Had physics for 2 years now on highschool, but there is a thing I am wondering about.  You know the in the height above the earth surface around where the satellites are (Or the ISS), I've calculated that there actually is a big amount of gravity-forces, even up there. (9.1 - 9.2 m/s^2) - How come that things aren't dragged down to earth, and why are you even weightless?  Why doesn't satellites fall down more frequently, and does it have something to do with their orbit-speed?  Okay, many questions here, but just a curious guy.
Well, this question has been puzzling me for kinda long time, many people believe that orbiting astronauts feel weightless because they are "beyond the pull of Earth's gravity"...How far from the Earth would a spacecraft have to travel to be truly beyond the Earth's gravitational influence? If a spacecraft were really unaffected by Earth's gravity would it remain n orbit? If so, what is the real reason for weightlessness in orbit?
Best way to get last identity inserted in a table Quickly read the last line of a text file? Looping through files with spaces in the names? I wrote the following script to diff the outputs of two directores with all the same files in them as such:  #!/bin/bash  for file in `find . -name "*.csv"`   do      echo "file = $file";      diff $file /some/other/path/$file;      read char; done   I know there are other ways to achieve this.  Curiously though, this script fails when the files have spaces in them.  How can I deal with this?  Example output of find:  ./zQuery - abc - Do Not Prompt for Date.csv How can I reinstall GRUB to the EFI partition? Was it just coincidence that Tahir Mahmood went on stage? Excel "if-then" formula IF(B4-40&lt;0,0,(B4-40))   Above is my formula to show only positive numbers above 40 in the given cell. If my hours are, let's say, 35, I do not want a value of -5; I want the cell value to be 0. Why is this not working? I'm answering a question with a suggestion to use rename, and I realize I don't know what package it comes from (as part of the answer, I imagine saying something like "if you don't have rename, it's installed as part of [package]").  man rename tells me to SEE ALSO: mv(1), perl(1) - so my first thought is that it was installed with perl.  A related answer, , helps me figure out that the perl package includes prename but not rename - and it turns out that my /usr/bin/rename points to /etc/alternatives/rename which points to /usr/bin/prename  So this is still kind of confusing.  Did /etc/alternatives/rename point somewhere else before I installed perl?  Is there a general way to tell which package something comes from? How to get Text to follow semicircular path, read left to right and oriented counterclockwise I'm using adobe illustrator, and I'm trying to get the text to orient from left to right(counterclockwise) and not upside down but I cannot get it to do that on the path I've created. Im pretty beginner with illustrator, any help would be greatly appreciated. thank you Completion of rational numbers via Cauchy sequences Can anyone recommend a good self-contained reference for completion of rationals to get reals using Cauchy sequences? What happened to the Yin half of Kurama? Did Naruto get both halves of Kurama after fighting Sasuke, or did the other half of Kurama die when Minato was killed? What novel had an isolationist Earth and the rest of humanity in a war of attrition against aliens? I've upgraded from 12.04 to 14.04 via command-line when my system froze, had to do REISUB and dpkg --configure -a to recover from crash after rebooting.  Now everything seems to work except automatically mounting external thumb drives and external hard disk drives. After plugging in said drives, they fail to show up on the left pane and remains unmounted. I can see the device if I run lsusb and fdisk though, so it's possibly to manually mount it but I'd rather resolve why it's not automatically mounting. Is floating point math broken? While traveling in the Berlin Tegel airport (TXL), I wanted to get on Wi-Fi. I found three unsecured networks in addition to a number of password-protected networks.   _Free_TXL_WiFi airberlin Berlin Tegel Airport WiFi   I had no idea which of these were an official Wi-Fi network provided by the airport and which were provided by other people, potentially for malicious purposes like capturing my network traffic. Presumably the official one uses a captive portal to allow internet access.  Is there any way to determine which Wi-Fi network is the official one provided by the airport? Would airport staff such as at the ticketing booths know? Are there official lists available somewhere?  I’d like an answer that is applicable to airports generally, rather than specific to the Berlin Airport. Also, please don’t just give a blanket “don’t use any public Wi-Fi network” answer; I know there are risks associated with it, but sometimes it is a necessity and so I want to know how to identify the airport-provided one.   suggests there are no official Wi-Fi networks, but the answers are six years old, so it’s not clear if things have changed or if none of the networks I saw were official. Bash Script if condition is always true When an option expires does that constitute a buy or sell A similar question recently asked about stock sales and option buys triggering wash sale rules.  If an option expires, is that considered a buy/sale ?  What I mean is: let's assume I have a call option with a target date of August 16. Now I sell the underlying stock somewhere before that (after July 16th). Does that trigger wash sale rules (if the option expires in the money, exercised by default) ?  Is an option expiring out of the money considered a sale ? How to assess the similarity of two histograms? Given two histograms, how do we assess whether they are similar or not?  Is it sufficient to simply look at the two histograms? The simple one to one mapping has the problem that if a histogram is slightly different and slightly shifted then we'll not get the desired result.  Any suggestions? What's the deepest reason why QCD bound states have integer charge? What's the deepest reason why QCD bound states have integer electric charge, i.e. equal to an integer times the electron charge?  Given that the quarks have the fractional electric charges they do, this is a consequence of color confinement. The charges of the quarks are constrained in the context of the standard model by anomaly cancellation, and can be explained by grand unification. The GUT explanation for the charges doesn't care about the bound state spectrum of the QCD sector, so it just seems to be a coincidence that hadrons (which are composite) have integer charge, and that leptons (which are elementary) also have integer charge.   Now maybe there's some anthropic argument for why such a coincidence is useful (in the case of proton and electron, it gives us atoms as we know them). Or maybe you can argue that GUTs naturally produce fractionally charged particles and strongly coupled sectors, and it's just not much of a coincidence.   But I remain curious as to whether Seiberg duality, anyons, some UV/IR relationship... could really produce something like the lepton-hadron charge coincidence, for deeper reasons. I suppose one is looking for a theory in which properties of bound states in one sector have a direct and nontrivial relationship to properties of elementary states in another sector. Is there anything like this out there?   (This question was prompted by muster-mark's many recent questions about fractional charge, and by a  that the hadron-lepton charge coincidence is a "semi-coincidence", which assured me that I wasn't overlooking some obvious explanation.) Two of my friends are getting married. They're both huge Doctor Who geeks, and actually met through a DW RPG. Their wedding invitation contained a very subtle DW reference (you wouldn't have been able to tell unless you were very familiar with the show yourself.)   Doctor Who's been running long enough that there are quite a few nice quotes for basically every occasion in life. I was hoping someone would know a nice wedding-related one, or maybe one about love, that I could include in a wedding card? I am trying to design a circuit and was wondering how to design it that the 12V 800mAH NimH battery I am using will not overcharge. I have researched trickle charging and as far as I understand, a zener diode that regulates the voltage down to about 13.3-13.7V should do. I chose a 14V Zener, taking into account the .6-.7V drop.   I have heard that trickle charging is not the best for the battery, but am not sure how much more work designing a smart charger would take.  I was also thinking of using another diode to prevent flow back to the panels from the battery.         &ndash; Schematic created using  The three voltage sources on the left represent the solar cells, with the NiMH battery on the right.  I was wondering if I needed any additional components if I were to use three 5.5V solar cells in parallel outputting 40mA (16.5V total at 40mA, regulated to 13.3V by the zener) in order to prevent overcharging.  A similar question to mine was asked at  However, this dealt more with a larger lead-acid battery and used a voltage regulator with a schottky diode.   This link discusses almost my exact same question, but I was confused to the answer given which said that up to 1.45V per cell could be charged, taking my max charge voltage up to 14.5V.   Considering I am only outputting 40mA to an  800mAH battery, it seems that I may not need any more battery protection, but would love any input.