Wikipedia:Reference desk/Archives/Science/2011 May 11

= May 11 =

Metronomes
Could someone explain the physics behind: http://www.youtube.com/watch?v=yysnkY4WHyM ?

It's obviously related to normal modes, but I can't make the connection. The description mentions conservation of momentum, but I don't see what that has to do with anything.

Please, the more detail the better! Thanks! 74.15.138.241 (talk) 01:11, 11 May 2011 (UTC)
 * One standard term for this is phase locking. It was known to Christiaan_Huygens, who (perhaps apocryphally) discovered it over a much longer time-span, by accident with two grandfather clocks coupled by the framing of an attic. You could see the same effect with children on swings coupled by a bungee cord. I think it is covered with a fairly accessible and informative use of ODE in Nonlinear Dynamics and Chaos by Strogatz. Basically, when slightly out of phase, each pendulum 'kicks' the other in a manner that slightly damps out-of-phase components of velocity while slightly reinforcing in-phase motion. Does that make sense? It's a really cool demo and phenomenon, enjoy! SemanticMantis (talk) 01:59, 11 May 2011 (UTC)
 * Also, Huygens called it an Odd_sympathy. SemanticMantis (talk) 13:30, 11 May 2011 (UTC)

Two pendulums oscillating at different frequencies can never synchronize! They will beat, not synchronize. So, how is this setup working? Well, both pendulums are changing frequency and synchronizing on a common resonant frequency, perturbed from each individual natural frequency. One isolated metronome, as a simple pendulum, prefers to oscillate at is natural frequency; but when coupled to the dynamic base (as shown in the video, the wobbly structure underneath it), the pendulum prefers to oscillate at its damped frequency. This is why a 192-beat-per-minute metronome is able to synchronize to a 180-beat-per-minute metronome. Neither metronome ends up oscillating at their own natural frequency! There's a very good coverage of the perturbation-theory needed to calculate damped system response in this textbook, Mechatronics (Alciatore & Histand), in the chapter on System Response for complex systems. Roughly, $$\omega_{damped} = \omega_{natural}\sqrt{1-\zeta^2}$$, where $$\zeta = \frac{b}{2m\omega_{natural}}$$ and b is the constant of velocity-damping. (See the text I linked for more detail on a dynamic b - in this case, we have a very complicated "effective" b that is due to the coupling to the base, which is moving). You will have to estimate these parameters from the system-response or from alternative measurements of the system properties. Once estimated, you can construct a Lagrangian in terms of generalized coordinates (I would pick the angles of deflection for each pendulum, plus one or two parameters for the vertical and horizontal deflection of the unstable base). Then, solve for the lowest energy-configuration, and note that the energy concentrates in the common-mode for the two pendulums (provided that you have reasonable masses, damping coefficient, and length scales). Nimur (talk) 14:09, 11 May 2011 (UTC)
 * Hi Nimur. So if I understood your answer, the "wobbly structure" changes the frequencies of the two metronomes so they they are close together, and so are able to beat? But why wouldn't they already beat? Their frequencies are supposed to be near each other already (both close to 192Hz). 74.15.138.241 (talk) 04:45, 12 May 2011 (UTC)
 * Sorry if I was unclear. I hope the confusion is not due to the terminology: beat frequency is the technical term for Δf (the difference in frequencies between two metronomes); and beat-frequency is not the same as the "tick" frequency (f - which is confusingly notated in "beats" per minute, as musicians commonly do).  If we measured everything in "Hertz" instead of "beats per minute," this confusion of terminology would evaporate.
 * If the frequencies were fixed, then Metronome A would oscillate at 192 bpm, and Metronome B would oscillate at 180 bpm; there would be a 12 bpm "beat frequency" that corresponds to the cycle time as A and B phase-synchronize, then drift out of synch, and then drift back in to synch again (... 12 times per minute, or Δf, the difference in frequencies). But what we saw in the video was different - they don't drift in and out of synch.  Instead, in the video linked, the metronomes start off out of synch, and then gradually adjust until they are always in synch.  For this sort of phase locking to happen, it is necessary for the frequencies of one or both metronomes to change, because there is a very simple fixed relationship between phase and frequency.  (It's silly to compare phase offset for non-identical frequencies, except as an "instantaneous" measurement).
 * So, my post above was outlining the basic mathematics about how a metronome can change its frequency, since as you have probably learned, a pendulum is supposed to swing at a constant frequency according to Newtonian principles; its frequency only depends only on its length, mass, and the force of gravity.  This only applies to a simple pendulum!  Complicated pendulums oscillate at whatever frequency minimizes their Lagrangian - which is a more fundamental description of the way the universe works, and is mathematically equivalent to the "three-law" formulation of conventional Newtonian mechanics.  In simpler words, if you dial in a 180bpm rate, and then wobble the metronome on a wobbly base, it won't actually tick at 180 bpm - the speed changed because the system became dynamical (in this case, it's not even a simple harmonic oscillator anymore, and needs a dynamic treatment).  In this video, the lowest energy-concentration for this system forces Δf to zero, (and then proceeds to force phase-lock on both oscillators).  Again, "beat frequency" specifically refers to the Δf between two oscillators; f1 and f2 are the "tick frequency" for each metronome).
 * This "theoretical academic exercise" is the fundamental science behind one of the most important engineering accomplishments of the last century: the ultra-precise phase-locked loop, which enables high-speed digital circuitry (such as what you will find inside a computer, an atomic clock, a GPS unit, a cellular radio-telephone, ...). Nimur (talk) 14:52, 12 May 2011 (UTC)
 * Thanks a lot!74.15.138.241 (talk) 16:55, 12 May 2011 (UTC)

Gas in the age of zombies
There's been a worldwide zombie apocalypse; that was a few years ago, and we mostly have the zombies under control. But there's only about 3% of the population left, and technological civilisation is in pretty poor condition. We've used up the available gasoline and diesel in the neighbouring city, and we'd still like to be able to drive around to scavenge for stuff. I figure we should be able to produce our own biodiesel. Here's what we have:


 * We have a surfeit of zombies and miscellaneous zombie bits. The dogs and birds won't eat them, and we're reluctant to use them as fertiliser. Is there any way we can recycle them into biodiesel of some kind?
 * Lots and lots of plastic, like plastic bottles and stuff. In general, there's the varied detritus of a modern industrial city.
 * Hardware scavenged from DIY stores, car repair places, plumbers' merchants, tanneries, aquarium supply places, dairies, breweries - all the service-sector light industries you'd expect in a major city, but not much heavy industry.
 * Lots of wood (both from forest and scavenged from buildings) and a fair amount of power-station coal.
 * Plumbers, electricians, mechanics, pipe fitters, and skilled handywomen. We have plenty of smart people who can read and learn, but whose life skills aren't very useful any more (like lawyers and Java programmers; can we turn them into biodiesel of some kind?)
 * We have a city, and its suburbs, and the surrounding agricultural land, to play with. All the vehicles, aircraft, ships, all the contents of shops and homes and offices and schools we could ever use.

and here's what we don't:
 * Much in the way of a modern chemical industry. All the major refineries and chemical plants were destroyed.
 * Electrical power, except for small generators that burn the very fuels we're running out of.
 * Much in the way of petroleum based fuels - much was used during the crisis (some as fuel, some for anti-zombie defence) and we've already scavenged what we can from cars, trucks, aircraft, petrol stations, tankers, barbecue supply places, and so forth.
 * The ability to produce from nature or the earth much of anything beyond basic agricultural crops. We're getting sick of Twinkies, so we need to eat what we grow (and so can't spend much effort growing crops for fuel). We don't have the manpower to mine or process metals or other minerals.
 * Any kind of chemical refining or processing capability. I dare say we could rig up a still.
 * Chemists, metallurgists, or chemical engineers. There's probably a high school science teacher around somewhere, but maybe not a good one.
 * We have limited capacity to cut and fabricate metal objects, but that relies on tanks of stuff like acetylene that cannot be replaced.

I appreciate that we could set up a wind turbine and charge electric car batteries from that, but when the world is still seething with the undead, range anxiety takes on a new gravity. And yes, you can have horses pull a Porsche, but zombies eat horses and horses know it.

So, my question is - how can we turn this into fuel for our bio-diesel adapted cars and trucks?
 * I'm sure we can make ethanol (with the zombies at least) but will the cars safely run on that?
 * Can we process oil-based paint (we have warehouses full of magnolia satin finish paint) into fuel?
 * Can we do anything worthwhile with all the plastic, beyond simply burning it to heat our bathwater?
 * Can we process the bunkering oil in the ships into something that the cars will take, without gumming up their works?
 * Can we realistically build a small synthetic fuel plant and turn all the coal into vehicle fuel?
 * What can we use to run our gas cutting torches and gas welding equipment once the proper fuel for them runs out?
 * Is there any other way we can make surrogates for gasoline, diesel, lpg, agvas, welding gas, and so forth?

Let's say we're near Leeds; a decent sized city with a temperate climate. There's no onshore fossil fuel production capacity, beyond exhausted or deep (and disused) coal workings.

Can we make fuel, or are we going to have to accept a Tolkienesque post-technological lifestyle from now on? -- Finlay McWalter ☻ Talk 01:26, 11 May 2011 (UTC)
 * I think you are intentionally making this harder than necessary. For starters, biodiesel is made from used vegetable oil by a number of people in their garages now. You can get most of the information you need to do it from Wikipedia (although some of the more practical stuff is only in the article history now.) 75.41.110.200 (talk) 02:08, 11 May 2011 (UTC)


 * Have you seen The Colony (U.S. TV series)? I remember seeing an episode where they found a truck load of rotten dead pigs, then rendered their fat and ran a diesel engine from it which they rigged as a generator.  Personally I'd prefer hydropower.  Zombies don't eat dams, do they? Wnt (talk) 03:07, 11 May 2011 (UTC)


 * If you're near Leeds, you should be within striking distance of some of the largest peat bogs in Europe at Thorne and Hatfield Moors. That should help to keep you warm for a few years while you fathom things out. --TammyMoet (talk) 09:12, 11 May 2011 (UTC)


 * If you insist on keeping existing automobiles running, I recommend converting them to Wood gas. That can be done pretty easily.  (Basically, when you heat sawdust it releases a flammable vapor which can be piped right into your engine.)
 * Wood gas would probably be enough to keep a car running around town. And once you've converted your car there's not much in the way of fuel prep. (You can find wood all over the place.)
 * I think it would be impractical for long journeys (It's inefficient, and there's a limit to how much wood you could carry, so you'd be stopping to chop wood pretty regularly.) so if you require a car for long trips you're going to need to make either bio-diesel or ethanol. Both are possible to make with simple tools, but very time consuming.  So this sort of fuel will be very precious to your community. Not to be burnt lightly.  APL (talk) 00:49, 12 May 2011 (UTC)
 * Here, I recommend memorizing this article before the Apocalypse. : Convert your Honda Accord to run on trash.
 * APL (talk) 00:54, 12 May 2011 (UTC)
 * Oh, by the way, the organization that posted that article sometimes calls themselves "APL", but there's no relation to my own user-name. APL (talk) 01:07, 12 May 2011 (UTC)

https://www.fbo.gov/index?s=opportunity&mode=form&id=91be9acbf2239974789b2749b84f73ad&tab=core&_cview=1 and http://www.navysbir.com/07_S/40.htm may be helpful, as should, , and. 99.39.5.103 (talk) 07:13, 16 May 2011 (UTC)

Young Earth?
So is Conservapedia supporting a young earth creationism and not other form of creationisms? It is not very clear to me. Though they have a page filled with evidences for a young earth. Aquitania (talk) 03:07, 10 May 2011 (UTC)


 * Who really cares? I don't think it's our job here to try to analyse irrational thoughts at Conservapedia. HiLo48 (talk) 03:06, 11 May 2011 (UTC)
 * Obviously the OP cares- that's why they asked. It's a perfectly reasonable question. Staecker (talk) 10:33, 11 May 2011 (UTC)


 * Belief in a young Earth is not a recent phenomenon. It is not even contemporaneous with the emergence of science.  At the time of writing of the ancient scriptures (such as the Old Testament) it was widely believed that the sun, planets and stars revolved around the Earth, the distance from the Earth to the sun was much shorter than we now know it to be, and the age of the Earth was very old by the standards of human comprehension - namely around six thousand years.  Ever since then, in cultures where the Old Testament and other ancient scriptures are revered, most people believed the Earth was created by a deity about six thousand years ago - that seemed like a long time to these people, most of whom were illiterate.  Modern belief in a young Earth did not originate with modern scientific discoveries and knowledge, it has its origins in obedience to the ancient scriptures.  Modern scientific information presented on this subject by young-Earth creationists has been gathered to vindicate what is taught in the ancient scriptures.  Modern scientific information did not initiate the belief in a six thousand year-old Earth.  Dolphin  ( t ) 03:51, 11 May 2011 (UTC)
 * The 6000 years in particular are a relatively recent invention. If you look at that actual numbers summed up by James Ussher, it's obvious that they were chosen not to reflect historical reality, but with significant artistic and poetic license. The idea that a history should teach about actual history first, instead of primarily teaching moral concepts and religious truths, goes back more or less to Herodotus. It wasn't a major concern for the writers of the Old Testament. So Ussher essentially fell victim to a cultural divide. Of course I don't want to suggest that the ancient writers had billions and billions of years in mind, but they were most likely not wed to their exact numbers or even genealogies. --Stephan Schulz (talk) 18:37, 11 May 2011 (UTC)
 * Thanks for the link to James Ussher. Very interesting.  Dolphin  ( t ) 07:55, 12 May 2011 (UTC)
 * for the OP's sake, I read the first 9 points of that page, and all of them are based on a fundamental ignorance of introductory geology. Any college level freshman year Geology 111 course in America would clearly and concisely explain away every one of those "reasons". To be honest, I was expecting better. The Masked Booby (talk) 03:54, 11 May 2011 (UTC)
 * Has any of you actually read the OP's question? "So is Conservapedia supporting a young earth creationism and not other form of creationisms?"... 80.123.210.172 (talk) 10:16, 11 May 2011 (UTC)


 * My judgement is that in general they tend towards YEC though some probably are old earth creationists. They seem keen to try and give the impression that the articles have a neutral point of view. Some of them might actually believe it is a neutral point of view for all I know. Anyway the article seems as well based as their recent attack on the special theory of relativity because it encourages moral relativism. Dmcq (talk) 12:04, 11 May 2011 (UTC)


 * In fact have you read 'Old Earth' on Conservapedia? It is more against it than I expected so I would say yes they are definitely in the YEC camp. Dmcq (talk) 12:12, 11 May 2011 (UTC)


 * I think Young Earth Creationists and Old Earth Creationists tend to really hate each other. I guess it's the "heretics are worse than unbelievers" mentality. Qrsdogg (talk) 19:39, 11 May 2011 (UTC)

Newborns are defenseless
Had the opportunity to observe a day in the life of a one-week old human a few days ago, and was dumbstruck by the profound uselessness (joking, helplessness) of the little guy. I flipped over to the Infant Mortality page but was disappointed to find no pre-20th century data. I am VERY interested in historical infant mortality! Having a baby is a tremendously stressful event in 2011 with all our modern medicine. How did people pull it off in Caesar's Rome? Alexander's Greece? Ancient Egypt? Hammurabi? pre-civilization? My cat had four kittens in a litter on her own 2 years back and did fine, and I've seen baby primates clinging to their mothers on TV, but seriously - this human? utterly useless! How did we ever manage? The Masked Booby (talk) 03:24, 11 May 2011 (UTC)


 * If you can put aside the fact that it was produced, and has appearances by, Ricki Lake, The Business of Being Born is actually a fairly interesting documentary which you might like. Dismas |(talk) 03:31, 11 May 2011 (UTC)


 * Different species display different levels of capability at birth. Some of these capabilities are essential for continuing life - for example, baby whales and dolphins have to be able to swim immediately after birth.  The evolution of the human being has optimised other capabilities in preference to being able to fend for ourselves immediately after birth - for example, our mental capabilities are unparalleled in the area of intellect, learning skills and self-awareness; and to achieve that we have significantly large brains and heads at birth.  This militates against mobility at a young age but it has been successful because human parents are much more competent at child-rearing than other mammals, including other primates.  Dolphin  ( t ) 03:36, 11 May 2011 (UTC)
 * Obstetrical Dilemma is relevant. -- BenRG (talk) 05:51, 11 May 2011 (UTC)


 * I appreciate the responses so far, but none of you addressed my core interest of historical infant mortality in various eras prior to the 20th century... The Masked Booby (talk) 09:10, 11 May 2011 (UTC)


 * How did we manage? Well, as well documented in many places not very well. The principal reason why the human race continued to increase even under adverse conditions for infants was by the simple strategy of many children. It is well known that Victorian families were much larger than today's and this was true not only in England but many other countries. There was no convenient contraceptive available for the average couple, indeed the most common contraceptive was probably breastfeeding. The fact that babies died frequently at an early age was realised by parents of previous centuries and this surely fed their wish to have large families to ensure the survival of some. Living conditions in medievel England for the working classes were appalling. Lack of food, lack of sanitation, lack of knowledge about health needs, the obligation to work, the lack of personal security and more all added to the difficulty in raising children. Lack of records prevent us having an accurate handle on infant mortality in previous centuries, then add to this the likelihood that in rural areas where poverty was worst many babies perished unrecorded. Recording births is a relatively recent obligation, before births were recorded it is difficult to see how we might accurately estimate infant mortality. Richard Avery (talk) 09:32, 11 May 2011 (UTC)


 * No doubt infant mortality was somewhere toward the high end of the range; still, I doubt that low-density tribal cultures usually faced the same pathogens or deprivation as women in such lugubrious places as medieval England or modern Haiti. Fertility was not under scientific control - there wasn't absolute safety from having children - but if desired it could be managed to a "less likely than not" degree with herbs and other low-tech measures (for example, monks eating their gruel made from hemp seeds; rue also worked). Wnt (talk) 12:14, 11 May 2011 (UTC)


 * A brief perusing of, say, 18th century graves (as can be done in Boston) shows an inordinate number of women who died in childbirth. It was not uncommon. Similarly it was not uncommon for babies and children to die; even into the 20th century, there are still places with high infant mortality rates. How did humans manage? Have more babies. It's not a coincidence that religious texts like the Bible say, "reproduce all the time, guys!" It's a basic survival strategy. There are all sorts of tales in literature of people trying not to get too attached to their babies because you wouldn't know which of them would live to even young adulthood. In general, if you can get beyond the infant/child stage, your lifetime mortality goes up pretty high. --Mr.98 (talk) 14:20, 11 May 2011 (UTC)


 * Similar studies to the ones Mr. 98 mentions have been performed in the UK, based on parish records and graves. One study (Bridging the Gap: Determining Long-Term Changes in Infant Mortality in Pre-Registration England and Wales, Chris Galley and Nicola Shelton, Population Studies, 2001, Vol. 1, No. 1, p-65-77, http://www.jstor.org/stable/3092925) looked at 26 parishes between 1570 and 1840 and found significant variations in infant mortality over time and in different geographic areas, the highest being around 300 deaths per 1000 in the late 18th century. However, they found it was often difficult to pinpoint cause of death. Another study on infant mortality in several Dutch provinces between 1812 and 1909 looked at causes of death as well as variations in mortality in urban and rural areas, and in families of different class. (Differential Infant and Child Mortality in Three Dutch Regions, 1812-1909, Frans van Poppel, Marianne Jonker and Kees Mandemakers, The Economic History Review, 2005, Vol. 58, No. 2, p272-309, http://www.jstor.org/stable/3698693). They are difficult to summarise; infant mortality rates seem to be between 100 and 300 per 1000 live births up until the beginning of the 20th century (depending on various environmental and other factors, and discounting events which would have increased IMR, such as famines, disease outbreaks etc.) If you search the reference desk archives, there have been a couple of previous questions about IMR, including this one which I remembered while typing. -- Kateshortforbob talk  17:51, 11 May 2011 (UTC)
 * A chart comparing infant mortality rates in differnt countries can be found here. The results for Austria and Sweden go back to 1800. Sweden's was 240 in 1800 and 2.3 in 2008. Alansplodge (talk) 17:57, 11 May 2011 (UTC)


 * (ec) Search engines are your friend, original poster. I know nothing about this field, but it took me about 8 seconds to google infant mortality 1700s, which yielded 200,000 results.  I also went to books.google.com and searched for infant mortality and got some good references.  This 1906 book says 120,000 infants were dying per year in England and Wales, and has a helpful table on page 3 showing a generally declining rate, from 154 per thousand in 1851-60, down to 138 per thousand in 1901-1905.  Further searching will yield data on other geographic areas, and perhaps an expert will come along and, rather than post a bunch of speculation, will point us to the book that is considered definitive on this subject.  Comet Tuttle (talk) 17:56, 11 May 2011 (UTC)


 * Just to add to this: there is a view of humans which describes us as basically technological marsupials. That is, we have evolved along with our technology for so long, that the 'natural' conditions for a newborn human baby include something to carry them in, like a sling. This allows our babies to be born at an earlier stage of development, which allows for larger heads while still fitting through the pelvis, which allows longer, slower development without endangering the mother as much as an 18 month pregnancy would! 86.164.60.255 (talk) 11:26, 14 May 2011 (UTC)

Recharging a laptop from a square wave inverter
Is there any actual evidence that recharging a laptop by plugging its power brick into a square wave inverter will reduce its battery capacity? Searching RV and boating forums results in several threads centered around claims that this has happened, but I've not been able to find any more reliable source. In my specific case, I am on a boat with and old Heart Freedom-25 12 VDC to 230 VAC square wave inverter. The power brick is designed to take 100-240 VAC (presumable sine wave) at 50-60Hz and produce 19 VDC. Would ugly transients from the square wave leak through to the output and damage the battery? —Preceding unsigned comment added by 203.82.93.46 (talk) 06:05, 11 May 2011 (UTC)


 * It's difficult to predict the interaction between the two inverters in series (the power brick is also an inverter). The spikes are more likely to damage your laptop's internal circuitry than its battery.  I've tried running my laptop from a cheap car inverter and it was almost unusable with erratic behaviour, so I haven't tried again.  As far as I know, no actual damage was done, and I'd risk charging the battery with the laptop switched off.  A single 12v to 19v inverter would be safer, but they seem to be rare.  Another alternative would be some smoothing circuitry to turn your square wave into something more like a sine wave.  There will still be some interaction between the circuits, but an old-fashioned high-current passive smoothing circuit will considerably reduce any spike risk (though it could alter the nominal voltage).    D b f i r s   06:57, 11 May 2011 (UTC)


 * The laptop's "power brick" is not an inverter - it is in fact the exact opposite - producing a DC output from an AC input by means of a rectifier. The power brick is in fact a switched-mode power supply. If it is well designed it should be able to tolerate a "noisy" AC supply and filter out the transients. However the most efficient way to obtain the required 19V to run and charge the laptop is a DC-to-DC converter (which is a different type of switched-mode converter) that will run off a 12V supply. The type that increases the voltage is also known as a boost converter. Roger (talk) 08:12, 11 May 2011 (UTC)


 * Yes, I should have written "contains an inverter". The switched mode power supply has other circuitry as well.  The inverter stage comes after the rectifier.  I agree that it is better to avoid going via 110-240v for the conversion (though all conversion involves AC).  The problem with the so-called DC-to-DC converters is that they are not readily available at reasonable cost.    D b f i r s   14:05, 11 May 2011 (UTC)
 * Is £18.77 unreasonable? (And, more importantly, do you need more than 1.2A?) If not, try . 80.254.147.84 (talk) 20:02, 11 May 2011 (UTC)
 * The actual cost of that unit is £24 and it is mis-advertised. It runs only LEDs.  General DC to DC converters cost about £100.    D b f i r s   21:40, 3 June 2011 (UTC)
 * (EC) Really? I find plenty of various price ranges, brands and build quality |utmccn=%28organic%29|utmcmd=organic|utmctr=laptop%2520dc%2520charger&__utmv=-&__utmk=158260154    . Even from a relatively reputable retail store  locally here in NZ which isn't exactly tech central. Some of these are apparently endorsed by manufacturers . 110V/220V inverters are also common but seem pointless if all you want is to supply a laptop and don't already have one. Searching I did find plenty of inverter recommendations (and for sale). I imagine one of the reasons why some people recommend inverters for this purpose even though DC-DC converters are relatively common and not that expensive other then ignorance is because it's easier to screw up with most car DC-DC converters, you need to make sure you select the right voltage or else your laptop may go bye bye (I personally suspect most laptops will tolerate even if not work properly with the relatively small range of available voltages but I'm not offering any guarantees). You may also screw up the polarity. Whereas if you have your original laptop charger and an inverter it's relatively plug and play. No different from any other universal laptop charger of course. P.S. Small scale boost converter ICs are of course very common nowadays used for things like LEDs and other components in battery powered electronics. Way less then what you're likely to need for a laptop of course. Nil Einne (talk) 20:13, 11 May 2011 (UTC)
 * May I confess to being amused by the "specifications" on Nil's third link? Not only is the formatting decidedly suboptimal, they appear to be using a definition of the inch that's 50 years (or however long ago 1 July 1959 is - arithmetic has never been my strong point) - out of date. Tevildo (talk) 21:50, 12 May 2011 (UTC)
 * Apologies, general DC to DC converters are expensive (typically £100), but perhaps those specially designed for laptops are more readily available and cheaper than I thought. I've never seen them on sale in the UK, but I'll search more thoroughly because I could make use of one.    D b f i r s   21:51, 11 May 2011 (UTC)

Vasopressin not used as a uterine stimulant?
Hi all. In this pharmacology prac that we did, we tested responses of the rat uterus to oxytocin and related drugs. The response to vasopressin is essentially zero whereas the response to oxytocin is quite high. There is one question about why vasopressin is not used as a uterine stimulant, and we have no idea. Literature articles seem to say that vasopressin is more potent than oxytocin in the early stages of pregnancy, but less potent in late pregnancy. Is this related to the question? If so, in what way? Sepytipsh (talk) 07:59, 11 May 2011 (UTC)
 * This is stated in a pretty confusing way -- I'm not sure whether you are asking why the body doesn't use vasopressin or why doctors don't use vasopressin. The second seems more plausible, but the fact that you yourself showed that it doesn't work seems like such an obvious answer that I have doubts that it is what you meant. Looie496 (talk) 17:24, 11 May 2011 (UTC)

Wine and Vinegar
Why is it that takeing a vinegar mouthwash, followed by a swig of a dry wine, makes the wine appear to be sweeter and taste fruitier? Plasmic Physics (talk) 10:56, 11 May 2011 (UTC)
 * Because the vinegar saturates the taste receptors which perceive sour tastes, so when you follow it with the wine, you taste only the sweet flavors. Its the exact same reason why the following phenomena occur:
 * When you are in a room with a strong smell for a long time, you stop detecting the odor, even though the source of the odor is still there (see Olfactory fatigue).
 * When you view a strongly colored picture for a long time, and then quickly look at a white surface, you see a "photonegative" of the picture. (see Afterimage)
 * The entire set of phenomena, including your wine tasting effect, is called Neural adaptations. -- Jayron  32  13:02, 11 May 2011 (UTC)

Oh, and I thought it was some kind of enzymatic reaction. Plasmic Physics (talk) 13:17, 11 May 2011 (UTC)

Keeping milk from freezing: How much vodka needed?
Hello, Wikipedians.

I have a refridgerator that sometimes goes a bit whacky, sending the temperatures a bit low. This is fortunate for me, because I like my milk and fizzy drinks very cold. However, not solid. I have some vodka available, and I was wondering, how do I calculate how much vodka is needed to keep 1 liter of milk from freezing at a given temperature (say, -2 C)?

Thank you in advance.

80.213.11.105 (talk) 12:21, 11 May 2011 (UTC)


 * If you completely ignore that the vodka and milk will separate - resulting in frozen milk and liquid vodka - then you are simply asking: What percentage of alcohol (ethanol) by volume will result in a freezing temperature of -2°C? See Ethanol (data page). There is a chart on "Properties of aqueous ethanol solutions" that lists the freezing temperature by percent volume. -2°C is 6% ethanol by volume. -- k a i n a w &trade; 12:51, 11 May 2011 (UTC)


 * Sorry for stopping short of the complete answer... As stated, you need 6% ethanol, which is 12 proof. You have vodka. What is the proof? Probably around 80, which is 40% ethanol. Assume you have M gallons of milk and V gallons of vodka. You will end up with a total of M+V gallons and .40V gallons of ethanol. You want .40V divided by M+V to be 6% (0.06). If my math is correct, given M, V will be 0.19M. -- k a i n a w &trade; 12:57, 11 May 2011 (UTC)


 * I suggest that you investigate whether the refrigerator thermostat is faulty. When you rotate the control there should be two distinct points where it clicks "on" and "off". Also leave a small plastic bottle of plain water inside; it will give some warning of when the milk is about to freeze. Cuddlyable3 (talk) 13:05, 11 May 2011 (UTC)


 * Of course this is not just a water/ethanol mix, there are other solutes. The question is how much of an effect on the freezing point depression will they have. Plasmic Physics (talk) 13:06, 11 May 2011 (UTC)


 * Freezing point depression is a colligative property, and so to a first approximation depends solely on the number of solute particles, but not on their identity. Thus, given that they are both non-eletrolytes, both, say, sugar and ethanol should have the same effect on a mole-per-mole basis.  -- Jayron  32  13:49, 11 May 2011 (UTC)


 * Considering that the actual content of milk can vary depending on its source and on how it is processed, you're not going to get an answer for your specific situation without simply trying it yourself. Post the results here when you're done.  148.177.1.210 (talk) 14:14, 11 May 2011 (UTC)


 * Stock your fridge full with bottles of water. This will decrease, or at least slow down, the fluctuations of temperature in your fridge, as you will have increased the specific heat capacity. It should also slow down the freezing once your fridge hits 0ºC, as the fridge will be sucking all that extra energy from the water's phase change. &mdash; Sam 63.138.152.219 (talk) 14:37, 11 May 2011 (UTC)


 * If the thermostat is the problem, that would probably just make the fridge run more because it would still be keeping the stuff at the same temp. Unless you put so much water in that it could not keep up I suppose.  Googlemeister (talk) 20:09, 11 May 2011 (UTC)


 * I don't think vodka and milk would separate, after all, vodka is just ethanol with water added to it, and milk is >90% water.. I hope it's for your white russians, and not for your breakfast cereal ;) Vespine (talk) 22:56, 11 May 2011 (UTC)


 * I doubt anyone (sane) would want to have Moloko Plus in their cornflakes! Roger (talk) 07:56, 14 May 2011 (UTC)


 * When you freeze milk, it separates, with most of it freezing but the fat staying liquid longer and migrating to the outside and top. So, if you blend in alcohol, I'd expect it to mix with the water portion, which would then freeze at a lower temp.  The fat, on the other hand, would still freeze at the same temperature as always.  It might be possible, with enough alcohol, to actually have the fat freeze first. StuRat (talk) 07:03, 12 May 2011 (UTC)

Question: Wouldn't the vodka spoil the taste of the milk ie you would get a vodkary milk. -- Tyw7  (☎ Contact me! •  Contributions )   → I took the one less traveled by, / And that has made all the difference. 15:22, 12 May 2011 (UTC)
 * Some people like that kind of thing: White Russian (cocktail) —Preceding unsigned comment added by 148.177.1.210 (talk) 16:28, 12 May 2011 (UTC)
 * Stu, but ethanol is also a fat solvent. Me thinks this would make a good experiment.. Vespine (talk) 04:18, 13 May 2011 (UTC)

Mass of a heated object
Hi. If I have an object on a scale, what would happen to the reading on the scale as the object gets heated? Thanks! --163.202.48.109 (talk) 15:29, 11 May 2011 (UTC)


 * The mass of the object will increase by a tiny amount (due to mass energy equivalence). But the scale won't track this mass increase. Instead, what will happen is that due to the heating, the buoyancy forces are changed. Also, you'll change the convection surrounding the object, so some momentum wll be imparted on the scales due to that. Count Iblis (talk) 15:55, 11 May 2011 (UTC)
 * The 15 kiloton yield Little Boy atomic bomb that was dropped on Hiroshima converted about 0.6 of a gram of mass into energy. That might give you a bit of an idea how much energy mass has. Vespine (talk) 22:51, 11 May 2011 (UTC)

Thanks. Will the rest mass of the object increase? And what does it mean that the energy of object increases? --163.202.48.109 (talk) 07:46, 12 May 2011 (UTC)
 * Yes, the object's rest mass increases. Dauto (talk) 13:19, 12 May 2011 (UTC)
 * And the energy increase means that the total energy in the form of the kinetic energy of the particles the object consists of and their mutual potential eenrgy increases. This energy is called "internal energy" and it leads to a temperature increase. Count Iblis (talk) 14:59, 12 May 2011 (UTC)

There is actually a simple high school level derivation of E = M c^2. Here you use that light has momentum, a light pulse of energy E has a momentum of E/c. You consider two objects of mass M that are floating in in deep space, free of any external forces. The center of mass of the system will have a constant velocity, this can't change because total momentum is conserved in the absense of external forces.

Suppose that both objects are initially at rest in our frame. Then one object emits a light pulse of energy E, which is completely absorbed by the other object. Then the object that emits the light pulse toward the other object, will start to move in the opposite direction with velocity E/(Mc). And when the other object absorbs the light pulse, it will get the same speed, but in the opposite direction. Total momentum is then conserved, so there doesn't seems to be anything nontrivial going on here.

However, the first object starts to move before the second object, because it takes time for the light pulse to arrive at the second object. Then this suggests that the center of mass of the system is shifting while the light pulse is underway, but that would require making assumptions about the mass of the light pulse. However, we can look at the moment the light pulse is absorbed by the second object. At that moment, the first object has moved some distance, while the second object has not yet moved, as it has just acquired a nonzero velocity.

But if the center of mass of a system is at rest in some frame, it cannot move in that frame if no external forces act on the system. So, also in this case, despite the fact that the first mass has moved and the second hasn't yet, the center of mass has not moved at all. This then implies that there has been a transfer of mass from the first object to the second object.

If the distance between the objects is L, then in the time L/c it takes for the light pulse to move to the second object, the first object moves a distance L/c E/(M c). Then since the center of mass is halfway between the two objecs, the center of mass would have shifted by L E/(2 M c^2), if there were no mass transfer. The mass transfer will this have to compensate for this. If a mass of Delta M is transferred to the second object, the center of mass shifts by (Delta M) L/(2M) in the opposite direction. So, you must have that:

L E/(2 M c^2) = (Delta M) L/(2 M) --->

E = (Delta M) c^2

So, the energy transfer of E between the masses is accompanied by a mass transfer of E/c^2. One can then conclude that any form of energy transfer is accompanied by a mass transfer of E/c^2. Energy in electromagnetic form can be converted into other forms of energy, so if you could transfer energy energy to an object wothout its mass changing, you could also do this indirectly via the above process after which the energy would be converted to thatother form. But then the mass would change. That would mean that two objects with identical physical states could have different masses, which is obviously impossible.

The conclusion is thus that rest mass depends only on the energy content of an object in its rest frame, and on nothing else. This then implies that rest mass is a redundant concept, it is synonymous with rest energy (the factor c^2 only arises because of the use of inconsistent units for lenghts and time intervals, the natural choice is to measure time and distances in the same units, by putting c = 1). Count Iblis (talk) 16:20, 12 May 2011 (UTC)

what does an atom look like?
Usually,orbitals are shown seperately. it makes me confused. I mean if we look an atom with all its orbitals TOGETHER (valence shells and others) what would it look like? for example what does the Fe atom look like (separately)?

are orbitals in inner shells placed inside the orbitals in outer shells?It will be great if you show me some images or something that can make me understand better.thanks a lot.--Irrational number (talk) 18:10, 11 May 2011 (UTC)


 * See atom. The picture at the top is a good representation of how the electrons form a large cloud around the nucleus. -- k a i n a w &trade; 18:20, 11 May 2011 (UTC)

Thanks but it didn't really help a lot.I want to know what more complex atoms look like. for example:1s2,2s2,2p6,3s2,3p4 what does this atom look like?--Irrational number (talk) 18:26, 11 May 2011 (UTC)


 * They all look the same. It is a tiny nucleus surrounded by a big cloud. The concept of orbitals is for understanding basic chemistry. Electrons don't actually stick to orbitals. -- k a i n a w &trade; 18:45, 11 May 2011 (UTC)


 * This page discusses some very cool tricks with scanning tunneling microscopy, used to produce (apparently) images of molecular orbitals. Here's some more images of atomic and hybrid orbitals from the Nature news blog.  In general, only the highest-energy orbitals can be imaged by these techniques. TenOfAllTrades(talk) 20:35, 11 May 2011 (UTC)


 * I was going to link atomic force microscopy, which has some similar pictures; AFMs can image atom-sized structures by measuring the electrostatic interaction force. But the question is, "what does an atom look like?"  (Emphasis added).  Atomic radii are smaller than the wavelength of visible light - so, at best, atoms look like fuzzy diffraction patterns.  We have to use non-visible light to probe details of atomic structure.  Nimur (talk) 21:16, 11 May 2011 (UTC)


 * An atom looks like a big fuzzy dust bunny. All the orbitals simply overlap, each orbital higher in energy will extend further from the nucleus. Ideally, we should be able to see something that resembles an uggly raspberry, but on most cases these features are smoothed out by atomic/molecular vibrations. Plasmic Physics (talk) 01:29, 12 May 2011 (UTC)

Thanks alot! I think my problem is somehow solved.--Irrational number (talk) 06:51, 12 May 2011 (UTC)


 * An atom is made of several entangled particles. The only way to properly show it is as a waveform in configuration space. It would have three dimensions for each particle, and each point would correspond to a configuration of the atom. — DanielLC 07:44, 14 May 2011 (UTC)

forms
how do u remove concrete forms? dosent it stick —Preceding unsigned comment added by Kci357 (talk • contribs) 18:19, 11 May 2011 (UTC)


 * As it dries, it shrinks a little. It separates itself from the forms. It can stick, in which case you just knock off as much of the form as possible. Sometimes the forms are not removed at all. -- k a i n a w &trade; 18:21, 11 May 2011 (UTC)


 * Release agents can be used to make it easier to remove forms from concrete. Wanderer57 (talk) 19:08, 11 May 2011 (UTC)


 * When I have poured concrete as in fixing steps, I've coated the plywood with motor oil to aid in getting it loose from the concrete. A "greener" release agent is rapeseed or canola oil. Edison (talk) 20:00, 11 May 2011 (UTC)

transformer
why is it so that when primary transformer is connected to A.C. the current in it is very small if the secondary circuit is open but increases when the secondary circuit is closed? —Preceding unsigned comment added by 175.110.91.49 (talk) 18:30, 11 May 2011 (UTC)


 * By "current in it is very small", are you using it to refer to the secondary coil? -- k a i n a w &trade; 18:57, 11 May 2011 (UTC)
 * No, it refers to the current in the primary coil. If the secondary circuit is open the current in the secondary is not small, it is zero.  Dolphin  ( t ) 23:10, 11 May 2011 (UTC)
 * See the article Transformer, which is quite thorough. If a transformer in good working order is connected to the proper primary voltage, then the primary current is relatively small, compared to the full load current. There is an "inrush" or "magnetizing" current lasting several cycles when the AC is first connected to the primary. Its size depends on the previous magnetism present on the core of the transformer, and the point in the AC cycle at which it is connected. The basic rule of transformers is "power in equals power out plus internal losses." If no current is being drawn out of the transformer secondary winding, then the primary current will be limited by a "counter EMF," or electromotive force opposite in direction to the input voltage. Another way of saying this is that when the secondary is open, the primary winding and transformer core act like a large iron core Inductor or Choke (electronics), in which inductive reactance opposes the flow of alternating current electricity. When current is drawn from the secondary, by connecting it to a load, this counter EMF is reduced, so more primary current can flow. In a badly designed transformer, or one with a shorted turn, or one connected to a higher voltage than designed for, or a lower frequency than designed for, the primary current with no load can be high enough to blow a fuse, trip a circuit breaker, or start a fire. Edison (talk) 19:48, 11 May 2011 (UTC)
 * Er, Inrush current is not the same thing as magnetising current Edison.--78.150.228.130 (talk) 14:18, 12 May 2011 (UTC) —Preceding unsigned comment added by 92.29.197.150 (talk)
 * Sadly, 78.150.228.130, you did not provide a reliable source for your claim. That is what engineers I worked with called it. Here is a reference which says "When an unloaded transformer is switched on, it draws a large initial magnetising current which may be several times the rated current of the transformer. This initial magnetising current is called the magnetising inrush current." Edison (talk) 00:00, 13 May 2011 (UTC)
 * But you didnt say magnetising inrush. You said inrush current was the same as (steady state) magnetising current. That is not true.--92.25.237.156 (talk) 17:08, 14 May 2011 (UTC)
 * That's an excellent answer from one whose namesake agitated against the advantageous use of transformers in AC power distribution and did the extreme publicity stunt of slaughtering innocent Topsy. Cuddlyable3 (talk) 10:59, 12 May 2011 (UTC)
 * Poor "innocent" Topsy the elephant. How many humans was it she killed before her owners had her killed, with poisoned carrots and AC electricity, as opposed to the other proposed plans of execution by hanging or shooting? Three humans? Maybe she should have been granted a fourth, fifth, or sixth human. (Three does not seem to be the magic number for present day Tilikum the "Killer" Whale). I've seen no evidence Thomas Edison was  there that day or even heard about the slaughter in advance.  He owned important patents for transformers and for AC electricity, although he favored DC for local generation supplying high density loads, as in commercial districts of large cities. Early AC transformers were inefficient and did not regulate voltage well as load varied.  AC distribution was typically overhead, and electrocuted many utility workers and members of the public in gruesome fashion in the 1870's-1880's, in contrast to his low voltage underground DC distribution, which provided basically uninterupted distribution within a mile or so of the local generating station.  The various "Edison" utilities in the late 19th century supplied alternating current (for distant transmission via transformer substations) as well as direct current (for the business district within a mile of the generating station). Each had its place in the scheme of things. By 1903, when Topsy was executed,  he had been out of the electrical distribution business for over ten years, and the "War of the Currents" had long ago been conceded as a victory for AC. Direct current supplies to high density downtown loads were replaced in the 20th century by AC low voltage network grids, which are still prevalent in major metropolitan areas today. DC supplies from utilities to commercial customers continued to the late 20th century, via inverters. Many commercial customers in the last decade of the 20th century still had DC motors powering fans, pumps and elevators. Edison (talk) 03:01, 13 May 2011 (UTC)
 * Edison reportedly suggested slaughtering the elephant by electrocution, captured the slaughter on film and released the film "Electrocuting an Elephant" that all may view here. If midgets took you captive in a circus, you would be justified in resisting them. Cuddlyable3 (talk) 13:45, 13 May 2011 (UTC)

dipole movement
why does Carbon dioxide does not have dipole movement and carbon mono oxide does have dipole movement(1.857D)? —Preceding unsigned comment added by 175.110.91.49 (talk) 18:50, 11 May 2011 (UTC)
 * Carbon-oxygen bonds create a dipole moment because the electrons in the bond are not shared equally between the two atoms. Oxygen gets a partial negative charge and carbon gets a partial positive charge, creating a dipole as seen in carbon monoxide.  Because carbon dioxide is symmetrical, the two dipoles cancel each other out - there are two dipole moments of equal strength in opposite directions.  148.177.1.210 (talk) 19:49, 11 May 2011 (UTC)

A video series like Zimbardo's "Discovering psychology" (1990)
are there any Educational-for-students video series like the one Zimbardo made in 1990? (revised in 2001)...? i really need to know, i would really much appriciate your help, even i you could ask someone for this, please do, it's very important for me!.

thanks. —Preceding unsigned comment added by 79.178.0.69 (talk) 22:38, 11 May 2011 (UTC)
 * I'm not familiar with the series you mention, but I've seen a few of the series available from The Great Courses and they're pretty good. But I'm just a lay person, so not sure if my opinion is very relevant. You can find what they have on psychology here. There's at least 2 specifically about psychology and several others on related topics. Some are heavily discounted but they're still not what I'd call cheap (for what they are they're probably cheap), maybe you can find them in a university library or something? Vespine (talk) 00:12, 12 May 2011 (UTC)


 * Phil Zimbardo is most famous for his Stanford Prison Experiment; his "Discovering Psychology" is used in high school and college psychology classes all over the world. What sort of educational video series are you seeking?  Another famous Stanford professor, Milton Friedman, created a very famous series of educational videos on economics, Free To Choose; in particular, they are aimed at a general audience, and espouse Friedman-esque economic theory.  Are you looking specifically for video series or general information about psychology?  ... educational series by Stanford professors? ...educational documentaries for a general-consumption audience?  We can help find better resources if you're more specific.  Nimur (talk) 00:29, 12 May 2011 (UTC)
 * Yeah, he's a pretty interesting character, sorry off topic but i just have to say I reckon that guy's true calling was to be a magician, just his "look" would have suited it so well, and tell me "The Great Zimbardo" doesn't have a great ring to it? lol.. Vespine (talk) 01:55, 12 May 2011 (UTC)

Hello Nimur!, many thanks for the long detailed response.

what i look for is Educational-for-student's video-series who explains\teaches Psychology both basic and progressive (similar to the way a book would explain it) but rather in an expamplarist way, with visualisations just like a well-done educational documentary series...

that's what Zimbardo's "Discovering Psychology" does, but the copy my university uses is in very bad video&sound-quality and i already watch it some times.

therefore i need somethings extra, i don't mind paying off coruse!, i just need you guys kind recommendations.

you have my best blessings!. —Preceding unsigned comment added by 79.178.0.69 (talk) 19:59, 12 May 2011 (UTC)
 * A very funny TV episode was on "To Tell The Truth," circa 1977, when the "mystery guest" was "Phil Zimbardo," who had written a book ("Shyness: What It Is, What to Do About It")” about "shyness." There was Phil Zimbardo, and a distractor who acted all "shy," and another guy. Pretty silly when one recognizes one of the contestants as Zimbardo immediately. Edison (talk) 03:17, 13 May 2011 (UTC)

Why does a dropped object land directly below where it is dropped?
I have copied these questions here from the Gravitation talk page, where they are off-topic.
 * If you drop an object here on earth, it gets draged around with the planets spin(we know this because when we drop something it falls exactly where we expect it to even though the planet is spinning), at what distance does this happen? is this drag relevant to the moon? Enertia is in a line, but the planet is spining. Im honistly starting to believe in two gravities?


 * If you believe it's Coriolis_effect then what keeps hot air baloons going around with the planet? "Gravity also drags?"!


 * Paul G Griffiths, Bristol UK 2011
 * —Preceding unsigned comment added by Gafferuk (talk • contribs) 21:17, 11 May 2011 (UTC)

David Wilson (talk · cont) 23:42, 11 May 2011 (UTC)
 * It's not accurate to describe a dropped object as being "dragged around" with the Earth's spin. To simplify the explanation of what actually happens I'll just consider the case when the object being dropped is located on the equator, and ignore the Earth's motion around the Sun (which can be effectively assumed to be very well approximated as being in a straight line for the purposes of this explanation).


 * At the point when the object is dropped it will be travelling eastward at about 1,700 km/hr, almost exactly the same speed as the point on the Earth lying directly below it. After it has been dropped it will continue to move eastward with this same velocity because of its inertia, and therefore It will continue to remain (almost) directly over the spot on the Earth above which it was dropped. At the same time, it will be accelerated downward by the Earth's gravity.  As a result it will fall along a parabolic path (to a very good approximation) and land on almost exactly the same spot above which it was dropped.


 * In theory, before the object is dropped it will be travelling very slightly faster than the point on the Earth directly below it, because it is slightly further from the centre of the Earth, and it will therefore land very slightly eastward of that point. The difference, however, is so small that it's effectively unnoticeable.
 * David Wilson (talk · cont) 23:42, 11 May 2011 (UTC)


 * Good question. The fact that objects, when dropped, land exactly below the point from which they were dropped (as far as the human eye can tell) was one of the reasons most people were reluctant to believe that the Earth rotated on its axis.  Instead, they found it easier to believe that the Earth did not rotate and the sun revolved around the Earth.  One of the earliest experiments to successfully demonstrate that the Earth did in fact rotate on its axis was performed by a Frenchman named Foucault.  He devised a device that would operate reliably, with very little friction, over many hours.  The effect of the Earth's rotation is so small (to the human eye) that it requires an experiment lasting many hours to satisfactorily demonstrate the Earth's rotation on its axis.  See Foucault pendulum.   Dolphin  ( t ) 02:29, 12 May 2011 (UTC)

Ok, fair, what feels strange though is I have a rocket here on earth and is at the rotation speed of the planet as its just sat there, when i fly off why would the rotation speed of the rocket increase to stay directly above its start point? there must be some drag going on here for the rocket to return exactly (atomic accuracy) to its start point if I stoped its thrust and it fell back down. In theory that is. In fact the rotation speed of the rocket must decrease on return. Something to think about too. There must be drag for all this to happen? —Preceding unsigned comment added by Gafferuk (talk • contribs) 03:34, 12 May 2011 (UTC)


 * It won't return to the same spot. It shouldn't do so, even in theory.  On the scale of humans dropping things, the effect of the Earth rotating is too small to notice, but if we are talking about rockets then one would expect to see a non-trivial deflection due to the Earth rotating under the rocket.  Dragons flight (talk) 04:27, 12 May 2011 (UTC)


 * Motion is relative. It can be only measured from a particular frame of reference. Take for example 2 people standing in a train and tossing a ball to each other. If your frame of reference is the train, the ball moves at the same speed in both directions. If your frame of reference is the ground, it moves faster when thrown in the direction train is going. You cannot look at motion in such definitive terms. Recently I read an article that claimed that when you stand still you are actually moving 600km/s if your frame of reference is our local galactic cluster. Try that on for size! 110.174.117.185 (talk) 09:58, 12 May 2011 (UTC)

A rocket that has angular momentum due to Earth's rotation does not necessarily lose that momentum. An illustrative example is the spinning ice skater who can increase/decrease her angular velocity by drawing in/extending her arms, and could repeat that indefinitely if the frictions with ice and air were zero. Launch sites for satellites are chosen near the Equator to maximise the fuel-saving contribution of Earth's surface rotation to their speed. Cuddlyable3 (talk) 10:45, 12 May 2011 (UTC)


 * There was a famous experiment intended to prove Galileo's theory, where a man fired a cannon vertically up into the air, then sat on the cannon. If Galileo's theory was correct that the Earth did rotate, then the cannonball would land to his west; otherwise, he would be crushed by the falling cannonball. The result was that the ball landed a few metres to the west, proving the theory. ~ AH1 (discuss!) 18:47, 14 May 2011 (UTC)