Wikipedia:Reference desk/Archives/Science/2006 September 11

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September 11

Identifying mission patches

Can anyone identify some blurry space mission patches? [1] there are four here we haven't been able to identify, but we got all the others. They range from all over the place, Canadian Astronaut Service, Shuttle missions, Apollos. One of them looks like they have a house on it, but I haven't been able to find anything. - A.J. 01:17, 11 September 2006 (UTC)

Darned if I know. But I was shocked to discover that we didn't have an article on mission patches—so I started one. If you're an enthusiast, please feel free to flesh it out. TenOfAllTrades(talk) 03:28, 11 September 2006 (UTC)

Don't know any of those four, but the bottom one I can identify as that space insignia. Sometimes called a vector, or a wishbone, it is like an "A" representing the abstract of a rocket. You know what I mean? — [Mac Davis] (talk) (Desk|Help me improve)

The ship in the movie Virus?

I've been exceedingly curious for apparently no reason as to what this vessel was for. As I remember, it looked real enough in the film. The movie claims that it's some kind of Russian space agency secondary control center but I cant find anything about that.

Appreciate the help

If I remember right they were on a tugboat. Maybe wrong movie. — [Mac Davis] (talk) (Desk|Help me improve)

Virus (1999 film) says Mac is right, it was a "sea tug".  freshofftheufoΓΛĿЌ  09:03, 11 September 2006 (UTC)

I'm pretty sure they are reffering to the russian ship which the tug boat crew boards with the idea of salvaging for large sums of money. (Little do they know that the ship has been affected by a sentient bolt of lightning form outerspace and that all manner of mechanized zombies await them! No, seriously, that's the movie plot.) I don't remember much about the ship though. -Razma Dreizehn

Microscope Eyes

Sometimes, under the right conditions, my eyes somehow reflect light and let me see microscopic thingies on the surface of my eyes. I can clearly make out hollow cells joined together in rather short groups. It looks like this: http://img242.imageshack.us/img242/7062/untitledzz4.jpg The 'cells' move across my eyes usually from up to down. This phenomenon happens in bright light, I think. I wear persciption glasses, but I think that it has happened without me wearing glasses too. Has this phenomenon ever been reported by other people, or am I the only one? What conditions do I need to have to see this more often?--Codell ^{[ Talk ▪ Contrib. ]} 03:20, 11 September 2006 (UTC)

Floaters, possibly? Melchoir 03:22, 11 September 2006 (UTC)

Yes, they're probably it. Thanks.--Codell ^{[ Talk ▪ Contrib. ]} 03:29, 11 September 2006 (UTC)

Nice illustration! — [Mac Davis] (talk) (Desk|Help me improve)

I get something like that, too. They are always out of focus with me, and I usually get them when I first wake up. I always assumed they were slime on my eyeball. After a few blinks they go away. I can't look directly at them, because moving my eyeball causes them to move. StuRat 05:11, 11 September 2006 (UTC)

because they're on your eyeball. And you know that, but still can't resist the urge to try and look at them, right? Btw, how was that photo in the article made? Did someone stick a camera in their eye? :) Probably not, but it looks pretty much like the real thing. DirkvdM 08:53, 11 September 2006 (UTC)

This is probably one of the most asked questions on the Science desk. It's still cool though, I always kept it a secret when I was a kid because I figured no-one would believe that I was seeing red sperm in my eyes.  freshofftheufoΓΛĿЌ  08:56, 11 September 2006 (UTC)

Under certain circumstances (usually, a bright deep blue featureless background), it is also possible to visualize the red blood cells moving in the capillaries in your retina. The Exploratorium has a gadget that can reliably provoke this effect, but given some time, you can usually see it with any deep blue featureless field. (I mention this just for completeness; your effect sounds like floaters.)

Atlant 15:02, 13 September 2006 (UTC)

That's cool. --Proficient 06:11, 14 September 2006 (UTC)

the famous salt problem

I seek to master the famous salt differential equations problem. how might i TraIN! Jasbutal 07:04, 11 September 2006 (UTC)

If it's so famous, how come neither I nor Wikipedia (salt differential equation) have ever heard of it? DirkvdM 08:55, 11 September 2006 (UTC)

Maybe this is it:

A tank is filled with 1000 L of brine, containing 15 kg of dissolved salt. Pure water flows into the tank at a rate of 5 L/min. The solution is kept completely mixed, so the concentration of salt is uniform, and the solution flows out at 5 L/min. How much salt is in the tank after t minutes? after 20 minutes?

The answer to that question is 13.6 kg by the way.  freshofftheufoΓΛĿЌ  09:00, 11 September 2006 (UTC)

It could also be the equation in geophysical fluid dynamics which at least one person has called "Conservation of Salt" - $\nabla ^{2}S=0$. Then again, thinking about it, that may just be an extension of the above problem - it's just a statement that the amount of salt in a system is based on the flow in and flow out. Confusing Manifestation 00:55, 12 September 2006 (UTC)

Time to freeze water?

Is there a formula for figuring how long it will take to freeze a given volume of water at a given below-freezing temperature? I couldn't find one with a brief web search, but figured there should be... -Goldom ‽‽‽ ⁂ 07:41, 11 September 2006 (UTC)

For one you'd have to know the starting temperature of the water. And then the contact area and the heat conductivity of the container. And the shape too, but I assume that if there will be any such formula it will assume a shape that has a simple geometric description, such as a cube. DirkvdM 08:59, 11 September 2006 (UTC)

And the pressure would also matter, as well as any impurities and nucleation sites in the water. StuRat 09:33, 11 September 2006 (UTC)

There is a specialised description, the heat equation, but it is probably more complex than what you're looking for. Xcomradex 09:13, 11 September 2006 (UTC)

You'd also need to know the pressure and the starting temperature of the water. I don't believe there is a formula as there is the unexplained (I would be delighted to hear any explanations) problem as to why hot water freezes faster than cold water when the same volumes (and shapes) are put in the same (below freezing) tempreature and the same pressure. —Preceding unsigned comment added by OEYoung (talk • contribs)

How can hot water frezze faster than cold? More energy has to be removed from the hot.--Light current 12:31, 11 September 2006 (UTC)

Visit the Mpemba effect page for some info on this counterintuitive situation. DMacks 12:37, 11 September 2006 (UTC)

Compare this problem with that of 2 capacitors of equal value charged up to different voltages. When they are discharged thruough equal resistances, which one reaches V volts first? Certainly not the one charged higher initially!--Light current 12:41, 11 September 2006 (UTC)

Thanks DMacks - I couldn't remember the name. I didn't believe it myself until I tested it. If you can come up with the reason for it it'd probably win you a nobel prize! —Preceding unsigned comment added by OEYoung (talk • contribs)

Water gives up dissolved gases when heated. Dissolved gases should lower the freezing point of a solution. So if it is previously heated but allowed to cool to the same temp as the cool water, it should freeze faster.Edison 19:05, 11 September 2006 (UTC)

Ayup, that's one of the seven explanations given on the Mpemba effect page. DMacks 21:14, 11 September 2006 (UTC)

Well its not pure water then is it? Its actually a different liqiud and can be expected to behave differently. You must not compare apples and oranges. THeyre different--Light current 00:20, 12 September 2006 (UTC)

Pure water doesn't exist (pure anything doesn't exist). So what we call 'water' is a range of solutions. Only when the impurities become too big an ingredient will we stop calling it water. Any rules on that? DirkvdM 09:06, 12 September 2006 (UTC)

olympic and islam

I "created"an article concerning muslim athletes participating in olympic games.

I am unable to locate the article.

I am understanding that anyone can write an article..

please advise.

• This question would be better placed at the help desk. Anyway, please sign your questions using the signature buttom or 4 tildes (~) so we can easily see who you are and what you edited. - Mgm|^(talk) 10:20, 11 September 2006 (UTC)
• Anyone can edit an existing article, but too write a new one you need to register an account and log in using the link on the top right of the page. You added this question with your IP address suggesting you're not logged in. - Mgm|^(talk) 10:22, 11 September 2006 (UTC)

Why did nobody die of a heart attack before 1923?

Whilst perusing the Uni of Manchester website [2] I came acroos the above statement.

Anyone have any idea as to where it originates from and also, if it's true?

--DPM 10:28, 11 September 2006 (UTC)

In the last century, heart attack has been the lay term and legal term for any type of sudden death in an adult attributable to myocardial infarction or any other heart disease. Heart attack entered common language in the first decades of the 20th century. It began to appear on death certificates in the early 20th century. The detailed concept of myocardial infarction in its strict sense (death of heart muscle because of interruption of blood supply) also dates to the early 20th century. The statement does not mean that no one ever died of a myocardial infarction before 1923 but that the cause was not recognized and described with the more familiar term. alteripse 10:55, 11 September 2006 (UTC)

This naturally raises the question of what it was called when somebody grasped their chest, then dropped dead, before 1923. StuRat 14:22, 11 September 2006 (UTC)

Well heart-failure and heart-shock go back to the 19th century, maybe English speakers didn't like to talk about it before then. Apoplexy more usually means a stoke but it sometimes refers to any fit, faint or attack. MeltBanana 14:43, 11 September 2006 (UTC)

Perhaps it has to do with nobody dying of cancer until recent years. — [Mac Davis] (talk) (Desk|Help me improve)

I doubt it. i would say the success of identifying people with weak hearts, medication and open heart surgury are more likely to be contributing to the increase in cancer. I have no data to back up this thought though. David D. (Talk) 20:50, 11 September 2006 (UTC)

By that, I was trying to imply that it is the diagnosis that began in 1923, not that heart attacks didn't happen. ;) — [Mac Davis] (talk) (Desk|Help me improve)

This is becoming more of a linguistic question than a science question; maybe the scholars over at the Language Reference Desk can help. --Ginkgo100 ^{talk · e@} 20:34, 11 September 2006 (UTC)

Not semantics, this is a pair of definite history of medicine questions. How was this type of death conceptualized and understood a century ago? How much has the rate of death from this cause (regardless of what it was called) changed between the 19th and 20th centuries. The first answer I gave was off the top of my head, but I have a few late 19th and early 20th century medical texts at home and I will see if I can give a slightly more precise answer. alteripse 21:01, 11 September 2006 (UTC)

The question is: Has there been an increase in deaths due to myocardial infarction since 1920 (or whenever)?--Light current 21:08, 11 September 2006 (UTC)

Usually these sorts of questions are easier to deal with if you pick more controversial "illnesses"—i.e. ADHD. Questions like the "heart attack" one are meant to destabilize even things which seem more concrete as well. The ADHD page unconsciously gives a good example of the sort of methodology that makes a historian cringe when it identifies ADHD in Ancient Greece — once you've decided on an arbitrary diagnoses, you can go back in time and read any disease into past writings, even though the conceptual/dianostic category did not exist at the time. --Fastfission 22:23, 11 September 2006 (UTC)

satellites

This is not homework.

Suppose there is a satellite in an orbit of 10r ( r is the radius of the earth) which falls back to earth due to a malfunction. What will be the speed with which it will impact the earth's surface ???????

Its terminal velocity--Light current 12:25, 11 September 2006 (UTC)

Thats not necesarily true. It could reach much higher speeds in space, and then not accelerate back down to its terminal velocity in the atmosphere. If it did hit at its terminal velocity, it would be a bit of a coincidence. Philc _T^E_C^I 13:58, 11 September 2006 (UTC)

I disagree. With an artificial satellite, the size is small enough and the Earth's atmosphere is thick enough that it would be sure to decelerate back down to it's terminal velocity, unless it burns up in the atmosphere first. StuRat 14:19, 11 September 2006 (UTC)

The smaller an object is the less it will be slowed down by drag. Most physicists would use the word accelerate in this situation to mean slow down - (the magnitude of) acceleration can be positive or negative. - Not Philc.
P.S. its terminal velocity.

Thank you anonymous person. StuRat, Decellerate is a non scientific word coined by the US scientific community to remove some ambiguity, but has since lead to common missuse of the word acelerate, it actually means a change in velocity, which means a change in direction and/or a change in speed. The shuttle is a view of the sort of shape you need to control your decent, incredibly wide in proportion to height and weight, sattelites and meteorites, etc, are not of good proportion for slowing down, and if they are large enough to impact before they burn up, would almost always impact at a much higher speed than terminal velocity. Philc _T^E_C^I 15:26, 11 September 2006 (UTC)

"Decelerate" seems like a perfectly good word to me...or shall we also have the temperature "heat back down" to freezing, and the budget "increase back down" to zero ? If you want to use the phrase "negative acceleration", that's fine too, although a bit formal for common usage, for my taste. StuRat 16:15, 11 September 2006 (UTC)

Thats my point exactly it is incorrect to assume acceleration is an increase it is not it is a change, if their is a change in temperature it does not imply a rise, and if there is acceleration it does not imply a rise in speed or even any change in speed, but a change in velocity, wether it be a increase or decrease in speed or a change in direction. Maybe you should consuclt the article beofre speaking again. Philc _T^E_C^I 16:34, 11 September 2006 (UTC)

Just as a "change in temperature" does not imply a temp increase, a "change in velocity" does not imply an increase. However, if something is heated, that means an increase in temp, and when it is cooled, that means a decrease in temp, just as something which is accelerated means an increase in velocity and if something is decelerated, that means a decrease in velocity. Now, you could refer to zero acceleration or zero deceleration to mean the object is not accelerating at all, and you could even refer to negative acceleration, or even negative deceleration, if you must. But to describe an object as "accelerating" when it is slowing down is horrid, and bound to confuse everyone. StuRat 12:28, 12 September 2006 (UTC)

I think one problem with the term "deceleration" in physics is that in one intertial reference frame, an object is slowing down - whilst in another intertial frame, the same object is actually increasing in speed. Both reference frames are equally valid viewpoints in which the laws of physics are identical - yet one viewer is seeing the object slow down - the other speed up. The force applied in both cases is identical (it's just the same object after all) Acceleration need not refer to a change in speed as well - a planet orbiting the Sun in a circular orbit at constant speed is continuously accelerating (towards the Sun). In useage within the general public - viewing from different reference frames are not usually important as we usually have the Earth as our reference frame - but imagine flying in a plane above heavy cloud - you don't have any perception of movement other than the rumble of the engines and occasional turbulence. Another one about reference frames is in, say a car crash. Ask someone about what happens, and they'll say that loose things in the car were "flung" forwards i.e. accelerating. Measure what's actually happening from outside the car - and they're slowing down. So my point is that acceleration is just the rate of change of velocity - and it has a direction (which you could regard as being in the + or - direction for linear changes in speed). But it's odd to talk about an object simultenously decelerating and accelerating as a reaction to the same force - when they're just being viewed by 2 different observers.Richard B 21:19, 12 September 2006 (UTC)

Ok, if dealing with an acceleration in a constantly changing direction, I take your point. However, acceleration may also refer to a scalar, where the direction doesn't change. In such a case the term "deceleration" for negative acceleration is perfectly clear. StuRat 22:37, 12 September 2006 (UTC)

That's not quite correct. Acceleration does not vary between reference frames - only uniform motion does. In your car crash example, the loose objects would not accelerate (ignoring gravity and air resisitance). The passengers would decelerate (disambiguation) - they would feel the force of the seatbelts slowing them down. From their reference point they will decelerate, the objects will continue in uniform motion. The same will apply to the observers standing outside the car - they will see the passengers decelerate and the loose objects continue.
Your arguements about the relative motions are perfectly acceptable for special relativity, but when dealing with changes in velocity one must use general relativity. The fundamental principle of relativity does not apply to accelerating frames.

I have no idea why you're so bent out of shape over the use of the term decelerate. I have a B.Sc. in physics and don't recall ever being told it was a naughty word. In any case, you're getting off the topic. It boils down to whether there's enough time for the object to decelerate, negatively accelerate or just plain slow down to terminal velocity before it burns up or hits the ground. Drag and barometric formula seem to have some pertinent equations, if somebody has the inclination to work on it (hint, hint). Clarityfiend 19:51, 11 September 2006 (UTC)

Decelerate is a scientifically incorrect term coined and regularly used by the american scientific community. It, like many other words, despite being officially useless, is commonly used, amongst those in that community. Its not a taboo word, it just inst a proper word, its fine to use it because everyone knows what it means, but my original point was, that you can accelerate so that your speed drops. Which is perfectly true, and I'm sure if you do have a BSc that you will know this. Philc _T^E_C^I 20:26, 11 September 2006 (UTC)

Sorry, but that's completely wrong. Accelerate does mean to increase speed, and always has. See the word origin here: [3]. StuRat 06:35, 12 September 2006 (UTC)

Speaking as a physicist, (in scientific use) accelerate does not always mean to increase speed. It means change in velocity - that's increase in speed or decrease in speed or change in direction of motion (or any combination). While to say decelerate is not incorrect, to assume accelerate means speed up is wrong (as is to correct peoples usage of the word).

Ur such an ass have you not tagged onto the fact were talking about physics terminology, not english words, and in physics, accelerate = changin velocity. FINAL!,(you cant have a rise in velocity, as you can change velocity while travelling at a constant speed, so is this a rise or a fall?). maybe this site would be of more help, it is an idiots guide to physics. [4] i linked to the section acceleration. For gods sake people. Get over yourselves, decelerate is used in common english, in which it is a word, but in science, it is basically scientific slang. Mate, get over yourself, its ok to be wrong. Philc _T^E_C^I 17:49, 12 September 2006 (UTC)

Philc, you are resorting to personal attacks and name-calling, which are completely inappropriate in Wikipedia, and not permitted. Please behave in a civil manner. StuRat 22:18, 12 September 2006 (UTC)

I know the rules, I just think you deserved it. Philc _T^E_C^I 18:27, 13 September 2006 (UTC)

Interesting. The entire American scientific community is using an incorrect term? Sez who? (And yes, I know quite well that acceleration is a vector quantity yadda yadda yadda.) Clarityfiend 22:11, 11 September 2006 (UTC)

The smaller an object is the less it will be slowed down by drag ... umm ... surely the opposite is true ? For an object travelling much faster than terminal velocity, magnitude of acceleration is approximately proportional to drag divided by mass (assuming drag >> weight); drag is proportional to cross-sectional area; mass is proportional to volume; so magnitude of acceleration is proportional to cross-sectional area divided by volume, and this ratio goes up as size of object decreases (assuming we keep shape and density fixed). Gandalf61 15:58, 11 September 2006 (UTC)

Agreed, I picture small grains of "sand" landing at thousands of miles per hour, and killing anyone they hit, if that was actually the case. Meanwhile, the meteor that killed the dinos would have just settled down like a feather. :-) StuRat 16:06, 11 September 2006 (UTC)

Hmm ou did take it a bit out of context, it can be assumed that any unmentioned variables were held constant, i.e. weight. Philc _T^E_C^I 16:29, 11 September 2006 (UTC)

Assuming that objects of different volumes have a constant mass is not reasonable. You should assume a constant density, instead. StuRat 06:18, 12 September 2006 (UTC)

Deceleration

Google gives 1.2M hits for decelerate. What does that prove?--Light current 21:10, 11 September 2006 (UTC)

Google has 1.2 million hits for blof, what does this prove? Philc _T^E_C^I 17:53, 12 September 2006 (UTC)

THis thread seems to have veered off topic. THe initial answer I gave was more than sufficient. I suggest a new hdg if you all want to discuss the correctness of the term 'deceleration'. --Light current 21:17, 11 September 2006 (UTC)

Depends. How does the malfunction alter its intial velocity. Does the malfunction cause it to leap into an elliptic orbit with astoundingly good impact parameters to allow a simple atmospheric reentry. Or does the malfuction cause the satellite to explode into <1 cm³ debric that rains down over an entire hemisphere? Does the malfunction cause the satellite to suddenly accelerate towards the planet at nearly the speed of light?

If we posit that the malfunction causes no initial acceleration of the satellite, then the dynamics are one of orbital decay which strongly depends on solar activity and sunspots. Especially at an altitude ot 64 Mm (earth radius times 10). At such an altitude, the density is very low (q.v. Image:Atmosphere model.png), we may read off < 1 microgram per cubic meter (achieved at 0.15 Mm) and (wildly) extrapolate (-9 orders of magnitute per 0.15 Mm) ~10^-3800 gram per cubic meter (with a huge irrelevant error, because...). This is lower bounded by the solar atmosphere. The solar wind is ~1 Tg/s of material moving at 450 km/s. At the orbital radius of the earth (150 Gm), the density of the material is ~5 proton masses per cubic centimeter. However, the satellite's original orbit is inside the Earth's magnetosphere, so the density is assumed to be a bit lower, by cyclic. Kepler's third law tells us that the satellite at 10r will orbit once every (384 Mm / 64 Mm)^-3/2 * 27 days ~= 1.8 days (Q.v. the Moon's orbital radius and period). The rate of decay will be negligible (due to the very low atmospheric density).

Satellite Orbital Decay suggests that the densities may be higher than expected from the above considerations (due to temperature fluctuations and mass fraction considerations not present in the above). This paper describes in some detail the effect of solar activity on the drag force, even for low-orbit sattelites like the Hubble Space Telescope and therefore should be a good starting point on the problem you've posed. -- Fuzzyeric 22:31, 11 September 2006 (UTC)

Hmmm...now that I think about it, it seems to me that there's a simpler way of looking at it. Just imagine a rocket leaving the Earth. It has to be going just over 11 km/s (about 36,000 km/hr) to get away. Reverse it and a satellite (ignoring for the moment whatever orbital velocity it has) would return at about that speed. Now, I remember from an earlier question posed here, that astronauts report that atmospheric drag is noticeable at about 120 km up. So, it seems unlikely that an object travelling at that speed would be able to decelerate to terminal velocity in that short a distance and time (it would probably come in at an angle, but still). My conclusion is that one of three things would happen: (1) it could come in at too shallow an angle and bounce off the atmosphere (as discussed in the movies Apollo 13 and Space Cowboys), (2) burn up or (3} hit at considerably in excess of terminal velocity. Clarityfiend 17:15, 12 September 2006 (UTC)

I don't think there's any easy way to calculate the answer. You'd need to know whether the malfunction caused its thrusters to activate. If it's a homework question, then it's probably after the difference in the potentials between r = 10R, and r = R, starting at v = 0, neglecting air resistance. Richard B 21:24, 12 September 2006 (UTC)

Sorry to bring up a topic that seems to have run its course, but I can't help but find the whole "accelerate/decelerate" debate quite amusing. I may not have a BSc, but I do have an LLB/BCL, so I'm familiar with the way members of certain disciplines tend to "borrow" words from the English language, mangle and distort their original English language definition, and then claim that they're using the word correctly, and you, a simple English language speaker are wrong in using its original, true definition. Let's be clear, science, like law, uses the English language, NOT the other way around. An example I always bring up is that according to "legalese", the English word "person" has been extended to include non-human entities such as corporations. According to "legalese", a corporation is a person! We actually had a rather funny discussion about the whole thing in law school. The professor stated, with a straight face, "If the law defines you as a carrot, you're a carrot!" The same thing seems to be going on here. I would never be so arrogant as to insist that a corporation, in reality, is an actual person. Sure, it may be the way we've twisted and contorted the English language to suit our needs, and that's ok. But all due deference must be given to the actual, real life, language from which we've borrowed, mangled and distorted certain words to suit our needs. I will never be a carrot, no matter what the law says. Perhaps the law may decide to consider me a carrot, but the English language does not. Likewise, in the English language, a person is a human being and a human being only. The "law" may consider a corporation to be a person, but the English language does not. Similarly then, to accelerate is to increase velocity and to increase it only. Sure, the scientific community may decide to define "acceleration" as whatever the hell it wants, and that's ok, if it contributes to a better understanding of science. But again, science uses English, not the other way around. Due deference must be given to the original source of the word. If you choose to mangle it, that's ok, but never be so arrogant as to forget its original source. To me, the only acceptable approach would be to say: "true, to accelerate indeed does mean to increase in velocity and to increase only, however, for scientific purposes the scientific community has chosen to define it differently". Loomis 22:06, 12 September 2006 (UTC)

I used the word accelerate in its physics meaning, in physics context, and was told I was wrong. I was not, and that basically the jist of it, languages have words, science has words, but accelerate in a context of physics is defined by physicists, in other contexts you can claim it means whatever you want, but the simple fact is, I was told I was wrong, when I was right. Philc _T^E_C^I 22:19, 12 September 2006 (UTC)

I must take issue with you here, Phil. You've proven to me in the past that you're a good guy, so I'm not exactly enjoying contradicting you. The fact is, though, that you didn't merely state that you were using a scientific definition of the word that differs from its true English language meaning. Rather, you did the opposite. You accused the "US scientific community" of "coining" a "non-scientific word", and further, you argued that it has "since lead to common misuse of the word accelerate". Phil. C'mon. That's ridiculous. You make it seem like English speakers should thank scientists for inventing the word "accelerate", and then humbly submit to their understanding of the word. The word "accelerate" is an English word. So is the word "decelerate". It's the scientists who are deliberately misusing the word, not the other way around. But as I said, there's nothing wrong with that, as long as the original source of the word is acknowledged. Loomis 22:44, 12 September 2006 (UTC)

Ok, I got a bit het up after the way in which it was implied I was wrong showed little or no understanding or acceptance of what I had said, and I will admit to knowing next to nothing about the origin of the word decelerate, I was told it was coined by the US scientific community, I cannot verify this though. But what I do know about is the physical meaning and in a physical context, I dont see how I said anything wrong. But anyway, I'm pretty sure decelerate is a pretty recently made up word, and fair enough, Im sorry, but accelerate just does not in a physics context imply a rise in speed. So yeh sorry for anythin else. Philc _T^E_C^I 18:08, 13 September 2006 (UTC)

It's not exactly recent, but rather over 100 years old: [5]. StuRat 13:11, 14 September 2006 (UTC)

Fair enough Phil, you've proven once again you're a good guy. No worries. :) Loomis 08:40, 14 September 2006 (UTC)

As for myself, I won't call him a good guy until he apologizes for the abusive language. StuRat 13:11, 14 September 2006 (UTC)

I didn't mean to speak on your behalf, Stu. You have every right to demand an apology. What happened, though, is that I saw a silly little argument blow up into a shouting match based on practically nothing. With all the terrorism, war, disease, bigotry and all the other nasty things going on in this world, I just thought it was a bit silly to get into such a heated, personal argument over such a silly topic as the definition of a word. It's true, Phil said some nasty things and should apologize, but on the other hand, my experience with him is that like me, he can put his foot in his mouth or over-react in some situations, but on the other hand, he's proven to me that deep down he's a good person. I say this because I was particularly touched one time when he actually took the trouble to write a clarification/apology on my userpage in another situation where he put his foot in his mouth. He was under no obligation to do so, but was decent enough to take the trouble to do it anyway. What I'm saying, as "referee" is that you're both good guys, and it would be a shame for either of you to hold any grudges. As such, I'd humbly "suggest" that Phil apologize for the harsh words, but it's really between you two, and I already feel like I'm sticking my nose too far into other people's business, so I'll leave it at that. Loomis 14:34, 14 September 2006 (UTC)

Fair enough, sorry sturat, name calling is out of order, and pathetic. I just get to aggrevated about these things. Sorry for calling you thos things, but maybe weve both been dicks anyway. Philc _T^E_C^I 20:08, 14 September 2006 (UTC)

Well, you're almost there, now if you can just manage to apologize without actually calling me a dick during the apology, I'd be happy. StuRat 07:19, 15 September 2006 (UTC)

(After edit conflict)Just another little thought so perhaps Phil can understand things better. I'm no scientist, but it would seem that the scientific community depends heavily on the use of formulas (or formulae for all you pedantic linguists!) to study and to expand their knowledge. Formulas, in turn, require very well defined variables. Again, I'm no scientist, but at the risk of sounding like a clueless moron concerning physics, I would imagine that scientists would have come up with such formulas as: Where V = velocity, T = time, A = rate of acceleration and Δ = change: ΔV = T x A. (I'm just guessing here! The whole thing is likely nonsense! Please be gentle! I'm just a simple lawyer, not a physicist!) In any case, whether the formula makes sense or not isn't really all that relevant. The relevant point is that to have a coherent formula, the variables must be defined as simply as possible. If scientists used the original English language meaning of the word "acceleration" they'd be forced to have two rather redundant formulas when only one is necessary, and to complicate matters worse, they'd have to add an additional variable. So instead of the simple:

• Where V = velocity, T = time, A = rate of acceleration and Δ = change: ΔV = T x A.

They'd be forced to say:

• Where V = velocity, T = time, A = rate of acceleration, D = rate of deceleration, in cases where velocity is increasing: ΔV = T x A, however in cases where velocity is decreasing: ΔV = T x D.

Makes the whole thing so much more complicated than it has to be, doesn't it? Instead, it was just taken as a given, for scientific purposes, that the variable "A" can have a negative value. Why not? Makes the whole thing so much simpler. I've got no problem with it. The mistake, though, was when scientists began to believe that their redefinition was actually more authoritative than the original English language definition that they had originally borrowed the term from.

Anyway, it's a big mess, but definitely not nearly important enough to warrant descending into a vicious shouting match with personal attacks and all. Loomis 20:33, 14 September 2006 (UTC)

It depends really, which is more important science or language could certainly pull some heated exchanges out of both corners. Philc _T^E_C^I 21:15, 14 September 2006 (UTC)

Ok I tried Phil, but you simply don't seem to understand my point. You simply don't seem to get what I'm saying. SCIENCE borrows words from ENGLISH. ENGLISH doesn't borrow words from SCIENCE. The English language is the origin of the word ACCELERATE. In the English language, ACCELERATE is defined by an INCREASE in velocity, and by an INCREASE ONLY. Scientists, for GOOD REASON, have chosen to DISTORT the TRUE meaning of the term ACCELERATE. That's how scientists have invented the counterintuitive notion of NEGATIVE ACCELERATION. It's all ok, but if you don't recognize that it's the SCIENTIST'S who are distorting the word, you're not giving due respect to its ORIGINAL English language meaning. Loomis 03:37, 15 September 2006 (UTC)

I don't see a conflict. Positive acceleration means to increase speed or velocity. Negative acceleration means to decrease speed or velocity, and a less formal synonym for this is deceleration. Zero acceleration/deceleration means to maintain constant speed or velocity. There is no need to use a "d" in the formula, as an "a" with a negative value has the same meaning. If you don't know if an object is increasing, decreasing, or maintaining speed or velocity, then just call it an unknown acceleration. Where I disagreed with Philc is that, if an object is known to be slowing down, I would ALWAYS say it is undergoing negative acceleration (or deceleration), I would NEVER just say it is accelerating, as that is bound to cause confusion to those who are using the ENGLISH meaning of the word (which will be many of the readers here). The only time such usage would be permissible, in my opinion, is if you are certain your audience is only scientists, which is not the case here. StuRat 07:33, 15 September 2006 (UTC)

OK, we hear you, mate. What was that about shouting matches .... ? JackofOz 03:49, 15 September 2006 (UTC)

Ummmmm... Guys? Many, many terms have a common English meaning and a more precise scientific meaning. To speak about one being more "true" or "correct" is kind of silly. Which one you use depends on how well your audience will understand what you're saying and how precise you need to be. Case closed. -- SCZenz 07:40, 15 September 2006 (UTC)

Loomis I do understand your point, but words dont really have a true meaning in the way you seem to mean, all words meanings change, so do the words themselves, new words come and old words go, I wouldnt agree that any word has a true meaning, just a meaning that is commonly agreed on. There was no need to get shouty. Philc _T^E_C^I 13:44, 16 September 2006 (UTC)

OK, OK. The shouting thing is definitely contagious! First I try to calm things down, then I myself get in on the act. How hypocritical can I be? How about we just forget about this one and move on, ok? :--) Loomis 07:06, 17 September 2006 (UTC)

Yeh to be honest, I dont think any of us really cares about this that much to let it get between us so, lets just forget about it. Philc _T^E_C^I 22:17, 17 September 2006 (UTC)

Elementary physics, based upon energy considerations, suggests that the maximum impact velocity (of a an object arriving from anywhere) would be about 7miles/s (11km/s). — Preceding unsigned comment added by 86.159.88.49 (talk) 04:02, 16 February 2016‎ (UTC)

Tfl Oyster system

Could you please tell me who supplied the equipment to Tfl for their Oyster cards system?

Sure, but next time why don't you try searching using the search box on the left - it's quicker! See Oyster card for the gory details. --Robert Merkel 12:59, 11 September 2006 (UTC)

.flv

Hi is there a free software taht transforms .flv files to otehr formats like mpeg4 or avi or 3gp etc somethign liek that? Thanks!

Yes, there is lots of software that works with FLV. Try searching with the search box on the left of your screen next time, it's quicker! --Robert Merkel 13:01, 11 September 2006 (UTC)

Solution of vessels

I already asked this question in great detail in August but I got no responses and then the question just got deleted off the wikipedia. So I'll try again but I am reluctant to write as copiously a≈s before. Also I was told there was nothing ever on about "solution of vessels" so maybe I'm not using the system correctly.

Basically, I was requesting information about the relative solubility of vessels (eg.wood, plastic, glass etc) containing (to make it simple) water (tho that is obviously not a constant as varies according to acidity, temperature etc.)

My query arose out of comments of a fastidious niece that she would not drink anything out of plastic bottles, because the "water got contaminated", but glass was OK. A retired scientist said that all this is a waste of time as the rates of solution are so miniscule as to be insignificant, "like glass flowing down a window pane!".

Anyway, I would just like to know. Does anyone have comparable statistics? 87.74.46.191 13:35, 11 September 2006 (UTC)Francis D. O'Reilly

Although we never came up with any stats, this issue was discussed extensively, and was archived after 7 days (not deleted), here:[6]. StuRat 13:51, 11 September 2006 (UTC)

Last I checked glass does not dissolve into water. — [Mac Davis] (talk) (Desk|Help me improve)

Agreed; but the rest do, with plastic being the worst, then metal, then wood. StuRat 16:00, 11

September 2006 (UTC)

Glass also does not flow downward in window panes. That is a myth resulting from blobby old blown glas being mounted in windows. There are ancient Roman bottles which have not shown any tendency to melt into a puddle like Silly Putty, but people assume 300 year old glass in a church window is melting.Edison 19:10, 11 September 2006 (UTC)

One way to come at this problem is to investiage hoaxes related to water containers leaching materials into their contents. This Snopes article describes a hoax claiming that the reuse of plastic water bottles can leach plasticizers into their contents. This is false. This article debunks the claim that microwaving in plastic containers will release carcinogens into food. -- 205.162.232.254 21:27, 11 September 2006 (UTC)

Those Snopes articles do say "FALSE" at the top, but that really isn't what they say in the body. On microwaving, for example, they said something closer to "when using a microwave safe rated plastic according to the manufacturer instructions, there is currently no evidence that dangerous levels of toxic chemicals are released into the food". This leaves open the possibilities that there are toxic chemicals, in dangerous levels, but this has not yet been established, or that using improper plastics or microwaving improperly will generate toxic levels of chemicals in the food.

Moreover, they seem to approach all questions with the attitude that "let's assume everything is healthy, unless we have evidence to the contrary", while many people, myself included, would say "let's assume everything (especially relatively new things) is dangerous unless we have specific evidence to the contrary". Obviously eating or drinking from plastic isn't immediately 100% fatal to everyone who does so, but if it caused a 10% increase in cancer, after 20 years, this wouldn't be easy to isolate as having been caused by plastic containers. So, I prefer to play it safe. If I can taste the plastic in my food or drinks, I don't eat it, for both safety reasons and because it's quite unpleasant. StuRat 06:11, 12 September 2006 (UTC)

Which leaves the question how much harm it could do. Some people don't rinse after washing the dishes. How much washing up liquid do they consume in a lifetime and how much harm can that do? Of course, all this is probably negligible compared to the exhaust fumes a city dweller inhales. And there are many other things that will have a negative effect (do you ever drink alcohol?) and the negativest effect might verry well be worrying too much about it all. I'm a happy smoker, for example. But I also take the stairs in stead of the lift, so that should compensate. :) DirkvdM 09:26, 12 September 2006 (UTC)

Yes, that will assure that you will be nice and thin while you're hacking up bloody pieces of lung. :-) StuRat 12:18, 12 September 2006 (UTC)

BTW, it's "instead", not "in stead". StuRat 12:18, 12 September 2006 (UTC)

StuRat, I think the Snopes article is assuming that without evidence of harm there is little good reason to assume it. But in any case the difference you are talking about is the difference between something like probabilistic risk assessment (popular in the US) and the precautionary principle (popular in Europe) approaches to hazards. --Fastfission 12:09, 12 September 2006 (UTC)

As a neurotic, I worry about far too many things. Some would even call me a "negativest". :--) Loomis 21:18, 12 September 2006 (UTC)

Need full citation for Gibbard and Kolfschoten chapter (glaciation timeline ref)

Hi,

I wondered if you could send me the full citation for the reference you use for the glaciation timeline. I was able to download the book chapter, but I have no idea where the chapter came from. Can you send me the title of the book, the year published, publisher, and location of publisher?

Thanks,

Emily Lemmon

Here is a the web site: [7]

It contains this relevant text:

Now published - A Geologic Time Scale 2004 Felix Gradstein, Jim Ogg & Alan Smith. **The Quaternary chapter [pdf] by P.Gibbard & Th. van Kolfschoten, which includes a CORRECTED version of the correlation chart, including the term QUATERNARY. pdf

StuRat 14:13, 11 September 2006 (UTC)

Portal Paradoxes

Any eds who know anything about this topic are welcome to look at this recently created article. As a definite non-scientist, I can't begin to tell if it's nonsense or original research (or not). --Dweller 14:31, 11 September 2006 (UTC)

Speaking as a scientist, a definate non-scientist you shouldn't have a problem with this definately non-scientific article.
For a more scientific approach to something similar the wormholes article should answer the questions posed in title article or else demonstrate that, even in principle, the situations presented are flawed.

Portal Paradoxes, in my opinion, should definitely be deleted. It is both an essay and original research. I've nominated it for deletion. --Allen 15:08, 11 September 2006 (UTC)

I agree. Rather a non-encyclopedic tone as well. — [Mac Davis] (talk) (Desk|Help me improve)

It appears to be complete pseudo science made up by someone who doesnt actually know anything about the subject. Philc _T^E_C^I 15:20, 11 September 2006 (UTC)

It appears to be referring to some type of portal from a video game, not a science topic at all. Unfortunately, they don't identify the game. StuRat 15:52, 11 September 2006 (UTC)

erm... they did. I came across the article when patrolling new articles. I deleted the advert. Twice. But left the article, feeling out of my depth on deciding if it was or wasn't guff. Anyway, thanks to those in the know for confirming it is, indeed, a load of tosh. --Dweller 16:26, 11 September 2006 (UTC)

Well, as I said, it is scientifically worthless, but, if it's accurate info for a particular video game, it could still be "encyclopedic", provided it identifies the game. After all, we have many articles on other games, like countless articles on Pokemon characters. StuRat 16:53, 11 September 2006 (UTC)

It doesn't even define what a "portal" is. Definitely not physics. Clarityfiend 18:59, 11 September 2006 (UTC)

In case you're still scratching your head what the article is about, it's about Portal (computer game). It's still perfectly deletable, though -- Ferkelparade π 21:18, 11 September 2006 (UTC)

Well somebody better merge some of it in fast than! I can't do it now because I should be doing work that is not Wikipediaing. — [Mac Davis] (talk) (Desk|Help me improve)

Isnt all this stuff covered in Wormhole? Oh yeah, just seen ref to that ^. THis page is pure fantasy nad of course should be deleted. But why are we discussing deletion here may I ask?--Light current 00:47, 12 September 2006 (UTC)

Maybe he should get Portal.... Crazy Fox (T|C|E) 23:49, 13 September 2006 (UTC)

700ml liquor + sertraline

A friend of mine is on sertraline for bipolar disorder, and has an intimate relationship with rum. I think the sertraline is taken once a day and then he drinks a 700ml bottle of rum (37.5% alcohol) on a single day. Every week. How big of a risk is there that he will become an alcoholic and/or bust his liver due to combined pill/liquor use? Jack Daw 15:47, 11 September 2006 (UTC)

I don't know about any drug interaction, but that much alcohol alone can certainly cause health problems. StuRat 15:54, 11 September 2006 (UTC)

Drinking spirits is the worst thing for the liver, I saw a documentary once and the doctor doing the liver transplant said that binge drinking spirits once a week was enough to do the damage and worse than say the equivalent alcohol dosage in beer/larger. Dont know anything about the drug.

I'll echo what's been said above. Drinking a fifth of liquor every day is going to hurt your liver whether or not it's in combination with other drugs. TenOfAllTrades(talk) 17:41, 11 September 2006 (UTC)

As for the alcoholism thing - someone who drinks a bottle of rum a day probably is an alcoholic already (though, of course, there's more to alcoholism than just drinking). Like any drug, sertraline takes its toll. Of course, if you're self-medicating that heavily, the antidepressant probably isn't working for you. Guettarda 17:49, 11 September 2006 (UTC)

He's been doing this stuff for maybe two years now, then stopped for two months (of course that was only what he told me), but telling from the alcoholism article I don't think there's any alcoholism yet. Jack Daw 20:30, 11 September 2006 (UTC)

Come off it! Anyone whose drinking a bottle of sprits a day is obviously an alcoholic! You should force your friend to see a doctor (or if you cannot afford that then at least AA for example) and get him treated to stop the drinking. With that amount of drinking, and the other drug, then its obvious that if he dosnt stop drinking he's going to be dead soon. Harsh words, but they need to be said to save your friend. 81.104.12.61 22:14, 12 September 2006 (UTC)

From Sertraline#Precautions

• Liver impairment can affect the elimination of this drug from the body. If someone with liver impairment is treated with sertraline, lower or less frequent dosage should be used.
• Patients should limit their alcohol intake while on sertraline (or any antidepressant). Because the liver is doubly taxed with processing both substances (in addition to any other drugs the patient may be taking), alcohol remains in the bloodstream longer, so the effects of alcohol may be more strongly and quickly felt by people taking sertraline or other antidepressants.

which meshes pretty well with what I (vaguely) remembered. Guettarda 17:58, 11 September 2006 (UTC)

"A 'Friend of mine' has a problem?"Edison 19:12, 11 September 2006 (UTC)

Yes? Unless you have some kind of evidence that it's me rather than said friend who has these problems, please refrain from that kind of comments. It would be pretty useless to denote my friend by any other "name" than 'my friend'. Jack Daw 20:30, 11 September 2006 (UTC)

I thought mixing alcohol and mood altering drugs could have have very undesirable effects.--Light current 06:10, 12 September 2006 (UTC)

Your bottle is likely 750 ml rather than 700 ml. The good news is that there is no longer much danger of becoming an alcoholic. Gene Nygaard 06:40, 18 September 2006 (UTC)

amyloid beta

Do mice naturally make amyloid beta (specifically in the brain)?

Yes, mice make amyloid beta. It is not identical to human amyloid beta, but close enough that researchers use mice to study Alzheimer's disease. --Ed (Edgar181) 19:50, 11 September 2006 (UTC)

Highly enriched Uranium

I searched wiki but could not find the relevant information. My specific questions are — who can manufacture (specifically, can Pakistan do it on its own?) 99.9% enriched U-235 and what are its implications. What will be the critical mass for Atomic bomb with this purity. {enrichment for little boy was just about 80%.}

Background for this question is that two Muslim terrorists were arrested on suspicion in Bareilly, India about a few years ago. Police found a white powder with them. They initially thought it to be a Drug. But, when they sent it to the Lab, they were shocked at the results, as it was 99.9%pure enriched U-235. Nuclear Submarines just use 90% EU. Remeber that This news was highly censored in India, so you wont find much about it in the archives. But it was once the front page news in The Times of India.nids(♂) 21:30, 11 September 2006 (UTC)

Well the obvious answer is that any one with the right plant and raw materials can do it. As you need enriched uranium for nuclear power stations, I would think most countries who have these, also have the enrichment facilites. THeres one just down the road from me! Iwould think tho that the stuff must have been made in a proper plant rather than in someone's shed. I dont know what compound of uranium is a white powder, but Im sure someone will tell us--Light current 21:37, 11 September 2006 (UTC)

You cant enrich to 99.9% in a shed. The One used in Nuclear power plants is enriched just about from 3% to 40%. Never more. 85% or more enriched EU is always called Weapons Grade. Most submarines just use about 50%. 90%(in special cases).nids(♂) 21:42, 11 September 2006 (UTC)

Im not aware of any specific problems in making more highly enriched uranium above the 50% you quote for sub use. Surely, you just leave it in the 'enricher' for longer?--Light current 21:52, 11 September 2006 (UTC)

it is not as simple as you think. Perhaps you would like to go through Enriched uranium. remeber that the critical mass reduces with enrichment and it is dangerous to enrich it beyond certain levels.nids(♂) 22:00, 11 September 2006 (UTC)

From that page: The critical mass for 85 % of highly enriched uranium is about 50 kilograms. Sounds like quite a lot to me!--Light current 22:05, 11 September 2006 (UTC)

Its the amount with 85% enrichment. Remember that Uranium is extremely dense metal. So the volume of 50Kg. is just about a litre and a half, (i.e. with 85%). Efficiency of critical reaction increases with enrichment.nids(♂) 22:16, 11 September 2006 (UTC)

Yeah thats the metal. Enrichment is done in gaseous form, is it not?--Light current 23:04, 11 September 2006 (UTC)

(edit conflict due to fire drill) the story sounds like bollocks to me, like most stories that invoke a grand conspiracy. For starters, uranium is a silvery metal which gains a black oxide coating, not a white powder, and compounds of uranium, such as uranyl nitrate, which aren't used in fission, are yellow. and the methods for isotopic refinement of uranium are complex, and require difficult to obtain equipment, and highly toxic materials. not beyond a state, but look at how much trouble iran is having. Xcomradex 21:55, 11 September 2006 (UTC)

I am sorry i cant quote much about the news as i told you that it was immediately censored. Nothing came again on TV or any news channel about it and they never published a disclaimer either. I doubt it to be completely wrong as it was the front page headline (atleast for a day).nids(♂) 22:02, 11 September 2006 (UTC)

I request you to leave out the background for this question as i cant defend it. Please answer the specific questions that i posted. Can pakistan do it on its own????nids(♂) 22:04, 11 September 2006 (UTC)

How are we supposed to know for certain? We can only make educated guesses -- as could you.--Light current 22:07, 11 September 2006 (UTC)

99.99% would be remarkably high enrichment; there wouldn't be many countries that could get it that high, if any can at all (I doubt it). After some point, you are really wasting resources to get that extra .01% enrichment—there are better, and easier ways to improve efficiency if you are resource conscious. Judging from that description it doesn't sound legitimate to me — the powder sounds wrong, and enrichment level sounds wrong.

Back to the original question—many types of reactors require at most 3-4% enriched uranium. Some don't require enriched uranium at all (i.e. a heavy water reactor like a CANDU). Reactors which require very highly enriched uranium are usually quite small — research reactors and submarine reactors, for example. I don't know how many places can enrich to 90%, but any enrichment facilities which can go up to that amount are usually under heavy IAEA safeguards, unless the nation in question is not a signatory of the NPT (like Pakistan and India).

Pakistan has a number of unsafeguarded uranium enrichment facilities, all using gas centrifuge technology, and their P-2 centrifuges are recognized as relatively advanced. The country certainly has the ability to enrich uranium to bomb-grade level—its tested nuclear weapons were uranium-core, if I recall. --Fastfission 22:18, 11 September 2006 (UTC)

I have a background knowledge about this subject and i know that it is illegimitate to waste resources after a certain point. But its benefit (for terrorists) are that the critical volume required could be as low as 80 ml (by my estimates). Pakistan for sure can do it to 90%, but i doubted about the figure i gave you in the beginning. With these outdated P-2 Techniques, i dont think that they can even go beyond 50%.nids(♂) 22:26, 11 September 2006 (UTC)

Yes, Pakistan can and did enrich uranium to bomb-grade. The other countries with known uranium enrichment facilities include the big 5 (USA, UK, France, Russia, China), India, and presumably Israel. Brazil has recently opened a centrifuge enrichment plant for making reactor fuel; however, a plant for making reactor fuel could probably be used to make HEU with some reconfiguration (Brazil's centrifuges are reportedly very advanced, as good as European and American ones). As well, Germany, Japan, and the Netherlands have centrifuge enrichment plants, and could also start turning out HEU if they really wanted to.

For completeness, there are a number of other countries who have developed enrichment technology such that they could make nuclear weapons, but haven't done so or have stopped doing so. To take the best known example, South Africa built an enrichment plant, and half a dozen nuclear weapons, but abandoned the program and dismantled both the enrichment system and the weapons when the apartheid state ended. To take another, Australia built a pilot-scale centrifuge enrichment plant, but did not progress beyond that stage by choice.

But could terrorists do it without the support of a state backer? Pretty unlikely. An enrichment plant is a very considerable industrial operation; the parts have to be made with very, very high precision or the centrifuges will simply disintegrate. Gas diffusion enrichment would require so much electricity that it would be obvious to all and sundry that there was something going on in the building concerned.

Nids' comment of a risk of a criticality accident when trying to reach HEU is interesting. I would have thought myself that it wouldn't pose that much of a problem in the centrifuges or the piping, as they are both very long and skinny. I could see that subsidiary parts of the plant might need to be carefully designed though. --Robert Merkel 23:10, 11 September 2006 (UTC)

I am skeptical of a 99.99% enrichment. 85% would be just fine, 95% is weapons grade isn't it? — [Mac Davis] (talk) (Desk|Help me improve)

Why do you say 85% is just fine? Did you have a particular purpose in mind?--Light current 23:44, 11 September 2006 (UTC)

How many purposes do Pakistani terrorists have for weapons grade uranium? Two? — [Mac Davis] (talk) (Desk|Help me improve)

(FYI, Mac Davis, you appear to have accidentally increased the purity by an order of magnitude - the question has three 9s but you wrote four 9s in several places.) —AySz88\^-^ 04:07, 12 September 2006 (UTC)

But 85% isnt weapons grade is it? So how is it 'just fine' ? Dya wanna make a real A bomb or just a dirty damp squib?--Light current 00:53, 12 September 2006 (UTC)

I think when you are talking about enrichment levels below 93.5% you are essentially asking about the difference between a nuclear weapon and a dirty bomb (assuming you do not have other very high-level technologies—I imagine that there are ways to increase the efficiency of a lesser enriched bomb if you could do things like use very reflective tampers and fusion boosting). --Fastfission 00:31, 12 September 2006 (UTC)

Well, that contradicts what I've read. A gun-type bomb made of 80% HEU would, apparently, work just fine, albeit with half the yield of the same amount of 90% HEU. See this article on the South African nuclear bomb. --Robert Merkel

I was going off of this article by a number of ex-nuclear weapons designers, though with them again one has to wonder what they consider the line to be between a "successful" nuke and an "unsuccessful" one (if you are just trying to make a relatively large explosion and a big mess, even a fizzle can be worthwhile). 80% is not technically weapons grade — I don't know what the predicted yield would be, but my guess it that we're talking about five kilotons or two at most, depending on the assembly mechanism. Very inefficient for such a large device but again it all depends on what you are looking for. It is hard to find values on the low-end of nuclear weapons work (Carson Mark has written a number of articles about low-grade nukes) in part because that's the sort of information they consider to be the most valuable to terrorists today (the irony is the big, complicated nuclear secrets of yesteryear are totally useless to terrorists, while the simple things, like "can you use research reactor plutonium in a nuke?", suddenly become very relevant). --Fastfission 12:02, 12 September 2006 (UTC)

enrichment used for little boy was just 80%. By the way, what will be the critical mass for 99.9% EU in your view.nids(♂) 12:15, 12 September 2006 (UTC)

Do we also accept that Pakistan can enrich U-235 to 99.9%.nids(♂) 12:23, 12 September 2006 (UTC)

So it turns out Mac may have been right all along. How the hell did he know that? --Light current 10:22, 12 September 2006 (UTC)

The Bin Laden terrorists supposedly laughed at José Padilla (alleged terrorist) when he proposed to centrifuge weapons grade uranium by swinging it in a bucket which he would hold while he spun around. Superman might have better luck, because he could turn coal into diamonds by squeezing it in his hand. Edison 17:15, 12 September 2006 (UTC)

You are taking the subject too lightly. Are you forgetting that all the terrorists have Pakistani support. Anything that Pakistan can do, is what that Al-Qaeda will have access to. I dont think it will be hard for a suicide attacker to diffuse a bomb from 99.9% Enriched Uranium. They will just need about 100ml volume of U-235.nids(♂) 20:30, 12 September 2006 (UTC)

All terrorists have the support of the Pakistani government? is that what you are saying?--Light current 22:26, 12 September 2006 (UTC)

Yes. Do you doubt it. Even after the reports that Osama is in Karachi in an ISI hideout.nids(♂) 22:59, 12 September 2006 (UTC)

Nuclear attack wouldnt have been a worrying factor had the terrorists not had any support from a government.nids(♂) 23:04, 12 September 2006 (UTC)

Does Dubya know about this? If so why aint he attacking Pakistan?--Light current 23:07, 12 September 2006 (UTC)

Yes Dubya knows it. The details for the answer why he isnt attacking Pakistan are for the Humanities desk. But i think that Pakistan is now a nuclear power, so this isnt possible.nids(♂) 23:17, 12 September 2006 (UTC)

So you are not actually asking a question here, but are making some sort of political statement as you seem to know all the answers anyway and just want conformation of your beliefs. Is that right?--Light current 23:35, 12 September 2006 (UTC)

Leave these questions. I was interested in knowing the critical mass for the HEU of 99.9%, and whether the pakistan has openly accepted that it has facilities to enrich U to 99.9%.nids(♂) 23:49, 12 September 2006 (UTC)

I was precise with my initial post. I had to reply to some of your posts as i knew, perhaps, more than you.nids(♂) 23:51, 12 September 2006 (UTC)

Found this on Urenco site:

Physical Characteristics of Uranium Hexafluoride As it can see from the phase diagram In figure 10, UF6 is characterised by an unusually high vapour pressure for a solid, e.g., 24 mbar at 0 °C, 107 mbar at 20 °C and approximately 1 bar at 56 °C. At this temperature UF6 is a white crystalline solid. The melting point of UF6 is 64 °C, with a vapour pressure of approximately 1.5 bar. The density of solid UF6 at room temperature is around 5 g/cm3. There is a large change in density to 3.7 g/cm3 when UF6 turns from the solid into the liquid state (diagram 11). The physical data of UF6 are given in the following table:

• Sublimations point at 1013.5 mbar 56.4 °C
• Triple point at 1516.5 mbar 64.02 °C
• Density (solid) at 20.7 °C 5.09 g/cm3
• (liquid) at 64.02 °C 3.668 g/cm3
• (liquid) at 148.9 °C 3.043 g/cm3
• Heat of sublimation at 64.02 °C 48 kJ/mol
• Melting heat at 64.02 °C 19 kJ/mol
• Vaporising heat at 64.02 °C 29 kJ/mol
• Reaction heat with water at 25 °C 211 kJ/mol
• Critical pressure 45.6 bar
• Critical temperature 230.2 °C
• Vapor pressure at 20 °C 106.7 mbar
• Molecular weight 352.07 kg/kmol

My bolding. Does this data fit with your story? --Light current 00:35, 13 September 2006 (UTC)

All that i am interested in knowing is that

1. What will be the critical mass for an atomic bomb with 99.9% enrichment.
2. can pakistan do it on its own.nids(♂) 00:57, 13 September 2006 (UTC)

Critical mass of U235

THis section has been moved to talk:critical mass as it is a discussion--Light current 02:31, 13 September 2006 (UTC)

Instantaneous Speed

Quite simpley, what is it. If one had to define it in the most explicit terms possible, how would one do so?

It the rate of change of position with respect to time.--Light current 22:00, 11 September 2006 (UTC)

Another answer is that it's the speed something is going at a given moment, as opposed to its average speed over time. --Allen 22:06, 11 September 2006 (UTC)

I'd say the best one can do, physically speaking, is to compare the position of an object at two times that are very close together. Its speed is then the distance traveled, divided by the time passed. In order to be truly instantaneous, mathematically one would like to pass to the limit, but in the real world one doesn't have that luxury. Melchoir 22:17, 11 September 2006 (UTC)

Well... "Instantaneous velocity" is defined by taking the limit. Q.v. formal description of velocity. It is the rate of change of the displacement, where the test time during which the displacement is allowed to occur is reduced. This process (in a macroscopic experiment) will asymptotically approach some value as the test time is allowed to go towards zero. Extrapolated to "test time = 0", we get the instantaneous velocity.

This is by analogy to defining the electric field. The electric field is defined according to the force a fictional test charge would experience when placed into the field at the position at which the field intensity is to be known. Similarly, we measure a displacement that would occur during a fictional time period as that period skrinks down to the instant at which the instantaneous velocity is to be known. -- Fuzzyeric 22:48, 11 September 2006 (UTC)

Shamelessly copied from the wiki page:

The instantaneous velocity vector (v) of an object that has position at time (t) is given by x(t) can be computed as the derivative:

$v={\mathrm {d} x \over \mathrm {d} t}=\lim _{\Delta t\to 0}{\Delta x \over \Delta t}$.

202.168.50.40 23:23, 11 September 2006 (UTC)

Perhaps a simple example is in order - suppose your car goes from zero to 100 mph in 10 seconds, and further suppose that the acceleration is constant over that time. Then your average speed over that time is 50 mph, but your instantaneous speed goes from 0 at the beginning to 100 at the end. For another example, which also highlights the difference between the speed and velocity, get your car up to 100 mph and drive it in a circle. Your average velocity over the whole circuit is zero - you wind up right where you started. Your instantaneous velocity is 100 mph in whatever direction you are travelling at a particular moment, and your instantaneous speed is just 100 mph. In fact, your average speed is also 100 mph, since your displacement from the starting position is 0, but your distance travelled isn't. Confusing Manifestation 00:45, 12 September 2006 (UTC)

further gravitational wave questions

I have read here that high frequency gravitational waves could be used for propulsion and moving objects, and that they could be created by quantumm effect http://arxiv.org/pdf/physics/0410022#search=%22high%20frequency%20gravity%20waves%22 Can anyone explain to me firstly how a gravity wave could move something, secondly is there even any proof that gracity waves with the force to move things [high frequency ones] even exist?

Robin —Preceding unsigned comment added by 80.6.38.240 (talk • contribs) 15:53, 11 September 2006

LIGO--Light current 23:23, 11 September 2006 (UTC)

No, LIGO is a (big budget) mainstream physics project; the cited eprint (surely unpublishable!) is another example of the kind of nonsense which is promoted by cranky websites like American Antigravity and GRAVWAVE LLC.. Some time back we had an article on somewhat similar claims by someone named Franklin Felber, which was deleted on the grounds that such crackpottery is very obscure and would never come up again :-/ In fact, people with more enthusiasm than knowledge keep tossing up stuff like this. See also Eugene Podkletnov.

According to general relativity, gravitational waves exist, possess energy, and can transfer momentum, but they interact very weakly with matter and are very hard to generate, for fundamental reasons. Mainstream physicists do not expect to be able to exploit them for manipulation of laboratory objects or for purposes of spacecraft propulsion. Rather, the goal of observatories like LIGO is to use (extremely weak) gravitational wave signals from very distant and very violent events to learn more about these interesting events. For a variety of reasons, gravitational waves should yield information not obtainable from electromagnetic waves. Try this.

Bottom line: just because you found it in the arXiv doesn't mean it isn't nonsense. There are many very good eprints there and unfortunately also some very bad ones.---CH 11:22, 12 September 2006 (UTC)

The big problem with using gravitational waves for propulsion is that they interact very weakly (as stated above). Some serious research has gone into the practicalities of using gravitational waves (well the fabric of spacetime really) for one very good reason. Spaceships using such a technology would not need to carry their fuel with them. Personally, I don't think it'll work. LIGO, however, might work. At the moment all we use to observe the Universe is electromagnetic radiation. Before the Universe was a certain size it was in the radiation dominated epoch. We have been unable to see anything in this epoch - it's like trying to see stars at midday. Gravitational waves wouldn't be (very much) effected by ambient radiation so we could actually 'see' objects.

Hmmmmm the article seems mainstream, do you have background in physics CH that you can say for sure that what they are proposing is crackpottery? heres another one that was apparently accepted for publication by American Institute of Physics http://www.gravwave.com/docs/Am%20Inst%20of%20Phys%20007.pdf and surely if gravitational waves usually interact waeakly surely high frequency ones would interact more strongly? since they can transfer momentum? so all EM waves can transfer momentum then? Robin

NB The AIP seems to have a policy of publishing crackpot papers in its conference series, apparently because a secretary in its offices was once murdered by a loony after the AIP rejected his crazy ideas. They are playing safe. — Preceding unsigned comment added by 86.159.88.49 (talk) 04:13, 16 February 2016 (UTC)

EM radiation can and does transfer momentum (p=h/λ), but from your question at the end so all EM waves can transfer momentum it sounds as if you are considering gravitational waves as a type of EM radiation which is not the case (although if you could prove it was you'd almost certainly win a Nobel Prize for your efforts). Higher frequency gravitational waves would not interact more strongly than lower frequency ones, although they would transfer more momentum in the same time period as lower frequency waves as more gravitons will be transferring momentum. The problem is actually generating these high frequency gravitational waves.
Having read only the abstract of the paper to which you linked, they don't seem to be trying to use gravitation to propel spacecraft, they are looking at using it as a method of observation/information transfer.

but if you read further they claim that high frequency gravitational fields could cause peturbations or even move objects, its in the abstact as well also move down to aplications under propulsion.. So you are saying that it is possible to move objects with an EM wave that can cause momentum tranfer of the air thus pushing the object. If high frequency gravitational waves do not work this way how wouild they move an object? Robin

Electromagnetic radiation can transfer momentum straight to the object it is moving. The articles on radiation pressure and solar sail should contain more information about that. In a quantum mechanical treatment of gravitational radiation, they would work in a similar way (although quantum gravitation is, at best, poorly understood) but this does not mean they (gravitation and electromagnitism) are part of the same phenomena. A general releativistic explanation is given in the paper.

Anons, sign your comments please!

Robin, the website you mention, gravwave.com is maintained by Robert M. L. Baker, Transportation Sciences Corp. in Playa Del Rey, CA. IMO this is indeed a crackpot website. Some clues: Baker's affiliation is apparently with Department of Information and Communication Technology, University of Trento, Italy, not with a physics department at all. (For some reason, I have noticed that Italy seems to have more than its fair share of fringe physics activity---I don't know why. There is a small group of physicists there who regularly post arXiv eprints which flatly contradict various elementary textbook computations; these eprints are flat out wrong, as any good student can easily verify.)

The site promises "important practical, commercial and military high-technology applications for HFGWs". This is rather a tall order, and the fact that it mentions "patented technology" should be an indication that the website is engaged in PR designed to attract investment. If you compare with mainstream sources such as this paper by Bernard Schutz or this paper by Kip Thorne, you should quickly find grounds for suspicion, even if you don't know much about physics, that something is probably wrong with Baker's claims. Note that Schutz and Thorne are the authors and coauthors respectively of two widely used general relativity textbooks, and are leading physicists who have affiliations with two of the most prestigious places in Germany and the U.S. respectively. As for "apparently accepted for publication by American Institute of Physics", I think you might be misinterpreting something. Can you cite an arXiv abstract page? Be aware that some "journals" actually accept almost anything, so "publication" need not imply at all that any paper represents mainstream physics. For example, the abstract page of the eprint by Fontana mentions "Space Technology and Applications International Forum-STAIF 2004". FYI, this conference (not a journal) often features some very oddball talks. In general, conference proceedings are not refereed publications and this series is particularly notorious.

I think I already said that gravitational waves can transfer energy and momentum (see the textbook by Schutz for a fine introduction to the basic theory of gravitational waves as treated in "linearized gtr"). See my user page for more about my training and background. Since I have solved the Einstein field equation thousands of times and am familiar with hundreds of exact gravitational wave solutions, including CPW solutions and exact solutions to the full EFE, you should probably assume that I am not misleading you here. Sorry if this is bad news. ---CH 04:12, 18 September 2006 (UTC)

Robert Boyle

Do you have any information on Robert Boyle?

Have you looked? obviously not--Light current 23:23, 11 September 2006 (UTC)

Yes. The best way to find it is to type "Robert Boyle" in the search box and hit the "Go" button. - Nunh-huh 23:25, 11 September 2006 (UTC)