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Can a strong gust of wind cause an avalanche? In particular, can an avalanche be triggered by the foehn winds that commonly occur in some mountain ranges (Alps, Rockies, etc.)? Thanks in advance! 67.170.215.166 (talk) 01:04, 7 June 2010 (UTC)
The lithium/lithium phosphide cell looks interesting (two different patents ):
Questions:
Oh and does anyone know of any more? 77.86.124.76 (talk) 02:03, 7 June 2010 (UTC)
Why elder people easily feels cold while the environment temperature is normal for other adults? roscoe_x (talk) 03:07, 7 June 2010 (UTC)
What are the neural substrates in goal directed learning? (Neurobiology of action). —Preceding unsigned comment added by Oxio-a (talk • contribs) 04:15, 7 June 2010 (UTC)
Well, within the context of contingency learning and extinction. —Preceding unsigned comment added by Oxio-a (talk • contribs) 04:35, 7 June 2010 (UTC)
Hi! Could anyone describe the eye structure for a toad? Thanks! ~ QwerpQwertus ·_Talk_·_Contribs_· 05:10, 7 June 2010 (UTC)
why the planets revolve around sun? and why they revolve around sun in an Elliptical path? is it due to the change in gravitation of sun? —Preceding unsigned comment added by 120.60.141.39 (talk) 05:42, 7 June 2010 (UTC)
whats the ph of 70 % nitric acid —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 09:00, 7 June 2010 (UTC)
i dont know what 1m or pKa means —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 23:22, 7 June 2010 (UTC)
Understanding Twin Paradox
The explanation that the difference of aging between the two twins is caused by acceleration or reversal of direction is not convincing if we compare two trips:
The voyager travels to a star distant 10 light years, starting with acceleration of 10 m/s till he attains 99% of the speed of light (what should take a little less than one year). He then proceeds with this speed until the same distance of about 1 light-year from the star and decelerates at 10 m/s2 until reaching a star at speed zero. Finally he returs to Earth in the reverse manner.
He then makes a second trip in the same way but to a star 20 light years from earth. The period and speed profile of the accelerations and decelerations will be the same in both cases, but in the second case the distance and time traveled at 99% of the speed of light would be about double.
If the age difference (and the respective clock markings) of the two twins were due to acceleration and / or direction reversal, the difference would be the same in the two cases.
Note: During the constant-speed step it is assumed that the ship rotates in order to generate a gravity of 10 m/s2 for the twin in order that he stays under normal living conditions.
Question: if the twin´s pulse rate were regular 60 per minute on Earth, how many beats he had accumulated at the main points of the travel? (start = 0, end of acceleration, start of deceleration, arrival at the star and the equivalent points at return.)
If the number of pulses of the traveler is much less than of his twin, then actually he has lived less during his trip. Also all chemical and biological reactions would follow this pattern. It is broadly similar to what happens to bull sperm kept in bottles immersed in liquid nitrogen: although its normal life is only a few days, it can be kept “alive” (actually in suspended animation) for more than an year because at this low temperature all chemical and biological reactions practically cease until the sperm is returned to normal temperature to revitalize and fertilize cows.
Question: If, starting with the ship´s departure, Earth sends a light signal every second, how many signals the ship has received at the main points indicated above? Also, if the ship sends a sequentially numbered signal every second (measured by the ship´s clock), at what time (earth clock) do these numbers arrive?
Question: IF the light signals from earth and from the ship are sent with a wave length of 600 nm, with which wave they will arrive at destination during the several steps of the voyage?
Question: in which reference frame (earth´s, ship´s, star´s) is the twin with his clock during acceleration and during constant speed, going towards star and going towards Earth?
In my opinion the problem of “understanding” the paradox as such does not exist because there is nothing in the universe what we really understand. We accept gravity, magnetism, electricity, matter, universe and life as facts and can treat many of them mathematically, but we do not really understand any of them. In the same way, what we need in the case of the twins is to know what happens, and this should be calculable by the formulae of restricted relativity and the Minkowski diagram.
07 June 2010 FJTREU 201.29.210.181 (talk) 10:21, 7 June 2010 (UTC)
It's always amusing to see what people think "causes" the twin paradox, and how passionate they might be about their convictions. For the analogous Euclidean situation, what "causes" two distinct paths between Kathmandu and Istanbul to have different (or possibly the same) lengths? Is it the angles of deviation from a straight-line course? Maybe so, depends on how you want to look at it. Either way, no one seems to regard the fact that two paths between these cities don't generally have equal lengths as paradoxical. Go figure.
By the way, there's no need to invoke exotic topologies or energy conservation issues to have two ships with zero proper acceleration meet at different times. Two freely orbiting clocks in the influence of a common central force, one in a circular and one in an elliptical orbit, can repeatedly meet and show different elapsed times between meetings. Tim Shuba (talk) 21:05, 7 June 2010 (UTC)
Asserting the geometry is a result of Mach's principle is even more problematic than asserting that acceleration is a cause. Currently, the Mach's principle article states, "Einstein's formulation [...] is not a fundamental assumption of general relativity." This is rather understated, e.g. top-notch relativity historian Michel Janssen gives a detailed account of the history in an essay entitled "Of pots and holes: Einstein's bumpy road to general relativity", especially from page 68 second paragraph through page 74, where Janssen writes, "Einstein had to concede that [Mach's principle] does not hold in general relativity."
I've yet to see any convincing invocation of Mach's principle to show anything concrete, and certainly not for the twin paradox. What general relativity does say is in the absence of nontrivial masses and energies, spacetime is flat, that is Minkowskian, and special relativity applies. Tim Shuba (talk) 13:24, 8 June 2010 (UTC)
The Solar sail article describes some designs of solar sail which would be kept stiff by the forces from spinning them. But why should the frame of refeance be the rest of the universe? If you took as your frame of referance the solar sail, then it would be static and the rest of the universe would be spinning around it. The solar sail should then go floppy. How can this be explained? How does "God" decide what the frame of reference should be in those circumstances? 92.24.182.231 (talk) 10:49, 7 June 2010 (UTC)
Another thing I've wondered about - I walk from A to B on the surface of the globe. I am stationary and the earth is moving. How much energy do I need to rotate the earth? 92.15.24.29 (talk) 20:08, 7 June 2010 (UTC)
The fact that I feel tired after walking 20 miles, and the fact that vechiles need fuel to travel, contradicts that assertion. 92.15.14.201 (talk) 23:12, 7 June 2010 (UTC)
I don't believe it. I would think I'd need a h*ll of a lot of energy to move something as massive as the earth. 92.28.243.59 (talk) 10:21, 8 June 2010 (UTC)
Do the above explainations also explain why "God" forces the earth to be the frame of reference rather than me? If I was the frame of reference, then I would have to deal with a huge amount of energy to start and stop the earth rotating under me when I went for a walk. 92.24.182.110 (talk) 11:31, 9 June 2010 (UTC)
I have someone who posted something on my talk page user talk:chemicalinterest#thank you about putting white phosphorus in potassium hydroxide, heating it and watching it glow and evolve what I think is phosphine gas. What is the reducing agent in that reaction (I know the oxidizing agent would be phosphorus)? Water isn't strong enough. --Chemicalinterest (talk) 12:03, 7 June 2010 (UTC)
If you read phosphine, you'll see that sodium hypophosphite (Na[H2PO2]) and sodium phosphite (Na2[HPO3]) are by-products.
This implies that phosphorus is both the oxidising agent and the reducing agent, i.e. it disproportionates.
Ben (talk) 14:05, 7 June 2010 (UTC)
Sorry, here I am referring to a response is to use White Phosphorus [P] reacts with Potassium Hydroxide solution [KOH] (concentration) and heating this mixture at high temperature, then you will get a Hydrogen gas like sulfur [H2S] Phosphorus is Hydrogen [H3P]. itself highly flammable substance and characteristic fish smell, its own fire in the air with a characteristic blue --I love chemistry (talk) 15:03, 7 June 2010 (UTC)
So it is the pyrophoricity of the phosphine that makes it glow; not the chemiluminescence of the phosphorus. Now its clear. --Chemicalinterest (talk) 17:49, 7 June 2010 (UTC)
Why wouldn't this work [3] —Preceding unsigned comment added by 90.7.162.110 (talk) 13:26, 7 June 2010 (UTC)
I see this frequently in food ingredients, but the entry on Corn Syrup doesn't seem to mention solids specifically. What are they and why are they used as opposed to liquid corn syrup? --70.167.58.6 (talk) 16:21, 7 June 2010 (UTC)
--Rajah (talk) 00:50, 8 June 2010 (UTC)
Why there are no straight lines in a perfect system like our nature? —Preceding unsigned comment added by 113.199.209.61 (talk) 16:30, 7 June 2010 (UTC)
And another somewhat arbitrary example: when a body like a meteorite strikes the planet, the blast and fragmenting ejecta can be deposited in "straight lines" or rays. Don't know if that qualifies as "nature," as in living organisms type nature, but since gravity is natural and so are force vectors, I leave my example. DavidH (talk) 00:57, 11 June 2010 (UTC)
Thanks Nil u really understood the question correctly. but not at first. simply the question is why not moths go flying towards sun in the morning? as per the first article suggested it could be becoz they want to hide from predators in light, then why not they should hide from them in night. going near light will make them a vulnerable prey.--Myownid420 (talk) 05:03, 8 June 2010 (UTC)
In nuclear fission, "It was clear to a number of scientists at Columbia that they should try to detect the energy released in the nuclear fission of uranium from neutron bombardment. On 25 January 1939, a Columbia University team conducted the first nuclear fission experiment in the United States,[18] which was done in the basement of Pupin Hall; the members of the team were Herbert L. Anderson, Eugene T. Booth, John R. Dunning, Enrico Fermi, G. Norris Glasoe, and Francis G. Slack. The next day, the Fifth Washington Conference on Theoretical Physics began in Washington, D.C. under the joint auspices of the George Washington University and the Carnegie Institution of Washington. There, the news on nuclear fission was spread even further, which fostered many more experimental demonstrations.[19]"
In Chicago Pile-1, "Chicago Pile-1 (CP-1) was the world's first artificial nuclear reactor.[4] CP-1 was built on a rackets court, under the abandoned west stands of the original Alonzo Stagg Field stadium, at the University of Chicago. The first artificial, self-sustaining, nuclear chain reaction was initiated within CP-1, on December 2, 1942."
So, my question is Was the Columbia experiment not artificial, not self-sustaining, or not a chain reaction? or some combination of those? I ask because it seems like to fission uranium, there would have to be a chain reaction, but I"m not clear on the self-sustaining part.
Thank you. --Rajah (talk) 16:47, 7 June 2010 (UTC)
don't want any medical advice ... just casual ... how can i whiten armpits? —Preceding unsigned comment added by KateGTG (talk • contribs) 18:02, 7 June 2010 (UTC)
My bulkhead light came with a packet of fittings and rubber seals, but also included were two of these. Can anyone identify this? It looks like some sort of sleeving for wiring but what is it's purpose? --78.148.138.14 (talk) 18:44, 7 June 2010 (UTC)
I expect that this only happens in certain situations, but when I took this photo, the autofocus only operated up to a certain zoom, after which it could not focus anymore. Switching to manual focus, I seemed to reach the maximum in either direction without focusing the image. The camera is a Panasonic HDC SD60 but I'm not sure this is relevant. Should I have opened or closed the iris? --78.148.138.14 (talk) 18:49, 7 June 2010 (UTC)
Et3N seems a worse leaving group than Cl-. After all Et3N is a nucleophilic catalyst but Cl- is not. Or is that R4N+ has repulsion with the partial positive charge on the carbonyl, allowing the Cl- to reattack and displace the tertiary amine? So actually, shouldn't the tertiary amine react, but not stay on for very long? John Riemann Soong (talk) 18:52, 7 June 2010 (UTC)
Okay, for a pendulum to have a period independent of its amplitude, the curve of the pendulum's bob must follow a cycloid. How was Huygens able to change the path that pendulum took? I would imagine that he had curves near the pivot so that as the pendulum swung, it would wrap around it. But what shape would these curves have to be? Would they be cycloids too? 173.179.59.66 (talk) 19:37, 7 June 2010 (UTC)
OP: Yeah I know that he ended up abandoning the cycloid thing. My question was more of a mathematical one. Is there an easy way to see that cycloidal jaws maked the bob move in a cycloid? 173.179.59.66 (talk) 03:04, 8 June 2010 (UTC)
1) @Dbfirs: I'm not 100% sure, but I think that a cycloid is tigher in this case, because you're comparing it to a semi-cirle of twice the radius of the generating circle in the cycloid...I think. In any case, the equation for the motion of the pendulum is d2x/dt + ω2sinθ = 0. If sinθ becomes θ, then the pendulum moves with simple harmonic motion. But sinθ < θ, so the time it takes for the bob to return to the equilibrium point would increases with increasing amplitude. But by letting ω increase with amplitude, this can "offset" the deviation of sinθ from θ. Because ω2 = g/L, L being the distance of the bob from the pivot, we require that L decrease with increasing amplitude, and thus the curve must be tighter.
2) @Dmcq: Yeah, I understand why the bob has to move in a cycloid, but why would cycloidal jaws cause the bob to move in a cycloid? After-all, semi-circular curves would not make the bob move in a semi-circle, right? 173.179.59.66 (talk) 14:14, 8 June 2010 (UTC)
I thought that the melting point of an ionic solid would be determined by the difference in electronegativity between the two elements composing the salt. But even though each alkali metal and alkaline earth metal halide follows the rule, some other ones don't. For example, why isn't beryllium oxide low melting because it is more covalent than caesium oxide, which is very ionic? --Chemicalinterest (talk) 20:21, 7 June 2010 (UTC)
Fusion is clearly a process that requires phenomenally high temperatures to work. How the hell have scientists managed to, or at least planned to, contain the plasma? I would have thought any conceivable metal unable to withstand such temperatures, but clearly I'm mistaken. Is the plasma prevented from touching the walls of the chamber, and conducted in a vacuum to prevent direct transmission of heat, or are there other components at work? Regards, --—Cyclonenim | Chat 23:20, 7 June 2010 (UTC)
why do my hard wood floors turn black if they get wet —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 23:23, 7 June 2010 (UTC)
how does water eat thru polyurethane thou? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 03:32, 8 June 2010 (UTC)
what? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 04:48, 8 June 2010 (UTC)
You are in a spaceship without any windows or external instruments. a) You are travelling at say 50% of the speed of light, and are captured into orbit by a massive object such as a star or black hole. Your spaceship traces a sharp curve around it, almost doubling back, and begins to orbit it. Does anything feel different from normal inside the spacecraft? Could you detect that your direction has changed or feel any force from the change in direction? b) You fall into a black hole. Does anything feel different from normal inside the spacecraft, or are you unaware of this happening? 92.28.247.252 (talk) 23:35, 7 June 2010 (UTC)