explain xkcd - User contributions [en]

2678: Wing Lift

2022-09-30T02:23:57Z

172.70.147.129:

{{comic
| number = 2678
| date = September 28, 2022
| title = Wing Lift
| image = wing_lift_2x.png
| imagesize = 679x358px
| noexpand = true
| titletext = Once the air from the top passes below the plane of the wing and catches sight of the spooky skulls, it panics, which is the cause of turbulent vortices.
}}

==Explanation==
{{incomplete|Created by a SPOOKED OUT BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

Wings can produce {{w|Lift (force)|lift}}.<ref name="Prandtl & Tietjens (1952)">{{cite book |last1=Prandtl |first1=L |last2=Tietjens |first2=O K G |author-link1=https://en.wikipedia.org/wiki/Ludwig_Prandtl |date=1952 |title=Fundamentals of Hydro- and Aeromechanics |publisher= Dover |isbn=9780486603742}}</ref> {{Citation needed}}

Randall previously dealt with explanations of wing lift in [[803: Airfoil]].

There are three actual reasons why airplane wings produce lift:
* {{w|Bernoulli's principle}} (which is the most frequently cited)
* The airplane wing is angled up at the front so that air hits the bottom and is pushed downwards.
* {{w|Coandă effect}} (The top is curved, so air going over the wing must curve downwards in order to avoid creating a vacuum above the back of the wing, and by Newton's third law, this results in an upwards force on the wing.)
The comic references all three of these reasons. Airflow splitting references Bernoulli's principle, while the air at the bottom being scared and fleeing downwards is similar to the actual effect, which is caused by air hitting the angled bottom of the wing. The air going over the top curving down references the Coandă effect, claiming that this effect is instead caused by the top-flow of air itself noticing the bottom side of the wing going down to investigate why the bottom-flow had fled. The mention of Newton's third law is indeed correct, even if the movement of the air is for the wrong reasons. In the title text, it additionally suggests that the top-flow henceforth glimpses the printed skulls, causing it to also chaotically flee, generating a wing's classic turbulant wake.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

[Caption at the top of the panel:] How a wing produces lift

[A diagram of the cross-section of a plane wing. It is large and rounded on the left end and flat on the bottom while the top curves down to meet it at a sharp point. There are many small arrows indicating the flow of wind, as well as captions.]

[The arrows come from the left of the panel, point towards the wing, and then half begin to go over and half begin to go under. A caption in the middle of this flow reads:] Airflow splits around the top and bottom of the wing

[A circle underneath the diagram is connected to an arrow which points to the underside of the wing. A repeating pattern of small black (simplified) skulls fills the circle and arrow. The caption to the right of this is:] Spooky skulls microprinted on the bottom of the wing frighten the air, which flees away downward

[The arrows begin to curve downwards after this caption, and are joined by the top arrows which have also begun to curve downward. In these arrows is a caption:] Top air goes to see what's wrong

[Both streams of arrows have joined and are pointing to the bottom right of the panel. In front of them is a caption:] By Newton's third law, downward deflection of air pushes wing upward

{{comic discussion}}

[[category:Engineering]]
[[category:Physics]]
[[category:Aviation]]

Talk:979: Wisdom of the Ancients

2022-09-02T05:07:32Z

172.70.147.129:

"There was uh, a thing called a segfault that made my computer like, all blurry and stuff." '''[[User:Davidy22|Davidy22]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 06:58, 2 February 2013 (UTC)

That was one reason why [http://stackoverflow.com/ StackOverflow] came to life: main authors fed up with (mis)using forums for query & answer site --[[User:JakubNarebski|JakubNarebski]] ([[User talk:JakubNarebski|talk]]) 23:03, 15 June 2013 (UTC)

Just two googling steps brought me here:
http://www.mirrorsoferis.com/forum/thread05232003a.html
Relevant for "Trivia"? Even the year fits! [[Special:Contributions/108.162.230.89|108.162.230.89]] 11:28, 12 September 2014 (UTC)
:From the HTML source:
::<tt>
::
::
::</tt>
:Cute theory, though. -[[Special:Contributions/108.162.254.126|108.162.254.126]] 12:23, 10 December 2014 (UTC)
::Even better, looking at other stuff in that source:
:: <td><input class="button" value="Log in" tabindex="104" title="Enter your username and password in the boxes provided to login, spin round three times, vomit, click your heels together and TA-DA!" accesskey="s" type="submit"></td>
:: Will this actually enter properly, or will those formatted tags not be input scrubbed? Tables ... [[User:Keybounce|Keybounce]] ([[User talk:Keybounce|talk]]) 08:34, 4 August 2017 (UTC)

:::Also, someone in 2003 couldn't have asked about a webcomic that was only launched in 2005. [[Special:Contributions/173.245.52.109|173.245.52.109]] 18:29, 3 October 2017 (UTC)

The link above seems to be dead now. DNS failed. [[Special:Contributions/162.158.167.15|162.158.167.15]] 09:03, 22 August 2016 (UTC)
: Working now --[[User:Keybounce|Keybounce]] ([[User talk:Keybounce|talk]]) 08:34, 4 August 2017 (UTC)

2nd paragraph of the explanation is nonsense! A forum post is nothing like a FAQ entry. The problem didn't get solved and was probably put away and forgotten. Happens all the time. {{unsigned ip|162.158.83.144}}

"The title text is a suggestion to forums to be aware of the fact that people are likely going to come across such posts in the future" My pet peeve is when I Google an error and get led to a post like in the comic, and one of the last comments is a person necro-bumping with new information on the same issue, but then a moderator locks the post because its X years old and needs to be left alone. This is the fucking Internet; data doesn't rot. [[Special:Contributions/108.162.212.83|108.162.212.83]] 13:52, 15 July 2017 (UTC)
: From my experience the top search result on google usually is a locked post with no answer (other than the polite suggestion to google it yourself). [[Special:Contributions/162.158.203.16|162.158.203.16]] 04:16, 3 September 2021 (UTC)
: data does rot, though? :P [[Special:Contributions/141.101.103.40|141.101.103.40]] 18:19, 8 September 2021 (UTC)

Try having a problem that Google has never heared of. My hard drive died last March, and in the process of learning that was what had happened, I had tried reinstalling the OS and got an error that yielded literally zero search results (it was Error 0xb9f3c820, by the way) --[[Special:Contributions/172.71.146.65|172.71.146.65]] 02:46, 28 July 2022 (UTC)
: Nice try. [[Special:Contributions/172.70.147.129|172.70.147.129]] 05:07, 2 September 2022 (UTC)

2651: Air Gap

2022-07-28T07:33:59Z

172.70.147.129:

{{comic
| number = 2651
| date = July 27, 2022
| title = Air Gap
| image = air_gap.png
| titletext = You can still do powerline networking, but the bitrate does drop a little depending on the lightbulb warmup and cooldown delay.
}}

==Explanation==
{{incomplete|Created by an AIR GAP-PROTECTED BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
In {{w|computer security}}, {{w|air-gapping}} is a measure used to secure sensitive computers or networks of computers by isolating them from the broader internet, since computers are often breached through the internet. In this comic, Randall suggests air-gapping your entire home power supply for security by using the light from a powered lightbulb to power a solar panel which powers the computer connected, such that there is no physical wired connection between your power supply and device, due to the gap of air between the lightbulb and solar panel. This is a large and very inefficient version of an {{w|opto-isolator}}.

The title text mentions that the computer can still be connected to the internet via the power supply by using {{w|powerline networking}} but that the bandwidth would be reduced by the lightbulb's warmup and cooldown delay, which would reduce the signalling rate the lightbulb could accomplish. Of course, using this power supply set-up with a gap of air to connect the computer to the internet would mean the computer is no longer air-gapped, assuming the computer's conventional networking (e.g. ethernet and Wi-Fi) was already disabled. In addition to having dubious security value, this set-up would be very inefficient in transmitting power to the computer due to the power losses inherent in converting the electrical energy to light energy via the lightbulb and back to electrical energy via the solar panel. It would also be unidirectional and thus useless for traditional networking, because necessary requests and acknowledgments would be unable to travel from behind the solar panel to the lightbulb.

==Why this would be inefficient==
Solar panels are less than 100% efficient - in fact, they generally have an efficiency far below 50%. Lightbulbs are also inefficient at converting energy into light-- for example, a standard incandescent lightbulb like the one shown in the comic would convert only about 5% of its energy into visible light, with the rest emitted as heat and unusable infrared light. Therefore, only a small fraction of energy would be transmitted between the two ends of the air gap, making the circuit require much more electricity and be much less cost-efficient.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[A solar panel and a lamp are pictured together, with the lamp pointed at the solar panel, and electronic equipment connected to the solar panel.]
:[Caption] Security tip: Increase the security of your home power supply by installing an air gap.
{{comic discussion}}