Wikipedia:Reference desk/Archives/Science/2009 June 23

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June 23

BDNF and Nuclear Accumbens

Does anyone know where I could find some information on micro-dissection techniques of the nuclear accumbens in California mice? (Peromyscus Californicus) I was also wondering what the significance of a Tyrosine hydroxylase antibody would be on localizing BDNF activity.(Specifically in the Nuclear Accumbens)

ArmyOfFluoride (talk) 01:20, 23 June 2009 (UTC)

For questions at that level of detail, your odds are better searching on Google Scholar than asking on Wikipedia. There are about half-a-dozen neuroscientists who hang out around here, including me, and I don't think any of us could address those questions. Regards, Looie496 (talk) 04:26, 23 June 2009 (UTC)

Come on, Looie... no harm giving it a try.  ;-)

Tyrosine hydroxylase (TH) is one of the enzymes involved in production of dopamine. Neurons that are stained by the TH antibody (see immunohistochemistry) will be the dopaminergic neurons. I'm not sure if the antibody will stain just the neuronal cell body or also the axon terminals. The nucleus accumbens article tells us that "Dopaminergic input from the VTA (ventral tegmental area) is thought to modulate the activity of neurons within the nucleus accumbens." Brain derived neurotrophic factor (BDNF) is vital for nervous system development and a quick search on PubMed reveals several relevant articles [1][2][3] suggesting that BDNF is particularly important in dopaminergic pathways. If I tried to connect the dots here I'd say that the significance of finding TH antibody staining in the nucleus accumbens is probably a marker for BDNF release/activity and that you might see varying levels of staining under different conditions that activate/inhibit the dopaminergic system.

With regard to micro-dissection, I would expect that the neuroanatomy of the California Mouse is similar enough to typical laboratory mice that you could work out the technique using any good microdissection atlas. "The Mouse Brain in Stereotaxic Coordinates" [4] is a classic. --- Medical geneticist (talk) 14:14, 23 June 2009 (UTC)

iPhone Oleophobic coating

Wasn't sure if I should put this in science or technology. But it seems more chemstry related. The new iPhone 3GS screen has an "Olephobic" coating that claims to reduce fingerprints and ease cleaning. How does something like that work? Will I harm the coating if I install a screen protector film on top of it? --Navstar (talk) 00:42, 23 June 2009 (UTC)

Oleophobic means something like 'oil rejecting' - so I presume it rejects the oils in your fingerprints. Any water-based substance would do that - so it's not magic. Using a screen protector makes having this fancy screen kinda pointless - and it's actually quite possible that a regular screen protector might not stick to it if it uses oil-based adhesives. Sadly, our Lipophobicity doesn't help much. SteveBaker (talk) 03:09, 23 June 2009 (UTC)

The Hydrophobe article desribes the reverse situation pretty well. Just replace 'oil' everywhere you see 'water' and 'polar' where you see 'non-polar' and you'll get the idea. --Shaggorama (talk) 05:07, 24 June 2009 (UTC)

Driving upside down in a tunnel

How would this work? Are they talking about driving on the ceiling of the tunnel (ala Men in Black)? Presumably the driver would start on the road and then have to veer up the wall until they were on the ceiling and then veer back down? Is that what they are talking about? Is that conceivable possible? NotAHen (talk) 05:54, 23 June 2009 (UTC)

I don't think you'd have to be travelling 190mph to drive upside down, for a short distance of course. What they're probably talking about is the effect from the body, presumably the spoiler, pushing down on the car while driving at high speeds, essentially sticking it to the roof of the tube. That would be pretty damn cool mind you. 124.154.253.146 (talk) 06:30, 23 June 2009 (UTC)

The reference confirms that, stating that that it's the effect of the downforce, and now that I think about it, the whole car is going to have to contribute to the effect, not just the spoiler. 124.154.253.146 (talk) 07:17, 23 June 2009 (UTC)

Theoretically it's possible, but I wouldn't believe it till I see it. And I sure as hell wouldn't volunteer to test it. People have been trying to do that for years, often with fatal results. I doubt this one will turn out different. The effect of gravity would far outweigh any upwards force the spoiler (or even the entire car) may have.Drew Smith What I've done 08:48, 23 June 2009 (UTC)

Roller coaster trains travel upside down without gravity throwing them to the ground, and they are far from aerodynamic. True they also stay upside down only a short distance. I don't see either train or car driving through the Chunnel upside down.- KoolerStill (talk) 09:10, 23 June 2009 (UTC)

They do employ scientists (don't they?), so I don't think gravity would "far outweigh" the downforce (er...upforce) of the car - any scientist would spot such an obvious flaw. I'm not saying it would work - just that I'm not sure the problem would be as simple as that. Vimescarrot (talk) 09:56, 23 June 2009 (UTC)

Roller coaster trains generally have wheels which affix to the top and bottom of a rail to enable them to hang on when upsidedown. They're of little relevance to this discussion. --Tagishsimon (talk) 10:01, 23 June 2009 (UTC)

Aerodynamic downforce on a racing car can be much greater than its weight. www.formula1.com says "A modern Formula One car is capable of developing 3.5 g lateral cornering force (three and a half times its own weight) thanks to aerodynamic downforce. That means that, theoretically, at high speeds they could drive upside down." But still sounds extremely difficult to achieve in practice with any reasonable margin of safety. Gandalf61 (talk) 12:24, 23 June 2009 (UTC)

That's not really correct. The downforce only has to be enough to allow the tyres to exert 3.5g of lateral frictional forces - you don't need 3.5g (or even 1g) of downforce in order to do that. Although a formula 1 car may well have that much downforce - it's not numerically related to the lateral cornering forces. My old autocross car could produce 1g lateral at just 40mph - but it hardly had any down-force at that speed...it was all down to having wide, sticky tyres and suspension that's stiff enough to keep all four wheels planted flat onto the road. SteveBaker (talk) 12:52, 23 June 2009 (UTC)

It's not complicated - the shape of the body of the car (and all of it's spoilers and other aerodynamic features) are designed to push the car downwards against the road to get better grip at high speeds. If the amount of that force exceeds the weight of the car then it could be driven at that speed along the ceiling of a suitable building - held up by the force of the air against the body. This shouldn't come as much of a surprise - that's what makes an aeroplane fly. If you took a typical light aircraft (a Cessna or something) and mounted a set of wheels on the roof - you wouldn't be surprised that it could fly along with it's "roof wheels" rolling along the ceiling...held up only by the airflow over its wings...and that's what this car is (theoretically) able to do. It's body is an inverted wing-shape. How you'd get the car to do this in practice would presumably to be to have a few miles of nice straight concrete pipe - maybe 20' in diameter (think about that scene in "The Italian Job" when the Mini's are driving through the sewer - driving up the walls of the pipe). The car accelerates until it's going fast enough for the downforce to exceed it's weight - then the driver slowly steers to one side - the car gradually creeps up the side of the pipe and across the "ceiling" until it's completely upside-down. So long as he never slows down - the car should stick to the top of the pipe without problems. SteveBaker (talk) 12:52, 23 June 2009 (UTC)

...aside from the possibility of fuel and oil starvation, due to the pickups not being immersed. -- Coneslayer (talk) 14:06, 23 June 2009 (UTC)

Since the claim would be easy to demonstrate in a scaled wind tunnel model one may reasonably ask why that has not been done? Cuddlyable3 (talk) 14:10, 23 June 2009 (UTC)

Because (a) it's not particularly useful and (b) we have airplanes that do precisely this thing - so it's hardly very exciting or valuable science. However, it IS the kind of thing the Mythbusters could get interested in trying! SteveBaker (talk) 18:20, 23 June 2009 (UTC)

In the DVD extra documentary for the Italian Job, it's mentioned that in test drives, they managed to get a Mini to go right round the pipe, including upside down - just once, and couldn't reproduce it for the live run. Obviously that's a simple loop-the-loop, rather than sustained upside down driving, but the mention of the pipe-driving scene reminded me of this anecdote. AlexTiefling (talk) 14:33, 23 June 2009 (UTC)

Funny how people are overcomplicating things here. A car driving on the roof is simply flying, like an airplane. All that's needed is enough lift, which is a function of body shape and airspeed. Looie496 (talk) 16:15, 23 June 2009 (UTC)

Well, there's a bit more to it than that. As Coneslayer says, a car isn't usually designed mechanically (or, indeed, structurally) to work upside down. Remember that the reverse downforce/lift only acts on certain components of the car's bodywork - for most of the car's components, down is now up. I think at the very least you would want to do a static test first - start car and hang it upside from a crane to make sure nothing important falls off. Like the engine. Gandalf61 (talk) 16:28, 23 June 2009 (UTC)

It's certainly possible that things like fuel feeds would go dry - but if you actually wanted to do it - that wouldn't be hard to fix. SteveBaker (talk) 18:20, 23 June 2009 (UTC)

There is stuff about that it Formula_1#Cars_and_technology but it is unsourced. I couldn't find the right page on f1.com earlier. What page gave you that stuff about G-force Gandalf61? ~ R.T.G 16:56, 23 June 2009 (UTC)

It's here. Gandalf61 (talk) 19:15, 23 June 2009 (UTC)

We should probably link to this toy car that can drive across a smooth ceiling. It's surprising how little it takes to make that work! SteveBaker (talk) 18:20, 23 June 2009 (UTC)

For one, your fuel gauge will not work properly. I will probably read a full tank no matter what your actual fuel level is. Granted this is probably not critical, short term. 65.121.141.34 (talk) 18:24, 23 June 2009 (UTC)

Hmmm - tricky. On the one hand, while you are driving at 180mph along the ceiling, you'll probably have more on your mind than what the gas gauge is reading...and on the other hand, if you do happen to run out of gas while driving at 180mph across the ceiling, it may be a bigger concern than if you were more normally positioned at the time! :-) SteveBaker (talk) 23:58, 23 June 2009 (UTC)

yawning + tone

I recently noticed that I could perceive a very small lowering in tone through headphones during a yawn (i.e., while my mouth is gaping open, and my jaw is extended). Could there be some reason for this, or am I just imagining it? I have tried this a handful of times. 124.154.253.146 (talk) 06:26, 23 June 2009 (UTC)

I've noticed something similar, so it's not just you. DISCLAIMER: I am not a proffessional. What follows is a guess. My guess would be that somehow the act of yawning makes the muscles flex in such a way that they push against the inner ears slightly. That wold account for a change in pitch.Drew Smith What I've done 08:53, 23 June 2009 (UTC)

Structural diagram of the cochlea showing how fluid pushed in at the oval window moves, deflects the cochlear partition, and bulges back out at the round window.

I know exactly what you mean - but I very much doubt that it's shifting the pitch of the note. What I suspect is happening is that by changing the shape of the ear canal, you're causing the higher frequencies within the music to be filtered out - or attenuated in some manner - resulting in only the lower frequencies getting through unmolested. So if you had two simple sine-waves being played at different frequencies - then as you yawn, the higher frequency note would get a lot quieter - and you might percieve that as a lowering in frequency - when in fact the lower frequency note is unchanged. SteveBaker (talk) 12:58, 23 June 2009 (UTC)

Provoke a yawn (I do it by thinking of cricket but that's just me) while intoning a steady aaaaaaaahhh. You may hear the tone change as the size of the resonant cavity of the mouth changes. Cuddlyable3 (talk) 13:54, 23 June 2009 (UTC)

Sounds are detected by hair cells that line the cochlea, a spiral-shaped structure that is thick at one end and thin at the other. Each frequency causes a different part of the cochlea to vibrate, by resonance. The sensory cells are not directly frequency-sensitive, they only know that the part of the cochlea where they are located is vibrating. My guess is that when you yawn, you either stretch or compress the cochlea, and then a given sound causes the vibration peak to move to a slightly different location. Looie496 (talk) 16:12, 23 June 2009 (UTC)

Another possiblity (or likelyhood, even) is that during the yawn, you activate the second smallest muscle in your body, tensor tympani which moves the malleus away from your tympanic membrane. This also happens when you are exposed to a really loud noise or chewing. (The smallest muscle, stapedius is also in the middle ear). -- Flyguy649 ^talk 18:09, 23 June 2009 (UTC)

Thanks! That sounds likely (the part about the missing high frequencies and moving vibration peak), moreso because there's a very obvious reduction in volume. Sorry for making everyone yawn! 124.154.253.146 (talk) 05:41, 24 June 2009 (UTC)

office temperature requirements.

≈≈≈≈ Wanting to know the legal temperature that a working office should be, Anyone know? ≈≈≈≈

As long as it's not at a dangerous temperature I don't think there are any requirements... Whats the background for the question? Context is always good.Drew Smith What I've done 08:49, 23 June 2009 (UTC)

More important, you're asking about the laws where? What country, state, etc.? Also, this isn't a science question. I suggest starting over and asking on the Miscellaneous desk, giving more detail this time. --Anonymous, 09:07 UTC, June 23, 2009.

Thanks for the reply, Its in the UK. I work in an office where there are several air con units in our room, there is one directly above our part of the office and this constantly breathes down our neck all day long, leaving us with stiff necks and several other ailments, Its just not very pleasant, and maintence insist on switching it back on when we switch it off. I have research it and see that a room should ideally be between 22.7 - 24.4 C but can not find if there is a legal requirement.

According to "Workplace (Health, Safety & Welfare) Regulations 1992" applicable in the UK, the temperature is only required to be 'reasonable'. There is an additional requirement that employers should provide thermometers to indicate the working-place temperature. Richard Avery (talk) 09:36, 23 June 2009 (UTC)

The OP's stiff neck and other ailments, and their likely cause, would need to be diagnosed formally by a doctor if one wants the annoyance to be taken seriously. Wikipedia cannot do that. Before seeking a legal remedy it would be diplomatic to suggest to a superior that making a change to the workplace could increase productivity. Cuddlyable3 (talk) 13:48, 23 June 2009 (UTC)

I actually read recently somewhere that policy on my campus states that temperatures should not exceed 90F, but that's pretty hot and hard to achieve, and that's policy, not law. I don't think it reaches that when the AC's broken in the summer, so you probably won't have much luck arguing this case. --Wirbelwindヴィルヴェルヴィント (talk) 17:25, 23 June 2009 (UTC)

Really, your manager should care about this and find a solution. I don't think you need to reach for "ailments" — any manager should find a solution for an employee that's actually physically uncomfortable at work. What does your manager say? Tempshill (talk) 17:57, 23 June 2009 (UTC)

The manager's concern will be based on how many people are in the "our" group the questioner mentions. If it is one person, there is not much need for concern. If it is 20 people, concern rises. -- kainaw™ 18:01, 23 June 2009 (UTC)

To answer the original question, the 1992 Regulations state that the minimum temperature for an office (strictly speaking, a workplace where the work is not manual) is 16 °C. You can even buy thermometers with this temperature specially marked. Unfortunately, this legislation was not written with air-con in mind. You can have an air-conditioned room in which the temperature oscillates wildly, causing great discomfort, while the average temperature is still correctly maintained. It is difficult to explain this to your boss, because all bosses are chosen from a genetic subgroup with thick hides. --Heron (talk) 21:03, 23 June 2009 (UTC)

Probably switching off that A/C would make the rest of the office unbearably warm. Did you check this before you repeatedly(I assume) turned off the A/C? APL (talk) 21:15, 23 June 2009 (UTC)

The manager agrees that it is too cold in the office and it is her who switches the A/C to a higher temperature (not warm air)/off but it is maintenance who come and turn it back on/the temperature back down. It's the whole office who agree that the temperature in the room is to low.

This is something I looked at a few years ago in connection with trying to show that people worked better at a comfortable temperature. But in fact there was very little about this and the bit I did find seemed to indicate you got more work out of people when it was slightly cooler than the recommended temperatures. Dmcq (talk) 09:50, 24 June 2009 (UTC)

Perhaps leave a note on the A/C asking maintenance to not reduce the temperature? Could just be a communication issue. 65.121.141.34 (talk) 13:20, 24 June 2009 (UTC)

Weighing in here due to my past career in Facilities Maintenance (i.e. the people who look after the aircon in offices, amongst many, many other things). The OP's problem is actually a very common one, often (though apparently not in this case) difficult to resolve because of different preferences amongst office sharers, and very localised 'microclimates' within a single office. We commonly encountered situations where a single occupant of a large office would complain that the ambient temperature was too low when everyone else affirmed that they were comfortable. (Anecdotally, the complainer was more often than not a middle-aged female in thin clothing, but the practical answer of "wear a cardigan" was not deemed diplomatic.)

As others have suggested, there are few regulations about office working temperatures with specific numbers, although I believe there is or was a (UK) requirement that it should be at least 65°F (18.3°C) by 1 hour after commencement time, and I see Heron cites a regulation requiring 16°C. However, the actual problem as described is probably due to specific draughts from some AC Units rather than the general air temperature or humidity. All office AC Systems have temperature controls, but these may not be accessible to the occupants, or may not be working properly: most ACUs also have adjustable flaps on the vents which alter the direction of the produced draughts.

Step one would be to request politely, through the channels that should be available, for Maintenance to check that all the ACUs are (i) working correctly and (ii) are set to appropriate temperatures; unless they've just had a 6-monthly (or whatever) planned maintenance check, malfunction or mis-setting is quite likely. A Dim View is taken of occupants just switching bits of the kit off, because this throws out the balance of the whole system (perhaps including that in adjacent offices) and may cause further problems (Aircon is something of a Black Art rather than just a science); opening windows is usually similarly contra-indicated, because then, instead of the system trying to heat/cool/dehumidify the Office, it will be trying to heat/cool/dehumidify Hampshire (or wherever you actually are).

Step two would be to identify exactly from where (i.e. which vents from which ACUs) the troublesome draughts are coming from. Maintenance should then be able to (i) adjust those vent's flaps to make their draughts miss their current targets, or (ii) failing that, to block those vents (usually just 1 out of 4 on any one ACU) with (e.g.) tape, or (iii) to install separate deflector panels on ceiling brackets or the like, or (iv) to switch off the offending Units entirely (probably not possible in this case), or (v) (really drastic) rearrange the Units' layout in the ceiling - I've seen all five done before. An alternative approach might be, if possible, to rearrange the desk (and other furniture) positions, which probably no longer match the way the office was originally intended to be laid out when the ACUs were installed.

Such AC draught problems are indeed both annoying and potentially serious, I've known sufferers to be made ill by them to the extent of taking sick leave. If Management or Maintenance grumble about the time and trouble of Steps one and two above, the OP needs to consider Step three, which is to call in the Occupational Health/Health & Safety Department to investigate, adjudicate, and if necessary stipulate solutions. Where available, Employee representatives or Union reps might also be resorted to. Hope some of this helps. 87.81.230.195 (talk) 17:35, 25 June 2009 (UTC)

In Essence is a Polar Shift of Magnetic poles - capable of being caused by Man through a Ultra-low Resonant Frequency?

I was fiddling with some science stuff and was thinking – if an ultra low frequency were directed to the mantle or core of the Earth, would it be possible for a non-geographical but a shift in magnetic poles? Now, I'm new to this field, so lamen's terms or explanations would be much appreciated.

Before I start doing any digging, is there any hint of evidence at all to this? Have we demonstrated that small magnets can have their polarities reversed through such means? In particular, a frequency of what? Does it need to be resonant (you left that out of the question proper)? Because otherwise it looks like some terms have been slapped together arbitrarily. — Lomn 12:12, 23 June 2009 (UTC)

This article points both to convection of molten iron in the Earth's outer liquid core driven by internal heat sources and to the magnetosphere driven by solar wind as responsible for the direction of the Earth's magnetic field. Considering the size of these forces may give pause to the OP's thoughts of changing it by shaking it. But who can say what might be possible when Dynamo theory quotes Albert Einstein who described the origin of the Earth's magnetic field as being one of the great unsolved problems facing modern physicists. Cuddlyable3 (talk) 13:34, 23 June 2009 (UTC)

Personally, I think the answer is "no you can't" -- the total energy requirements would be just too tremendous. 76.21.37.87 (talk) 04:39, 26 June 2009 (UTC)

Soft drink and obesity

Soft drink does not contain fat. Then how it causes obesity? DavidCop (talk) 12:38, 23 June 2009 (UTC)

Soft drinks are rife with calories (in this case, sugar), and the body typically converts unused calories to fat. — Lomn 12:46, 23 June 2009 (UTC)

(ec) Eating fat isn't what makes you fat. The body will convert any excess calories into fat. Soft drinks are high in sugar, that's where the calories come from. Eating lots of fat is bad for you because it damages your arteries (if memory serves, I can't find the relevant Wikipedia article, although I'm sure one exists), not because it makes you fat (although it will if you eat enough of it, of course). --Tango (talk) 12:47, 23 June 2009 (UTC)

(ec²) I read a British medical study a few years ago (it was probably a few years old when I read it) that found a correlation between drinking soft drinks (both regular and diet drinks) and obesity. It is a correlation, not a cause and effect. The lifestyle of drinking soft drinks is a lifestyle that includes increased caloric consumption and decreased exercise. So, you shouldn't use the phrase "causes obesity". -- kainaw™ 12:50, 23 June 2009 (UTC)

Just thought to include a couple anecdotes: Mountain Dew is running an ad campaign now that it "fuels" gaming (especially World of Warcraft). Do you really need 220 calories to sit in a chair and play a video game. Also, if you've ever worked in a fast-food restaurant, you've taken the order: Two cheeseburgers with extra fat sauce, super-large fries, two apple pies, cookies, and a large diet Coke. -- kainaw™ 12:54, 23 June 2009 (UTC)

Dude, it's the taste, not the diet-ness.... Tempshill (talk) 18:02, 23 June 2009 (UTC)

I've never understood people that like the taste of diet coke, it tastes far worse in my opinion... --Tango (talk) 18:56, 23 June 2009 (UTC)

Fun fact : Diet Coke uses the Coke II formula, not the Coca-Cola formula. APL (talk) 21:05, 23 June 2009 (UTC)

I'm in the UK. I don't think we've ever had anything with the Coke II formula. Our article doesn't seem to support your claim (although it makes some incomprehensible comments about diet coke, do you have a source? --Tango (talk) 22:45, 23 June 2009 (UTC)

Diet Coke was introduced first. Coke II was the diet coke formula with real sweetener. This statement appears unsourced in our Diet Coke article and it appears on snopes. I have read it other places as well, but that's all I feel like digging up at the moment. Perhaps the references at the snopes article can help. The Coke II article is a mess regardless. APL (talk) 23:33, 23 June 2009 (UTC)

If the definition of "large" in the fast-food restaurant in question is what it is in some, then that could still be a significant reduction in the total calories in the meal. --Tango (talk) 15:15, 23 June 2009 (UTC)

It should be noted that calories are a measurement of energy, thus aren't actually converted to fat. However soft drinks contain saccharides that can be converted to triglycerides, which are stored in adipocytes (which make up adipose tissue - colloquially known as fat). --Mark PEA (talk) 15:05, 23 June 2009 (UTC)

Indeed, I apologise for my imprecise language. My point was that it is the number of calories you consume that is significant, not where they come from. (Well, it's a little more complicated due to the body absorbing calories better in some forms than others, but it's a decent approximation to the truth, at least.) --Tango (talk) 15:15, 23 June 2009 (UTC)

In other words, gaining/losing weight does not need to be overly complicated. If you consume significantly more calories than your burn, you will likely gain weight. If you consume significantly less calories than you burn, you will likely lose weight. Yes, it is a lot more complicated if you want to make it an exact science, but the average person doesn't care about the exact amount of fat gain per calorie consumed. -- kainaw™ 17:36, 23 June 2009 (UTC)

So fat people are created by eating fat? You need to brush up on your information --70.167.58.6 (talk) 17:19, 25 June 2009 (UTC)

You can certainly get fat by eating fat, but you can also get fat by eating a lot of sugar and 0 fat (unless you can get rabbit starvation that way). 65.121.141.34 (talk) 13:24, 26 June 2009 (UTC)

Toe-nails

I remember learning long ago (and, common sense confirms) that all of the parts of the human body serve some physical or biological function / purpose. The only part, I was told, that did not seem to fit into this model was the appendix. For years, scientists assumed it served no purpose whatsoever (at least, today ... as opposed to millions of years ago). (As a side note, I guess that modern science is now questioning this idea and has theorized on some functions that the appendix serves.) Anyway ... on to my question. I was thinking about the finger-nail, and I was puzzled about its function. After some thought, I was able to convince myself of a few things ... for example, peeling, plucking, pulling, grabbing, holding, scratching, and the like. Then, my thoughts turned to the toe-nail. I cannot for the life of me think of any purposes whatsoever that they serve. The only thing that I can (half-heartedly) think of ... is that they serve as an outer shell to "protect" the surface of the toe. But, that is hardly convincing to me. Does the toe-nail serve any function at all? Or am I missing something very obvious? I am referring to human beings, by the way. Thanks. (Joseph A. Spadaro (talk) 14:01, 23 June 2009 (UTC))

From our article, Nails act as a counterforce when the end of the finger touches an object, thereby enhancing the sensitivity of the fingertip, even though there are no nerve endings in the nail itself. Could the same apply to toes? Vimescarrot (talk) 14:35, 23 June 2009 (UTC)

It is also possible that our feet evolved from fully articulate appendages (like hands) and toe nail is just a hold over from that time. Livewireo (talk) 15:07, 23 June 2009 (UTC)

Toenails also give a small amount of protection to the end of the toes. Might not be much, but better then nothing. 65.121.141.34 (talk) 15:08, 23 June 2009 (UTC)

The human toenails are relics of claws that once were useful for climbing and fighting. Now that the foot is optimised for bipedal walking they serve only to slightly stiffen and protect the passive toes (and provide a refuge for fungus). Cuddlyable3 (talk) 15:19, 23 June 2009 (UTC)

It's not true that every part of the human body serves a purpose. The appendix is pretty useless, for example. Generally, every part served a purpose at some point in our evolutionary history (although there is no absolute requirement for that to be the case, things can just happen coincidentally), but it's not uncommon for that purpose to no longer be relevant. --Tango (talk) 15:21, 23 June 2009 (UTC)

See Vestigiality for details. --Tango (talk) 15:23, 23 June 2009 (UTC)

Questions of the form "Why is (some biological detail) there?" presume an intelligent plan rather than random evolution. A debate about who designed the human body went like this: It was designed by a mechanical engineer, for only he could have made all the wonderful joints. No, says another, it was designed by an electrical engineer for only he could have designed the complex wiring of the nervous system. No, says another, it was designed by a civil engineer, and a bad one at that, because no good civil engineer would lay a sewer pipe through an entertainment district. Cuddlyable3 (talk) 19:26, 23 June 2009 (UTC)

I think toenails would go the way of the Dodo bird if they didn't serve some purpose. Bus stop (talk) 19:46, 23 June 2009 (UTC) Bus stop (talk) 19:46, 23 June 2009 (UTC)

They may be, but this kind of stuff doesnt happen over night. The appendix stopped being relevant thousands of years ago and a vestigal tail is still observable in a fetus. Check back in about 10,000 years, our feet may be toe-nail free. Livewireo (talk) 20:42, 23 June 2009 (UTC)

Thousand of years? really? Dauto (talk) 22:26, 23 June 2009 (UTC)

Yes, really. Well, I don't think there is universal agreement, but it's certainly a popular theory that the appendix become pretty much useless when we changed to our modern diet, which happened maybe a few tens of thousands of years ago. --Tango (talk) 22:41, 23 June 2009 (UTC)

I'm not sure I buy that. By modern diet, do you mean cooked food? 71.203.58.148 (talk) 04:08, 24 June 2009 (UTC)

Not necessarily. It might be since the invention of agriculture. Control of fire goes back much further than that. I'm really not an expert on the function of the appendix! --Tango (talk) 13:22, 24 June 2009 (UTC)

They do serve a cosmetic purpose. Would you marry someone without toenails? A toe looks better with a toenail. Many features on humans make them more attractive, and so will tend to be retained across generations. Graeme Bartlett (talk) 22:33, 23 June 2009 (UTC)

You only think they are attractive because the lack of a toenail suggests something is wrong and something being wrong means the person won't make a good mate. --Tango (talk) 22:41, 23 June 2009 (UTC)

The thing about this evolutionary stuff is that it's not enough for something to be functionally useless for evolution to dispose of it. It has to materially REDUCE the ability of the creature to survive and reproduce...that's the only way that possessors of the "no toenails" gene can take over the world from the "with useless toenails" people. We do find that (for example) almost all animals that live in dark caves eventually evolve to lose their eyesight - but eyesight is an expensive thing to maintain - it's not just the eyeballs, it's muscles, eyelids, brain function. Without eyes, they need less energy - needing less energy, they can survive better. But I don't think toenails - which are dead material and grow at glacial rates need much energy. They simply aren't a disadvantage...so they won't get selected against. Toenails have been useless pretty much since we descended from the trees - we've had PLENTY of time to lose them - yet they are still here.

Another possibility - and a quite likely one IMHO - is that the exact same gene controls toenail and fingernail growth. Fingernails are incredibly useful. Perhaps we simply cannot lose our toenails without also losing fingernails - and thereby suffer such horrific disadvantages that the "no nails anywhere" gene is selected out whenever it pops up.

SteveBaker (talk) 01:30, 24 June 2009 (UTC)

Related question - are there any animals with toes but no toe nails? Jay (talk) 10:15, 24 June 2009 (UTC)

Alright people, you're missing it completely. Toe-nails keep the bones in your toes from breaking through the skin. The ends of the bones in your fingers and toes are sharp, and if you didn't have nails the skin around these sharp bones would be very prone to movement. The movement would, over time, wear the skin down and eventually tear. Thus, humans evolved fingernails and toenails.Drew Smith What I've done 04:35, 24 June 2009 (UTC)

Do you have a source for that? Vimescarrot (talk) 10:02, 24 June 2009 (UTC)

I'm glad I've got cheek-nails - to keep my cheeks from moving near my sharp teeth. Otherwise my teeth would obviously be sticking out the side of my head --Polysylabic Pseudonym (talk) 13:01, 24 June 2009 (UTC)

Toe nails can be trained to do what finger nails can. Mark Goffeney and Tony Meléndez might be using them to play the guitar, and Bill Wedekind might be using it for pottery. Jay (talk) 11:39, 24 June 2009 (UTC)

I'd like to point out that our article on the appendix has links to references that the appendix is not totally vestigial, but may contribute both to the immune system and to sustaining gut flora. Considering the high incidence (and mortality!) of appendicitis and peritonitis, it's hardly surprising that natural selection would otherwise allow it to remain. The comparison to toenails is not valid (especially since ingrown toenails rarely kill you...). Matt Deres (talk) 16:28, 24 June 2009 (UTC)

Maybe toenails are nature's first steel-toe boots. Bus stop (talk) 17:16, 24 June 2009 (UTC)

Something that occurred to me is that in addition to other possible reasons mentioned above, toenails may also serve as an honest signal of the health of an individual, since nails can present a recent health history to prospective mates. JSBillings 01:37, 25 June 2009 (UTC)

Possibly in a superficial way, but not as a reliable indicator. Many people have serious illnesses and perfect toenails, while I am perfectly healthy and have a disgusting looking ingrown toe-nail (that needs another surgery, I might add).Drew Smith What I've done 06:34, 25 June 2009 (UTC)

A number of the replies above assume that natural selection will continue to work on humans in the future as it has in the past. In the last couple of hundred years we have being working quite hard to counteract it, at least in prosperous parts of the world. Now it's perfectly conceivable that this will turn out to be a short-lived blip, but it's also possible that we will go the other way and do our best to eliminate all natural selection. Either way, I do not find it convincing that toenails will be selected on in any way. --ColinFine (talk) 23:40, 27 June 2009 (UTC)

Try taking out all your toe nails for 2 years and let us know if there was any diffrence to your health standard of living ect... :) Chromagnum (talk) 08:17, 28 June 2009 (UTC)

Landing on the Moon

It seems like landing on the Moon is an insanely complicated process (ie no atmosphere to slow you down). In the future if civilians were able to fly there via a commercial flight would there be a safer method of ensuring you don't plummet into the ground at 14 km/s? TheFutureAwaits (talk) 16:23, 23 June 2009 (UTC)

A space elevator is an option, I believe. (If memory serves, it wouldn't need to be as strong as one on Earth, but would need to be much longer - I'll look that up in a moment.) Several redundancies in your propulsion system would reduce the risk substantially, as it does on airliners today. I guess you could design a landing pad that in some way cushions the impact, either directly with lots of springs or something, or by slowing the descent of the landing craft before it makes contact via big magnets or something. I don't know of any serious proposal along those lines and I'm not sure it is necessary. --Tango (talk) 16:30, 23 June 2009 (UTC)

My memory would appear to be accurate. We have an article on the topic (of course!): Lunar space elevator. --Tango (talk) 16:33, 23 June 2009 (UTC)

Hmm according to the article that's not the best option: "One disadvantage of the lunar elevator is that it may not be able to carry human passengers. The rate at which cargo is transferred would be too slow, normally taking weeks to reach its destination.[2] Humans would be able to get there faster by using rockets to and from the moon." I'm wondering if there's some method by which you could make powered landings safer. On the Earth the atmosphere slows you down as you lose altitude but on the Moon you GAIN speed. TheFutureAwaits (talk) 16:52, 23 June 2009 (UTC)

One of the entries into the Google Lunar X Prize was for producing a rocket that could fly (50 or 100 meters) into the air, fly sideways for another specific distance, and land gently in a small moon landscape replica. Only one (on this particular occaision) managed it but it was really careful. I doubt, IMO, it was going over 14 miles per hour at touchdown (was it?). ~ R.T.G 16:53, 23 June 2009 (UTC)

The OP said 14 kilometres per second. (Although I'm not sure why - the Moon's escape velocity is only 2.38 km/s so that's the fastest you could hit unless you actually thrust in the wrong direction.) You need to be careful interpreting the results from the Lunar X Prize - it took place on Earth, so everything was scaled to compensate for the higher gravity. You may need to multiply the landing speed by 6 or something to get the lunar equivalent, I'm not sure. --Tango (talk) 17:46, 23 June 2009 (UTC)

The Lunar X prize stuff doesn't relate to landing from orbit - it's only about hopping around on the lunar surface. SteveBaker (talk) 18:11, 23 June 2009 (UTC)

As I said, redundancies in your propulsion system is probably all you need. If you have more descent engines than you strictly need you can afford for one of them to fail. Add some redundancies to the control system as well, and you should have a pretty safe lander. Airbags could be deployed in an emergency (I don't think they would be very good for routine landings, they would make getting out afterwards a little tricky). You could eject in little capsules with airbags, perhaps? --Tango (talk) 17:46, 23 June 2009 (UTC)

Just as a note, it's not clear that the lack of atmosphere makes lunar landings more complicated. An unpowered craft has no option to glide, true. On the other hand, there's no issue with heat of re-entry, there are no crosswinds, there's no need for a minimum safe flying speed, there's no need for designs that emphasize aerodynamics over capacity, and so forth. As noted above, you'd want redundancies in your critical systems, but that's a requirement for conventional aviation already -- much less the sort of safeguards that are required for spaceflight. I expect the safety considerations for commercial lunar travel will strongly resemble, in principle, the same considerations the airline industry uses today. — Lomn 17:54, 23 June 2009 (UTC)

Generating 1/6th of a g for the sustained amounts of time you need to land isn't really challenging - look at the tiny engines that got the apollo moon landers from the lunar surface back up into orbit. The majority of the mass of the system will be fuel - so having multiple rocket motors for redundancy is the obvious way to go. I also don't agree with the OP that the landing process is insanely complicated. Rockets are relatively unsophisticated machines - there isn't a whole lot to go wrong compared to (say) the engines on a 747. The problem with apollo was that every pound that had to be launched from the moon back to the earth had to be launched in one single craft in the opposite direction first. For sustained lunar colonies, a much better approach is to do what they did in the 2001 movie - which is to have separate craft for getting you out of the earth's gravity well that can concentrate on one really huge explosive push...versus the more sustained, but gentle push you need to get down onto the moon. SteveBaker (talk) 18:11, 23 June 2009 (UTC)

Just to make it clear, NASA is moving strongly in the direction of 2001. The Constellation program divides up cargo launch, crew launch, trans-lunar injection, and lunar landers as more-or-less independent systems. The problem (and discrepancy from 2001) is that reuse is minimal. Unfortunately, this will be a hard problem to crack. In order to re-use a special-purpose lunar craft (say, the one for Earth/Moon orbital transfers), you have to re-fuel it. Until there's a viable space-based fuel supply, the only option to re-fuel is to launch fuel from Earth. As Steve notes above, this is inefficient. However, it's comparatively cheap to launch a rocket engine along with that fuel supply. Rather than design a refueling system with all the additional risk it entails, we opt to launch the entire set of hardware repeatedly. — Lomn 18:48, 23 June 2009 (UTC)

Any permanent lunar colony should have its own fuel supply. All the plans I've seen involve finding somewhere with plenty of water ice that can be split into hydrogen and oxygen (a.k.a. rocket fuel) using solar power. --Tango (talk) 18:52, 23 June 2009 (UTC)

Indeed - the moon is a tricky problem. If indeed there is water ice in sizeable deposits in deep polar craters (where they would always be shaded from the sun and water from cometary debris could collect over billions of years) - then it makes sense to go there. With ample water and sunlight, we can make oxygen, drink the water, grow food and make rocket fuel and hopefully have electricity to spare. A long-term base would be able to figure out what other stuff could be extracted from the lunar soil - with the hope that metals could be extracted and solar panels mass-produced. If the amount of water there is large enough, this could be a very useful thing. But if there is little or no water there - then going to the moon is always going to be a hideously difficult and expensive proposition. The only reason to go there then is if there is something amazingly valuable there. There is a possibility that certain rare helium isotopes are to be found there in large quantities that would make building fusion reactors a much more reasonable proposition - so mining helium and shipping it back to earth would be a profitable reason to go there - despite the insane costs involved. But bootstrapping ourselves up to the point where we could have massive earthmoving and refining facilities there is an exceedingly difficult thing...I doubt we'll ever do that. SteveBaker (talk) 23:51, 23 June 2009 (UTC)

I think recent missions have confirmed the presence of significant amounts of water ice on the moon, although I don't know if they've confirmed it is accessible. He-3 is only useful if someone figures out how to make a fusion reactor that produces more energy than it uses - I'm optimistic, but there isn't really any reason to believe we'll get that worked out any time soon. The far side of the moon is a good spot for radio astronomy, although I'm not sure that will justify a manned mission (a space telescope at Earth-Moon L2 would work pretty well, by my calculations) it could contribute towards justifying one. If there is plenty of accessible water then it could work well as a waystation to the rest of the solar system (you only need to launch the fuel from the Moon, not the Earth). --Tango (talk) 01:46, 24 June 2009 (UTC)

There's also a lot of titanium and zirconium ore on the Moon, so that may be one more reason to go there... —76.21.37.87 (talk) 04:50, 26 June 2009 (UTC)

Isn't it cheaper to reach certain comets than to reach the lunar surface? Comets can be mined for water. —Tamfang (talk) 17:24, 26 June 2009 (UTC)

Venus Flytrap care

I recently purchased a Venus Flytrap. It is a really fascinating plant and so far it has trapped a couple of flies. I have done some research on these plants, however,my question is for anyone who has experience in caring for flytraps...specifically, how much food do they need? Is it possible for them to eat too much? I have actually fed it a housefly which it eagerly trapped, but I am wondering if that is a habit I should avoid. thanks and cheers, 10draftsdeep (talk) 20:24, 23 June 2009 (UTC)

Overfeeding can be harmful for VFTs although how much that is will depend on the size of the plant, though the article says that digestion takes about 10 days to complete. You actually don't really need to feed it at all as it is still a plant and will photosynthesize for almost all of its needs. I assume you have already read the article we have? 65.121.141.34 (talk) 20:52, 23 June 2009 (UTC)

Photosynthesis is how the plant get's its calories. The traps are to supplement the nutrients brought up by the roots. VFTs do well in poor soil because they're not dependent on the soil to provide nutrients. APL (talk) 20:54, 23 June 2009 (UTC)

Warning : Anecdotal evidence follows

I've owned a flytrap for several years. After several failed attempts to keep one alive, I started watering this one only with distilled water. It's been alive for about six or seven years now.They're supposedly very sodium sensitive, so I recommend it if you're in an area that has too much salt in the water supply.

Otherwise, it is possible to overfeed them. Each trap can only close an average of two to four times before the entire leaf dies. (Smaller traps seem to be able to survive more closings than larger ones.) So "teasing" the plant just to watch it move is absolutely not advised. If you kill off all the leaves at the same time, either from over-feeding, or "teasing" or whatever then it will have a difficult time recovering.

They can survive just fine with no bugs at all, but I've found that a few bugs a month seems to make them grow faster.

Many people say that you need to hibernate them in the winter, by placing them in a fridge. I've never bothered. I just keep mine on the windowsill, it dies back a little in the winter but never completely. (Some people do report that their VFT dies off entirely in the winter, but still recovers in the spring. So if your plant goes brown around October, don't throw it out until at least June.) APL (talk) 20:54, 23 June 2009 (UTC)

It takes them roughly ten days to digest, however they will not need to be fed "meat" for another week after they are done digesting. They are very sensitive to sodium (as APL said) and potassium. Again, photosynthesis gives the plant most of it's calories. Do not, however, "hibrernate" your VFT. They are tropical plants, and in the wild they don't experience much of a "winter".Drew Smith What I've done 04:29, 24 June 2009 (UTC)

Ahem. Tropical?? This looks rather like the Carolinas (US) to me (native habitat in red) and we do get winter there.71.236.26.74 (talk) 06:59, 24 June 2009 (UTC)

VFT is native to tropical and sub tropical rainforests. You're pic is inaccurate.Drew Smith What I've done 08:08, 24 June 2009 (UTC)

The VFT article states that "Although it has been successfully transplanted and grown in many locales around the world, it is found natively only in North and South Carolina in the United States, specifically within a 60 mile radius of Wilmington, North Carolina" (and uses a similar map to show distribution). Is this totally wrong, then? --Kurt Shaped Box (talk) 10:25, 24 June 2009 (UTC)

Yeah, according to Insectivorous plants‎ by Charles Darwin, VFT is native to south american tropical rainforests. As far as I can tell, Home Depot invented the whole "native to the carolinas" thing to sell more VFT's in the states.Drew Smith What I've done 11:54, 24 June 2009 (UTC)

Oh dear. If you're correct on that (and I have no reason to doubt you), then that false claim has been present in some form in the article since 2003!... --Kurt Shaped Box (talk) 11:59, 24 June 2009 (UTC)

It also appears to be all over the web now! --Kurt Shaped Box (talk) 12:12, 24 June 2009 (UTC)

Do you have a more recent source to that effect?

Personally, I would be very surprised if VFTs evolved somewhere without seasonal variation. APL (talk) 13:04, 24 June 2009 (UTC)

(outdent.) Oh good. I was right. Thank goodness. I hate being wrong.

From "Insectivorous Plants" by Charles Darwin.

Chapter XIII : DIONAEA MUSCIPULA.

(Emphasis Mine.)

"THIS plant, commonly called Venus' fly-trap, from the rapidity and force of its movements, is one of the most wonderful in the world.* It is a member of the small family of the Droseraceae, and is found only in the eastern part of North Carolina, growing in damp situations. The roots are small; those of a moderately fine plant which I examined consisted of two branches about 1 inch in length, springing from a bulbous enlargement. They probably serve, as in the case of Drosera, solely for the absorption of water; for a gardener, who has been very successful in the cultivation of this plant, grows it, like an epiphytic orchid, in well-drained damp moss without any soil. The form of the bilobed leaf, with its foliaceous footstalk, is shown in the accompanying drawing (fig. 12)."

Frankly, I'm ashamed of Charles Darwin for being suckered by Home Depot's conspiracy to sell more potted plants. :-) APL (talk) 13:10, 24 June 2009 (UTC)

Very odd. My copy clearly has "south american tropical rainforests" where your's has "eastern part of North Carolina". I can upload a picture of it if anyone really wants to see it. I have no doubt that my copy is defective, but I believed it for the longest time...Drew Smith What I've done 13:23, 24 June 2009 (UTC)

Could it be that your copy is a later edition (or an earlier one)? --Kurt Shaped Box (talk) 13:33, 24 June 2009 (UTC)

I have no idea. It's a few years overdue from the library in Maryland, and has no edition number, and the copyright page is either non existant, or ripped out before I got it...Drew Smith What I've done 13:55, 24 June 2009 (UTC)

To see venus fly traps in action, go to http://video.google.com/videoplay?docid=2802047796785763024
GlowWorm.

File:Insectivorous Plants Drew's copy.jpg

Please note: This text was later demonstrated to be a hoax Nil Einne (talk) 03:50, 27 August 2009 (UTC)

Drew, could you upload an image of your text passage? This would be a rather odd "error" in a book, and seems intentionally inserted, by whoever printed it. And I'm really astounded for what reason anyone should insert such a factual error in a copy of Darwin's text. --TheMaster17 (talk) 15:07, 24 June 2009 (UTC)

You'll probably have to open the file to be able to read anything, but there it is.Drew Smith What I've done 15:52, 24 June 2009 (UTC)

Googling for the phrase "and is found only in the eastern part of North Carolina, growing in damp situations" brings up this link "Insectivorous Plants" by Charles Darwin - so this is obviously not uncommon. Weird! SteveBaker (talk) 18:18, 24 June 2009 (UTC)

The copy in Project Gutenberg also says North Carolina. SteveBaker (talk) 18:29, 24 June 2009 (UTC)

I'm no expert, but I would bet money that the "North Carolina" version is more accurate to reality, regardless of whichever Darwin actually wrote. VFTs respond too well to seasonal variation to have evolved in a rain forest.

My theory is that Darwin was working from a sample sent to him from some other naturalist and somehow got confused about where it came from, then he corrected it in subsequent printings of his book.

My theory doesn't completely explain Drew's book, however. Does he unknowingly have a rare first edition? Or did some subsequent reprinting use the original un-corrected manuscript? APL (talk) 19:12, 24 June 2009 (UTC)

Interesting. A google search for Drew's version turns up nothing at all. I was hoping it would at least turn up somewhere discussing revisions to the book. APL (talk) 19:26, 24 June 2009 (UTC)

Interesting. This is something that someone in the know about VFTs (do we have any certified carnivorous plant experts here?) should probably look into. I wouldn't discount the possibility that the version you have may be the 'corrected' one. I think I'll ask over at Wikipedia:WikiProject Carnivorous plants. --Kurt Shaped Box (talk) 16:31, 24 June 2009 (UTC)

Anyone got a first edition at home to solve this one once and for all? 65.121.141.34 (talk) 18:52, 24 June 2009 (UTC)

Who would have thought that my hungry little plant would result in an investigation of Mr. Darwin? :-) Also, thanks for the responses. cheers, 10draftsdeep (talk) 20:00, 24 June 2009 (UTC)

Hi, all. I'm responding here from the note at WT:CPS. The copy of Drew's book is certainly in error. The only native populations of Dionaea are in North Carolina. There are also some naturalized populations in the Florida panhandle that come from seed spread there intentionally. I have no idea where Drew's copy comes from; is there a title page at all? Anything to indicate what edition, reprinting, etc. this would be? The correct sentence states North Carolina: 1875 London version (large pdf, page 301 of the pdf), 1875 New York version (large pdf, page 303 of the pdf), the 1888 London version that was revised by Francis Darwin (image, not a large file), and even the 1876 German version (image link). I'd like to know more about Drew's book, where it came from, when it was written, but I doubt we'll ever know why this phrase was changed. I'm exceedingly interested, though. Historical fraud? An attempt at humor? Who knows... Thanks for giving WP:CPS a heads up on this one. Interesting... Rkitko ^(talk) 21:16, 24 June 2009 (UTC)

I also note that Drew's book appears to be hand typeset, and the typesetting is different (longer length of each line) than any of the editions of Insectivorous Plants that I've ever seen. It may have been an unauthorized reproduction? --Rkitko ^(talk) 21:25, 24 June 2009 (UTC)

As I said before, it's a few years overdue back to a library in maryland, is missing the copyright page (or never had one), and mentions no edition number. I can't find anything that mentions when it was printed, though I must note that the pages are already much older than my 1960's copy of boxcar children, so it's at least 50ish years old...Drew Smith What I've done 05:34, 25 June 2009 (UTC)

This book has had 21 English language printings. The official Second Edition was in 1888, with revisions by his son. It was included in a Collected Works published in 1989, which has editors, so possibly changes were made. An online version says "...Droseraceae, and is found only in the eastern part of North Carolina...." but it is not clear which edition it is drawn from.

The typesetting in Drew's book, with unjustified margin and uneven inking, looks like it could be an old printing. More likely it was a facsimile printing of an older edition, as public libraries don't usually lend out 100 year old books.

Darwin did spend some time in various parts of South America, but none in North America. Any VFT he saw appears to be one cultivated outside its normal habitat {"..for a gardener, who has been very successful in the cultivation of this plant, grows it, like an epiphytic orchid,.."}.

The German on-line version is incomplete, and does not appear to contain this paragraph for back-translation purposes - KoolerStill (talk) 16:49, 25 June 2009 (UTC)

Please note For the benefit of future readers do note that 'Drew's copy' was later determined to be a hoax User talk:SteveBaker#Refdesk Cold Case : (permanent link) and later confirmed by Drew User talk:Drew R. Smith#I'm tired of all this (permanent link). I have added a note to the image's caption to mention this Nil Einne (talk) 03:50, 27 August 2009 (UTC)

Height and Growth

What behaviorial and environmental factors affect a person's height during growth? What is the relationship between sleep and growth? Deltawk (talk) 21:37, 23 June 2009 (UTC)

Check out Human_height#Determinants_of_growth_and_height. --Tango (talk) 22:35, 23 June 2009 (UTC)

What is the mechanism for air leaking from car tyres?

My wife and I have almost identical cars - bought new on the same day from the same car dealership. They both have run-flat tyres with tyre pressure monitoring and they are both about 4 months old.

Yesterday, the low pressure tyre pressure warning light tripped on my wife's car - and it turned out that three out of four tyres were quite low on air...so she pumped them up and reset the tyre monitor and everything seems OK today. Except that, this morning, my car showed a low pressure warning - and all four of my tyres were down to around 20psi (they are supposed to be 33psi).

The thing is that while the two cars are of identical age and near-identical type - they are driven totally differently. I push mine quite hard - my wife is doing a great "little old lady" impersonation. I drive 40 miles a day - she probably does more like 10 - although we both take 360 mile road-trips every few weekends in order to visit my son - so my milage is about twice hers.

So is the rate of air leakage merely dependent on things that these cars have in common - which would make this be an entirely expected thing? Or should I be concerned that some annoying person is letting the air out of our tyres? (Neither car is garaged right now).

What is the mechanism that allows the air to escape? I'd kinda imagined that hard cornering might affect the seal between tyre and wheel...but with one car flung into corners with extreme enthusiasm and the other driven very gently indeed - that doesn't seem to be the case.

Any ideas? SteveBaker (talk) 23:27, 23 June 2009 (UTC)

I believe that for tires in good condition the mechanism for air loss is essentially the same as the reason that balloons go flat: air diffuses through the rubber over time. Tires, being much thicker and more durable than balloons taks months to go flat as opposed to days for the typical party balloon, but I would guess the same principle applies. Of course, old and abused tires may have actual cracks in the rubber which could significantly accelerate the process. Dragons flight (talk) 00:01, 24 June 2009 (UTC)

That certainly fits that both cars lost pressure at almost identical rates...these are practically new tyres and they're "run-flat" so they have super-thick side-walls in order to support the weight of the car as they deflate. SteveBaker (talk) 01:12, 24 June 2009 (UTC)

Don't dismiss the possibility that it could just be a coincidence. --Tango (talk) 01:36, 24 June 2009 (UTC)

I certainly wouldn't dismiss coincidence...but the rate of air loss doesn't seem like a particularly random process...so that's not the most obvious explanation. SteveBaker (talk) 14:58, 24 June 2009 (UTC)

Gradual air loss probably isn't random, but running over nails in the road is. (You would have probably noticed a large puncture, but it could be something fairly small. Have you checked the pressure since pumping them up? --Tango (talk) 16:09, 24 June 2009 (UTC)

There are no obvious punctures - and the automatic tyre pressure warning system hasn't complained about low pressure - and it's been more than a day. They also didn't go all the way flat - there was about 20psi in each. So I don't think it's a rash of punctures (just as well - those runflats are hard to repair and they cost a small fortune to replace!) SteveBaker (talk) 18:03, 24 June 2009 (UTC)

In the short term, (i.e. a few years) the tires will wear evenly, and get flat at roughly the same time. As time progresses your tires will take a lot more permanent damage, and by the time the cars are ten years old your tires will deflate significantly faster than hers. It won't be too serious, but it will be annoying.Drew Smith What I've done 04:25, 24 June 2009 (UTC)

Based on my life experience of about 12 cars and the amount of times I have had air loss from tyres, I think you should think about tampering. The chances of one tyre losing air spontaneously and with careful driving are quite low: the chances of three tires losing pressure at the same time seem to me to be extremely low without some form of deliberate intervention. Richard Avery (talk) 06:28, 24 June 2009 (UTC)

Tires tend to loose air faster in warm weather. Since you are in Texas and it's summer it's bound to be nice and toasty. Your wife's car and yours are also most likely exposed to the same temperatures. Don't have any source, but IMHO air leakage occurs more through the valve than permeating through the walls. BTW I was surprised how much less often I had to inflate tires in Europe than in the US (south). --71.236.26.74 (talk) 06:43, 24 June 2009 (UTC)

It's certainly insanely hot right now - we've had a couple of 103 degF days recently. But doesn't the heat cause the air to expand and INCREASE the pressure? SteveBaker (talk) 14:58, 24 June 2009 (UTC)

Probably yes, but wouldn't this higher pressure lead to even faster diffusion of the air through whatever route it is taking (walls or valve)? As far as I remember my physics training, this should be the case. --TheMaster17 (talk) 15:10, 24 June 2009 (UTC)

Heat will expand air and increase pressure, which helps the tire lose air more quickly if it is indeed migrating out through the rubber. 65.121.141.34 (talk) 15:08, 24 June 2009 (UTC)

Well, perhaps - but wouldn't that just put the pressure back to where it usually is (albeit with less air)? We might expect an abrupt drop in pressure when the air temperature drops - but this is summer in Texas...it hardly even cools off at night! SteveBaker (talk) 18:03, 24 June 2009 (UTC)

But hang on a minute, I thought the original issue was the difference in tyre pressure in the two identical cars. Any external effect might be expected to show the same results on both cars, so if the temperature is thought to be to blame (I can't for the life of me see why. After 7 years living in southern Spain where summers temperature regularly reached 110F I never had a single problem with low tyre pressure) surely both cars should show similar problems. Seems to me we are looking for a cause that affects Steve's car but not his wife's. Or have I got this wrong? Richard Avery (talk) 19:57, 24 June 2009 (UTC)

I don't think you understood the question. The two cars DO produce identical results - suspiciously identical given how differently they are being driven on a daily basis. If the air loss is only due to weather, rubber composition, age, etc - then I shouldn't be surprised that the low pressure warning systems on the two cars triggered within 24 hours of each other...but I find it hard to believe that driving style/speed/etc and number of miles driven has absolutely zero impact, which makes me suspect that some idiot has been letting air out of our tyres for some stupid reason. SteveBaker (talk) 22:38, 24 June 2009 (UTC)

Ah, Yes, Always read the question carefully before attempting your answer. Richard Avery (talk) 06:03, 25 June 2009 (UTC)

(unindent)In my opinion driving styles and miles driven must have an influence: Driving more (and faster) would heat up the tires for a longer time, speeding up diffusion. And I think we all agree that whatever route out the air is taking, diffusion is the mechanism. So Steve, I think you have a malicious neighbor ;-) --TheMaster17 (talk) 08:07, 25 June 2009 (UTC)