So this is possibly a misunderstanding of the meaning of , but all the Physics texts, sites, and wiki that I've read don't clear this up for me:  In the simplest case with the simplest statement, work is force times distance.  If you push with a force $F_{1}$ on an object that doesn't budge because of friction, you do no work.  If your friend helps push and you still apply the same force $F_{1}$ and the thing moves, all the sudden you're doing work and it's not really because of what you're doing.  Moreover, if you continue applying the same force, and your friend increases her force so that the thing moves faster, and covers a greater distance, again you're doing more work and by no fault of your own.  This just seems paradoxical, and maybe the only sensible answer to this paradox is "Well, the physical notion of work is not the same as the everyday notion of work," but I'm wondering if anyone can say anything about this to make it feel more sensible than just accepting a technical definition for a word that doesn't seem like the right word to use.
I read the definition of  as  $$W ~=~ \vec{F} \cdot \vec{d}$$  $$\text{ Work  =  (Force) $\cdot$ (Distance)}.$$ If a book is there on the table, no work is done as no distance is covered. If I hold up a book in my hand and my arm is stretched, if no work is being done, where is my energy going?
Why does "for good" mean "forever"? A very recent and similar  was closed asks what "for good" means.  While general reference can answer the question, I became curious as to the etymology of the idiom.   around got me nowhere, which is unusual.  The closest I found was a thread in :     OED   for good (and all): as a valid conclusion; hence, as a final act, finally.    15.. Parl. Byrdes Aij, Than desyred al the Byrdes great and smal to mewe the hauke for good and all. 1603 in Crt. &amp; Times Jas. I (1849) I. 25 D’Auval.. is gone for good and all. 1687 CONGREVE Old Bach. I. i, Ay, you may take him for good-and-all if you will. 1711 SWIFT Jrnl. to Stella 4 July, This day I left Chelsea for good, (that’s a genteel phrase). a 1732 T. BOSTON Crook in Lot (1805) 37 He was obliged for good and all to leave his country. 1850 J. H. NEWMAN Diffic. Anglic. 324 Throw off, for good and all, the illusions of your intellect. 1882 W. E. FORSTER Let. To Gladstone 10 Apr. in T. W. Reid Life (1888) II. viii. 421 This morning we released Parnell—not for good, but on parole.   However, this only traces some historical usages, and suggests that for good and all used to be a more popular version of the current idiom.  Is there anything more substantial?  Why did "for good" come to mean "forever"? How to calculate Area Under the Curve (AUC), or the c-statistic, by hand I am interested in calculating area under the curve (AUC), or the c-statistic, by hand for a binary logistic regression model.  For example, in the validation dataset, I have the true value for the dependent variable, retention (1 = retained; 0 = not retained), as well as a predicted retention status for each observation generated by my regression analysis using a model that was built using the training set (this will range from 0 to 1).  My initial thoughts were to identify the "correct" number of model classifications and simply divide the number of "correct" observations by the number of total observations to calculate the c-statistic. By "correct", if the true retention status of an observation = 1 and the predicted retention status is > 0.5 then that is a "correct" classification. Additionally, if the true retention status of an observation = 0 and the predicted retention status is &lt; 0.5 then that is also a "correct" classification. I assume a "tie" would occur when the predicted value = 0.5, but that phenomenon does not occur in my validation dataset. On the other hand, "incorrect" classifications would be if the true retention status of an observation = 1 and the predicted retention status is &lt; 0.5 or if the true retention status for an outcome = 0 and the predicted retention status is > 0.5. I am aware of TP, FP, FN, TN, but not aware of how to calculate the c-statistic given this information. How can I find all files that do NOT contain a text string? What concise command can I use to find all files that do NOT contain a text string?  I tried this (using -v to invert grep's parameters) with no luck:  find . -exec grep -v -l shared.php {} \;   Someone said this would work:  find . ! -exec grep -l shared.php {} \;   But it does not seem to work for me.   has this example:  find ./logs -size +1c  &gt; t._tmp while read filename do      grep -q "Process Complete" $filename      if [ $? -ne 0 ] ; then              echo $filename      fi done &lt; t._tmp rm -f t_tmp   But that's cumbersome and not at all concise.  ps: I know that grep -L * will do this, but how can I use the find command in combination with grep to excluded files is what I really want to know.  pss: Also I'm not sure how to have grep include subdirectories with the grep -L * syntax, but I still want to know how to use it with find :) This might be a duplicate of  but that question is 5 years old and unanswered.  When I'm in drive.google.com and I open a G Suite file (either double-click or select &amp; press enter) in Firefox it opens in a new window whereas in Chrome it opens in a new tab.   Why do they do that? Is this a browser-specific quirk or a Google setting (that I haven't found)? Is there a way to control the behavior? I'd like them both to open in tabs, but presumably the same answer would be relevant in the opposite direction too. Aufbau principle in modern quantum theory Finding the null space of symmetric matrix generated by outer product Let $p, q \in \mathbb{R}^n$ such that $\|p\| = \|q\| = 1$ and define $$A = pq^T + qp^T$$ Find the null space of $A$.    I am not having very much luck. I have managed to show that $p + q$ and $p - q$ are eigenvectors, but I can't seem to connect those two. I know that since $A$ is generated by an outer product, it is of rank one. That implies that the rank of the null space is $n - 1$, but I can't seem to get any further. Can anyone help? Follow a question I've come across a few interesting questions over the last few months on Stack Overflow. They're not necessarily questions I need an answer to, but the questions are nonetheless very interesting, and now I want to know what the answers are.  I don't want to add this question to my favourites because I have my really handy posts in there.   Ideally I would like to have another kind of shortlist to which I can add these posts. I would get notifications just as if it were my own post, without having these as favourites.  What do you think of that? It would be available only for questions, and you would receive notifications just like the author, for new answers and comments on the question (not comments on the answers).  You could browse the posts you're following, as well as stop following them.   The thing is sometimes I come across a semi interesting question and upvote and maybe even comment, but I never hear about it again, because sometimes it's just not interesting enough to remember.  Like I said in the comments, I don't feel like the favourite list is really for this. I want in-your-face red dot notifications for new answers on brand new interesting questions I find. The favourites is for that post with an answer that you know you'll need again. Why is my camera limited to a shutter speed of 1/250th when the flash is up? Sometimes in bright backlight and with large aperture (f2.8) I want flash at high shutter speeds.  But when I pop the flash up on D7000 it caps the shutter speed to 1/250th, which overexposes the shots and makes everything look like a nuclear bomb just went off.  What's the logic behind the limiting of the shutter speed when using flash? Is there anything I can do to get flash  + faster shutter speeds? Semicolon or dash? $$\sum_{n = 1}^\infty \frac{(-1)^n}{p_n}$$ where $p_n$ is the $n$th prime.  I have computed this to 10000 rather than infinity. My results suggest that convergence does happen but it's very slow. But I can't even be sure about the first few digits: $-0.26959$?  I have looked at the "questions that may already have your answer" and some of the "similar questions," but they involve somewhat different formulas. We are developing a C# application for a web-service client. This will run on Windows XP PC's.  One of the fields returned by the web service is a DateTime field. The server returns a field in GMT format i.e. with a "Z" at the end.  However, we found that .NET seems to do some kind of implicit conversion and the time was always 12 hours out.  The following code sample resolves this to some extent in that the 12 hour difference has gone but it makes no allowance for NZ daylight saving.  CultureInfo ci = new CultureInfo("en-NZ"); string date = "Web service date".ToString("R", ci); DateTime convertedDate = DateTime.Parse(date);               As per :     UTC/GMT Offset       Standard time zone: UTC/GMT +12 hours   Daylight saving time: +1 hour   Current time zone offset: UTC/GMT +13 hours     How do we adjust for the extra hour? Can this be done programmatically or is this some kind of setting on the PC's? I clean-installed Ubuntu 11.10 today, and then installed VirtualBox.  This required me to add myself to the vboxusers group, and since 11.10 seems to no longer have a graphical app to add users to a group, I ran the following command:  sudo usermod -G vboxusers stephane   This is a problem.  I now see what I should have run instead is:  sudo usermod -aG vboxusers stephane   The end result is I'm no longer in the groups I should be in.  Including whatever group is required to run "sudo".  When I run any command as sudo now, I get the following:  $ sudo ls [sudo] password for stephane:  stephane is not in the sudoers file.  This incident will be reported.   Is there a way to fix this, or do I need to re-install from scratch again? X, along with Y, "were" or "was"? I was interested in the following sentence which appeared in a   in The Washington Post, Politics, (WHO RUNS GOV).     She, along with Mark Childress, were set to be Daschle's deputies at   the White House before he stepped down.   Can someone clarify if the fragment "She, along with Mark Childress, were set to" is ungrammatical, as I think it is?  I would reword were with was because I think that the subject of the sentence - obviously, in grammatical terms - is "She", not "She" and "Mark Childress", but I'm not sure on this correction.  More precisely, I'm not so sure that "She, along with Mark Childress" is equivalent to She and Mark Childress with regard to the effects on the grammatical numbers. I would like to travel in the USA for a period of 3 - 6 months. But I want to spend some time working for my employer (remote work) and getting paid by the employer. Is this possible under a tourist visa (B1/B2)?  I hope this is OK since I will not be getting paid by a US employer. I am in the IT trade so all that I will be needing is my own laptop and a connection to the internet. The money I earn would actually help me pay for the expenses I get during the holiday. Execute shell commands in Python I couldn’t find any proof on the internet. I would appreciate an elementary proof , but any help would be appreciated!  Thank you. How do I calculate number of hours > 24 in Excel? I've got an excerpt of my spreadsheet below. It's a time tracking application containing a start date/day, a session ID and the duration of the session. Column A is populated by adding the duration in Column D. I'm trying to total the durations, but keep getting incorrect values in cases where the total duration is > 24 hours.  Consider        A                   B        C                D          1  2012/05/22 01:00  |  Wed  |  Session 23341  |  9:00 2  2012/05/23 10:00  |  Wed  |  Session 23342  | 22:00 3  2012/05/25 08:00  |  Fri  |                 |  0:00   As you can see, the date differential between A2 and A3 demonstrates that the value of 22:00 in D2 represents a duration of 46 hours (05/23 10:00 + 46:00 = 05/25 08:00). However, Column D is only displaying the 22:00 in excess of a full 24 hour day.  My attempts to read D2 have included int(d2) = 0.00  /  int(d2)*24 = 0.00  /  hour(d2) = 22.00  /  int(a3-a2)*24 =0.00 etc. and have been unsuccessful in pulling a value of "46".   How can I accurately represent D2 to achieve accurate summary data? Why can't I associate files with Excel after upgrading to 2010? MS SQL Server: Do multiple queries in a batch ever execute in parallel and if so what happens when the second query is dependent on the first? Fly and Two Trains Riddle