timo

Whether it´s an approx or not might to some point depend on your boundary conditions you enforce to your problem. If you assume that one of the masses stays in place, then the equations given in the wikipedia link simply hold true and you´ll have uneven escape velocities. If you want the problem to be physically meaningfull (no artificial forces keeping one of the masses in place) and still want one of the masses to remain in the same position, then "yes": One of the masses must be much heavier than the other so that its movement can be neglected.

Thinking is great, knowing is sometimes better: They do cancel out: http://en.wikipedia.org/wiki/Escape_velocity under "Calculating an escape velocity". That´s neither obvious nor even true. It´s the energy required to seperate them that must be equal for both cases (moving away the heavy mass or moving the light mass). Since the velocity (squared) is the energy divided by the mass, the velocity must be uneven if the masses are. EDIT: But I think I start to imagine where your problem lies: The calculation assumes that the mass not moved stays at the same place. This is obviously a good approximation for a small mass leaving a big mass. But if you strip away a big mass from a small one you´d need some ways of making sure that the small one stays in place and doesn´t follow the big one due to the gravitational attraction.

I dunno. I think that statement is heavily biased by your viewpoint. A lot of people working in the fields of solid state physics, optics, experimental/applied nuclear physics or biophysics would probably not agree. On-topic: I don´t really know if it´s possible to understand physics without math. Given that physics is supposed to be a quantitative model for nature and that I´d have a hard time quantifying something without using math I´d tend to "no". But -as this forum demonstrates from time to time- it is very well possible to entirely misunderstand physics without math. @Saint: I´m not really convinced if Tom spoke of an engineering degree when he talked about a degree in physics. Some physicists actually don´t like it if engineers tell them "I´ve learned the same physics as you - plus more" (only thing that´s worse is chemicists claiming that ). And they also don´t like being called engineers (I could guess the groups listed above would be called that by Severian, though) as it´s not really considered a token of appreciation. And one very important thing for your future life: Never argue with a mathematican. Those heartless borg only know "right", "wrong" and "cannot be decided within the given set of axioms" ...

That´s an interesting statement. How come? Because you´re not pushing the button yourself or because it´s another way of execution? Or because "monster" naturally doesn´t apply to yourself? EDIT: I can pretty much guess your answer so there´s no need to give me one if you didn´t like my comment. It was merely though as a cause for thoughts that you´re hopefully not offended by.

No, you don´t. You have to "Use the law of conservation of energy". In this case: Energy initially stored in the spring = energy "destroyed" by friction. I wouldn´t see any, except if trucks in your area are lighter than typical cars. EDIT: If you like a mathematical proof for that the truck has more kinetic energy, try this one: Let v, V and m, M be the speeds and the masses of the car and the truck, respectively (capital letter for the bigger one), then: E(car) = 0.5 mv² < 0.5Mv² < 0.5MV² = E(truck) However, I don´t think such an inequality would be asked from you in a test.

I wrote a pretty long response on that reply which was a bit disappointing to be honest. But then, I decided that I actually don´t really want to contribute to this thread any more so I´ll strip it down to: Thx for the answer, I think I see your point. I you reread my post in the context of the preceding post (well, actually rereading my post again should suffice) you´ll see that I didn´t say that electrons are rigid bodies.

7 TeV for each proton. Information on the LHC can be found on the cern homepage http://www.cern.ch

, he really said this?

As you can see on http://en.wikipedia.org/wiki/Stress-energy_tensor , the relevant quantity that enters the Einstein equations (which relate spacetime curvature to energy) is the energy-momentum tensor (called T, there). Photons add to that tensor so they contribute to spacetime bending (see the energy momentum tensor for an ideal fluid on the same page). If I recall that correctly, the photonic contributions and the fact that they do not come with a rest-mass share is important for cosmology in the early universe. But I´d have to read that up at home to be sure about that.

Electrons bounce off each other and are not particulary well known for their internal elasticity. Why do you think bodies bounce off each other at all? And what´s a COG ?

I´m afraid I didn´t understand you last post Swansont. Who cares? You could deny the whole classical mechanics with the same argument (it´s unphysical - particles with definite position and momentum cannot exist). And the nonexistance of internal degrees of freedom is in fact the reason for the collision to be perfectly elastic. Which conditions exactly do you mean which are "mutually exclusive"? You are aware that "fixed distances" only applies to particles within the same rigid body, I hope. Didn´t understand that, either. But that´s probably related to my non-understandings above.

Afaik, "rigid body" means that the distances between parts (atoms) of the body remain fixed which rules out shattering of the bodies. The "completely" is just a superfluous adjective.

They will bounce off each other. The force that ultimately responsible for bodies to bounce off each other is the electrostatic force. It exists regardless whether the bodies are perfectly rigid or not.

Or perhaps Black Holes are simply a mathematically valid solution of the Einstein equations and therefore as prone to "I think it is..."-interpretations as the derivative of cos(x) with respect to x. But to say at least something the majority here will want to hear: @iamasmartgirl: I´m not sure if your post was serious, but in case it was: - anti-matter and dark matter are not the same things - at least in principle. Anti-matter is the charge-conjugated counterparts of the particles we usually encounter every day and is well covered by current mainstream physics theories. Dark matter on the other hand is some extra matter that is needed to let cosmological theories coincide with experimental observations. It could be more or less anything. But many attempts to refer this extra matter to ordinary well known particles/phenomena have failed so far due to different reasons. Therefore, some physicist think it is a form of matter that is not part of current mainstream physics. - Annihilation of matter and anti-matter does not result in nothingness but -due to conservation of energy which is positive for both- in some kind of radiation.

Yep, see my edit

EDIT: I misunderstood the question, I´m afraid. So the first part that was here is skipped, now. Generally, relations involving cosines and sines often become trivial if one rewrites then as the linear combination of exp(ix) and exp(-ix).

Wow, RyanJ is starting a thread about a friend who got into trouble running a pyro site because someone used the informations to cause trouble and you post a link to a (possibly) similar site in the very same thread. I think it takes a bit of self-esteem to do that considering that some people (like me) might find that a bit inappropriate, especially when considering that the first reply to the thread included the following: "However, it underlines why we don't allow that sort of posting on SFN. We can get in serious trouble as well as you guys, so please bear that in mind before making posts on the subject." EDIT: To be a bit on-topic, at least: I dunno what actual information your friend had on his/her pages, RyanJ. However, I think it´s a bit naive to think a "you must not use this bomb to harm anyone"-disclaimer before "how to make a bomb capable of causing a lot of harm"-instructions is going to impress anyone to say the least. We could hand out weapons to anyone who wants one, otherwise. We just need a "don´t use it to threaten or harm other people"-button on the case.

Are you sure about that? If I remember correctly, there is no interaction term in the theoretical description of Bose-Einstein condensates (ideal gas approach). So there´s no reason why the particles should bond to form a solid. A basic, very easily understandable but yet (to my limited knowledge) correct description of Bose-Einstein condensates can be found here: http://www.colorado.edu/physics/2000/bec/ But to briefly give my opinions on "what does it look like?": To see something you have to have photons being reflected by it. However, in this case you have to have a way of "illuminating" the BEC with photons without heating it up in the process. I don´t know to which extend this is feasible. Perhaps the link I gave in above does have some answers.

Perhaps if you spoke less of idiocies and criminal conspiracies in science and made you posts have some actual content other than a few links to your hompage, your posts would´t sound as silly as they do now (at least to me, that is). The titles of your threads alone give the reader the impression: "Great, another guy who´s to stupid to understand physics and blames it on physics" . This is is not really the best possible start if you´re really interested in people reading your stuff. Or didn´t you wonder why your threads are -apart from discussions about how to translate the german word "Geschwindigkeit"- mostly ignored? Or do you think that proves you´re correct because noone tries to correct you? Btw.: From my experience it is a good idea to clearly state what your message actually is even though it takes away a lot of space for evasive maneuvers ("hey, I didn´t say this, that´s only your interpretation!"). Just my 2 (euro-) cents about proper posting style.

I didn´t browse the pages Severian suggested but if you´re interested in CERN and especially the LHC you could also visit the CERN homepage itself: http://www.cern.ch . At first, the page might seem a bit confusing but there´s a lot of information to be found there.

@Pentcho: Not that I understood what you´re talking about at all. But the fact that there is a common word for velocity and speed doesn´t mean that both interpretations are correct. You have to determine from the context which one is meant. @LazerFazer: Honestly, I´ve never heard of the term "lineare Geschwindikeit" before. This doesn´t nessecarily mean that this term doesn´t exist but it´s most certainly not widely used, nowadays. Well, perhaps it was during Einstein´s times.

Because he didn´t have the time posting it here before he was banned .

I´ll assume that n are natural numbers: Recursively it would look something like: int sumSqr(int n) { if (n<=0) {return 0;} else {return n*n + sumSqr(n-1);} } But as already mentioned by RyanJ, iterative method are usually preferable over recursive one when it comes to efficiency of the code (recursive looks nicer on the source-lvl though): 1) Calling functions takes processing time. 2) Calling functions takes up memory. A way to get rid of the multiplication is realizing that the distance between two squares of two ajdecent natural numbers increases by two with each step. Consider (0², 1², 2², 3²,4²,5²,...) = (0,1,4,9,16,25). The difference beween two ajecent squares is (1, 3, 5, 7, 9) and as you see increases by two in each step. A code using this would look something like this: int sumSqr(int n) { int result =0; int delta = 3; int nSquared = 1; for (; n>0; n--) { result += nSquared; nSquared += delta; delta += 2; } return result; } On modern machines (pentium and up) it´s probably not worth getting rid of the multiplication, it´s as fast as an addition if I remember correctly.

http://en.wikipedia.org/wiki/Newtons_Laws_of_Gravity

Do you think the horizontal velocity matters for the question how long the stone will be in the air?