explain xkcd - User contributions [en]

2201: Foucault Pendulum

2019-09-18T17:08:40Z

Trueflint: /* Explanation – fixed some grammar, smoothed some awkward sentences */

{{comic
| number = 2201
| date = September 11, 2019
| title = Foucault Pendulum
| image = foucault_pendulum.png
| titletext = Trust me, you don't want to get on the wrong side of the paramilitary enforcement arm of the International Earth Rotation and Reference Systems Service.
}}

==Explanation==
{{incomplete|Created by the International Earth Rotation and Reference Systems Service. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
[[Black Hat]] is attending what appears to be a guided tour of a museum with a {{w|Foucault pendulum}}. [[Megan]] is explaining to him, [[Cueball]] and [[Ponytail]] about the device which demonstrates the rotation of the Earth.

Black Hat, being himself, immediately sees an opportunity to cause chaos and seizes it with both hands, quite literally — he grabs the pendulum, which causes the others to shout after him to stop. At first this would seemingly be for fear of ruining the delicate demonstration. However, in the final panel, the [[:Category:News anchor|news anchor]] [[Blondie]] reveals to us that by arresting the motion of the pendulum, Black Hat has somehow stopped the rotation of the Earth. However, it was only briefly, since the local {{w|geophysicists}} managed to wrestle him down, and it must be assumed that they then quickly restarted the pendulum and thus the Earth's rotation.

This of course is blatantly impossible, since the Foucault pendulum's motion is tied to the Earth's rotation, not the other way around (at least in any significant way, see below). A Foucault pendulum is a regular {{w|pendulum}} that swings from a bearing that allows rotation in any direction, like your shoulder joint instead of your elbow, as a demonstration that the Earth is rotating beneath it. If the Earth were stationary, the pendulum's plane of oscillation would not change relative to its immediate surroundings, but the Earth is not stationary, so the pendulum's plane of oscillation will appear to rotate over the course of a day, although in reality it is the Earth that rotates. The low-friction bearing doesn't allow the rotation of the Earth to affect the motion of the pendulum, so it tends to stay aligned with its original inertial reference frame rather than with its surroundings, which rotate with the Earth. A Foucault pendulum located at one of the poles will take a full day to "move" one full round. At the equator there is no movement, and in between it will take longer than 24 hours (24 hours divided by the sine of the latitude).

The fact that the Earth's rotation does not influence the motion of the pendulum does NOT mean that other forces can't affect it - for example, someone running up and manually repositioning the pendulum. Of course, the apparent rotation of the pendulum's plane relative to the Earth is an effect of the planet's motion, rather than the cause of it. Thus, stopping a Foucault pendulum manually does not entail pausing the rotation of the Earth.

If it were somehow possible for a Foucault pendulum to control Earth's rotation (see above), Black Hat would probably not want to alter the momentum of the pendulum if he were not at one of the Earth's poles. That is assuming he was told that it was related to Earth's rotation and assuming that he would prefer to preserve his own life over creating chaos (unless he has some means to prevent his being slammed into a nearby wall at the speed of sound). This is because, if the rotation of the Earth were to be stopped for even very short amounts of time (a few seconds), it would cause everything on Earth that wasn't bolted/fastened to the ground to move eastward compared to the now stationary ground. Objects near the Equator would suddenly be moving at a speed of 300-360 meters per second, likely causing the death of most lifeforms on Earth beneath a certain latitude almost instantaneously. Those close enough to the poles may survive, though. Also this will cause massive windstorms, tsunamis, volcanic and tectonic events on a scale not previously observed on Earth. This would likely cause a mass extinction event and wipe out 99% of humanity in the initial events (which would eventually lead to our total extinction). It is possible that Black Hat's grabbing the pendulum would cause a gradual slowing prior to stopping, minimizing the issue (though this doesn't seem to be the case), but the results would still be catastrophic, as the aforementioned events are still likely to occur (specifically the tsunamis and volcanic events). However, as mentioned above, if this pendulum were located at the South Pole, then Black Hat and other people around him would not be affected immediately, and he could both do it, survive and be stopped again. The question is whether there would be any more news stories to cover this, given what would happen to the rest of the world! If there was no one to readjust the pendulum's rotation, then certain events would happen after the initial damage (see this video [https://www.youtube.com/watch?v=q_T7L8rt1Ec]). [[Randall]] previously covered this scenario in detail in his [[what if?]] book, see [https://io9.gizmodo.com/xkcds-creator-explains-what-would-happen-if-earth-stopp-1625068208 XKCD's Creator Explains What Would Happen If Earth Stopped Spinning].

To be completely correct, the angular momentum of the Earth+pendulum system is constant, so that when Black Hat "stops" the pendulum's rotation with respect to the Earth, he actually transfers to the pendulum some of Earth's angular momentum, thereby ''slightly'' slowing Earth's rotation. But the order of magnitude of that effect is (at most) in proportion to the pendulum-to-Earth mass ratio. Earth's mass being ~6 x 1024kg, the effect for any practical pendulum would be beyond the 20th decimal place and would therefore go totally unnoticed.

The title text mentions the [https://www.iers.org/IERS/EN/Home/home_node.html International Earth Rotation and Reference Systems Service], an organization providing standards for global time and reference frames; this organization would have a very rough day after the fiasco with Black Hat. The title text refers to a (probably) fictional paramilitary enforcement arm of this organization and the foolishness of tangling with such a force. If Foucault pendulums were somehow able to influence the rotation of the Earth in any measurable way, the IERS enforcers would probably strictly control their installation and monitor their use (and misuse). Black Hat is likely in for a rough day as well. It seems likely that some on this team are geophysicists, since they were the ones who took Black Hat down.

==Transcript==
:[Megan is addressing Cueball, Black Hat and Ponytail as they are looking a pendulum, which consists of a large swinging sphere with a spike beneath it hanging on a string coming down from above with seven small markers under it. Megan is pointing at it while it is swinging towards them, as indicated with lines behind the sphere and the string.]
:Megan: This Foucault pendulum demonstrates Earth's rotation. It stays in a fixed plane while the Earth rotates under it.

:[Close-up on Black Hat holding a hand to his chin.]
:Black Hat: Hmm, really.
:Black Hat: So that means...

:[Zoom out to Black Hat running to the pendulum grabbing it with both hands. He knocks over two of the seven markers that can now be seen to be small pegs standing up on he floor beneath the pendulum. A line goes from his hand on the pendulum up to a sound bubble. Two people off-panel yell at him.]
:Character off-panel 1: Hey!
:Character off-panel 2: Stop him!
:Sound:''Grab''

:[Blondie as a news anchor uses her held out hand to indicate Black Hat who is shown on a screen next to her. There is a caption in two lines above it. The first line in normal text, the second line in white in a black rectangle. There are further unreadable text below the picture.]
:Blondie: The Earth's rotation was briefly halted today until geophysicists wrestled the intruder to the ground...
:Breaking
:''news''

{{comic discussion}}

[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Blondie]]
[[Category:News anchor]]
[[Category:Physics]]

2201: Foucault Pendulum

2019-09-11T20:55:42Z

Trueflint: /* Explanation: title text */

Talk:2201: Foucault Pendulum

2019-09-11T20:46:28Z

Trueflint:

I take it the pendulum is somewhere deep underground, which would shield Black Hat from the cataclysmic side effects?
Besides, they have several backup pendulums that while not enough to maintain rotation are sufficient to slow the half enough to preserve life.[[Special:Contributions/108.162.212.149|108.162.212.149]] 20:11, 11 September 2019 (UTC)

If the pendulum could really affect Earth's rotation, Black Hat wouldn't need to stop the pendulum entirely; he'd only need to prevent its plane of oscillation from rotating. Another thought: if the pendulum and Earth's rotation were really bidirectionally linked somehow, there would probably be nothing Black Hat could do to alter the pendulum's plane of oscillation -- any more than he could alter the rotation of the Earth with just one human being's strength. That last thought doesn't seem to be the case within this story, though, or else the final frame's news report wouldn't have happened. [[User:Trueflint|Trueflint]] ([[User talk:Trueflint|talk]]) 20:46, 11 September 2019 (UTC)

2201: Foucault Pendulum

2019-09-11T20:36:00Z

Trueflint: Added a few links to characters

2201: Foucault Pendulum

2019-09-11T20:34:11Z

Trueflint: Just a bit of proofreading

2201: Foucault Pendulum

2019-09-11T20:19:30Z

Trueflint: Initial transcript

1540: Hemingway

2015-06-19T18:58:48Z

Trueflint:

{{comic
| number = 1540
| date = June 19, 2015
| title = Hemingway
| image = 1540.jpg
| titletext = Instead of bobcat, package contained chair.
}}

==Explanation==
{{Incomplete|Finished with Edit Conflict assimilation, but prior author(s) invited to rejig}}

This comic is a reference to the six-word short story {{w|For sale: baby shoes, never worn}}, which has been attributed to famous author {{w|Ernest Hemingway}}; however, [[Randall|Randall Munroe]] explicitly states that this might not be the case at all. The comic plays on the fact that the original story takes the form of a short advertisement that might have been seen in a newspaper, and for these examples uses various modern 'standards' that did not exist in Hemingway's time.

Each example remains six 'words' long!

(Title-text obeys this meme, also.)


Most exhibit common 'click bait' wording, such as "This Weird Trick...", whilst others make use of annotating tokens from an online site. One line references Roguelike conventions for item descriptions, obviously also unfamiliar to Hemingway's generation and there's also a direct example of HTML formatting tags from the early 1990s; the <BLINK> tag was infamously introduced to the early Netscape browsers. 
Others poke fun at the tragedy that the original story suggests. The six words (For Sale: Baby shoes, never worn) are written like an advertisment, and the reader is supposed to infer that the baby who would have worn the shoes must have died. Randall tries to make the reader infer other things.
'For Sale: This gullible baby's shoes' suggests that the seller somehow tricked the baby out of its shoes. 'Baby shoes for sale by owner' suggests that a very intelligent baby is somehow selling its own shoes.

In the case of the HTML, the normally invisble-and-rendered tag elements can be seen and are part of the six words count. This could have been due to 'sanitising' of uploaded text where HTML tags (other than any that are specifically allowed, like it appears Strikethrough formatting might be) are deliberately deactivated by the server, or because the incorrectly closed final tag breaks any intended rendering support.

The title text (and the penultimate line in the comic itself) makes a reference to the third pane of [[A-Minus-Minus|325: A-Minus-Minus]] in which [[Cueball]] says: 'Instead of office chair, package contained bobcat'

==Transcript==
[Caption above comic:] 
Hemingway's Rough Drafts 
[A list of rough draft titles] 
For sale: This Gullible Baby's Shoes 
Baby Shoes For Sale By Owner 
<strike>Actually, There's no evidence Hemingway wrote</strike> 
Free Shoes, Provided You Overpower Baby 
For Sale: Weird Baby's Toe Shoes 
For Sale: Baby Shoes [an "Amazon Prime eligible" logo] 
<strike>Though popularly attributed to Hemingway, the</strike> 
This Weird Trick Covers Baby Feet! 
For Sale: Baby Shoes, Just Hatched 
Sale: Seven-League Boots (Expedited Shipping) 
Complete this survey for free shoes! 
''Shoes'', by Ernest Hemingway (citation needed) 
This is my greatest short story. 
For sale: Baby shoes (-1) [cursed] 
<blink><marquee>Baby Shoes!</marquee><blink> 
For Sale: Baby-sized Saddle, Bobcat 
Hemingway Busted for Craigslist Shoe Scam 
{{comic discussion}}

Talk:32: Pillar

2015-06-04T17:15:09Z

Trueflint:

I have oft wondered about the color thing.
[[Special:Contributions/71.178.11.180|71.178.11.180]] 21:49, 23 October 2012 (UTC)
Bigger problem- how do you know there are other people?

The incessantly thumping bass from your neighbour's "music" is a bit of a clue. :-)
[[User:BinaryDigit|BinaryDigit]] ([[User talk:BinaryDigit|talk]]) 09:23, 30 March 2013 (UTC)

Is that Comic Sans (the font) in the top left? [[User:Caagr98|Caagr98]] ([[User talk:Caagr98|talk]]) 15:06, 17 April 2013 (UTC)
:Augh, it is Comic Sans! [[Special:Contributions/173.245.52.29|173.245.52.29]] 21:00, 5 February 2014 (UTC)

Also, it could be that Righty doesn't see a pole, but a pillar, as suggested by the title of the comic. That's why he asks, "What pole?", implying, "I only see a pillar". {{unsigned ip|173.245.62.75}}

The song "Shpadoinkle" from Trey Parker and Matt Stone's "Cannibal! The Musical" begins with the line, "The sky is blue, and all the leaves are green." [[User:Trueflint|Trueflint]] ([[User talk:Trueflint|talk]]) 17:15, 4 June 2015 (UTC)