ManOfSteel

Yes, of course. I don't know yet how the output looks in SPSS (I will get it tomorrow), but in Excel there's a SUMMARY table right before the ANOVA table that shows the sample size, sum, average and variance.

It's all clear now. Your explanation is very interesting and helpful. Thank you.

Hello and thanks for your reply. The latter. I'm trying to compare the average number of cigarettes smoked in 9 countries. So I have 9 averages/means, each for a different country (sample). It's actually an imaginary example and the 9 numbers are fictious. I'm just trying to understand if and how such a particular case would work, because I might need it later. So if I have nothing but the 9 means, is there any way to do it or is it just impossible?

Hello, I have 9 means for 9 separate samples. I would like to compare them (with a software) to know if they are significantly different. What test(s) should I use? A Student t-test for mean comparison? Can it be done with Excel, as it's the only software I've got right now? But if it can't be done with Excel could you show me how to do it with SPSS? Thank you for your help.

So they do not collapse on each others under their gravitational forces because a centrifugal force (angular momentum) dating back to the formation of the solar system is holding them back as if they were flying apart from each others. Am I getting it right? Thank you everybody.

Then why didn't it happen a long time ago with the sun and Earth, for example. What's holding them back? Do they have an initial velocity? Where is this initial velocity coming from then? Is it coming from a centrifugal force? Then where did this centrifugal force come?

Thanks. Just one more thing. To get back to our three objects, why don't all three fall on each others, collapse and merge into one more massive object? Is it because none of them is massive enough and therefore the curvature of space-time they cause is not enough for any object to pull another completely (to free-fall on another)? In the case of the three objects, one object free-falls from its origin toward another object. With the distance between the two decreasing, so does gravitational potential energy. On the other hand, kinetic energy increases at the same rate of the decrease of the gravitational potential energy because the object is accelerated by gravitation while free-falling. So the sum of both energies is null.

Thank you for the fast replies. Klaynos, My post? No no, don't worry! I was motivated to post this because of a discussion on another forum. Could you give me more information on each element of the formula or point me to a page explaining them? Objects are in a free fall. Massive objects cause curvatures in the space-time continuum and they follow a straight path in this curved space-time. It's correct, isn't it? But what I don't get is: what the free fall thing does really mean? Does it mean that each of the two objects is in fact "falling" toward the other just in the same way a ball falls toward the ground when dropped? However Earth does not fall toward the ball because the ball is not massive enough to curve space-time greatly? Is this what gravity really means? Atheist, How so? I don't understand. Isn't it like two persons pulling the same object from opposite directions with the same force? The object cannot move, all right. Is that what you mean by the gravitational force being zero? But the gravitational field of both objects (or the pulling force of the two persons) are still there. It's just that the effect is null because the forces are equal. Did I get it right? Gravity generates energy (potential energy?). If a massive object causes a gravitational force, it should also be emitting energy. If energy cannot be created or destroyed, only transformed, does the mass of the object remain constant? Do I make any sense?

Hello, Suppose there are two equally massive objects and a third object in between. Each of the two objects is pulling the third of the middle in an opposite direction. Does the gravitational force of one of the two objects cancel the gravitational force of the other? Is there any loss in mass? Or gain in energy? Why are two objects attracted to each others? Thank you in advance. PS: I'm not sure I posted this in the right forum as it is both related to classical physics and general relativity. So moderators, feel free to move it.

Thanks very much. That'll be all (for now at least ).

Thanks for your replies. Observations show that some matter absorbed by the black hole may then be violently rejected out of it at the poles, AFAIK. But what happens to the rest? Is it integrated to the singularity itself? In that case the singularity could keep on gaining mass, getting a theoretically infinite mass. Then, what could stop it from engulfing entire planets, stars or even galaxies with its infinitely strong gravitational field, eventually resulting in an exponentially powerful black hole (even more than supermassive black holes)? I also have some additional questions: - What are the latest discoveries about naked singularities? Are they even possible (outside a simulation)? - Do they not have an event horizon? In that case, would it be possible to see the singularity?

Hello and thank you for your answers. The distance between the singularity and what? Its own particles? A black hole was once a star like our sun. It has the same mass as the star had, just at a higher density. Am I right so far? So does density have anything to do with the gravitational force or does gravitation only depend on the mass of the body? In other words, is the gravitational field (and the curvature of spacetime) around the black hole of the same intensity as the gravitational field (and the curvature of spacetime) that was once around the star? And the same goes for a person on Earth and another on Pluto, right? So a hypothetical person living near the solar surface would have his life extended by several earth years according to an observer on earth, while the other person living on Pluto or in deep space would die before his parents on earth even though both persons were in the same conditions before the experiment began. I was reading the article about the "gravitational singularity" on wikipedia and there is something that is not clear: I understand the "geodesic" as a "straight line in a curved spacetime". Is that correct? What do they mean by the "smooth manner"? And by "limit", do they mean the straight line ends at the singularity? Why is that?

Hello, I would like to have your explanation about these two things that I can't understand. 1. I don't understand how, according to some physicists, the Universe is considered to be flat like a sheet of paper? What exactly do they mean by that? 2. Also, what do physicists mean when they say matter is so dense in a black hole that spacetime is bent or that the curvature of spacetime becomes infinite? Do they mean that ALL matter, when passing near the black hole, is deviated from its normal course just like light is refracted when passing through a prism? Also how does it change the "time" part of spacetime? Does time pass slower or faster than it would if there was no black hole? Thank you in advance. PS: I'm sorry if this has already been posted, but I'm not familiar with the forum yet.