Wikipedia:Reference desk/Archives/Science/2008 April 20

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April 20

Animals that can jump the furthest

Hi, Thanks everyone for your help. What we were after was what animals can jump the furthest distance (not in relation to their size or weight,) but just the longest distance.Cheers M and Z

We wanted a list of animals that can jump the furthest in asending order. Thanks Max and Zoe

Well, M and Z, here[1] for lots of speculation. Scroll down to Merlynson S. who says he got it from Planet Science.com. Must be a 10-year olds homework rush. Julia Rossi (talk) 06:17, 20 April 2008 (UTC)

Vicky has it right in that list, the answer is spittlebug. When you see the little white things that look like spit, attached to plants, those are nests of spittlebugs, they have the highest power-to-weight ratio. It'll take me a little while to look through my trivia questions to find the reference. Franamax (talk) 06:24, 20 April 2008 (UTC)

See Froghopper and this. I always knew someday I'd find that trivia is not useless - it's wikipedic! Franamax (talk) 06:40, 20 April 2008 (UTC)

Shoot. My trivia's just been upgraded. ; ) Julia Rossi (talk) 09:10, 20 April 2008 (UTC)

Well, I'm still ten years old, and I still do my homework late :) The distribution of hair has changed a bit though. Franamax (talk) 12:23, 20 April 2008 (UTC)

As far as I can tell, a flea, a froghopper, and a human being can all jump about the same height and distance. But that's not "impressive", so people divide by the animal's body weight and use that as their metric instead. Apparently what's really impressive to these people is inverse body weight, since the jumping distance seems to be largely uncorrelated with species. But it gets worse: looking at the BBC article, I see that the froghopper's jump is described as more impressive than the flea's because the froghopper is heavier! By that metric human beings are about 10,000 times more impressive than the froghopper. So if you really care about this question, you're going to have to choose a silly and meaningless metric out of the large collection available. I gather that the maximum of distance times weight among the insects is the froghopper. The maximum of distance divided by weight might be the flea, I suppose. The maximum of mere distance could be humans for all I know. The minimum by any of these metrics would include such animals as elephants and wolf-men. Hope this helps. -- BenRG (talk) 13:37, 20 April 2008 (UTC)

Whereas when I look at the BBC article I see "force per body weight" (in contrast to my power/weight ratio stated above), and froghopper=400X, flea=135X, us=2-3X. The metric is force/body weight, it was after all published in a modest magazine - I will dig up the paper tomorrow, just to be sure. Franamax (talk) 14:31, 20 April 2008 (UTC)

This discussion reminds me of [2] which had a whole bunch of things like this Nil Einne (talk) 15:52, 20 April 2008 (UTC)

Why traffic lights do not have different shapes?

It would be easier to color blinds to perceive them. Mr.K. (talk) 08:50, 20 April 2008 (UTC)

Maybe that they are already in different positions helps. Nice idea though. Julia Rossi (talk) 09:14, 20 April 2008 (UTC)

Some already do. See the image to the right for one example. GeeJo ^(t)⁄_(c) • 12:49, 20 April 2008 (UTC)

It seems that that traffic light has different shapes because it does not have the usual vertical orientation.--Russoc4 (talk) 15:59, 20 April 2008 (UTC)

As noted, in a few places different shapes are used. But the color of a light can be distinguished (by people with normal vision) from a lot greater distance than its shape. So if there are drivers who have to rely on the shape, the fact that they can't see it until they're close to the intersection creates a problem anyway. So really there's little advantage in making the change, and it's cheaper for all the color lenses to be the same shape.

(But here's an interesting point: in recent years color-filtered incandescent lights have begun to be superseded in traffic lights by clusters of LEDs, which are more efficient, and more strongly colored, and longer-lasting as well. I wonder if this design change would also change the economics enough to make it practical for different shapes to be introduced with no downside. Clearly a cluster of 60 or so LEDs can be made in a squarish shape as easily as a roundish one, as long as the exact number of LEDs used is not critical.)

--Anonymous, 19:18 UTC, April 20/08.

The position of the light (top-middle-bottom) is much easier to distinguish than the shape. Therefore we do not need a shape discriminator. If we ever decide to use a single light instead of three lights, We can shift to the time domain: steady light means "STOP." Slow blink means "GO". fast blink means "Caution." no lignt at all means "this signal is broken: treat as a four-way stop." -70.177.166.200 (talk) 23:41, 20 April 2008 (UTC)

A little bit of this "time domain discrimination" is already taking place. Here in New Hampshire, we still hace some places where the traffic signals are few and far between. In these places, the red signal light often incorporates within it a white xenon flash lamp element so the red signal is actually perceived as "red with an occasional very bright white flash". The intent, of course, is to draw your attention to the traffic signal that miles and miles of traffic-light-free crsuising have conditioned you to not expect.

Atlant (talk) 12:58, 21 April 2008 (UTC)

Contrariwise: the position of a single light is almost impossible to distinguish -- unless it happens to be daytime.

If there are multiple lights, of course, it's another matter. See Railway signals#Position light signals for some examples in another domain. --Anon, 01:17 UTC, April 21, 2008.

Time domain runs into problems with other uses. For instance where I live, some three-color lights function differently at different times of day. Solid red means stop until green, blinking red means stop, proceed when traffic is clear. Solid yellow means slow, about to turn red - but blinking yellow means proceed with caution but light will not turn red. And horizontally mounted lights interfere with the red on top scheme as well. I like the shapes idea. Too bad I have never actually seen it used. Rmhermen (talk) 14:22, 21 April 2008 (UTC)

In order to be "universally" understood, the total amount of information the signal can contain needs to be pretty low. "Stop" / "Go" / "Caution" is a pretty good compromise, with almost everyone understanding the intent. Though this leaves some colorblind individuals disadvantaged, the overall benefit due to simplicity is probably overwhelmingly worthwhile. If the signal is sufficiently complex, it will start to confuse people (at a rate proportional to the complexity). Most drivers understand "flashing red" to mean "stop sign"-like behavior, but some do not - and this creates a potential hazard. Similarly, "red square", "green circle", etc, are pretty straightforward, but some non-zero percentage of drivers would be confused by this, and that could create a hazard which might outweigh the advantage for color-blind drivers. Nimur (talk) 00:33, 26 April 2008 (UTC)

Tangential and radial components of a current

In Magnetoencephalography it says: "Whereas scalp EEG is sensitive to both tangential and radial components of a current source in a spherical volume conductor, MEG detects only its tangential components." Could anyone explain to me what is meant by the tangential and radial components of a current source. I had no physics at school after the age of 14, so I would prefer a rather elementary explanation. Thank you! Lova Falk (talk) 09:12, 20 April 2008 (UTC)

A radial movement is a movement from some center point outward. A tangential movement (in this case) is a movement that is parallel to a given circumference. A current is made up of moving electrical charges. Such a moving charge induces a magnetic field. The lines of force of this field form concentric circles around the path of the charge. Imagine your hand grabbing a cable with your thumb up. Then the magnetic lines of force are represented (very approximately) by your fingers. A magnetic line of force is what a freely gimbaled compass needle would align with - and what a not quite free needle tries to align with. You can measure the strengths of the field my measuring the force that tries to align the needle (although modern systems work very differently), and from measuring the magnetic field in different places you can compute some of the properties of the original current. --Stephan Schulz (talk) 09:35, 20 April 2008 (UTC)

functional groups

If a compound has both a ketone and an aldehyde functional group which one do you use to name it? thanks Qcsaets (talk) 12:07, 20 April 2008 (UTC)

When naming chemicals, if you have a ketone and an aldehyde in the same molecule, you name them both within the formula. I'm not very good on nomenclature so i'll let someone else give you an example, but yeah, you write the formula to include both. Regards, CycloneNimrod^Talk? 12:17, 20 April 2008 (UTC)

So if i had butane as an example as, C-C-C-C-CHO would be butanal. C-C-C(=O)-C (not sure how to write it) would but Butone. C-C(=O)-C-C-CHO would be.... "3,butone,1,al"? or something....? Qcsaets (talk) 13:03, 20 April 2008 (UTC) Thanks...

Me again, i had a read of this, http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry#Order_of_precedence_of_groups and it sort of sorts out the aldahyde/ketone thing, and from what i gather the correct name would be 3oxobutan1al? Qcsaets (talk) 13:38, 20 April 2008 (UTC)

You have 5 carbons in the first example, so it would be "pentanal". Note that you don't need to say which carbon is the carbonyl, because an aldehyde by definition is at the end. A 4-carbon chain in which the second is a carbonyl would be "butanone". Note that because you only have 4 carbons, there is only one way to have a ketone in that molecule (if the carbonyl were on either end, it would be an aldehyde, and the two middle carbons are equivalent). Aldehyde usually does take precedence over ketone; if you do use an aldehyde as the parent chain, the carbonyl of that aldehyde is defined as carbon #1. A 4-carbon chain with an aldehyde and a ketone could be 2-ketobutanal or 3-ketobutanal. DMacks (talk) 16:36, 20 April 2008 (UTC)

Forget that- understand now. Thanks Qcsaets (talk) 17:06, 20 April 2008 (UTC)

Do solar cells heat up your house?

Less expensive solar cells are known for their low efficiency (less than 10% or even worse). Does it mean solar cells generate much more heat than electricity? If your roof is made of ordinary tiles, then you installed solar cells on your roof, would the solar cells actually heat up your roof and make your house hotter and cost you more in air condictioning in the summer?

Some scientists believe that in a few decades, dirt cheap solar "paints" would be available for ubiquitous solar energy conversion. You paint solar cells to the building's exterior then enjoy the free energy. Would it be the "hottest" solution to our energy crisis?

Can we circulate water under solar cells so the heat generated by the solar cells can provide you with cheap hot water? -- Toytoy (talk) 12:20, 20 April 2008 (UTC)

Well, if your roof is black already, then installing solar panels isn't likely to make much difference. If it's a lighter color, then adding black solar panels on top of it might make your house hotter. It depends on a lot of things, though, including the thermal conductivity of your roofing material and whether or not there's an air gap between the solar panels and the roof. My personal guess would be that, all in all, it's probably easier to lose the extra heat than to hang on to it — if you wanted to make your house warmer by adding solar panels, you'd have to deliberately install them in a way that maximizes heat transfer into the house.

And yes, solar water heating does work and is used in practice. I see no reason why you couldn't combine it with photovoltaic cells, either. —Ilmari Karonen (talk) 13:11, 20 April 2008 (UTC)

What I am thinking about is the latest generation of "painted on" energy conversion materials. The efficiency of these materials shall be very low as they convert most of the sunlight into heat. If you paint your walls with these materials, wouldn't it make your summers even worse because they transfer most of the heat into the building. -- Toytoy (talk) 13:48, 20 April 2008 (UTC)

So don't paint them on your walls — paint them on some cheap plywood or aluminum sheeting or whatever and mount that over your walls, making sure to leave an airgap. Problem solved. Anyway, the problem is not specific to such high-tech electricity generating paints; painting your house a darker color will heat it up just as much regardless of what the paint is made of. If anything, a paint that generates electricity should be slightly cooler than a traditional paint of the same color, since the traditional paint will turn all of the absorbed energy into heat. —Ilmari Karonen (talk) 14:49, 20 April 2008 (UTC)

At least some of that inefficiency may also be due to reflection. The efficiency is a measure of the electrical energy generated compared to the total amount of light incident on the cell. So reflected light is counted toward the ideal (maximum possible) energy production, but doesn't go directly into heat production. --Prestidigitator (talk) 18:18, 20 April 2008 (UTC)

No matter how inefficient the solar cells are, they're still infinitely more efficient than shingles. Assuming you have black shingles, they're turning 100% of the energy into heat, rather than 80% or whatever it is. Of course, if you have light shingles, that doesn't really apply, as most of the wasted energy is reflected as light. — DanielLC 20:12, 20 April 2008 (UTC)

Solar cells are usually mounted above the roof rather that directly on the roof, becaus most roofs are not steep enough or ar not oriented due south. Therefore, almost all of the heat is moved away by convection on h efromt and back side of the panels. The actual roof is shaded by the panels, which decreases the heat input. Even if you do not have solar cells, you could make you r attic a lot cooler by mounting panels above the roof with lots of air flow below the panels. This is not common practice because ti's a lot cheaper to ventilate the attic.If your attic is hot in the summer, you should ventilate it regardless of whether or no you have solar cells on your roof. -70.177.166.200 (talk) 23:18, 20 April 2008 (UTC)

Extra heat is bad in the summer but good in the winter. A theoretically ideal rooftop installation will combine electricity generation with heat management, capturing the heat in the winter, and dissipating it in the summer or using the heat for low-power-density applications like heat-powered cooling. Residential solar is costliest power in terms of injuries per watt, because a single installation does not generate very many watts, while residential rooftop work results in a lot of injuries. Therefore, it better to implement a combined system with both solar calls and solar-thermal collectiohn, because the same number of tripr to the roof will result in more overall power. -70.177.166.200 (talk) 23:31, 20 April 2008 (UTC)

“ Residential solar is costliest power in terms of injuries per watt, because a single installation does not generate very many watts, while residential rooftop work results in a lot of injuries. ”

I tend to agree, but this needs citation lest it fall under the category for original research! Nimur (talk) 00:37, 26 April 2008 (UTC)

Leaves

When the wind blows, why do leaves travel in a circular motion?

24.197.166.190 (talk) 16:14, 20 April 2008 (UTC)XYZ

Probably because of vortexes and other complicated and turbulent phenomena that manifest in wind, esp. at small scales. The leaves themselves are also irregular in the same and are going to be subject to changing the path of whatever light wind is blowing them. --Captain Ref Desk (talk) 17:14, 20 April 2008 (UTC)

Thanks to CRD's intro, you will now enjoy turbulence and aerodynamics. Julia Rossi (talk) 23:26, 23 April 2008 (UTC)

Oldest tree.

What is the world's oldest tree? 99.226.39.245 (talk) 17:34, 20 April 2008 (UTC)

I believe it is a tree (a bristlecone pine?) somewhere in the Southwestern U.S. named Methuselah. It is said to be about 5,000 years old, I think. California redwoods can also live for a long time. Zrs 12 (talk) 17:43, 20 April 2008 (UTC)

Hey, I was right. From the bristlecone pine article:

Currently, the oldest (acknowledged) living organism known is a bristlecone pine tree nicknamed "Methuselah" (after Methuselah, the longest-lived person in the Bible), located in the Ancient Bristlecone Pine Forest in the White Mountains of eastern California, and measured by core samples to be 4,789 years old.

However, also from the bristlecone pine article:

Swedish researchers found a spruce in Dalarna that has been dated to just under 10,000 years old

The thing about the spruce is clarified by the list of long-living organisms article, which states:

A cluster of Norway Spruce in Sweden includes roots that have been carbon dated to 9,550 years old, which would make them the oldest known trees in the world. Individual trunks only last up to about 600 years, but the roots from which they grow have survived throughout the entire period.

Also, from the Maximum life span article:

the Bristlecone Pine called Prometheus was a little older still, 4,844 years, when it was cut down in 1964.

You may also want to refer to the Methuselah (tree) article.

Zrs 12 (talk) 17:47, 20 April 2008 (UTC)

This article is confusing in that I'm not sure if it's one tree or just a few trees with the same genetic makup, the oldest of which has died. Perhaps it's the same as Pando, which would make pando the oldest tree. 99.226.39.245 (talk) 17:56, 20 April 2008 (UTC)

Well, the Pando is a clonal organism. It's root system stays alive but only sprouts trunks when conditions are favorable. It all depends on what you mean by tree. If you mean trunks, limbs, etc. (ie above ground components), it will be the bristlecone pine; however, if the roots suffice then it would be the Pando. Zrs 12 (talk) 19:03, 20 April 2008 (UTC)

See also Lomatia tasmanica.--Shantavira|^{feed me} 07:49, 21 April 2008 (UTC)

Degrees vs. Radians

What is the advantage of using radians as opposed to degrees? Zrs 12 (talk) 19:09, 20 April 2008 (UTC)

Ok, so there is naturalness and elegance ( 1). Any others? Zrs 12 (talk) 19:18, 20 April 2008 (UTC)

No, that's really about all there is. --Anon, 19:22 UTC, April 20/08.

And it's plenty enough! --Stephan Schulz (talk) 19:24, 20 April 2008 (UTC)

Remember that radians are really a ratio of two lengths. The arc subtended by one radian on a circle has an arc length equal to the radius, and it is very convenient too that for small angles $\sin \theta \approx \tan \theta \approx \theta$. You could say that is the same thing expressed in the section referenced above, but I find it a more comfortable way to think about it. --Prestidigitator (talk) 01:34, 21 April 2008 (UTC)

See Radian#Reasons why radians are preferred in mathematics. Basically when you use degrees in calculus you get powers of ${\frac {\pi }{180}}$ appearing all over the place, which disappear when using radians. -- Q Chris (talk) 07:36, 21 April 2008 (UTC)

All this brings an interesting point, though: the radius is the key characteristic of the circle. That means our definition of $\pi$ as the circumference / diameter was not an entirely wise one (even though, mathematically, it doesn't matter). Because of that, we frequently have to use $2\pi$ or a doubling factor in calculations involving it. The glory of a named constant should be given to the ratio circumference / radius, which is 6.2831... :) . There's an article on this topic: Pi is wrong!. Of course, it's all too late now. — Kieff | Talk 08:01, 21 April 2008 (UTC)

I've always felt that two pis are better than one. Cherry $\pi$ is preferred.

On a (slightly) more serious note, physicists deserve some credit for creating new units when it suits them. Given Planck's constant, h, the early quantum physicists found that inconvenient factors of ${\frac {h}{2\pi }}$ kept cropping up. Rising to the challenge, the reduced Planck constant $\hbar$ – equal to ${\frac {h}{2\pi }}$ – was invented.

Not being satisfied with that one small step, physicists have since gone for a variety of systems of so-called natural units, in which important universal constants like $\hbar$, c, G, etc. are pegged at exactly one – it makes the math way easier! – and the universe is adjusted to match. TenOfAllTrades(talk) 11:56, 21 April 2008 (UTC)

Quantum teleportation

Alright so here's another question:

This quote is from [3] "In other words, although M and B have never been in contact, B has been imprinted with M's polarization value, across the whole galaxy, instantaneously.

This does not mean that faster-than-light information transfer has occurred."

How are these two sentences not contradictory (The article says they're not but never explains)? Zrs 12 (talk) 19:37, 20 April 2008 (UTC)

The article is actually fairly bad. But the principle is simple. You send out two entangled photons. When you measure the polarity of one, you also know the polarity of the other. But this does not transmit information from place A to place B - in principle it is no different from Kirk (on Earth) and Spock (on Vulcan) both seeing SN1987A at the same time. Sure, they see the same thing at the same time despite being light years apart, but no information flows from one to the other. --Stephan Schulz (talk) 22:17, 20 April 2008 (UTC)

B doesn't magically take on M's properties when you do something to M. The way quantum teleportation actually works is this: the sender causes M to interact with A (which is one half of a Bell pair) in a certain way and then measures the state of the system, getting two bits of information. Those bits are sent to the recipient, who operates on B (which is the other half of the Bell pair) in a way dictated by those two bits, recovering the state of M. In other words, it's not teleportation, it's a way of sending quantum information (qubits) when all you have is a classical communication channel. In practice it's useless because generating and storing Bell pairs is much, much harder than just sending the qubit over a quantum channel (and you need a quantum channel anyway in order to send B to the recipient in the first place). -- BenRG (talk) 23:55, 20 April 2008 (UTC)

Personally I'm with Schrödinger. The fact that you can't know a system's state until you measure it doesn't mean it doesn't have a definite state before you measure it; it just means it might have any state when you do somehow measure it. Hence the term "unknown." No quantum mechanical explanation has ever managed to present a solid argument to the contrary in my opinion, since they all boil down to, "But at that point your observation has measured, and thus influenced, the system." --Prestidigitator (talk) 01:43, 21 April 2008 (UTC)

It seems like you believe in a local hidden variable theory, so I refer you to Bell's theorem. —Keenan Pepper 02:00, 21 April 2008 (UTC)

They are contradictory. The first quotation is imprecise. Teleportation takes place in four steps. 1) An entangled pair of qubits is shared between two parties. 2) The qubit to be transmitted and the senders entangled qubit are measured in the bell basis. 3) The classical bits from the resulting measurement is transmitted across a classical channel. 4) The recipient applies a transformation based on the recieved bits to his copy of the (previously) entangled qubit.

After step 2, to some extent, information is imprinted on the recipients qubit. It depends on your definition of information. Usually, information means one can measure the qubit and and learn something new. Unfortunately, immediately after step 2, a measurement of the recipients qubit would yield 1 with 1/2 prob as it was before step 2. In other words, by my definition, no information is transmitted after step 2. The speed of step 3 is limited by the speed of light and the bottleneck in the entire process. Skippydo (talk) 02:53, 26 April 2008 (UTC)

Second messenger system

In the cAMP signal transduction system, a hormone detected outside a cell causes the activation of adenylyl cyclase within the cell, which produces cAMP, which in turn activates a protein kinase chain. It seems that this setup loses the information about what the initial hormone is - why don't all of the different hormones that work by the cAMP system cause exactly the same effects in every cell? --Iaerhoiee (talk) 19:54, 20 April 2008 (UTC)

One good reason for this is what cells are expressing the receptor for the hormone. Also, depending on the receptor subtype, it may be coupled to a different second messenger, like phospholipase C. Wisdom89 _{(T / ^C)} 19:59, 20 April 2008 (UTC)

To elaborate on wisdom's point, here is an excerpt from a college-level cell bio text book, The World of the Cell (6th ed.):

• An increase in cAMP concentration can produce many different effects in different cell types. When cAMP is elevated in skeletal muscle and liver cells, the breakdown of glycogen is stimulated. In cardiac muscle, the elvation of cAMP strengthens heart contraction, whereas in smooth muscle contraction is inhibited. In blood platelets, the elvation of cAMP inhibits their mobilization during blood clotting, and in intestinal epithelial cells, it causes the secretion of salts and water into the lumen of the gut. Each of these reactions is an example of the preprogrammed response discussed earlier" (398)
• "By preprogrammed, we mean that cells have a greater repertoire of functions than are in use at any particular time. Some of these cellular processes remain unused until particular signals are received that trigger them. We might compare the activation effect of a messenger to the stimulation of a reflex. In the knee-jerk reflex, for example, the nerve connections are already in place that can cause the leg to extend in response to a tap just below the knee, but the tap is needed to activate the reflex." (395)

--Shaggorama (talk) 10:12, 28 April 2008 (UTC)