Wikipedia:Reference desk/Archives/Science/2008 June 18

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June 18

Metal detectors and gold

I'm watching Law & Order: Criminal Intent, and the detective says gold doesn't set of (security) metal detectors. Is that true? Thanks. Imagine Reason (talk) 03:30, 18 June 2008 (UTC)

Pretty sure all conductors set off metal detectors. My high school physics teacher (who had a Ph.D. in physics, actually) did tell us before 9/11 that you can theoretically make a gun from lead and walk extremely slowly through and not trigger it though. --Wirbelwindヴィルヴェルヴィント (talk) 03:48, 18 June 2008 (UTC)

Security metal detectors use alternating current to detect conductive metals. Gold is a conductor. Please see metal detector#Security screening for more details. By the way, I should mention before other Wikipedians start embarassing me that I am learning the art of sucking up to StuRat. --Mayfare (talk) 04:03, 18 June 2008 (UTC)

Metal_detector#Discriminators mentions gold, but I've little idea what it says. Imagine Reason (talk) 05:44, 18 June 2008 (UTC)

It sounds to me like it's referring to metal detectors for detecting old treasure or lost valuable items. For those sort of metal detectors, you probably want them to detect gold, but not necessarily iron or other metals likely to be used in items that you are not interested in finding. You therefore need to discriminate between these sort of metals. The trouble is, according to the article tinfoil is close to gold from what the metal detector sees, therefore there is a strong risk you will make a metal detector that misses out not only tinfoil, but gold as well. However presuming you are referring to the types used in airports, my guess is they want to detect most metals. The primary discrimination is probably in size. You don't want them to detect any tiny bits of metal as you may end up wasting too much time having to manually search people for any such tiny bits of metal and/or may get too complacent. Nil Einne (talk) 10:26, 18 June 2008 (UTC)

Question about inventors/mechanical engineers.

Hello,

Does anyone have any information about Henry Boltrek? He is the man who invented the modular escalator and many other people-moving items. I have been able to find information on some of his patents, and on his service record during WWII in Normandy and the Battle of the Bulge. However, there does not seem to be much on him specifically as an inventor. Thanks in advance.

Cheers,

Josh —Preceding unsigned comment added by 123.200.254.253 (talk) 04:26, 18 June 2008 (UTC)

Bees & Orangutans

What is the specific term used for male bees? What are female & male orangutans called? Thanks.Macmayi (talk) 06:42, 18 June 2008 (UTC)

Male bees are drones. Mac Davis (talk) 08:27, 18 June 2008 (UTC)

As far as I'm aware, there are no specific male/female names for most or all primates. They're simply male/female. [1] However you could call them 'orangutan jantan' for males and 'orangutan betina' for females I guess since the name originates from Malay... Nil Einne (talk) 10:19, 18 June 2008 (UTC)

Thank you Mac Davis & Nil Einne. Info & website given was helpful.Macmayi (talk) 10:45, 18 June 2008 (UTC)

I am searching for a circuit of blood pressure monitoring machine

Dear Sir I am searching for a circuit which is used in making blood pressure monitoring devices. if you have any information about such type of circuit can you please send it on my email-id removed i will be really thankful to you warm regards Devinder —Preceding unsigned comment added by Tvmteleshopping (talk • contribs) 06:45, 18 June 2008 (UTC)

Hi, I've taken the liberty of removing your email address from your post, to prevent spam. We answer questions here on this board. AlmostReadytoFly (talk) 08:47, 18 June 2008 (UTC)

Are you searching for a circuit board or circuit diagram ? StuRat (talk) 13:11, 18 June 2008 (UTC)

What is the SPF of hair?

A coworker came back from a skiiing trip and got a short haircut and beard trim after he got back. I could clearly see a tan line around his forehead and neck where the hair once was. It made me wonder what SPF does hair have and at what density? For example, does body hair ever reach the density to provide protection or is it just on the head where hair is densest? --69.149.215.102 (talk) 12:47, 18 June 2008 (UTC)

I believe dark hair is completely opaque to ultraviolet light, so you just need enough to block the sunlight and that provide's an infinite Sunlight Protection Factor. I'm not sure about blonde and/or white hair, that may not be completely opaque to UV. StuRat (talk) 13:08, 18 June 2008 (UTC)

Sorry to nitpick, Sturat, but the entire point of SPF is to quantify opacity, beyond the binary "opaque"/"transparent". Nothing is "opaque" if the incident radiation is of sufficient intensity. Unfortunately I have no idea what the relative opacity of hair would be with respect to standard commercially available sun-block. Nimur (talk) 14:48, 20 June 2008 (UTC)

Nothing is opaque ? I beg to differ, but a meter thick wall of steel is rather opaque to UV, unless you have enough of it to melt the steel. StuRat (talk) 05:41, 21 June 2008 (UTC)

Vegetable oil in diesel motor

May I use vegetable oil in the diesel motor of a car? Would be a mixture 50/50 be possible? 80.58.205.37 (talk) 14:32, 18 June 2008 (UTC)

Have you read our articles on biodiesel and vegetable oil used as fuel? — Lomn 14:40, 18 June 2008 (UTC)

New vegetable oil will likely cost more than diesel, even at today's inflated prices. However, if you get used oil from a restaurant and filter it, that makes for cheap fuel, and, unlike diesel, it smells good. StuRat (talk) 15:16, 18 June 2008 (UTC)

Many diesel engines (especially the older ones) are quite satisfied with running used vegetable oil. You may want to check with the manufacturer of your vehicle, and more-so if it is currently under warranty. That said, my family owns and 1964 Mercedes-Benz diesel pontoon-style station wagon (former ambulance) that runs with used vegetable oil from a local restaurant. We are happy to take their waste oil as fuel, and they are happy because they no longer must pay to dispose of it. Depending on your climate (notably, the cold areas), you may need to heat your oil before combustion to lower the viscosity. Because we live in northeast USA where there are often below 0^•C temperatures, we still use regular #2 diesel in the stock fuel tank and have constructed an alternate tank with heated pipes for the vegetable oil. The car is started on diesel and run until the oil system has heated, and the fuel is then drawn from the oil tank by way of a solenoid fuel switch and pump.

By using 50/50 oil/diesel, and depending on climate, you may reduce the need to heat your oil. Good luck. Freedomlinux (talk) 15:33, 18 June 2008 (UTC)

I'm not sure about that. Wouldn't the part that congeals just separate out and clog up the plumbing ? StuRat (talk) 16:27, 18 June 2008 (UTC)

Yes. Same problem with mixing diesel and unleaded gasoline, or mixing ethanol and gasoline, or mixing... About the only thing I've ever found to mix well for a reasonable amount of time is 10W40 oil and gasoline - primarily used in 2-stroke engines. It doesn't work as well as proper 2-stroke oil, but it is good enough if you mix, pour, and ride right away. -- kainaw™ 00:29, 19 June 2008 (UTC)

One liter cooking oil costs 0.79 euros and one liter diesel 1.45 euros. I suppose that the cooking oil has less energy than the diesel, but it is still much cheaper. 80.58.205.37 (talk) 12:27, 19 June 2008 (UTC)

Wow, I guess that's due to higher fuel taxes in Europe. I don't think vegetable oil is cheaper in the US. StuRat (talk) 14:14, 20 June 2008 (UTC)

Specifically to the original question, depending on your vehicle yes you can mix veggie oil directly with diesel, and use it as fuel. You may run into difficulties with particular model, but I have on several occasions added cooking oil directly to my the tank of my 82 Mercedes Diesel. These models years are notorious durable (78-83). Yes, generally veg oil does gel at lower temps than diesel, especially the weather treated diesel you find in cold climates, during the winter months. In some countries this may be illegal, in that Environmental laws may limit the fuels that are permissible in cars to the ones that are government approved. If you are going to make a habit of running Veg Oil in your car, you may still want to filter it, as inline fuel filters are far to permissive to filter raw fuels, and although I don't know for a fact the raw oils are going to pose a problem, it seems possible/likely that the are not filtered down to the level of engine fuel - Will K Jan 22 2010

reaction torque

i want to know about reaction torques , where can i find some detailed and relaible account?? like the first 2 laws of motion can be extended to rotational dynamics as well, is it always right to say that to evry torque there's an equal and opp torque???--scoobydoo (talk) 15:06, 18 June 2008 (UTC)

No, because linear motion can be changed into rotational motion and vice versa. For example, after a cue stick hits a pool ball, the ball has a torque, although the cue stick had none. This is similar to the laws of conservation of mass and conservation of energy, which aren't conserved under E=mc², but freely converted into one another.StuRat (talk) 15:12, 18 June 2008 (UTC)

Yes, for every torque there is an equal and opposite torque. The conservation of linear momentum means that forces in a closed system sum to zero, and similarly, the conservation of angular momentum means that torques in a closed system sum to zero. Note that to calculate torque or angular momentum, you need to pick an axis. If you change the axis halfway through the calculation, you'll find that the torques don't sum to zero anymore.

In response to StuRat: there is no physical difference between linear and rotational motion, it's just two ways of looking at motion. Movement in a straight line can be broken down into angular and radial velocity with respect to an axis. -- Tim Starling (talk) 18:09, 18 June 2008 (UTC)

Male animals killing young

Was just watching in a documentary how male lions (when a new alpha takes over as dominant in the pack) kill any cubs hanging around, so that his genes will be dominant and so wiping out genes from rivals (was so sad to see the little lion cubs trying to uselessly defend themselves, it broke my heart). I have also read that bears do too, but I don't think canines like wolves do, or herbivores like elephants, or whales/dolphins.Not sure if there are cases of humans doing this. In which kind of animal species do this occur then? (I can only think of lions and bears). Thanks for info, --AlexSuricata (talk) 15:31, 18 June 2008 (UTC)

I'm pretty sure cats do it sometimes (see [2]) Nil Einne (talk) 16:12, 18 June 2008 (UTC)

I think it's rather common in the mammalian world. Infanticide (zoology) has lots of info and this link does, too. — Scientizzle 16:15, 18 June 2008 (UTC)

There is some analogy with a new leader in a hereditary monarchy killing off all close contenders to the throne, including brothers, cousins, and uncles. I think this was popular during some periods in Byzantine history, and in the Osman empire (must be the water of the Bosporus ;-). --Stephan Schulz (talk) 16:35, 18 June 2008 (UTC)

Isn't that fairly different because he's killing off those closely related to him (becuase they may kill him before he kills them) rather then those not at all related to him (which is why lions etc do it). The lion equivalent is like Scar trying to kill Simba and Mufasa (except lions don't actually have hereditary monarchies in practice...) Nil Einne (talk) 17:32, 18 June 2008 (UTC)

There are certainly past examples, such as the Russian Revolution (1917), where new leaders gained power that they had no heriditary right to and consequently feel it is useful/necessary to exterminate everyone with a bloodline claim to the power they are trying to preserve. Dragons flight (talk) 23:09, 18 June 2008 (UTC)

We see a usually more muted version of this genetic competition in humans, whose step-parents and step-children find it hard sometimes to be even genial to each other. On a tangential topic, humans (eg Spartacus) and other animals are known to kill weak offsprings. Some wonder if abortions are a technological implementation of that desire sometimes. Imagine Reason (talk) 05:10, 19 June 2008 (UTC)

Abortions in response to a detected abnormality in the foetus, certainly. The usually stated goal is to avoid the child suffering, but avoiding the "waste" of resources involved in bringing up a child that probably won't survive to carry on the bloodline probably does go through people's minds. --Tango (talk) 12:08, 19 June 2008 (UTC)

Surely you mean Spartans, not Spartacus? Algebraist 15:52, 19 June 2008 (UTC)

LOL, yes. Thanks for the correction. Imagine Reason (talk) 03:06, 21 June 2008 (UTC)

Coefficient of restitution

Hi! What does the coefficient of restitution depend on? I know that it's the ratio of velocity of separation of 2 bodies after collision to the velocity of approach, but how can we determine e, if we just know all the properties of the body, including initial velocity? It will only be of use, if we could determine it without knowing the final velocities, so that we may predict the velocities after collision using the value of e for 2 bodies, right? 116.68.77.43 (talk) 15:46, 18 June 2008 (UTC) A 15-year old HELLO?? Is there anybody to answer this question???? This is about inelastic collisions, what you have in school-level physics..................116.68.75.162 (talk) 14:10, 20 June 2008 (UTC) A 15-year old

aircraft carriers

aircraft carriers with a flat deck must have their bridge, conning tower, etc on one side. Now if you look here (image thumbnailed to reduce size -- TenOfAllTrades(talk)), these are all on the starboard (right hand) side. Why? Are there any with it all on the left hand side?

Early aircraft carriers varied wildly in design, with the British going so far as to retain the center superstructure on early efforts like HMS Furious. HMS Eagle appears to have been the first carrier to sport the starboard island design, and in lieu of evidence to the contrary, it seems reasonable to assume it was an arbitrary choice that became convention. Note, though, that many other early carriers, such as the USS Langley, used no superstructure, and the Japanese aircraft carrier Akagi used a port-side superstructure. — Lomn 17:08, 18 June 2008 (UTC)

A correction: our article on flight decks notes that rotary engines on early carrier aircraft tended to cause yaw to port, so a starboard-side superstructure reduced the odds of collision on takeoff and landing. — Lomn 17:23, 18 June 2008 (UTC)

Another possibility is that the photo is inexplicably reversed, as many images everywhere are sometimes. You may have noticed this in places like the internet or TV. 75.171.250.184 (talk) 20:40, 18 June 2008 (UTC)

The pennant numbers painted on the side of the ships disagree with your hypothesis. —Preceding unsigned comment added by 86.166.234.157 (talk) 21:52, 18 June 2008 (UTC)

Additionally, the article specifically notes that the Akagi and Hiryu were constructed with port-side superstructures in an attempt to improve multi-carrier flight operations. — Lomn 22:40, 18 June 2008 (UTC)

Just speculating here, but wouldn't the starboard-side superstructure let the signal-flag people hide where it's safe and use their right hand for signalling? That's assuming take-off goes forward and landing comes from the stern. Franamax (talk) 23:07, 19 June 2008 (UTC)

Assuming you're talking about the landing signal officer, in the US Navy they've always stood on the port side of the flight deck. --Carnildo (talk) 20:56, 20 June 2008 (UTC)

Juniper Trees

If I cut off the top 10 feet on a 40 foot Juniper tree, will that kill the tree, or will it just stop the growth upward of the main trunk, with the remaining branches with green leaves, etc., continuing to live and grow ? —Preceding unsigned comment added by 66.220.120.183 (talk) 17:09, 18 June 2008 (UTC)

Googling for "topping trees" has nothing nice to say about that practice. --Sean 20:27, 18 June 2008 (UTC)

Catching seagulls

According to the SAS Survival Guide, seagulls can be caught by tying a rock to some food and throwing it up into the air. Apparently they will catch it midair in their mouths and drop to the ground, too heavy to fly, where they can be caught and presumably consumed. My question is a) does this actually work and if possible, b) how heavy of a rock would you need? bibliomaniac15 22:33, 18 June 2008 (UTC)

I've read the same survival guide, and consider it a reliable source, so I expect it works. I don't imagine a particularly large rock is required, but I don't really know. A small (and, importantly, unexpected) change in weight ought to be enough to confuse the gull. You would need to kill it (club it, probably) very quickly once it crashes, since it may be able to take off again once it's prepared for the extra weight. At the very least, it could escape on foot. --Tango (talk) 23:05, 18 June 2008 (UTC)

I think you should just use the heaviest rock you can throw at least as long as it can stay in the air long enough for the seagull to snatch the bait.--Apollonius 1236 (talk) 00:14, 21 June 2008 (UTC)

I'll get slapped for original research, but here goes anyway...

As a kid, before the advent of peta and environmentalism and all that, every now and then we'd go down to the beach (in Seattle), buy an order of Fish & Chips with extra chips, and go across the street to eat it. One order of F&C was a plenty good lunch portion; the extra order of french fries was to break into inch-long pieces and toss into the air, the sole purpose of which was to provoke a Seagull Fight.

So, in answer to part of the question, the seagulls definitely have the flight skills to pick off pieces of airborne food.

That said, I just can't imagine it working by wrapping a piece of cheese around a rock, for example. You'd have better luck tying a length -- 10 feet? -- of string or fishline around the cheese or frenchfry, and hold the rock in your hand; the bird will typically swallow the bait whole. The trick, then, would be to reel in the bird before he disgorges it.

Yeah, that could work... --Danh, 70.59.79.230 (talk) 23:36, 18 June 2008 (UTC)

If you want to be sure of catching your meal, use a fishing hook on the end of the line (or fashion a hook yourself). Anglers sometimes to have to reel bait-snatching gulls in to free them - once the hook goes in, they're completely stuck. They usually panic and entangle themselves in the line too - which would be a plus for a prospective hunter.

You could also have a fellow survivor bury you horizontally in the sand, leaving only your face exposed (which they would then cover with a towel or similar). Sprinkle some bait atop your shallow grave, wait until you feel a gull land in the area of your chest, then grab it from below in true ant lion style. There are loads of videos on YouTube of people doing this - the gulls never, ever seem to expect an attack from beneath. --Kurt Shaped Box (talk) 23:54, 18 June 2008 (UTC)

Hydrogen cars

Sheik Yamani predicted a few things about oil, cost of, etc years ago according to a recent interview. In the light of oil reserves lasting the next 20 to 30 years, he now predicts cars will run on hydrogen. How will that work? Julia Rossi (talk) 23:45, 18 June 2008 (UTC)

You can use hydrogen as fuel in an internal combustion engine. I don't know the details, but the wankel engine used in the RX8 was designed to also run on hydrogen. Obviously this would require some changes, such as to the fuel system, but I believe the engine internals don't need to change for this. One problem ecologically is coming up with ways of getting hydrogen fuel that don't screw up the environment. See also Hydrogen economy. Friday (talk) 23:50, 18 June 2008 (UTC)

Using hydrogen in internal combustion engines is possible. But if you have clean hydrogen, it's much better to use in in fuel cells to create electricity and drive your electric car, with less noise, better torque, fewer moving parts, and, usually, higher efficiency. --Stephan Schulz (talk) 12:22, 19 June 2008 (UTC)

Thanks Friday, there's probably nothing that wouldn't screw up the environment – even if it was plain water. Why wouldn't someone like Yamani suggest hydrogen and not, say canola oil? (which yes, would also probably wreck things). Julia Rossi (talk) 00:04, 19 June 2008 (UTC)

If you pretend that hydrogen is freely available from the hydrogen fairies from gumdrop forest and only look at the cars, hydrogen is a clean fuel. When it burns, it creates water. Oil (regardless of the kind of oil used in combustion engines) is a hydrocarbon. The hydro part of the hydrocarbon is hydrogen - nice and clean. The carbon part is, as is easy to guess, carbon. It creates carbon dioxide, carbon monoxide, and can even mix with pollutants to get a few more creative things going. So, the dream of a clean fuel continually points to hydrogen. Of course, the problem is getting the hydrogen. Those damn hydrogen fairies haven't done their part to make this all work yet. -- kainaw™ 00:10, 19 June 2008 (UTC)

Ironically hydrogen isn't scarce. It's the most abundant element in the universe. It's just rare on Earth (when not bonded in a molecule). You can extract it from water through Electrolosis though. ScienceApe (talk) 02:53, 19 June 2008 (UTC)

Yep. Find a clean industrial-scale source of electricity and you can generate all the hydrogen you need. It's just a problem of finding that power -- in effect, the environmental problem has only been shoved upstream. — Lomn 02:50, 19 June 2008 (UTC)

Nuclear power plants seem to be the solution. ScienceApe (talk) 02:55, 19 June 2008 (UTC)

I concur, and from a global warming perspective, nuclear is ideal. That consensus has not yet emerged, however, from a general environmental perspective. — Lomn 12:57, 19 June 2008 (UTC)

Note however if your hydrocarbon is produced by plants then effectively it all comes the atmosphere, there is no net addition of carbon dioxide provided you don't use non biofuel sources to grow the plants, or process the biofuels. Of course, if you are using petroleum to power your car or make fertilisers then there is... The other problem is that the efficiency can be low since you produce a lot of waste that you don't use, which means you need a lot of land. And there may be a high initial cost of greenhouse gas emission to the atmosphere, if you are clearing existing forests or swamps, although this is only a one time thing. There is also the additional cost of loss or primary forest or swamps and the associated ecological cost. Then there are the potential additional polutants you mentioned and the potential competition with food. But from a purely carbon dioxide POV, you can't really argue hydrogen is 'cleaner' then biofuels provided the conditions I mentioned are met (post land-cleared, no use of petroleum or other 'unclean' sources to produce the biofuels) Nil Einne (talk) 10:38, 19 June 2008 (UTC)

I think he means that since oil reserves will be exhausted, the world will turn to its second-favourite energy source, coal. Hydrogen can be used to store energy from the coal, for use in cars. Thus we can continue polluting the environment unabated for perhaps another 200 years, despite the exhaustion of oil reserves. -- Tim Starling (talk) 06:16, 19 June 2008 (UTC)

I'm not so sure. AFAIK, there are no significant coal reserves in Saudi Arabia. Remember who Yamani is, I suspect his hope/belief is that solar power would be used to produce a big proportion of the hydrogen. Deserts are of course excellent places for solar power... So the Middle Eastern economies including Saudi Arabia will go from being all about oil to being all about hydrogen. This also partially speaks as to why he thinks hydrogen and not biofuels. Growing plants in deserts is never easy. Producing hydrogen is no problem in a desert since you only need water and even sea water is fine. Of course there are various problems to solve including the efficient production of hydrogen and transport of hydrogen (which is going to be more difficult then biofuels). Nil Einne (talk) 10:31, 19 June 2008 (UTC)

Noone linked Hydrogen vehicle so I thought I should. Zain Ebrahim (talk) 10:05, 19 June 2008 (UTC)

I'll predict here that hydrogen will turn out to be a bad idea, at least in the gaseous form. It's such a small molecule that it creeps into everything and corrodes it, you need stainless steel to contain it, the welds have to be perfect, it's not sustainable as an infrastructure. We'll go down that path and then discover how immensely reactive it is. You think breaching a gasoline tank causes an explosion? Just wait until car crashes split open a tank of hydrogen. I'm just sayin'. Franamax (talk) 23:26, 19 June 2008 (UTC)

Hydrogen embrittlement is a problem, but plain corrosion is not that bad. And hydrogen will burn, but is usually well-behaved in doing so. Remember, we have used large amounts of hydrogen in traffic before. It was not perfect, but surprisingly safe. --Stephan Schulz (talk) 23:42, 19 June 2008 (UTC)

Gotta love that blue "before" link, and scrolling down to the "Oh, the humanity" picture - although most of the deaths were from jumping to the ground, and the fire was on the canopy glue, not the hydrogen contents. You're right that embrittlement is the major problem, although as I recall from my refinery days, the cracks and crevices were corrosion initiators. Hydrogen can find the least flaws and exploit them. Ten years distant and no sources to hand, so I'll leave it go. I'll hold back my commentary until a tank of pressurized hydrogen is released into the midst of a vehicle accident. Highly reactive reducing substance meets abundant oxidator, i.e. the atmosphere. Just like the concept of pumping CO2 underground, it all works fine - until it breaks. Just sayin' is all... Franamax (talk) 05:03, 20 June 2008 (UTC)

Is hydrogen embrittlement as much of a problem if liquid hydrogen is used? Intuitively if the H2 is not under such high pressure, it would not penetrate metal so easily. But I don't know if that's true.Fletcher (talk) 13:58, 20 June 2008 (UTC)

I don't think anyone is seriously considering storing compressed gaseous hydrogen in production cars. The weight of the pressure vessel would be prohibitive. See Hydrogen storage for lots of more practical ideas. -- Tim Starling (talk) 14:00, 20 June 2008 (UTC)