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June 10

Feisty baby gull...

Has anyone else here ever seen a gull chick deliberately starting a fight with an adult bird - and winning? Today, I had the opportunity to observe a colony of nesting Black-headed gulls at close quarters in their natural habitat. I noticed that most of the gull pairs had built their nests on small salt marsh 'islands', meaning that space was at a premium. The gulls (being typical gulls) were of course bickering, squabbling and pecking each other constantly over minor territorial encroachments and airspace above the nest. What surprised me, however was to see one of the older chicks joining in.

This particular bird was about 2/3 adult size with partially-grown wing feathers, so he/she was probably about three weeks old, or so. Yes, this youngster was starting fights with any adult gull which came too close to his mother's nest. Not only was he starting fights, more astoundingly he was winning them too! While I was watching, he must've seen off about 15 intruders with his chest-puffed, charging pecks. He certainly wasn't staying on his side of the line either - more than once, he chased an adult gull all the way across the island and into the water with his heel-snapping, causing absolute pandemonium amongst the uninvolved sitting hens. I just can't understand why the adult birds were prepared to take that from a chick...

Oh yes, in answer to the question someone asked the other day - it seems that baby gulls of this species *can* and do swim. I saw birds that were no more than a couple of days old trying to swim away from their nests (much to the annoyance of the parent gulls, who would corral them back, scolding loudly). They seemed to be fully waterproofed too. --Kurt Shaped Box (talk) 01:59, 10 June 2008 (UTC)[reply]

That sounds like behavior typically associated with species that have ascribed social status. That is, the offspring of the "alpha pair" may have the right to push around others, even adults. Do gulls exhibit such a complex social pattern as this ? 67.38.24.177 (talk) 03:04, 10 June 2008 (UTC)[reply]

I don't think so but I can't say for certain. I'm not as familiar with this species as I am with some of the others. --Kurt Shaped Box (talk) 14:39, 10 June 2008 (UTC)[reply]

gravitational redshift

The Pound-Rebka experiment showed that gamma rays lost energy/frequency as they fell through the building, due to gravitational redshift. Only by moving the emitter downward relative to the receiver could the gamma rays be given enough (doppler) frequency to be absorbed. This diagram and relativity-common-sense would seem to support that "time" runs slower for things (like photons) undergoing acceleration.

But the gravitational redshift article (and general relativity) says that light originating from a stronger gravitational field will have longer wavelength when received by an observer in a weaker gravitational field. Redshift for deceleration now! Which is it? The former makes more sense to me.. like a pendulum, the left-right motion of the wave in the horizontal direction stays the same, but the wavefront moves faster due to acceleration from gravity. So a stationary observer sees "more wave" go by for each cycle.. a redshift. So which is it for falling light? Redshift or blueshift? .froth. (talk) 05:27, 10 June 2008 (UTC)[reply]

Blueshift. If you move deeper in a gravity well, then you gain energy. Since photons can't actually move faster, the way this is manifest is by their blueshifting to higher energy state. Dragons flight (talk) 05:36, 10 June 2008 (UTC)[reply]

Fans and heating/cooling

Two questions:

If I put my hand in front of a fan, I can feel lots of air getting blown out. But if I put my hand behind the fan, I can barely feel any air getting sucked into the fan. So where does the air getting blown out the front of the fan come from? It feels like there's way more air coming out then getting sucked in.
It's summertime, and for the moment, I'm in a house without an air conditioner. At night, when the temperature drops, the second floor rooms stay way hotter than the first floor rooms and way hotter (by 5 to 10 degrees Fahrenheit) than the outside environment. Presumably, what is happening is that all the hot air from the first floor is rising up to the second floor and then getting stuck in the second floor rooms without being able to go out. I've tried opening all the windows on the second floor, but the temperature seems to still refuses to drop by much up there, probably because there is close to no wind these past few days. I was thinking that I could improve air circulation by sticking fans in the windows. My question is, if I did so, which way should I stick the fans? Would it be more effective in cooling the rooms to have the fans blowing cooler air from outside into the hot rooms, or to have the fans blowing the hot air inside the rooms out the window?

—Lowellian (reply) 07:09, 10 June 2008 (UTC)[reply]

Fan pushes air which is in front of its blades. It does not suck from behind. Window fan, or as I call it Exhaust fan may solve your problem. manya (talk) 07:33, 10 June 2008 (UTC)[reply]

I'm sorry, manya, but your explanation isn't correct. Fans generally take air from one side of the blade disk and push it out the other side of the blade disk. With regard to the original question, if the fan were mounted in a duct, so that all of the air was constrained to travel within the duct, I think you'd find that air flow would feel the same on either the inlet or outlet sides of the fan. But room fans aren't mounted within a duct so the airflow isn't so constrained. I think the cause of the effect is two-fold: air flows into the fan blades from a variety of directions and a rather large "subtended angle". Because of the large subtended angle, the inflowing air can move at a pretty low velocity and yet move into the blades a large volume of air. On the outlet side, though, the moving air stream is probably more focused, so the same volume of air needs to now move at a higher velocity. A second-order effect is that the outlet air stream probably tends to drag surrounding air along with it, decreasing the stream's velocity but further increasing its volume (in the same fashion as a jet pump moves more water). This would probably be a lot easier to explain if the Reference Desk were equipped with a wind tunnel so you could see, via the smoke streams, the various flows of air. ;-)

With regard to exhaust fans, see whole-house fan.

Atlant (talk) 12:06, 10 June 2008 (UTC)[reply]

Good answer! --Anonymous, 00:01 UTC, June 11, 2008.

The best way to clear out the air in a room is to have one window fan blowing air out, and another one across the room blowing it in. I speak from broken-air-conditioner-in-102-degree-weather experience. --Sean 12:56, 10 June 2008 (UTC)[reply]

I'm with Atlant with his explanation. To explain it slightly differently, the air being blown out of the fan is focused to travel in a specific direction by the shape of the blades, therefore the moving air takes up a given volume (lets call it x for fun). On the 'input' side of the fan, there is no such restriction on where the air comes from. As the blades push the air directly in front of them out of the way into the volume x above, there is a (momentary, instantaneous, imaginary, useful for this exercise) vacuum that is created because there is no air present. To keep the air pressure in the volume constant, the atmosphere rushes in 'uniformly' and 'from all directions'. Because its coming in from all directions, it occupies a greater volume and (as Atlant said) the flow rate is lower because theres a greater volume flowing.

To address your second concern, Sean is correct. Having all fans blowing outward would be the least useful solution because (assuming theres no other source of air) all of the air would have to travel through the rest of the (substantially warmer) house before it could reach the second floor, which would minimize cooling capacity. If all the fans face in, you'll get lots of cool air in but the warm air in the house will still be present increasing the amount of air that needs to be cooled. But having an equal number pushing in and pulling out will bring an influx of cool air (what the first method lacks) and also remove warm air (what the second method lacks). If done correctly, it will also reduce the amount of electricity needed compared to the other two. EagleFalconn (talk) 13:28, 10 June 2008 (UTC)[reply]

You don't even need the fans - just opening one window at the front of the house and one at the back (and the internal doors inbetween) will create a significant flow of air through the house. The fans will increase the effect, especially if there is no natural wind, but they aren't essential for the basic principle. --Tango (talk) 15:25, 10 June 2008 (UTC)[reply]

Here's an article I wrote on home cooling with fans: [1]. It seems to answer most of your questions listed under part 2. In your case, I recommend blowing cool air in on the lower floor and out on the second floor. Note that this will cool the lower floor more quickly than the upper floor, though, as the hot air on the lower floor must first move to the upper floor before being exhausted. You might want to sleep on the lower floor if it remains too hot upstairs. The other option is to have fans blowing in and out on both floors.

Note that the inside temp often increases after sunset because the exterior walls, which have been absorbing sunlight and changing it into heat, begin to radiate this heat inside the house. The delay between when the sunlight is absorbed and the heat reaches the inside has to do with the thickness of the walls and their thermal conductivity. Something like a 6 hour delay is typical for the average brick house. Thus, if the hottest point outside is at 3 PM, the hottest point inside may not occur until 9 PM. Hosing down the brick wall periodically may also help to reduce the heat which they contain. Be sure to close any windows, first, though. StuRat (talk) 20:52, 10 June 2008 (UTC)[reply]

I'll throw a couple more tidbits into this dicsussion, as I too lived in a house with no central AC for 25 years.

If you only have one fan, have it exhaust the hot air.
If there's any breeze at all, use it -- don't try to exhause hot air into the wind!
If you have a built-in fan in the bathroom (a "fart fan"), use it too -- it's closer to the ceiling than anything else.
Having a fan blowing on you is pseudo-cooling; you're increasing the evaporative effect but doing nothing to cool the rest of the room.

And despite all that, sometimes you just have to sleep on the floor in the basement :-). --Danh, 67.40.166.141 (talk) 23:49, 10 June 2008 (UTC)[reply]

I have to disagree on using a single fan for exhaust. That will result in a slight negative pressure in the home which may cause air to backup down chimneys, may suck in bugs and dust when you open exterior doors, etc. Also, a room in which the fan blows inward will quickly cool, and the air circulation will make it feel even cooler than it is, so that's a good place to sleep. StuRat (talk) 04:59, 11 June 2008 (UTC)[reply]

StuRat, the "single exhaust fan" is the exact working concept behind the whole-house fan. The idea, of course, is that you don't just exhaust from the house, you also open "inlet" windows , usually concentrating on the room(s) that you're currently occupying. This (and the damper that you've installed on your chimney) prevents pulling soot, bats, etc. down the chimney or radon from below the basement floor. And because the exhaust fan is usually located remotely from you, you don't hear it very much. I've lived in two houses now that had whole-house exhaust fans and found them to be very useful. Their principle disadvantage is that because you're circulating exterior air through the house, you're alos bringing in pollens and other exterior pollutants.

With regard to bathroom exhaust fans, before anyone implements that strategy, be sure you know where the exhaust from you bathroom fan goes! Some just recirculate through an activated carbon filter and those will be worse-than-useless in helping to cool you. And some that are meant to exhaust to the outside aren't properly installed. My curent house was an example of this. All our various bathroom fans exhausted into wall spaces and the previous owner's use of these fans resulted in nothing but the creation of rot. Mis-exhausted fans won't help keep you cool either.

Atlant (talk) 11:54, 11 June 2008 (UTC)[reply]

I suppose I'm biased here because we have a defective chimney with no cap or damper (which led to a friendly visit from our neighborhood squirrel doing his Santa impersonation), and the whole house smells of smoke when I have more fans blowing out than in. However, even in a home without a fireplace or with one tightly sealed, there are still exhaust vents from the water heater, furnace, and dryer (unless they are electric), so creating negative pressure in the home could cause those to back up. If they are properly functioning and enough windows are open they likely won't back up but will only work somewhat less efficiently. Another risk is that negative pressure can pull air out of the wall spaces, which might have mold spores in them, while a positive pressure would push the air in the wall spaces outside. However, as blowing air in (with windows open where you want to exhaust air) will result in just as much air exchange as blowing air out, why take the chance if you have the choice ? StuRat (talk) 14:59, 11 June 2008 (UTC)[reply]

One further point. I live in a house with an unfinished attic above the second floor. The "ceiling" of the attic is simply the underside of the roof structure, and the "floor" is the structure supporting the second-floor ceiling. The important thing is that the attic space is not thermally part of the house, but is part of the outdoors; the attic "floor", not the "ceiling", is covered with insulation. If your house is like this, it may be helpful to increase the ventilation between the attic and the outdoors by adding vents; since the attic is heated during the day by sunlight on the roof, ventilation reduces heat buildup. It may also be desirable to increase the amount of insulation, both to reduce warming of the second floor by the attic in summer and to reduce heat loss through the attic in winter. --Anonymous, 00:01 UTC, June 11, 2008.

Thanks for all the advice, everybody! Keep cool! ;) —Lowellian (reply) 05:27, 14 June 2008 (UTC)[reply]

Physics -- Force, Mass and Acceleration

I've been asked this question by somebody who found it in a book (which didn't bother to provide the answer): We know that F=ma. If we consider a constant acceleration, and then plot a graph of the force required to give/achieve that acceleration against different masses taken, the graph assumes the form of a curve. Why is it so, knowing that the relation between force and mass is linear? 117.194.226.154 (talk) 08:11, 10 June 2008 (UTC)[reply]

I'd be interested in seeing a sample of that graph, or at least the specific axes used (and anything else non-obvious, like not being simple/unconstrained linear motion, etc). As described, F vs m for some constant a should indeed be linear as you say. DMacks (talk) 08:17, 10 June 2008 (UTC)[reply]

I think the only reason it would curve is if a is being factored into the graph, and is only held constant at intervals, but not during the entire length of the graph, or else if a was always the same value it would be linear as stated.--十八 10:06, 10 June 2008 (UTC)[reply]

Yeah, it should be a straight line, unless we're missing a key detail. Of course, a line is a type of curve by the strict mathematical definition, so perhaps that's what it means... a rather strange way to say it, though. --Tango (talk) 12:48, 10 June 2008 (UTC)[reply]

Yeah, assuming a vacuum with no other forces acting on the mass, it should definitely be a straight line. Certainly in many realistic situations you would get a curve, though, due to things like air resistance or friction on the surface it's travelling on - is that perhaps what the book was referring to? ~ mazca ^talk 12:53, 10 June 2008 (UTC)[reply]

I suppose it could have a slight curve to it, because the gravity of the mass of the object to be accelerated is also attracting the mass of the observer, thus reducing the acceleration of the object away from the observer (or increasing the acceleration toward the observer). However, this effect would be beyond what could be measured, unless you were dealing with a rather massive object. StuRat (talk) 20:21, 10 June 2008 (UTC)[reply]

The question wasn't about gravity, it was about an arbitrary force. --Tango (talk) 22:42, 10 June 2008 (UTC)[reply]

The point is that if you have any two objects with mass (one being the observer and the planet, ship, etc., where they are located) there will be some gravitational attraction, which will affect acceleration of one object relative to the other, and therefore the force you must apply to achieve any desired acceleration. This has such a minor effect for objects of any reasonable mass that it can safely be ignored, but the effect would become measurable for massive objects. StuRat (talk) 04:51, 11 June 2008 (UTC)[reply]

I'm sorry, but I don't have any sample of that graph. The book didn't provide any. It only said that force was plotted on the y-axis, and mass on the x-axis. But I've been assuming that the graph was somewhat like a rectangular hyperbola. 117.194.225.216 (talk) 06:43, 11 June 2008 (UTC)[reply]

Do you have any details of the book (Title, Author, ISBN number) so we can try and find it online? SpinningSpark 06:58, 11 June 2008 (UTC)[reply]

Perhaps it has to do with the fact that as the mass approaches infinity (speed approaches lightspeed), the force required to achieve a certain amount of acceleration increases non-linearly? F=ma fails to hold at relativistic levels. Imagine Reason (talk) 14:56, 15 June 2008 (UTC)[reply]

Gyroscope

Why angular momentum is in direction of rotating axis?Shouldn't it be in the direction of spin? —Preceding unsigned comment added by 220.240.81.247 (talk) 12:40, 10 June 2008 (UTC)[reply]

The direction of spin is different on different parts of the spinning body, and at different times. Consider the hour hand on a clock, for example. At 12, the hand is moving to the right, at 3 it's moving down, at 6 it's going to the ~~right~~ left at 9 it's going up. The direction of the axis is the only direction which is constant (that's basically what "axis" means), so it's the only one you can usefully use in the definition of angular momentum. --Tango (talk) 12:51, 10 June 2008 (UTC)[reply]

At 6 it's going to the left. Am I allowed to just change your comment to fix minor mistakes like that? — DanielLC 14:22, 10 June 2008 (UTC)[reply]

Thanks! I've fixed it. I wouldn't mind you just correcting it, but others might - it's easiest just to reply like you did. --Tango (talk) 15:21, 10 June 2008 (UTC)[reply]

Neptune

A diamond on Earth retains a certain shape and hardness(?). What would happen to a diamond if it was placed on the planet Neptune? Will it become harder or change in any way? --Vincebosma (talk) 15:45, 10 June 2008 (UTC)[reply]

Also, what would happen if a human spaceship attempted to land on Neptune? --Vincebosma (talk) 15:45, 10 June 2008 (UTC)[reply]

This sounds like it might be a homework question, so I won't give you a complete answer. I think the first thing you need to consider is what you actually mean by "placed on" and "land on" - Neptune is a gas giant, there is no land, at least not without going deep down into the thick atmosphere. The things you'll need to consider when determining what will happen to things on Neptune are pressure and gravity. Our article on Neptune will give you some data that should help with that. --Tango (talk) 15:52, 10 June 2008 (UTC)[reply]

I guess I'm flattered you thought this was a homework question, but I am a 35 year old man with no homework. Just a curious question. So considering Neptune has no land, the question about diamonds and human spaceships won't matter. I was trying to determine what would happen to things like diamonds and human spaceships on planets (with land) that are at least 20x larger than Earth pressure-wise and gravitational-wise. --Vincebosma (talk) 15:57, 10 June 2008 (UTC)[reply]

Planets that large are almost certain to be gas giants. They will have a solid core, but it's a long way down. There will be very high temperatures and pressures, which diamonds can probably survive intact, but spacecraft wouldn't. You might find Galileo (spacecraft) interesting - it sent a probe into the atmosphere of Jupiter, which was destroyed by the harsh conditions (after sending back lots of useful data) - the article gives some details. It is possible to have spacecraft in the upper atmosphere, though, see Floating city (science fiction) for (a little) more information. --Tango (talk) 16:32, 10 June 2008 (UTC)[reply]

What you need is a phase diagram for carbon. We don't seem to have one on Wikipedia, but Google should find you several. If you know the local temperature and pressure, you can determine whether your diamond will be stable. I note that diamond is a pretty stable allotrope of carbon at high pressures and moderately high temperatures (thousands of degrees). There has been speculation in the past that the core of Jupiter may be (mostly) a large diamond, formed by the heat and high pressure. There's also suggestion that Jupiter will have layers of other rather exotic materials as well, including metallic hydrogen. TenOfAllTrades(talk) 17:19, 10 June 2008 (UTC)[reply]

According to our Neptune article, the core is several thousands of degrees hot, so a diamond could burn (if oxygen was present) or melt (but the high pressure might prevent this). StuRat (talk) 20:15, 10 June 2008 (UTC)[reply]

Hi. Well, probably due to its low density compared to earth, Neptune only has about ~2% more gravity than earth at the cloudtops (I don't remember the exact figure). Also, it has been theorised that the pressure at the cores of Uranus and Neptune can put methane under enough heat and pressure so that it forms diamonds (the CH₄ is stripped of its hydrogen, which forms metalic liquid hydrogen, then the leftover carbon is compressed into diamonds). It might be better to land on a moon of Neptune with reasonable gravity such as Triton, but it's -225C there. Depending on which layer of Neptune you are in, you may have to face temperatures anywhere from -240C to +15000C, gravity anywhere from 0.5x Earth to 220x Earth, and gasses from hydrogen to methane to ammonia. There might also be electrical storms in the planet. Hope this helps. Thanks. ~A H 1^(TCU) 21:11, 10 June 2008 (UTC)[reply]

That 220g figure sounds highly suspect to me, do you have a source for that ? StuRat (talk) 04:43, 11 June 2008 (UTC)[reply]

Hi. Actually, no, I just calculated based on OR and that gravity goes up up the square of distance. Thanks. ~A H 1^(TCU) 00:30, 14 June 2008 (UTC)[reply]

In that case, I'd love to see your assumptions and calculations, because I suspect there's a big mistake in there somewhere. I'm guessing you're using a point-mass model, which is highly inaccurate within a planet's atmosphere. With gas giants, at the top of the atmosphere the density is very low, so there is a great distance to any substantial mass, so the gravity is low. At the bottom of the clouds/top of the ocean, the density is much higher, but there is a great deal of mass above you pulling upwards, which cancels out much of the gravity pulling down. At the bottom of the ocean/top of the solid core, the density is even higher but the mass above is greater yet, so there still is a major effect of the pull upward working against the pull downward. There's also a great deal of mass on the sides of your location, which, of course, also cancel each other out.

Gas giants also spin at a rapid clip, reducing the gravity substantially, due to apparent centrifugal forces. Note that our Neptune article states that the "equatorial surface gravity" is only 1.14g. This NASA fact sheet confirms that info: [2]. Note that Saturn and Uranus even have less gravity than Earth. StuRat (talk) 05:05, 14 June 2008 (UTC)[reply]

Physics

Are there any scalar quantities which are formed by a product of 2 vector quantities? Can anybody give some examples of such. —Preceding unsigned comment added by 124.43.211.252 (talk) 16:19, 10 June 2008 (UTC)[reply]

Yes. See Mechanical work#Force and displacement for one example. --Tango (talk) 16:34, 10 June 2008 (UTC)[reply]

(edit conflict) Yes, there are several. It's unlikely that anyone here will answer your homework question for you, however. I'll give you a hint—force is a vector quantity. I suggest you examine the basic physics formulae that you've been taught and look for scalar and vector terms. TenOfAllTrades(talk) 16:38, 10 June 2008 (UTC)[reply]

Have you read dot product? Graeme Bartlett (talk) 06:16, 11 June 2008 (UTC)[reply]

Do your own homework, kid! 117.194.226.115 (talk) 18:11, 11 June 2008 (UTC)[reply]

Intelligence enhancing drugs

Have there been any drugs that show a positive correlation between intelligence and their use? ScienceApe (talk) 16:41, 10 June 2008 (UTC)[reply]

Have you looked at Nootropic? Friday (talk) 16:42, 10 June 2008 (UTC)[reply]

Do any of these replies help?--droptone (talk) 11:59, 11 June 2008 (UTC)[reply]

Wired Magazine actually covered this topic briefly in their May issue. Check it out here. They suggest adderal, Aniracetam, aricept, methamphetamine, modafinil nicotine, rolipram, and vasopressin may potentially "boost cognitive output," although many of these drugs have negative side effects and may also be illegal in your area. --Shaggorama (talk) 07:54, 15 June 2008 (UTC)[reply]

Looking-glass protein

Assume we found an alternate form of life identical to something we know is edible(say, an apple), except that the structure of its proteins and other molecules was opposite in chirality to that of life as we know it. If we ate such "looking-glass" food, would it be poisonous, or just pass through the body inertly? Would it even be possible for mirror-imaged proteins and molecules to form complex life similar to ourselves and what we eat? —Preceding unsigned comment added by 207.233.86.164 (talk) 17:30, 10 June 2008 (UTC)[reply]

There is no real bias within chemistry and chemical reactions for specific chiralities. That is to say that enantiomers have the same chemical properties. If we were to come across an apple that had the opposite chirality (for example, all the sugars in it were the enantiomer of dextrose) its effects would be difficult to say arbitrarily. There are certain molecules that the body would simply allow to pass right through as its different chirality would make it neigh impossible for any proteins to sucessfully catalyze the digestion. On the other hand, there are also molecules for which the change in chirality would make them horribly horribly poisonous. See thalidomide. There is no reason for biology to be biased towards R molecules, and to my knowledge research is being done to determine why that bias arose. If I recall correctly, the current theory has something to do with the strong force, which seems a little off kilter to me but I'm not really qualified to judge. (EagleFalconn) 17:46, 10 June 2008 (UTC)[reply]

The main theory I know of is that the chirality of organic molecules is purely by chance - it just happens that the first life forms to be successful were of that chirality and every life form since has therefore also been. It's an interesting issue, and has many consequences for the fundamental ideas of evolution. To the best of my knowledge, there is no reason why life couldn't form with everything the exact mirror image of what we observe. Interaction between life forms of each type (for example, us eating a mirror-apple) would be unpredictable, as you say, but interactions between molecules of one type should be indistinguishable from interactions between molecules of the other type. --Tango (talk) 17:53, 10 June 2008 (UTC)[reply]

Right, my point in the above comment was to say that there is a theory that states that R may have been favorable due to a strong force interaction, which is to say that it wasn't entirely chance but there was something driving it (perhaps competitive reaction kinetics). Interestingly, it isn't necessarily true that just because an interaction works R,R that it will work S,S. As I say above, enantiomers have the same chemical properties, however diastereomers do NOT. So just because we know what an R sugar coupling with an R protein will do, we don't know if it'll do the same thing with the S sugar and the S protein. EagleFalconn (talk) 19:38, 10 June 2008 (UTC)[reply]

That sounds off...unless there's a third chiral thing involved (external entity or noticeably affected by low-level like asymmetric Force), enantiomers are completely structurally identical and perfect 3D mirror images, so why wouldn't one think R-substrate + R-enzyme would be identical and bind identically (except perfectly enantiomerically) to S-substrate + S-enzyme? If they don't, then enantiomers aren't really "perfect mirror images". DMacks (talk) 19:48, 10 June 2008 (UTC)[reply]

I agree. Except for the possibility of very small effects with the strong or weak nuclear forces, the laws of physics are invariant with respect to taking mirror images, so the S versions of things should interact with each other in the same way the R versions do. --Tango (talk) 20:08, 10 June 2008 (UTC)[reply]

Well, but we know that diastereomers have different chemical properties (R,R != S,R != R,S != S,S) so while individually the substrate and the protein would be chemically identical to their enantiomers, wouldn't (A) the diastereomeric compound they make have different chemical and physical properties depending on whether it is R,R or S,S? And therefore, (B) Wouldn't the metabolization therefore have different requirements that the remainder of our body, having only been mirror imaged as opposed to also having metabolic processes changed (temperature, activation energy provided, catalyst (since R,R,R would, again, have different properties than S,S,S etc), would be unequipped to meet? We might say that its a small change, but biology is very sensitive to small changes because of the complexity of the systems. I'm guess I'm not really following your disagreement, do you disagree with point A or B? Also, I agree that the strong force thing is weird, I'm just repeating something I found in my organic textbook (Loudon 4th edition) that I used in my optics class. EagleFalconn (talk) 13:51, 11 June 2008 (UTC)[reply]

As long as you take the mirror image of absolutely everything, it shouldn't make any difference (except the results will all be mirrored, of course). When we say they have different chemical properties we mean in relation to everything else staying the same, if everything else is mirrored with them, the properties should be identical. Symmetry under parity inversions is a pretty fundamental law of physics. Incidentally, I think it's the weak force, not the strong force, which violates it (at least, that's what it says in that article), and the weak force governs things like radioactive decay, chemistry (and therefore biochemistry) is governed by the electromagnetic force, which is symmetric. --Tango (talk) 14:08, 11 June 2008 (UTC)[reply]

I looked up a citation, Loudon 4th Edition page 277 and 278. First part addresses enantiomers forming diastereomers (the substrate binding to the enzyme/protein):

Enantiomers have different reactivities with chiral reagents because diastereomers have different free energies. Just as diastereomers differ in their other physical properies they also differ in free energies. In this case, the transition state for the reaction of one enantiomer is the diastereomer of the transition state for the reaction of the other. Because diastereomeric transition states have different energies, the reaction of one enantiomer occurs more rapidly than the reaction of the other (Note that we may not be able to predict which enantiomer will be more reactive)
— Marc Loudon, Organic Chemistry 4th Edition, page 277

Emphasis not mine, by the way. I believe that the above guarantees that R,R would have a different reaction rate than S,S. In addition:

Disatereomers in general have different reactivities toward any reagent, whether the reagent is chiral or achiral. The reason is that, in the reactions of diastereomers, both the starting materials and the transition states are diasteromeric, and disastereomers have different free energies. Consequently, their standard free energies of activation, and hence their reaction rates, must in principle differ...We may not be able to predict which alkene is more reactive or by how much, but we can be sure that the two alkenes will not be equally reactive.
— Marc Loudon, Organic Chemistry, 4th edition, Page 288

This part indicates that the substrate, once bound to the protein, will also have different energetics. Does this sound reasonable? EagleFalconn (talk) 14:42, 11 June 2008 (UTC)[reply]

(outdent). Those quotes are exactly what we're saying and is what you're misinterpretting: it's talking about each of two enantiomers of one compound reacting with the same (one constant) enantiomer of another. See where it says diastereomeric transistion states are different? That means it's an S+S vs S+R type of comparison, not S+S vs R+R (which would be enantiomeric). So it's talking about how a "normal" enzyme reacts with its natural-sugar substrate vs with the enantiomer of that sugar, not how the enantiomer of the enzyme reacts with the enantiomer of the sugar. Or how the (enantiomeric) product of the (enantiomeric enzyme + enantiomeric sugar) would react with the rest of biology in a "normal" (non-enantiomeric-world) system. Consider hands and gloves: left hand fits into left glove identically to how right hand fits into right glove. But left vs right hand fit differently into left glove. And (left hand in left glove) shakes hands with someone else's left hand identically to how a (right hand in right glove) shakes hands with someone else's right hand, but (left hand in left glove) shakes differently with someone else's left hand vs right hand. DMacks (talk) 16:06, 11 June 2008 (UTC)[reply]

Point conceeded, thanks. The point that I was missing was that S+S is the enantiomer of R+R. EagleFalconn (talk) 16:23, 11 June 2008 (UTC)[reply]

Regarding specifically proteins and amino acids, and the effect of eating an apples with opposite chirality proteins: I'm pretty sure that the D-isomers of amino acids have greatly reduced bioavailability. This comes up because some chemical treatments that foodstuff might be subjected to, such as strong alkali, tend to racemize amino acids. ike9898 (talk) 19:52, 10 June 2008 (UTC)[reply]

Increased Gravitational Pull on Earth

What exactly will happen if the gravitational pull on Earth increased ever so slightly? Such as, will I weigh heavier, will certain animal or plant species suffer and die off, etc. --Vincebosma (talk) 19:43, 10 June 2008 (UTC)[reply]

That depends on what you mean by "ever so slightly". The Earth's gravity already varies by very small amounts depending on where you are (by about 0.5% or so), and that clearly doesn't have any major effects. It needs to be taken into account for some satellites, I believe, so changing the strength of gravity by less than a percent would probably mess up GPS, but that's about it. Everything would weigh more, but not enough to cause any significant effects. If you increase gravity enough, though, things would start to be unable to support their own weight and would collapse. How much you would need to increase it by depends on what you want to collapse, I don't have any example figures for you, though. I expect it would increase air pressure, although it may in fact decrease it above a certain altitude (the scale height would decrease). I'm not sure what effects that might have, but it could well affect the climate. It would cause the moon to move closer, shortening the length of a lunar month and increasing tidal forces. There are probably all kinds of other effects I haven't thought of, as well. How significant each of them will be depends on how much you increase gravity. --Tango (talk) 20:05, 10 June 2008 (UTC)[reply]

How about as a reference, instead of weighing 200 lbs, due to the increase, I weigh 250 lbs.....--Vincebosma (talk) 20:09, 10 June 2008 (UTC)[reply]

Among other things, the moon's orbit will destabilize causing it to impact Earth. Everything else is pretty minor at that point. (Assumes 25% more gravity w/ no other physical changes) — Lomn 20:31, 10 June 2008 (UTC)[reply]

A 25% increase in gravity would cause the moon to impact the Earth? I'll have to find the back of an envelope, but that sounds unlikely... Do you have the numbers for that, or are you just guessing? --Tango (talk) 21:51, 10 June 2008 (UTC)[reply]

According to the back of my envelope, a 25% increase in Earth's gravity would cause the Moon's closest approach to each to be about 2/3 of what it is now, that's nowhere near enough to hit the atmosphere and impact Earth. (Note, there are very rough numbers - I'll try a more accurate calculation in a sec.) --Tango (talk) 22:02, 10 June 2008 (UTC)[reply]

(The more accurate calculation is proving more complicated that it's worth, the 2/3 figure should be pretty close, and it's far far outside the atmosphere, so there's plenty of margin for error. --Tango (talk) 22:11, 10 June 2008 (UTC))[reply]

You're right, my back of the envelope was way off. — Lomn 23:27, 10 June 2008 (UTC)[reply]

But would that closer approach allow the Moon to much more efficiently strip off the atmosphere? That could have a somewhat negative impact. (takes a deep breath) Franamax (talk) 16:44, 11 June 2008 (UTC)[reply]

Clarify that - the moon is not in the atmosphere per se, but it is now sweeping out a zone with a higher density of gas molecules (I mailed my envelope with the water bill, no idea how much higher). Wouldn't moving the swept zone closer to the breathable part of the atmosphere increase the outward diffusion? Or not? Franamax (talk) 16:53, 11 June 2008 (UTC)[reply]

According to exosphere, the atmosphere ends at about 10,000km above the surface of the Earth, although I'm not sure how that's defined, seems pretty arbitrary to me. That's 16,000km above the centre of the Earth. At 2/3 it's current distance, the Moon would be about 270,000km away. That's a whole order of magnitude bigger, I think we can safely ignore all atmospheric effects. --Tango (talk) 17:42, 11 June 2008 (UTC)[reply]

You might have quite a number of buildings and bridges in the world collapse. Although many structures were built with tolerances that could handle a 25% increase in constant load, many others weren't. Those structures that are already near their maximum safe load would collapse. The nearer moon and increased gravitation would affect the tides, which could affect certain parts of the ecosystem. All creatures would have to develop stronger muscles to support their bodies, and the hearts would have to work overtime, leading to shorter lifespans for most creatures above the size of a large insect. The jumps made by skateboarders, skiers, etc. wouldn't look as impressive as they do now. Actually, just about anything you stop to consider would be affected in some way. 152.16.16.75 (talk) 10:22, 16 June 2008 (UTC)[reply]

Jumping from big heights

I have recently seen the Bourne Ultimatum (great film by the way) and was a bit confused by the ending. Bourne supposedly jumps from a ten, I think, storey building into a river and survives. This doesn't strike me as terribly realistic and I'm sure I wouldn't be quite as successful if I tried it. Is this Hollywood bending the laws of reality for its own needs again or is there some military training that can prepare you for jumps like that? Is it actually be possible? Thanks. 92.0.243.212 (talk) 20:16, 10 June 2008 (UTC)[reply]

Outside Magazine says "The highest Olympic-level dive distance is ten meters (33 feet), with good reason. Beware of injury at around 15 to 20 feet and know what you're doing above 30 feet. Anything over 50 is pro territory." The Discovery Channel explains "Perhaps the biggest misconception about cliff diving is that the diver is cushioned by the water below—this could not be further from the truth. When leaping from a cliff that is over 70 feet high, a diver hits the water at over 46 mph, regardless of his or her body weight." (70 feet is 21 metres) I do not know the answer to the training part of the question. WikiJedits (talk) 20:51, 10 June 2008 (UTC)[reply]

At the very least, you would expect him to break his legs on impact (did he at least land feet first? Diving head first from that height would almost certainly kill you!). Other than landing feet first, so your legs take the impact, not your head, I can't see anything you could be trained to do that would help. There is an urban legend about throwing something ahead of you to break the surface of the water so it won't be so hard when you hit it, but as far as I know, that's complete nonsense. --Tango (talk) 21:50, 10 June 2008 (UTC)[reply]

Kinda funny you should say that as, if you haven't seen all the Bourne films, in the first one he falls what looks like at least 10m from the top of a stairwell but survives because he was good enough to push some else over first and land on them. But again, could just be Hollywood's attempt at the wow-factor. 92.0.243.212 (talk) 20:29, 11 June 2008 (UTC)[reply]

You could be trained to execute a parachutist's landing where you hit with feet, then thigh, hip, shoulder, to spread the energy out. Also, according to one of those "Worst-Case Scenario" books, you should clench your buttocks so that a jet of water doesn't tear a hole in your colon. --Sean 22:50, 10 June 2008 (UTC)[reply]

The Golden Gate Bridge at 750 feet (220 m) is a popular spot for suicidal jumpers. Despite the extreme height, relatively cold water (50-60 F / 10-15 C), and frequent strong currents, about 2% of jumpers nonetheless survive. So it is certainly possible. A person like Bourne in peak physical health who presumably knows how to enter the water in a controlled way might well have a decent shot of executing a 100 ft dive, though it certainly wouldn't be easy or a sure thing that he would survive. So I'd say it is certainly possible, though I wouldn't recommend it. Dragons flight (talk) 22:07, 10 June 2008 (UTC)[reply]

See La Quebrada Cliff Divers, which daily dive off 45m cliffs - this is more than most 10 storey buildings. I assume that they survive ;-). I have dived 10m. If you enter the water optimally (for me that is vertical, feet first, as I'm a ~~craven coward~~ rational person), there is very little impact stress. If you are more than a little off, you get quite a kick. I don't want to experience what happens if you enter the water uncontrolled... --Stephan Schulz (talk) 22:24, 10 June 2008 (UTC)[reply]

I'm not going to give this a try but by 'optimally' what do you mean? A pencil dive, feet first? Would your body be tense, to keep you in that pencil shape, or relaxed, so that you don't break your bones on impact? 92.0.243.212 (talk) 20:33, 11 June 2008 (UTC)[reply]

Interesting. Seems you can do it, if you know what you're doing. Shows what I know! --Tango (talk) 22:40, 10 June 2008 (UTC)[reply]

This is a bit off topic, but I seem to recall that the water in at least some diving events is aerated. Is this primarily to give the diver a visual reference, or is it intended to provide a degree of cushion on entry? -- Tcncv (talk) 01:14, 11 June 2008 (UTC)[reply]

I don't know if the aeration actually exists, but if it did it would lower the surface tension of the water and lessen the impact force. However, the same amount of work would still need to be done to stop you, and so you'd need a deeper pool to do it.EagleFalconn (talk) 13:55, 11 June 2008 (UTC)[reply]

I know they have a small spray hitting the surface to make it easier to see where it is (so you know when to stop somersaulting, or whatever). I don't think it has any affect on the landing, though. I'm not sure how significant surface tension is to the impact force, I think it's just the fact that liquids are incompressible that makes them seem so solid (the water can't compress like a crash mat, it has to move out of the way, and that takes time). --Tango (talk) 14:00, 11 June 2008 (UTC)[reply]

I'd suspect that the small spray is just to be able to tell where the surface is. To my knowledge and experience, surface tension and viscosity are coupled effects which are the impact force, as they directly relate to the incompressibility of the liquid. EagleFalconn (talk) 15:57, 12 June 2008 (UTC)[reply]

Just to correct a misconception: the surface tension is negligible. The relevant dimensionless number is the Weber number which in this case works out to be about 10 million. Given that surface tension effects are only important if We is less than or approximately equal to one, we may safely ignore surface tension. Robinh (talk) 13:17, 13 June 2008 (UTC)[reply]

(edit conflict):

Surface tension is one of the variables in the Weber equation, so it is clearly not negligible
I've never seen this before, but it looks like it's about fluids in motion so it probably isn't that useful in describing swimming pools.

Feel free to correct me if i misunderstood something here. --Shaggorama (talk) 07:38, 15 June 2008 (UTC)[reply]

Robinh is correct. The Weber number calculation says that forces from surface tension are a factor of 10 million smaller than forces from inertia. That's negligible. The velocity in question is the relative velocity of the body (i.e. the diver) normal to the fluid interface (i.e. hitting the water). JohnAspinall (talk) 20:41, 16 June 2008 (UTC)[reply]

Cat spray / Territorial marking

This question relates to a "cat pee" question posted by another user above. I'm convinced that the stuff that cats "spray" when marking their territory isn't urine. From having to clean it up, I know that it is oily and extremely musky. I assumed it was some sort of gland secrection, but our articles on cat and territorial marking refer to this stuff as urine. Can anyone clarify whether or not it is urine? ike9898 (talk) 20:18, 10 June 2008 (UTC)[reply]

I believe it is urine, but does include certain gland secretions which give it the distinctive smell (well, distinctive to cats - just smelly to us!) --Tango (talk) 21:45, 10 June 2008 (UTC)[reply]

It is urine plus anal gland secretions. According to this paper the secretions contain volatile fatty acids (which might constitute the greasy feel), putrescine, cadaverine, and ammonia(which contributes to the unholy smell). The secretion-urine mix also contain lipids and dead cells.--Lenticel ^(talk) 22:48, 10 June 2008 (UTC)[reply]

. . .another cup of tea anybody?! Richard Avery (talk) 06:47, 11 June 2008 (UTC)[reply]

ball lightning?

Hi. This morning there was a big thunderstorm where I live (southern Ontario). A friend told me he heard ball lightning. He reported the following:

Two seconds of hissing, then a loud thunderclap
It sounded like a Roman Candle (firework)
The lights went dim noticeably for about 10 minutes, occasionally flickering, then suddenly went back to full power
He had read a book containing information about ball lightning before the thunderstorm
Location: less than 500 m from where I was at the time, was indoors

The thunderstorm:

Can be classified as severe, but no warning was issued
Lightning every several seconds
Rainfall rate showing up as dark-red on The Weather Network radar
Was located near a cold front
Occured before 8 am EDT, did not weaken overnight
Was located near central-eastern USA the night before, preceded by a few severe and non-severe thunderstorms in S. Ontario the afternoon and night before
Severe thunderstorms lasted roughly 15 mins, entire storm roughly 25 mins, rain roughly 30 mins

I noticed:

Frequent and bright lightning, sometimes within 1 km
Thunder loud enough to wake me up
Strong winds and gusts, ~80 km/h
No noticible disruptions in electricity
Widespread puddling of rain
Enough rain to cause a mess indoors if the window is open
Wind carrying still-falling rain nearing the ground producing waves

So, is it plausible that ball lightning really occured, and are these conditions condusive to ball lightning formation, or are there other plausible explainations? Thanks. ~A H 1^(TCU) 20:54, 10 June 2008 (UTC)[reply]

God how I miss living in Southern Ontario, in the countryside, and watching those biggg storms come through. Torrential rain, blasting wind, hail - we only get polie thunder where I am now, you're lucky! Franamax (talk) 16:59, 11 June 2008 (UTC) [reply]

Without having seen the actual ball lightning, I don't think there's a lot that can be said. We don't know enough about ball lightning to know what conditions are conducive to it; in fact, we barely know that it even exists. Sure, it's plausible. And I'm sure there are other plausible explanations. The only weird part of what your friend describes is the hissing sound. I'm thinking maybe it was a transformer exploding. I don't specifically remember hissing sounds before transformer explosions I've heard, but it sort of rings a bell. Plus that would explain the localized disruption in electrical service. --Allen (talk) 21:21, 10 June 2008 (UTC)[reply]

If he didn't see ball lightning, why assume it was ball lightning? Hissing could be electrical arcing followed by the bang of a high voltage fuse fuse opening to clear the fault. Ten minutes later a utility troubleman could have replaced the fuse or closed a normally open switch to restore power. Scientists are somewhat skeptical about ball lightning. I would expect it is some sort of plasma of heated and electrically charged gas. Edison (talk) 00:00, 11 June 2008 (UTC)[reply]

Heard but didn't see is somewhat unreliable. I concur that the hearing was likely from the hydro system. In a similar storm in a similar location, I heard a serious ka-boom accompanied by a very clear sizzling sound (which you could also describe as hissing), out towards the road. The next day I had to call in for $400 worth of repairs to the control unit of my Miele washing machine. Draw your own conclusions. Franamax (talk) 17:07, 11 June 2008 (UTC)[reply]

I think the answers above are on the right track; a more mundane electrical problem is always going to be more likely than a rare one - that's just stating the obvious. That being said, I have heard some claims that ball lightning may make a hissing sound. I also enjoyed the lightshow; the wife and I stayed up until 1 AM Tuesday morning to watch the lightning and we noted that the storm was odd in a couple of ways - extreme variations in rainfall (brief bursts of intense downpours, then long intervals with no rain), a great deal of lightning - only a small portion of which was accompanied by significant thunder, even when the flashes were relatively close, and a kind of pseudo-eye where the updraft of the cell had presumably created a large indentation. I wouldn't be at all surprised to learn that weird electrical phenomena had been seen during the storm; I was quite surprised there weren't any tornadoes (at least confirmed, so far as I know). Matt Deres (talk) 13:58, 12 June 2008 (UTC)[reply]

Hi. However, he says he has experienced transformer explosions before, and the lights went fully out but that was in a different country so explosions here might be different. Thanks. ~A H 1^(TCU) 21:08, 16 June 2008 (UTC)[reply]

About mirrors, and short sightedness

So I'm short sighted. Let's take this scenario: I am looking into a mirror which is six feet away. There is an object behind me which is 60 feet away. Ordinarily, I'd not be able to focus on this object very well, but I'm seeing this object behind me in the mirror. So there are two questions:

Will I be able to focus on the object? Am I focusing six feet away, or seventy-two feet (distance to mirror + distance from mirror to object) away?
Why?

Apply this scenario to an SLR camera and you'll see why I'm asking. Thanks guys. :D Lewis Collard! (lol, internet) 21:25, 10 June 2008 (UTC)[reply]

No, I don't think you would. You're trying to focus seventy two feet away, because that's how far the light has to travel. You can focus on the mirror itself, if you want; then you'll see clearly the dust and lint on it, but not the distant objects it reflects. --Allen (talk) 21:31, 10 June 2008 (UTC)[reply]

Whoah. Lewis Collard! (lol, internet) 21:36, 10 June 2008 (UTC)[reply]

I agree, you need to focus 72 feet away. I'm not sure what an SLR camera has to do with it - a camera contains a lens which focuses the light, rather than a plane mirror which just reflects it. --Tango (talk) 21:42, 10 June 2008 (UTC)[reply]

And what if I took the lens off? (I'd do this right now, but it's dark here...) Lewis Collard! (lol, internet) 21:49, 10 June 2008 (UTC)[reply]

Well, actually there's more than one lens, so it would depend on which one you removed. Single-lens reflex camera has a nice diagram showing them all. --Tango (talk) 22:26, 10 June 2008 (UTC)[reply]

Let me try a slightly more helpful answer: If you remove all the lenses (which is probably what you mean), the light would not be focused and you would get just a small amount of random light hitting the film/sensor and you wouldn't get a proper image forming. --Tango (talk) 22:37, 10 June 2008 (UTC)[reply]

As someone who owns an SLR, I tried exactly that. The result when I looked through the viewfinder: a uniform light-colored field. The result of taking a picture: a uniform 15% grey image. --Carnildo (talk) 23:49, 10 June 2008 (UTC)[reply]

Sounds about right. What were you pointing it at, and with how much light? --Tango (talk) 00:11, 11 June 2008 (UTC)[reply]

My living room, lit by indirect sunlight. Not much color or brightness variation. --Carnildo (talk) 21:39, 11 June 2008 (UTC)[reply]

In an SLR camera, there's a translucent "focusing screen" between your eye and the mirror. This screen is similar to a piece of frosted glass. The lens forms an image on the focusing screen, which you can see. But since the focusing screen is translucent, not transparent, you can't just look through the viewfinder and see through the camera without a lens to form an image—just as you can't look through the frosted glass on your boss's office door. (As a side note, when a lens is mounted and you see an image in the viewfinder, your eye is focusing on the image that's formed on the focusing screen. But that's only a couple of centimeters from your eye, which is closer than you can usually focus. This is possible because the viewfinder has a little lens, similar to reading glasses, that make the focusing screen "look like" it's far enough away to focus on, typically about 1 meter. Some cameras have an adjustment to this apparent distance, to accommodate different people's vision. Look up "diopter adjustment" in your manual.) -- Coneslayer (talk) 18:12, 11 June 2008 (UTC)[reply]

Thanks, guys, my question has been answered. Lewis Collard! (lol, internet) 22:48, 13 June 2008 (UTC)[reply]

Photosystems and Primary electron acceptors

Hello, in high school biology, my master teacher taught me that in photosynthesis, light photons hit the photosystems I and II and causes them to pass their electrons to the primary proton acceptor. The primary proton acceptor then passes them to plastiquinon to go to the cytochrome complex. My question is, where is the primary proton acceptor in relation to the PS? http://en.wikipedia.org/wiki/Image:Thylakoid_membrane.png according to this diagram, is the primary acceptor INSIDE/PART OF the PS? Applefungus (talk) 22:06, 10 June 2008 (UTC)[reply]

Toenails

Why do we still have toenails? Are they just left over from our evoloutinary ancestors? But in that case do chimpanzees need to toenails? (im not even sure if they do!) Or do they actually serve some purpose? Thankyou x —Preceding unsigned comment added by 217.44.210.227 (talk) 22:22, 10 June 2008 (UTC)[reply]

Why do we still have an appendix? ;) Just because they are no longer functional does not mean they will automatically be lost. That's not quite how evolution works. Regards, CycloneNimrod ^talk?_contribs? 22:25, 10 June 2008 (UTC)[reply]

People can actually die from ingrown toenails, which cause infection (my grandpa died that way, with diabetes, age, and nursing home neglect contibuting to it getting out of control). So, there may be some evolutionary pressure to lose them, if they no longer serve any purpose. StuRat (talk) 22:48, 10 June 2008 (UTC)[reply]

Perhaps, but remember that evolution isn't a conscious entity, it doesn't solve every problem a species has. Just because toenails can be a danger, this doesn't mean that a specific mutation is going to happen in which toenails don't grow and which will pass down to the next generation. Also there is a big debate about whether or not humans can still evolve in that way, considering how we now, for the most part, treat everyone equally regardless of disease. Increasing medical capabilities also make it less likely. Regards, CycloneNimrod ^talk?_contribs? 22:51, 10 June 2008 (UTC)[reply]

Objects slipping from your hands and objects protruding from the ground are two reasons why toenails serve some function. They might not be the most effective protections if you bang your foot against a root or rock but they did served a purpose in our savanna dwelling ancestor and still do for the barefoot aficionados of today. That they might be disappearing would be an interesting study subject. 200.127.59.151 (talk) 23:12, 10 June 2008 (UTC)[reply]

There's actually a new hypothesis out about the appendix. --Allen (talk) 00:52, 11 June 2008 (UTC)[reply]

That they are small or not is genetic. They actually do function to protect and add sensitivity to the tips[3]. Like fingernails, they protect the sensitive nerve endings on the tips of our toes and fingers. Rather than see them as clawing tools, see them as little shields. And you might like this from Nail Anatomy[4] (it's a download document) about function and purpose:

There is also an important role in offence and defence. Proprioception is gained from pressure of the pulp against the hard underside of the semi-rigid nail plate. The nail plates give form and shape to the pulp of the digit and, by attachment to the distal phalanx control and stabilise the pulp. On the foot, the toe nail is most importantly functional in its proprioceptive role, its defence of the digit and in control of the toe pulp.

Julia Rossi (talk) 00:55, 11 June 2008 (UTC)[reply]

And note that just because you can die from something doesn't make it much of an evolutionary pressure. As your very example points out, your grandfather's toenails had no effect on his ability to reproduce, only being a problem late in life and when complicated by other late-in-life illnesses. I doubt they are disappearing—they seem like a pretty basic part of primate anatomy, and without any pressure against them, they're not going to be going anywhere fast. --98.217.8.46 (talk) 00:56, 11 June 2008 (UTC)[reply]

Yes, but younger people can die from them, too, especially if they have diabetes and ignore the problem. I suffered from infected ingrown toenails myself. If I hadn't lanced to abcess and treated the area with hydrogen peroxide I might not be here now. (If you are eating while reading this, you can thank me for helping you with your diet.) :-) StuRat (talk) 04:39, 11 June 2008 (UTC)[reply]

As you leap up and run to correct your diet, you can thank toenails for giving information to the brain[5] through the pressure incurred that helps keep you upright in your flight and when walking gingerly back to your seat. StuRat this may be the document for you! Julia Rossi (talk) 05:44, 11 June 2008 (UTC)[reply]

That doc lists one of the uses of toenails as "assisting in oral maintenance" ... wouldn't that result in picking the seeds from this morning's preserves out of one's teeth only to replace them with toe jam ? :-) StuRat (talk) 06:30, 11 June 2008 (UTC)[reply]

Well if you have diabetes, I think you have more serious problems then toe nails. I would venture to guess the evolutionary pressure would be on something else, perhaps what causes diabetes in the first place not on your toe nails. As for the more general problem of ingrown nails, I don't think it would have been a big problem until recently since the biggest causes, are problem ill fitting shoes and poor nail maitence. I don't think shoes until say the past few thousands years were likely to be very tightly fitting and I doubt people cut their nails much at all Nil Einne (talk) 10:32, 11 June 2008 (UTC)[reply]

Actually, damage to the feet is one of the main risks for diabetics. I don't know the reasons, but I'm sure Wikipedia has an article on it (try diabetes!). Of course, that's one of the main risks for diabetics today, we've only recently learnt how to manage the condition, so diabetics even just 100 (or maybe even 50) years ago would probably have died long before their feet started having problems, and you can't get much evolution in 4 or 5 generations (except in exceptional circumstances is that tautologous?!). --Tango (talk) 13:25, 11 June 2008 (UTC)[reply]

The problem with diabetics and foot injuries is that they have restricted blood flow to their feet, which means that injuries do not heal, since the white blood cells needed to fight infection don't arrive. Thus, even a minor injury to the feet (like an ingrown toenail) can present a high risk to a diabetic. StuRat (talk) 14:31, 11 June 2008 (UTC)[reply]

Wierd Subconscious Dream

I have had this on my mind for a very long time. Sometimes, when Im in bed, I experience a sense that my room is a lot more spacious than it actually is, and I am really small compared to my surroundings. I can usually "feel" as if I was aware of all the walls, the format of my room. I am usually not very tired when this happens, and Im wide awake. Also, in conjunction with this, I get a feeling or subconscious image of a small circle rolling tensely on an extremely perfectly smooth surface. Usually, the surface suddenly breaks in this seemingly endless continuity of smoothness, and it starts to get extremely bumpy, and the ball doesnt roll smoothly. This gives me a very desperate and anxious feeling. This "image", however, is purely 1 dimensional, and it is usually in a grey color. When the surface the ball is rolling on becomes chaotically uneven and incontinuous, I get a really anxious, uneasy, desperate feeling. I am pretty sure all of this is subconscious, however it is not a dream, because none of this could happen in real life, like a dream. The image and consequent feeling I get is like a television screen, I mean thats what I see. I want all of you to know I dont suffer from any kind of mental disorder I know of, maybe just a bit of stress. If anyone can identify what this is and its name, it would be greatly appreciated. —Preceding unsigned comment added by 189.4.19.134 (talk) 22:42, 10 June 2008 (UTC)[reply]

Sounds like astral projection, if you're willing to believe in it. There's little scientific evidence (if any) for it, though. Regards, CycloneNimrod ^talk?_contribs? 22:49, 10 June 2008 (UTC)[reply]

Actually, now I think about it, it's probably more related to some form of lucid dreaming. These can be exceptionally strange and are more believable scientifically (although there is still very little research for it) Regards, CycloneNimrod ^talk?_contribs? 22:53, 10 June 2008 (UTC)[reply]

That's gnarly. I actually get a similar perception of expansion sometimes as I'm going to sleep as well. When it happens, it's when I'm "half-awake," not quite asleep but certainly on my way to unconciousness, not entirely unaware of my surroundings but also very much inside myself. Unlike your experience, I don't feel as though the whole room is expanding so much as the inside of my head. it's hard to articulate my experience. If there isn't a word for this sort of thing, there should be, but don't think it's that unusual. Your brain does some funny stuff as you drift off to sleep and it's probably a little different for everyone. Also, just thought i'd point out: something isn't "subconscious" if you are actively conscious of it (you perceive it). --Shaggorama (talk) 08:03, 15 June 2008 (UTC)[reply]