timo

@ Welcome message: Dunno the one you meant but it sounds quite nice, yes. @ more news: I never found a news here that actually interested me. Isn´t it such that everyone can post a news? So if you want more news, post some. @ setting up a science wiki: What exactly are the expected advantages over wikipedia?

Oops, I almost knew I overlooked something.

The "bosons are force carriers"-statement is only true for elementary particles of the standard model. It does not apply to particle compounds such as atoms. What exactly is your problem with the photons in the box?

Also want to try ... [math] \ce{Al + Cu -> Au + Cl} [/math]

I´m not completely convinced that the standard geometry assumed for our universe fits the periodicity-conditions I saw in two of the papers. The black hole metric certainly doesn´t which is why I didn´t understand your initial post.

Thank you for listing some papers. Now if you´d also tell me what your post is about at all I might even consider reading one or two of them to debate with you. I hope that´s not too much to ask for.

I assumed Vi = "initial velocity (at height=0)", Vf = "final velocity (at maximum height=d)", a = "gravitational constant", d = "height". Then from conservation of energy you get to Epot(h=d) + Ekin(h=d) = m*a*d + 0.5m*Vf² = 0.5m*Vi² = Ekin(h=0) => 2ad = Vi² - Vf². I didn´t really look at his calculation so he might have used another convention than his nomenclature suggested to me. EDIT: Oh, I think I see now what you mean swansont (negative sign because <a|d> < 0). I´m not sure how common it is to use vectors in these kind of problems.

Because Vfy gives you the change in height. If Vfy>0 your height will be increasing within the next moment' date=' so you obviously aren´t at the peak, yet. If Vfy<0, then the height was greater just an instant before => also not the peak. The key to these kind of problems is to realize that for this part you can comepletely forget about the motion in horizontal direction. Just calculate the time it takes the cannonball to reach it´s maximum height and then to fall down. Question c) can be easily solved by the same principle as in b). Only that this time you ignore the movement in up/down-direction. Knowing the total time of flight this one becomes really easy. Didn´t check your numbers in part a). The formula "2ad = Vi² + Vf²" gave me quite some headache till I understood what it was supposed to be. It´s wrong, anyways. It´s supposed to be "2ad = Vi² - Vf²". Of course, in your case that won´t matter as Vf=0.

Either use the a from above or calculate it out explicitely (and possibly more correctly) by using Newtonian Gravity. The average is [math] \frac{\int_T a(t) \, dt}{8 \text{ month}} [/math] where T is the time-interval of length 8 month you are taking the average over. Care to tell us what you need that for in exchange for possibly better-suited answers?

Imho, it´s either an OpenGL-demo by some hobby programmer or a hacked satelite.

If I remember that correctly, the ideal gas does not undergo any phase transitions. Therefore you can probably forget about the pV = nRT which 5614 presented you. I´m really bad at thermodynamics so I´m probably not going to be much of a help, here. But one thing you might want to look in are "phase diagrams". They do not give you a rate of evaporisation (Q1) but at least the give you the points where the phase transitions occur (Q2). Another interesting thing to look up in this context is the "Clapeyron equation" which gives an approximation for the phase boundaries (hopre I remember that correctly ... I did mention that I´m bad at thermodynamics, did I?). Just out of interest: Which crystals do sublimate ?

There is no "equation" giving you the primefactors of a number. As a matter of fact, many encryption methods base on the fact that you need algorithms to determine the prime factors which take quite long. A simple algorithm (non-optimized, just the first and most straightforward thing that comes to my mind right now) for getting the prime factors of a number would be something like this: remnant = number->value div = 2 while remnant > 1: if (remnant modulo div = 0): remnant := remnant / div, number->AddPrimeFactor(div) else : increase div by one end of while loop Reducing the string representation is then quite straightforward and will work the way you already proposed: Look for common primefactors and divide nominator and denominator by it.

I could bet that in the typical studio it´s very bright. That is because the aliens that appear in TV need the energy of the light to keep their human disguise stable. There was a secret NASA paper about this somewhere on the net but the page was shut down. The author mysteriously disappeared shortly after he proclaimed to release a second secret paper which should show the detailed plan of the aliens which want to take over the earth by controling all the media.

Never heard of RPG which might be a good hint for its importance. What do you mean by a "diffused language" (non-native english speaker, in case you wonder about my question)?

Let measure (whatever it´s supposed to be for now) be called m. Now m -> m' < m 1m' + 1m < 2m but: 1m + 1m = 2m and (possibly more importantly): 1m' + 1m' = 2m' In words: One "new measure" + one "new measure" = 2 "new measures". Hope that helps.

Yes. Except perhaps for the fact that the schwarzschild-radius is a "distance" while the event horizont is the "sphere" created by that radius.

That´s not correct. The 2nd line would be: a²b + b²c + c²a > (a+b+c)(abc)

Well, let´s forget about the lightmass for a second. There is no way to treat light correctly in classical mechanics and I just realize that I run into problems imagining how a semi-correct treatment would look like. A much more important point is this one: The event horizont is not characterized by the radius where the escape velocity would exceed the speed of light. It does, but this is only a result of a relativistic mechanism. The condition set by the event horizont is a much stricter one: Nothing can escape this radius. This is in contrast to the "escape velocity" you used above since the latter gives the velocity to escape to infinity. So even if you limited yourself to velocities <c, it would be possible to escape your "event horizont". Simply kick your particle long enought till it´s close to d. Then, kick it so that it´s outside of d (d is the distance you calculated above, in case you didn´t notice it). Then, kick it to it´s escape velocity and say goodbye. The "kick it till it´s outside of d" will not be possible in a black hole scenario. Huh, how much background of general relativity should I suppose here? Within spacetime, particles can only travel on a certain subset of all possible directions. These are the so-called light-cones. Gravitiy can bend these light-cones. At the event horizont, the light-cone is bent in such a way that is completely points inward. No such thing as limited directions of movement exist in classical mechanics which makes the analogy a little hard.

I originally wrote [math] \pm \vec r /r [/math] because nowhere I see a convention about signs (r=r1-r2 or r2-r1 ?) or naming (the force excerted on object one by object two is the negative of the force excerted on object two by object one - which is F?). But then, I left it out to avoid confusion.

My question actually was a bit of rhetorical because I was hoping that you´d actually do the calculation to see that your assumption of an escape velocity runs into problems. I didn´t really expect you to copy-paste a solution from wikipedia. Nevertheless, if you inspect the line above the one you quoted, you might see where the problems lie.

The forumla you present above (the right hand side) actually gives the magnitude of the force, not the whole vector. You have to multiply this magnitude by a direction unit vector ([math] \vec r / r [/math]) to get the vector. Also, r is not a vector but a distance: The magnitude of the displacement vector. So it´s a simply product of to reals in the denominator.

How do you calculate the escape velocity? And what mass do you asuume for light? And why?

I´m no chemicist but this "the orbitals get filled one after the other" is a rule of thumb, at most. E.g. the Lanthanides have one 5d electron. After this, the 4f orbital is filled first before the elements continue on with filling the 5d. You should be able to find the electron configuration in any semi-decent periodical table.

This reminds me of this nice little picture: http://photos1.blogger.com/img/200/1549/320/retarded-1.1.jpg

^^ It wasn´t what I was saying, at least. Might still be true but my main point was that in a black hole scenario you hit the singularity before you reach r=0.