Wikipedia:Reference desk/Archives/Science/2009 May 6

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May 6

Wouldn't adding any potential energy to a system make something infinitely massive?

Since lifting an object increases it's energy, wouldn't it therefore increase it's mass? And wouldn't this in turn increase it's energy even further, making a cycle? Since energy is rest mass + kinetic+other forms of energy etc. Also: Should I be using it's or its in my first sentence? That one has always bugged me, since I am showing ownership of the property, but I'm not sure if ownership transfers over to pronouns. If they don't then the un-contracted form being it is, would not make sense in that sentence. —Preceding unsigned comment added by 141.218.35.51 (talk) 00:47, 6 May 2009 (UTC)

You mean its. "It's" means "it is", "its" means "belonging to it". "Its" is the equivalent of "his" and "hers" - you don't write "hi's" or "her's", so you don't write "it's". That's how I remember it, so it might work for you. Yes, lifting an object does increase its mass, but that doesn't increase its energy, it just increases the amount of energy you need to add to the system to lift it. --Tango (talk) 01:08, 6 May 2009 (UTC)

Thanks for the quick response to my grammatical question, I knew it felt wrong. "when energy of any kind is added to a resting body, or to a system of bodies, the increase in the mass as seen by a single observer (or as seen from any given inertial frame) is equal to the energy added, divided by c²." This was taken from the energy-rest mass equivalence article here. Wouldn't this cause the lifted object to experience increased mass? —Preceding unsigned comment added by 141.218.35.51 (talk) 01:19, 6 May 2009 (UTC)

Under ordinary conditions (Earth-like gravity), if there were an increase in mass (I'm not sure there is), the increase in mass would be negligibly small. The extra energy to raise that would be near-infinitesimally small. The extra energy to raise that would be ludicrously small, etc. (See Geometric series.) Now if that mass started at the event horizon of a black hole, there might be more of a problem, but I'll leave that to the next responder. -- Tcncv (talk) 02:43, 6 May 2009 (UTC)

Lifting an object increases the energy of the system of object and Earth. The energy is neither located in the lifted object nor in Earth, it is contained in the Gravitational field. It is in principle possible to calculate the precise distribution of energy in space by solving the Einstein field equations of general relativity for the two bodies and inspecting the resulting vector field of gravitation (way beyond my abilities). Afaik, gravitation is self coupled, so the infinite looping self attraction effect you describe should actually exist in the field and be part of the solution automatically. Nevertheless, energy conservation applies normally, the kinetic energy of lift is converted to gravitaitonal energy of precisely the same amount. The center of mass of the energy also remains wherever it was before due to momentum conservation. —Preceding unsigned comment added by 84.187.80.238 (talk) 03:16, 6 May 2009 (UTC)

I just looked it up a bit further. Quoting from Stress-energy tensor: "However, in general relativity there is not a unique way to define densities of gravitational field energy and field momentum." So, it's not that simple to locate. —Preceding unsigned comment added by 84.187.80.238 (talk) 03:35, 6 May 2009 (UTC)

So I don't really understand where the mass is contained, if it is the gravitational field, what is the form in which it takes? 141.218.35.51 (talk) 03:45, 6 May 2009 (UTC)

I would guess virtual gravitons. But quantum gravity is not well worked out even at a theoretical level. --Trovatore (talk) 04:25, 6 May 2009 (UTC)

With regard to the infinite cycle problem, you have to be careful about how you are changing the potential energy of the object in your thought experiment. If I am holding a book on earth, and you define the system to be me+the book+earth, there is no energy being added to the system when I raise the book higher off the ground, I'm simply converting the electromagnetic potential energy stored in my muscles into another form of energy. So in that example, the relativistic mass does not change. Adding energy to the system would mean transferring it from an outside source, for example hitting the planet with light from the sun, or redefining the system to only encompass the Earth + the book. Truthforitsownsake (talk) 12:47, 6 May 2009 (UTC)

Gravity well thought experiment

To expand on the prior topic: Suppose we start with two masses in space which are gravitationally attracted to each other. As they approach they each gain kinetic energy and loose potential energy (potential energy becoming negative). When they collide, they merge and the potential energy becomes heat which eventually radiates away. With that loss of energy is a loss of mass as observed from outside the system. Now, suppose I were to descend into their gravitational well and measure their mass from there. Would my measurements equal the sum of the original two masses? To put it another way, would my observations from within the gravity-well be different than those at a distance? I know general relativity predicts gravitational time dilation, but what else changes? (..in layman's terms please, sans any stress-energy tensors and the like.) -- Tcncv (talk) 04:21, 6 May 2009 (UTC)

Yes. Measuring the mass (by measuring gravitational attraction) of the objects near them gives their individual rest mass. Measuring the combined mass of the system from far away returns the sum of masses of the objects minus binding energy. This is actually a good definition of a bound system: If the combined mass of the system is smaller than the sum of mass of the parts, it is bound. The mass loss from the collision will not be detectable before the radiated energy passes beyond the observers position. If you would keep it near the masses, by using mirrors for example, the mass of the whole thing would never change at all, because even as radiation the energy still attracts the observer, just like before. —Preceding unsigned comment added by 192.109.111.157 (talk) 18:16, 6 May 2009 (UTC)

Thank you. -- Tcncv (talk) 03:49, 7 May 2009 (UTC)

Confusion alert. What is true is that the sum of the two masses infinitely far away equals the sum of the masses after colliding PLUS the E=mc^2 mass equivalent of the heat radiation from the collision (as 192 said, the binding energy) (including any gravitational radiation, which may be zero in this case, I'm not sure (I seem to remember that a gravitational dipole doesn't radiate ((This whould be a new question)))). The confusion is your statement "observations from within the gravity-well be different than those at a distance". The size of the gravity well is infinite, there is no "outside it" (except at the conventional 'infite'distance). —Preceding unsigned comment added by 128.32.146.97 (talk) 03:57, 8 May 2009 (UTC)

Pls help me wid my hw?

q1-if light bulbs are connected to other bulbs just like in a series circuit such as in Christmas lights,they get dimmer .why is that? q2-if light bulbs are connected to other bulbs just like in a parallel circuit such as in household wiring .they stay bright .why? q3-how long light bulb last ?what happens to light bulb when it gives it's last glimmer I HAVESEARCHED EVERYWHERE google ,wikipedia ,my textbooks but i couldn't find it —Preceding unsigned comment added by Srijan89 (talk • contribs) 07:40, 6 May 2009 (UTC)

• Power is voltage times current. If you connect (identical) light bulbs in a series, the voltage drops in equal parts on each bulb. Thus there is less of a potential at each bulb, the current is lower, and hence less light is emitted. Another way of looking at this is to look at the resistance of the chain - it goes up, hence the current goes down.
• In parallel (and, strictly speaking, connected to a perfect power source with perfectly conducting cables), the same voltage is applied to each bulb, and hence they all glow with the same brightness.
• It depends on usage and model, but the way they die is usually by breaking the filament, either mechanically or by vaporization.

--Stephan Schulz (talk) 07:52, 6 May 2009 (UTC)

See also Series and parallel circuits —Preceding unsigned comment added by 82.44.54.169 (talk) 07:54, 6 May 2009 (UTC)

Noisy flies

Recently, in the last week, there were two occurences of the presence of a noisy fly in my house. The first, was precisely five days ago where the presence of the fly was known to me for sometime. During the morning and afternoon, it appeared that the fly was attracted to food, like other flies. It was extremely noisy, large and slow, making it easy to kill. However, it was most difficult to determine its location, as often it would sit still unless disturbed. At night, I happened to notice the fly, flying around a light source; it seemed quite far away from my position. I walked along (in my house) with no notice of it, for at least 10-15 metres. Then, to my surprise, I found it idle on my neck. I could not see it and therefore could not determine the exact second when it landed there, but having placed my hand on my neck alarmed me. The fly, to this sudden movement, responded by making a loud buzzing noise - extremely loud to my ear considering that it was on my neck. Within an instance, I noticed it on the wall in front of me. It came a surprise to me that a fly could travel such great distance in so little time, when, in my experience, such flies had been easy to kill and recognizable by their lack of agility. I approached the fly, and within an instant, killed it.

The next time that the presence of such a fly was beknownst to me, was merely a few hours ago. It seemed that the fly was attracted to any light source, often flying near the windows through which the light of the sun shone. It was therefore easy for me to trap the fly behind some curtins. Upon doing this, I heard a great buzzing noise - although I was certain that this fly was actually a fly, rather than a bee. The fly seemed to fly at a low altitude, making it somewhat inconspicuous. In the end, however, I killed it, in the same manner as that of the previous incident.

Based on the previous observations (concisely: loud buzzing noise, slow to move but quick in flight, large, inconspicuous, attracted to light - all in comparison to the average fly), what is the exact species of this fly? Based on my understanding of flies, I would predict this fly to be either a deer fly or a horse fly. However, despite being on my neck for sometime, the fly did not bite me. On the other hand, the flies which I have described seem more aggressive compared to other flies. It also seems that the ratio between the presence of these flies in my house, to the presence of the average fly in my house, is about 1:1. Furthermore, rarely is there such a fly during the summer season. Does anyone have any specific ideas regarding the species to which this fly belongs and the exact name of this fly? Thankyou for any remarks, and apologies for the somewhat long and narrative-like question that I am asking. --PST 10:09, 6 May 2009 (UTC)

Photo? location? SpinningSpark 10:43, 6 May 2009 (UTC)

Sounds to me like 1 of the Calliphorid flies or "dumb house flies". They would naturally overwinter in the burrows of animals but your walls or basement seem fine to them. As they warm up, like all ectotherms, they become active. They are attracted to light then since it would mean the way out of the animals burrow. As to why they landed on you, well they do lay thier eggs on other bugs and even eartworms but i doubt they thought you were one of thier potential hosts. Likely just seeking warmth. The Buzzing is likely just a predator avoidance thing, annoying yes, but harmless and effective. Most adults are pollen feeders. I would leave a light on near the door then just scoop the little buggers outside in the a.m. to continue thier important work!

I know the above is unsourced but hey, you asked!!! 67.193.179.241 (talk) 15:34, 6 May 2009 (UTC) Rana sylvatica

Franz Kafka, is that you as the OP? I'd recognize your prose anywhere.

No man, I am not the op. 67.193.179.241 (talk) 12:44, 8 May 2009 (UTC) Rana sylvatica

Cartridge specifications

Hi. In the 7.62x39mm cartridge (for example) what does the 7.62 stand for? I thought it was the bullet diameter, but apparently it's not. Also, why do they use 2 measurements instead of 1, like 9mm or .45? And what is shown by those specifications (9mm etc)? Thanks in advance —Preceding unsigned comment added by 122.255.2.65 (talk) 11:59, 6 May 2009 (UTC)

See Caliber tells you everything you need to know. SpinningSpark 12:10, 6 May 2009 (UTC)

See 7.62x39mm, believe it or not. —Tamfang (talk) 06:49, 10 May 2009 (UTC)

Can you explain me this?

First sorry for the title that doesnt says anything, but english is not my first language and I hope that you will understand what I am trying to know.The question:Why does a Cell-phone when lying on a table and ringing(vibrating) move? The phone should represent an Inertial frame and should not move as long as no force from outside is acting on it or am I wrong? Please explain. Thank You. DST —Preceding unsigned comment added by DSTiamat (talk • contribs) 12:51, 6 May 2009 (UTC)

If there weren't any other forces acting on it then you would be right, it would vibrate but its centre of mass would remain stationary. However there are other forces - friction with the table, gravity (particularly if the table isn't perfectly level), maybe even air resistance. --Tango (talk) 13:15, 6 May 2009 (UTC)

You are assuming that the vibrations are not directional. Every action has an equal and opposite reaction. So, if the internal little weight moves quickly in one direction, the rest of the phone will move slightly in the other. Most of the vibrators spin. So, they are moving in a circle. The phone, therefore, moves in a circle in the opposite direction. Combine that motion with the friction between the phone and the table and you get a seemingly random drift across the table. -- kainaw™ 13:21, 6 May 2009 (UTC)

If the little vibrator inside spins in one direction and the phone the other way would this apply even if the phone would be in vacuum(no friction whatever) and whit 0 gravity acting on it?

"So, if the internal little weight moves quickly in one direction, the rest of the phone will move slightly in the other"-Does this not violate the conservation of momentum? I understand that THIS IS conservation of momentum but if u see the Phone as one sytem who suddenly begins moving?Or should it not be seen this way? Explain please —Preceding unsigned comment added by DSTiamat (talk • contribs) 13:51, 6 May 2009 (UTC)

The phone is a single system with stored energy (the battery). This is no different that wondering why a car moves when you press your foot down on the accelerator. The stored energy (released by combusting gas) causes motion. In the phone, the stored energy in the battery is released to cause motion. -- kainaw™ 13:55, 6 May 2009 (UTC)

The comparation is not the best because a car INTERRACTS whit the road through the weels where the phone does not(vacuum etc), i think it has something to do whit the moving of its centre of mass as Tango said, the momentum in case of the car is clearly conserved ( car moves one way, earth other etc) —Preceding unsigned comment added by DSTiamat (talk • contribs) 13:58, 6 May 2009 (UTC)

The vibrator moves one way and the phone moves the other - that's conservation of momentum. The vibrator will then move back to where it was (that's what "vibrate" means!) and the phone will do likewise. That results in the phone jiggling around on the spot. Its orientation may change, but its position will remain constant. Until you introduce external influences, that is. If you get more friction while the phone is moving in one direction than when it is moving back, for example, you'll end up with the phone moving slightly. If that same movement happens with each vibration, the phone will move across the table. --Tango (talk) 14:05, 6 May 2009 (UTC)

Yes Tango i understand perfectly what you are explaining it is logical i figured this out myself BUT lets pretend that the vibrator only does one half cicle not moving back (no more vibrator i guess) and the Phone moves a bit one way, now If u see the Phone as an closed system (not knowing whats inside) this would violate the law of conservation of momentum isnt it? Hope that now you are understanding and sorry but the car example has nothing to do whit it. —Preceding unsigned comment added by DSTiamat (talk • contribs) 14:13, 6 May 2009 (UTC)

I've just fixed your replies, DSTiamat, please use :: before your responses, not spaces -- MacAddct1984 ^{(talk • contribs)} 14:35, 6 May 2009 (UTC)

The phone's battery is powering the vibrator, allowing it to move the phone. If you applied your logic, DSTiamat, nothing would be able to move unless acted upon by an outside force. -- MacAddct1984 ^{(talk • contribs)} 14:41, 6 May 2009 (UTC)

Most vibrators spin, they do not vibrate. So, the vibrator does not "return". It just spins round and round. The phone spins in the opposite direction. The vibration is caused by the offset weight of the vibrator. I feel that the questioner's problem is the assumption that the motion is being created out of nothing. I was pointing out that it isn't created out of nothing. It is energy stored in the battery, converted to motion by the little motor in the vibrator. It is not safe for work to search for pictures of cell phone vibrators - so I did it for you and here is a page with a picture of some.-- kainaw™ 14:40, 6 May 2009 (UTC)

If you don't know what is inside the phone, then you can't tell whether momentum is conserved or not. The moving phone only appears to be violating conservation of momentum because you are assuming there are no moving parts inside it, so you are assuming that its centre of mass is moving as its casing moves. If you reverse your reasoning and assume conservation of momentum instead, so you assume that the phone's centre of mass is not moving, then you can infer from the movement of its casing that the phone must contain a vibrating part, moving in the opposite direction to its casing. Gandalf61 (talk) 14:42, 6 May 2009 (UTC)

Thank you Gandalf really, shed some light, the other 2 battery posts are really off, showing that they didnt grasped my question. —Preceding unsigned comment added by DSTiamat (talk • contribs) 14:44, 6 May 2009 (UTC)

Sorry about the misunderstanding. IIRC, a vibrator in a phone works is like an unbalanced centrifuge. When a centrifuge spinning at high speeds is unbalanced, it will shake violently. So a vibrator acts on the same principle, just on a smaller scale. -- MacAddct1984 ^{(talk • contribs)} 15:00, 6 May 2009 (UTC)

The confusion here is in the word "move" - which is a little vague. There are three kinds of motion involved here:

• The cellphone bodily moves across the table. This is only possible because of friction with the table - and only if the friction is more as it moves (say) left to right than right to left. With wood-grain surfaces, that's possible. So as the phone moves one way, it slips easily - when it moves the opposite way, it doesn't overcome 'static' friction - so it wobbles gradually in one direction.
• The cellphone vibrates because inside there is a tiny rotary electric motor with an offset weight on it. the center of gravity of the phone moves in a small circle RELATIVE TO THE BODY OF THE PHONE. So if your phone was suspended in a zero-g vacuum - it would still appear to vibrate (move in a small circle) because although it's center of gravity wouldn't move at all - the body of the phone would need to move in order to keep the center of gravity stationary.
• Because the vibrator is a rotating frame of reference - a phone floating in space would spin in the opposite direction to the vibration motor inside. But when the phone is constrained by the desktop, it can't do that.

SteveBaker (talk) 15:12, 6 May 2009 (UTC)

Thank you Gandalf and SteveBaker really clever guys they understood what I was actually asking.

 TY, DST  —Preceding unsigned comment added by DSTiamat (talk • contribs) 15:59, 6 May 2009 (UTC) 

The reason the phone doesn't end up where it started if the vibrator moves quickly in one direction and slowly back (slowlyback-QUICK-slowlyback-QUICK) is beecause the slow movements leave it STATIONARY because of friction. It's the same as a jar. if you're in a jar and hit a basketball against the glass again and again and again and again, you could slowly move in that direction. That's because when it gets back to you, you catch it slower, so that there is literally 0 movement of the glass jar (due to friction of the ground) but when you throw it against the glass the quicker movement is able to overcome friction so that you move 0.001 meters for example. Do it enough times and you end up moving in that direction. But what about in space? In space if you are strapped in the center of an object and you keep throwing a basketball at the same wall and catch it on it's rebound back to you, you will NOT budge. When you catch the basketball again strapped to the center, even if you're doing it MORE SLOWLY, there is no FRICTION that makes this "more slow" movement = 0.
In conclusion: it's quite simple: your cell phone moves because friction makes it so that a force that would normally result in slow movement in fact results in 0 movement. So whereas in a vacuum it would vibrate like this: sachay slowly to one side, quickly to the other, slowly to one side, quickly to the other (remaining in the same net location), on the table it does this: sachays quickly to one side, remains still, sachays quickly to one side, remains still, ending up moving in that direction. The "remains still" part is where the vibrator, in space, would be countering the movement it just made, as it moves back so it can make it again... 79.122.21.123 (talk) 19:11, 6 May 2009 (UTC)

If the motor inside the phone did move faster left-to-right than right-to-left, then I'd agree with you - but the thing that makes it vibrate is a very simple rotary motor - there isn't likely to be much variation in speed when going left-to-right versus right-to-left.

However, I think I have a MUCH better explanation. Thinking a bit more carefully - I think the reason is this:

• The motor rotates at constant speed - moving an eccentric mass around in a small vertical circle. It can't be a horizontal circle because the motors they use (at least, all the ones I've seen) are long and thin and could not be mounted with their long axis perpendicular to the screen. If it DID use a horizontal circle, the phone would go into a flat spin every time it rang...and that's not what we see.
• We know that the center of gravity of the phone is trying to remain stationary - Newtons' laws.
• Now consider the motion of the eccentric mass that's attached to the vibration motor. Let's suppose it's travelling on the downward part of it's counter-clockwise circular motion:
  • As the eccentric mass moves downwards towards the table - the body of the phone has to move upwards in order to keep the center of gravity stationary. Despite gravity, this lifts the body of the phone a tiny distance off the table (or at least reduces the pressure it exerts onto the table).
  • Then - as the mass rotates a further quarter turn (counter-clockwise) - it's moving to right. Because there is little or no force between phone and table - there is little or no friction the phone moves easily to the left.
  • However, gravity starts to pull the phone back towards the table and in the next quarter turn of the motor, the mass goes upwards - pushing the body of the phone yet harder down. Now the phone is pushing hard against the table.
  • In the fourth quarter turn the mass is moving to the left - but the phone is pushed hard against the table - so it doesn't slide so easily to the right.
• Hence (in this scenario), the phone moves across the table from right to left in little 'hops' - even if the frictional forces are entirely symmetrical and the vibration motor rotates at constant speed.

Of course if the table isn't flat the phone may start to bounce around and hit the table in more complicated ways - with individual corners of the phone hitting or jumping - so this idealised motion may not be what happens in practice.

SteveBaker (talk) 23:13, 6 May 2009 (UTC)

that's very long steve, could you summarize it in a sentence the way I did with m ine? 94.27.231.41 (talk) 11:17, 7 May 2009 (UTC)

I don't see any previous post from your present IP address. But no - what I wrote is about as concise as I can make it and still convey my explanation adequately. SteveBaker (talk) 13:02, 7 May 2009 (UTC)

(sarcasm alert) How about, "The phone hops like a tiny little bunny." Most Some people like things simplified to the point of cuteness at the expense of truthfulness or understanding. -- kainaw™ 21:36, 7 May 2009 (UTC)

Spider Question

I've got a huge, hairy black spider in my kitchen with yellow and black triangle markings down its back. Anyone know what it is? Thx in advance --Anonymous07921 (talk) 13:41, 6 May 2009 (UTC)

Where is your kitchen? It helps to limit the search to spiders that live in your area. -- kainaw™ 13:43, 6 May 2009 (UTC)

Is the spider in a web? on the wall? Running around on the floor? How big is huge? 3" across? 6"? more? 65.121.141.34 (talk) 13:49, 6 May 2009 (UTC)

My kitchen is in Lawrence, Kansas ;). It was trying to climb my trash can (don't ask me why). And its about as big as my palm. --Anonymous07921 (talk) 14:16, 6 May 2009 (UTC)

Does it look like a garden spider? -- kainaw™ 14:23, 6 May 2009 (UTC)

No, it looked poisonous.....it was huge, fat, hairy, and, in addition to the triangle markings, had a yellow and black stripe on its head. --Anonymous07921 (talk) 14:26, 6 May 2009 (UTC)

Poisonous things get you sick when ingested/absorbed; venomous creatures bite you and inject venom. Sorry, it's a pet peeve of mine. -- MacAddct1984 ^{(talk • contribs)} 15:32, 6 May 2009 (UTC)

Perhaps the OP was considering the culinary properties of the spider. Why assume that his concern was being bitten by a large arachnid after all? 65.121.141.34 (talk) 15:43, 6 May 2009 (UTC)

Culinary? Lol, yeah, it was in my kitchen :D. I'll get some seasoning and a frying pan and make some roast spider like that guy from Cast Away :D --Anonymous07921 (talk) 16:54, 6 May 2009 (UTC)

That is a cultural view. In Cambodia, fried tarantulas are rather popular. But for the record, I did not expect that you were seriously contemplating consuming the spider. 65.121.141.34 (talk) 16:56, 6 May 2009 (UTC)

But still, i have acute arachnaphobia, to the point where I'm repulsed so much by any kind of spider that I don't even want to squash it with a boot......I generally try to avoid any kind of spider, especially ones as bid as my palm....*shudders*....yeah, well, cambodia can keep their fried tarantulas ;) --Anonymous07921 (talk) 16:58, 6 May 2009 (UTC)

I strongly suggest deep fried spiders to pan fried. Some beer batter and horseradish sauce will go nicely. As for the type, the only yellow and black spiders I've ever seen in Kansas City are the garden spiders (which can get very large and bristly) and jumping spiders (which are very small). The four dangerous spiders in the are are neither large or yellow/black. They are the brown recluse, black widow, hobo, and yellow sac spiders. -- kainaw™ 17:02, 6 May 2009 (UTC)

Lol....I've seen several brown recluses running around outside, and there's ocassionally a black widow in my freakin' bathtub *shudders again*, but it probably is a garden spider --Anonymous07921 (talk) 17:06, 6 May 2009 (UTC)

If it is a garden spider, let it outside. They make huge webs and eat tons of nasty bugs. I try to keep them happy around my house in Charleston because they keep the palmetto bugs in check. I just wish they'd handle the mosquitoes better. Gotta figure out how to invite a few bats over. -- kainaw™ 17:20, 6 May 2009 (UTC)

Lol, just make sure they're not vampire bats ;)....ok, spider's back outside --Anonymous07921 (talk) 17:43, 6 May 2009 (UTC)

Nest box#Bats. --Sean 18:42, 6 May 2009 (UTC)

My guess is a wolf spider, but without a picture it's hard to say. Looie496 (talk) 18:31, 6 May 2009 (UTC)

No, it's not a wolf spider.....it was probably a garden spider --Anonymous07921 (talk) 18:52, 6 May 2009 (UTC)

We learn something every day – thanks, MacAddct! —Tamfang (talk) 06:59, 10 May 2009 (UTC)

Google "camel spider bite" and click on images....that guy's leg looks pretty messed up. --Anonymous07921 (talk) 18:58, 6 May 2009 (UTC)

I would suggest taking a picture with a digital camera; all though this portal is brilliant for just about everything i feel the best person to ask would be the old guy in your neighbourhood who has lived there all his life; he may smell a little funny and start droaning on about the war while forcing you to have a game of Dominoes for his wisdom; but he will no doubt be able to tell you what type of spider it is and if it is going to sink its fangs into your flesh!!!!Chromagnum (talk) 05:21, 7 May 2009 (UTC)

planetary search

Scientists have discovered many stars that have planets at great distance using things like stars wobbling from planet gravity or a bit of dimming from a planet "eclipsing" the star. At what range from our solar system, would our scientists be able to detect that our own solar system has planets using their current methods? 65.121.141.34 (talk) 13:59, 6 May 2009 (UTC)

Comment this sounds a little like a homework problem Dougofborg^(talk) 14:39, 6 May 2009 (UTC)

No it doesn't! Not even remotely! SteveBaker (talk) 14:51, 6 May 2009 (UTC)

Gotta agree with Steve there. This is a bizarre question to pose for homework! Vimescarrot (talk) 14:53, 6 May 2009 (UTC)

Well, there are several techniques - but the one that uses doppler shift in the star's light as the star is moved slightly by the planetary gravitation ought to work at any range - providing enough light can be obtained from the star to do some sort of spectrographic analysis...and that's more a matter of how long you're prepared to point the telescope at the star than it is to do with distance. Similarly - the methods that rely on the planet eclipsing the star (and the star eclipsing the planet) will also work at almost any range if you're prepared to wait long enough. However, those tricks don't work well for very small planets because the amount of spectral shift is just too small - so planets like earth, mercury, mars and venus (yes, yes, AND pluto) are probably too small for us to detect at any range unless they are very close to the star. Uranus is probably too far from the sun - so even though it's quite large, it's not very detectable. However, Jupiter and (to a lesser degree) Saturn ought to be pretty detectable over extremely large distances if your alien astronomers are patient enough. So far, the most distant exoplanet we've found is 22,000 light years away(!) - so I imagine that we'd be able to at least detect Jupiter and perhaps Saturn at those kinds of distances. However, even as close as a dozen light years, we don't yet have the technology to detect Earth. Detecting something like Haumea (on the Wikipedia front page today!) would be utterly impossible by any known means - until very recently, we couldn't even detect it orbiting our own star when we're 9 light-minutes away! SteveBaker (talk) 14:51, 6 May 2009 (UTC)

Pluto is no longer a planet, Steve. Sorry to break the news. :( Vimescarrot (talk) 14:56, 6 May 2009 (UTC)

Pluto is not an IAU planet. It's still a planet. I decline to recognize the authority of some silly organization like that to dictate my usage of language by way of a vote.

By the way, not only is Pluto a planet, but so are Titan and the four largest moons of Jupiter, and I'd probably throw our own Moon in there too. However I'm not so sure about the gas giants. How can something be a planet if there's nowhere to land? --Trovatore (talk) 17:28, 6 May 2009 (UTC)

Well, the real planets are the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn. Everything else is some newcomers opinion. --Stephan Schulz (talk) 17:36, 6 May 2009 (UTC)

The range of detection will depend on the size of the planet (larger ones can be found farther away) and the size of the star (smaller ones have their planets more easily found). Our article on extrasolar planets and our list of extrasolar planets probably provide a good baseline, though. Going off planets within two masses of Jupiter, the farthest known system is MOA-2007-BLG-400L, 20000 light years distant. That's also more or less the limit of finding any planets. On the other hand, said star is only about 1/3 as massive as the sun, and said planet orbits at about the distance of Venus. Quick back-of-the-envelope calculations suggest that Jupiter's influence on the sun would be about 1/100 that of this system, so I'd ballpark about 200 light years for detecting a solar system with a sun-sized star and a Jupiter-sized planet with Jupiter's orbital characteristics. — Lomn 14:55, 6 May 2009 (UTC)

I expect that would largely depend on just how hard and how long we'd try to find planets around that particular star we call the Sun. OGLE-2006-BLG-109L is a star 4,900 light years away, where two gas giants were discovered similar enough to Jupiter and Saturn. Equendil Talk 14:55, 6 May 2009 (UTC)

"Current techniques" have a wide range of resolution capabilities. Keck observatory states that the angular resolution ranges "0.04 to 0.4 arcseconds for individual telescopes, depending on target and instruments used" - that's a variation of a factor of 10x using the same facility! As always, you have to define the hypothetical situation very carefully. With current technology, we have the capability to build much much higher resolution optical telescopes (but we just don't have the science research budget to do it). Consequently, your range of answers will vary by orders of magnitude unless you select a specific technique, specific observational platform, etc. Nimur (talk) 15:01, 6 May 2009 (UTC)

I would also imagine that it is going to depend on where you are relative to the solar plane? If you are looking down on the solar system, a planet would never move in front of the sun, making planets harder to detect and greatly reducing your range then if you are in line with that plane right? 65.121.141.34 (talk) 15:08, 6 May 2009 (UTC)

Yes, depending on technique. Such a scenario rules out eclipses but should be ideal for observing gravitational wobble. — Lomn 15:36, 6 May 2009 (UTC)

Not really, as "gravitational wobble" is not usually detected via the parallax (which is very very small), but via spectroscopic shifts. In other words, you want the star to wobble towards you and back again, not to wobble around on a plane perpendicular to your vantage point. --Stephan Schulz (talk) 16:41, 6 May 2009 (UTC)

Can our hops, or released bodies from the ground cause slip with respect to the Earth rotation?

Hi, Wikipedia

Nowadays I'm trying to figure out how a mass body behaves when changing its position normal to the earth surface and I hope you can help me in this topic and confirm the correct statement with evidences or equations. I assume ideal conditions where no air, or any object might contribute in friction losses. I will be so grateful if someone studies the following equations carefully and confirms whether or not possible.

Estimated 3D view of the Earth rotating with a body moving vertically to represent the body anticipated slip. Tariq A 6-May-2009

One example is an oscillating ball vertically or a repelled magnet that is released from the ground to become free in a vacuum at a specific height. I'm afraid I'm not that confident of the mathematical model to be used because I lack for advanced mechanics. I tried using simple equations with the following assumptions:

1- Initial circular velocity of the floating body must be the same of that derived from angular velocity when the body was still on the ground. This is due to the conservation of energy that was only Kinetic.

2- No friction of any means exist.

3- Gravity variation with height is negligible.

According to the previous assumptions, my equation went this way:

$\omega _{1}={\frac {2\pi }{T}}={\frac {2\pi }{24*3600}}\,$ rad/s,

$v=\omega r\,$

$r_{1}=R_{e}cos(laltitude)\,$

$r_{2}=(R_{e}+h)cos(laltitude)\,$

$\omega _{1}r_{1}=\omega _{2}r_{2}\,$

$\omega _{2}={\frac {\omega _{1}r_{1}}{r_{2}}}\,$

$Slip=d\omega =\omega _{1}-\omega _{2}=\omega _{1}(1-{\frac {R_{e}}{R_{e}+h}})\,$

If h is varying with time this will lead to a differential equation or can be approximated by converting h into an average value (h_av = 2/3*h_max) and so the previous equation can be used as follows:

$d\omega =\omega _{1}(1-{\frac {R_{e}}{R_{e}+h_{av}}})=\omega _{1}{\frac {h_{av}}{R_{e}+h_{av}}}\,$

And the time required to cause a full rotation slip will be when

$d\omega *T_{r}=2\pi \,$

where Tr is the Time required to cause 1 full rotation offset (lag).

and so:

$T_{r}={\frac {2\pi }{d\omega }}\,$

In terms of day time, T it will be:

$T_{r}={\frac {2\pi (R_{e}+h_{av})}{\omega _{1}h_{av}}}\,$

and finally can be simplified to:

$T_{r}=T{\frac {R_{e}+h_{av}}{h_{av}}}\,$

or more approximated,

$T_{r}=T{\frac {R_{e}}{h_{av}}}\,$ —Preceding unsigned comment added by Email4mobile (talk • contribs) 09:02, 7 May 2009 (UTC)

Where T is the normal day = 24*3600 second.

--Email4mobile (talk) 19:41, 6 May 2009 (UTC)

Is coriolis effect what you are looking for? --Tango (talk) 19:44, 6 May 2009 (UTC)

I don't think it is related to coriolis effect. To make my question more clear; assume you're bouncing repeatedly at the Equator, normal to the Surface and forget about the latitude now. If we try to average your jumps (average potential energy) and returns to the ground; there results a fixed point above the ground where you're initiating your jumps by let's say height H. because your initial speed at the equator was the same rotational speed for the Earth it is supposed to be constant with height and hence, the angular velocity must be less at H which will cause a lag or offset proportional with time. This time may be several tenths of thousands of years (if hav=0.3m then T will be around 58000 years)to complete $2\pi$ lagging rotation. This is of course true only if my calculations and analysis was correct. --Email4mobile (talk) 21:18, 6 May 2009 (UTC)

Are you saying that the jumping will induce a drag on the rotation of the Earth? Or are you referring to an effect akin to a Foucault pendulum? --Jayron32.talk.contribs 01:42, 7 May 2009 (UTC)

It seems to be independent of coriolis and Foucault pendulum effects because as you can see from the last simplified equation; the lag time (by one rotation) is only a function of the vertical hop (h)! —Preceding unsigned comment added by Email4mobile (talk • contribs) 08:52, 7 May 2009 (UTC)

Stirring vs. jiggling

This is partly scientific, partly sociological.

I was told many years ago by my chemistry teacher that the quickest and most efficient way of mixing a soluble solid (such as sugar) into a liquid (such as tea or coffee) is to stir it in a roughly circular motion, and that "jiggling" the spoon up and down, or even side to side, in the liquid is less efficient. That always rang true with me, and it seems logical. I always stir, never jiggle. Firstly, I want to know if what I was told is scientifically correct.

If so, what could explain the phenomenon that "jiggling" is something that, in my experience, is done more by men than by women, who prefer to stir. Men are supposed to be the logical/scientific ones, yet women seem to have the right approach here. If it has something to do with men not wanting to be seen doing something in a "feminine" way, that's probably for a different desk, but any comments would be appreciated. -- JackofOz (talk) 21:46, 6 May 2009 (UTC)

It sounds completely unlikely to me. Certainly, the turbulance caused by the spoon will be sensitively dependent on the shape of the spoon, the size of the container and the precise speed and trajectory of the spoon. There is no reasonable way to calculate that - so this would have had to have been determined experimentally...but it seems highly unlikely that they'd have tried a huge range of spoons, containers, stirring speeds AND techniques...so in all likelyhood this is junk science of some kind. I'm also completely unaware of any sexual bias in stirring techniques...assuming I'm not alone in this unawareness - it's unlikely that men (in general) are specifically stirring in one way or another because they want to be different from women. I think you're WAY over-thinking this. SteveBaker (talk) 22:42, 6 May 2009 (UTC)

I should point out that the tip given by the chemistry teacher was not about tea, coffee and sugar per se. It was about dissolving some granulated solid chemical (NaCl, probably) into a liquid chemical, in a flask, in a lab. We were being shown how to conduct some experiment. Some students started using a glass stirrer and just shook it around in the liquid, but she said not to do it that way but stir it in a circular motion. I just extended that principle to tea and coffee; but I always did it that way anyway, because my mother taught me to stir, not to shake or jiggle. Mothers are the ones who generally do most of the cooking at home, so they ought to have a few ideas about the best ways of doing these things. My partner, who's a chef, says he was also taught at cooking school to stir rather than jiggle when preparing food. -- JackofOz (talk) 00:15, 7 May 2009 (UTC)

Chemistry-lab glass stirrers are typically thinnish rods. Moving such a rod semi-randomly (i.e. "jiggling it") in a beaker of liquid would only generate small-scale currents in the liquid, both because the rod is has a small cross-section and because the movements caused by the jiggles would partly cancel each other out. Stirring in a consistent circular direction, on the other hand, would cumulatively build up a larger-scale circular swirl that would catch up more of the solute more quickly.

Stirring with a spoon is somewhat different, because the shape of the spoon creates large scale movements in the liquid much more easily: even jiggles will have significant effects. Nevertheless larger-scale movements (so long as they don't slop the beverage out of the cup!) would still mix things a little faster.

Circular stirring creates a whirlpool effect that tends to concentrate solutes in the centre of the vessel, slowing their dissolution: this can easily be observed with a transparent solvent (such as tea without milk) in a transparent vessel (such as a glass teacup); to counteract this, when stirring beverages circularly I myself tend to reverse the direction of stir a couple of times. An alternative method is to move the spoon back and forth along a diameter of the vessel, which avoids any local concentrations and is, I suspect intuitively, the most efficient method, but generates more uncontrollable movements in the liquid level, risking spillage.

One often stirs beverages in a social situation, where efficiency is not the sole factor: considerations of etiquette also apply. Jiggling one's spoon is more likely to cause a vulgar clatter than gentle circular stirring, and side-to-side movements more likely to slop. These factors might matter more at a family meal on the best tablecloth and less in an all-male works canteen.

Both the chemical and the sociological aspects of this question would be eminently suitable for research. The dissolution rates of standardised amounts of suitable solutes and solvents in identical vessels, varying the style of stirring and nature of stirrer, could be investigated. Equally, a survey of techniques tabulated by sex, approximate age, class, ethnicity and locality (for example) could be carried out in public cafeterias and the like. Perhaps these would make suitable Science Fair Projects. 87.81.230.195 (talk) 02:55, 7 May 2009 (UTC)

There are other considerations too besides effectiveness. Something like NaCl is going to be soluble enough to dissolve quickly regardless of how you mix it; it probably doesn't matter much if it takes 5 seconds to fully dissolve or 7 seconds. However, swirling is less likely to cause solution to splash out of the container, which will cause an unmeasurable loss of material, and will introduce error into any quantitative measurement. So even if it WERE more effiecient to dissolve by jiggling, it is messier and probably thus is a bad idea regardless. --Jayron32.talk.contribs 03:30, 7 May 2009 (UTC)

I'm glad you mentioned locality, 87. Another thing I've also noticed is that people living in rural areas tend to "jiggle" their tea/coffee with their spoon more than city people, who tend to stir it. And younger people tend to jiggle, older people tend to stir. Completely OR, but that is my experience. Don't ask me why I notice these things, I just do.

Jayron, this lesson from my 1968 chemistry class is one of the few things I remember about the course, but it's clearly imprinted on my brain for some reason. The reason the lecturer gave was that it would dissolve more quickly by stirring than any other way, but I can see that there would be other good reasons for stirring too. The lecturer was an American woman, if that's at all relevant. -- JackofOz (talk) 04:49, 7 May 2009 (UTC)

Russian "quarantine" after spaceflight?

An article on Gamasutra about a lawsuit mentions that Richard Garriott was in "quarantine" in Russia after his spaceflight. Quarantine? Really? Is this an accurate description? Do they really quarantine cosmonauts after a flight, and why? Tempshill (talk) 22:02, 6 May 2009 (UTC)

Hmm maybe not a perfect description, although the NASA used to quarantine astronauts when they came back from the moon (see Lunar Receiving Laboratory). I suspect in this case it was more "observation" than quarantine, but don't really know. TastyCakes (talk) 22:16, 6 May 2009 (UTC)

See here also. TastyCakes (talk) 22:21, 6 May 2009 (UTC)

Right - but that stopped in the early 1970s, hence my surprise the Russians may still feel the need to quarantine stuff that comes back from space. Tempshill (talk) 00:05, 7 May 2009 (UTC)

Birds tapping on windows

My partner and I have a pet cockatiel named George, in a large cage. It's perfectly happy there, and it's outside the house. A few weeks ago, a hawk was attacking the cage and frightening George, so my partner decided to put her (yes, George is a girl, a fact we only discovered when she started laying eggs) into a smaller cage and bring her inside the house. It was near a window where she and other birds outside could see each other. One bird in particular, a magpie, started to tap on the window with its beak. This would happen maybe a dozen times in the space of a few minutes, usually in the morning. I'd eventually get sick of it, shoo the maggie away, and that would be the end of that. Until next morning. We decided the hawk problem was no longer an issue, so we've now returned George to her normal cage outside. But this damn magpie still taps on the window every morning, as if George is still inside the house, when she plainly isn't. When George was inside, once I'd shooed the magpie away, it wouldn't return till the next day. But now, when I shoo it away, it comes back after a few minutes and starts tapping again. This goes on for a few hours now, whereas before it was only a few minutes. I can't swear it's the same magpie every time, but it looks like it might be. What's going on here? Is the magpie remembering the time when George was inside the house, and not connecting the bird that's outside now with the bird that used to be inside - or is it doing something it might have done anyway? I sort of doubt the latter, because we have a lot of birds around the house, but this window-tapping never happened until George was brought inside. -- JackofOz (talk) 22:42, 6 May 2009 (UTC)

Are you sure it was a magpie and not a raven? Edison (talk) 23:58, 6 May 2009 (UTC)

Oh, how droll. -- JackofOz (talk) 00:18, 7 May 2009 (UTC)

Could it be coincidence and nothing to do with George? Maybe it's only seeing its own reflection? Either way maybe you can cure it of the habit by putting white out on the window (the stuff they use on greenhouses)? David D. (Talk) 02:24, 7 May 2009 (UTC)

It's not uncommon for birds to attack their own reflections in a window. Maybe the first time the bird was trying to attack George, but got confused by its own reflection and keeps returning because it has a "memory" of an "intruder magpie" there. Looie496 (talk) 02:49, 7 May 2009 (UTC)

I'd say that it's pretty likely that the bird is just going after its own reflection. I had a Common Blackbird doing the same thing to my window on four separate occasions yesterday. Most bird species do not understand the 'reflection = me' concept, though interestingly, the European Magpie apparently does. I assume that we're talking about the Australian Magpie here though? --Kurt Shaped Box (talk) 03:32, 7 May 2009 (UTC)

Yes. They're clearly less intelligent than their European cousins. -- JackofOz (talk) 04:34, 7 May 2009 (UTC)

Try hanging a bit of aluminum foil outside at the window. Magpies (check post about a week ago) like shiny things. It may have been after your bird's mirror (If she has one) or other shiny things or reflections. Funnily enough a lot (all?) of them don't like aluminum foil. That may deter them from going after other shiny things it sees in your window. As a plus it doesn't cost more than a bit of string and a couple of minutes to put in place. Another common recommendation, cutting out the Silhouette of a hawk, may not work; because in the battle of evolution quite a few bird species now flock and attack hawks and thus may actually attack your window rather than leave it alone. BTW (OR) We have a stupid woodpecker that for some strange reason loves attacking our gutters. It has actually managed to peck a hole in one place. Sometimes there's no accounting for a bird brain :-) 71.236.24.129 (talk) 17:47, 7 May 2009 (UTC)