Wikipedia:Reference desk/Archives/Science/2006 December 28

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December 28

adhesives

I am looking for an adhesive that can be used with the same plastic overhead transparencies are made of but that is not water based and therefore will not oxidize a polished or anodized aluminum plate to which it is attached. I've tried petroleum based spray adhesive that works like contact cement (and probably is the spray version) but even though it is advertised as remaining clear it turns the transparency white. I need to be able to see the aluminum through the transparency. All water based adhesives either do not stick well enough or oxidize the aluminum and turn it gray or black in splotches depending on thickness. If it is possible to make one-of decals and the adhesive they use will not turn white or oxidize the aluminum plate and their cost is compariable then I interested in knowing about them as well. Thanks in advance. 71.100.6.152 01:04, 28 December 2006 (UTC)

Cyanoacrylates ("Superglue")? FYI, transparencies are usually polyester ("Mylar").

Atlant 01:20, 28 December 2006 (UTC)

I've used both superglue and hot melt glue but unfortunately it only works on the edges. With the hotmelt glue I also tried application of a shrink wrap heater but the tranparency curled at the temperature of the glue. I need the adhesive to coat the entire interface between the aluminum plate and the transparency which is simply not possible (except perhaps in some sophisticated factory setup) using either one. (8.5 x 11 inch sheet) 71.100.6.152 01:31, 28 December 2006 (UTC)

I tried the super glue again to see if I could get enough to seep under the plastic but in some places the plastic rataind large bubble areas which simply refused to fill with adhesive. After a day when the super glue finally dried it left a ridge around these bubbles with the plastic held high above the aluminum. Perhaps using more superglue or thinner plastic or using some kind of pretreatment would eliminate this problem but since the super glue also desolved the adhesive holding the ink to the plastic the super glue can not be used. Besides the bubble problem it also did not dry perfectly clear is some areas leaving white dots and small splotches. 71.100.6.152 19:40, 29 December 2006 (UTC)

Superglue will work much better if you coat the aluminum with "hardener" or "cyanoacrylate accelerator." It hardens within seconds. Have you tried epoxy? Even better might be the liquid polyester used for casting clear paperweights. Many hardware stores have this stuff, but they call it "finishing coat" for making fiberglas.

Haven't tried epoxy yet although that is on the list. Polyester resin sounds like it might work except again for the problem of the ink which is on the backside of the plastic. What is next on the list is the adhesive used in packing tape an on other plasitc membranes. The hardner idea is a problem as well since the plastic needs about 5 minutes worth of positioning, etc. which a hardener would not allow. 71.100.6.152 03:36, 30 December 2006 (UTC)

Transformation of energy

Suppose a car crashes into another object. Part of the kinetic energy of the car is converted to heat and sound, and some is absorbed by the other object. Some of the energy is used in deforming parts of the car. If energy can't be destroyed, and energy was put into deforming the car, in what state does the said energy now exist? BenC7 01:35, 28 December 2006 (UTC)

Heat. The process of deforming the car generates heat due to friction inside the material. For example, if you bend a small metal tube or stock back and forth a few times, you will feel the heat being generated because of the friction. --70.6.95.38 01:44, 28 December 2006 (UTC)

Yeah, this is what I suspected. Ta. BenC7 04:32, 28 December 2006 (UTC)

Some of the energy may have been converted to potential energy, like in a compressed spring that is kept from expanding by its surroundings, and may yet be harvestable (in theory).  --Lambiam^Talk 08:58, 28 December 2006 (UTC)

An obvious example of this is if the car ends up perched high up on a guard rail, retaining wall, or hillside; clearly, some portion of the vehicles' kinetic energy was expended lifting the car that ends up perched and it's now available as potential energy.

Atlant 12:51, 28 December 2006 (UTC)

Electronics: IC that will take a 0-5V analog input and output a 0-100% PWM

PWM signals are most often generated with a microcontroller. Can you generate such a signal with just one integrated circuit (not a microcontroller). It is possible to generate such a signal with two 555 timers but I am not interested in this solution.

The output frequency should be at least 30 kHz.

You wont get 0 to 100%. maybe 10% to 90%. Look here [1] --Light current 01:55, 28 December 2006 (UTC)

PWM generator chips are ICs which convert a DC level into a PWM output. Many of these are designed for use in switch mode power supplies. Unfortunately, the devices designed for switch mode power supplies tend not to allow the mark-space ratio to alter over the entire 0 - 100% range. many limit the maximum to 90% which is effectively limiting the power you can send to the motors. Devices designed as pulse generators should allow the whole range to be used. Examples are:

ST

SG1524
SMPS
May operate at up to 100% duty cycle

SG3525A

Maxim

MAX038
Signal generation
PWM output only between 15% and 85%. Generates triangle & sine waves too.

Atmel

U2352B
PWM Generator for speed control of portable tools
Includes integrated current limiting circuitry for output MOSFETs.

TI

TL494
SMPS
Max 90% duty cycle

TI

UC2638
PWM generator for motor control
Provides many other features for DC motor speed control.

71.100.6.152 02:00, 28 December 2006 (UTC)

(After edit conflict) This page of PWM generators, linked from our article about PWM (and copied & pasted by 71.100.6.152), suggests that there are ICs that can do what you're after, and gives a circuit using an STMicroelectronics SG3525A chip. -- AJR | Talk 02:20, 28 December 2006 (UTC)

Ear infection

Where do ear infections come from? My doctor tells me it isn't something you catch from another person, so where does it come from? --Auximines 11:44, 28 December 2006 (UTC)

See our articles on Otitis.  --Lambiam^Talk 12:54, 28 December 2006 (UTC)

(edit conflict) When you have any sort of congestion, the ever-present bacteria in your respiratory system tends to get pushed up your eustachian tubes into your middle ear where it finds a nice, warm, moist, very-hospitable environment and it then floureshes, producing otitis media.

Atlant 12:56, 28 December 2006 (UTC)

I've gotten them from swimming pools (which apparently weren't adequately chlorinated). StuRat 16:01, 28 December 2006 (UTC)

Yes, Otitis externa (a.k.a. swimmer's ear) is the other popular manifestation.

Atlant 16:48, 28 December 2006 (UTC)

Birds' hearing

How do birds have such acute hearing when they have no external ears? Their ear is just a small hole and in most birds, it's completely covered by feathers. --84.64.4.91 11:55, 28 December 2006 (UTC)

Apart from the owls, most birds do not have particularly good hearing, and in most cases (apart from the songbirds) their hearing is tuned to a relatively narrow waveband. Indeed, some small birds, such as the sparrow, cannot hear a low human conversation. However, all birds make up for this with excellent eyesight, and (again apart from the owls) a wide field of view.--Shantavira 14:25, 28 December 2006 (UTC)

Futuristic Glass Touch Sensor

I want to embed glass marbles in a metal casing, and give these marbles a glow from light within the casing. I need these marbles to act as switches. Microswitches behind the marbles wont do, because it will create an entry into the metal case for rain etc. when the switches are depressed, plus the simple weight of the glass marble on the switch will likely be enough to trigger it. I really want it so you just have to touch the glass and you activate that switch - would it be possible using a photo-sensitive device pressed against the other side of the marble? But since the marble is backlighted, the effect of putting your hand over marble would be to increase reflected light in dark conditions and reduce entering light in light conditions? --Username132 (talk) 13:24, 28 December 2006 (UTC)

Using LEDs, you can very rapidly pulse (modulate) the "glowlight". This would then allow you to use a sensor that detects any rapid change in the amount of modulated glowlight reflected back to your sensor. Unless very matte-black-gloved, a finger pressed against the marble would increase the amount of reflected glowlight. And since the glowlight is pulsing, you can use electronics to distinguish the reflected glowlight from the overall ambient light.

You can probably optimize this by clever placement of the emitters and sensor(s).

Atlant 15:36, 28 December 2006 (UTC)

Super Duper Bright LEDs

According to Wikipedia's article on Candela, a 100W incandencent bulb produed about 120 000 mcd of light. On this basis, must this ebay seller be lying about his item? LED's that produce as much output as a 100W incandecent? And using just 0.1W, no less! According to Wikipedia on LEDs, efficiency is at about 32 lumens per watt for LEDs but for this 130 000 mcd light, that's over 17 000 lumens or 170 000 lumens per watt? --Username132 (talk) 14:17, 28 December 2006 (UTC)

And please keep in mind that the maximum theoretical efficiency of a light source is 683 lumens/watt for a monochromatic green source at 555 nm; see Luminosity function. NO WHITE LIGHT SOURCE can approach this value because your eyes become less and less sensitive as you move away from your eyes' peak sensitivity at 555 nm.

Atlant 15:39, 28 December 2006 (UTC)

So they really are lying? That's unethical! --Username132 (talk) 17:57, 28 December 2006 (UTC)

I'm afraid that's eBay for you. It is all based on trust. I once bought some binoculars on eBay and they were way below spec. And there are usually a few air guitars being "sold" on eBay too.--Shantavira 19:00, 28 December 2006 (UTC)

Whoa! I've been looking for one of those. X [Mac Davis] (DESK|How's my driving?) 20:09, 28 December 2006 (UTC)

Carbon nanotube

If super capacitors are made of nothing more than Carbon nanotubes emersed in sulphuric acid then are they used to make plates and how are the plates connected to the exterior as well as arranged inside an enclosure? Adaptron 16:18, 28 December 2006 (UTC)

Our supercapacitor article describes them as also being made with organic aerogels which are then reduced down to extremely-porous carbon structures. Certainly supercaps were in production before the big boom in carbon nanotubes, buckyballs, and et al.

Atlant 16:55, 28 December 2006 (UTC)

Suicidal animals

Appart from my pet turtle who "jumped" form the 5th floor window, do we know of a tendency in some individual animals to being suicidal? Keria 16:40, 28 December 2006 (UTC)

Lemmings are the classical example, whether true or not. Members of certain political parties are also alleged to fill the bill from time-to-time.

Atlant 16:44, 28 December 2006 (UTC)

Lemmings are real animals? Where have I been? --Russoc4 17:27, 28 December 2006 (UTC)

I don't believe lemmings are suicidal unless they're being chased off a cliff by Walt Disney's crew. Vranak 17:30, 28 December 2006 (UTC)

Your turtle (like my friend's rabbit) probably wasn't suicidal. Turtles are very near sighted (in order to focus on the food directly in front of them) and so would not be able to see or understand the distance represented by more than a couple feet. At the same time, they evolved in an environment largely without cliffs and high places, and so probably lack the instinct to know that fall == bad. So, I am guessing it was more a case of the turtle being too blind and dumb to know better. Dragons flight 17:36, 28 December 2006 (UTC)

See Overtoun Bridge.--Shantavira 19:02, 28 December 2006 (UTC)

Whales beaching themselves is one possibility. Other explanations have been offered, but the way they frequently beach themselves immediately again once pushed out to sea makes me rather suspicious. StuRat 19:20, 28 December 2006 (UTC)

comment deleted. -- Rick Block (talk) 20:42, 28 December 2006 (UTC)

Animals can't be suicidal, unless they've already passed on their genes for sure, or can think complex enough to be able to do it. How is the validity of that statement? X [Mac Davis] (DESK|How's my driving?) 20:07, 28 December 2006 (UTC)

I think you're saying that their actions don't count as suicide unless they understand what death is. I think some animals, besides people, do have a basic understanding of death. Elephants, for example, go to the "elephant graveyard" and visit the bones of their relatives periodically. They appear to have an emotional reaction. StuRat 20:58, 28 December 2006 (UTC)

Hmm...My understanding is that elephant's graveyards are myths, which is supported by the article. Even if they were true, we wouldn't know for sure if the elephants really understood the concept of death or if they were just following an instinct without understanding what the result would be. —Cswrye 17:12, 29 December 2006 (UTC)

Thank you very much Keria 13:46, 29 December 2006 (UTC)

Killer Whales beach themselves as a technique to catch seals. I am sure that they make mistakes sometimes, and go too far. Also, it has been found that SONAR destroys something in whales/dolphin's middle ear which inclines them to beach themselves more. Saw that last thing on a doco a long time ago, so it may be out of date research. --liquidGhoul 14:11, 29 December 2006 (UTC)

While not strictly committing suicide, some eusocial insects will "sacrifice themselves" for the greater good of the hive/colony. This can be justified genetically (and is very elegantly described in The Selfish Gene). However, its not that they are choosing to die, simply that sterile insects willingly take action that will almost certainly lead to their death in order to protect the fertile members of their hive/colony and thus propagate their collective genes. They take on suicide missions, if you will. Rockpocket 03:16, 30 December 2006 (UTC)

wearing rubber gloves

I've noticed that some restaurant workers put on latex glove to handle food but then touch everything from garbage to scratching their private parts with the gloves on as if the true purpose for the gloves is to keep their own flesh from becoming contaminated. Is this lack of sufficient regulation or training or just failure to comply on the part of such workers. (BTW Even emergency room intake personnel have been seen doing the same thing. Hope it is not true for nurses and doctors.) -- 71.100.6.152

You're right, this is a common practice. There need to be procedures set up to avoid this. For example, at the Subway sandwich shop, employees remove and toss out their disposable gloves when they handle money, then put a new set on for the next customer. In larger restaurants the best way to handle it would be to have one person who handles the register and another who handles the food. Garbage and cleaning tables should also be handled by somebody else. Cooked and uncooked foods should also be handled by different people. At hospitals, failure to establish and follow proper hygiene procedures regularly causes infections and deaths. The root problem is insufficient punishment for those who violate procedures. For example, any employee caught not washing their hands after using the toilet should be fired immediately. Unfortunately, that almost never happens. StuRat 19:14, 28 December 2006 (UTC)

Yes I think the Subway method is quite good. I go there regularly and have never seen any unhygenic manoevers. On thing that bothers me tho' is when they put on the platic gloves, they actually touch them with ungloved hands 8-)--Light current 19:20, 28 December 2006 (UTC)

Good point, they need a fixture that holds the sterile gloves in place while they put them on. StuRat 19:56, 28 December 2006 (UTC)

They better not touch the fixture, or I'd be worried! X [Mac Davis] (DESK|How's my driving?) 20:04, 28 December 2006 (UTC)

Pfft, I worked in a subway (eeeat fresh!) and you don't want to know what happened to the food before it entered that plastic bin and made it's way to the front. Gloves are there to placate germophobes. If you want sterile food, simply raise it's entire mass to 175F, cool, and enjoy! As for me, what's a few more germs? As long as I don't get a booger shot on my sandwich, I won't be grossed out in the least. --Anonymous

Another good point, the entire food prep area should be visible to the public, not just the final sandwich prep area, if we are to shame them into proper hygiene procedures. StuRat 20:49, 28 December 2006 (UTC)

Yeah then thered be no room for customers at all! 8-)--Light current 02:42, 29 December 2006 (UTC)

Haha, but that's why we have immune systems, eh? --Chickenflicker---♣ 04:36, 29 December 2006 (UTC)

No. That's why we need immune systems, haha. 71.100.6.152 04:51, 29 December 2006 (UTC)

Just as a side note, the gloves used in food handling are not sterile, any more than condoms are sterile. They're useful as barriers only. - Nunh-huh 19:28, 30 December 2006 (UTC)

Rubber gloves engender a false sense of cleanliness security. I'll look for a citation, but I've read several places that the material in sanitary gloves is a better breeding ground for microbes than human skin is, so clean hands are better for food preparation than gloves. Of course, you never know how clean someone's hands are, but still... Anchoress 19:41, 30 December 2006 (UTC)

Yes, but you can be reasonably sure nobody just wiped their butt with a new set of rubber gloves. Also, the scum under the fingernails must be considered. StuRat 19:58, 30 December 2006 (UTC)

Why does chalk cause fever?

Some kids have used (or still use) as school-evasion strategies chalk, because chewing it caused fever for a short time, without causing any noticeable side-effect. What might be the cause of this phenomena? What effect does a bit of chalk have on the organism? Why? Is it even dangerous? Don't consider this question as a seeking of medical advice... I was just wondering... --86.125.180.178 18:06, 28 December 2006 (UTC)

• Interesting question and I don't know the full extent of the answer. Naturally occurring chalk is a form of Limestone (calcium carbonate) that is very soft and porous. However, regular chalkboard chalk that is commonly used in schools is made from the mineral Gypsum (calcium sulfate) rather than calcium carbonate. I do know that many people, including myself, are mildly allergic to the calcium sulfate found in processed chalk, it is known to cause respiratory and breathing problems in many people but I have never heard of it causing a fever. Perhaps this is just another symptom of an allergic reaction that some people experience? I would be interested to hear any other insights--Nebular110 18:19, 28 December 2006 (UTC)
• I don't know either, but calcium sulfate (aka E516) is commonly found in bread (such as baker's delight bread) as a "Flour treatment agent". —Pengo ^{talk · contribs} 01:01, 29 December 2006 (UTC)

This is ridiculous. If someone can supply enough detail to make a brief trial, I guarantee we can get this published and it will be in every newspaper in the country and twice around the world within a week. This would be an extremely well-known phenomenon if it were true. Many medical treatments in the late 19th and early 20th centuries for a variety of infections involved intentionally attempting to induce a fever. Dangerous infections were even caused intentionally to try to cure worse ones. If a fever could be induced by something as simple as calcium sulfate or calcium carbonate every doctor would know it and it would be on every differential diagnosis list as a cause of FUO. Thanks for the chuckle. alteripse 02:34, 29 December 2006 (UTC)

You mean it's all an urban legend? If I remember correctly I've seen some schoolkids actually trying it out and becoming sick. Were they just pretending (or maybe placebo effect??), or does the chalk used for blackboards contain something else besides the calcium sulfate or calcium carbonate? I know there are higher quality chalks, so the must be a difference. Anyways, thanks for the answer. --86.125.180.178 19:22, 30 December 2006 (UTC)

Soret band? yes/no

Does vitamin B12 emit light in the visible range like a true heme, or does it lack a strong absorption band?--74.66.242.190 18:10, 28 December 2006 (UTC)

The Spectral Database for Organic Compounds is a good place to start with questions like this. Sadly, they only appear to have ESR and IR data for B12; perhaps a derivative and/or precursor would have UV/Vis data? StevenBrown 08:23, 30 December 2006 (UTC)

Painful but nonlethal stabbing

What places on the human body can be stabbed, without killing, but so painful the person stabbed is forced to surrender? PitchBlack 18:18, 28 December 2006 (UTC)

Metadiscussion of old irrelevant heading deleted. -- SCZenz 22:11, 28 December 2006 (UTC)

The places with the most nerve endings and the least arteries. e.g. feet and hands. Why do you ask?--Shantavira 19:07, 28 December 2006 (UTC)

The joints are particularly fragile and vulnerable, and damage to them will severely disable someone. I'm not so sure about the chances of killing someone with a joint injury, but I don't hear about that a lot. — Kieff 21:51, 28 December 2006 (UTC)

If you can get a clean stab into someone, chances are that you could disable them without resorting to such extreme measures in the first place. Vranak

Well according to Reservoir Dogs, abdominal stab wounds are excruciating, but you take days to die from them. Don't know if that fits, or if it is in fact correct. Anchoress 08:23, 29 December 2006 (UTC)

Stabbing anyone is very dangerous because any cut can cause bleeding in addition to pain. Even though your intent might not be to kill an assailant you could still be charged with a crime such as manslaughter or even murder even in an obvious situation of self-defense since it is up to the court to determine if your actions were justified and not the police. If you want to deliver pain to an attacker in self-defense use a non-lethal stun gun but remember you can still be charged with a crime by the police. (See: Eggshell skull rule and consult a lawyer for legal advice.) -- 71.100.6.152 17:16, 31 December 2006 (UTC)

Suffering from exposure to Frost, cold and water

If a guy falls into a lake out the wild in forexample harsh winter weather with -15 C degrees (nevermind the ice, lets just say it cracks somehow) and his nearby friend manages to reach him and save him by grabbing him with one arm (a quite strong arm mind you) then i guess the poor bastard who fell into the water is quite done for. Any idea/opinions on how fast he would freeze to death ?

And quite interesting i think, how would this friend/guy who pulled him up fare ? how would his arm and hand fare ? (Ofc, his hand has to be put into the icy water and get wet to pull his friend up - say he's quite strong and able to do so with only one arm) I take it chances would be BIG for him to soon suffer from frostbite, or would he DEFINATELY suffer from it without a shadow of a doubt in such a harsh climate? At least his fingers and hand would be greatly in risk, no ? However, if he quickly dry the arm and hand as best he can with something dry and then wraps arm/hand/fingers in as much cloth he can to generate warmth, he should be able to fully "recover" and save his arm/hand/fingers, no ? - even though they are out in the wild with extreme cold...

The one who fell into the water would probably go into shock or something and he would freeze to death (in minutes, wouldn't you agree?)

The one who 'saves' him and gets his arm wet tho, he has quite realistic chances of saving his arm if he quickly does as i described, no ?

By the way : is there any page(s) you could link me to that tells of 'freezing to death' and the process as it unfolds until ones death?

and the process of suffering from exposure to cold and frost in any way ?

I don't know what to search for then.... i have searched for Frostbite ofc, but it doesnt fill all my needs for information on the subject.

Thank you, Krikkert

Well, the water, being liquid, can't be colder than about 0C (you said it was a lake, so no salt water here) . So frostbite merely from contact with the water isn't an issue. The issue is how quickly one's body loses heat into the chilly water. I can assure you that it is possible to survive a dunk into chilly water; the key is how long you remain in the water and how much additional heat you lose once removed from the water. Your body has quite a bit of thermal mass and your fat layer provides some thermal insulation, enough to withstand at least a few minutes [2]. I suppose being rescued into -15C air is probably a pretty bad situation, but even then it depends on things like wind chill effect and whether there's any shelter nearby.

Atlant 20:56, 28 December 2006 (UTC)

Frostbite, and especially hypothermia, have some info about times and specific physiological effects. My Merck Manual notes "Sudden immersion in very cold water may cause fatal hypothermia in 5 to 15 minutes; however, a few people, mostly infants, have survived for as long as 1 hour completely submerged in ice water." The mammalian diving reflex is an interesting ability that explains why some people have been rescued and revived after even after many minutes fully submerged. DMacks 05:12, 29 December 2006 (UTC)

...however, it is typically only infants that have it. Further on "surviving a dunk into chilly water", there are people who do this on purpose: see Ice swimming. On the other hand, most of the people killed when the Titanic sank died of hypothermia (the ocean temperature was just below 0°C), and as the Merck Manual says, it didn't take long. --Anonymous, December 29, 05:32 (UTC).

On the sun...

I was reading the article on the sun, and was absolutely intrigued by this line- 'Tidal effects from the planets do not significantly affect the shape of the Sun, although the Sun itself orbits the center of mass of the solar system, which is located nearly a solar radius away from the center of the Sun mostly because of the large mass of Jupiter.' Now, this raised a number of questions to me-

• Where exactly is this center of orbit? 'Nearly a solar radius away from the center of the Sun' would mean within the sun itself, would it not?
• Does this orbit change? Surely, at different points in the orbits of the larger planets, this center of gravity for the solar system would be at different points?
• How long does the sun take to orbit this?
• Do the planets orbit the sun, as I have always been taught, or do they orbit this center of gravity?
• Does the sun move at all, apart from this?
• What about with other bodies? Surely, if this is happening to the sun, it could also happen to the earth, so that it circles a point slightly outside its own central point, because of the center point of gravity within the Earth-Moon system?

I understand astrophysics as far as getting me an A* at GCSE science goes, but not far beyond that. Any answers to these questions would be very appreciated. Thanks! J Milburn 20:19, 28 December 2006 (UTC)

The center of rotation of a system of two objects is called a barycenter. The only barycenter well outside the larger of the two objects I know of in our solar system is Pluto, due to it's large moon Charon. (Check out the barycenter link, it has many of the answers you seek.) StuRat 20:27, 28 December 2006 (UTC)

It may also help to remember that if you exclude the sun, Jupiter makes up more then half the mass of the solar system, this means if you combined all the other planets you still won't have as much mass as Jupiter! So the other planets may have a small effect on the sun, but not nearly as much as Jupiter. Also, when you say, is it orbiting the sun or the centre of gravity those are not really mutually exclusive. Like in any gravity system, even the earth/you system, two bodies exert force on each other. Pound for pound, you exert as much gravitational force on the earth as it does on you. If you were in orbit it would seem that you were spinning around the earth and the earth was stationary, now imagine you get bigger and bigger until you have as much mass as the earth, all of a sudden, the earth is orbiting you as much as you are orbiting the earth! And to the outside observer it looks like you are actually both orbiting some invisible point in-between you. Vespine 21:39, 28 December 2006 (UTC)

The barycenter article was very helpful, the animated gifs basically explained the whole thing to me! When combined with the description given by Vespine, I basically have the answers I was looking for. Thanks! One of my other questions was not really related to the others, however- is the sun moving through space? Perhaps orbiting something big, perhaps aimlesly floating, perhaps being thrown outwards? J Milburn 22:51, 28 December 2006 (UTC)

The sun as the centre of our solar system is in orbit around the galactic centre of our galaxy the Milky way. It's ALL orbits man!:) Vespine 23:02, 28 December 2006 (UTC)

Incidentally, no one can tell you precisely where the barycentre of anything is. See n-body problem.--Shantavira 09:26, 29 December 2006 (UTC)

We may not be able to solve the n-body problem analytically, but it is easy enough to find the barycentre of a given n-body system.  --Lambiam^Talk 10:13, 29 December 2006 (UTC)

From what I know, Kepler's first law says that all planets orbit the sun in elliptical orbits, and the sun is just one focus. - AMP'd 03:53, 30 December 2006 (UTC)

That law is based on observation. It is a consequence of Newton's laws, but only if the system consists of one star and one planet, and the mass of the planet is much smaller than that of the star. Both conditions are not fulfilled in the solar system. The effect of the planets on each other is not negligeable. Because of that, the whole system is believed to be chaotic.  --Lambiam^Talk 16:30, 30 December 2006 (UTC)

Is there really any difference between "friction" and "collision"

Is this a meaningless or illusory distinction? Is it meaningful only in the context of classical mechanics? NoClutter 20:38, 28 December 2006 (UTC)

You could read the Friction and Collision pages and read the definitions to see why they are different. :-) Imaninjapirate^{talk to me} 01:22, 29 December 2006 (UTC)

Which parts of those two articles should I focus on? The parts that I personally wrote myself? Or the parts in between the lines that invisibly address this specific issue. {:-)x2} NoClutter 12:18, 29 December 2006 (UTC)

This is a topic of relatively current research, I believe. The bottom line is that it's all really the electromagnetic force between the electron fields of the edge atoms. But the exact nature of frictional drag is pretty complex. Sometimes, it's just collisions between surface irregularities, but sometimes it's quantum mechanical in nature. Sadly, I don't have any good links for you... maybe I'll look for some at some point. -- SCZenz 12:23, 29 December 2006 (UTC)

Faster-than-light aspects

May be I'm missing the relevant points that already exist, but is it theoretically possible that if the faster-than-light speed is achieved, the spaceship pilot will see only darkness, and also because the spaceship moves faster than light, it will be invisible in all spectra? (if so, I assume that the spaceship would be virtually invisible for all unless the pilot reduces the speed). Is it also possible that the FTL would be unachievable in the gravity fields due to indescribable gees? --Brand спойт 20:45, 28 December 2006 (UTC)

No, no, and sorry but no. Theoratically FTL is not possible, c IS the fastest absolutely anything can go. Maybe some reading of the Speed of light article may help. People can make guesses as to what could happen if FTL was possible, but those guesses would go against currently held theories. Vespine 21:27, 28 December 2006 (UTC)

Theoretically, FTL is possible. See Tachyon (which is not a Star Trek invention). What you can't do (as mere matter) is reach the speed of light, by either accelerating, or in the case of tachyons, decelerating. (On the other hand, theoratically, StuRat is not possible.) Clarityfiend 01:22, 29 December 2006 (UTC)

But to REALLY stretch the imagination, I'll let go my previous bias to reality... A pilot travelling faster then light would not just see darkness, just as a pilot flying faster then sound doesn't go deaf. A pilot exposed to faster then sound airflow would probably go deaf, if his head wasn't torn off by the wind first, because the air pressure would exceed the speed of sound (sic).. So, a pilot going FTL would probably see BRIGHT WHITE rather then dark because the light pressure exceeds the speed of light... NEXT: Moving faster then the speed of sound creates a sonic BOOM, far from silent running. So, similarly, something travelling FTL might create a lux boom, where light stacks on top of itself and reaches an observer all at once. or, if say the FTL traveller was in orbit, they would appear as a SOLID ring in all places of the orbit at once! And finally, gees are only felt during acceleration, so no, that wouldn't be a problem as long as you didn't accelerate too fast. The shuttle accelerates at 3g, or about 30m/s per second, at that rate, you could reach the speed of light in about 115 days, according to my calculations... Can someone check that? That seems low, c doesn't seem so infinite when you put it like that:)Vespine 22:59, 28 December 2006 (UTC)

Yes, 115 days is about right. Of course, staying at 3g for 115 days would be very bad for your health. It takes about a year at 1g, which would be far more pleasant. These calcs, of course, use Newtonian physics; relativity would become more important closer to the speed of light. Specifically, the amount of elapsed time would appear to be less to an observer aboard the ship, by about half, I would guess. StuRat 01:00, 29 December 2006 (UTC)

Or maybe the light reaching you would be travelling at c, the same as any other situation. But probably blue-shifted enough to incinerate you. Peter Grey 04:53, 29 December 2006 (UTC)

Under the Newtonian laws of physics, I calculate that it takes 117.94 days to reach a speed of c = 299792458 m/s for a body subject to a constant acceleration of 3g, where the standard acceleration of gravity g = 9.806650 m/s². Under the laws of special relativity, I find that in the same time (for a stationary observer, but with acceleration taken in the framework of the moving body) it will obtain a speed of 0.76 c. After one year the velocity is 0.9959 c. It always remains less than c.

To consider what would happen if we could get beyond the speed of light, we have to invent a new set of laws for physics. So for example this might cause a build-up of resonating ripples in the space-time continuum that cause it to vanish in a wisp of quantum foam. Or the mass of the object becomes so large it turns into a black hole. Or the spaceship turns into hot apple pie and its pilot into cinnamon ice cream – there are no limits to the possibilities.  --Lambiam^Talk 08:49, 29 December 2006 (UTC)

Lambiam hits on the issue pretty well. If we're saying relativity doesn't stop you from reaching c, the mechanism that replaces it becomes very important. Without picking one, there's no way to answer. -- SCZenz 12:25, 29 December 2006 (UTC)

stream velocities for Red River (USA)

Hi, I'm trying to find stream velocity for various points on the Red River (USA). I mean the Red River that forms the border between Oklahoma and Texas, then Arkansas and Texas, then entering Louisana and joining the Mississipii.

I'd like to find a map of the avg velocites for different months, but I haven't been able to find anything at all. thanks in advance68.221.112.103 22:14, 28 December 2006 (UTC)

Do you mean flow rate rather than velocity? Historical (and realtime) stream gauge data can be found at the USGS National Water Information System web site.EricR 23:06, 28 December 2006 (UTC)

No, I really mean velocity--I'm planning a rafting trip. I saw that site and tried to use it, but never got it to give me the data:it assumes I know the site names in its database a priori.

thanks for checking on that. any other ideas, even offline?

68.221.112.103 23:15, 28 December 2006 (UTC)

Egg shells

What is the best way to either dissolve or crush (Finely powered) Egg shells for the purpose of human consumption? 71.100.6.152 22:55, 28 December 2006 (UTC)

I'm not entirely sure why someone would want to eat egg shells, but have you tried leaving them in vinegar overnight, it softens the eggshell right up and looks pretty damn cool! -It makes the eggs bounce as well!- Benbread 02:46, 29 December 2006 (UTC)

Not sure, never done this before. Perhaps a food processor/blender might work? --Wooty Woot? contribs 02:48, 29 December 2006 (UTC)

When I'm preparing scrambled eggs for my pet birds to eat, I just wrap the shells in kitchen roll and hit them/go over them with a rolling pin a few times. Mix the shell back in with the beaten egg, scramble, serve some to my psittaciformes (good source of calcium), eat what's left myself (crunchy but not bad). This isn't actually a specific diet choice, it's just a shame to waste food. --Kurt Shaped Box 03:12, 29 December 2006 (UTC)

Better to get your calcium carbonate by eating Tums or another antacid tablet. If you're going to eat eggshells, make sure they're ground fine enough not to damage your membranes and that they've been thoroughly sterilized. -THB 03:15, 29 December 2006 (UTC)

The idea originated when I was in high school as a possible means of helping to prevent Gout. However, anyone who includes calcium tablets in there diet (for one thing as a means of preventing nose bleed especially in older people who are taking a regular dose of asprin) then so long as the shells can do no damage on the way down... I guess if you eat salad you could use vinegar to disolve the shells and add a little oil but then you would have to cut back on other sources of calories. Thanks. 71.100.6.152 04:48, 29 December 2006 (UTC)

Mortar and pestle --Seejyb 04:58, 29 December 2006 (UTC)

Have you tried putting the egg shells into a bag and hitting the bag with a large hammer? That will deliver a lot of force and ensure that the shells are thoroughly crushed. --Bowlhover 05:02, 29 December 2006 (UTC)

After some experimentation I have found that what works really well is to first let the shells dry and then use a coffee grinder or handheld wand type sharp bladed mixer. The shells turn into grains of sand which can be added to yogurt. That way you do not have to throw the shells away and if you can't eat the yokes you can aways feed them to your cat or pet lizard. 71.100.6.152 19:51, 29 December 2006 (UTC)

Doesnt calcium carbonate dissolve in acetic acid? —The preceding unsigned comment was added by Light current (talk • contribs) 04:24, 30 December 2006 (UTC).

As in vinegar? Yes. But I think the calcium is still digestible as Calcium acetate maybe??? 71.100.6.152 17:23, 31 December 2006 (UTC)