BASED ON NEWTON'S 3RD LAW my question is based on newton's 3rd law . An elephant pushes a rabbit with $250 N$ force , then the rabbit should also apply $250 N$ force but the rabbit is only capable  to apply $25 N$ force . Why does this happen? . According to Newton's 3rd law the rabbit should also apply this much of force .
Based on newtons third law If an elephant can apply 250N force and a rabbit can apply 25N force , and if they are pulling each other , then elephant will pull with 250N force and according to newtons third law the rabbit should also pull the elephant with 250N force.then from where do the rabbit got the extra 225N i.e.(250-25=225) force??? can anyone please explain.
Create a trigger on all the last_modified columns in PostgreSQL In PostgreSQL 9.5, I have tables with columns in the form   prefix_last_modified timestamp without time zone NOT NULL DEFAULT  (clock_timestamp() AT TIME ZONE 'UTC')   I was looking for a way to set the last modified value automatically updated at each update of the rows, and I found  that defined the function:  CREATE OR REPLACE FUNCTION update_modified_column()  RETURNS TRIGGER AS $$ BEGIN     NEW.modified = now();     RETURN NEW;  END; $$ language 'plpgsql';   Now, I'd like to know if there is any way to pass the column name to the PostgreSQL function and to execute it to the NEW row? E.g.  CREATE OR REPLACE FUNCTION update_modified_column(varchar column)        RETURNS TRIGGER AS $$     BEGIN         NEW.column = now();         RETURN NEW;      END; $$ language 'plpgsql'; Change audio output depending on which one is on I have a PC that is hooked up to my HDTV (via a long hdmi cable) and to a monitor, which is in another room. I have speakers directly plugged to the PC audio out. The PC is next to the monitor and speakers.   I am not sure but I think Windows can play sound on only 1 audio device at a time. And I can only set 1 device as the default output. I can get sound on the TV or speaker depending on which device I set to default. But I would have to do this every time I switch between using my TV or my monitor!   Is there some way to configure such that sound plays through the TV if the TV is on, else it plays in the speakers? If this is not possible, then the next best alternative would be to get the sound to play on both the devices at the same time. I need a list of integers from 1 to x where x is set by the user.  I could build it with a for loop eg assuming x is an integer set previously:  List&lt;int&gt; iList = new List&lt;int&gt;(); for (int i = 1; i &lt;= x; i++) {     iList.Add(i); }   This seems dumb, surely there's a more elegant way to do this, something like the I am planning to travel to India (COK airport, Kerala) from United States. I want to take my laptop as well as my tablet (iPad). Am I allowed to take both in my backpack with my documents related my work. I think I am allowed to take only one computer as per the rule. Will the customs consider my iPad as a computer?  What all I can take?   One of my friends took 2 laptops (1 work and 1 personal) and had trouble at the airport.  Also I am planning to take some wristwatches (7 of them, each avg price is 45 $). I read in a website that I can take stuff up to max 35000 INR. Is that true? In that case, how will I manage my stuff? (Sorry to re-post this, I have lost access to my original account.)  I've recently installed Kubuntu 18.04.3 on a new AMD Ryzen 3000-series-based system. The system is installed on a SATA SSD, specifically on an Ext4 partition, with a SATA HDD formatted in NTFS mounted for storage. The system has been in use for a few days, with a maximum uptime of two days (so far).  My issue is this: the HDD indicator light on the case flashes every 1-3 seconds, even when the system is idle, and there is no obvious reason to access the disk. The flashes are not regular: sometimes the light is dark for as long as 3 seconds (obviously it is difficult to time such short intervals -- I am approximating), sometimes there are a few quick pulses less than a second apart. The flashes seem to vary in duration as well -- sometimes very brief, sometimes nearly a second. Unmounting the secondary HDD does not appear to have any effect.  Some searching lead me to try iotop. I ran sudo iotop -Pao, and waited until 10 flashes of the HDD light had occurred. This is the result:   6887 be/4 root          0.00 B      0.00 B  0.00 %  0.02 % [kworker/u64:1-events_power_efficient]   433 be/3 root          0.00 B      0.00 B  0.00 %  0.02 % [jbd2/sda2-8]  6302 be/4 root          0.00 B      0.00 B  0.00 %  0.01 % [kworker/u64:0-events_unbound]   The "kworker" processes seem to switch between various states, such as "events_power_efficient", "events_unbound", and "events_freezable_power_". The jdb2 process does sometimes write to disk, though that was not observed here (even though, as I said, 10 flashes of the HDD light occurred). The computer was otherwise idle during this test.  My searches also lead me to check /var/log. The result of ls -lth | head is as follows:  -rw-r-----  1 syslog adm             951K Aug 27 19:49 kern.log -rw-r-----  1 syslog adm             594K Aug 27 19:49 syslog -rw-r-----  1 syslog adm             528K Aug 27 19:49 ufw.log -rw-r-----  1 syslog adm              53K Aug 27 19:48 auth.log -rw-r--r--  1 root   root             40K Aug 27 19:15 Xorg.0.log -rw-rw-r--  1 root   utmp             79K Aug 27 18:29 wtmp -rw-r--r--  1 root   root              55 Aug 27 16:28 prime-offload.log -rw-r--r--  1 root   root              30 Aug 27 16:28 prime-supported.log -rw-r--r--  1 root   root            1.2K Aug 27 16:28 gpu-manager.log   I have no experience interpreting log files, so I don't know if anything here is out of the ordinary.  If the kernel version is relevant, the output of uname -r is 5.0.0-25-generic.  My questions are, 1. Why is my HDD light flashing, even though there is no obvious disk activity, 2. Does this indicate some kind of problem with my system that needs to be fixed, and 3. If so, how do I fix it? The light itself does not bother me -- if this is just a sign of a normal, healthy Ubuntu install, then no problem. My concern is that something is wrong, and if so, I would like to fix it.  Thanks in advance for your time.  In response to heynnema (in the original posting of this question), the issue occurs even at the log-in screen, before I log in. So, it is not tied to my user account. However, it does not occur in the BIOS, suggesting that it is specific to Kubuntu (or at least, to the SSD Kubuntu is installed on). I wanted a list of sub-domains of Stack Exchange that are not mentioned over here   Some of the sub-domains I found which were not mentioned are       Are there any other which are not mentioned?    Mentions by , ,             Other mentions below which are not mentioned in "All Sites" but are mentioned in the drop down menu on the top left of the Stack Exchange website         Any other website that's left out ? Why does this CSS margin-top style not work? Partial Sums of Geometric Series The problems that appear in difficult math competitions such as the IMO or the Putnam exam are usually very difficult and require some ingenuity to solve. They also usually don't look like they can be solved by simply knowing more advanced theory and the such.  How do people typically come up with these problems? Do they arise naturally from advanced mathematics (the somewhat infamous 'grasshopper problem' from the 2009 IMO comes to mind - to my not exactly knowledgeable mind this problem looks like it popped out of basically nowhere)? What is the perspective that mathematicians take when seemingly "inventing" these problems with no theoretical motivation to them whatsoever? hotel occupancy counting problem The multiple-choice question:  A hotel has four vacant rooms. Each room can accommodate a maximum of four people. In how many different ways can six people be accommodated in the four rooms? (A) 4020 (B) 4068 (C) 4080 (D) 4096.  My attempt:  If there were no 'four person' constraint, the six people could be accommodated in $4^6=4096$ ways. however, this number includes combinations with 5 or 6 people in one room, which should be excluded.  If one room has 5 occupants, one other room has 1 occupant. The number of '1,5' combinations is ${{4} \choose {2}}$=12. If one room has 6 occupants, the other three rooms have no occupants, and there are four such combinations.  I believe the answer should be $4096-12-4=4080$, but am not confident. I'd be grateful for any comments on my attempt. 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