timo

Not really.

Why would the effect cancel out instead of doubling ? Ok, that was just a joke question but I hope my message that it´s very speculative to draw conclusions about the behaviour of an unknown/unfamiliar mechanism came through. In this case, I think your problem might stem from a misconception of how human vision works: When I program a raytracing program (a type of program that visualizes how an observer would view a virtual 3D world), then for each pixel on the screen I shoot an appropriate ray from the observer's position through the world. At some point, the ray will collide with some object in the 3D world. I figure out the color at this point of collision and paint the pixel accordingly. That is an easy way to determine what an observer within a world sees but it's not how it physically works. Your eyes don´t emit light rays that scan through the area. Light from the surrounding falls into your eyes. Construction of the image is done by your brain which usually -in lack of better information and usually also correctly-so- assumes that the light ray reached your eye in a straight line. That can lead you to see object at the wrong position. You get a simple example of seeing things in incorrect position when you take a look into a mirror: The light emitted by you is reflected in the mirror and arrives at your eye - that is the part of the process where light is bent. But in the second step, the reconstruction of the image by your brain, there is no bending effect that undoes the previous bending. Your brain assumes the light ray having travelled in a straight line and it therefore reconstructs a picture in which you are standing inside/behind the mirror. In short: Your vision does not correct for effects of light bending. Let´s get the previously-said back onto the topic of light being bent by gravity and extend the scope to the question how you acutally figure out that light is bent. I´ll do so using the image below; it´s the result of a numerical calculation enhaced by my extraordinary skills with windows paint: The bending of light in a gravitational field can be observed when a ray of light passes close by a large mass. Let´s stay to the lower guy first. The light from the object you want to observe (the red ball) is emitted, bent on a massive object (a black hole here, but anything does in theory) and hits your eye. You brain, not knowing about the black hole (it´s black, you can´t see it ) thinks the ray came in straight and reconstructs the object at a different position (green dot). Ok, so far you know that you´ll see an object in an incorrect position when the light emitted by it is bent on its way to your eye. That doesn´t yet tell you how you can ever figure out if light bending really exists (for most objects being observed actually travelling there to check out the real position is not an opportunity). You can check the bending if the position of the bending object changes. The amount of bending is directly dependent on the distance of the light ray from the bending object. Look at the upper guy. The bending object (still the black hole from the lower guy) is farther away from the light ray than before. As you can see, for the upper guy the misconception about the red balls position is significantly smaller than for the lower guy. That´s the key to one method to verify light bending: Observe a star for which you know a massive object will soon cross the connection line between it and you. If you´re lucky, you can see that the appearent position of the star will change when the massive object passes by and restore to the original one after the massive object is gone again. Enough for now, I´m already scared at the thought of proof-reading what I just wrote I find it hard to give a definite answer here because every easy thing I could say here without going deep into detail would be wrong to some extend. Let´s say it this way: In modern physics forces play a much lesser role than in Newtonian physics (including Newtonian gravity). Conceptually, the important feature in GR is the geometry of spacetime. Forces felt by the objects as a result of this do in some sense exist, but they usually play a minor role. In short: Yes, we´re redifining gravity (whatever that is ...).

Hi Linda and welcome to SFN. To PM (private message, that´s what it´s called here) another member, you can either click on that member's user name and select "Send a private message to ..." from the appearing menu or you can select "User CP" from the menu bar on the top to go to your profile page and then select "send new message" from the menu on the left. I don´t know what questions you have for whom but generally I´d think you should simply ask your questions publicly by starting a thread. That´s what a forum is for - you hadn´t had much to read yourself if all communication here was by PM.

[math] \vec v = \vec v_e \, \ln \frac{m}{m_0} [/math]. Hover your mouse over the equation to see the latex code. To write TeX in this forum you must enclose the code like "[ math] here goes the code [ /math]" (without the spaces, of course). I highly recommend getting used to TeX as soon as possible. It´s easy to learn and very powerful in writing articles/posts containing mathematical formulas. The equation is what I originally thought of, although I was rather thinking in terms of trying to derive it than simply stating it (since simply stating it is a no-brainer, it´s written in the wikipedia article). You can derive the equation on wikipedia from conservation of momentum. Since total momentum is conserverd you can set dp/dt=0. If you plug in a suitable term for dp/dt, you can solve something for something (change in velocity for amount of fuel spent solved by integration, in this case). What I want to say: dp/dt = d(mv)/dt = dm/dt v + m dv/dt or something similar can be an important step in deriving the equation on wikipedia and the result might resemble an integrated version of it. But that is not because it was anything rocket-specific but because of a more fundamental principle of physics: Conservation of momentum.

I´m not even sure there is any. I made up the term. What I was meaning basically was any investigation of the matter beyond hollow phrases. Be it a complete solution of the movement equation, be it an investigation of the amount of fuel necessary to achieve a specific change in velocity, be it a quantitative statement of the momentum change that results from a small amount of fuel spent or be it whatever interests you.

Given the number of new and/or updated threads was ~38/day the posts probably were a few more. Counting posts/time-unit shouldn´t be too hard: Take the total number of posts (currently 305,787), wait a little, take the difference between the new and the old number and divide it by the time waited to get the daily count. There are also a few old ppd numbers floating around for comparison. You might scan Martin's posts for that.

You can theoretically discuss about "real causes" for gravity. But the issue is: If you find two or three causes that lead to the same effects how are you going to distinguish them? And in case we agree that you cannot: What´s the point in looking for explanations beyond investigating the effects? The standpoint of physics is pretty simple on this issue: Physics tries to explain how things work, not why they do so.

Being happy with my TI-30 I am probably not really a big help to you on this topic. But questions about scientific calculators appear here from time to time. So perhaps you can scan over these threads to see if there´s useful info in them: http://www.scienceforums.net/showthread.php?t=22579&highlight=scientific+calculator http://www.scienceforums.net/showthread.php?t=5688&highlight=scientific+calculator

If I understood you correctly then you want to replace a gravitational field with some unknown source of radiation which, in contrast to the gravitational field that pulls (whatever that might mean and whyever you think so), pushes objects together. And the reason is that you replace mere effects (gravitational fields and their impact on objects) with a real cause - some unknown radiation that pushes? I think I prefer my "little green gremlins eat space between massive objects"-hypothesis for a cause. It´s a bit less abstract than some unknown form of energy.

I´m afraid I don´t understand what you are saying or trying to say.

I was hoping that some people who don´t already know the whole physics behind it get interested in the topic and try to find a/the/some solution for themselves or even together. Your input is very welcome, of course. But I think we should wait for some more replies by others or some feedback from Christie, first.

It shows barely visible greyish blue stripes on a black background on one LCD and better visible blueish grey stripes on another LCD..

The basic idea is the following: - Due to the pressure, the water wants to escape the container. It can do so only in one direction (at the rear end of the rocket). - The water leaves the rocket with a certain velocity and hence carries a certain momentum p (the actual value is not relevant here, just note that it´s not zero). - Momentum is a conserved property which means that if you give the water a momentum p at the same time somewhere else a momentum -p must be obtained. In this case, it is the rocket whose momentum changes by -p. - Often, a change in momentum means a change in velocity. In this case, from p = m*v is follows that v = p/m. So if the momentum of the rocket changes by -p, its velocity changes by -p/m. Well, that´s about it. The momentum of the outstreaming water is compensated by the rocket by gaining momentum and hence increasing velocity. Please note that above is only an attempt to explain what is happening. Several terms like the mass where not explained properly and can become a bit tricky as soon as you really start doing calculations. That leads me to some request to the other sfn members: On sfn, there is the tendency to greet every new member who presents his theory of everything with the words "show us the math" whereas very little (well, basically "no") math or real physics is used in the "real physics sections", either. I think some work on this subject (rocket equation) should be challenging but feasible and most importantly interesting for many people in here. So it would be nice to see some explanations/discussions on the rocket equation in this thread, even if it´s just failed attempts to solve the problem (oh, and since I see that coming already: With that I explicitely don´t mean the link to the corresponding wikipedia article(s)). EDIT: Oh, and btw: Welcome to SFN, Christie.

In short: Yes.

I´d spontaneously think so, yes. Let me just add that it might be better to think in the lines of "gravitational fields are created by energy" than in the lines of "grav. fields are created by mass" because mass can sometimes be a disambiguous term. (oh, and the "... created by energy" is not the whole picture, either - so don´t overstretch it). Electromagnetic waves (=light) and all other forms of energy contribute to the gravitational field. To explain my 1st post: I was not arguing that photons around a black hole would not increase its mass (I could have done so, though). I was trying to clearify that your jump from "I found a source for gravity" to "so it could be dark matter or dark energy" is a bit (more than a bit) hasty. You´d neither get the distribution required for dark matter nor the exotic properties of dark energy with your ... well, it´s still just black holes with a bit more mass. The amount doesn´t matter. The effect is either zero or not. If it´s zero, then it will also be zero for a lot of <stuff - light here>. If not, then it´s non-zero also for small amounts.

Let´s say light circeling a black whole would contribute a significant amount of energy: How does that fit into the picture of either dark matter or dark energy? What would be the similar properties?

Arkain101 ... that name rings a bell: http://www.scienceforums.net/showthread.php?t=15237.

You are aware that your group consists of one person, are you? Of course some persons have an IQ higher than the average - a good guess would be 50% of the people. And of course you can take those 50% of all people, put then in the group "have an IQ higher than average" and then find out that all members of this group have an IQ which is higher than the avergage. For the "how much difference is there": I don´t know Einsteins IQ but I´ve attached a little image showing the distribution of IQ within a test group: Tough question. On the one side I would spontaneously think I like having a certain amount of iq that allows me to live an independent life, i.e. being able to orient in society without a guide. On the other side, most <insert your countries political correct term for mentally disabled people here> I´ve met were just as happy with their lives as the non-disabled. I´m tempted to say no.

That is an equation attributed to and presumably also used by Einstein. There is, however, indeed a forumla which is called "Einstein equation" (and often used in the plural because you can write it as multiple equations): http://en.wikipedia.org/wiki/Einstein_equation . The Einstein equation basically describes the geometry of space-time as a function of the distribution of the masses in it (that´s not completely correct but I wouldn´t want to go into too much detail here). Yet, the Einstein equations do not resemble the equation presented by Mystral and I´ve neither seen them nor would I even know what the symbol before the a and b is.

If I understood you correctly then you have two masses in 2D space where one of the masses can be accelerated and you also have the additional restriction that the distance between the masses must shall remain constant. Spontaneously, I think the solution to the problem is treating the 2-mass system as one system which can move and rotate. Any force (acceleration of the ship) can be decomposed into a vector parallel to the connection line of the masses and a vector perpendicular to it. The share parallel contributes to the acceleration of the 2-body system in 2D, the share perpendicular contributes to its rotation. That should give you good if not even correct results. I don´t want to send you away from here but I think for such a specific kind of question you will most likely get better answers in the Math&Physics section of the forums on http://www.gamedev.net - they had some pretty competent people in there a few years ago when I was still active there (but check the tutorials first in case your question is a common one and already answered in them).

Yes. Recommended movie: "2001 - A Space Odyssey" by Stanley Kubrick.

Reading is out. Gone the way of mutual respect.

I know two: 1) Take a stone and drop it. If it falls down then gravity has arrived at it. 2) Stand up and rotate around your own axis repeatedly and quickly (doesn´t matter which axis - but maximum respect if you get that to work with any other than the vertical one). If you do that sufficiently fast and long you´ll fall to the floor => Spin creates gravity.

It is indeed what a thoughtful newbie needs: A pointer to the most fundamental flaw in his approach/theory/whatever. I still claim that the day the people that present their private theory of how everything works will start to listen to each other then there is a chance that something usefull might come out of it.

(2x+10)(x+3/2) = 2(x+5)(x+3/2) = (x+5)(2x+3) = ... Yes, there is an infinite number of ways to write it down. I suppose the (x+2)(2x+3) is what your teacher wanted since it seems to be the easiest (looks nicest to me). For the squares, there´s three solutions: 1) Most people will understand if you write x^2. 2) My keyboard has a button for it: x². Not sure if the button exists on US keyboards. 3) It´s a good idea to get used to TeX early which this forum is a good place for. For using TeX, you have to put the TeX code between [ math] and [ /math] (without the space). The command for putting something in the exponent is the "^" of 1) (one reason why most ppl will understand it), so in your case [math] 2x^2 + 13x +15 [/math] (hover the cursor over the image to see the code I entered).