Well, I do not believe that Earth is flat, but I met some conspirationistas believing that all physics we learn in school is twisted, all the Earth's pictures from space are photoshopped by NASA, etc, etc.   So those guys wanted to put a satellite into orbit, take some pics, and see for themselves.   Of course, a satellite won't stay above a flat Earth, but what other very simple means to prove/check that earth is round (well, geoid) do we have?  I am looking for simple means, available to anyone, that do not need any external tool or knowledge that a naysayer would reject.   Some things I've considered:   Meteorological balloon with camera and a phone with GPS, with a parachute to recover it. It has been done by amateurs, and in good conditions, you can see the Earth's curvature. Measure the Sun's height above horizon at noon at two different latitudes. The difference, along with some simple geometry would give you Earth's diameter.
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Assume you've come in contact with a tribe of people cut off from the rest of the world, or you've gone back in time several thousand years, or (more likely) you've got a numbskull cousin.  How would you prove that the Earth is, in fact, round?
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The question I am working on is, &quot;Consider the following. (a) Find the angular speed of Earth's rotation about its axis. rad/s (b) How does this rotation affect the shape of Earth?&quot;  I am fully capable of solving part (a); however, I am not sure how to describe the effect earth's rotation on its shape. I tried to search my textbook for the answer, but could not find anything. Is there an actual effect on the shape?
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A person dismisses an otherwise valid argument, because some of its proponents support it for the wrong reason.  How is this fallacy called?  EDIT: Here is an example. A person defends the idea that the earth is flat. In an interview he asks several skeptics and each one of them responds "The earth is round because if you dig deep enough you'll reach the other side". The person then shows that this is a circular argument and then concludes that the earth is flat.
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Possible Duplicate:          I made a little research about this and found this article  that states the explanation of the moon being bigger at the horizon  is still debated.   I found this which looks pretty 'big'  but however this kind of repetitive shots  show no decrease in the aparent moon radius.  What I am trying to understand is if it is a real illusion, if the atmosphere makes the image bigger or what other explanation could be possible and of course plausible.
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My understanding of orbital mechanics is very limited, but as I understand geostationary satellite, they stay in place by having an orbital speed corresponding to the spot they're orbiting over.  So my basic intuition tells me that it's not possible to have a geostationary satellite over the poles, since they're effectively standing still, and to my knowledge, a satellite must keep a certain velocity to keep from getting pulled down by gravity.  Am I missing something?
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According to General Relativity I am being accelerated upwards by planet earth while writing this question. But a curious person on the the other side of the planet relative to me would have the same experience. That means we are accelerated in opposite directions, although earths diameter do not seem to increase. How can this be?
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I know there are similar questions on StackExchange but I think it is different and detailed.  The earth is spinning 465 meters/second so why don't we jump and land on a different location?  I googled about this question and I got some answers:   When we jump, we (and the atmosphere itself) also spin along with the earth so we don't land at a different location. (But why we are also spinning along with earth ?) The earth is so big and we are very small relative to earth so the tiny jump won't make any difference.   But according to answer 1, We are also spinning with the earth. But the question is, "why are we also spinning along with earth" ??  Regarding the answer 2, it won't make any difference but logically it doesn't make sense or I just don't understand it.  Here is the followup question,   "When we jump why don't we thrown out of earth due to centrifugal force of the spinning earth ??"  Please provide some detailed answer to these questions. With logic if possible.   This phenomenon is not possible I know, but even if it exists, then traveling will be so easy, we just have to hang on space (with help of helicopter etc.. ) and we can travel the whole world in 24 hours :D
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Edit : Added a picture for better understanding of my querry. All the texts I have studied has used an non-inertial frame to explain the phenomenon. But every time I see something explained with pseudo forces, I try to realize in real forces.   But in this case I tried to explain it in a frame which is centered in Earth's center and not rotating. But I couldn't explain what happens to the tangential component (to the point on Earth's surface where $g$ to be measured) of centripetal acceleration in this scenario. It doesn't cancel out.   But then I thought the tangential component is so low that practically it would have no effect.  Is my explanation wrong?
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I saw a video some days ago () of a schoolgirl successfully launching a balloon into space which later popped and landed ~47 km from launch site.  If I vertically launch an object (say via balloon or rotors) from the surface of a spinning planet with an atmosphere like ours, then as it rises, will the planet's surface move away below it, or will the object rotate with the earth? (Assume that there are no local strong winds relative to the atmosphere, and it is completely calm.) The latter would mean the atmosphere, being itself a collection of such objects (air molecules), also spins with the planet.  Related SE question:   It seems from common sense that since at launch the object shares the motion of the surface it would keep rotating with the planet, and hence would later land at the launch site. However, as it ascends, the lateral speed required to maintain the same angular velocity with the planet rises linearly. Where would it get this extra momentum/energy from? From the rotating atmosphere? How did the atmosphere get moving in the first place then?  It might seem a lot of questions for a single SE post, but they're all connected, so a single explanatory answer should suffice.
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We may choose a non-rotating earth as our reference frame and ask ourselves: how about the planetary and stellar motions. A star at a distance of 10 million light years would turn around the earth in 24h with a velocity of 10^18 m/s.   A friend once told me that actually articles have been published delving into this problem, e.g. to prove that fictitious forces emerge from the choice of such a bizar reference frame that ensure that the earth is still (somewhat) flattened at it's poles.  Questions:  1) Does anybody know of such a publication?  2) I know that even such speeds of 10^18 m/s are not in contradiction with relativity because a limiting velocity only exists for exchange of information, which apparantly does not occur. Still: could anybody explain why such bizar velocities are allowed?
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The belief is that the earth is round.   Do 'the belief' and 'that earth is round' correctly show apposition here?
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I sent this problem to Presh Talwalkar who suggested me to send it to this site. I tried many things but was not able to find the correct solution.   I made various segments trying to get an equilateral triangle similar to the Russian triangle problem, but no success.  I also tried to flip the triangle UFO over side NO but again no success.   I tried to find like triangles, but not enough.  Could you please give me a hint?   Thanks, R. de Souza
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If you draw a big triangle in Earth 2D surface you will have an approximated spherical triangle, this will be a non euclidean geometry.  but from a 3D perspective, for example the same triangle from space, it could be depicted as euclidean in 3D.  Then why we talk about non-Euclidean instead of adding 1 dimension?  It is easier the non-Euclidean approach? I don't see how!  Sorry if the question is perhaps naive, but this is a long time doubt for me, so I will be grateful for an answer.
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To be clear, yes, we can see everything from Google Earth or other satellite imagery, but that doesn't mean we can explore it.  GE can't see into forests, canyons and caves.  Has every mountain been scaled? Has every ocean depth been mapped? Has every jungle been navigated?  Basically, the question is, is there any part of our planet left to explore? To put your foot on a rock and shove a flag in the ground and name it whatever you please.  What are the main areas left for exploration that someone might want to try and do.  Clearly not every square foot of the Sahara has been navigated, but that's a bit harder than say, a North American forest.
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Total newbie with basically no physics knowledge here :) I would welcome any correction to the steps of my reasoning that lead to my question, which could easily turn out to be invalid :)  My current understanding is that General Relativity is definitely accepted by the vast majority of scientists, and that according to General Relativity spacetime is curved by the presence of mass.  I also seem to understand that not as many scientists (although probably still the majority) agree that extra dimensions of space exist.  But if we agree that spacetime can "curve", aren't we automatically saying that extra dimensions of space exist?  I mean, if I grab a stick and I bend it, it becomes curved with respect to our good old 3D space. The stick needs to be in a 3D space, with respect to which it can be straight or curved.  So, if the thing that gets curved is not an object in space but space itself, doesn't space need to be in "another" space in order to be curved?  I apologize in advance if I used inaccurate terms here, which I most likely did :)
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What level of error do I encounter when approximating the earth as a sphere? Specifically, when dealing with the location of points and, for example, the great circle distances between them.  Are there any studies on the average and worst case error compared to an ellipsoid? I'm wondering how much accuracy I'd be sacrificing if I go with a sphere for the sake of easier calculations.  My particular scenario involves directly mapping WGS84 coordinates as if they were coordinates on a perfect sphere (with the  defined by the IUGG) without any transformation.
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For years I have been very fascinated by the "mystery" aspect of gravity. Functionally, we understand it for our applications, but in my (limited to my 3 quarters of undergrad general physics) understanding, we don't know why it exists or how the "pull" works.   To provide an example of what I mean: there has to be some "measurable material" of gravity between, say, the earth and the moon -- some kind of 'graviton' (not that it needs to be a particle or anything, I have zero claims as to the nature of how gravity does what it does). The [butchered] saying of "pluck a flower and move the furthest moon" originates because gravity in theory, has an infinite range (right?) and moving a flower on earth could maybe move an atom on Jupiter ever so slightly.  Anyway, similar to how we had "very good" hypotheses about the existence of Higgs boson that the LHC 99%+ confirmed, do we have any "very good" hypotheses in regards to the fundamental way how gravity does what we have long-known it to do?