timo

I don't need either m-theory or quantum theory to fantasize about parallel universes. So in this sense: yes.

That is one (very informal) way to think of it. In practice, I've never seen symmetries being introduced to an already-quantized model, so at the point where susy comes in, no such thing as the graviton exists in the theory, but only some crude notion of "gravity", at best. Supersymmetry is kind of special in an additional way since it already is an extended version of the concept which (in naive approaches) later gives rise to gravitons. It's more like supergravity being the result of adding gravitons to supersymmetry.

Your point is ... ?

That does work to a certain degree, especially for trivial corrections ("hey, the charge of an electron isn't 10 Coulomb"). However, at some level, correcting things can take an enormous amount of time to sort out what the article actually says, what is wrong with it, correct it in a way that non-experts can understand and is a consistent view over a broad range of scientific fields, possibly look up references for rather obvious things, and implement the changes such that they still fit into the logical structure of the article. When I was still relatively active on Wikipedia (German language version), I found that often the best way to correct a non-trivial mistake is rewriting the article from scratch. Things get worse when you get to a higher level of scientific education since new opportunities to spend your time open. Writing or properly correcting two Wikipedia articles, which comes with nasty copyright requirements, is about the effort of writing a publication for a science journal (not counting the research, of course). I tend to prefer spending my time on the latter and that is consistent with what I've seen over the 4 years I've been lurking around at WP: people tend to drop out about the time they start their PhD.

Into the large trash bin behind the house. I already asked Capn about it. The basic line is that the new forum software does not support user albums (or only as an add-on which would cost money), anymore. If your albums contained images you desperately need (never put anything on sfn-related webspace that you are not willing to have deleted without previous notice! I know what I speak of) , you could ask Capn to dig out your old images.

That's only what the undergrads are being told. In reality, it is much harder. Explanations must be stripped off as many details as possible [*] without losing valuable arguments supporting your claim. Thereafter, you have to make your mediocre work sound as spectacular as possible without technically lying. That is the real challenge. See here for, let's face it, not-sooooo-unrealistic examples (my favorite being "correct within an order of magnitude" except that in my field people use "in qualitative agreement"). But it indeed transfers over to sfn B) [*] I am currently reading a physics paper which on first glance seems to be a bitter fail in this respect (though potentially interesting science-wise). They not only tell the reader which hardware they ran their computer simulation on (I don't really care that much about that information), but even that they programmed in C (or C++) on a system running on Windows XP, and that they consider rewriting their program in CUDA (that might be remotely interesting wasn't it for the fact that virtually everyone does so) .

Then the p in the equation you gave is not the momentum but its magnitude, simple as that (it's only a letter "p"). I don't know how to answer your question. Where does the direction of velocity come from? (comment: in a more formal approach to physics, momentum indeed inherits its vectorial nature directly from velocity) In case that helps you, here's a two equations relating momentum to other vectorial entities: [math]\vec p = m \vec v[/math], [math] \vec p = \hbar \vec k[/math]. The 2nd comes relatively close to your original equation since it also relates momentum to properties of a wave (k is the so-called wave-vector).

That's a different equation. What guarantees that the two p are the same? And what guarantees that delta-p is the same as p? Or to make things simple: the p in your OP is the magnitude of the momentum. Bottom line: "p" is just a letter, not a physical entity. What it stands for depends on the context (there's rumors about chemists in physics exams who plug in 298 K when calculating an angular frequency via [math] 2\pi / T [/math]).

Nope. But why do you think that p is a vector?

I have not looked into the current issues. But perhaps to put it into scale for you: street riots can almost be considered part of the French culture (it's tempting to date this tradition back to 1789). It's no state of absolute emergency as it might be considered if it happened in the US or UK, but something that occurs rather frequently like perhaps once every two years or so. Last time I heard about was street riots in Grenoble this summer after police shot some robbers (if someone is interested: random link I found). The time before was perhaps last summer after police chased a kid who then hid in a transformer facility and died of electrocution. Drastic protests against political decisions are "typically French", too. But I don't have an example at the moment. So to answer your question: I think apart from the obvious fact that people have to "give away something" it is a general expression of disappointment with "the government" and also a bit of French lifestyle (possibly related to the large amount of African immigrants living in France). And I don't quite see why it is surprising that young people also care about retirement age. They are at least as affected as the older ones. In fact, if the change is implemented gradually (which I would expect), then they are those who are affected the most.

1) http://www.scienceforums.net/topic/51925-mathematical-probability-puzzle/ 2) http://www.scienceforums.net/topic/51010-probabilities/ Incidently, the 1st thread was started by you

Consider assuming Ufinal=0 (what does that mean?), then do the same calculation assuming an initial velocity of 28 m/s, then compare.

I suppose it is ok to give a few more hints. The magic term here is: integration. Cut your object into small pieces that you can handle, let the pieces be really tiny (leetspeak-term: infinitesimal), possibly make some approximations, then put the pieces together to form your structure (which is where adding up contribution from different pieces comes in - note that an integration is just a limit of a summation when the pieces become tiny).

The formula is correct but note that the field strength g is not exactly equal to the force F exerted on an object in that field. The question asked you to compare the forces, not the field strengths. Btw.: It's cool that you take the effort to create an image of your formula, but you can also just write g = G*M/(r^2); people will also understand that. Yes, that's the only meaning that seems to make sense, here. Then keep it as the unknown variable "r" for now and hope that it drops out in the final answer. The star with 27 times the mass must have 27 times the volume of the other star, then. But since volume wasn't in your equation above, that information does not seem necessary at the moment. What you do know is that you have two masses m1 and m2, and that they are related by m1 = 27*m2 (assuming planet 1 is the heavier one), so each appearance of m1 in your equations can be replaced by 27*m2. Just keep parameters about which you know nothing as unknown variables (like the distance "r" between the two planets) and see how far you get. In this case, all of the unknowns drop out at some point (since homework questions tend to be give all the information required to solve it).

Providing you with the answer plus the way to get there when you haven't even said how you want to approach the question is not the idea of the homework help forum. So please say a few words how you think you might solve the question, what you already tried to solve it, and where you got stuck. One thing that I find remarkable though: Do you actually understand what the question asks you to calculate? I don't. Does the question ask for the gravitational force applied on a person standing on their surface or does it ask about the ratio of the forces the planets exert onto another? Hint: if you can answer that then set up a formula for the respective forces and you're almost done.

I'd say because especially on a science forum, the idea is -or at least should be- that expressing an opinion or idea is the product of some brain activity beyond that of a Chimp. So if I actually do think before I post, I can as well express that properly. "lol" basically is "I find it funny but don't bother with or am not capable of the effort to specify why or in what respect". EDIT: Also, keep in mind that the audience of a science forum contains at least a few actual scientists. As a scientist, you are actually also a professional writer to some degree, since already at the level of a PhD student (at least usually) it is required that you publish research results in journals.

a charged object that accelerates, i.e. has an acceleration [math]\vec a \neq 0[/math], of course.

... and also different from saying that it was a scalar, btw.

Something that most people would understand is "sqrt(x)" to denote the square root of x. Of course, "root(x)" would also be understood. Since [math] \sqrt x = x^{1/2} [/math], "x^(1/2)" would be understood, too.

For what? Compared to what? You'd certainly be looked down upon if you cited it in a scientific work. It's certainly more reliable than the average webpage of a random stranger or the average sfn forum post.

Your solution is correct. But note that: - You might have misread the original question. Check that what you presented as a question is what actually is asked for. - In the future, please add your calculation to your question. It helps the people to understand what you are doing and possibly point out errors in it. Also, the more information you provide, the more likely it is that someone helps you. Usually, it is far easier to go through someone's calculation than to first solve the problem, then compare to the result the person got, and then start guessing what might have gone wrong.

The gravitational field of an object is generally not Gm/(r^2), where r is the distance from the center of mass. That is only true in some cases. Your result for 1) is pretty obviously wrong, unless you believe that an infinite gravitational force works in the center of a ring (that would give a whole new aspect to a wedding). The 1st question could be solved without integrating (i.e. just from reasoning). I doubt you'll get around these nasty integration signs in the 2nd one.

I'd not care about the exact wording, not "introduce xi", and instead show the equivalence the other way round, i.e. starting with the expression involving xi and working back from there. It's about 5 lines of handwriting.

You do not need to learn it quickly. You have a few years, I think. I think I learned a lot from watching TV series in English, and a bit from posting on this forum. Using a spell-checker helps a lot.

Learn English. This is no offense. At MIT, courses are in English. And your English is not good. Some universities accept pupils. Take one or two physics courses at the university in your city if you can.