How can I avoid being overcharged when taking a cab?

Question: I've heard that taxis will frequently scam foreigners by overcharging. How can I reduce the chance of this happening?
Comment: Depends heavily on the location: In Shanghai: too cheap to worry about it. US: Take an Uber, London: take the tube, it's faster and cheaper.
Answer: Contrary to @Ginamin's answer, my advice, based on traveling in Mexico, as well as practically everything I've ever read on the subject, is to never use a metered taxi and always agree to a price up front.
The best prices are usually had when you pay at a kiosk, such as found at a bus station or airport.
Case in point:  Yesterday I arrived in Morelia, Mexico, and took a taxi from the bus station to down town.  I paid at the Kiosk.  Cost:  $35 pesos. Today when I returned to the bus station, I was lazy, and took a metered taxi.  $70 pesos!!!
I've also been ripped-off by a metered taxi once in Tijuana, where the taxi driver kept the meter running while he filled up at the gas station!!!
Taxi meters can also be tampered with to run fast.  Some are distance-based, some are time-based.  Taxi drivers with time-based meters may drive extra slow.  Taxi drivers with distance-based meters may take longer routes.
There are just too many ways to rig a taxi meter, unless you're in a jurisdiction where you trust the local government to enforce fair metering practices.  So my advice is to never use a metered taxi, unless you're in such a place.
The book Travel Advisory, which I recently read, also suggests to always take only official taxis, and always agree to a price before entering the taxi. Never use a metered taxi.
In summary:

Always know a fair price before you look for a taxi.  Ask a friend, or ask a receptionist at your hotel or at the airport what a fair price is to your destination.  If you can't do this, ask multiple taxi drivers before accepting a ride.
Always agree to a price before getting into the taxi.
Never trust a taxi meter. It can be rigged.
Worse, don't trust an un-metered taxi when you haven't agreed to a price first.
When possible, arrange your taxi travel through an official taxi kiosk (usually available at airports or bus stations, and perhaps some hotels)
Ask the locals for any nuances in taxi travel where you'll be staying.
Comment: Depends on the country. In Mexico, unmetered taxis may be a better options, but the exact opposite is the case in, say, Thailand.
Comment: Perhaps this is a bit too anecdotal, but my biggest issue with agreed prices is it inspires dangerous driving. Several times I've been in a traffic jam with a driver and an agreed upon price and his response was insane driving. I've nearly lost a hand to one experience. I never agree on a price because there is no money in traffic jams OR stop lights... but that is just my two cents.
Comment: *shrug. Most meters I've run into charge for time, as well.
Comment: Of course that problem isn't unique to agreed-upon prices.  The same motivation exists when a taxi meter is tied to the odometer.
Comment: In Mexico, most seem to be time based. In the U.S. the only ones I've ever seen were distance based.  But I haven't used much taxi travel in the U.S., so my experience there may not mean much.
Comment: Just time-based? Curious. Most taxis I've been in world-wide have a charge per distance and per time. For instance, Taiwan is 5NTD for .3Km and another 5 NTD for every 20 seconds that the taxi is not moving.  I don't know about US meters either.
Comment: Well I can't swear to it being *just* time-based in Mexico.  Just my casual observation of meters has seemed to indicate that the meter goes at the same speed whether we're moving or not.
Comment: Also, Ive had issues with drivers trying to renegotiate with a pre-agreed upon price, never with a meter. In the Philips and in Russia I've had drivers pull over an demand more money. A pre agreed price may be common "advice" but I so strongly disagree with it. I've even had a friend kicked out of a cab in the middle of nowhere because he refused to pay more.
Answer: Always, ALWAYS get a metered taxi. If the taxi driver says no meter, get a different one. Meters almost always run cheaper than the flat rate taxis.
Also, know where you are going.
I usually have my iPhone with GPS so I can watch where we are going in case the diver decides to circle the block a few times. Getting to know the major street names is also good advice. 15 minutes with a map and a marker and you can save yourself a ton of money.
EDIT: You can ask the desk person at your hotel or hostel which cabs are reliable and trustworthy.
EDIT 2: Also, just a personal comment here. I'm an expat. I've been living in Taiwan for about 4 years now. I speak Mandarin reasonably well and can even yell some stuff in Taiwanese when the occasion calls for it. Yet, I still get scammed sometimes. Over a long enough timeline, it will happen... but the goal is to mitigate the amount of times it happens and how much they get from you.
Comment: Not all cities have metered taxis, and meters are often doctored.  (Ran into one in Delhi once that was running around 5x faster than usual!)  Also, in many cities the fastest route between points A and B is not even close the shortest route, so the GPS will not be helpful unless he's literally driving in circles.
Comment: I wouldn't say that at all. A GPS may not be SOMETIMES useful, but it is far more helpful than sitting there wondering where the hell your driver is taking you. Also, there are typically well represented companies. I'll edit it to point that out as well.
Comment: I have to downvote this, because it's simply not good advice in many, if not most places.  See my answer for more details.
Comment: @Flimzy You are allowed your opinion, but I would beg to differ. As I said, just jumping in a metered taxi is not a good idea. You should always know where you are going and the approximate cost. You let a taxi driver run the meter at a gas station? That is silly. Use a well respected taxi and you will be fine... generally. I would strongly disagree with your arguments, but to each his own, I suppose.
Comment: @Ginamin: Between just jumping into a metered or unmetered taxi, I would clearly choose the metered option.  But those aren't the only two options.
Comment: When I was taking a black cab in London, when we stopped at our destination, the driver kept the meter running and made it increase as we tried to find our money to pay the driver.
Answer: Depends on the country.  Sometimes it's better to use meter, sometimes not.
Here are my tips:

Ask lobby/local how much they think your ride should cost.  If you want, you can take a cab without meter now based on this price.
Do NOT take any taxi that is waiting outside of tourist hotspots/hotels.  In many countries, these guys are the scamming drivers waiting for tourists to walk out.  In some countries, they will even refuse to give rides to locals as they wait for gullible tourists.  Just walk away as far as you can and hail a passing cab down the street.
Answer: During my trip to Costa Rica, we were advised to only take red taxis, as they are metered and regulated.  But even when we got in the "right" cab, the driver didn't use the meter anyway, and so we had to negotiate the fare.
Despite our precautions, the drivers managed to pull a few tricks ("15 Dollars?  No, 15,000 Colones!"), and over the course of the 4-day trip, we still managed to overpay by about $20-25 across all our taxi trips.  Ah well.
From my trip to CR, here's what I learned:

Only use official taxis displaying the correct designation/emblem/sticker/etc.
Negotiate your fare with the driver before you get into the cab.
Make sure both the amount and the currency are agreed upon.
If there is a language barrier, try to learn the language basics before you go and/or bring a friend who is fluent.
Comment: I would say if they won't run the meter get out. Eventually you will find a cab to run the meter. Don't let cab strong arm tactics scare you, stick to your guns ;) In Thailand, I once had to go through 6 cabs before I got one that would actually run the meter.
Comment: Your first point is very clearly a locality-specific one.  I think your other points are very good ones.
Answer: From experience in India, many popular tourist routes are prepaid. The amount is decided by a regulatory authority such as the government or transport commission. For instance, the drive from the airport to destination X will cost only a Y amount of rupees. This ensures that drivers do not (in their own interest) meander their way to your destination in an attempt to drive up meter charges. The prepaid charge is usually paid ahead of time at a kiosk, which then issues a voucher to be given to the driver.
For more custom travel needs, an option is to negotiate a flat daily rate based on duration (and not distance traveled). Again, there are standard rates for this hire in India.
Answer: Finally: If you do realise that you are actually getting ripped off (e.g. the driver is asking for more than was agreed, you realise the meter is totally rigged), remember that the money is in your hand.
You can just get out of the taxi, and you should do so before paying. That way, you are in control of what you pay. Note that this won't work if your luggage is in the back.
Answer: Depends on the country.
Generally, in a place you're visiting for the first time and where scams are frequent, it's better to agree on the fare upfront. This way you will pay more than the ideal metered fare, but you limit surprises and scams.
If you know your way around already or the place is generally civilized and safe (e.g. Western Europe, Japan or Thailand), metered fares tend to be cheaper.
Knowing what the fare is supposed to be upfront helps in both cases, but is especially important with no meter. Looking at a map helps, and hotel front desk might help if they aren't in the business of hawking their own cabbies (in return for a commission).
It's good to know what the official or reputable taxi companies are (if they exist), and how to recognize their cars.
If you're going without meter, always clearly agree the amount and currency up front, and perhaps even write it down. If you have many pieces of luggage, and especially if you place it in the trunk, your bargaining power in case of a conflict is significantly reduced. Have small bills available (cabbies often pretend to have no change), and count your currency carefully when paying (some cabbies switch similar-looking bills).
Answer: In addition to the answers specifically about taxis, you may want to do some research on alternate taxi-like transportation: Uber, Le Cab and similar.


How does the sound of the neck pickup differ from the sound of the bridge pickup?

Question: How does the sound from neck pickup differ from the sound from bridge pickup in an electric guitar?
Answer: The existing answers all have part of the answer, however it is a bit more complex.
As No'am and teodozjan commented, the neck pickup sound is rounder and has more bass, and Tim mentioned vibrations at the neck being bigger so more bassy. But as you'll see from this picture (from Wikipedia) the pickups actually have a different balance of harmonics.

As an example, the middle pickup in this image has 2nd, 3rd and 4th harmonics at a higher amplitude than the fundamental, which changes the tonal quality significantly.
And the neck pickup has a very low 4th harmonic component.
So yes, the neck pickup is generally more bassy, but it's the balance of harmonics that really changes the sound. And that balance also changes as you move up the neck - less so for the bridge  you can see from the picture, but very much for the neck (giving some wonderful tones with barre chords above 10th fret as used by many jazz players)
Comment: I like this answer +1. Never understood, though, why the neck pup is where it is - on my tele, and almost the same on strat, it's impossible to hear the 4th natural harmonic played with the neck pup on, as it's picking up nothing due to the node (no vibration) being exactly there. I also wonder, did Leo put the pups there on purpose, or was it serendipity?
Comment: This is how he earned his Phd. in mayhem!
Comment: Awesome best answer answer one can give!!!
Answer: The sound from the bridge pickup generally has more treble and "bite", whereas the neck pickup has more bass and sounds more "rounded". Each sound has its use.
Answer: Pups pick up vibrations from the strings and turn them into electric signals going to the amp. If a pup is under a string where the vibration moves the string less, as in close to the end, it results in a loss of bass tone. So, even with identical pups, - as in the majority of guitars- the bridge pup is under the part of the string which vibrates less, for the want of a better word, than the neck pup, which is nearer the middle of the string, so will see larger vibrations. So, the sound from it will be mellower, more bassy, richer.
Add in the modern approach of using different pups in each place, often with phasing facility, and it's a whole new can of worms.
Answer: Sound of pickups changes in similar way to picking in different area on acoustic guitar.
Sound from bridge pickup has more treble and it is often used as lead tone and rhythm playing while playing heavily distorted.
Sound of neck pickup has more bass in it sound and is often used as clean rhythm and heavily distorted lead tone.
Gibson called neck pickup rhythm and bridge treble but this was misleading for beginners playing modern music.


Should the comments on this question be deleted?

Question: Given some of our recent discussions on meta, it seems the community is particularly sensitive to moderator deleting comments that are related to moderator behaviour. This question has a "not constructive" flag raised against one of the comments, which has brought it to my attention. It seems to me that all the comments form a discussion that is not relevant to the question, but may be the basis of a useful chat/meta discussion, unfortunately the only options available to moderators is to leave the comments or delete the comments. Should the comments be deleted?
Answer: These without a doubt meet the criteria for deleting comments:

they offer nothing of value to either the author of the post or to future readers.

These are meta-comments about the potential closure of the question. The only vote to close the question has long since aged away. There is no ongoing debate over closing the question (and the question never even came close to bring closed, by moderators or anyone else). The entire conversation is almost two years old.  The person who posted those comments was invited to bring the concerns to meta, and declined to do so.
Given the current vote counts on this question which was about a much more borderline case, I don't think there's any reason to believe that the community majority would want to keep those comments around.
Comment: I didn't notice that it was 2 years old ...
Answer: Here is a second shot at posting what really is an answer to the question.  That answer had a feature which proved to be distracting and controversial, so I am trying again without it.

Moving comments to meta is much less potentially objectionable than deleting them outright. It would be easy enough to keep one or more meta questions open for the purpose of transferring comments that pertain to moderation (and/or other meta issues).
The point of the meta site is to provide a platform for discussions of site mechanics. It is natural that many discussions of site issue begin on the site itself, and I don't like to see discussions which begin there deleted outright. However, "I have moved this discussion of site issues to the dedicated place for site issues" ought not to be problematic to anyone.
Note also that moving such discussions seems easier and faster than wondering whether or not to delete them and especially to having discussions about the suitability of deleting questions.
I do not myself see much of value in the present comments, and deleting comments that are more than a year old and have not been acted upon is not a problem to me. But I think that the general practice of moving comments to meta rather than (or technically speaking, along with) deleting them is a good one. I hope it does not take much more work for moderators to do this. If it does, a streamlined way to move comments to the meta site seems like a eminently reasonable feature request.
Comment: @ff524: Oded's answer to the question you link to says that this feature *has* been implemented in some form.  Is the implementation not suitable for this purpose?  (I would prefer moving comments to meta -- as a veteran SE user, I tend to view the chatrooms as being an afterthought to the entire SE experience, but I'd get over it: somewhere is a lot better than nowhere).
Comment: Since there is currently no tool for moderators to move comments, I object to this suggestion on the grounds that it would be a hassle for moderators. If [this suggestion](http://meta.stackexchange.com/questions/93444/provide-a-tool-for-moderators-to-migrate-comments-to-chat) is ever implemented more broadly, I would gladly use it in place of deletion when warranted.
Comment: @ff524 - "...would be a hassle for *everyone*", not just moderators.
Comment: @PeteL.Clark no the tool Oded talks about is not suitable. It only kicks in if the post is automatically flagged as "having too many comments", which doesn't happen that often on AC.SE.
Comment: What @StrongBad said. By "implemented more broadly" I meant "available on demand" or "available whenever a user has raised a flag." Right now, it's not available often, and when it is, it's almost always in situations where comments shouldn't be moved.
Comment: One of the comments there alluded to the fact that moderators can trigger the tool by goosing the number of comments.  I agree that that is not an ideal implementation.  If you say that it makes it impractical...OK, I believe you.


I'm trying to make my character look big, strong, and imposing, but it always ends up cute and fat. What am I doing wrong?

Question: Here is a quick example sketch:

This is supposed to be a big, strong, evil, imposing demon-sculpture, but to me it just looks a bit too cute and cuddly. What should I be doing to make it look more scary?
Comment: Hey @BenJackson, that's some good advice. I just looked up "[cuteness](https://en.wikipedia.org/wiki/Cute)" on wikipedia. Quite informative. Maybe you should expand that into an answer so people can vote on it?
Comment: Not exactly my definition of cute and cuddly!
Comment: Look up a general description of what humans consider cute and try to avoid it.  Your character has large eyes, a relatively large forehead, a large head compared to the rest of its body.  These are characteristics of juvenile animals that we find "cute"
Comment: @Yisela: thanks for the vote of confidence, but I did say **too** cute and cuddly :). I was going for the spawn of evil, go mad with fear kind of scary, not the big, angry dude who looks like he could knock you out kind...
Answer: I think you are on the right track already with your character. You just need more definition in order to relay the emotion or personality.
See the brown marks I added.

Simply adding facial definition & detail will help bring out the "evil" in the character. Note how the eyebrows protrude a bit more now. More wrinkles at the bridge of the nose makes him 'snarl'. Depth lines around the cheek bones define the face and give some age.
Also, add more detail in the body (i.e. muscle tone) to keep the character from looking "soft".
It's very helpful to have a small mirror handy when drawing so you can mimic facial expressions and positions to find key points draw.
Comment: Hey, thanks. The point about the brow ridges is quite inline with the [wikipedia page on neoteny](https://en.wikipedia.org/wiki/Neoteny#Neotenous_traits_in_humans) - and I think the face wrinkles also work the same way, making the face look older. I think maybe I need to make the head smaller relative to the body, and the teeth larger. I really like the redlining, hope to see more of that on this site!
Answer: Consider reducing the size of the head. It is out of proportion to the body.
If you look at most cute and cuddly cartoon characters, their features are exaggerated to make them look more cute. Most cute characters have overly large heads and eyes…mimicking a baby's appearance.
In this case, your characters does not look cute, however the fact that your character's head is so large may be aligning with big-headed cartoon characters (and babies).
I suspect if you reduce the size of the head a bit, say 80%, you'll get a more fierce looking character.
See here for head sizes and proportions:
http://en.m.wikipedia.org/wiki/Body_proportions
You want to be more towards the adult side of the scale and less towards to baby side.
I also think your character's arms could be a bit longer, they too are a bit out of proportion. One of my favorite drawing books is a book on human anatomy - maybe check out some good anatomy books online/at the library, it will help. Or just Google drawing the human body, etc.
For example (simple scaling reduction of the upper head, and then further reduction of the eyes in GIMP):
Comment: Hey Chsweb, I tried it, and it's a definite improvement. I added the image, without other modifications, to your answer, since I can't post it in the comments. Hope that's ok.
Comment: +1 good answer, many styles of art deliberately put head size out of proportion to get an extreme position on the cute-fearce scale. Eye size is another - large eyes relative to the head size increase cuteness. Fantasy art characters often have tiny (but extremely detailed, prominently placed) heads, and [many styles use oversized heads for cuteness, particularly in Japan](http://graphicdesign.stackexchange.com/questions/18828/)
Answer: You have to revise the proportions.
Google for the proportions comparison of a grown-up and child - the most pronounced difference is the size of the head. Reduce it - after all brute characters are rarely smart ;-)


How the uniformity in exchange rates are achieved?

Question: Suppose it takes 1200 euros to visit Suriname. and I am from India.
Now first i converted 1200 euros to inr which came as 93689 rupees .
Then just out of curiosity, I tried converting 1200 euros to usd first and then
I converted that amount of usd to inr. And i found it came back to same 93689 rupees. Like, it could happen in this way that euros to usd rate is something different so that either I get a higher rupee figure or a lower one. So How come there is the same amount, no matter I convert it directly from eur to inr or indirectly eur-usd-inr ???
Comment: I'm not sure where and how you are converting this. 95000 Euro are about 7.42 Million INR. Your numbers seem way off.
Comment: A grave mistake i committed. Thankx to you. Nonetheless the basic question remains the same.
Answer: If it were different, then this would produce something called "arbitrage". When arbitrage appears, it generally disappears rather quickly as people take advantage of it. For instance, suppose that Eur -> USD -> Inr gave a better rate than Eur -> Inr. Then what would happen is that people would use Eur to buy USD, use it to buy Inr, then use the Inr to buy Eur. They could then cycle through this again and again, making more and more money. This would drive up the demand for USD in Eur and Inr in USD, making those prices higher, until eventually the arbitrage disappears.
It's complicated a bit by transaction costs (I would expect that if you do Eur -> USD -> Inr you'll get a slightly worse rate than if you do Eur -> Inr, because you'll be paying exchange fees twice), but without fees, every path between two currencies should end up with the same rate.
Comment: @vikrantbhattacharjee If you could do all this at one bank, then all the money that ends up in your pocket would come out of the banks pocket. You would assume that they figure this out. Now if one bank in India gives you say 7,500,000 rupees for 95,000 Euros, and the bank next door to it gives you 95,000 Euros for 7,400,000 rupees then one of them will figure out that they are losing money because they can't replace either their rupees or their Euros with the cash you gave them.
Comment: in that cyclic portion, wouldnt the price of Eur in Inr also increase, because people at the same time would love to buy more Eur in order to benefit from arbitrage? and if that happens, then the real disparity would remain the same, just a nominal increase in the figures would continue, isnt it? how should i justify the convergence in prices then?
Comment: Years ago when the Euro was introduced, one department store in Britain accepted Euro notes, paid the change back in Pound Sterling, _and had the exchange rate the wrong way round_. So people went to the store with a €100 note, bought some cheap items and got enough change to go to the bank and buy another €100 note, back to the store and repeat.


How do Jedi leave the Jedi order?

Question: In Star Wars: Episode II: Attack of the Clones, Mace Windu says that Count Dooku is a former Jedi.  Mace speaks highly of him, so it's clear that Dooku left the order on good terms.  Later in the same film, Obi-wan makes it sound like it would be difficult for Anakin to leave the Jedi to be with Padme.  Why would Dooku be able to leave the Jedi order, but Anakin not?  What's the process to do so?
Comment: I always assumed it wasn't that it is hard to leave the order, but that Anakin was special and it would be hard for HIM to leave the order.
Comment: Ask to Ahsoka Tano.
Comment: Yes, New Zealand is far away enough to be used as an acceptable substitute for a galaxy far far away.
Comment: If someone was a discipline issue or for whatever reason disagreed with the council, the Jedi council could ask them to leave the order. This may not necessarily mean they would pursue the dark side. Maybe they wanted to have a family.
Comment: One obvious difference is that when Dooku left, the Jedi were not at war.  In New Zealand, at least, when we are at peace a soldier can resign with three months notice, but once war is declared I presume you're stuck for the duration (couldn't find a reference).  But *my* impression from the movie (which, admittedly, I haven't rewatched recently) was that Obi-Wan was not necessarily saying that Anakin would not be allowed to leave, just that it would be morally wrong for him to do so.  (It is his destiny, yada yada.)
Comment: @Möoz - Or the Gryffindor. Or the Darth Vadoor.
Comment: Wasn't that guy a senator or something? If so, the Council may have let him go in return for him supporting pro-Jedi policies?
Comment: Through the front door, without looking back.
Comment: @Valorum Or maybe through the Dumbledore?
Comment: They walk out the front door.
Comment: They give their managers a two week notice?
Answer: I can't seem to find the exact way that Jedi leave the order (presumably, they would tell the Council they wanted to leave, but this is only a possibility, not necessarily the way that they would leave), but it does seem that Dooku is a special case, as he was of a noble family and he would have had a life that he could return to outside of the Jedi Order. Few other Jedi could say this, most having entered into the Jedi order at a very young age.
An about.com article notes that Anakin could probably have left the Order, but that, had he done so, he probably would have been even more susceptible to Chancellor Palpatine's manipulation and, secondly, would have had no one to attempt to keep him away from the dark side.
Wookieepedia says that the way of the Jedi Order is was a "life-long path" and that "a Jedi usually remained part of the Order their entire life".
Although this answer gives no definite insight on how a Jedi might leave the Order, I hope that this answer might help you to better understand why a Jedi might choose to leave it.
Comment: Thanks, Tony, I was unsure how to put links using a mobile device.
Answer: In the "new order" (in the 3rd Dark Nest trilogy), Luke ask Jedi to leave the order if they cannot put the order as their first priority.
Tenel Ka decides that she cannot be both a Jedi and the Hapan Queen and she surrender her lightsaber.
From the "The Swarm War" book:

"She held out her lightsaber to Luke. "It is with great regret that I must surrender this. I simply cannot fulfill the duties of a Knight in the Jedi order.
I understand." Luke accepted Tenel Ka's lightsaber, then pushed it back into her hand. "But please keep your lightsaber. You earned the right to carry it, and that can never be taken away."

I would assume that when a Jedi leaves, he/she/it will leave all jedi attributes (robe, lightsaber, holocrons, ...) and become a civilian.
Answer: The Jedi have a hall in which they commemorate every Master which has peacefully left the order, i.e turning to the Dark Side means you don't get commemorated, Dooku was commemorated there when he initially left.
This tells us that even if it's harsh only the Masters count and to commemorate every Knight or worse Padawan who left would be a exercise in futility as their numbers are much much greater.
Though I would suspect that it would also be easier to leave the lower on the ladder you are.
The EU showed us that Force Sensitives which didn't make the cut for Padawans, had other less glamorous roles they could fulfil in auxiliary organization to the Jedi Order (healing, education, agriculture) given that these organizations have recruits means that former younglings who didn't make the cut still felt they would have a better life in these organization rather then returning and trying to be a slicer (programmer) for example.
That does not speak well of the non-Force related education the Temple gives its younglings.
Presumably Anakin could have just left the order and married Padme, but remember he went from a lowly slave to Jedi prodigy, the super star of his generation, going from that to even the status of war hero/Senatorial husband was a downgrade.
And of course he sincerely believed the only way he could save his wife was through the Force, without the Jedi's accumulated knowledge it would have been impossible.
References:
Jedi Service Corps: The organization I spoke of which took in, Force Sensitives which could not make the cut for/had the desire to serve in the Jedi Order proper. Interestingly it has it's roots in Jedi who did not want to serve in a martial manner in the last great open war the Jedi had with the Sith.
The Lost twenty: The conditions for getting a bronzinium bust after leaving the Jedi Order are attaining the rank of Master before leaving and not leaving in order to combat the Order (i.e turning to the Sith). The Link stressed that the Jedi did not hold a grudge for them leaving, although that might be slight propaganda and heads right after people left.
Comment: This answer has some good information, but cites to actual Star Wars resources would help improve it
Comment: I added some citations to Wookiepedia :)
Answer: Jolee Bindo left the order to be self exiled. Dooku left and retired back to his homeworld, so it seems as long as the Jedi don't pose a threat they can leave. Granted sometimes people like Dooku slip through the cracks though.
Comment: Ah good old Jolee Bindo. I miss the Old Republic games!
Answer: In the Path Of The Jedi officially licensed book, a Jedi Initiate may leave if he/she fails to pass their Initiate Trials. Same goes for Padwans who cannot pass their Jedi Knight Trials. The Council may also ask a Jedi Initiate, Jedi Padawan, or even a Jedi Knight to leave should the Council not sense the Force as their destiny or working in their future.
So, presumably, If a Jedi Knight/ Padawan/ Initiate asks to leave then the Council would probably have to take a vote (the book also mentions the Council's word as LAW multiple times throughout so,) and then determine if the request should be denied or granted.
I would also guess that should Anakin have asked he would have been denied because of his connection to the prophecy. Should he truly have wished to leave he could have told them about Padme and how he felt he couldn't be a Jedi without her... Even then I honestly doubt they would let him go... Mace Windu would probably vote to have him leave. But he never liked Anakin anyway. In SW:TOR it was mentioned that the Council has allowed Jedi to marry under special circumstances and I feel that being the Chosen One might certainly count towards a "special circumstance". He would more likely need MUCH MUCH more training in letting go, and in controlling his meddlesome visions. Let's face it, Anakins fall to the dark side was only based upon his vision of Padme's death. Padme only dies because Anakin turned to the Dark Side. Anakin only turns to save Padme... Thus the whole vision was redundant. No vison; no turn; no death; no Vader.
Answer: Jedi Apprentice establishes that Obi-Wan nearly didn't become a Jedi at all because no Knights wanted to take him on as a Padawan and set up that Qui-Gon's former padawan had left the order to return to his family and live a life as a noble on his home planet.
During the Clone Wars, Ahsoka Tano was removed from the Order to be tried for treason and was able to refuse readmittance later. Combined with the fact that Anakin was nearly denied entry into the Order period due to being too old set up that not all force sensitives are required to be or even allowed into the Order.
There are also several Jedi, including Kento and Mallie Marek, who left the order to get married, or to pursue other goals, such as Bardan Jusik joining the Mandalorians.
Comment: Could you provide sources for the things you mention? Like the novel titles, episode numbers, etc.
Comment: Also, you're mixing a grab-bag of canons here including references to characters who only feature in "Legends" novels, young-reader books and the various video games.

How do Jedi leave the Jedi order?


How can I make cupcakes lighter?

Question: I'm a new baker and I've had some pretty decent cupcakes but I feel that they are more thicker then wanted. What can I do to make them lighter?
Comment: Welcome! I've removed your general request for help because here we like to focus on specific topics so asking for general advice is out of our scope.  To help us out, can you please let us know the recipe and method for your cupcakes? Without it, we won't be able to tell you what to change to improve them.
Comment: Yes of course I'm sorry it didn't come to mind
Comment: You might want to consider the recipe you're using.  I'd consider going with the approach of chiffon cake.  Whip the egg whites, and then fold them into the rest of the batter.  (you'd mix the yolks in when it calls for the eggs, but it looks like yours calls for whites only)
Comment: And the best advice for baking : get an oven thermometer.  You'd be amazed at how much ovens can vary from what the dial says.
Comment: I am not sure I understood what do you mean by "lighter", especially when contrasted to "thicker". Do you mean you have too few holes in your crumb (they are too dense), or something else?
Answer: My best guess is you are probably over mixing the batter. When you over mix, gluten networks develop leading to a denser and chewier texture.
You should mix the batter until "just combined" which just means until you can no longer see the ingredient you just added.

http://www.cupcakeproject.com/2014/05/what-happens-when-you-overmix-cake-batter.html
Comment: If they want to show real problems w/ over mixing, you have to cut it open.  you'll have this strange tunneling, where bubbles tried to escape but got trapped by the gluten.  It looks like insects have been crawling through.  (it happens most often w/ muffins)

How can I make cupcakes lighter?


Are the verisimilitude and realism tags necessary?

Question: In this question, two new tags were created: verisimilitude and realism. I'm not sure that we need these tags, and I highly doubt we need both. Is there a different tag they should both become synonyms of, should we synonymise one to the other, or should we leave it as is?
Comment: See This Reddit thread: http://www.reddit.com/r/rpg/comments/8xpqa/youre_an_elf_that_uses_magic_you_dont_get_to_talk/
Comment: To be Fair I feel that I should state the question was put on hold because both realism and verisimilitude were deemed to be too broad/specialized historical knowledge outside the scope of RPG.SE
Comment: @JoshuaAslanSmith so should we remove both tags?
Comment: @GMNoob thats my real opinion, that neither tag is appropriate, especially since 2 whole new tags were created that are synonyms on a question that was closed. Didn't post it as answer because I wasn't sure if it would be deemed appropriate.
Comment: @JoshuaAslanSmith I think it's a valid answer. The lack of a tag might be a good hint that a question is likely off topic.
Answer: Here's the executive summary:
No, we don't need the tag(s) now, but we should not kneecap our future selves by informally banning them either.

Here's the actual answer that leads to that conclusion.
Trying to figure out whether we need the tag(s) is a bit like asking which carriage is faster: you can't ask which carriage is faster until you put horses in front of it, and then it's really a matter of which horses are faster. So the first question that should be asked isn't whether we need the tags, it actually is:
Are questions about verisimilitude or realism on-topic?
I'd say they're on-topic yes. They are, as we would expect the terms to get used, inherently about roleplaying games and the use thereof. However, being on-topic isn't enough to make a question acceptable here. RPG plots are also on-topic, but questions about where to find lists of plots are un-acceptable for our site's scope regardless of topicality. In the case of questions about verisimilitude/realism, the most likely thing is that questions will be inherently subjective. So the second question to ask is:
Are there any questions about verisimilitude or realism that aren't Bad Subjective?
I'm fairly confident saying that not every question about verisimilitude/realism is going to be subjective in the bad way. For example, the question that inspired this isn't problematic because it's subjective, it's problematic because it's (maybe) out of scope by requiring real-world poison expertise, and (maybe) too broad for asking about poison in RPGs in general. I happen to disagree with both, but that's beside the point since the point is: neither charge is founded on it being too subjective, and that's not the sort of thing people around here are going to fail to point out when a question is being evaluated for close voting.
So, verisimilitude/realism questions are on-topic, and at least some of them are going to be acceptably objective or good subjective. That leaves a final question:
Do we need a tag(s) to describe and categorise these questions?
I'd say no, with a caveat: I wouldn't go on a witch-hunt against the tag, I wouldn't ban it. My imagination is limited by humanity so therefore my provisional "no" answer is also limited – it's entirely possible that some questions will show up that demonstrate the tag's usefulness. In that case, the site would be poorer for having, I dunno, unofficially banned it or something. We should allow it to naturally show up again so that we have the chance to see if there are any questions that prove its worth. And if there really aren't any such questions, then none will show up. So:
No, we don't need the tag. But we might need it for future questions. Leave it an open question.

That said, should the poison question be reopened, I do think it deserves one of these tags...
If we do need the tag(s), do we need both?
No, we don't need both. Keep one – verisimilitude is the one to keep – and synonym realism to it.
Why verisimilitude instead of realism as the word to keep? "Verisimilitude" means "to have the seeming of realism; to behave in a way that makes sense; to have internal fictional consistency". That's what people mean when they use "realism" in an RPG context, so even when they say "realism", they are actually meaning what the word "verisimilitude" means. Thus, that's the word we should use and synonym to.
Answer: Neither
While both are synonyms and the argument could easily be made why one is better than the other; neither tag should be kept because both were created from whole cloth as part of a question that was ultimately closed for both being too broad (never really nailed down a system or series of systems) and too specific (real-world historical poisons knowledge) and thus outside the scope of the site. People can and will ask verisimilitude/realism questions, but since both terms are very, very vague and their application extremely system specific and tempered by personal opinion they should not exist as tags. Someone looking for answers regarding the verisimilitude of D&D's vancian casting will not be aided by the verisimilitude of Cyperpunk 126.96.36.199.'s Friday Night Firefight System.
Comment: Great answer, much better than mine. I hadn't considered that they might need to be replaced with system specific tags
Comment: @SevenSidedDie Its a vague term not because the meaning of the word itself is vague, but because it means a different thing to each person whereas a tag like D&DNext or Shadowrun5e are much stronger tags. I'm saying a system tag plus a description of verisimilitude is superior to a verisimilitude tag plus a description of the mechanics at work.
Comment: I will grant that it's very system-specific though, so I'm not disagreeing with this answer. Still, people who say it means something different to them than what it actually means are usually just engaging in goalpost-moving shenanigans to win arguments, and don't get a vote in what the word means.
Comment: So basically these tags should be replaced with the system that the question applies to?
Comment: @GMNoob yes, I feel that's the only way to get a real answer that might meet site guidelines.
Comment: On the contrary, "versimilitude" is not at all vague. [It has a very specific definition.](http://en.wiktionary.org/wiki/verisimilitude) It's a good word, and useful. The people who insist on arguing over its meaning have given the illusion that it's vague, but it isn't; those people are just wrong and should consult a dictionary.
Answer: Verisimilitude probably isn't used by folks nearly as often as realism. But instead of getting rid of verisimilitude entirely, maybe just make it a synonym for realism. That way, people searching for verisimilitude will find the relevant topics, and we can condense the two into a single category. Clearly, when people are using either of these labels, they're probably trying to accomplish the same thing.
Answer: I have removed all instances of both.
Answer: Remove verisimilitude. I've never heard it used to mean what this question indicates it means. Nobody will search for it, and frankly, I doubt anyone else will use it.
realism, on the other hand, has actual potential value as a tag, and I would like to see it stay. It's a common term for this context, and one people might actually use.
Comment: See here:  http://www.rickneal.ca/?p=308
Comment: @GMNoob I'm sure somebody uses the term, but I'm not sure it's a commonly-used identifier - if it's not, it wouldn't be good as a tag.
Comment: "Verisimilitude" is a very common word in RPG circles, that is used in contexts where people argue that "realism" is meaningless in a game about imaginary things. (Those people are silly, but that's beside the point.)
Comment: Then we should delete both tags?  Nobody has used either tag before. But the one person who did, thought that both were needed.
Comment: @GMNoob Well, the [tag:realism] tag actually has a clear purpose, in my opinion. I think it makes sense to keep.
Comment: I stand corrected.
Answer: I would get rid of verisimilitude and keep realism. Its a more common, easily recognisable word that people will understand. I would query whether verisimilitude is too narrow a term - how many questions would legitimately use it as a tag? How many questioners would even consider their question needing it?
Comment: see here: http://www.rickneal.ca/?p=308
Comment: Apparently as many questions as need a realism tag.
Answer: I suggest combining them into one tag.  verisimilitude-realism.
Versimilitude is a very common word in some gaming circles (the ones I read), which is used instead of realism.  The reason for this, is that there is nothing "realistic" about a Fantasy world.
But there is no reason to have two tags, as it's really the same idea with one using more accurate language than the other.
See this blog post for more about it:  http://www.rickneal.ca/?p=308
Also this reddit thread
People are more likely to type in "realism" by hand, but by having the hyphenated tag, we can avoid such confusion or debates in the questions, trying to understand what type of "realism" the questioner is asking about.
Comment: I agree with the reasoning but disagree with the conclusion: [versimilitude-realism] goes against every tag-naming convention we use.
Comment: "Verisimilitude vs. realism" is a classic example of "I've redefined this term to be wrong, to force you to use this other term instead!" ["Realism" has a long and storied tradition as a term outside of gaming](http://en.wikipedia.org/wiki/Realism_%28arts%29).
Comment: @AlexP it does, but that has nothing to do with what realism means inside of gaming or rpg culture.  When someone asks "Where are the bathrooms on the air ship?" It becomes a realism question.


Can I compute the mass of a coin based on the sound of its fall?

Question: The other day, I bumped my bookshelf and a coin fell down. This gave me an idea. Is it possible to compute the mass of a coin, based on the sound emitted when it falls?
I think that there should be a way to do it. But how?
Comment: What if it falls on a carpet or sand, not making much noise?
Comment: I made a movie inspired by this: https://www.youtube.com/watch?v=0gedMXoTgTY
Comment: @staticx [indeed it was](http://www.reddit.com/r/theydidthemath/comments/2992yp/computing_the_mass_of_a_coin_based_on_the_sound/), thought the post was familiar when I saw it in the hot questions section
Comment: Meta posts about this question: http://meta.physics.stackexchange.com/q/5908/2451 and http://meta.physics.stackexchange.com/q/5940/2451
Comment: @jt0dd: Reddit or Hackernews might have posted it
Comment: It would depend on the material of the coin, the impact surface, and the environment. As we know, sound travels through a medium. Hence, the frequency and wavelength will vary.
Answer: So, I decided to try it out. I used Audacity to record ~5 seconds of sound that resulted when I dropped a penny, nickel, dime, and quarter onto my table, each 10 times.  I then computed the power spectral density of the sound and obtained the following results:

I also recorded 5 seconds of me not dropping a coin 10 times to get a background measurement.  In the plot, I've plotted all 50 traces on top of one another with each line being semi-transparent.
There are several features worth noticing.  First, there are some very distinct peaks, namely the 16 kHz and 9 kHz quarter spikes, as well as the 14 kHz nickel spike.  But, it doesn't appear as though the frequencies follow any simple relationship like the $ \propto m^{-1/3}$ scaling the order of magnitude result Floris suggests.
But, I had another idea.  For the most part, we could make the gross assumption that the total energy radiated away as sound would be a fixed fraction of the total energy of the collision. The precise details of the fraction radiated as sound would surely depend on a lot of variables outside our control in detail, but for the most part, for a set of standard coins (which are all various, similar, metals), and a given table, I would expect this fraction to be fairly constant.
Since the energy of a coin, if it's falling from a fixed height, is proportional to its mass, I would expect the sound energy to be proportional to its mass as well.  So, this is what I did.  I integrated the power spectral densities and fit them into a linear relationship with respect to the mass.  I obtained:

I did a Bayesian fit to get an estimate of the errors.  On the left, I'm plotting the joint posterior probability distribution for the $\alpha$ intercept parameter and the $\beta$ slope parameter, and on the right, I'm plotting the best fit line, as well as $2\sigma$ contours around it to either side.  For my priors, I took Jeffrey's priors.
The model seems to do fairly well, so assuming you knew the height that coins were dropping and had already calibrated to the particular table and noise conditions in the room under consideration, it would appear as though, from a recording of the sound the coin made as it fell, you could expect to estimate the mass of the coin to within about a 2-gram window.
For specificity, I used the following coins:

Penny: 1970
Nickel: 1999
Dime: 1991
Quarter: 1995

Edit: Scaling Collapse
Following Floris, we can check to see how accurate the model $ f \sim E^{1/2} m^{-1/3} \eta^{-1} $ is.  We will use the data provided, and plot our observed power density versus a scaled frequency $f m^{1/3} \eta E^{-1/2}$.  We obtain:

which looks pretty good.  In order to see a little better how well they overlap, I will reproduce the plot but introduce an offset between each of the coins:

It is pretty impressive how well the spectra line up.  As for the secondary peaks for the quarter and nickel, see Floris' afterthought.
Landing Material
Someone in the comments asked what happens if we change the thing the coins fall onto.  So, I did some drops where instead of falling onto the table directly, I had the coins fall onto a piece of paper on the table.  If you ask me, these two cases sounded very different, but their spectra are very similar.  This was for the quarter.  You'll notice that the paper traces are noticeably below the table ones.

Coin Materials
The actual composition of the coin seems to have a fairly large effect.  Next, I tried three different pennies, each dropped 5 times.  A 1970s brass penny, A 2013 zinc penny and a 1956 bronze penny.

Large Coins
Hoping to better resolve the second harmonic, I tried some other larger coins:

Notice that the presidential dollar has a nicely resolved second harmonic.  Notice also that the Susan B dollars not only look and feel like quarters, they sound like them too.
Repeatability
Lastly, I worried about just how repeatable this all was.  Could you actually hope to measure some of these spectra and then given any sound of a coin falling determine which coins were present, or perhaps as in spectroscopy tell the ratios of coins present in the fall.  The last thing I tried was to drop 10 pennies at once, and 10 nickels at once to see how well resolved the spectra were.

While it is fair to say that we can still nicely resolve the penny peak, it seems nickels in the real world have a lot of variations.  For more on nickels, see Floris' second answer.
Comment: And lo and behold! Coin spectrography was born!
Comment: @alemi how did you compute the power spectra densities?
Comment: This was a while ago, but I believe it was either Welch's method in `scipy.signal.welch` or a basic `scipy.signal.periodogram`
Comment: @MarkBensen That would be interesting to know.
Comment: Would you be able to drop a handful of coins and calculate the sum? (similar to Rainman)
Answer: If you have the dimensions and material of an object, you can compute both the mass and the normal vibration modes. Just the mass is not enough - a large paper "coin" will have a different fundamental frequency than a small tungsten sphere.
A summary of everything that comes below - the result of several edits, and including a nice interaction with the other answer from Alemi:

The relationship between the fundamental frequency of the "ping" of a
coin and its mass is given (approximately) by
$$m \propto \frac{t\sqrt{E}}{f^{1/3}D}$$ where
$E$ = Young's modulus $t$ = thickness $m$ = mass of coin $D$ =
diameter of coin$f$ = fundamental frequency

Here are the details of how I got there...
If you assume that all "coins" are of the same aspect ratio (ratio of diameter to thickness) and made of the same material, then it is indeed possible to compute the relationship between fundamental frequency and mass. From dimensional analysis, if we assume that frequency is a function of

$\eta$: aspect ratio (dimensionless: initially assumed constant for all, ignored)
$D$: diameter ($\text{m}$)
$\rho$ density ($\text{kg}/\text{m}^3$)
$E$: modulus ($\text{kg}/\text{m s}^2$)

Then the combination of the above that gives us units of $1/s$ is
$$f = \text{const} \cdot \frac{1}{D} \sqrt{\frac{E}{\rho}}$$
Combining this with the mass of the object which is proportional with $\rho D^3$, then assuming $\rho$ is constant (so we can take it out of the equation) we get
$$f = \text{const} \cdot m^{-1/3}E^{1/2}\\
m = \text{const} \cdot E^{3/2}f^{-3}$$
In other words - mass decreases with the third power of the frequency for coins with the same material and aspect ratio.
But that is not how US coins work. From the US mint website, I extracted the following:
$$\begin{array}{|c|cl|cl|cl|cl|cl|}
\hline
\text{Coin} & \text{Mass} & & \text{Diameter} & & \text{Thickness} & & \text{Material} && \text{Aspect ratio} \\ \hline
\text{Penny} & \quad 2.500 && 19.05 && 1.52 && \text{Zn*} && 12.53 \\ \hline
\text{Nickel} & \quad 5.000 && 21.21 && 1.95 && \text{Cu-Ni} && 10.88 \\ \hline
\text{Dime} & \quad 2.268 && 17.91 && 1.35 && \text{Cu-Ni} &&13.27 \\ \hline
\text{Quarter} & \quad 5.670 && 24.26 && 1.75 && \text{Cu-Ni} &&13.86 \\ \hline
\text{Old 1c.} & \quad 3.11 && 19.05 && 1.52 && \text{Bronze} && 12.53 \\ \hline \text{* copper plated...} \\ \hline
\end{array}$$
So the material isn't always the same, and neither is the aspect ratio. That's going to make it a little bit hard to prove or disprove the relationship.
Still - let's have a shot at it.  From the experimental data (@alemi's answer) I read the fundamental frequencies as follows:
$$\begin{array}{|c|cl|}
\hline
\text{Penny} &  12.6\\ \hline
\text{Nickel} &  12.4\\ \hline
\text{Dime} &  12.8    \\ \hline
\text{Quarter} &  9.2    \\ \hline
\end{array}$$
Now the interesting two are the quarter and the dime since they have the same material and the most similar aspect ratio (13.3 vs 13.9, so only a 5% difference).  From the ratio of their masses (2.500), we would expect the ratio of frequencies to be 0.74 ($2.5^{-1/3}$). And the observed ratio is 0.72. That is really quite close...
Put another way - if you knew the frequencies for the dime and the quarter, and you had to estimate the mass of the quarter from the dime, you would obtain
$$\begin{align}\\
m &= 2.268 * \left(\frac{12.8}{9.2}\right)^3\\
&= 6.11\end{align}$$
which is an error of about 7% or less than 0.5 g. I think that is spectacular given there is a factor 2.5 difference between the dime and the quarter.
Encouraged by this result, I decided to see if I could get agreement for the four coins given their different aspect ratio and material. Since both bronze and Cu-Ni alloys have a wide range of Young's modulus, I had to guess a bit (all values in GPa):
$$\begin{array}{|c|cl|cl|}
\hline
\text{material} & \text{Range (GPa)} & & \text{Value (GPa)}\\ \hline
\text{bronze} & \quad 96-120 && 110 \\
\text{Cu-Ni} & \quad 120-156 && 120   \\ \hline
\end{array}$$
Next, I had to deal with the aspect ratio. After thinking about this, it was plausible that a larger aspect ratio (thinner coin) would have a lower frequency, so I decided to see what happened if I made frequency dependent on $1/\eta$. This led to the following "expected frequency" formula:
$$\text{expected} = \frac{\sqrt{E}}{m^{1/3}\eta}$$
Computing this with the new mass for the penny (3.11 g) I obtained the following plot for the relationship for each of the coins:

In this plot, the red stars are the numbers (scaled to fit the same chart) that would have been obtained without taking account of the aspect ratio; the blue circles correspond to the values with the $1/\eta$ relationship taken into account. Clearly, this improved the fit. Pretty convincing, given the relatively noisy data...
AFTERTHOUGHT
There are multiple frequencies visible in the sound recordings that @alemi showed. Some of these are easily explained by looking at the multiple modes of a simple circular plate - see for example Waller, 1938 Proc. Phys. Soc. 50 70.
Two images from that publication: first, the vibration modes:

And next, their relative frequencies:

This shows that the first harmonic is 1.7x higher than the fundamental frequency.  Looking at the data, we see that is indeed about right: in fact, for the quarter we are even seeing the second harmonic (at 2.3x of the fundamental).
The question of the splitting of the fundamental frequency is a bit trickier. If you have ever played with an empty coffee mug, you may have noticed that when you tap the rim, the pitch changes depending on whether you tap right across from the handle, or at 45-degree offset from there. This is because there are two symmetrical modes - one where the handle is a node, and one where it is an antinode. The latter has a slightly lower frequency.
A similar thing may happen with the nickel: when you look at the image of a pre-2005 Nickel, you will see that there is more material in the north-south and east-west direction. This means that there are two vibration modes: the one with nodes in blue, and the one with nodes in red:

Obviously, when the blue lines are the nodes the frequency will be slightly higher.
LITERATURE
I found a paper where this is discussed in some more detail - broadly it agrees with everything said above, and even came up with very similar values for the frequencies (measured and modeled). You can read it at http://me363.byu.edu/sites/me363.byu.edu/files/Emerson_Steed_CoinIdentification.pdf
Interestingly, the authors were unable to capture the sound of the penny, although their model suggested a frequency close to the one that @alemi measured (13.1 kHz). They showed the first vibration mode as

which is a nice colorful 3D representation of the mode described by the 1938 Waller paper.
Comment: Late, but hey. Concerning the details of the spectrum the (famous?) article by Kac might be of interest, too: Can one hear the shape of a drum? [The American Mathematical Monthly,Vol. 73, No. 4, Apr., 1966](http://www.jstor.org/stable/2313748)
Comment: @mikuszefski: That is exactly what I think. One can use the wave equation or the eigenvalues of the Dirichlet problem of a cylinder to derive rigorously Floris' ingenious result via diamensional analysis with more details.
Answer: This is not an advertisement.
Under the rubric of "do try this at home", I wanted to share one more thing that I discovered after writing my previous answer - but it is so unrelated to that answer that I thought it better to write this as a separate post.
I discovered two interesting things. First, when you spin a coin on a hard surface, it "rings" with the characteristic frequencies that @alemi observed during a drop. Second, for three dollars you can get an app on your iPhone that beautifully visualizes this. I don't normally plug a product (my only relationship with the maker of the app is that I bought it…), but here I go… The app is called "SignalSpy"; it's only been on the App Store for a few days, and it didn't have any reviews yet. It has four different modes: oscilloscope, spectrum, levels, and spectrogram. Although all four modes are interesting, I found the spectrogram worked best for these experiments.  Here is an example of a screenshot I took when I spun four different gold coins (the Dutch 10 guilder coin - same coin, but different years):

In this plot, the time axis is moving to the left - so new spectra appear on the right, and the oldest spectra "roll-off" on the left. You can see that I spun a few different coins - the last four bands are the four different coins spun one after the other. Most things are quite repeatable: the fundamental frequency is a bright band around 8.2 kHz, there is a faint band at 11, then a cluster of bands around 17.5 - 19 kHz.
To make this experiment work properly, I placed the phone on a granite countertop in a quiet room. I spun the coins about 6 inches from the bottom edge of the phone (where the microphone is on the iPhone 5) - any closer and the "rumble" of the coin rolling on the surface dominates the spectrum. At this distance, I was getting nicely resolved modal frequencies.
I repeated this experiment with 31 different types of coins - the advantage of doing a lot of traveling. Some coins are amazingly consistent - the 10 yen, the Canadian 2 dollar, the half Shekel, … - while others are quite variable. The one that really stood out was the US nickel. In particular, the "mode splitting" that was observed earlier is quite puzzling. On some nickels, it doesn't show up at all; on others, it is very significant. This suggests that my earlier explanation (modes relating to the relief on the coin) can't be the whole story. And yes, I did check that the orientation of the face and the building (Monticello) is consistent across all the coins.
I have tried to measure whether there was a difference in roundness (an elliptical shape would cause mode splitting), or in planarity (if the coin is not flat you would expect mode splitting). Within the accuracy of my digital caliper (nominally 0.01 mm), I could see no obvious effect that I could trace to either of these, but I'm going to try to repeat this experiment when I have access to more accurate measurement equipment - both to measure dimensions and weights. That might be a while though.
Let me show you what the spectra of a collection of nickels (sorted approximately by a degree of splitting) look like:

I did not spin all 20 coins in quick succession - in fact, this is a composite of several screenshots I took on my phone, and I added the larger scale on the left to help measure the peak positions.
I discovered an interesting factoid about the nickel - by law, its weight is allowed to vary quite a bit - with a nominal mass of 5.000 grams, it has an allowed tolerance of 0.194 gram (see http://www.law.cornell.edu/uscode/text/31/5113). I have not had the chance to get the detailed specifications of all the coins I measured - when I do, I will evaluate my formula above and see whether the formula I had derived earlier holds over a wide range of sizes and materials. I am hoping that the aspect ratios will be sufficiently different that I can explore whether the "linear in $\eta$" assumption is true or not.
I am sharing this in the hope that others will start experimenting - this is a really easy and cool experiment to do. The app works on the iPad as well.
Comment: An equivalent app for android devices is [Spectral Audio Analyzer](https://play.google.com/store/apps/details?id=radonsoft.net.spectralview), which is free to use and pretty flexible, though there are [several other choices](https://play.google.com/store/search?q=spectrogram&c=apps&hl=en_GB) which I haven't tested.
Comment: There's also phyphox ([website](https://phyphox.org/), [fdroid](https://f-droid.org/en/packages/de.rwth_aachen.phyphox/), [google](https://play.google.com/store/apps/details?id=de.rwth_aachen.phyphox), [apple](https://apps.apple.com/us/app/phyphox/id1127319693)), which gives you access to all sorts of sensors on your phone.
Answer: I don't mean to take anything away from the previous great answers, but the "simple and to the point" answer is, a very qualified, yes.
By qualified, I mean one must know the coin's composition, thickness, diameter(or shape), density distribution, country of manufacture, etc.  If we make assumptions and restrictions, then it becomes possible to calculate the mass of the coin (to some degree of accuracy), from its "ping" frequency. The formula to use, is the one provided by Floris.
Comment: If we know thickness,
diameter(or shape), density
distribution, we don't need frequency to measure mass of coin. Simply use M =DV.
Comment: @AnubhavGoel true, but the question is if, by hearing and recording  the sound of a coin you can know what coin is . The question is not about measuring the mass of a coin.
Comment: @anna v I read question again and it is about computing mass.
Answer: I think that the main question is somehow connected with energy equation $E=m c^2=\hbar \nu$. In turn my answer is connected with the question 3D Elastic waves in a glass. My first impression was that coin exabits some elastic deformation after collision and that this deformation can be analyzed with using eigenfunctions. Really, several tested cups and glasses are shown spectrogram with highest picks related to eigenmodes as demonstrated in Figure 1.

But coins actually not follow this rule. Sound from impact of coin with some
wooden, metallic or stone object has very low frequency compared to the main mode as it shown in @alemi answer. Also we can use sound tracks to distinguish coins, it is not so precise as in a case of cups or glasses. Nevertheless we could discus some detector of coins to make sound more related to individual coin. As detector we may use, for example, metallic box like a tin. As we put coin in a can and shake, then it produces very specific sound for every coin. For example, I have tested  3 Canadian coins - quarter, 1 dollar of 2018 and 2 dollars of 2005 in an empty tin from Akbar Ceylon tea. There are 3 very different sound tracks shown in Figure 2

Therefore we may conclude that every coin produces specific sound but it is not related to the mass only. In Figure 3 shown equipment I have used for my experiment - empty tin, computer and coins.

Note, that Canadian coins 1 dollar and 2 dollars have very special design - see Figure 3. Nevertheless I try to compute eigenvalues using my code published here - see Figure 4. The first 3 modes for quarter and  loonie  are very close (values in Hz are shown over figures) while masses are differ - 4.4 g and 6.27 g respectively. It is why we can't use sound from impact only to distinguish  them. On the other hand they have different sound in a can - see Figure 2.
Comment: I'd like to add that this question is definitely *not* connected with $E=mc^2=\hbar\nu$. This equation relations energy to rest mass and in turn relates the energy to the frequency of a matter wave. Matter waves are quantum mechanics and we are dealing with classical objects. Plugging in the mass of one gram gives a frequency of the order $10^{47} \text{Hz}$ which is way too high to be relevant here.
Comment: @AccidentalTaylorExpansion I think that somebody could understand sense of humor in my post :)
Answer: Coins of different composition and shape will give different sounds . Lets consider simillar shape and compostion of coin, and changing only its mass. Also it falls from same height and on same surface.
Let the coin is metalic (iron).
When it falls on surface it will produce noise. By law of conservation of energy, heavier the coin more the potential energy will be converted in kinetic energy and more will hence be sound by striking down.
Hence you just need to measure its amplitude in decible to know its sound.
PS: You can also use duration of sound, as they will also vibrate and produce sound for different time intervals
PS2: Changing composition of coin will produce different frequencies, which can again be easily measured and then callibrated by amplitude.
Answer: The answer to this is yes .
If the coin dropped on a drum it would sound a note whose amplitude would be proportional to its mass since force on stretched drum surface would be proportional to mass.The drum obeys Hooke's law force is proportional to extension.
Get a decibel meter!
Answer: Basically, the answer is yes if sound generation is the only thing that's causing energy loss when a coin drops from a height and smacks into something massive like the ground. How? Well, in this scenario, all the energy loss happens as sound. In this ideal inelastic collision scenario, where there's only sound as the energy loss (no friction, no heat, no squishing), the sound energy made is equal to the kinetic energy the coin had just before it hit the ground. If you drop the coin straight down without spinning it and giving it a push, its kinetic energy is just from its fall, which equals its initial gravitational potential energy ($m.g.h$). Here, $m$ is the coin's mass, $g$ is gravity, and $h$ is the height. Now, we find $m$ via $mgh = S$, where $S$ is the total sound energy released.
But what if the coin starts spinning when you drop it (if you accidentally give it some rotational energy)? In that case, the equation becomes $mgh + R(m, d) = S$, where $R$ is the initial rotational kinetic energy given to the coin, depending on its mass ($m$) and diameter ($d$) via the inertia moment $I$ of the coin. If you also give it a little shove initially (giving it some speed), then the equation becomes $mgh + T(m) + R(m,d) = S$, where $T(m)$ is the initial translational kinetic energy given to the coin.
So, theoretically, you could figure out the mass of the coin just by measuring the total sound energy released and using the above equations. But in reality, it's almost impossible to track $T(m)$ and $R(m,d)$ in every situation as they are also material dependent, so the practical answer is probably NO. Hope this helps!


Is there a media-handling module that can handle midi files?

Question: I've been using MP3 Player to provide an on-page mp3 player, but I also need to be able to handle midi files. Right now the best I can do is allow them to be uploaded into the "mp3 file" field, but when it renders the node, it just gives a link to the file, which mean you have to navigate to the file (or open it in a new tab) for the browser to play it.
Answer: MIDI files can be embedded straight into the page with the <object> tag, so there should be some way to then output that with the link that views gives you at the moment. If you went with a separate field then it's be easy enough to do with Views output rewriting.
After a quick look for a flash solution, it seems that flash itself doesn't have any support for MIDI, so a flash based player is unlikely.
Comment: On top of this, you could simply write a Custom Formatter (http://drupal.org/project/custom_formatters) to output the FileField you use for your MIDI files with the  tag or any other HTML wrapper you'd like to use.
Answer: If you actually want a module to do this, you can look at the Audio module. However, this module is currently said to be "unstable", even though over 3000 sites report having it installed. So with that many users it might be worth taking a look at anyways. The author also has an alternative suggestion using FileField and SWF Tools modules.
Answer: You can use the Media module in conjunction with either MediaElement or the MediaFront module to handle MP3 files.


Firefly - getting rid of parts (dumping cargo)?

Question: I just played Firefly the board game for the first time. I ended up with a ship modification that made spare parts invalid, but I had about 6 of them in my cargo hold. I was on a supply planet and wanted to buy fuel, but all of my cargo and stash spots were full. I looked for any thing in the rule book that talked about selling the spare parts (or dumping them)...couldn't find anything. What's protocol for getting rid of fuel or parts to make space?
Answer: From the official FAQ,

Question: How do I get rid of stuff on my ship I don't need or want anymore?
Answer: On your turn, you may dump Fuel, Parts, Cargo or Contraband at any time. You may drop Fugitives and Passengers off in any sector with a Planet. You can't toss them out the air-lock in deep space! This does not use an Action and can be done during another Action, on your turn.

You also have the option to trade with other players. From the rules,

When two or more players' ships are stopped in the same Sector, players may buy, sell and trade Crew, Fuel, Parts, Cargo, Contraband, Ship Upgrades and Gear to one another without restriction. Players are free to discuss and make these deals outside of the normal turn order and other players may take their normal turn while bargains are struck. Dealing with others players in this fashion does not require using an Action. The opportunity for Trading ends when one of the players leaves the sector.

There doesn't seem to be any option of selling back to the house, but we house-ruled they can be sold off at half-price at Suppliers. This has allowed people that would otherwise have been eliminated from the game to keep on playing.
Comment: Your house rule is of course fine, but if you felt it was necessary, did you by chance miss the "make work" rule that allows you to take $200 for a Work action on a planet?
Comment: @sitnaltax, No, I am aware of it.
Comment: Thanks. We used a house rule that it could be part of a buy phase, but will make it part of any action in the future. i also like the idea of the sell at 1/2 price when on a supply planet.
Answer: You can space (dump out the airlock) anything, but you cannot dump passengers or fugitives unless there's a planet in the sector.  There is a crew member you can hire that allows you to sell parts to any solid contact, in addition to cargo and contraband.  You can also buy, sell, or trade any of these items (or fuel) with another firefly in the same sector.  These are the only ways to get rid of items in your cargo hold and stash.
Spacing things, selling to contacts, and trading with another firefly does not require an action, and can be done even if it's not your turn.


Cannot open my external hard drive anymore

Question: I was using it to back up two laptops: an IBM ThinkPad running Xubuntu 11.10 with a Qimo session, and an LG R200 running Ubuntu 11.10.
I had previously backed-up both computers, several times using Deja Dup, into separate folders onto the Seagate hard drive. At one point, I copied some files directly into another folder on the Seagate, from the R200 without using Deja Dup.
I was in the process of copying some of these files again and got an error message that there was something wrong with a file and the Seagate hard drive is blocked. I tried to do a regular back up using Deja Dup and got a similar error message. The same when I tried to back up the ThinkPad.
How can I get my Seagate 2TB Expansion Drive to work again?
The error message was this or similar:
Error mounting: mount exited with exit code 13: $MFTMirr does not match $MFT (record 0).
Failed to mount '/dev/sdb1': Input/output error
NTFS is either inconsistent, or there is a hardware fault, or it's a
SoftRAID/FakeRAID hardware. In the first case run chkdsk /f on Windows
then reboot into Windows twice. The usage of the /f parameter is very
important! If the device is a SoftRAID/FakeRAID then first activate
it and mount a different device under the /dev/mapper/ directory, (e.g.
/dev/mapper/nvidia_eahaabcc1). Please see the 'dmraid' documentation
for more details.

Comment: What is the actual error message?
Answer: I had this happen recently. For me ntfsfix worked.
First, open a terminal and install ntfsprogs
sudo apt-get install ntfsprogs

Then to check and fix the NTFS drive with this command:
sudo ntfsfix /dev/sdb1

where /dev/sdb1 is the location of your drive.


MIDI keyboard for sound design

Question: I just moved and don't have my Casio Privia at my disposal. Right now I'm on a pretty tight budget and am looking at either the M-Audio Axiom 25 or Oxygen 25. Does anyone have any experience with these keyboards or have any other suggestions? Thank you all!
Answer: I'm afraid that I don't have experience with those specific keyboards, although they're pretty commonly used ones. I use the first-generation Novation Remote25; it's festooned with knobs and sliders, but the MIDI controller assignments and setup is a real pain. A real control surface separate from the keyboard is more ideal, but if you lack a specific control surface, it can offer at least some faders and pots. But be sure to check out how easy the keyboard's controls are to customize, and how many settings you can save!
Answer: I have an older Oxygen keyboard, and I like it okay -- the one thing I feel I'm always missing when I compose is decent drum pads.  I'd say go Axiom.
Answer: We have over a dozen oxygen 8s all of which are still going strong, some of which are the original midiman model. Whichever model you buy the m-audio keyboards are a safe bet.  If you play the piano the semi-weighted keys on the axiom are a lot better. If you don't play the piano then the lighter oxygen keys will help when you need to trigger samples quickly.
Answer: As a guitarist I put my eye on AKAI MPK Mini - looks like very flexible controller to put short phrases, bass lines, parameters changes
Answer: I use an Akai LPK25.  It's good for jotting down ideas but I wouldn't really use it to record entire (timed) parts that often.  Has a great arpeggiator though.  It's a very basic keyboard designed for portable use, but it has much better feel and velocity response than all others in its class, and has a cool arpeggiator.  The rest of the time, I just use my Korg MS2000 as a MIDI controller if I need to.  Amazing synth!
Answer: Thanks for all the suggestions. I think I'm going to go with the Axiom 25.

MIDI keyboard for sound design


How do I draw a portion of a texture onscreen in OpenGL?

Question: I have a sprite sheet loaded as an OpenGL texture, and I'd like to draw a portion of that texture sequentially for animation. Is there an actual OpenGL command to draw part of a texture? I can get it done by modifying the U and V components when drawing the texture, but I'm not sure if there's a more elegant/correct method of doing this.
Answer: Using a part of the UV space is the "correct" way. It's used for almost every full screen operation (except clear and some resolve ops). Avoid blitting and tex copy as much as you can.
Using UV and geometry gives you a lot of flexibility, you can rotate/zoom images and batch together sprites that share the same atlas. Just be careful about pixel center and filtering so that sprites don't bleed into each other.
Answer: Set UI transformation matrices, set U/V/vertex coordinates for quad, draw. Nothing more to it, really.


Can the skills shown in Kuroko no Basuke be achieved in real life?

Question: I recently started watching Kuroko no Basuke and have watched it up to episode 5. The skills shown up till now are ridiculous. Can those skills be achieved by people in real life? I'm taking about physical abilities like speed, jump, agility, etc., not stuff like the Phantom Pass.
Comment: I'm voting to close this question as off-topic because it is an out of universe question
Comment: See http://meta.anime.stackexchange.com/questions/808/is-anime-physics-a-tag-we-should-keep
Answer: Seeing as you're on episode 5, this is going to have spoilers.
While the "Misdirection" which makes him invisible is probably at least rooted in reality, I don't think it can be taken as far as the TV series makes it out to be. It would be one thing to misdirect someone who's defending, but to make yourself invisible to people watching from the crowd or the bench is a little bit incredulous.
The "Invisible Pass" is something that is described as more of a "tap pass" and it uses misdirection. That's probably something that people do in real life, though again, maybe not to the fantastic results we see in the show.
The "Ignite Pass"/"Ignite Pass Kai"/"Cyclone Pass" are probably things that you could see basketball players do, but the way they're animated and the speed in which they're shown in the show makes it impossible in real life.
The "Vanishing Drive" is another misdirection, and like the first invisibility misdirection, it's probably something people can do in real life against a defender, but everyone else in the arena would obviously still be able to see the player. In the show, it makes it seem like Kuroko goes right through the defender for everyone, not just the defender.
The "Misdirection Overflow" is clearly something that can't be done in real life given how spectacular the effect can be. The explanation of how this trick works isn't sufficient in making players "disappear" and trick everyone. Stuff like this make Kuroko seem more like an illusionist instead of 1 among 10 players on a court.
The "Phantom Shot" is really just an odd way of shooting the ball. It's something people can surely do in real life, but why would they if they can shoot normally? It's unique in the show's story because Kuroko can't shoot.
I think that's as far as they've gotten so far in the anime.
Comment: thanks but what about other stuff except these special moves like the speed they move and turn at is that possible
Comment: @NoLifeKing That's harder to say, for the most part, the regular basketball looks no different to me than watching NBA highlight reels so I don't see why not.
Answer: Many of Aomine's formless shots are unachievable outside the realm of lucky. Midorima's shot arc is excessive but the half-court shot (without the crazy arc) is within reason. Murasakibara's quickness and speed can be explained, but that crazy power with that body frame is insane. Akashi's emperor eye. A good eye, tons of experience, and athletic ability. Kise's Copy... well, there's plenty of people out there that are like that. The zone is explainable, but the reasoning on how it can be "tapped" into (in the anime) is dubious.
My two cents on Kuroko's misdirection and Misdirection Overflow:
Most coaches and players define misdirection as putting their attention on themselves to create space for others (which is Overflow). Kuroko's misdirection if applied in real-life only allows for, at most 3 1/2 feet of separation. It's almost unbelievable to shake somebody's line of sight that it distracts the defender to lose sight of their mark entirely.
Physical abilities alone, outside of the generation of miracles, they're all normal (and achievable). Hyuuga's streaky shooting, Takao's Hawk Eye, Kasamatsu's speed, Kiyoshi's right of postponement... They are all within reason
Watch a Japanese basketball game... There's a great disjoint on how basketball is played in Japan in real life and Japan in the anime world.
Answer: I think misdirection can be achieved by learning, because if you learn to constantly use silent steps and slide your feet for a moment, you'll eventually get the disappearing down. Since it's on a daily basis for me, it's like being an assassin or ninja being sneaky. That's my conclusion.
Answer: Highly possible to do all of these things, including the phantom pass. Though, your height and the strength in your legs would have to be incredible to pull of the jumps and continue running as they do. But all can be achieved, the phantom pass is more of an actual technique used in basketball.
Though you won't see something like that used often, coaches teach fakes more than they do misdirection. It requires no ball handling; well at least almost none. If you want to achieve misdirection, most is natural. The misdirection or 'phantom pass' used in Kuroko no Basuke, is most achieved naturally.
It's not something easily taught, I can naturally use it. It's as simple as a fake, maybe even easier. Stay invisible until you know you have a chance to score, call for a pass earlier to who you plan to pass to you. Once you arrive at the rim, almost like a phantom, the players not paying attention to you. Jump at the rim, since you are most likely to be blocked at a shot, put your hand up if above your shoulder and grab the ball, in that instant, shoot it back over your shoulder to an open teammate on the three point line or one with a defense who doesn't expect you to do so. If the ball is passed too low, lower your hand to the ball, the palm of your hand facing behind you. After you feel the ball in your hand, either grab and pass in that instant. Or you can hit it back down in an instant to your teammate, just like above, open or with a defender who doesn't expect it.
For jumping, it's just like in the anime, train the strength in your legs, hauling things back and forward on sand. Leg workouts of any kind, you'll be able to jump in no time. I've got an insane jump but I have to jump over and over, just like in the anime. Kagami's jumps only get higher. You start using more and more strength to put yourself into the air, realizing you need to use more strength. Your body responds to this and launches you higher.
The agility is possible, but very-very hard. The speed is the same as anything else, work your legs, train on getting faster, and the higher you raise your stamina, the faster you'll be able to run, as well as maintain the speed. Sorry for the 10 page long response. But it's not really easy to explain how all of the skills you mentioned can be obtained, as well as performed.


What are the security benefits or risks of HTTP/2?

Question: Since HTTP/2 is starting to get adopted by more and more sites everyday. Are there any security benefits or known risks regarding HTTP/2?
Comment: Multiplexing should make traffic analysis slightly harder.
Answer: RFC 7540 Section 10 is a security consideration section that documents a number of security considerations when implementing and/or using HTTP/2. Briefly:

10.1.  Server Authority
10.2.  Cross-Protocol Attacks
10.3.  Intermediary Encapsulation Attacks
10.4. Cacheability of Pushed Responses
10.5. Denial-of-Service Considerations
10.5.1. Limits on Header Block Size
10.5.2. CONNECT Issues
10.6. Use of Compression
10.7. Use of Padding
10.8. Privacy Considerations

Most of the regular security considerations for HTTP/1 are also still valid, as HTTP/2 has the same application level semantic as HTTP/1.
Answer: From a cryptographic point of view, HTTP/2 requires to support at least TLS1.2 which means the communication channel will be encrypted using AEAD ciphers i.e. state-of-the-art crypto.


Any way to specify a non-returned value for an RKEntityMapping?

Question: Because I am working with a non-KVC REST service I have a need to designate a bool attribute isSpecial by the request URL rather than by any of the returned JSON. For instance, if I make the request http://www.service.com/GetObject?isSpecial=no then I would like to specify that the attribute isSpecial is NO. Now I can probably accomplish something to this effect by adding multiple response descriptors, one for each of GetObject?isSpecial=yes and GetObject?isSpecial=no, but then I need to have a way of defining a special attribute mapping - I am not mapping attributes from key paths to key paths, but rather by request URL. How might I accomplish this?
Answer: You could look at using routing with path patterns and using the pattern meta data during mapping. I'm not sure you can pull out the queries individually so you may need to have a method on your managed object subclass which takes the meta data and extracts the parts you want to store.


Can a relatively small subset of random numbers be permuted and reused and still guarantee good expected running time for an algorithm like quicksort?

Question: So this is sort of a general question but I'll limit the discussion to randomized quicksort to make it clear. Suppose generating "true" random bits is hard, e.g. because it requires measuring something in nature that can be considered essentially "random" like the 50th binary digit after the decimal point in wind speed at some location recorded in miles per hour. Or maybe quantum outcomes observed that can be considered truly random. Whatever. So we do the following: We generate $k$ "truly" random bits and then we re-use these $k$ bits over and over by using a pseudo-random number generator to permute them. In terms of $k$ (the number of initial truly random bits) and in terms of the total count of numbers to be sorted, $n$, and assuming the permutation algorithm of the $k$ initial random bits repeated over and over is known to an adversary, can we assert that an algorithm like quicksort will have good worst-case expected running time, assuming that "random" bits are used in the algorithm in the natural way to choose a pivot? How do $k$ and $n$ play into the worst-case expected running time? If we need $k = \Omega(n \log n)$ initial truly random bits to assure good worst case expected running time, that isn't very interesting. But maybe we can do somewhat ok with asymptotically fewer initial random bits?
Comment: The idea of taking a relatively small number of random bits and "stretching" them into a longer pseudorandom sequence has definitely been studied. Unfortunately, it's not my field and I can't remember what it's called.
Comment: Are you asking about theoretical results (what we can prove?) or practical techniques (what will work well in practice, even if we can't prove it?)?  The answer will differ according to which you want to know about.
Comment: @D.W. Empirical results may be interesting and suggest what types of theoretical results can be proven, but I posted in this forum because I'm most interested in the theoretical results, whether they are proven or well-formulated and empirically supported conjectures.
Comment: OK.  Well, in practice, if you have a small random seed (160 bits of true, uniformly random bits), you can stretch it into an arbitrarily long stream of pseudorandom bits that are good enough for use with any randomized algorithm.  So, in practice, all you need is 160 bits of randomness; using crypto-strength PRNGs, you can stretch this to an unlimited number of bits that are indistinguishable from truly random (though we can't prove it works).  See http://cs.stackexchange.com/a/41723/755 and http://cstheory.stackexchange.com/a/29130/5038 and http://cstheory.stackexchange.com/q/27974/5038.
Answer: The question you're asking deals with the topic of derandomization, and you're proposing a specific technique for derandomization, namely using pseudorandom number generators. There are other techniques suck as using k-wise independent distributions and the method of conditional expectations. The holy grail in the field is proving the conjecture P=BPP, which states (informally) that we can always get rid of randomness, though the resulting algorithm could be slower; more precisely, it states that if you have a randomized polytime algorithm for something, then there exists a deterministic polytime algorithm for the same problem.
In your particular case, you don't need random bits at all, since you can use the linear time median algorithm to guarantee a running time of $O(n\log n)$ for quicksort. The AKS deterministic primality test is likewise a specific derandomization of randomized primality testing. P=BPP, in contrast, gives a general derandomization technique that works for every (polytime) algorithm; ad hoc derandomizations are still meaningful, since they could be more efficient (like in the quicksort example).
Comment: Yes I'm aware of deterministic median finding, so my quicksort question is more a question of what happens if we generate $k$ random bits, and adversary knows our pseudo-random generator that repeatedly permutes the $k$ bits to get enough bits to perform all the pivot selections (where the pivot selection is done according to how many next bits are needed in the "seeded random" bit stream, i.e. $\lceil{\log_2(m)}\rceil$ bits to choose a pivot if we are working with $m$ numbers to sort). As I recall, median finding requires extra memory so only storing $k$ random bits could be advantageous.
Comment: It is very doubtful that this approach results in an $O(n\log n)$ algorithm, since PRNGs are slow.
Comment: I'm assuming that the pseudo-number generator is something simple and something that perhaps cannot really improve the situation that much because the adversary knows exactly what the pseudo-random number generator for permutation is. So it might even be valid to assume that the pseudorandom permuter just returns the $k$ bits in the same order every time. I'm not sure but maybe. If that's the case, then the worst case expected running time in terms of # original random bits $k$ and # numbers $n$ to sort is still an interesting question, ignoring the PRNG since the adversary knows it.
Answer: If your adversary knows the $k$ input bits and your PRNG, they can apply the techniques used in McIllroy "A Killer Adversary for Quicksort", Software: Practice & Experience 29:4 (1999), pp. 341-344, and you are toast. How large $k$ has to be to make this infeasible to brute-force is another question.
No, "randomized quicksort" doesn't guarantee anything, it just makes the bad case(s) shift around at random (so it is very unlikely to hit them repeatedly with somewhat repeatable input permutations, as are common in "real world" uses). If you want some sort of guarantee, look for Musser "Introspective Sorting and Selection Algorithms", Software: Practice & Experience 27(8) (1997), pp. 983-993 (Introsort). Most standard C/C++ libraries use some variant of this for sorting.


What made Einstein believe (or know) that time was affected by speed and gravity?

Question: How did he come up with this idea before there was any experimental data to prove this?
Answer: See ON THE ELECTRODYNAMICS
OF MOVING BODIES, by A. Einstein, where he explains the prior experimental evidence, and then shows the logic for Special Relativity.  He was not the first to show the relative timekeeping of moving clocks, this was already known from the analysis of the Michelson-Morley experiments.
Einstein recognized early on that gravitation was inconsistent with Special Relativity, and sought new principles, including the Equivalence Principle. By applying this to his "Elevator" thought experiment, he was able to predict the gravitational red shift.
Ultimately, he used prior experimental results plus Maxwell's equations, and sought for logical, self-consistent theory with predictive power.
Comment: This is a technical explanation that does fine, and thoroughly answers the question; however, I've since come across a more intuitive example: Superman flies as fast as a speeding bullet, but if he flies slightly slower than the bullet, the bullet speeds away at a speed equal to the difference of their two speeds. However if he flies at .99c , photons will still speed away at 1 c. For this to be possible with s=d/t, time must slow. This example just got it to click. Thank you much.
Answer: That time is affected by speed was suggested before Einstein by Larmor, and was motivated by experimental data, namely the Michelson-Morley (later also Trouton-Noble) experiments to detect the ether wind. As for gravity its influence on matter came out of general relativity as a side effect, its development was driven by different issues: equivalence of inertial and gravitational masses and the Mach's principle, which led to the general covariance requirements (equivalence of all frames, inertial or not) philosophically, and the perihelion of Mercury experimentally, see Why did Einstein develop General Relativity?
To explain the negative result of the experiments Fitzgerald in 1889 and Lorentz in 1892 introduced the length contraction for moving objects. But as Larmor pointed out in 1897 the length contraction by itself was not enough to explain the effect, the time had to be dilated as well. Larmor then showed that if the intermolecular forces were of electromagnetic origin obeying the Maxwell electrodynamics then  length contraction and time dilation (as measured by devices so composed) will follow. As we would now say this is because the Maxwell electrodynamics is invariant under the Lorentz transformations, which Larmor also introduced in 1897, two years ahead of Lorentz. He presented his theory systematically in his book Aether and Matter (1900).
Of course, to Fitzgerald, Lorentz and Larmor contraction and dilation were just apparent effects caused by dynamics of clocks and rulers that in no way affected the "true" absolute time and absolute space. In turn, Einstein's insight was that it is the "apparent" effects that were the physical ones, and the ether with the absolute space and time attached to it were the unphysical. Einstein therefore "transformed" the time dilation effect from illusion to reality, and from dynamic to kinematic and universal (not just affecting electromagnetic phenomena), rather than came up with it. Perhaps unsurprisingly, Lorentz and Larmor (and even Poincare) rejected Einstein's re-interpretation, they saw no need to abandon their old school theories on the basis of experiments they already explained.