Wikipedia:Reference desk/Archives/Science/2008 March 3

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March 3

feeder fish

i need to know the habitat for the guppy and goldfish feeder fish. what would i do to habitate these fish? brie —Preceding unsigned comment added by 70.149.24.57 (talk) 00:03, 3 March 2008 (UTC)

I'm not sure what you mean by "habitate", but if you are asking about their habitat with the idea of releasing them, Don't! It's against the law in most areas to release aquarium or pond fish into the natural environment. By doing so, you risk introducing an invasive species or introducing diseases into natural bodies of water. If this is not what you meant, please clarify.--Eriastrum (talk) 00:42, 3 March 2008 (UTC)

I'm think (s)he's asking what sort of aquarium habitat would be suitable for raising the fish. -- MacAddct  1984 ^{(talk • contribs)} 01:38, 3 March 2008 (UTC)

guppy goldfish The answers are there87.102.93.158 (talk) 10:31, 3 March 2008 (UTC)

Or why not just search for "guppy keeping breeding" or whatever??87.102.93.158 (talk) 10:32, 3 March 2008 (UTC)

Or even "guppy habitat"87.102.93.158 (talk) 10:33, 3 March 2008 (UTC)

Did you mean 'natural habitat' or 'aquarium' habitat?87.102.93.158 (talk) 11:09, 3 March 2008 (UTC)

What if Jupiter were more dense?

Jupiter, when compared with the terrestrial planets, is relatively light for its size (1.326 g/cm³). If Jupiter were the density of, let's say, Earth (being the most dense at 5.5153 g/cm³) would it have any noticeable gravitational effects on the other planets? -- MacAddct  1984 ^{(talk • contribs)} 01:29, 3 March 2008 (UTC)

Noticeable? --hydnjo talk 01:39, 3 March 2008 (UTC)

Most likely yes, all gravitational forces created by an object within the solar system would produce an effect/change. I'm assuming the user asking the question is thinking hypothetically, as if it were possible to change the density of the planet now. Wisdom89 _{(T / ^C)} 01:42, 3 March 2008 (UTC)

Yeah, just to clarify: All of a sudden, Jupiter's density became that of Earth's, while remaining the same volume that it is now. Would it be enough to significantly alter the orbits of surrounding planets or is it relatively negligible when compared to the Sun's current effects? -- MacAddct  1984 ^{(talk • contribs)} 01:46, 3 March 2008 (UTC)

I think a precise definition of "noticeable gravitational effects" is required. Even at its present mass, Jupiter does have significant effect on the solar system, creating stable orbits for the objects of the asteroid belt. Any mass change of Jupiter would change those stable orbits, which would be visible from Earth. At some critical value(s), Jupiter's mass would be large enough to destabilize other orbits. The mathematics of n-body orbital dynamics and stability is not trivial, so it's hard to say off hand what the required mass would be, say, to destabilize Earth's orbit. Nimur (talk) 06:01, 3 March 2008 (UTC)

Also, I can't help but probe your hypothetical "all-of-a-sudden" transition. What other things stay constant? Is the total angular momentum of Jupiter preserved, or is its orbital velocity preserved? What about the moons of Jupiter? Should we allow their orbits to collapse, or increase their velocities or masses to create new stable orbits for them? A lot of hypothetical questions self-defeat, if you pursue the nitpicky side-details. Nimur (talk) 06:07, 3 March 2008 (UTC)

Another way to ask the question would be, if Jupiter had the density of the Earth, then would the solar system exist in its current state? If not, what would be altered? That takes care of the all-of-a-sudden dilemma. Wisdom89 _{(T / ^C)} 08:56, 3 March 2008 (UTC)

Scull preservation

Dug up an animal scull and want to preserve it. Can i boil it in salt water and then soak it in hydrogen peroxide to make it white again?

JERRYLEGO (talk) 02:06, 3 March 2008 (UTC)

Do you mean a scull or a skull? :-) —Steve Summit (talk) 03:08, 3 March 2008 (UTC)

Have an ant hill handy? Some sun, wind and weather? Julia Rossi (talk) 09:37, 3 March 2008 (UTC)

I love to see animals rowing. Edison (talk) 19:50, 3 March 2008 (UTC)

Your best bet, if there's a university, or museum of natural history nearby, is to call the department of anatomy or biology and ask if you can use their "bug room" to clean your skull. Dermestid beetles Dermestes maculatus are the best workers for the job. - Nunh-huh 02:58, 5 March 2008 (UTC)

physics

what is a fly wheel?84.254.189.64 (talk) 08:49, 3 March 2008 (UTC)

See the article Fly wheel. Cheers! Wisdom89 _{(T / ^C)} 08:54, 3 March 2008 (UTC)

Animals used to attack forts

Which animal was used in the olden times for climbing onto high walls of forts? —Preceding unsigned comment added by 220.224.109.59 (talk) 12:26, 3 March 2008 (UTC)

Tortoise? Perhaps another animal name used as an analogy? AlmostReadytoFly (talk) 12:34, 3 March 2008 (UTC)

Just wondering is this a joke, or riddle, or as suggested above a siege machine with an animal name??? Otherwise perhaps a monkey with explosives attatched87.102.93.158 (talk) 14:02, 3 March 2008 (UTC)

I'm not sure if war elephants were used for this, but it might work for a wall that was only about 10 feet tall. They could also smash down taller walls, unless they are made of thick stone. StuRat (talk) 19:11, 3 March 2008 (UTC)

Many "animals" were used in siege warfare. In addition to the Testudo formation, in ancient times, a tortoise referred to a covered, wooden shed on wheels, which was effectively a mobile shield defense, which could be adapted to many tasks during a siege: digging, ditch filling, boarding bridges, cover for the rams etc; by the Middle Ages these were given other names, including cat, owl, weasel,rat, sow. There's also a little-known wolf, which seems to have been used as a defence; it had iron gratings which could be snapped shut, trapping attackers in its jaws. A scorpion was a type of throwing machine; there's a raven, which was like a ram with a hook for pulling walls down. Wikipedia seems a little lacking on references to these, although at Siege engine you can see some tortoise/sow covers over some engines. And, of course, there's the Trojan Horse. If you want real animals, then Olga of Kiev supposedly destroyed a town by attaching burning tinder to birds' feet; John I captured Rochester Castle by burning the fat from 40 pigs; the Franks dropped hot oil, wax and fish on the attacking vikings during the Siege of Paris (885-886); see Early thermal weapons (if I might plug the article I'm currently working on) -Gwinva (talk) 00:21, 4 March 2008 (UTC)

Of course, there's the ram as well, which I managed to mention without referring to the sheep! Gwinva (talk) 02:38, 4 March 2008 (UTC)

Oxide solubility

Hi,

-which oxides of nitrogen, sulphur, phosphorus and carbon are soluble in water (I just need one example each)? Is there even one for nitrogen? I would also need their water solubilities, so it'd be great if you could point me to a reference where I can find these values.

Thanks, Duagloth (talk) 13:05, 3 March 2008 (UTC)

Nitrogen oxide and read the links to the different compounds.

Similarily carbon oxide, sulfur oxide

Also read Oxide it has a list - search this page for 'phosphorus'

Yes there are soluble nitrogen oxides

Note searching the web for "element + oxide" does work well and there are many pages aimed with education in mind eg http://www.google.co.uk/search?hl=en&q=phosphorus+oxides&meta=

Hint - many of these react with water to give new compounds.. Carbon dioxide is an exception - though it too does react a bit. Only a few are unreactive to water.

Don't forget to check the 'infobox' on the right eg Carbon dioxide right table sub heading "Solubility in water" gives 1.45 g/L 87.102.93.158 (talk) 13:58, 3 March 2008 (UTC)

If you have a text book try looking in the index or chapter headings for 'periodicity' and oxides - it's quite a common topic. —Preceding unsigned comment added by 87.102.93.158 (talk) 14:00, 3 March 2008 (UTC)

Acceleration

How can we detect whether a body is moving with acceleration or not?I mean to say that if we find something is moving with constant velocity with respect to a man living on the earth, it is moving with acceleration alongwith the motion of the earth because the earth itself is moving around the sun.If it is moving with constant velocity with respect to the solar system it is again moving with acceleration with respect to the galaxy etc etc.What is the absolute reference with respect to which we can measure acceleration of anything? Thank You —Preceding unsigned comment added by 202.70.64.15 (talk) 15:14, 3 March 2008 (UTC)

Inertial frame of reference may help. I believe the short answer is that no one frame of reference is inherently superior to any other. Friday (talk) 15:19, 3 March 2008 (UTC)

Coupled with that, it may be useful to make it explicitly clear that there is no "absolute" frame of reference. As Friday notes, any arbitrary frame is valid, and frames are generally selected for convenience. — Lomn 16:01, 3 March 2008 (UTC)

Acceleration can be measured with an accelerometer. The only problem is that an accelerometer cannot distinguish between gravitation and the more common sense of acceleration. You can get different measurements for acceleration by taking your measurements in different reference frames, but inertial reference frames will always agree on whether the accelerometer reads zero. Someguy1221 (talk) 19:19, 3 March 2008 (UTC)

The cheapest type of accelerometer is simply a cup of coffee. If you are accelerating, you will spill your coffee. If you are not accelerating, you will not. You can detect acceleration with relativity (you can't distinguish absolute movement of any sort between two inertial frames, but you can between accelerating frames), but, as Someguy1221 points out, you can't distinguish acceleration from gravity. But in many cases that doesn't really matter unless you are seriously worried about mysterious gravitational fields showing up unannounced. --98.217.18.109 (talk) 23:26, 3 March 2008 (UTC)

Energy Question

If the world is full of energy and matter then why is it so difficult to harness energy? —Preceding unsigned comment added by 202.70.64.15 (talk) 15:18, 3 March 2008 (UTC)

Because energy has to be in a useful form. You were given answers to a similar question above (March 1, once the archives kick in). — Lomn 15:58, 3 March 2008 (UTC)

Also we don't know how to harness all of it efficiently. There are technological hurdles to overcome. 64.236.121.129 (talk) 17:39, 3 March 2008 (UTC)

Lice in a sauna

Hi, can a sauna be an ultimate method of getting rid of lice? AFAIK they don't survive in temperatures above 60°C. Gil_mo (talk) 15:26, 3 March 2008 (UTC)

A google search for 'sauna lice' shows that it's often claimed as a good method, but I haven't found anything I'd cite as a reliable source so far. AlmostReadytoFly (talk) 16:20, 3 March 2008 (UTC)

Body hair, sweat and evaporative cooling - the same mechanisms we use to survive sauna temperatures - would also provide a survival advantage to the lice. If you get the air temperature next to your skin up to 60 deg C, then you will burn within a matter of seconds. So will the lice, but there's easier ways of getting rid of the little suckers. Mattopaedia (talk) 02:07, 6 March 2008 (UTC)

what is electris current?

i want to know what is electric current really made of. most say it's flowing electrons but others speak of electromagnetic waves, sighting low drift velocities as evidence. i've read wiki's page on electric current but am still confused. please help. scoobydoo (talk) 16:22, 3 March 2008 (UTC)

Instantaneous electric current is, by definition $i(t)={\frac {dQ}{dt}}$. If you're not familiar with calculus, read the article derivative. --Taraborn (talk) 17:59, 3 March 2008 (UTC)

In semi-laymen's terms is the movement of charge measured in coulombs divided by time in seconds. Wisdom89 _{(T / ^C)} 18:01, 3 March 2008 (UTC)

I'd go with the flowing electron model. The simplest way to think of electrons is as spherical particles, but a more correct way to think of them is as quanta of energy with a probability function describing their position. Pick whichever model you find most comfortable. StuRat (talk) 19:18, 3 March 2008 (UTC)

Electric current is exactly the flow of charged particles (typically, electrons, in most circuits; ions in some other cases). Nothing else is electric current. Electromagnetic waves can cause current; or they can be caused by current; and the complex interaction of current and waves are found via the application of Maxwell's equations of electrodynamics. In the case of "drift velocity", it is accurate to say that the drift velocity of an individual particle may be much slower than the net transfer of power through a system. In this case, the energy is propagating as a wave, closely coupled to a current. Because current can also travel as a wave, it is possible for a current to propagate farther than any individual charged-particle moves. This commonly happens when you turn on a switch to an electric light in your house. The electrons may never actually move from the switch through the light - but they each individually move such that energy propagates through the circuit. Nimur (talk) 19:46, 3 March 2008 (UTC)

Electric current can also be the flow of holes in a semiconductor or of positive ions. It is not always electron flow. Edison (talk) 19:50, 3 March 2008 (UTC)

(Depending on your school of thought, Edison, "hole transport" is just a different mode of electron transport)... and I did also mention ions, such as in some fluorescent lights and chemical batteries! Nimur (talk) 21:19, 3 March 2008 (UTC)

Your explanation was excellent. But I seem to remember, from an electrical engineering class long ago, an experiment which showed that hole current was the flow of positive charges rather than negative charges. Edison (talk) 02:58, 4 March 2008 (UTC)

For understanding drift velocity versus energy transfer, maybe this analogy will help. There's a glass bottle sitting on the ground, out of reach, and you want to tip it over. One way is to throw a rock at it. In that case the atoms making up the rock actually travel the whole distance from your hand to the bottle. Another way is to take a long stick (which happened to be conveniently lying on the ground between you and the bottle) and push the bottle with that. In that case the atoms making up the stick only move a small distance, much less than the length of the stick. Electricity works like the stick; the electrons (or holes or whatever) move only a small distance, but a small forced movement of electrons at one place in the circuit (the power source) is very quickly transmitted the whole way to the device being powered. -- BenRG (talk) 00:06, 4 March 2008 (UTC)

Travel in Space

If I was to travel in space in what could broadly be described as a straight line (from an Earth Orbit) at a constant acceleration of 1 gravity (32 feet per second per second) how long would it take:

a) For me, as I would experience duration, to pass within 93 million mile of the nearest star to the our Sun

b) From the viewpoint of an observer on Earth, who may use that reference point, to plan on receiving a radio signal in 4 1/2 years time from that point

c) Could I assume that if I was to accelerate for half the distance and decelerate for half the distance, duration (as both I and the observer on Earth would experience) be more or less exactly twice the answer to (a) above —Preceding unsigned comment added by Paul Hayward (talk • contribs) 17:16, 3 March 2008 (UTC)

(a) is basic calculus. a(t)=9.8 m/s²; v(t)=9.8t m/s; f(t)=4.9t². 93 million miles (150 billion meters, give or take) takes about 175000 seconds or 2 days. Your speed caps at about 0.6%c, so relativity can be safely ignored.

(b) I don't follow. Do you want to go 4.5 light years? Ignoring relativity, that would be 93 million seconds or about 3 years. However, that's a theoretical top speed of 3c. I'm not comfortable enough with the math for relativity to do any back-of-the-envelope calculation.

(c) Not at all. It's double the time to go halfway, which is not the same. In accelerating past your destination, the second half (distance) of the journey continues your positive acceleration. When stopping at your destination, the second half is under deceleration. It takes about 125000 seconds to go halfway from the Earth to the Sun at 1g (note that this is around 2/3 the transit time in (a)) so about 250000 seconds or 3 days to stop at the sun. Two days acceleration followed by 2 days deceleration would place you back at the Earth's orbit on the far side of the sun. — Lomn 18:42, 3 March 2008 (UTC)

I think the original question is trying to conceptualize travel and communication to Proxima Centauri, the star nearest to our solar system; the final destination being approximately earth-like orbit around Proxima Centauri.

First of all, the idea of traveling in a straight line defies orbital mechanics, but supposing that you wanted to waste a lot of effort and fuel to correct your trajectory to be "straight-line"-like, it could probably be done. It is not likely you could do this with a "constant acceleration", because you are working against a variable gravitational field.

In the interest of scientific accuracy, I think you should not try to apply straight-line kinematics to this problem; traveling across immense gravity wells is not the same at all as traveling on a straight road. See orbit for an introduction to the math you should apply to calculate your travel time, energy consumption, and trajectory. After you find the set of orbits which satisfy the fundamental gravitational constraints, you can begin worrying about things like speeding up to relativistic velocities. Nimur (talk) 19:54, 3 March 2008 (UTC)

Regarding the fuel bit, if you can sustain 1g indefinitely, then I figure to hell with any sort of efficient least-energy approach. Orbital mechanics matter to spacecraft because you can't accelerate willy-nilly. — Lomn 21:45, 3 March 2008 (UTC)

I'm a bit concerned about the calculation of 'top speed'. Neglecting the orbital speed of the Earth, a one gee acceleration (about 10 m/s^2) gets to 0.5 c (about 1.5e8 m/s) in about 1.5e7 seconds, or about six months. Relativity is definitely going to rear its ugly head.

In response to Nimur's comments, I will observe that while neglecting orbital mechanics is a bit sloppy, being able to supply a constant one-gee thrust over years of flight duration allows one to 'brute force' one's way out of quite a lot. Earth's orbital speed is about 30 km/s, which could be completely negated by a bit less than an hour's thrust. At Earth's distance from the Sun, acceleration due to solar gravity is less than 0.1% of one gee; nearly negligible. Yes, you're climbing out of a gravity well, but (per Lomn's comment) if you can pull one gee indefinitely then you can pretty much ignore the effect of the Sun and the planets. TenOfAllTrades(talk) 22:37, 3 March 2008 (UTC)

In special relativity the time it takes to travel a distance d at a constant acceleration a starting from rest is exactly ${\frac {c}{a}}\cosh ^{-1}\left(1+{\frac {ad}{c^{2}}}\right)$. By a happy accident, one gee times one light year is very close to c² (within about 3%), so at one gee acceleration the time in years is about cosh⁻¹ (1 + distance in light years). For small values of x, cosh x ≈ 1 + x²/2, so for short distances the time in years is around ${\sqrt {2\cdot {\mbox{distance in light years}}}}$, which is also the Newtonian answer. For large values of x, cosh x ≈ e^x/2, so for long distances the time in years is around $\ln(2\cdot {\mbox{distance in light years}})\,\!$. So the distance traveled is exponential in the time taken—you can travel a billion light years in about two decades (or four decades if you start decelerating halfway). But there are two serious problems. First, the amount of fuel you need is also exponential; second, at high enough speeds the CMBR and cosmic dust are blueshifted to lethally high energies. -- BenRG (talk) 23:26, 3 March 2008 (UTC)

Mineral residue in pan after boiling water

The air in my home has been extremely dry as of late, causing me to get nosebleeds. I've been trying to add moisture to the air by boiling water, but there is always a white residue of minerals and whatever else may be in drinking water stuck on the pan. What is this residue and is there anything I can add to the water for the residue to bind to instead of crusting up my pot? It's rather hard to scrub off... Also, why is it never apparent when food is in the water boiling along with it? Does the residue soak into the food (e.g. noodles) and is this unhealthy? Thanks! Jihiro (talk) 17:18, 3 March 2008 (UTC)

Why not just get a Humidifier? 64.236.121.129 (talk) 17:38, 3 March 2008 (UTC)

Thank you, but that's not the point. If I wanted to spend money on a humidifier, I wouldn't be taking the cheap easy way. ^_^; Jihiro (talk) 17:48, 3 March 2008 (UTC)

Spend the 15 bucks and get something that actually works. IMO, it's the simplest solution. 64.236.121.129 (talk) 15:35, 5 March 2008 (UTC)

You're right that it's minerals. For its composition and more, see Hard water. moink (talk) 17:51, 3 March 2008 (UTC)

There are coils of metal wire that usually go in kettles to which the 'scum' will preferetially attach. Unfortunately I can't remember for the life of me what they are called. But you need one of those.87.102.93.158 (talk) 17:54, 3 March 2008 (UTC)

I always assumed that the reason the buildup doesn't show up when boiling food is that you don't go through as much water; you boil the water for maybe 10 or 15 minutes, then you turn it off and dump the water. When humidifying, you're boiling for longer, and all the water that gets into your air came from the pan, leaving those minerals concentrated enough to condense (crystallize?) onto the pan. Since money saving is important to you, you might want to look at the utility cost difference, since boiling water on a stove is pretty inefficient. jeffjon (talk) 18:20, 3 March 2008 (UTC)

Some thoughts (are you moist with anticipation ?):

1) Minerals can build up from boiling food in water, but rarely do, since you don't typically boil much water away when food is prepared, dump the remaining water containing the minerals, and wash the pot after, which removes any small quantity of minerals along with the food residue.

2) Humidifiers also accumulate mineral residue, unless you use distilled water, which is rather expensive when used in such quantities. An exception is an ultrasonic humidifier, where the minerals don't accumulate, but rather go into the air. This might sound like an advantage, but having things like chlorine from the water vaporized into the air is quite annoying (it eventually becomes a white dust on the furniture), so it becomes even more important to use distilled water.

3) My suggestion: use the junkiest old pots you have (or can scam from friends and relatives) for boiling water, and don't worry about the mineral buildup. Avoid aluminum pans, however, or those with a nonstick surface, as you will sooner or later boil the pot dry and burn it. Fumes from overheated aluminum and nonstick pans can be toxic. An old cast-iron pot would be good to use.

4) You might also want to prepare more boiled foods in winter, like soup, since the extra heat and humidity is appreciated then, and use the microwave oven more often in summer, when heat and humidity are to be avoided.

5) Also be careful not to boil too much water, as the air in a house in winter can only hold so much moisture. If moisture starts condensing on windows and exterior walls, it's time to cut back on boiling water, as it's no longer staying in the air but only providing a breeding ground for mold.

6) If you have kids in the home, I wouldn't boil water either, as having a pot of boiling water on the stove all day dramatically increases the chances that they will suffer serious burns.

7) If you have a gas stove you use to boil water, beware that combustion products from the flames are filling your home. While the small amount produced by cooking isn't normally a problem, the much larger quantity of combustion products from continuous boiling of water can build up to toxic levels, as well as deplete the oxygen supply. You could, of course, open a window or two, but there goes the heat and humidity, too. If this is the case, you may need to bite the bullet and buy a humidifier. Another option is to just leave pans of water out so that evaporation will do the job for you. Water will, of course, evaporate much more slowly, but placing many trays of water where air from the furnace blows on them will help to speed things up a bit. This also has the advantage of being safer and cheaper.

8) The shower can also be used to humidify the house. If you would normally take a bath, instead turn it to the shower setting and fill the tub that way. To prevent the humidity from condensing out on the bathroom mirrors and walls, leave the door open and use a fan to blow air in and out of the bathroom. Also, don't drain the bath or shower when done, but leave it there at least until room temperature, and better yet until right before the next bath or shower.

9) To help with the nosebleeds, try a spray mister device that will spray saline solution into your nostrils. You should be able to find them in the pharmacy section of any store. If you also get chapped lips, use lip balm to help with that. If you have dry skin, use moisturizer. You should also check with your doctor, as nosebleeds can be a sign of disease.

10) Be sure to drink lots of water, as that helps keep your nose, lips, and skin moist.

11) As for food absorbing minerals, I doubt if much of this happens, but some of those minerals that are absorbed, like calcium and iron, are helpful, while others are not, like sodium and arsenic. However, the quantity absorbed of the unhealthy minerals is likely too low to matter. StuRat (talk) 18:26, 3 March 2008 (UTC)

Anyways, the residue usually is mostly CaCO3. It's hard to scrub, but it easily yields to any form of acid. Get vinegar or better a neutral vinegar concentrate, put 3 tablespoons or so in the pot, and let it stand for a while, then rinse and repeat as necessary. Heating the pot speeds up the process (but don't boil away all the vinegar). --Stephan Schulz (talk) 18:31, 3 March 2008 (UTC)

Why buy a device to spray liquid into your nose? Just inhale a few drops of tap water. It can't hurt, and I think it helped me when I had that problem. The other thing I did was, if I did get a bleed, to insert a tissue soaked in ice water into the nostril repeatedly until the cold stopped the bleeding. That way there was no residue of blood to become itchy when it dried. (Yes, this is Original Research.) --Anon, 22:51 UTC, March 3, 2008.

Can't hurt? If you've ever been swimming, you'll know that water up the nose hurts like the blazes. --Carnildo (talk) 23:51, 4 March 2008 (UTC)

I didn't mean that much water. --Anon, 00:53 UTC, March 5.

My humidifier fills up with mineral crust too if it is not emptied. You get concentrated mineral water. Graeme Bartlett (talk) 22:15, 3 March 2008 (UTC)

Sometimes it's enough to leave bowls of water in different areas and just trust in evaporation. And I agree with the tips especially keeping yourself hydrated, balm and nasal sprays and the bath water -- Julia Rossi (talk) 07:35, 4 March 2008 (UTC)

Dog run and swim speeds

Approximately how fast can a dog run, and how fast can it swim? The number doesn't need to be exact, in fact I will probably round it to something convenient. I am thinking of a black lab or a golden retriever, some kind of domestic dog that plays fetch. moink (talk) 17:43, 3 March 2008 (UTC)

From our article Greyhound (the fastest dog), it can reach speeds up to 72 km/h. The smallest and weakest breeds are slower than an average adult human, so probably less than 25 km/h or even 20 km/h. As for the swimming speed, I think they're pretty slow, slower than a front crawl swimmer, so my guess is... about 4km/h. --Taraborn (talk) 18:19, 3 March 2008 (UTC)

Given that the world-record-holding dog can swim 6.4 km in 73 minutes (5.3 km/h), Taraborn's guess is probably reasonable for average dogs. Moink, consider whether you want a burst speed or a sustained speed (like the above). For comparison, the human world record for a 10km run (26:17.53) is only about 67% the average speed of the record 60m sprint (6.39s). jeffjon (talk) 18:31, 3 March 2008 (UTC)

Thanks. I was hoping to be able to choose them to be two elements of a Pythagorean triple, but that's not happening it seems. So I'm going with a tenth of one, and choosing run speed=6.1 m/s, swim speed =1.1 m/s. Should be close enough to not require too much suspension of disbelief. moink (talk) 19:08, 3 March 2008 (UTC)

It sounds like you're squaring the velocities - are you trying to calculate the kinetic energy of a running dog? Nimur (talk) 19:56, 3 March 2008 (UTC)

No, I'm writing a homework question based on this experiment. Actually, following a link there to the published paper, the mathematician's Welsh Corgi ran at 6.4m/s and swam at 0.91 m/s. I only found the link after asking this question, figuring I should see if there was a published source for anecdotal story I had heard. moink (talk) 20:30, 3 March 2008 (UTC)

Circuit analysis

Was running over some circuit analysis and I met the emphasized point that you don't connect voltage sources in parallel or current sources in series because it would break down Kircoff's laws. So in reality what happends if you do these connections?Bastard Soap (talk) 19:10, 3 March 2008 (UTC)

Voltage sources and current sources are idealized concepts used in circuit analysis. No such devices exist in reality. What happens when you hook up various power-providing devices in various ways depends on the devices, and can sometimes be destructive. For example, hooking two sets of alkaline batteries with different nominal voltage outputs (which means different numbers of cells in series inside the battery), in parallel, will cause the higher-voltage one to charge the lower-voltage one, and can cause the latter to explode, getting acid all over your carpet. moink (talk) 19:18, 3 March 2008 (UTC)

For ideal current sources in series, there would have to be two different currents in the same wire, which is impossible. For two ideal voltage in parallel, there would have to be two different potential differences between the same two terminals. It would be a mathematical impossibility. For actual sources of current or voltage like batteries, regulated power supplies, or transformers, if the difference was very significant large currents could flow, damaging equipment, making wires heat up, making storage batteries explode, or (hopefully) blowing fuses. In the real world, two voltage sources connected by wires or even large copper bus bars would have the resistance of the wire or bus bar between them, and if its fraction of an ohm were put into the circuit analysis. you could calculate the huge current that would flow until something blew. Fault analysis in power systems works something like this. Edison (talk) 19:48, 3 March 2008 (UTC)

At a certain stage in standard academic treatment of the electrical engineering curriculum, the concept of "ideal" voltage and current sources ceases to exist. At this level of analysis, realistic models of a device are used; sometimes the configuration is such that it will be a "current source" or "voltage generator" circuit - and is a fairly standard "textbook" topology. In that case, connecting two model current-sources in series, for example, will have a real and calculable result - maybe you will over-current or under-current, change the voltages unexpectedly, etc. Furthermore, if you end up with an out-of-range parameter, your device may be destroyed as Moink and Edison described. Nimur (talk) 20:05, 3 March 2008 (UTC)

When jump-starting a car, you connect the batteries in parallel, and until you connect them they're at different voltages because one's charged and one's flat. Once you've connected the extra battery to the flat one, the voltage across both of them will be about the voltage across the extra battery. AlmostReadytoFly (talk) 00:28, 4 March 2008 (UTC)

A current source in the real world or for calculation purposes would be a very high voltage with a very high series resistance. Suppose you have 1,000 volts with 1,000,000 ohms in series, to produce 1 milliampere through a direct short. If instead of a direct short you presented 500 ohms between your thumb and index finger, the current would be 1,000/1,000,500 or .9995 milliamperes, 99.95% of the short circuit current, or the same current for all intents and purposes. (I have experienced such phenomena, and it is not pleasant!) A voltage source could be modelled as having a shunt resistance which was very low resistance, so that it would maintain about the same voltage even if you connected a very low resistance across it. See also Current source , Voltage source , Norton's theorem , Thévenin's theorem , and Kirchhoff's circuit laws. Edison (talk) 02:56, 4 March 2008 (UTC)

plate tectonics

is there evidence that suggest that the theory of plate tectonics is wrong? if so what. —Preceding unsigned comment added by 205.202.37.130 (talk) 19:44, 3 March 2008 (UTC)

I thought that by now it was fact. Is there anyone that doubts plate techtonics? The Flat Earth Society, maybe? 206.252.74.48 (talk) 19:49, 3 March 2008 (UTC)

See plate tectonics. This model is widely accepted. Friday (talk) 19:56, 3 March 2008 (UTC)

It is certainly not accepted amongst hard line biblical creationists as the time scale is not compatible with the Bibles' time line (if taken literally). This Google search turns up a random selection of their sites [1]' SpinningSpark 21:25, 3 March 2008 (UTC)

Sure, but the questioner asked about evidence, which is apparently neither necessary nor sufficient for the YEC crowd. --Sean 21:33, 3 March 2008 (UTC)

The Answers in Genesis site has a page on catastrophic plate tectonics along with supporting "evidence". Wikipedia also has a section discussing it on Flood_geology#Runaway_subduction. It seems like the standard creationist strategy: Take everything science has already discovered but come up with an explanation for a much shorter time span. -- MacAddct  1984 ^{(talk • contribs)} 22:46, 3 March 2008 (UTC)

This may be irrelavent but I personally think that there are more plates on Earth than previously thought, even if some of their faults don't extend perfectly from the surface to the mantle. Thanks. ~AH1^(TCU) 22:02, 3 March 2008 (UTC)

I vaguely remember a claim that said that the relative motions of the plates do not add up, so that something is wrong, but again that is not evidence, and it probably was some inaccurate figures. Nowdays accurate GPS measurements can demonstrate movement. These also show that the plate model may not be as simple as is drawn with solid plate seperated by fault lines, and that there are regions of ground that are being compressed or stretched. (which of course is demonstrated by complex faulting or folding). Graeme Bartlett (talk) 22:11, 3 March 2008 (UTC)

If there were any evidence that it were not true it would not be an accepted scientific theory--Shniken1 (talk) 22:55, 3 March 2008 (UTC)

Um, actually in practice it doesn't quite work like that. There are often anomalies to any theory that don't quite fit but unless they are judged to be major it is assumed that they are either slight problems with the data or collection or otherwise will be explained later by a better theory. If scientists threw out any theory the second there was a problem with it then they'd have precious little left. Both General relativity and Quantum mechanics have at their core a major problem (they are incompatible with one another) but they are both considered accepted scientific theories though all physicists believe at some point they will be succeeded or improved one way or another. --98.217.18.109 (talk) 23:10, 3 March 2008 (UTC)

You could have a look at the arguments advanced by the proponents of the Growing Earth Theory and expanding earth theory (more or less the same thing), but they aren't very convincing. 200.127.59.151 (talk) 22:58, 3 March 2008 (UTC)

There are very very few who doubt plate tectonics. Karsten M. Storetvedt, Professor emeritus at the University of Bergen, Norway, has published a book about his own alternative theory: "Global Wrench Tectonics – Theory of Earth Evolution", ISBN 82-450-0072-8. According to this theory, the continents have just been twisting back and forth a bit. To my knowledge he is absolutely alone in supporting this view. EverGreg (talk) 13:07, 4 March 2008 (UTC)

Why no self poisoning?

Looking at the world's most poisonous creatures, for example, the King brown snake, Inland Taipan, marbled Cone snail, Australasian funnel-web spider and seeing that many kill their prey that way in order to eat them (not just in self defense), how come the poison doesn't affect eating it? Julia Rossi (talk) 23:05, 3 March 2008 (UTC)

Speculating a little here: The poisons are quite likely not as harmful when consumed orally as when injected. But even if they were just as potent orally, the predator would still be getting a smaller dose per unit time, because it presumably doesn't eat the whole thing at once after killing. And finally the predators may well have evolved some level of resistance to their own venom. --Trovatore (talk) 23:12, 3 March 2008 (UTC)

See Snake_venom#Immunity. It seems that most snakes are immune to their own venom, and some snakes are even immune to the venom of other snakes. This is probably because of the presence of antibodies that target the venom. --98.217.18.109 (talk) 23:18, 3 March 2008 (UTC)

Looking at it from a natural selection point of view, it's safe to assume that all poisonous-creature mutants who were born without immunity to their own poison but with a desire to eat their poisoned victims have long since gone extinct. --sean —Preceding unsigned comment added by 69.134.115.242 (talk) 00:02, 4 March 2008 (UTC)

Because the venom of most snakes is not toxic when ingested. Most snakes are not immune to their own venom. Note that the claim that they are in the snake venom article is unreferenced. (Species which feed on poisonous snakes, such as king snakes, are another matter.) This is a serious problem in zoos: In captivity, some species go a little wacko and bite themselves, with fatal results. However, except for a few species such as spitting cobras (which I assume must be immune), snake venom requires injection into the lymph (elapids) or blood (vipers) to be affective. You can drink most cobra or viper venom without ill effects, and similarly snakes can eat poisoned prey without ill effects even without immunity. kwami (talk) 00:23, 4 March 2008 (UTC)

Thanks all, that was fast! and explains a lot. To digress, I was also wondering about the poison-as-defense creatures (the Golden Poison Frog for example) getting close to each other, yet not dying, and it turns out they have inbuilt resistance factors. Interestingly, they get their poison from a beetle that carries it. Makes that old saying about meat and poison creepily more than a truism. Cheers, Julia Rossi (talk) 03:25, 4 March 2008 (UTC)

Chromosome number changes

I believe I have a good understanding of how evolution works, but I have not yet seen how evolution explains the difference in the number of chromosomes between organisms. Humans have 46; but some species have over a hundred, and it is (as best I have found) always an even number. Could someone direct me to an overview of how this process works? It might make a worthy addition to the evolution or the chromosome article, if it has not been explained there yet. Thanks. ~ S0CO^{(talk|contribs)} 23:00, 3 March 2008 (UTC)

The change in numbers can happen when a chromosome splits, or two join together. This could happen with a cross over mistake, a virus insertion break, or a repair mistake, or even a complete doubling due to failure to divide properly. It still has to be explained why the change can be preserved and that the organism is still fertile, and its offspring are still fertile. Bacteria have one chromosome. What caused Eucaryotes to have multiple chromosomes? Graeme Bartlett (talk) 08:00, 4 March 2008 (UTC)

Multiple chromosomes are benefitial for three reasons I can think of. Firstly, multiple chromosomes increases the ease of mitosis given the very large eukaryotic genomes. Secondly, changes in chromosome number allows a new method of possibly benefitial mutation. I have a hard time seeing how likely that one is, but there must be something to it given the variety in chromosome number between species. And finally, and most clearly benefitial, homologous recombination of chromosome pairs allows for nearly error-less reconstruction of a damaged chromosome (relative to the other methods available for fixing the loss of entire base pairs). For the OP, the mechanisms for changing chromosome number are described in chromosomal abberation and nondisjunction. Someguy1221 (talk) 08:27, 4 March 2008 (UTC)

see [2] for a theoretical basis for the evolution of chromosomes (and click on 'related articles" for more such.) - Nunh-huh 08:29, 4 March 2008 (UTC)

It seems that the inter-relation between chromosome structure (karyotype) and evolution is not at all clear. Chromsome number can vary between quite closely related species (see List of number of chromosomes of various organisms), and in some cases there is chromosomal polymorphism within a single species. Our karyotype article says "Although much is known about karyotypes at the descriptive level, and it is clear that changes in karyotype organization has had effects on the evolutionary course of many species, it is quite unclear what the general significance might be". Gandalf61 (talk) 10:38, 4 March 2008 (UTC)

How did Darwin account for this? I'm sure he would've been challenged. Zain Ebrahim (talk) 12:47, 4 March 2008 (UTC)

Darwin was not aware of the role of chromosomes in heredity. Although chromosomes were first observed in the 1840s, their role as carriers of genetic material was not established until Theodor Boveri carried out experiments with sea urchin eggs in 1901/1902. On the Origin of Species was published in 1859, and Darwin died in 1882. It is sometimes forgotten that Darwin developed the theory of evolution without any clear idea of the mechanism of heredity or any knowledge of modern genetics - which makes his achievement all the more remarkable. Gandalf61 (talk) 15:04, 4 March 2008 (UTC)

The reality is that the chromosome number is always changing in the evolutionary time frame. The degeneration and potential loss of the Y chromosome is well documented. Likewise doubling chromosomes is not uncommon, especially in plants leading to polyploidy. This is associated with genomic shock which leads to many rearrangements and deletions in the doubled set that soon become unique. Breeders have utlized this to vastly improve crops such as brassica and wheat. Finally chromomes can stick together to reduce the number. This appears to have haapened to the human chromosome 2 that has identity to two different chromosomes in the chimpanzee genome. This phenomena is known as Robertsonian translocation. It is also responsible for Familial Downs Syndrome that is a form of trisomy that is not due to a third chromosome 21 but due to a mutant chromosome that some people carry that has chromosome 21 co-joined to another autosome. David D. (Talk) 16:47, 4 March 2008 (UTC)