I don't know if gravity or the speed of the drop would prevent us from jumping, but would something like this be possible?  If it's not possible on the ground, is it possible in the ocean?  I'm sorry in advance if I used the wrong tag. I had a hard time figuring out which tag out of the physics tag to choose. If someone can kindly correct me, that would be awesome.
Imagine you're trapped inside a free falling elevator. Would you decrease your impact impulse by jumping during the fall? When?
Gray iTunes album tracks I noticed that a few tracks from an album appear gray.    The tracks are downloaded, I can play them if I double click them explicitly, but they don't play as part of the album. If I click the album's "play" button, they're skipped (1 gets played, then 3, then 4, etc.)  Why is this happening and how can I prevent it?    I saw a similar question, , but that's not what I'm experiencing — for me, the songs do get downloaded and everything appears to be OK, they just get skipped when playing the album. Proof that in a field $x=0$ is equivalent to $x=-x$ Let $F$ be a field and $x\in F$. If $x=-x$ and $1\neq -1$, then $$0=\frac{x+x}{1+1}=\frac{1+1}{1+1}x=x.$$ This means that the statement in the title is true if and only if $1\neq -1$. But how do we know that $1\neq -1$ for an arbitary field? Can you cast a spell at a higher level, even if it doesn't have an "At higher levels" entry? Many spells have "At higher levels" that provides for more targets or more damage.  For example Magic Missile can be cast as a second level spell and shoot 4 missiles instead of it's 3 as a first level spell.  Can a spell without that verbiage, such as Firestorm be cast in higher level slots for the same effect as the lower level spell? Back when the first discussion about deleted questions came up, I  building an official unofficial read-only archive for good deleted SE content.  I had a plan to build something like this:    Each link would point to a 1:1 scraped StackOverflow (or other SE network) deleted question (of course with a big fat disclaimer to the top, historical data, legal stuff, yada yada yada - and of course after asking Stack Exchange for permission, seeing as this would go far beyond what the CC license allows.)   I also registered a domain name that would (IMO) suit nicely, overflown.org.  However, when thinking about it, I realized doing this properly is a lot of work. You would have to:   build a scraper that can use a 10k+er's OpenID to fetch the deleted question (using the API or the data dump is for wusses. If we go through all this trouble, we want a historical document of what the site looked like "back then", right?) edit the page's DOM to remove dynamic elements, remove the "deleted" CSS classes, remove all the voting abilities from the buttons, and add the "this is historical data" disclaimer fetch - this is the biggest part and applies even if you use the API or data dump - all linked image resources (even those from imgur - even images used only in deleted questions could be purged one day), store them, and link them fetch all associated CSS style sheets and store them intelligently - preferably in a way that you don't fetch a copy of each file for each page (as normal page scrapers do), but also in a way that doesn't break if SE update their style sheets   long story short, I won't be in a position to build this any time in the foreseeable future - with old work, new work, and studying, I really have enough on my plate already.  Of course, if somebody else in the community feels like giving this a try, cool! But what I was really thinking is - maybe this is something Stack Exchange should build after all?   I know Jeff's  on these questions is used to be     @system I did think about a sweet place for them, in the bitbucket. – Jeff Atwood♦ Dec 29 '10 at 1:54   but come on. Think about it:     Future deletion discussions and changes in on-topicness policy would become way more relaxed because the popular and loved stuff has a place to go. A site for "overflown" questions could be curated by selected community members, who decide whether a contribution deserves to be archived or not.  A separate domain name (I'm happy to donate overflown.org for the purpose if desired) and the separate site design would create enough distance to the Stack Exchange network: it would be crystal clear that this read-only archive is for historical purposes only, and the existence of a question there does not mean you can ask something similar on one of the live sites. The pages would be 1:1 scrapes of what the site looked like at the time of the scraping, making it a general historical archive as well. These questions traditionally drive a lot of traffic. The possibility of continuing to show ads in the usual places would allow Stack Exchange to take advantage of that traffic without endangering content quality on the SE network. Hosting an archive like this is a job for a business, not us regular joes. A private project hosted by some community member can go down once they forget to pay a bill, or decide they want to password protect their private blog or photo album. The ideal place to host a site like this is at a company with professional admins that intends to stay online for a long time.    How about it? Confidence interval interpretation in linear regression when errors are not normally distributed I have text file. Task - get first and last line from file after   $ cat file | grep -E "1|2|3|4" | commandtoprint  $ cat file 1 2 3 4 5   Need this without cat output (only 1 and 5).  ~$ cat file | tee &gt;(head -n 1) &gt;(wc -l) 1 2 3 4 5 5 1   Maybe awk and more shorter solution exist... On , I have my favorite tags filter. I setup email notifications for it and now I'm thinking I overdid it on the frequency. Trying to change the settings, I clicked on the edit link in the email notifications box to the right, except nothing happens. There are no JavaScript errors and the HTML for the link is simply &lt;a class=&quot;edit&quot;&gt;edit&lt;/a&gt;. This seems like unfinished planned feature. Update: Using Chrome Version 29.0.1547.66 m Same on Firefox 23.0.1  Both edit links are not working. Further Update Events capture:  Update 2014-02-03: Here's what the subscription tab in the network profile looks like. How to compare the output of \ref to a number? There were so many discussions about an Ubuntu with RR. They were so many pros and contras. At the end ubuntu wont be changed, the 6 month cycle system wont be changed. Thats fine!   But because there are so many people who would like to use an ubuntu with RR Im asking myself why isnt there an Ubuntu Derivate with RR. I couldnt found one, there are a loooot of Ubuntu Derivates but no RR. Is it just impossible? I mean Ubuntu = 6 months cycle, so the derivate have to be a 6 month cycle too? Is there no other option? Or are there already some smart guys trying to solve this problem? Thank you! Let $S = \{ax + by: x,y \in \mathbb{Z}\}$  and let $e &gt; 0$ be the smallest element in $S$. Prove that $e \mid a$, and hence prove that $e = \gcd(a,b)$  I'm afraid I can't provide much of my initial working here because I'm at a loss of how to start.  I suppose that to show $e\mid a$ I would have to show that $eg = a$ for some $g \in \mathbb{Z}$. But I have no idea how I would do this. MySQL cartesian product between two SELECT statements Prove that $f(x)\in \mathbb{Z}[x]$ such that $f(0)$ and $f(1)$ are odd has no integer roots What to do with random effects correlation that equals 1 or -1? Not so uncommon occurrence when dealing with complex maximal mixed models (estimating all possible random effects for given data and model) is perfect (+1 or -1) or nearly perfect correlation among some random effects. For the purpose of the discussion, let's observe the following model and model summary   Model: Y ~ X*Cond + (X*Cond|subj)  # Y = logit variable   # X = continuous variable   # Condition = values A and B, dummy coded; the design is repeated  #             so all participants go through both Conditions   # subject = random effects for different subjects    Random effects:  Groups  Name             Variance Std.Dev. Corr               subject (Intercept)      0.85052  0.9222                              X                0.08427  0.2903   -1.00                      CondB            0.54367  0.7373   -0.37  0.37                X:CondB          0.14812  0.3849    0.26 -0.26 -0.56 Number of obs: 39401, groups:  subject, 219  Fixed effects:                  Estimate Std. Error z value Pr(&gt;|z|)     (Intercept)       2.49686    0.06909   36.14  &lt; 2e-16 *** X                -1.03854    0.03812  -27.24  &lt; 2e-16 *** CondB            -0.19707    0.06382   -3.09  0.00202 **  X:CondB           0.22809    0.05356    4.26 2.06e-05 ***   The supposed reason behind these perfect correlations is that we have created a model which is too complex for the data that we have. The common advice that is given in these situations is (e.g., Matuschek et al., 2017; ) to fix the overparameterized coefficients to 0, because such degenerate models tend to lower the power. If we observe a marked change in fixed effects in a reduced model, we should accept that one; if there is no change, then there is no problem in accepting the original one.  However, let's presume that we are not interested only in fixed effects controlled for RE (random effects), but also in the RE structure. In the given case, it would be theoretically sound to assume that Intercept and the slope X have non-zero negative correlation. Several questions follow:   What to do in such situations? Should we report the perfect correlation and say that our data is not "good enough" to estimate the "real" correlation? Or should we report the 0 correlation model? Or should we maybe try to set some other correlation to 0 in hope that the "important" one will not be perfect anymore? I don't think there are any 100% correct answers here, I would mostly like to hear your opinions. How to write the code which fixes the correlation of 2 specific random effects to 0, without influencing the correlations between other parameters? What are some examples of awkward sounding but grammatically correct sentences? What are some examples of awkward sounding but grammatically correct sentences? Cap colour in IPL If a player is the highest run scorer and at the same time is the highest wicket taker in IPL, which colour cap would he wear? What is the intuition behind the unit normal vector being the derivative of the unit tangent vector? I've seen the math, but... It just doesn't make sense to me. How is the slope going to point perpendicular to the vector that is clearly a straight line not going in that direction? PHP error in .xml file? Does "std::size_t" make sense in C++? In some code I've inherited, I see frequent use of size_t with the std namespace qualifier.  For example:  std::size_t n = sizeof( long );   It compiles and runs fine, of course.  But it seems like bad practice to me (perhaps carried over from C?).  Isn't it true that size_t is built into C++ and therefore in the global namespace?  Is a header file include needed to use size_t in C++?  Another way to ask this question is, would the following program (with no includes) be expected to compile on all C++ compilers?  size_t foo() {     return sizeof( long ); } Number after list name I'm sure this is a really simple setting I'm having trouble finding. If I delete a web part then add it again, there is a number in brackets after the title that goes up by 1 each time. How do I get rid of this? Series of books featuring dragons, enchanted forests, magic swords, etc When I was younger I read a series of 3 or 4 books involving largely traditional mages/dragons/enchanted forests.  I'd like to buy it for some of my younger extended family members but I can't remember the name of it.  Here's what I remember from this:   I read the last book first, in which the son of a woman turned out to be largely one of the main characters in the other books takes an enchanted sword into a forest on a quest to do something. At one point in one of the earlier books the group was travelling through a swamp like area to get to a tower where a witch(or mage lived). There was a king (possibly the son's father) who was frozen in a castle during the last book. The evil mages/witches would melt (but not die) when some spell was cast on them. I read the series circa 1992 (estimated), comparable to the DragonLance series it was geared towards a younger audience (I don't remember any sex/brutal slayings of anyone). I believe in the first book the mother of the son in the last book runs away from home and becomes something of a maid to a dragon. I can't remember if there were evil dragons or not, I seem to remember that at least some of them were good (or at least largely neutral).   If I think of any other details I'll add them.