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 2d awarded Popular Question Mar 24 revised What is “Dynamical phase transition”? Small typos corrected Mar 24 suggested approved edit on What is “Dynamical phase transition”? Jan 29 accepted Metric components transformation under change of coordinates Jan 29 comment Metric components transformation under change of coordinates This must be a really stupid question but what do you mean substitute in the expression?Make a Taylor expansion? Jan 29 asked Metric components transformation under change of coordinates Dec 9 revised Influence of charged particle's own electric field on itself added 4 characters in body Nov 17 awarded Notable Question Oct 10 awarded Yearling Oct 7 awarded Popular Question Mar 20 awarded Curious Jan 7 awarded Disciplined Oct 10 awarded Yearling Oct 8 comment Why does the sea horizon line always seems to be at the same height as one's eyes? @CarlWitthoft Ah, I didn't know. I only new the word in my language. So looked it up wikipedia in portuguese, looked the same article in english and thought that it was that the word I was looking for ^^ Thank you. I also learned linguistics today. Oct 8 comment Why does the sea horizon line always seems to be at the same height as one's eyes? Hum. I see your confusion. You're schema has one problem: scale. Your altitude will never be greater than the earth radius. Let me make a drawing and gather my comments as a proper answer. Hopefully i'll address your doubt. Oct 8 comment Why does the sea horizon line always seems to be at the same height as one's eyes? Well, no =) The triangle is just a simple visualization tool. Obviously you can pick any other kind of triangle to visualize the setup. The rectangular triangle has one advantage, though, at least for me. It's quick to prove my assertion mathematically if one uses the Pythagorean theorem and the definition of cosine. Oct 8 comment Why does the sea horizon line always seems to be at the same height as one's eyes? @CarlWitthoft English isn't my main language and in my main language we say "cateto" for cathetus. I don't know any other word for it, actually. Out of curiosity, since this comment will most likely be erased, what do you call a side of a triangle rectangle that isn't the hypotenuse? Oct 8 comment Why does the sea horizon line always seems to be at the same height as one's eyes? +1 for a very good question. My suggestion: draw a triangle rectangle with one cathetus horizontal and another vertical (imagine you're are on the top of that cathetus). Now take the horizontal cathetus to be very big. What happens to the angle between that cathetus (horizontal) and the hypotenuse (your line of sight)? Oct 7 awarded Popular Question Sep 17 comment Differentiation in general relativity The index $\mu$ is called a dummy index that's why it can be replaced be any other letter in the (implicit) sum. See Einstein notation.