Wikipedia:Reference desk/Archives/Science/2009 March 14

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< March 13 << Feb | March | Apr >> March 15 >
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 14[edit]


How do soundwaves travel from a radio or TV? —Preceding unsigned comment added by (talk) 01:59, 14 March 2009 (UTC)

The same way they do when you speak or make any other sound. The electrical signals inside the radio (or whatever) cause an electromagnet coil to pull or push a small magnet that's glued onto the back of the loudspeaker cone - when the cone moves forwards, it pushes a higher pressure "wave" of air ahead of it - and when it moves backwards it creates a region of lower pressure. It does this hundreds or thousands or even tens of thousands of times per second depending on the pitch of the sound it's producing. The waves travel outwards through the air like ripples when you toss a pebble into a pond (well, kinda) and those ripples eventually reach your ears where the waves of high and low pressure alternately push and pull your eardrum. That in turn causes pressure waves through fluid inside your ear - which wiggles some tiny hairs that are connected to nerve cells that turn those vibrations into electrical signals for your brain. SOund waves are a little bit different from waves in a pond because they push and pull at the air rather than moving it up and down like the water waves. That allows them to travel in three dimensions instead of just along the surface as water waves do. Hence the sound 'ripples' move outwards in spherical patterns instead of circles as water waves do. Sound waves move at somewhere around 700 miles per hour - so the sound waves seem to travel pretty much instantaneously. SteveBaker (talk) 02:09, 14 March 2009 (UTC)
Were you asking how they travel from the radio or TV to your ear, or how they get to the radio or TV in the first place, --ChetvornoTALK 06:25, 14 March 2009 (UTC)

In what year in firearms history was antimony first added to lead in the manufacture of bullets?[edit]

I would like to know in what year in the developmen of firearms was antimony first added to lead in bullet manufacture to cut down on lead deposits in the bore. —Preceding unsigned comment added by (talk) 05:53, 14 March 2009 (UTC)

This page says: "Antimony has been used in shot since the 1800s, but did the Spanish use it in musket balls in the 16th century? I don't know." Given that antimony-lead alloys have been known about since ancient times ["The Elements of Murder: A History of Poison" by John Emsley], it's likely that antimony-lead was used right from the beginning of firearms. --Heron (talk) 14:19, 14 March 2009 (UTC)

Orbits of moons[edit]

As far as I know, all the planets orbit the sun in (almost) the same plane. Do the moons orbit their planets in the same plane ? Are there moons whose orbital plane makes a wide angle (say > 45 deg) to the plane in which the planets orbit the sun ? WikiCheng | Talk 06:05, 14 March 2009 (UTC)

All of the planets orbit the Sun in roughly the same plane (now that we don't count Pluto as a planet). And most of the planets have moons (and maybe rings) which orbit in approximately the same plane. However, the "moon planes" are often different from the "planet plane". StuRat (talk) 06:50, 14 March 2009 (UTC)
See Irregular moon. Dauto (talk) 06:57, 14 March 2009 (UTC)
Longer answer:
It depends on how the moon is formed. If it is a body that originally orbited the Sun and which was later by captured by the planet (such an event must involve the influence of a fourth body), then its orbit can be inclined at any angle. According to the articles on these irregular moons and the Kozai mechanism, inclinations above about 55° are unstable in the long term. One moon with an inclination above 45° is Margaret.
Larger moons that are formed with the planet or broken off it by a giant impact will be regular moons, with low orbital inclination (with respect to the planet's equator, not the ecliptic).
--Anonymous, 06:59 UTC, March 14, 2009.
Take a look at Uranus. The whole planet, rings and moons are tilted at about 98° to the plane of Uranus' orbit round the Sun. Astronaut (talk) 11:06, 14 March 2009 (UTC)
Which is why I said "with respect to the planet's equator". See also the item above about whether that description is appropriate. --Anonymous, 20:04 UTC, March 14, 2009.


What do you get if you mix a liter and a quarter of 2.2 % alcohol and the same quantity of 4.6 % alcohol? The answer at first glance would seem to be the average of the two, but I'm doubtful of that (seems too easy). Could you guys help me out? Thank you so much in advance. Killiondude (talk) 07:19, 14 March 2009 (UTC)

Think of it this way: if you have one liter of mixture at 2.2%, how many liters of alcohol is there? Ditto for the 4.6% solution. Combine the two, you have two liters of which X+Y liters is alcohol; how many percent is that X+Y of two liters. (Yup, taking the average does work.) (talk) 09:48, 14 March 2009 (UTC)
When you mix, say, 1L of 100% ethanol and 1L of water, you get something less than 2L of the solution. However, as you've only got small alcohol amounts (look like beverage-ballpark concentrations?) the volume should not change very much, so yes, you can just take the average. (talk) 10:40, 14 March 2009 (UTC)
Okay, thanks! Killiondude (talk) 19:16, 14 March 2009 (UTC)

Cataract surgery[edit]

Cataract#Cataract_surgery says that operations have been happening since 600BC. It also says that local anaesthetics are used. What would have happened to 600BC patients? And does anyone have any idea how the idea of operating on an eye to cut out milkiness might have come about? -- SGBailey (talk) 08:34, 14 March 2009 (UTC)

Nothing? Well they may have used opium or something but I suspect in many cases nothing was used. I'm not sure but I don't think cataract surgery is the extremely bad when it comes to pain (but I'm not volunteering to try it). You might be interested in surgery and anaesthesia which discusses this (surgery very briefly although it does say "Before the advent of anesthesia, surgery was a traumatically painful procedure and surgeons were encouraged to be as swift as possible to minimize patient suffering") Nil Einne (talk) 13:25, 14 March 2009 (UTC)


Hi all I would just like to make it clear I am not requesting any medical advice from anyone, I am merely rearching the diagnosis and treatment of jaundice. After hours of research, there are a few things which still confuse me, I hope someone can help. First of all, are doctors looking for elevated concentrations of bilirubin in the bloodstream when taking the full blood count? I read somewhere that elevated conjugated bilirubin suggests obstruction of the common bile duct and elevated unconjugated (insoluble?) bilirubin means that there has been excessive destruction of red blood cells. If it is suspected that hepititis is the cause of jaundice I believe doctors use 'viral markers' for heptititis A,B and C to try and ascertain whether or not this is the case. What are viral markers and how is this test conducted? Presumably a blood sample taken to search for the presence of either of the hepititis viruses? When a gallstone obstructs the common bile duct I believe removing the gall bladder is an option - but I thought - upon removing the gall bladder would not the gall stone still be there causing an obstruction? Also does anyone know what causes the dilation of the bile duct when it is obstructed? Sorry to ask so many questions - I am not expecting one person to answer the whole lot if you can answer just one it would help a lot. Many thanks. —Preceding unsigned comment added by (talk) 15:35, 14 March 2009 (UTC)

As you suggest we can't provide medical advice here, but it seems that your questions can be answered fully without providing medical advice. Our Jaundice article does contain a great deal of relevant information and links to more, including answers to many of your questions.
  • Not sure what you mean by "full blood count", so I don't know how to answer the first question. The total and direct bilirubin levels are included in many blood chemistry panels, but are not included in the cell-counting tests often referred to as a complete blood count.
  • Our article on Hepatitis has information on the various causes, and links to each of those with info on the markers. The markers are generally measured in a blood specimen as you surmise. There are many markers, so recapitulating that content here might not be sensible. If you have specific questions, just ask and I'm sure people here can answer.
  • A gallstone in a bile duct can result in increased pressure behind the obstruction, resulting in dilated ducts. There are a variety of ways to remove the stone, addressed here. You're correct that removing the gallbladder would only remove a stone in the gallbladder itself or in the removed portion of the cystic duct.
I hope this helps. --Scray (talk) 16:15, 14 March 2009 (UTC)
(After EC) A complete blood count (CBC) is really only measuring blood cells (red blood cells, white blood cells, platelets) and some other indices that are useful in some circumstances). Measurement of serum bilirubin is a separate test, although it is also performed on blood sample.
Before answering the rest of your questions, here's a quick blurb: Bilirubin is a degradation product of heme compounds, among which the most abundant is probably hemoglobin in the red blood cells. When a red blood cell is lysed, the hemoglobin is converted to (unconjugated) bilirubin and transported to the liver, where it is enzymatically conjugated to become more water soluble. The conjugated bilirubin then makes its way through the bile canaliculi into the gall bladder, where it is stored before being ultimately excreted into the small intestine for disposal in the feces.
Hemolysis will result in a temporary increase in uncongugated bilirubin. The liver is usually functioning normally, however, so any bilirubin that is conjugated there will be disposed of normally through the gall bladder. The consequences of a gall stone blocking the bile duct depends on its location. Since new bile is being continuously produced by the liver, a blockage will create distension of the bile system upstream of that location (like damming a river or an accident on a highway). Depending on the location of the stone, you might just get distension and inflammation of the gall bladder (cholecystitis), or it might block the flow of bile from the liver and therefore cause conjugated bilirubin to "spill" into the bloodstream, since there's nowhere else for it to go. Surgeons can sometimes use endoscopic surgery (ERCP) to pluck a stone out of the bile duct but if the gallbladder is inflamed, a cholecystectomy is performed. Note that because of the anatomy (see bile duct), there is still flow of bile from the liver through the common bile duct even after the gall bladder is removed.
In acute hepatitis there is damage to the liver cells, such that when they burst open they release their contents (including liver enzymes and conjugated bilirubin) into the bloodstream. Chronic hepatitis that leads to cirrhosis might eventually reduce the enzymatic capability of the liver such that unconjugated bilirubin predominates. It depends on the situation. The tests that are usually done to detect viruses (including those that cause hepatitis) are blood tests based on either the patient's antibodies -- which can indicate current or past infection -- or detection of the viral nucleic acid using polymerase chain reaction (PCR) or other such tests. The advantage of the latter molecular tests is that if properly calibrated they can give information about viral load. Does this help? --- Medical geneticist (talk) 16:40, 14 March 2009 (UTC)
  1. The "full blood count" does not test for bilirubin. Bilirubin is part of the screen called liver function tests.
  2. The article "Jaundice" answers your next questions.
  3. Markers of viral hepatitis are blood tests for specific antigens and antibodies.
  4. Cholecystectomy removes stones that are already present in the gallbladder. It also prevent new stones from arising. If a stone is blocking the common bile duct, the commonest procedure is ERCP to remove the stone.

Axl ¤ [Talk] 18:05, 14 March 2009 (UTC)

light in context with black holes[edit]

It has been observed that the path of light turns in the presence of black holes. But there can not exist any gravitational force as light has no mass. Please explain.--Lightfreak (talk) 16:58, 14 March 2009 (UTC)

See gravitational lens. The mass bends spacetime, while light takes the shortest path through spacetime. There is no "gravitational force" in General Relativity—just warping of spacetime and associated accelerations. -- (talk) 17:04, 14 March 2009 (UTC)
While's explanation is ideed correct, it is good to point out that even within newtonian approximation a light ray trajectory would bend. In newtonian mechanics the path of a particle under a gravitational field is independent of the particle's masss, depending on the particle's initial velocity alone. Dauto (talk) 17:59, 14 March 2009 (UTC)
True, true. Indeed, the question is not whether the light is bent by gravity, but by how much. GR and Newtonian physics predict different values for it and are thus distinguishable experimentally along this line (among a few others). -- (talk) 18:06, 14 March 2009 (UTC)
Photons (which make up light) most certainly do have mass - but only by virtue of their speed. Their 'rest mass' is zero. Also, the path of light is bent by much more ordinary objects than black holes. In fact, Einsteins theory of relativity predicted this - and the scientists who verified his theory did so by carefully measuring how starlight is bent by the mass of our sun. (They had to wait for a total eclipse to be able to do this - so it took a few years.) As others have said, gravity bends space - so the photon (in a sense) is travelling in a straight line through space that has been bent - hence it APPEARS to be travelling along a curve to outside observers. Anything with mass bends space to some degree or's just that the amount of the bending is so small that it's not really noticable for things like stars(!) unless you have some pretty sophisticated equipment...but around a black hole, it's very noticable. SteveBaker (talk) 21:31, 14 March 2009 (UTC)

thanks!--Lightfreak (talk) 08:11, 15 March 2009 (UTC)

domestic turkeys[edit]

How many domestic turkeys are there in the world? We have numbers for most domestic livestock, shhep, pigs, cattle, but not turkeys and I would like to know. (talk) 17:00, 14 March 2009 (UTC)

 :Here are the 2000 US production figures. [1] You'd have to go country by country and need a lot of time and a calculator. This site has an overview. [2] Good luck. (talk) 17:56, 14 March 2009 (UTC)
The UN agriculture estimates are available at: [3]. The database includes the ability to search by individual country, by region or by world total. Turkeys are one of the tracked products. They have the figure of 636,000,000 turkeys slaughtered in 2007[4] giving 5,885,012 tonnes of turkey meat. They do not, however, tell howe many animals are alive in total, only how many are harvested. And this entry includes the code A which means "May include official, semi-official or estimated data" Rmhermen (talk) 15:58, 16 March 2009 (UTC)

Why is it that bullets often don't have nice round numbers for their calibers?[edit]

The article on firearm cartridges lists many types of cartridges. Many of them seem to have strange values for their calibers. For example, in the case of the .308_Winchester, 0.308 inch is not a nice round number either in metric or in U.S. customary units. Is there a reason for choices like that? —Preceding unsigned comment added by (talk) 19:17, 14 March 2009 (UTC)

I kinda suspect this relates back to when bullets were simple spherical lead balls. They would probably have specified the bullets by weight - so the weight may have been a nice round number - but the resulting caliber would have turned out to be some inconvenient number. But that's a guess - I don't know for sure. Alternatively, our article caliber discusses bullet sizes but about the only thing that sheds any light on this is the confusion between measuring the diameter of the barrel to the outsides of the grooves or the inside. I suppose that a nice round-number 0.3" internal diameter might grow to 0.308 measured to the bottoms of the grooves. I'm sure someone here will know better. SteveBaker (talk) 23:26, 14 March 2009 (UTC)
The article on the Winchester links to its "parent case", the .300 Savage, though that's a bit confusing because both the .300 savage page and the winchester page list the actual bullet diameter as .308. Could one of those be a mistake? (talk) 23:31, 14 March 2009 (UTC)
Right - but the 0.008" (eight THOUSANDTH's of an inch!) difference sounds like just the right amount to account for the 'rifling' - the spiral grooves inside the barrel. The bullet has to 'take the rifling' - meaning that it has to squash into those grooves. Eight thousandths of an inch sounds about right to me. SteveBaker (talk) 01:03, 15 March 2009 (UTC)
OK, but my issue was that although both have the same diameter (and presumably a 0.008" rifling), one is called a .300 and the other a .308. Is it reasonable to think that they may have chosen to brand the Savage with its base diameter, but the Winchester with its diameter + rifling thickness, perhaps to distinguish them or for some other marketing purposes? If so, that would imply that the "not nice" caliber of the Winchester was, at least in part, a marketing choice. (talk) 04:12, 15 March 2009 (UTC)
According to caliber: "In firearms, the caliber is the approximate diameter of the bullet used. In a rifled barrel, the distance is measured between opposing lands or grooves; groove measurements are common in cartridge designations originating in the United States, while land measurements are more common elsewhere."...does that explain it? 8 thousandths of an inch sounds like a believable difference between land and grooves. SteveBaker (talk) 04:50, 15 March 2009 (UTC)
No, the caliber names are not this precise. They are historical names, often, and the physical diameter, rifling or not, is not precise to the "name" of the bullet. What's more, there are some rounds that have roughly equivalent sizes (7.62mm and .30-06, for example), but are not precisely the same size or round. Rifle rounds and their caliber should be understood as rough approximations of their size, but not precise measurements. This makes sense too when you realize that many of the most widespread rounds were invented over a hundred years ago (the 30-06 is the -06 because it was invented in 1906). Shadowjams (talk) 10:47, 15 March 2009 (UTC)
The rifling is important because without it the bullet could 'roll' around some random axis and the magnus effect would deflect the bullet reducing acuracy. Dauto (talk) 01:48, 15 March 2009 (UTC)
Well...yes...but what does that do to explain the dimensions people choose for bullets? SteveBaker (talk) 04:50, 15 March 2009 (UTC)

The answer to this question is not scientific. It's more a consequence of history, marketing, and randomness. A number of rounds were made in imprecise diameters for unknown reasons. But once they were established, it was an issue of relative changes. More critical, the secondary number on many cartridges, after you get past the ".30" or "7 mm", are purely issues of powder, marketing, or historical significance. To make it even more complicated, many calibers are not what they seem to be. A number of bullets have "calibers" that are very different from their actual fractions of an inch measurements. For a little bit of background check out Gregg Lee Carter, Guns in American Society, isbn 1576072681, page 102-03. It's available on Google books. There's a small section that will explain a little bit of the insanity. If you want a historic reason why a particular cartridge is why it is, I don't know it, but if you find it out, please add it to the appropriate article. Shadowjams (talk) 10:42, 15 March 2009 (UTC)

Why do some ducks quack constantly?[edit]

Having observed a lot of mallard ducks recently, I've noticed that the males in particular seem to quack almost continuously when just walking or swimming around(especially if they're with females). Is there any reason for this constant noise-making? (talk) 21:07, 14 March 2009 (UTC)

Same reason some young man need noisy motorcicles, I suppose. Dauto (talk) 21:11, 14 March 2009 (UTC)
Er, are you sure it is the male that is quacking? As far as I know it is only the female that quacks. Here is what Steve Madge and Hilary Burn say about Mallards in their reference book Waterfowl (p. 211): "Voice. Quite vocal, especially female. Male utters a soft, rasping 'kreep'. Female's most obvious call is a series of quacks, quite mocking or laughter-like in delivery, descending towards the end, 'QUACK-QUACK-QUACK-quack-quack-quack...', heard mostly in late summer and autumn. Similar descending series of quacks are uttered by several other females of the genus." Possibly the mallards you are observing are hybrid or feral domestic ducks that haven't read the book I quote. This still doesn't answer your question as to why they quack so much, regardless of whether they are male or female.--Eriastrum (talk) 22:50, 14 March 2009 (UTC)
Certainly our article duck says that only the females quack. Bird vocalization says that short 'calls' like quacks are used to keep the flock together and to alert fellow flock members to danger. Perhaps they are only quacking when you are nearby and posing a danger to them. You might not think you are a danger but...mmmm...crispy duck with orange sauce. SteveBaker (talk) 22:51, 14 March 2009 (UTC)
Your answer may be overpopulation. "Duck territories" on ponds and in public parks are much closer together than they ought to be. That has led to lots of unfavorable behavior changes. Things like a bunch of juvenile ducks getting together and gang-raping a female, females getting drowned by a bunch of males trying to mate, juveniles of both sexes getting killed by older ducks; all that has been described as a result. Apparently experts have some special terms for male quacking. (All male ducks in the poll refused to quack when questioned :-) OR: Male Mallards have been observed to issue a variety of calls/quacks for different purposes: food call (cascading downwards), mating call, attack/retreat calls (the Donald Duck like enraged screams), "ranging quack" issued while a pair is together to keep the female close, particularly in uncertain situations. (This is a sort of under his breath grumble and may be what you have heard.) Although it may seem counterproductive to get noisy when a predator is near, lots of birds making noise in different directions actually confuses most predators because they find it harder to decide which one to go chase. Eriastrum's explanation that what we see most often are actually some hybrids might have something to do with it, too. Particularly interbreeding with domestic species, because the above behavior has been observed in public parks on 3 continents. (Does our KurtshapedBox do ducks, too, or just gulls and doves?) (talk) 10:26, 15 March 2009 (UTC)
The "ranging quack" sounds about right; the male mallards I've seen usually make this (fairly quiet and nearly constant) sound when with a female. (talk) 16:21, 16 March 2009 (UTC)

CO2 in an aquarium[edit]

Hi. Let's say a small aquarium has an abnormally high pH level. Would blowing in one's breath through a straw help to lower the pH? Or would this have too small an effect or would it be more harmful than helpful to the occupants? Thanks. ~AH1(TCU) 21:37, 14 March 2009 (UTC)

So your theory is that dissolving CO2 from your breath will create enough carbonic acid to make a measurable difference? Well, you're right that there is CO2 in your expelled breath and that when you dissolve CO2 in water it makes carbonic acid...but the question is "how much?". Gut-feel says not enough to make a difference. Only 5% of your exhaled breath is CO2 - and only a tiny amount of that will actually dissolve in the water because it's not under enough pressure and you're probably making quite big bubbles where the interface between water and gas doesn't have enough area to allow much of that CO2 to meet the water before the bubble reaches the surface of the tank. When they carbonate fizzy drinks, they use pure CO2 at a pressure of 100 to 150 psi. SteveBaker (talk) 22:49, 14 March 2009 (UTC)

I agree, especially as it's a "small aquarium" with an "abnormally high pH level". You're better off giving small, regular water changes with more stable pH water. (talk) 23:41, 14 March 2009 (UTC)

The effect you may be looking for is dispersing more oxygen in the tank and thus encouraging aerobic rather than anerobic entities to thrive. This would allow ammonia from fish waste to get broken down. The problem is twofold: You'd stir up sediments from the bottom or your aquarium, thus severely decreasing water quality until the population has changed. Your exhaled air contains less oxygen than the ambient air. (Not sure how big an effect that would have). Incremental water change suggested above sounds good. Also ask at your local aquarium supplies store. They usually have several products available to counteract acute ph imbalance. (like e.g. tablets, "green sponge" filter, powder etc.) Which product you need depends on a lot of things including what fish, plants and other creatures you keep, temperature, size of your aquarium. etc. So either call ahead and ask or bring as much data on your aquarium as you can. This page might also be useful. [5] - (talk) 06:19, 15 March 2009 (UTC)