Wikipedia:Reference desk/Archives/Science/2008 June 12

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June 12

Succession in Commmunities

What happens to the number of kinds of plants as the years pass? —Preceding unsigned comment added by 72.67.191.161 (talk) 03:13, 12 June 2008 (UTC)

The number of species of plants on Earth has increased from zero to many millions. A more specific answer will require a more specific question. --Sean 13:51, 12 June 2008 (UTC)

automatic sphygmomanometer

How does the machine measure the diastolic reading ? In manual readings it is when the sound of the pulse dissipates.Thommo123 (talk) 03:36, 12 June 2008 (UTC) Paul

See Korotkoff sounds. If the machine pumps the cuff pressure up sufficiently high and then slowly releases it, the point will come when Korotkoff whooshing sounds are heard at the brachial artery, at the pressure when the systolic pressure is sufficient to force blood through the restriction caused by the cuff. The K sounds continue with each heartbeat as the pressure drops until the diastolic pressure is reached, at which point the K sounds stop. Blood pressure machines I have dealt with just record the sound from the microphone and the pressure, and sends these two pressures to the readout. A comparator or trigger circuit can monitor the microphone sounds to decide when the K sounds are being produced. Edison (talk) 04:00, 12 June 2008 (UTC)

What about the ones that give continuous blood pressure readings? Surgeons on TV are always saying "BP's dropping", and they aren't constantly pressurising and unpressurising a cuff, as far as I can tell. --Tango (talk) 14:28, 12 June 2008 (UTC)

BP measured as described, by a trained human, with a mercury manometer, is be considered to be very accurate. It can also be a flawed measurement, if apprehension about the test causes an increase in BP. A continuous measurement at least avoids that stres, but may be more of an approximation, with computerized corrections, per Blood pressure, based on an external pressure transducer. Edison (talk) 18:54, 12 June 2008 (UTC)

Berembang tree

What is a berembang tree? I know it is in Malaysia. I also know that fireflies thrive on it and twinkle among the berembang trees like lights on Christmas trees. But that is all that i know. Any help......

TCGKennedy —Preceding unsigned comment added by TCGKennedy (talk • contribs) 04:00, 12 June 2008 (UTC)

The Berembang tree also known as the Crabapple Mangrove is botanically called Sonneratia caseolaris. You can find mor information about it at this link. [1]and some photos here [2]

Richard Avery (talk) 06:49, 12 June 2008 (UTC)

I believe these are common in Kuala Selangor which is well known for its firefly park [3] [4]. It sounds a bit like what you're referring to Nil Einne (talk) 09:58, 12 June 2008 (UTC)

Modeling a Body Moving in a Fluid

I am not a Physics expert so I can only say that this is a Fluid Dynamics question but I don't even know where to look for this specific equation or what is it called. Basically, we already know that the faster a car moves (in air of course), the lower its MPG becomes because it takes more energy. This is the same as if I filled a bathtub with water and tried to move my hand through it. If I move slowly, it is easy. The faster I try to move, the harder it becomes. So my question is, is there a page on wikipedia (or in one of the books) or even somewhere else online, which talks about the general form of this equation (preferably with the constants gives)? I just want to know what exactly happens to my MPG as I increase my speed on the highway. I can guess that it decreases exponentially but how rapidly. If I double my speed, how does my MPG change? Thanks!69.232.109.213 (talk) 04:45, 12 June 2008 (UTC)

Drag (physics)#Drag at high velocity is probably what you want, along with Fuel economy in automobiles#Physics background. AlmostReadytoFly (talk) 09:18, 12 June 2008 (UTC)

Thanks, this is exactly what I was looking for.68.126.127.207 (talk) 03:13, 13 June 2008 (UTC)

Robotic spacecraft maintains air pressure?

Does Robotic spacecraft maintain air pressure inside? If yes, what are benefits of air inside? I can think of using circulating air to control temperature inside. If air escapes in space, will there be any problem? —Preceding unsigned comment added by Ranemanoj (talk • contribs) 04:42, 12 June 2008 (UTC)

Generally no, but this may vary by design (though I can't think of any such designs offhand). Maintaining pressure means adding weight, something all spacecraft avoid where possible. Additionally, air is actually a rather lousy means of transferring heat -- metal conducting or radiating heat is preferable. Air unexpectedly escaping into space would result in unexpected thrust, which would have to be countered with fuel expenditure. — Lomn 08:02, 12 June 2008 (UTC)

If air is not desired, before launch, is it pumped out thereby creating vacuum inside spacecraft? Can is be designed such that, before take off from earth, spacecraft contains air, but as it goes up in low pressure air or space, air goes out gradually without creating thrust? Are there any instruments which are sensitive to pressure which may malfunction due to loss of air? 203.129.237.147 (talk) 11:25, 12 June 2008 (UTC)

If memory serves, Sputnik 1 was pressurised. I don't know of any other unmanned (and unanimaled!) space craft with internal pressure. All you need to do is make sure it isn't air tight, and the air can escape as it launches - the trust would be insignificant if it happens during launch when you have air resistance and rocket motors producing far more force. Also, if it escapes evenly from all sides, the trust will cancel out. They might pump the air out just to be on the safe side, I don't know, but I wouldn't think it was essential. --Tango (talk) 14:23, 12 June 2008 (UTC)

The laser diodes of some spacecrafts are sealed and contain dry air, because optical sufaces are sensitive to the change of atmosphere. Normally all Instruments on a satelite have to proofe that they are capable to vent the atmosphere within during launch. Stable compartments which can hold vacuum or normal eart atmosphere are a lot of mass and are avoided.--Stone (talk) 14:57, 12 June 2008 (UTC)

Martian North Pole

Just a quick question...When it is said that the Phoenix probe is on the north pole of Mars, I assume they mean relative to Earth's north pole? (Which is really the south magnetic pole...) I've also heard 'the north pole of the sun', this has the same meaning?--Shniken1 (talk) 04:59, 12 June 2008 (UTC)

That's a really good question. Seriously. Wiki has a detailed article discussing the various definitions of the poles of astronomical bodies, which answers your question very nicely. In brief, yes, the standard definition is as you say, but it is not the only one possible. Best regards, --Dr Dima (talk) 05:57, 12 June 2008 (UTC)

Actually, the Earth's North pole is the Earth's magnetic North pole as well. The pole of the magnet that gets attracted to the Earth's North pole is named as the magnet's North pole. In fact, the North pole of the Earth is the pole in which all magnetic lines of force converge. So a magnet's North pole point's to the Earth's North pole. In case of a magnet, the North pole is the pole from which the magnetic lines of force diverge. 117.194.226.11 (talk) 09:37, 12 June 2008 (UTC)

Yes, but if you consider the Earth as a magnet (it functions much like a bar magnet, if you don't look too closely), the Earth's magnetic north pole would be the magnet's south pole. This is due, I believe, to lazy people changing the English language - what we call the "north pole" of a magnet was originally called the "north seeking pole", which makes much more sense. --Tango (talk) 14:20, 12 June 2008 (UTC)

Except...Mars doesnt have a planet-wide magnetic field, so it has no "magnetic north pole". The only pole on Mars is the rotational pole, and as you say, it is only North because it is in roughly the same direction as our own magnetic north pole.

I wonder in the future, when we first visit another solar system, which way will be consider "north"? -RunningOnBrains 21:09, 12 June 2008 (UTC)

Probably the same way we do in this solar system - the direction closest to Earth's north. --Tango (talk) 21:21, 12 June 2008 (UTC)

One could also use the angular momentum vector of the planet to unambiguously define a north and south pole. Outstairs (talk) 06:40, 13 June 2008 (UTC)

Huh? The north magnetic pole is located near Ellef Ringnes Island in Nunavut. That's below 80N. The south magnetic pole is located near 65N so how are these exactly at the poles? Thanks. ~AH1^(TCU) 00:57, 14 June 2008 (UTC)

Did anyone claim the magnetic poles were exactly at the geographic poles? If they did, they were completely incorrect, but I can't see anyone claiming that. --Tango (talk) 15:44, 14 June 2008 (UTC)

Similar to the answers from Tango, Dr Dima and Outstairs, my reply to a related question at Talk:Phoenix (spacecraft)#Northern hemisphere followed the definition from poles of astronomical bodies and does not depend on magnetism:

See Poles of astronomical bodies, which has "The north pole is that pole of rotation that lies on the north side of the invariable plane of the solar system". The north side is that determined by the Earth's geographic north "side". So looking at the solar system from "above" (think of a spaceship launched from Earth's north pole straight up), looking "down" one sees all the planets' rotational North poles.

In turn, the Earth's geographic north pole does not need to depend on magnetism either, but is just defined historically (by Northern Hemisphere dwellers).-84user (talk) 14:23, 14 June 2008 (UTC)

I think all the talk about magnetism was just an aside. --Tango (talk) 15:46, 14 June 2008 (UTC)

Baseball

Hello. A pitcher throws a ball at 28 m/s [S] toward a batter. The ball contacts the bat for 2.0 ms and leaves the bat at 46 m/s [N]. What is the displacement of the ball when contacting the bat? The answer key multiplied the average velocity by time. Why? Thanks in advance. --Mayfare (talk) 06:00, 12 June 2008 (UTC)

Why what? --Dr Dima (talk) 06:05, 12 June 2008 (UTC)

I think Mayfare's asking why "the answer key multiplied the average velocity by time". But what I don't get is what is the question in the first place, as in, what do we have to calculate here? 117.194.226.11 (talk) 09:31, 12 June 2008 (UTC)

If the answer did indeed multiply the average velocity by a time then it would have produced a distance, and it is not at all clear how this could be a physcially meaningful quantity in this scenario. I suspect there may be a numerical coincidence here somewhere. It would help to know the units in which the answer was given (as well, of course, as knowing the full question, as pointed out above). Gandalf61 (talk) 09:50, 12 June 2008 (UTC)

Perhaps it's a misapprehension of the calculation. The average acceleration of the ball is Δv/t = (28 + 46)/2ms. The average of the speeds is (28+46)/2.

What was the question on the paper? AlmostReadytoFly (talk) 10:34, 12 June 2008 (UTC)

The speed averaged over what? You need to know how long it's travelling at each speed. Also, the question said average *velocity*, so you need to throw a minus sign in there somewhere. --Tango (talk) 12:39, 12 June 2008 (UTC)

Not averaged over anything. The point was that a naïve misinterpretation of the answer could be the reason for confusion. AlmostReadytoFly (talk) 13:20, 12 June 2008 (UTC)

Ah, sorry, you said "average of the speeds", not "average speed", my bad. It's a fairly meaningless number, though. --Tango (talk) 14:17, 12 June 2008 (UTC)

The question is asking how far the ball traveled while it was still in contact with the bat. The average velocity it traveled at while on the bat is (46 - 28)/2 (assuming contant acceleration for simplicity) the dispalcement is then the average velocity multiplied by time. -- Mad031683 (talk) 19:41, 12 June 2008 (UTC)

So if it left the bat at the same speed that it arrived (say 28 m/s in both cases), you'd have an average velocity of (28-28)/2 = 0 m/s, and you would calculate a distance of 0 m no matter how long it was in contact. I'm still not seeing the physical significance of this calculation. -- Coneslayer (talk) 19:50, 12 June 2008 (UTC)

The physical significance is the distance between where the bat starts and where it finishes. In your example, the bat would move backwards as it slows the ball down, and then forwards as it speeds it up in the other direction, ending up at the same place it started, hence the 0. In the case given by the OP, the bat would end up further forward than where it started. This is all assuming constant acceleration, though, which seems very unlikely to be even approximately true. In my experience of hitting balls, the bat moves forward far more than it moves back, regardless of the difference in speeds, this is probably because the bat is already moving before it contacts the ball. Keeping the bat still until the ball hits is more the ball bouncing off the bat than you hitting the ball with the bat. --Tango (talk) 19:57, 12 June 2008 (UTC)

Here's a simple answer: all basic physics problems can by answered by looking at units. displacement is meters, velocity is meters/second. Therefore, velocity (m/s) x time (s) = displacement (m). dig it? --Shaggorama (talk) 07:15, 15 June 2008 (UTC)

Covalent Bond

I am a little confuse at the definition of covalent bond,it is the bond formed due to the sharing of electron,i say how is it possible becoz electron has the same charge they should repel each other how atom share orbitals (electron) —Preceding unsigned comment added by 202.125.143.78 (talk) 06:25, 12 June 2008 (UTC)

Covalent bonds do indeed share electrons and this is because electrons are actually more happy to be in pairs than they are on their own. I don't really know how this works out, I too would have thought they'd repel each other but i'll leave that to someone else. Regards, CycloneNimrod ^talk?_contribs? 06:44, 12 June 2008 (UTC)

(ec) Electrons certainly seem like they should repel each other because they have the same charge, but electrons in orbitals can be more stable when paired. Crazy, eh? Electrons have a quantum property called "spin" that can be either of two values, and an orbital can hold one of each: a spin-paired set is often more stable than a single electron in an orbital. The idea of two electrons (of opposite spins) per orbital isn't limitted to covalent bonds, by the way: consider how you do electron configuration for individual atoms, with two s electrons, etc. DMacks (talk) 06:51, 12 June 2008 (UTC)

Electrons do indeed repel one another! Please keep in mind, however, that for a covalent bond to be formed, you must also have at least two atomic nuclei in the neighborhood. And while these nuclei are electrically repelling one another, they are also electrically attracting all the electrons in the neighborhood! So things settle down into this nice snuggly, er, that is low potential energy arrangement we call a covalent bond. It's only when people ask questions about why the arrangement isn't even snugglier than we observe that you need to invoke things like the Pauli exclusion principle. --arkuat (talk) 10:28, 13 June 2008 (UTC)

The most powerful earthquakes...

...occur on Destructive Plate boundaries. Am I right? Thanks 79.78.3.4 (talk) 07:32, 12 June 2008 (UTC) (Moved from Humanities) 79.72.162.214 (talk) 09:46, 12 June 2008 (UTC)

Some of the most powerful earthquakes, though rare, occur in the middle of current plates. See New Madrid Seismic Zone as an example. This particular zone is on an ancient "failed rift" that never evolved into a plate boundary. -Arch dude (talk) 11:52, 12 June 2008 (UTC)

All the most powerful earthquakes, M_w 9.0 or greater, since 1900 have occurred on destructive plate boundaries, see our article Megathrust earthquake. Mikenorton (talk) 09:19, 13 June 2008 (UTC)

Science do not solve all of man's problems

I was aked to state my opinion on whether or not I agree with the above mentioned statement 'science do not solve all of man's problems.

i simply said, "issues in today's society or environmentally/ globally even!!!always seems to have some sort of scientific reasoning behind it.How ironic that as a people we are put together to work colaboratively, but wait if there is too much friction, we do have a solution its called proven speculation namely science..what happened to reasoning"

Now I am required to elaborate on this statement.

My question to you is 1. help me to elaborate and give facts to my statement. 2. Give and enlighten me on your opinion and what you would of said (provide). 3. A answer with an opinion that differs from mine.

Thank you in advance

Regards

Miss Inquisitive —Preceding unsigned comment added by 41.241.47.178 (talk) 10:41, 12 June 2008 (UTC)

Although this post seems like homework, do research whether the level of knowledge regarding the conception and birth of a human child has any effect on people's views on abortion. That would be a case where people can know the relevant scientific facts and yet still disagree on an issue.--droptone (talk) 11:37, 12 June 2008 (UTC)

I recommend you think about what science is not. For instance I would say that science cannot solve ethical problems. AlmostReadytoFly (talk) 13:25, 12 June 2008 (UTC)

That there are problems that science cannot solve is [1] obvious, and [2] unremarkable. A more interesting question would be, "Are there problems which are solved better by something other than science?". It would be fun to argue that everything that is not science is equally ineffective as science at "solving" ethical problems. - Nunh-huh 16:52, 12 June 2008 (UTC)

Your first step there is to define "solve". --Tango (talk) 18:54, 12 June 2008 (UTC)

Just some general essay writing advice (since it sounds to me from the prompt that you're writing an argumentative essay): to elaborate on your own opinion, first start by picking apart the question and clarifying it to yourself to help understand what an answer to it should even look like. Is science supposed to solve problems? says who? what kind of problems does science solve, or is it supposed to? What does it mean for one of these problems to be "solved"? How would the world be different if science solved all of man's problems? Once you've figured out what the question is asking and how you want to approach it, try to think of a specific example (or 2 or 3)that illustrates your point. Then try to imagine if someone disagreed with you what arguments they'd raise, and address each in turn. --Shaggorama (talk) 07:10, 15 June 2008 (UTC)

blood

who invented the blood —Preceding unsigned comment added by Anandh heart (talk • contribs) 13:07, 12 June 2008 (UTC)

Nobody. We've always had blood. There's no individual who discovered blood either, as people have been injuring themselves and others since prehistory. AlmostReadytoFly (talk) 13:40, 12 June 2008 (UTC)

Firstly, as AlmostReadytoFly pointed out, blood cannot be invented, moreover, just because of the injuries, even animals that came to existence before humans must have noted it. —KetanPanchal^taLK 13:56, 12 June 2008 (UTC)

You could take a look at intelligent design, if you really want to. --Tango (talk) 14:16, 12 June 2008 (UTC)

And if you are actually asking who discovered the circulation of blood, see Ibn al-Nafis, Michael Servetus and William Harvey. Gandalf61 (talk) 14:22, 12 June 2008 (UTC)

There are some new artificial blood. Wasn't a single person who created them though. ScienceApe (talk) 15:24, 12 June 2008 (UTC)

S/he's not actually asking anything. This 'question' was posted on the Entertainment desk at the same time. You shouldn't waste time with this one, but I'm not the boss of you. -.-; Kreachure (talk) 15:55, 12 June 2008 (UTC)

We are obviously very literal here at WP:RD/S. The responses to this question at WP:RD/E are more ... umm ... creative. Gandalf61 (talk) 16:02, 12 June 2008 (UTC)

I did. Those who don't believe me will be condemned to my torture chamber. Imagine Reason (talk) 15:04, 15 June 2008 (UTC)

Exponential equation, solve for I0?

I have been struggling for some time (like 2 years pretty much!) to solve the equation given below for $I_{0}$:

$I=I_{0}\cdot e^{I_{0}\cdot t}$

I have tried to use Lambert's W function to find $I_{0}$, however the solution does not converge at the high values of $I$ that I am using. The equation is used to correct the measured signal intensity $I$ for a given detector deadtime $t$.

How can I solve this equation without using Lambert's W function (Which doesn't work). I'm sure (and really hope) that there is a much more simple way of solving this. Thanks Jdrewitt (talk) 16:49, 12 June 2008 (UTC)

I doubt that can be solved without using Lambert's W function. Lambert W function#Evaluation algorithm gives some ways to calculate its value outside the disc of convergence of its Taylor series, does that help at all? --Tango (talk) 17:16, 12 June 2008 (UTC)

I'll give it a go, since the evaluation algorithm section links to the desy webpage, there is a good chance that they developed it to try and solve a similar deadtime problem. Thanks, Jdrewitt (talk) 17:49, 12 June 2008 (UTC)

Since you aren't going to get a better closed-form solution than with W, why not just solve the equation numerically? I'm assuming that all your variables are positive (since you talked about I being "large"): then the function on the right is strictly increasing with $I_{0}$, and you should be able to apply something trivial like bisection search to it. (Since you're starting with the unbounded interval $[0,\infty )$, you'll have to start with some sort of interval-widening until you bracket the solution: evaluate the sign of $I-I_{0}e^{I_{0}t}$ at 1, 2, 4, 8, ..., until it changes (to negative) and then do the bisection search on $[2^{n},2^{n+1}]$.) Of course, other approaches like Newton's method might work better, but Newton's method in particular seems to converge very slowly for this function (18674 iterations with $t=3,\,I=5\times 10^{5},\,\varepsilon =10^{-6}$ like I tried). --Tardis (talk) 23:49, 12 June 2008 (UTC)

There are several numerical methods implemented as computer programs like Newton Raphson which are used for solving large matrix equations like tohse describing a power system which do not have a determinate solution. You may wind up with a small error term if you are successful. There are ways of determining whether you have found a good solution, and tricks for approaching that solution. I greatly admire those who are comfortable with such mathematics. I just use it. Edison (talk) 04:05, 13 June 2008 (UTC)

Magnetic monopoles and turning matter into energy

It seems that magnetic monopoles potentially can turn matter into energy. Is this process 100% efficient? Can it perform 100% conversion like antimatter? Will any of the energy be released as harmless neutrinos like in antimatter-matter reactions? ScienceApe (talk) 18:54, 12 June 2008 (UTC)

Given that the existence of magnetic monopoles remains conjuncture and speculation, much less their actual behavior, no answer can be given. — Lomn 19:26, 12 June 2008 (UTC)

Not even theoretical predictions? If we assume proton decay takes place? ScienceApe (talk) 20:50, 12 June 2008 (UTC)

Various grand unified theories do predict that magnetic monopoles will catalyze nucleon decay. I think the decay modes are the same as without the monopole, e.g. $M+p\rightarrow M+e^{+}+\pi ^{0}\,$ where M is the monopole (see proton decay). Whether this could be turned into a safe energy source I can't say. It's not "100% efficient", but neither is matter-antimatter annihilation—not all of the energy comes out as photons and you can't turn the photons into useful work with 100% efficiency anyway. -- BenRG (talk) 22:49, 12 June 2008 (UTC)

But will it turn a given piece of matter into its energy equivilant. And will any of that energy be in the form of neutrinos? ScienceApe (talk) 02:05, 13 June 2008 (UTC)

One hypothesis I read years ago stated that just one monopole was possible in this universe. Good luck finding it. Polypipe Wrangler (talk) 10:19, 18 June 2008 (UTC)

Eye myopia

I just recently got glasses for my myopia. I heard that the more you wear your glasses/contacts, the "lazier" the eye muscles get, making them more dependent on the corrective agents, thus making your vision worse. Is this true? I want to wear my glasses, but not at the expense of my eyesight. DISCLAIMER: NOT MEDICAL ADVICE (AND ALL THAT BLAH BLAH BLAH)...JUST WANT TO KNOW THE SCIENCE BEHIND IT. Thanks for your help. --71.98.22.225 (talk) 21:33, 12 June 2008 (UTC)

I've heard the opposite... I believe that, in some cases, wearing correct lenses can help your eyesight improve. I'm not sure what those cases are, though. --Tango (talk) 21:40, 12 June 2008 (UTC)

Unlike eyeglasses, contact lenses can mold the shape of the cornea, at least temporarily.Scray (talk) 01:57, 13 June 2008 (UTC)

What you heard doesn't sound well-informed. Are you thinking vision therapy? Applies to some conditions... Julia Rossi (talk) 09:40, 13 June 2008 (UTC)

When I first got glasses, I could watch T.V without them, but now, even though my power hasn't increased one bit, I find it more difficult to do things without my glasses. So, in a way, I've grown more dependent on them than I was in the beginning. My dad says that it's your perspective that changes, i.e, you get to know what perfectly clear vision is like, so you feel uncomfortable with anything less than perfect. Hope I have helped you. Have a nice day! 117.194.227.13 (talk) 06:15, 15 June 2008 (UTC)

Need Help in Finding an article previously found in Wikipedia

Wikipedia has an article that I recently read about an unusual mental condition in which a person can see spoken words, musical notes etc. in the air. And sometimes in colors. And in some individuals the colors are different depending on whether the other person speaking the words has a change in his/her emotions.

The Wikipedia article went on to give a fairly long list of famous people, both past and present, with this condition. George Gershwin was mentioned. Possibly Leonard Bernstein, other artists and composers.

I would greatly appreciate your advising the name of this mental condition.

BMany thanks,Bob Christman at <email removed - see page header> —Preceding unsigned comment added by 65.13.109.109 (talk) 22:40, 12 June 2008 (UTC)

I'd guess you were looking at Synesthesia, or the associated article List of people with synesthesia. Confusing Manifestation(Say hi!) 22:47, 12 June 2008 (UTC)