So, we know that the gravity is responsible for pulling the Moon towards the Earth. But because it moves in an orbit, it makes me think that there must be a force that is causing the moon to travel in the direction other than the Earth's. So it doesn't fall straight to the Earth.
Why doesn't the Moon fall onto the Earth? For that matter, why doesn't anything rotating a larger body ever fall onto the larger body?
Modular Arithmetic - Find the Square Root I have a large hole in a mesh that I'm trying to fill:    I've been trying an approach like this:    I'm finding it quite tough, since the number of vertices around the perimeter of the hole don't match a grid.  Is there a better approach to filling a hole like this? The terminal gave me these errors when updating the software with sudo apt update.    Hit:1 http://it.archive.ubuntu.com/ubuntu bionic InRelease Hit:2 http://it.archive.ubuntu.com/ubuntu bionic-updates InRelease                                                                                        Hit:3 http://it.archive.ubuntu.com/ubuntu bionic-backports InRelease                                                                                      Hit:4 http://security.ubuntu.com/ubuntu bionic-security InRelease                                      Hit:5 http://archive.canonical.com/ubuntu bionic InRelease                 Traceback (most recent call last):                       File "/usr/lib/cnf-update-db", line 8, in &lt;module&gt;     from CommandNotFound.db.creator import DbCreator ModuleNotFoundError: No module named 'CommandNotFound' Reading packages list... Done E: Problem executing scripts APT::Update::Post-Invoke-Success     'if /usr/bin/test -w /var/lib/command-not-found/ -a -e /usr/lib/cnf-update-db;       then /usr/lib/cnf-update-db &gt; /dev/null; fi'   E: Sub-process returned an error code     These are the results of sudo apt install --reinstall command-not-found  Reading package lists... Done  Building dependency tree         Reading state information... Done 0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded. Need to get 0 B/5.188 B of archives After this operation, 0 B of additional disk space will be used. (Reading the database ... 225797 files and directories currently installed.) Preparations for extracting ... / command-not-found_18.04.4_all.deb ... Extracting command-not-found (18.04.4) on (18.04.4) ... Configuring command-not-found (18.04.4) ... libdvd-pkg: Package libdvdcss2-1.4.2-1 was removed, stop processing...   When I tried the command sudo apt update again after reinstalling command-not-found, the results were the same as described in the first text block. Vertical spacing for two consecutive figure environments How to determine if a type implements a specific generic interface type How do you properly use namespaces in C++? File names for JSP include directive to avoid compilation of them How to ignore spaces before footnotes How long does a sequence need to be to be guaranteed to have a monotonic subsequence length k? The sequence 7, 2, 4, 1, 4, 8 has an increasing subsequence length four (2, 4, 4, 8) and a decreasing subsequence length three (7, 4, 1). It has other monotonic (increasing or decreasing) subsequences too, but none longer than four.  How long does a sequence need to be to be guaranteed to have a monotonic subsequence length k? How to do binary calculation？ X Windows special programs: do some of these still exist? I've got a circuit in the basement carrying a handful of outlets.  This circuit has no ground wire.  I want to add a couple of outlets and want them to be grounded.  I may even want gfci outlets on them in the future.  I have no reasonable way of getting a ground wire to the panel but I do have easy access to another circuit that does have a ground wire.  Is it acceptable to borrow or share a ground wire between circuits?  If not, why not?  Both circuits are 20A with 12 AWG wire. Redirect stdout over ssh I would like to run  something &gt; file   on a remote system through ssh, but if I run  ssh host something &gt; file   the redirection is executed locally as ssh etc &gt; file  I've tried it with ' or '' or dd or with a pipe | instead, but I can't get it to work. How can this be done? How to use itemize in Table environment I want to create a table like the picture below, and i wish to itemize the lamba_1 > lamba_2 > 0 using 'item style', which is the cell of each categories. Can someone help me? Why doesn't the command "ls | file" work? I've been studying about the command line and learned that | (pipeline) is meant to redirect the output from a command to the input of another one. So why does the command ls | file doesn't work?  file input is one of more filenames, like file filename1 filename2  ls output is a list of directories and files on a folder, so I thought ls | file was supposed to show the file type of every file on a folder.  When I use it however, the output is:      Usage: file [-bcEhikLlNnprsvz0] [--apple] [--mime-encoding] [--mime-type]         [-e testname] [-F separator] [-f namefile] [-m magicfiles] file ...     file -C [-m magicfiles]     file [--help]   As there was some error with the usage of the file command Changing password? I would like to change my password.  I have followed the instructions in  but I cannot find the "my logins" hyperlink. Theoretically if I were able to build some sort of device that let me sit 1 foot away from the surface of the Sun (or any star for that matter) without being vaporized, would a star produce any sort of audible sound at that distance?   From my understanding, sound waves need a medium to propagate through (air, water, etc).   Does this mean that all stars are completely silent (in the audible spectrum of frequencies at least) as they fuse  hydrogen into helium?   I know stars emit radio, xray, infrared, ultraviolet electromagnetic waves, but how about audible (20 Hz to 20Khz) frequencies?   For some reason it seems like this process would produce some sort of sound. Circuitikz symbols in TikZ circuit library Some time ago, I asked about . wh1t3 wrote: "However, as far as I know there is nothing the circuitikz package does that the TikZ circuit library can't."  So if it is true that the tikz library is more powerful, how do I get all the symbols described in the  using the TikZ circuit library?  Especially I am missing the symbols for ammeters and voltmeters. What is the speed of time? How to determine if $n (n \geq 2)$ given numbers can be summed up to a certain number? I'm interested in knowing if there's a theorem for checking if combinations of $n$ given positive numbers can be summed up to a certain number.   For example, if I was given $n = 2$ numbers, which are $k_1$ and $k_2$, and I was asked if I could make a combination like $n_1 * k_1 + n_2 *k_2 = C$, all $\in \mathbb{N}^+$, I could check remainders to see if it is possible.   However, if $n = 3$ or higher, how could I check if combinations of $k_1, k_2, ..., k_n$ can be summed up to a $C$? Thank you for any inputs!