explain xkcd - User contributions [en]

Talk:1175: Moving Sidewalks

2013-02-19T17:43:47Z

77.99.26.23:

I'm not quite sure what the joke here is supposed to be. Many have tried to develop variable speed walkways, as one can see in [http://worldwide.espacenet.com/searchResults?page=0&compact=false&ST=advanced&locale=en_EP&DB=EPODOC&CPC=B66B23%2f26%2flow patents]. There was even a pair of these that were installed circa Y2K in the Paris subway (Châtelet-Les-Halles, IIRC), which is renowned for its long passageways. It is AFAIK no longer in service, I don't know why. When I saw it an attendant was present to watch over for making sure that users wouln't fall. This contraption is way more complicated than standard rubber-belt conveyors with its meshing steps. --[[Special:Contributions/70.52.115.181|70.52.115.181]] 15:59, 18 February 2013 (UTC)

I know what I'm building this weekend... [[Special:Contributions/207.237.164.241|207.237.164.241]] 06:22, 18 February 2013 (UTC)
:I just wonder if it is possible to remove these stupid posts and the panel on top of them from my treadmill without breaking it... {{unsigned|89.174.214.74}}

Isn't "of" suppose to be "off" in the title text? {{unsigned|67.161.114.84}}

Do anybody know examples of such belts. The ones I recall has all one-speed-only [[User:Spongebog|Spongebog]] ([[User talk:Spongebog|talk]]) 10:43, 18 February 2013 (UTC)
: At Toronto Airport they have double speed moving sidewalks, that accelerate by stretching the panels. --[[User:Johnsmith|Johnsmith]] ([[User talk:Johnsmith|talk]]) 08:43, 19 February 2013 (UTC)

I was under the impression (from the alt-text), that they would take the belts inward traveling faster until they hi-five. Then, as they sped away, they would change sides and repeat the process. 10:56, 18 February 2013 (UTC)

I don't see why they are positioned as they are. If they were taking the belts inward, they would take advantage of the momentum imparted by the belts and be going much faster than their stride would normally take them. The way they are positioned, they would have to be running to just catch up to each other in the middle. [[Special:Contributions/64.121.163.170|64.121.163.170]] 11:06, 18 February 2013 (UTC)

:This is surely the point. They have to run faster as they get closer. [[Special:Contributions/77.99.26.23|77.99.26.23]] 12:00, 18 February 2013 (UTC)
:: Has the picture changed? Now it seems as if they where going faster to the middle. --[[User:Johnsmith|Johnsmith]] ([[User talk:Johnsmith|talk]]) 08:48, 19 February 2013 (UTC)

There doesn't appear to be any 'trick' to this one. Like the commenter above, I initially thought they were being taken towards each other by the conveyors. I thought the joke was that they would be accelerated to a ridiculous speed which would make it impossible to high five without obliterating each other, but the alt text didn't indicate anything like this and I looked again and realised I had read way too much into it. It's probably most sensible to interpret the speed multiples as relating to the first belts, not the last one you were on. This makes the difference between the '5x' belts going at 5x the speed of the outer ones, instead of 100x if each was the specified multiple of the last. If this alternative situation were the case, the outer belts would have to be going very slowly (of the order of 0.1m/s) for them to ever be able to high five. [[Special:Contributions/77.99.26.23|77.99.26.23]] 12:00, 18 February 2013 (UTC)

The appears reminiscent of Improv Everywhere's prank, "High-Five Escalator" http://improveverywhere.com/2009/02/09/high-five-escalator/ [[User:JamesCurran|JamesCurran]] ([[User talk:JamesCurran|talk]])

I'm sure I would fall over trying to use this one. --[[Special:Contributions/173.49.75.121|173.49.75.121]] 14:09, 18 February 2013 (UTC)

Randall updated the comic, explaining that he meant to draw the arrows going the way Cueball and Megan are facing, not opposite. I'd change the wiki, but I don't get it now. :) [[User:Zpletan|Zpletan]] ([[User talk:Zpletan|talk]])

The Comic has been changed: "Oops! I originally put up a version with backward sidewalk arrows. I should know better than to edit and post comics while sleep-deprived. Sorry!" [[Special:Contributions/86.32.218.17|86.32.218.17]] 14:28, 18 February 2013 (UTC)

I don't think they're going a multiple of the previous belt, but a multiple of base speed. Just my 2 cents :) Also, I think the belts are moving toward each other to get the ultimate "high five" in terms of velocity of the impact. {{unsigned|161.31.32.81}}

I don't see why anyone would think the "5x speed" etc would mean 5 times the previous tile. Seems obvious to me that the first tile is moving at some speed, the second tile is moving twice that base speed, the third moving 3x that base, etc. So when the pass each other their moving at 10x the base speed. Assuming the base speed is something reasonable, something near a typical walking speed, the high five would take place at a speed similar to if they were just sprinting past each other. Hardly a "ridiculous speed which would make it impossible to high five without obliterating each other." [[Special:Contributions/67.51.59.66|67.51.59.66]] 16:58, 18 February 2013 (UTC)

:As you'll see from my comment, I only thought something like this might be implied on first glance before I looked at it properly. Honestly it just doesn't seem that awesome to have a series of conveyor belts that allow you to high five a person at sprinting pace. I briefly suspected Randall might have been getting at some feature of physics or mathematics, like the story of the guy who asked for payment for something in grains of rice placed on a chessboard, starting with one grain in the corner and doubling for each square. But no. It's just two people high fiving each other. [[Special:Contributions/77.99.26.23|77.99.26.23]] 17:43, 19 February 2013 (UTC)

Does anyone think this may be a reference to "The Caves of Steel" a novel by Isaac Asimov? As I recall there was a global system of moving belts of various speeds that were used for transportation.
: That's what I thought of immediately. [[Special:Contributions/128.84.127.95|128.84.127.95]] 19:17, 18 February 2013 (UTC)
: Or Heinlein's "The Roads Must Roll". [[Special:Contributions/173.8.183.86|173.8.183.86]] 19:41, 18 February 2013 (UTC)
:: Also Clarke's ''The City and the Stars'', for the {{w|Big Three}} trifecta. But in those stories, the different-speed belts were arranged in parallel, like lanes of a highway, rather than in series. So you'd accelerate by stepping sideways from belt to belt.
::[[User:Wwoods|Wwoods]] ([[User talk:Wwoods|talk]]) 20:30, 18 February 2013 (UTC)

Seriously, they're playing a game of Robo Rally [[User:schmammel|talk]]

I would love to see this sidewalk placed in a Bison habitat.[[Special:Contributions/94.191.187.81|94.191.187.81]] 05:04, 19 February 2013 (UTC)

Is it just me - or was this comic fixed after it was initially uploaded? I could've sworn the original had either the arrows backwards or the people on the wrong sides - They would've been fighting the sidewalk. 09:59, 19 February 2013 (UTC)
:As an edit to this, I was correct. This is a mirror of the comic on Gizmodo, showing the error. http://img.gawkerassets.com/img/18f07q9hveoaepng/xlarge.png {{unsigned|‎77.98.193.149}}
:And it seems that when fixing it, Randall changed all the arrows, rather than moving the people. [[User:JamesCurran|JamesCurran]] ([[User talk:JamesCurran|talk]])

I wonder, what is the pace of the centerbelt? Is it 5x, 6x or maybe about 5x where that belt start, accelerating to 7x (or even more?) at the high five location and then slowing down till about 5x at the end? [[Special:Contributions/86.82.116.63|86.82.116.63]] 16:30, 19 February 2013 (UTC)

Talk:1175: Moving Sidewalks

2013-02-18T12:00:52Z

77.99.26.23:

I know what I'm building this weekend... [[Special:Contributions/207.237.164.241|207.237.164.241]] 06:22, 18 February 2013 (UTC)

Isn't "of" suppose to be "off" in the title text? {{unsigned|67.161.114.84}}

Do anybody know examples of such belts. The ones I recall has all one-speed-only [[User:Spongebog|Spongebog]] ([[User talk:Spongebog|talk]]) 10:43, 18 February 2013 (UTC)

I was under the impression (from the alt-text), that they would take the belts inward traveling faster until they hi-five. Then, as they sped away, they would change sides and repeat the process. 10:56, 18 February 2013 (UTC)

I don't see why they are positioned as they are. If they were taking the belts inward, they would take advantage of the momentum imparted by the belts and be going much faster than their stride would normally take them. The way they are positioned, they would have to be running to just catch up to each other in the middle. [[Special:Contributions/64.121.163.170|64.121.163.170]] 11:06, 18 February 2013 (UTC)

:This is surely the point. They have to run faster as they get closer. [[Special:Contributions/77.99.26.23|77.99.26.23]] 12:00, 18 February 2013 (UTC)

There doesn't appear to be any 'trick' to this one. Like the commenter above, I initially thought they were being taken towards each other by the conveyers. I thought the joke was that they would be accelerated to a ridiculous speed which would make it impossible to high five without obliterating each other, but the alt text didn't indicate anything like this and I looked again and realised I had read way too much into it. It's probably most sensible to interpret the speed multiples as relating to the first belts, not the last one you were on. This makes the difference between the '5x' belts going at 5x the speed of the outer ones, instead of 100x if each was the specified multiple of the last. If this alternative situation were the case, the outer belts would have to be going very slowly (of the order of 0.1m/s) for them to ever be able to high five. [[Special:Contributions/77.99.26.23|77.99.26.23]] 12:00, 18 February 2013 (UTC)

Talk:1145: Sky Color

2012-12-12T14:00:23Z

77.99.26.23:

Of course with '''''vertical''''' mirror vertical axis is selected: perceived switching of left and right (really close with far to mirror surface). When '''standing on''' '''''horizontal''''' mirror we will perceive switching bottom from top. --[[User:JakubNarebski|JakubNarebski]] ([[User talk:JakubNarebski|talk]]) 09:09, 10 December 2012 (UTC)

You're certainly correct, but I think that the original question is not really asking about text (or other things) which are perpendicular to the mirror, but rather text which is parallel to it (and thus the close vs. far doesn't come into it). For example, when reading signs in your rear view mirror or holding a book in front of your chest while looking in a mirror. I've added a little bit to the explanation to attempt to help clarify what's happening in that situation. I'm not sure if it really helps or not. [[User:KeithyIrwin|KeithyIrwin]] ([[User talk:KeithyIrwin|talk]]) 10:00, 10 December 2012 (UTC)

Easier way to describe it: Imagine you hold a piece of glas. Write on the glass and hold it in front of the mirror, so that you can see both the original text and the mirrored text. Both versions of the text will look identical. So the mirror doesn't change anything. [[Special:Contributions/62.220.2.194|62.220.2.194]] 11:10, 10 December 2012 (UTC)

Another way: draw a line between the real object and its reflection. Things are reflected around that line. If that line is going up & down (relative to your eyes), then things are reflected left/right (relative to your eyes). If that line is horizontal (again relative to your eyes), then things are reflected top/bottom. So it's not so much whether the mirror is horizontal or vertical, but rather what direction you are looking into the mirror (although that can be influenced a lot by the mirror's orientation).[[User:CityZen|CityZen]] ([[User talk:CityZen|talk]]) 04:17, 11 December 2012 (UTC)

I always wonder: Since the sky goes from red to blue to red and the optical spectrum goes from red to green to blue. How come the sky is never green?
: Because of human color perception. You only perceive green in polychromatic light when said light is stronger in the middle wavelengths than the low or high wavelengths; in other words, you would need a process in the sky that removed ''both'' the high and low wavelengths from white light. As the sun sets, only the lower wavelengths are removed, so you perceive yellows and reds -- this perception of color is "one-sided", i.e. it is not interfered with by even longer wavelengths. By the way, sometimes you do see green briefly in the sky, it's called a [http://en.wikipedia.org/wiki/Green_flash Green Flash]. --[[User:Prooffreader|Prooffreader]] ([[User talk:Prooffreader|talk]]) 16:41, 10 December 2012 (UTC)
::I used to go outside after a rain storm during the day, and sometimes the sky would seem very green. The effect could last for hours. [[Special:Contributions/76.122.5.96|76.122.5.96]] 12:15, 12 December 2012 (UTC)

This sentence doesn't make sense: "(from "his" right to left instead of from "his" left to right)" [[User:Trek7553|Trek7553]] ([[User talk:Trek7553|talk]]) 15:15, 10 December 2012 (UTC)

Repeat Character Watch: The girl has appeared previously in [[842: Mark]], [[892: Null Hypothesis]], [[1058: Old-Timers]], and [[1104: Feathers]] (A similar looking character also appears in [[635: Locke and Demosthenes]] but this is actually the character Valentine from the book Ender's Game). The mother is seen in comics [[806: Tech Support]] and [[813: One-Liners]]. [[User:Lcarsos|lcarsos]]_a ([[User talk:Lcarsos|talk]]) 18:12, 10 December 2012 (UTC)

About [http://www.explainxkcd.com/wiki/index.php?title=1145:_Sky_Color&diff=22416&oldid=22414 this edition]: 1/(x^4) does not look like a root to me. IMHO the forth root of x would be more like x^(1/4) but it's not the formula from the comic. (I'm too lazy to try to type lambda). [[User:Lmpk|Lmpk]] ([[User talk:Lmpk|talk]]) 19:00, 10 December 2012 (UTC)

:You are correct. It's been fixed. The editor that made that edit was probably confusing 1/x4 with x1/4, the latter of which would indeed be the fourth root. [[User:Lcarsos|lcarsos]]_a ([[User talk:Lcarsos|talk]]) 19:53, 10 December 2012 (UTC)

[http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html This page], linked from the explanation says that "the most strongly scattered indigo and violet wavelengths stimulate the red cones slightly as well as the blue, which is why these colours appear blue with an added red tinge." -- this seems rather strange. Assuming the cones are simulated based on frequency/wavelength, ultra-blue colors shouldn't stimulate the red cones because the electromagnetic spectrum is linear, not circular, despite the appearance of similarity between violet and red. Or am I missing something? --[[User:Waldir|Waldir]] ([[User talk:Waldir|talk]]) 16:14, 11 December 2012 (UTC)
: If you look at the response curve (middle of cited page) you'll see that red receptors have two peaks, one in the red wavelengths, and another (very tiny one) in the violet. That's why purple (which is red + blue) looks so similar to violet, and why the "color wheel" works. [[Special:Contributions/207.225.239.130|207.225.239.130]] 21:59, 11 December 2012 (UTC)
:: PS: "first years" is an idiom. Wouldn't that be "first year students" to be proper English? [[Special:Contributions/207.225.239.130|207.225.239.130]] 22:05, 11 December 2012 (UTC)
:::Idioms are "proper English" too. There is no doubt about what is meant here (or at least, I hope there isn't, but perhaps there are regional differences that mean some English speakers don't say "first years" to talk about students in their first year), and the register is not unduly colloquial for this kind of a site. 14:00, 12 December 2012 (UTC)