "." before the 9 and 7, so I thought the OP was stating velocities of "7c and 9C" rather than ".7c and .9c." I have zoomed in a bit and now they are visible. Some publications have a style sheet using "0.7" rather than ".7" so people don't miss the decimal point. Hence my response mentioning "superliminal"and "hyperspace." I agree with the 0.982c responses, since the formula can be worked, using all speeds relative to c as s=(0.7+0.9)/(1+(0.7*0.9/1**2))=.982. If one enters 9 and 7 rather than 0.9 and 0.7, the result would be a surprising 0.25. [User:Edison|Edison]] (talk) 16:06, 25 November 2011 (UTC)


 * Well, as Ben said, each ship is more likely to measure the actual speed of each ship relative to the local stars and planets, unless, of course, the ships are on a collision course or at war, and they want to know how long they have to take evasive action, and, even then, their computers would probably work with separate speeds relative to the local obstacles. I don't think a captain of a spaceship would ever say that the other ship's speed was 0.982c, since that figure is just an observed rate of reduction of separation, not an actual speed, though I suppose she might quote that figure as a relative speed of approach.  (I should have realised that some people were not seeing the decimal point.)   D b f i r s   17:00, 25 November 2011 (UTC)


 * This time BenRG is not making any sense. A rate of reduction of separation is just another name for SPEED. 71.101.41.253 (talk) 19:37, 25 November 2011 (UTC)


 * It was my phrase, not Ben's, and I used it as a synonym for the relative speed of approach as observed from either ship, not for the speed of either ship, or for the speed of approach measured in other reference frames. The answer depends on who is doing the observing and on how they make the measurements.    D b f i r s   23:51, 25 November 2011 (UTC)

Thanks for the answer, 140 et al. Did you guys know that rocks can't take measurements?! Crazy! Goodbye Galaxy (talk) 18:06, 25 November 2011 (UTC)


 * That's correct. Only observers can observe a speed of approach, and rocks can't observe. An observer following one of the rocks but not quite keeping up with it would observe a faster "rate of reduction of separation" between the rocks.    D b f i r s   00:07, 26 November 2011 (UTC)


 * Hopefully, even if the OP doesn't learn to add relativistic speeds, at least s/he will learn how to correctly write numbers. (hint: the zero before the point is not optional). 71.101.41.253 (talk) 19:37, 25 November 2011 (UTC)
 * Jeez louise. Better lynch me for it. Goodbye Galaxy (talk) 19:50, 25 November 2011 (UTC)
 * Calculators understand numbers entered without a zero before the point just as readily as we understand people who fail "to write correctly" in obedience to another spurious and unhelpful style guide that forbids a split infinitive. Cuddlyable3 (talk) 00:40, 26 November 2011 (UTC)


 * Except that this is not an spurious style guide since, as we saw in this very thread, the absence of a leading zero causes some people to misread the number and that's a serious problem. Dauto (talk) 23:56, 28 November 2011 (UTC)