So I just read this and it didn't make any sense     It is not necessary for the rocket exhaust to push against anything   EXCEPT THE SHIP ITSELF. You see, when the combustion of fuel takes   place inside the rocket (think of a long vertical cylinder with the   'bottom' open) the exhaust gasses produced expand quickly in all   directions. The molecules slam into anything in their path exerting a   small force each. Thus some molecules push against the 'right' side   and some push against the 'left' side, and all these sideways forces   cancel each other out. Some molecules slam against the 'top' of the   cylinder, but since there is no bottom of the cylinder, there is no   force to cancel this out! Therefore the net force will be in the 'up'   direction.   By the very definition; there would be no movement still. Also engines require oxygen to burn which doesn't exist in a non existent environment. up, left, right, are not directions.
I know Newton's third law of motion might be the answer for this but still I am wondering how the rockets could thrust in the empty space and move in the opposite direction. I guess an astronaut wouldn't be able to push in the empty space with his hands or legs to move himself, but with a rocket engine it's possible. How? What might be the explanation for this in General Relativity?
Assuming I have no infinite scroll or anything else going on in my theme: Is there a way to enqueue my custom Gutenberg block styles and scripts so they are only (lazy) loaded in the front-end when the block is really used? Something like is_active_widget, just for blocks?  If I enqueue them inside a enqueue_block_assets function they're added to any site.  On github, I found this  , but it sounds like it's more on bundling than conditional load, so I still hope they didn't leave that optimization opportunity out - otherwise any other site will soon be junked with 20 additional scripts from numerous Gutenberg block plugins people install and only use once on a page (think of large image gallery block scripts for example).  Thanks &amp; Regards! Why are the number of false positives independent of sample size, if we use p-values to compare two independent datasets? If I run the R code below, it will generate two independent vectors then test them to see if they are related in some way (i.e. p-value &lt; 0.05).  If I repeat this 1,000 times, then 50 of these (5%) will have a false positive, with a p-value &lt; 0.05. This is a type 1 error.  If we increase sampleSize to 1000, or even 100,000, the results are the same (5% false positives).  I am struggling to understand this, as I would have thought that if we collected enough samples, the chance of a false positive would drop towards 0 (just like correlation).  So, I guess my question is: "How is it possible that the number of false positives, based on p-values generated from comparing two independent datasets, be independent of sample size?".  # R code to demonstrate that with a large dataset, we can still  # get significant p-values, purely by chance.  # Change this to 1000, and we still get the same number of false positives (50, or 5%). sampleSize = 20  cat("Sample size:",sampleSize,"\n")  set.seed(1010093) n=1000 pValues &lt;- rep(NA,n) for(i in 1:n){     y &lt;- rnorm(sampleSize)     x &lt;- rnorm(sampleSize)     pValues[i] &lt;- summary(lm(y ~ x))$coeff[2,4] } # Controls false positive rate fp = sum(pValues &lt; 0.05) cat("Out of ",n," tests, ",fp," had a p-value &lt; 0.05, purely by by chance.\n",sep="")  ----output---- Running "true positives - none.R" ... Sample size: 1000  Out of 1000 tests, 52 had a p-value &lt; 0.05, purely by by chance. Remove the extra headers from the e-mails sent do { ... } while (0) — what is it good for? Possible Duplicate:          I've been seeing that expression for over 10 years now. I've been trying to think what it's good for. Since I see it mostly in #defines, I assume it's good for inner scope variable declaration and for using breaks (instead of gotos.)  Is it good for anything else? Do you use it? How to list the properties of a JavaScript object? Say I create an object thus:  var myObject =         {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};   What is the best way to retrieve a list of the property names? i.e. I would like to end up with some variable 'keys' such that:  keys == ["ircEvent", "method", "regex"] Birthday line to get ticket in a unique setup At a movie theater, the whimsical manager announces that a free ticket will be given to the first person in line whose birthday is the same as someone in line who has already bought a ticket.  You have the option of choosing any position in the line. Assuming that you don't know anyone else's birthday, and that birthdays are uniformly distributed throughout the year (365 days year), what position in line gives you the best chance of getting free ticket? Printing out Stack Overflow/Exchange Q&As including comments? How do I make Windows 10's File Explorer open "This PC" by default? I know how to do that on Windows&nbsp;Vista and Windows&nbsp;7, and I know how to do that on Windows&nbsp;8 and Windows&nbsp;8.1, but neither of the ways work with Windows&nbsp;10; it always defaults into the "Home" view.  (I am basically reposting  for Windows&nbsp;10.) What causes the expansion of space? New top bar quick reference guide / Where has the link to  gone? I've had at least one question featured as a "hot network question" and during that time it got thousands of views in the course of a few days. But if you look at that question now you won't have any way of knowing that that's where the bulk of its view count came from.  Is there a way to find out if an arbitrary question has been a "hot network question" or not? A friend sent a long a file (a .rar) he wanted me to check out for him before he installed it.  I downloaded it and unrared it with no problems, but it was full of .exe's instead of the intended contents (fonts) so I advised him to delete it immediately and not use.  I then proceeded to do the same, but the folder simply will not delete. Oddly the files went fine, and I never ran anything, but this is what I'm seeing:   Could not find this item  This is no longer located in C:\Users\This_User\Desktop. verify the item's location and try again.   I've tried the following things with no help:   Using "Unlocker" to Unlock and delete Using move on reboot and rebooting Using PendMoves (from sysinternals) and rebooting Elevating a cmd line, doing a dir /x to get the short name of the folder, and then del 'shortna~1' Moving the folder to a new folder and then trying to delete the parent folder   I'm on Windows 7 RTM, very fresh install. Any thoughts?  Update: Just to confirm, I've run Hijack this and half a dozen other malware detectors, and everything came back clean (no extra processes, no other obvious badness). Rebooting in safe mode didn't help either. Using strtok with a std::string I have a string that I would like to tokenize. But the C strtok() function requires my string to be a char*. How can I do this simply?  I tried:  token = strtok(str.c_str(), " ");    which fails because it turns it into a const char*, not a char* My book tells me that of the solutions to the Lagrange system, the smallest is the minimum of the function given the constraint and the largest is the maximum given that one actually exists.  But what if we only have one point as a solution? How to know whether Lagrange multipliers gives maximum or minimum? How can I take pictures through a skyscraper, airplane, or train window? I find that I take a lot of pictures through skyscraper and vehicle windows (those that are impractical or impossible to open). There are all kinds of problems with taking photographs through windows: reflections from light inside, dirt on the window, etc. My technique mostly involves placing the lens directly on the window glass and shielding it from lights reflecting from above.   Are there any non-obvious gizmos / techniques for easily shooting through windows? I've heard that a polarizing filter might be used in this situation, but I don't carry one around most of the time. Besides, most of the pictures I am interested in taking are in low light situations (at sunset or in a moving train, etc). Is convex surface normal in cast iron skillet? I am new to cast iron skillet. I have cooked with it several times and found the Lodge 12" cast iron skillet has a convex surface which is not observable unless you pour oil on it.  When I cook, the oil move to rim of the skillet and makes the center short of oil. Is it normal?  EDIT: I added the photo of the stove and skillet for reference What function satisfies $F'(x) = F(2x)$? I've found some code that could add a modifier but none can set parameters like Octree. QGIS: ESRI shapefile .shp no longer appears in list of file types under Add Vector Layer I recently installed QGIS 2.18.4 after using ArcMap for many years. I want to add several existing ESRI shapefiles (.shp) created in Arc, to a QGIS project. To add a new layer in QGIS, I select the "Add Vector Layer" button and then click "Browse" to go find the layer. Then I navigate to the proper folder. However, the drop down menu at the lower right of the "Open an OGR Supported Vector Layer" window does not include ESRI Shapefile on the list. The first one on the list is GeoJSON. Everything after "G" appears to be okay (all the way down to "X-Plane/Flightgear") but any file formats from A through F have been cut from the list. Since "ESRI" starts with "E" it does not show up on the list. Strange thing is when I first installed QGIS, ESRI Shapefile appeared on this list. So I must have accidently done something to change how that list is populated and I want to know how to change it back.   If I type in the name of the ESRI shapefile that I know is in the folder, it and all other files starting with those letters appears in the prompt window that appears. And QGIS will correctly load the Shapefile. However, I want to be able to see all those ESRI Shapefiles without having to know and type in the first letter so it will appear in the prompt. I want it to appear in the file type drop down (or drop up?) menu. How to encrypt external devices using a cross-platform solution?