Wikipedia:Reference desk/Archives/Science/2008 September 7

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September 7

Why do rockets need to be explosive to reach escape velosity?

Years ago there was a short-lived TV show starring Andy Griffiths ("Salvage 1"). In this show, he was a junk collector of things in Earth orbit and (he hoped) on the moon. One of the unique things about his approach to travelling to outter space was to avoid the current explosive rocket approach and instead used a gradual accelleration approach to achieve orbit. On the surface, this seems to make some sense al a gradually accellerating your car at the intersection rather than doing a "jack rabbit start."

My questions is: what are the physics behind the need for an explosive accelleration to achieve orbit rather than the gradual accelleration premise of this TV show? —Preceding unsigned comment added by 209.161.211.89 (talk) 00:53, 7 September 2008 (UTC)

I remember Salvage 1, so it must have played on the American Forces Network in Germany. I recall the line, "The Vulture has landed". I don't recall the gradual approach to orbit. --—— Gadget850 (Ed) ^talk - 01:15, 7 September 2008 (UTC)

It's more efficient. All the time you're moving upwards, rather than being in a stable orbit, you have to burn fuel just to maintain your position (and more to move up). It's best to get into orbit as quickly as possible to minimise the fuel used up in that way. --Tango (talk) 01:17, 7 September 2008 (UTC)

Check out rocket engine. --—— Gadget850 (Ed) ^talk - 01:19, 7 September 2008 (UTC)

(edit conflict) Yay, finally one that I can answer. Theoretically speaking, it actually doesn't matter how you approach the task of escaping Earth's gravity, as long as you have a Δv large enough to reach escape velocity. However, the problem is that of all the propulsion technologies out there, chemical rocketry is the only one that has a high-enough specific impulse for a reasonable payload/total mass ratio, a high-enough thrust-to-weight ratio to counter Earth's gravity, and is deemed sufficiently safe to use. We could definitely use nuclear propulsion, but it is socially unacceptable to do so. Titoxd^{(?!? - cool stuff)} 01:26, 7 September 2008 (UTC)

However, what that delta-V is depends on how long it takes you. See gravity drag. --Tango (talk) 01:34, 7 September 2008 (UTC)

In simple terms, before you reach orbit, you're using fuel to do two things: 1) Maintain your current position above ground, and 2) increase your speed towards orbital velocity. The quicker you get into orbit, the less fuel you need to use for (1), which is why current rockets accelerate so hard. Once you're in orbit, you can use gentler, more fuel-efficient technologies like solar sails and ion drives to move around. --Carnildo (talk) 01:37, 7 September 2008 (UTC)

Hence the "theoretically speaking"... Titoxd^{(?!? - cool stuff)} 08:55, 7 September 2008 (UTC)

Indeed, the most efficient way (in terms of propellant/payload mass ratio) to launch a spacecraft into orbit would be to fire it from a cannon, putting all the acceleration (except for the final orbital insertion burn) at the very start of the climb. In practice, of course, the stress this would subject the launch vehicle (not to mention any passengers or other payload) to would be prohibitive, so our current rockets are essentially a compromise between fuel efficiency and limits of practical construction. —Ilmari Karonen (talk) 01:51, 7 September 2008 (UTC)

If you were launching from the Moon, where there is no atmosphere, the cannon launch method would work better than on Earth, where if the spacecraft emerged from the muzzle of the gun at orbital velocity near the ground, as in the Jules Verne story [[[From the Earth to the Moon]]] it would decelerate and fall to the ground due to the resistance of the air, if it did not burn up first. It is better to reach high velocity only at an altitude where the air is very thin. I expect that higher G acceleration is more efficient of fuel,except for the burning up in thick atmosphere problem, and the killing the passengers from high G force problem. Rising very slowly would be extremely wasteful of fuel in a rocket. Edison (talk) 04:20, 7 September 2008 (UTC)

On the Moon, you could launch sideways and go straight into orbit (you would need a circularisation burn at some point) rather than going straight up and then going sideways to enter orbit which you need to do on Earth because of the atmosphere. That's the best way to make use of a cannon style launch (see mass driver). --Tango (talk) 04:49, 7 September 2008 (UTC)

See also this thread from a couple of weeks ago. --Anonymous, 05:35 UTC, September 7, 2008.

Of course, you don't need a rocket if you have a space elevator ! Gandalf61 (talk) 08:45, 7 September 2008 (UTC)

Once you are off the planet surface and out of atmosphere engines with slow steady accelaration start to have advantages such as light sails, Bussard ramjet and tether propulsion. SpinningSpark 09:42, 7 September 2008 (UTC)

You don't need to get off the ground with chemical rockets, though. You can use a rocketship/airplane hybrid craft. Using airplane technology while you're still in the atmosphere. The Scaled_Composites_White_Knight carried Spaceship One into the air on conventional jet engines and then dropped it before Spaceship One's rocket engines kicked in. . APL (talk) 16:07, 8 September 2008 (UTC)

Right. Here is a thought experiment: What would happen if we built a spiral-staircase tall enough to reach geostationary orbit? It would be 165,000 miles tall. We could don our space-suits and walk up it (with frequent stops to catch our breath!)...and with the gentlest of push from the topmost step, we'd be in orbit. No "escape velocity" required - no rockets - nothing. SteveBaker (talk) 17:39, 8 September 2008 (UTC)

Well, of course you don't need escape velocity if you only want to go into orbit. When you push off the top step you are, however, at orbital velocity for the given altitude, as the tower is rotating with the Earth. But if you built the tower even higher, you could reach escape velocity in the same way -- that is, the escape velocity for the altitude you were at. The concept is called a space elevator, among other names; see that article for a list of them. --Anonymous, 21:43 UTC, September 9, 2008.

Contents of Drinking Water

What are the contents in the potable/drinking water and what is the ideal percentage of each of the constituents? —Preceding unsigned comment added by 59.97.48.77 (talk) 02:04, 7 September 2008 (UTC)

Did you look at water treatment? Normally there should be water close to 100%. Some dissolved air and carbon dioxide prevents it having a flat flavour. Usually water will be treated with lime to increase it's pH so that it does not dissolve pipes. Other ingredients like chlorine may kill unwanted lifeforms, but really you want zero of this! In the middle east, salt is added because locals prefer their water to taste salty. Ideal percentages of minerals and contaminants may come down to an economical choice - is it worthwhile to remove the contaminants? Graeme Bartlett (talk) 05:53, 7 September 2008 (UTC)

The absolutely pure water taps in the chemistry labs at my uni have warnings saying the water is harmful if consumed frequently. I'm not sure of the details, but presumably there is something about the minerals in water that is important. --Tango (talk) 05:57, 7 September 2008 (UTC)

See Tonicity#Hypotonicity for the general explanation but there might be a specific page with information regarding aqua dest..

/wrt chlorine, you need some means to keep the pipes without microorganisms. That is why you have chlorine in tap water, but I never understood why in the US tap water is chlorinated when you can have clean pipes using ozone. Which is much less toxic and doesn't have any taste. --Ayacop (talk) 10:06, 7 September 2008 (UTC)

Ozone is toxic too. Maybe it's more expensive/less readily available. --Russoc4 (talk) 13:39, 7 September 2008 (UTC)

Water purification#Disinfection notes that "the main disadvantages of ozone is that it leaves no disinfectant residual in the water". I know that my local water system aims to leave a set (ppm) level of chlorine at the customer's tap, to ensure that no harmful organisms sneak in between the supply and the consumer. There really isn't a way to guarantee that one of the decades-old pipe somewhere in the supply system doesn't have a pinhole leak, or some dead pocket where bacteria can establish a colony. I've been in small towns in the US where they were confident enough in their system not to use chlorine, but in a city of any size, there is just too many worries not to have some sort of residual disinfectant capability throughout the supply line. -- 128.104.112.147 (talk) 19:03, 7 September 2008 (UTC)

Hah! Talk about synchronicity. The Sept. 9 question in the New York Times science column q+a is "Is it safe to drink distilled water? Does it leach minerals out of the body?" It's safe, according to "two experts on water quality and nutrition at Cornell". Clarityfiend (talk) 22:32, 9 September 2008 (UTC)

college student seeking advice

Hello, I am a first year student at Mohawk College enrolled in the social service worker course. My main goal for the future is to become a "family therapist". I have experience dealing with people who suffered from alcohol and drug addiction, and I was able to help them gain some will power and get help for themselves. Ever since then, I have had this sudden urge to help anyone and everyone who struggle in life. When I first applied to Mohawk I was under the impression that once I graduated with a degree in social service worker, it would be much easier to apply and be accepted to a university. After doing some research at different universities surrounding our area, I have been unable to find any course that has any relation to "family therapy". If you have not yet figured out where I am going with this, it is that the "social service worker" title is not going to satisfy me. I want more than that...

If you have any advice, or school suggestions, or course suggestions..PLEEEAAAASE respond ASAP

Thank you :)

Trippy123 —Preceding unsigned comment added by Trippy123 (talk • contribs) 03:09, 7 September 2008 (UTC)

Marriage and family therapists#Licensing and Degrees might help. --Tango (talk) 03:41, 7 September 2008 (UTC)

In Ontario Canada, a Social Worker and a Social Services Worker (though governed by the same College) tend to provide two different services based on their education and experiences. Speaking from personal experience, I would suggest that you complete your SSW and then apply to a university for a Social Work program. In my opinion (having supervised students from there, the WLU has one of the best clinical programs around. Also, remember, the university degree is only the starting point: you will need on-going training for several years to come. I completed my BSW (after my BA) and found that until I had my MSW, my oportunities were limited. I also participated in the Introductory and Advanced levels of Brief Therapy in Toronto - this was the BEST clinical training I have ever had and well worth the money!.

So, be patient and plan carefully. I have been at this for 20 years and still have a ways to go!

Brett, MSW, RSW —Preceding unsigned comment added by 69.77.185.91 (talk) 20:54, 8 September 2008 (UTC)

Molar polarisation

how and why is molar polarisation related to molar refractivity? —Preceding unsigned comment added by 59.103.63.240 (talk) 07:29, 7 September 2008 (UTC)

See molar refractivity and compare the Clausius–Mossotti relation with equation (18) for molar polarisation in this. SpinningSpark 10:08, 7 September 2008 (UTC)

Meiosis combinations

Can someone confirm if the number of different gametes possible during meiosis of a human is 2^23? —Preceding unsigned comment added by RMFan1 (talk • contribs) 11:54, 7 September 2008 (UTC)

Even without addressing the specific combinatoric calculation, we can say that's a very low number, because you've ignored the likelihood of recombination, which occurs, on average, slightly more than once per chromosome pair per meiosis. GIven that recombination can occur at so many different locations, the number of different possible gametes is virtually unlimited. - Nunh-huh 12:11, 7 September 2008 (UTC)

why can I listen to the radio on my computer?

Sometimes I can listen on the speakers of my computer to the radio. The sound is quite faint, but it is clearly a radio emission. I have no special program or hardware for that purpose. Why is that possible? —Preceding unsigned comment added by Mr.K. (talk • contribs) 12:10, 7 September 2008 (UTC)

Could be a lot of things, more information is needed to answer fully. You don't say whether it is broadcast radio you are hearing or something else. Taxi radios, for instance, are notorious for being badly adjusted and badly shielded and get picked up by all kinds of things. Broadcast transmitters can be a problem if you live near one. Do you get internet from your cable TV company? sometimes cable companies put analogue signals down the same cable and poor filtering and/or earthing could be your problem. Finally, are you sure you have not connected to a radio station with your web browser and just have the volume turned down? SpinningSpark 15:06, 7 September 2008 (UTC)

It's perfectly possible. If the length of the cable is exactly right to make an efficient antenna, then a strong AM radio station can induce enough energy into the wire to be audible through the speaker. I've had it with an MP3 player and a pair of headphones - so it's not just leakage from cable TV. You can probably get rid of it by shortening or lengthening the cable - perhaps by coiling up any unused length. If all else fails, go to your local Radio Shack (or local equivalent) and buy a "Ferrite bead" and thread the cable through it a couple of times - that'll usually fix the problem. (You see quite a few computer-type cables with ferrite beads built into them for this exact reason.) SteveBaker (talk) 18:34, 7 September 2008 (UTC)

A connection or plug which is not a good solid metal to metal jint, like a loose conection with a bit of corrosion, can easily act as a rectifier, just like a crystal radio or a Coherer. It does not need to be tuned to a particular frequency, but could output the audio of the closest/strongest transmitter through the speaker, with no amplification needed. The distributed capacitance of the wires is enough to create an audio signal with the accidental rectifier of an imperfect metallic junction. I had a stereo speaker once that did this. See also the "foxhole radio" example at [1] on Youtube. Edison (talk) 20:18, 7 September 2008 (UTC)

Lucille Ball (of "I love Lucy" fame) claimed that she had a loose tooth filling that acted as a radio receiver and resulted in music playing in her head. She claimed (bizarrely) that she had on one occasion picked up the sound of morse code - which eventually turned out to be a Japanese spy's radio transmitter located somewhere close to the LA studio where she was working. SteveBaker (talk) 02:52, 8 September 2008 (UTC)

Actions of people with mental illnes or people using drugs

Do mental illness and drugs only take away the constrains to do something or do we come to new ideas in these circunstances? —Preceding unsigned comment added by Mr.K. (talk • contribs) 12:16, 7 September 2008 (UTC)

Well I don't know about mental illness except that in most cases people with it don't have any new ideas that are worth anything to them or others. The idea that insanity is linked to genius is, in all but a handful of cases, totally false.

As for drugs. When on drugs it is common to think that one is getting a flood of new ideas. But in a more sober light most of these are pretty stupid, unoriginal, and uninspiring. I am dubious of the notion that people on drugs think about the world with any more clarity than those not on drugs. It is certainly true that one gets lots of notions. But most of them really aren't anything worth writing home about. There are of course rare exceptions (e.g. it has been said that Kary Mullis claimed to have been inspired to create PCR while on LSD). --98.217.8.46 (talk) 14:07, 7 September 2008 (UTC)

I disagree with User:98.217.8.46. People with manic-depressive disorder are notoriously super-creative when they are in a manic phase. Sadly, they pay for it in their depressive periods - but there is no question that some of the greatest minds in history have been manic-depressive. Similarly, people (like myself) with high-functioning Autism or Asperger's have long been known to be unusually creative in the extremely narrow areas that interest them. So there is no doubt that some conditions of "mental illness" are certainly able to cause new ideas that are extremely worthwhile to others. So let's dismiss what 98.217.8.46 said and try to answer the original question.

Some drugs act like natural chemicals that are in the normal brain - things like beta-blockers which are known to improve people's ability to pass exams by calming them down. It's hard to imagine that these wouldn't cause new ideas to form that otherwise would not. Not being a nervous wreck clearly improves thinking ability - which clearly causes new ideas to form. On the other hand, many "recreational" drugs operate by basically trashing your brain - wrecking the delicate neural sheaths and basically "shorting out" your neurons - and (predictably) causing all the things that make people on those drugs seem so stupid or perhaps comical. So it's hard to make a general statement - other than that there are some occasions with some drugs where new ideas might appear that would not otherwise have done so.

I guess the hard part about this question is whether that "takes away the constraints to do something". I don't think that's quite the right reason. Alcohol certainly makes people less inhibited ("takes away constraints") - but lots of drugs and mental illnesses do the complete opposite. My condition (Asperger's syndrome) certainly adds a lot of constraints (inability to handle body language and appropriate eye contact for example) - but on the other hand it removes a constraint that "normal" people have about spending LONG periods of time studying a narrow topic. When I was writing the Wikipedia article about the Mini Moke - I knew relatively little about this rather obscure car - I bought literally every single book ever published about it - I scoured eBay for old car magazines that discussed it - and I basically geeked-out on reading this pile of material - 8 hours a day for an entire week. I know now more about the Mini Moke than almost anyone on the planet! (Trust me - this is not very useful) You'd have gotten bored out of your skull by the end of the first chapter. So my condition resulted in a constraint being removed. But whether that resulted in new ideas is certainly rather debatable. (Well, I did get the new idea that I want to spend $10k importing a rusted out Moke from Australia and spending months fixing it up because they are so amazingly cool...but (for example) my Wife didn't find that idea "useful" - so it hasn't (yet) come to fruition.)

So there is no doubt whatever that some drugs and some mental conditions DO cause new ideas to form - whilst others to the exact opposite. I don't agree with the "why" of it though - and it's certainly not true of all mental conditions or all drugs - so we should be careful not to generalize.

SteveBaker (talk) 18:23, 7 September 2008 (UTC)

I think the problem here is with the definition of mental illness. Perhaps it is more appropriate to use the word “condition” in cases where there is a possibility of a positive effect. --S.dedalus (talk) 23:18, 7 September 2008 (UTC)

Well - I don't know - use whatever word you like, it doesn't really change the fact that many people who are practically crippled by their "problem" can also gain huge benefits from it - intellectually. Call it a problem, a condition, and illness, a blessing or a curse...that doesn't really change anything. Personally, if it's something you can cure - it's an illness. You can pretty much cure manic depressive syndrome with drugs - but the cure (for some of those people) is not always something they want. Very few Asperger's people want to be "cured"...I'd certainly resist it very strongly. SteveBaker (talk) 01:32, 8 September 2008 (UTC)

I'm not very surprised to hear that you have Asperger's, Steve; you have a kind of a pedantic approach to things that I have experienced with others with that condition. (It's probably a pretty useful trait for someone working the Ref Desk, too.) Speaking from my own personal experience, I've had my struggles with depression, and I can certainly attest that the manic phases can be very creative. I've kind of mellowed out over the years, though, mostly by learning to read my own signals and adjusting my behavior and circumstances to avoid high-risk situations that trigger unwanted reactions. (In simple terms, this means that, for example, I try to avoid letting myself get sucked into cycles where I don't sleep nearly enough, if at all, and work for extended periods of time until I crash. It sounds stupidly simple, I know, but it took me a bunch of years to figure that pattern out well enough to anticipate it.)

Anyway, my point is, I do a lot of creative work, and some of it has certainly been produced in the more manic periods of my life. Good work, too. I'm tempted to say that those are exceptionally creative phases, but honestly, I don't know whether that's just a mindset where I work hard and the creativity is so strongly present simply because it's contrasted by periods where there isn't any. These days, when I'm more balanced about that stuff, I don't really feel any less creative. All in all, considering that there have been periods when I've been entirely uninterested in, well, most everything in my life, I'd say that on average, I'm probably getting more done now than before.

To kind of answer the original poster's question, I definitely think that it's possible for one to be very creative when under the influence of drugs or suffering from a mental condition, possibly more so than when one would be otherwise -- but I think it would be a mistake to assume that the drugs or the condition themselves are the cause, rather than a catalyst. -- Captain Disdain (talk) 09:39, 8 September 2008 (UTC)

Obviously whether mental illness has creativity to it depends on one's definition of mental illness. I wasn't putting Autism or Asperger's in that category; I was thinking of depression and schizophrenia in particular (and I write this as someone who has done a lot of work relating to the history of mental health—for every occasional "genius" who suffers from these particular conditions you have a thousand people who can barely get out of bed, people who in a pre-pharmacological time would have to spend their whole lives in institutions). I suppose the main take-away point here is that one's definitions are rather important. --98.217.8.46 (talk) 13:50, 8 September 2008 (UTC)

Racism or learning from experience?

Moved to Humanities desk at Wikipedia:Reference desk/Humanities#Racism or learning from experience?

xenophobe in ethimological sense

If a person has a phobia against foreigners (xeno), could he be called xenophobe? Does these king of people exist? —Preceding unsigned comment added by 88.6.158.246 (talk) 12:54, 7 September 2008 (UTC)

Yes, yes. See Xenophobia. --98.217.8.46 (talk) 13:39, 7 September 2008 (UTC)

Although, the term is usually used to describe a dislike of foreigners, rather than a fear of them, per se. --Tango (talk) 23:02, 7 September 2008 (UTC)

I suppose the question was that if there is a psychological condition called "xenophobia" similar to agoraphobia and other phobias. —Preceding unsigned comment added by Mr.K. (talk • contribs) 18:39, 8 September 2008 (UTC)

Yes it commes from the greek words xenos (ξένος)-stranger and phobia (Φοβία)-fear. the oxford dictionary contains the word xenophobia and it is the psycological condition of fearing-hating stranges... for example see the rednecks in america!!!

79.166.35.82 (talk) 16:11, 9 September 2008 (UTC)

Beta decay, the weak force and W- boson mass

If beta minus decay occurs by a down quark changing into an up quark by the emission of a W^- boson, how can a W^- boson have a much higher mass than the entire decaying neutron? -- Aeluwas (talk) 13:34, 7 September 2008 (UTC)

Virtual particles in a Feynman diagram don't generally satisfy E² = p² + m². They're said to be "off the mass shell." -- BenRG (talk) 14:04, 7 September 2008 (UTC)

Specifically, this is allowed if $E\cdot t\lesssim \hbar$, where t is the life time of the particle (i.e., the duration of the decay process). --baszoetekouw (talk) 19:30, 7 September 2008 (UTC)

The Bernoulli family and the "Bernouilli" one

Apparently the second spelling of their family name is incorrect, but I've stumbled upon that spelling many times, especially in Spanish publications. Is it just a bad habit that has become widespread in the Spanish community or am I missing something? --Taraborn (talk) 18:03, 7 September 2008 (UTC)

I don't know about this particular family, but I'd hesitate to tell other people they can't spell their own names. Spelling is an arbitrary thing; spelling of names from other languages or countries even more so, as Ellis Island can attest. I've seen highly amusing rants about "MacDonald" being the only correct spelling -- odd for a name that began as Mac Dhomhnuill. I'm sure that type of certitude gets all the consideration it deserves from Godfrey James Macdonald of Macdonald, 34th hereditary chief of Clan Donald. --- OtherDave (talk) 19:52, 7 September 2008 (UTC)

Bernouilli certainly seems to be common, and not just in Spain; Wikipedia has it as a redirect. this errata list shows "Bernouilli" being corrected to "Bernoulli" which, while not definitive, is certainly indicative that it is an error. SpinningSpark 20:07, 7 September 2008 (UTC)

I'd be hesitant to claim something as a definite error for a family whose country has at least four languages and who lived very early on in the emergence of the idea that every word has one correct spelling. Bernoulli is certainly the standard spelling in modern English though. Algebraist 00:10, 8 September 2008 (UTC)

Stroke article in The Lancet

There was recently (May 10th) a really good article on stroke in The Lancet. It can be found here: doi:10.1016/S0140-6736(08)60694-7 Would anyone be able to provide me with a copy, preferably digital? —Cyclonenim (talk · contribs · email) 20:18, 7 September 2008 (UTC)

Try at WP:WRE. It's a great but underused resource. --Shaggorama (talk) 22:34, 7 September 2008 (UTC)