Wikipedia:Reference desk/Archives/Science/2007 July 30

= July 30 =

six-legged logging robot
I remember watching a show on the history channel (I believe) about the history of logging. When it got up to modern innovations, there was a six-legged robot which I believe was Swedish and roughly the size of a truck. It was designed with legs so as to be able to navigate over obstacles and difficult terrain, and to avoid doing damage to the forest floor--the legs would spread the weight out, and didn't scuff up the turf like wheels or treads do.

Unfortunately I can't manage to find any of this online. There's the occasional mention in robotics or mecha fandom forums, but all the links are dead. I have yet to even find a picture. Google searches turn up a million different things, like buggy chat-logging bots, but not giant forest logging robot bugs. Does anyone know more about this, or know where I can find more information? 172.145.184.137 00:19, 30 July 2007 (UTC)


 * I guess it's mentioned here: Talk:Mecha (however, the address given there doesn't seem to work). It seems to be made by Finnish company "Plustech Oy" (or something like that). Such search in Google actually gives some links with pictures. There also seem to be some scientific articles mentioning it. --Martynas Patasius 01:00, 30 July 2007 (UTC)


 * Here's a rad video:  --TotoBaggins 13:39, 30 July 2007 (UTC)

cfl lamps
why cf lamps are said to lessen the electricity expense?
 * Why don't question askers bother to read articles like Fluorescent lamp before they ask? Nil Einne 02:07, 30 July 2007 (UTC)


 * Or the even more on point Compact fluorescent lamp article.


 * Atlant 11:58, 30 July 2007 (UTC)


 * Short answer: they are more efficient. They use less electric energy to produce the same amount of light.  (Also, they last longer than conventional incandescent bulbs.) —Steve Summit (talk) 03:12, 30 July 2007 (UTC)
 * another short answer: they don't make as much heat. Gzuckier 17:38, 30 July 2007 (UTC)

A Question
I understand that I shouldn't be asking help for my homework, but I'm merely seeking guidance here and have conjured up a answer previously... So here it is, the question asks to describe the change of speed over time for 'the first 4 seconds of a sprinter's 100 m race', and here is the possible answer:

It started off at high speed (due t the first burst of speed from the launch pad, or whatever it is called) then the speed drops slightly (as the energy from the outburst is countered by resistance...) then the speed builds up until it reaches a point (I'm wonderin if this point should be higher/lower/equal to the first burst of speed) then levels off til the end.

Thanks!


 * That answer doesn't make sense. "as the energy from the outburst is countered by resistance"?!?! I certainly don't believe that the speed drops at any point in the first four seconds.  Your words reveal a serious misunderstanding of simple Newtonian mechanics which is (probably) what the question is trying to test you on...and you don't know it...at all.  Firstly - you need to clearly understand the difference between work, force and energy and between speed/velocity and accelleration and (perhaps) how drag works...although I'd be surprised if it were much of a factor here - the question probably even says "ignoring the effects of air resistance" somewhere.  Since this is homework, I'm not going to tell you the answer.  However, I'd like to point out that the reason you get homework is not to have you find the answer - but to learn how to get it.  So start reading those six articles (or your physics text book which probably states it in simpler language) and maybe you'll learn something!  Oh - and the 'launch pad' things are called 'blocks'.

Sorry for the trouble, I guess I wasn't thinking straight earlier on... well, I think the first bit of my previous 'answer' ought to be ignored, leaving the later bit where the speed builds up from 0m/s to a certain pt then levels til the end...right this time?


 * There would be an almost constant acceleration to near 10m/s in something like 0.1 secs, then for the rest of the 4 secs the runner would decelerate slightly when both feet are off the ground (air resistance), then re-accelerate when one of his legs are on the ground. I don't know the period of the average 100m runner's stride, it's probably a cycle of period 0.4s or thereabouts, so a periodic dip every 0.2s or so.
 * This is completely guess work and OR :) - maybe they accelerate over a few strides, but still i wouldnt imagine much acceleration over the last 3 seconds besides keeping up with air resistance Capuchin 09:47, 30 July 2007 (UTC)
 * I really don't believe air resistance is significant at 10mph. The formula for air resistance says that the drag force is proportional to the square of the speed - and the amount of power consumed to overcome that drag is proportional to the cube of the speed.
 * We know that at 120mph or so (terminal velocity for a skydiver with his arms and legs spread out to deliberately slow himself down) the drag force is equal to the weight of your body. At half that speed, (60mph) the drag is four times smaller. At 30mph it's 16 times smaller, at 15mph it's 64 times slower - so at a 10mph run (and for someone who has arms and legs not splayed out with a baggy paracuting suit) - the force due to drag is maybe 1/200th of the weight of our skydiver...tiny...having lighter shoes will have a bigger effect! SteveBaker 23:38, 30 July 2007 (UTC)
 * Not true! For sprints, air resistance is absolutely critical.  The acceleration of a sprinter is much less than 1 g.  A world class 100 m averages closer to 20 mph (actually a bit faster than that).  To cover 100 m in 10 s, the acceleration is 2 m/s², that is, 0.2 g.  If the air resistance at 20 mph is 1/50 of the runner's body weight, that's a 10% effect in how fast they can accelerate!  Even a 1% difference would be quite significant for races.  OK, I see now that you may have meant the runner doesn't slow down appreciably over the course of a single stride.  That is certainly true.  --Reuben 01:27, 31 July 2007 (UTC)
 * Exactly - sure there is some air resistance - but it's the same for everyone - so the fact that a 1% difference in accelleration can win or lose the race isn't the point here. The question is whether it has the ability to slow you down between paces to any measurable degree...I really doubt that.  I guess one significant question is whether the sprinter endeavors to keep one foot pushing against the track at all times - or whether he/she spends appreciable time in free-fall with neither foot providing traction as (say) a hurdler would?  Logically - to get the most from your muscles, you'd want to always be pushing against the track because 'air time' is wasted.  But I guess that's simply geometrically impossible under the circumstances - if one foot was always on the ground at all times, that would be a walking race - not running.  But as far as the OP is concerned, he has far bigger concerns with getting this homework done. Just ignore air resistance! SteveBaker 01:55, 31 July 2007 (UTC)

Computer games causing migraines
Hope this in the right place - it seemed to vaguely fit under 'biology', heh.

3D games like first person shooters and platform games give me massive migraines and make me feel sick - curious as to whether there is an article about this on Wikipedia? I'd search for it myself, but I'm not really sure what to look for :) Thanks in advance! Kamryn · Talk 10:02, 30 July 2007 (UTC)


 * Oh never mind - found what I was looking for in motion sickness :) Kamryn · Talk 10:07, 30 July 2007 (UTC)


 * There are other possible reasons why you could have a headache or feel sick after playing games. Are you playing on a TV or Computer Monitor? If you are on a CRT monitor, make sure you have the refresh rate turned up higher. Two other things that work for me (Personal Research, don't take it as fact, but motion sickness is depedant on the person yes? :D) is "zooming-out" in those types of games, I.E. play in third person mode if possible instead of looking through the "eyes" of the character. Also, incredibly smooth animation/frame rates gives me a headache, perhaps due to the fluidity of the motion, so I tend to turn the graphics options a little higher to maintain at around 30FPS (which spikes downards and causes jerkiness so often) instead of higher frame rates. --GTPoompt (talk) 12:55, 30 July 2007 (UTC)


 * My little sister has never been able to play 3D video games (well, if it's locked in a 2D perspective with "depth" that's one thing but you know what I mean) because she's unable to visualize the full 3D environment around her from the image data available at any one time on a 2D screen. This isn't a matter of fogetting what was behind you the instant you turn around, but rather not being able to construct a 3D visualization (or usually more importantly just a 2D overhead view) from just the player's perspective. And games with dynamic third-person cameras are even worse for her since it's an extra level of disorientation when the camera moves relative to the character. Also she's disoriented by the 3D projection onto the screen- I guess she overrelys on parallax effects and such to assist in depth perception. Any one of these things could be your problem --⁪frotht 15:14, 30 July 2007 (UTC)


 * How old is your sister? That really surprised me: "she's unable to visualize the full 3D environment around her from the image data available at any one time on a 2D screen", unless, maybe, she's very young. --Taraborn 22:38, 30 July 2007 (UTC)


 * This sounds strange since ultimately the image is rendered on to the 2-D retina on the back of the eyeball. It's rather easy to fool.  In fact, can she watch movies which is basically the same principle.  --Tbeatty 06:21, 31 July 2007 (UTC)


 * She's 14! As for movies, you don't exactly need to do anything to watch a movie, while in a game you need to have a pretty firm grasp of your environment for tasks such as path finding and defending yourself from enemies... in games like counter-strike (especially on smaller maps like gg, fy, aim, etc) you need to know right where your team is covering and where you're sure no enemy could be if you don't want to get shot in the side or the back --⁪frotht 16:17, 31 July 2007 (UTC)


 * I'm also pretty sensitive to some kinds of game (and other 3D graphic display)...and I'm a professional game programmer! Several things I've observed:
 * I'm more affected when someone else is in control than when I'm playing...yet I can watch 3D animated movies on TV or in a movie theatre without any problems???
 * The larger the screen - the worse it is. Try using a smaller screen.
 * The greater the disparity between the field of view of the camera in the game and my own eyes, the worse it is.  Most games use a wider field of view than our real eyes - and we sit so far back from the screen (typically) that the screen subtends maybe 20 degrees of your view - where the game is drawing maybe 60 to 90 degrees.  This is odd because it's in direct contravention of (2)...but there it is.
 * Poor framerates make it much worse. A game that runs at 60Hz is much less troubling than one that runs at 20Hz.
 * In games where the eyepoint skids sideways as you turn your avatar around - they'll make my stomach turn sour in less than a minute - guaranteed!
 * 1st person games are much worse than 3rd person...except for driving games where the reverse is the case. (Go figure?!)
 * 2D games and 3D 'god' games like Civ or SimCity where there is no perspective, never bother me.
 * Some specific games are bad - for no reason I can explain. All of the James Bond games on Nintendo machines make me want to puke...no matter whether I play in 1st person or 3rd person or even in parts of the game where you're driving a car or something.  Dunno why.
 * As for your sister...it's rare these days but: Babies are commonly somewhat cross-eyed at birth and usually learn to focus and get their eyes lined up within just a few days. In a few rare cases where this doesn't happen and the baby stays cross-eyed for weeks or months, the part of the brain that is responsible for 3D 'understanding' never develops.  Of people born in the 1970's or earlier, this is amazingly common - maybe 10% of people have the problem.  These people are often unaware of their condition until they try to use 3D glasses or those stereogram things...which do nothing for them.  More recently, doctors test babies for this problem and work to fix it before it's a permenant problem - so it's much rarer these days.  I did see somewhere an article on the 'net by a lady who managed to teach herself to see in real 3D at age 30 or 40 years - so it's possible that it can still be fixed. SteveBaker 23:22, 30 July 2007 (UTC)
 * I'm also one of the people for whom some video games trigger migraines. I first discovered it with DOOM, and since then I've noticed that pretty much any first-person shooter does the same thing. A few other games do it -- I think the frame rate does have something to do with it. Pity, too; it's usually the games I'm most interested in that do it. (Messes me up for a whole day; requires crawling under the pillow in a dark room.) --jpgordon&#8711;&#8710;&#8711;&#8710; 22:18, 31 July 2007 (UTC)


 * There was actually a really interesting article by Oliver Saks in the New Yorker a few months ago about binocular vision and the amazing fact that some people who do not have it (being born cross-eyed or otherwise unable to physically form a coherent binocular image) were able to reasonably develop it at a much later age in life after a lot of terribly difficult training. I forget the details but it was pretty interesting, and Saks suggested that this probably meant that the "you need to develop it when young or it is impossible" paradigm (which has been around for a loonggg time) is probably not the whole story. --24.147.86.187 23:57, 30 July 2007 (UTC)
 * Just an FYI: it's Oliver Sacks. 38.112.225.84 06:10, 31 July 2007 (UTC)


 * Right - that's true. As I explained, there was a lady on NPR who managed to train herself to see in 3D for the first time at age maybe 30/40 years (it must have been a stunning revelation!) - and gradually, over the course of many months gained full 3D vision. So yeah - it's possible to get it back.  But I still think it's true to say that if you didn't just happen to get it right soon after birth then it's not going to come back "naturally" when the vision problem is corrected - it takes active training...and the suggestion was that it's neither easy nor certain. See  for example. (Oh great...they called the patient "Stereo Sue"...sheesh!) SteveBaker 01:40, 31 July 2007 (UTC)

alkyl group
Why is the alkyl group electron releasing? In the wikipedia, it just said in reference to hydrogen, alkyl groups are electron releasing constituents, is there a reason to explain this besides it is just because of inductive effect?
 * As there are no multiple bond mesomeric structures or lone pairs the inductive effect is the only cause for this behavior.--Stone 15:20, 30 July 2007 (UTC)
 * Could also do hyperconjugation from the H on the first C of the alkyl chain. DMacks 17:57, 30 July 2007 (UTC)
 * Right!--Stone 07:32, 31 July 2007 (UTC)

Radio powered
If crystal radioes can create sound by remodulating the powerful-enough radio waves, is it possible to instead harness the power of the radio waves to power something? Like self-recharging batteries or something? And would this be anywhere near anything that could be considered efficient? (not that blasting hundreds of square miles with radio waves and letting the escaping ones go to waste is efficient in the first place..) --⁪frotht 15:01, 30 July 2007 (UTC)


 * Yes it can be done. No it is not efficient. I think they have used sound powered electronics once when the electronics didn't need much power and couldn't be hooked up to the power lines. It was a lot easier than replacing the batteries on all of those devices periodically. I can't remember the exact circumstances. Radio powered also wouldn't work in Faraday cages, although you probably wouldn't spend much time in them. You might be able to have a radio output in your house to power wireless devices in a not too inefficient way, but I don't know if this is what you want. — Daniel 15:26, 30 July 2007 (UTC)


 * See also wireless energy transfer. --TotoBaggins 15:46, 30 July 2007 (UTC)
 * Radio-frequency identification RFID chip is also powerd by the radiofrequency absorbed by the antenna.--Stone 16:07, 30 July 2007 (UTC)

The principal problem you face is the inverse-square law; as you get farther and farther from a typical omnidrectional (+/-) radio broadcasting antenna, you need an enormously large receiving antenna to intercept even a small fraction of the original broadcasting power. That 50,000 watts that WABC is pumping out in the New Jersey Meadowlands has become just a few microwatts when it reaches your crystal radio; that's why the volume of sound produced by the earpiece is so low.

On the other hand, microwave power transmission uses a focused beam of microwaves to move power from one point to another. Over the distances that are envisioned, it's pretty easy to build antennas big enough to beat the beam dispersion caused by the inverse square law.

Atlant 16:40, 30 July 2007 (UTC)
 * Sure. I remember an article in Popular Electronics in the early 60s or so, which was a transistor radio powered by tuning a second tuner to any powerful station around. Gzuckier 17:40, 30 July 2007 (UTC)

Global Warming?
Is it true that global warming is caused by Merecats?--172.144.134.131 16:04, 30 July 2007 (UTC)
 * Absolutely, You've penetrated their plan to turn the whole world into appropriate territory for them to live in. Now you have to go into hiding. Gzuckier 17:41, 30 July 2007 (UTC)
 * Do you mean to ask whether global warming is caused by mere cats, or by meerkats? If there were enough of them suspended in the atmosphere, I think they would both cause cooling rather than warming. --Reuben 17:52, 30 July 2007 (UTC)
 * Yup. Meerkat Manor will soon be retitled Meerkat World and air 24 hours a day. Clarityfiend 20:07, 30 July 2007 (UTC)
 * Um, to answer the question a little more explicitly: No, not unless one could make an argument that they contribute to a significant portion of the CO2 in the air.Mrdeath5493 02:56, 31 July 2007 (UTC)

Plant defense
Plant_defense_against_herbivory states three different chemical groupse of compounds used for protection against herbivores: nitrogen compounds (including alkaloids, cyanogenic glycosides and glucosinolates), terpenoids, and phenolics. The groupe of altered fatty acides is not mentioned. But substances like Cicutoxin or Falcarinol are also used against herbivores and they derive from the condensation of acetyl CoA and subsequent dehydrogenation to form the double and tripple bonds. Should this group be included?--Stone


 * You seem to know a lot about it - and it sounds like you are probably right - it should be added. However, please remember the importance of referencing your sources - that is what makes your addition totally non-controversial. SteveBaker 23:04, 30 July 2007 (UTC)


 * You are right, referencing the facts is important. I will add the group of chemicals to the article!--Stone 07:32, 31 July 2007 (UTC)


 * I think there are some plants that have enzymes that destroy vitamin B. Any animal that dines exclusively on that kind of plant will get a vitamin deficiency and die. GB 10:55, 1 August 2007 (UTC)

Animal reproduction
One thing I find fascinating about sharks is that they are able to give birth three different ways, and are even known to reproduce asexually. What other groups of animals have such reproductive diversity? Enoktalk 21:44, 30 July 2007 (UTC)
 * I seem to recall it being a plot point in the original Jurassic Park novel that certain frogs had the ability to change sexes. See Hermaphrodite for more on that front. --Mdwyer 01:56, 31 July 2007 (UTC)

Sharks go back about 450 million years. In contrast, the live-bearing mammals go back about 170 million years. Our ancestor at 450 mllion years ago gave rise to all amphibians, reptiles, birds, and mammals as well as Sarcopterygii fishes such as coelacanths and lungfish. In other words, they have had plenty of time to diversify into such a broad range of reproductive strategies. --Aranae 03:56, 3 August 2007 (UTC)

Paper
How much paper is produced from an average sized tree? (In printer paper sheets, preferably). I would like to cite this for a letter to the editor at the Windsor Star. Thank you. Crisco 1492 23:48, 30 July 2007 (UTC)


 * According to http://www.bc.com/ (a paper company) a cord of wood (128 cubic feet) produces "nearly 90,000 sheets of bond-quality paper or 2,700 copies of a 35-page newspaper".  comes up with 80,000 sheets...so that's probably about right.  How many cords do you get out of one tree?  Well, it varies wildly between age and species of course...the US forestry service defines a tree suitable for cutting down as: A live tree of commercial species at least 9.0 inches d.b.h. for softwoods or 11.0 inches for hardwoods, containing at least one 12-foot sawlog or two noncontiguous 8-foot sawlogs, and meeting regional specifications for freedom from defect....so let's go with 10" diameter and 16' length.  That's 35 cubic feet.  But paper pulp can use more of the branches and skinnier stuff - so it's probably a lot more than that for paper as opposed to solid planks and stuff.  I'm going to guess 50 cu.ft per tree.  So 2.56 trees is a cord - and a cord is 90,000 sheets of typing paper or 2,700 copies of the Windsor Star.  I think they're getting about a thousand newspapers per tree.  The Windsor Star website says that they use 25% to 30% recycled content - so you should probably assume 1500 copies per tree to be on the safe side.  I think you'd be on shakey ground if (as I suspect you are about to) you start telling the newspaper that it's causing massive deforestation because it printed something you didn't like! SteveBaker 01:22, 31 July 2007 (UTC)


 * Nah, if it were something about what I didn't like, it would be how I go through all my red pens proof editing their articles :P (not seriously, i only go through one a month). Actually, it is resume related. So thus, if 90,000 sheets of paper are taken from one cord, and a cord is approximately 2.56 trees, then the amount of printer paper would be around 35,150 sheets.

Thanks Steve. Crisco 1492 14:38, 31 July 2007 (UTC)


 * Ah! Sorry for jumping to the wrong conclusion. Anyway - that number has a massive error bar on it - but at least you know where the numbers came from and how it was worked out.  That oughta be enough for a job application...unless of course you are applying as a fact-checker...in which case maybe you should check my facts first!  Good luck with the job hunting. SteveBaker 20:06, 31 July 2007 (UTC)


 * I wish I had what I had written. It is actually a letter to the editor about how much waste is produced by the mass distribution of resumes to businesses where the majority of people read it once, then toss it, or never give the resume to the manager. I also suggest using online jobfinder sites such as www.jobbank.ca or www.monster.ca to find a job, and suggest local businesses use free email providers to set up a designated email address for job applications to be received. Besides the fact that it is more environmentally friendly, it is also more efficient being as the manager is practically guaranteed to see it. It is all under the penname Kevin Mayflower, and I think it turned out rather well. Good guesses though. Crisco 1492 00:07, 2 August 2007 (UTC)


 * I would seriously doubt that distribution of resumes was a significant depletor of forests! Resumes are generally kept down to one or two pages with a cover letter - three sheets, tops!  That means that you can get 30,000 resumes out of one tree!  If you are on a crusade to save paper - lets get rid of the three inch thick pile of advertising crap that arrives every week along with one telephone/electric/water bill every week in my mailbox.  In the apartment complex I live in, there are about 300 apartments and one big area with mailboxes.  Everyone comes along, opens their mailbox, takes out the one letter and dumps all of the rest straight into the trash can provided.  I've never seen anyone so much as glance at the paper-spam.  I probably toss out an entire lifetimes' worth of resumes every week - that's got to be a thousand times as much waste.  If we could stop just 1% of the paper spam in people's mailboxes, resumes would be a non-problem! SteveBaker 12:08, 2 August 2007 (UTC)


 * I totally agree. However, with a viable alternative to spreading resumes, why do we continue to use paper? As for the spam, it is continued (imo) simply because people believe that the recipients actually look at it, while spam in email tends to be immediately deleted w/o a glance. However, admittedly most people never take a look. I believe that the rate for response in mail-based advertising is between 3 and 4%. While we're on the subject of paper saving, may I suggest the papers placed on trays in fast food restaurants which only serve the purpose of advertising, and then are thrown out? Crisco 1492 17:11, 2 August 2007 (UTC)


 * Actually - I think the fast-food things are done like that for a reason. I believe that they place the paper in there so the food doesn't touch the tray.  That in turn allows them to claim to the health inspectors that the standard for cleanliness of the tray only has to be comparable to that of a table-top - and not to the standard of a dish or plate.  That allows fast food places to have an employee give each tray a quick squirt of some kind of cleaning agent and a quick wipe and to put them straight back into service instead of having to have a huge and expensive dishwasher of sufficient size and capacity to clean trays to the standards of a 'slow-food' restaurant's plates.  So probably, that's the reason for the paper - and the fact that they can smother it with advertising is a mere bonus. SteveBaker 03:34, 3 August 2007 (UTC)