explain xkcd - User contributions [en]

2675: Pilot Priority List

2022-09-22T13:22:54Z

172.69.33.129: /* Explanation */ Missed a pipe!

{{comic
| number = 2675
| date = September 21, 2022
| title = Pilot Priority List
| image = pilot_priority_list_2x.png
| imagesize = 369x548px
| noexpand = true
| titletext = CELEBRATE: Serve passengers tiered cakes shaped like the airspace class diagram
}}

==Explanation==
{{incomplete|Created by an ELUCIDATE, EXPLICATE, ANNOTATE, DEMONSTRATE, AND ILLUSTRATE CHECKLIST. Do NOT delete this tag too soon.}}

The [https://elevate-aviation.com/blog/pilots-priority-checklist "ANC" Pilot Priority Checklist] is a list of three guidelines, sorted by priority, that pilots should follow to prevent them from being distracted. Failing to follow it might make the plane crash or suffer other problems. As a {{w|mnemonic}} device, all the activities end in ''-ate''.

# '''Aviate''' means "Keeping the plane in control". If the pilot fails to do this the plane might crash. That is why this should be the highest priority for the pilot.
# '''Navigate''' means "Knowing where you are and where you're going". Failing to follow this might make the plane go into restricted airspace, for example, or make the journey take too long, or cause the flight to crash into terrain obscured by clouds.
# '''Communicate''' means talking to air traffic control (ATC) through radio. In the standard list this is the lowest priority because talking through the radio might distract the pilot from other more important or urgent tasks.

By defering all activities until the prior need is deemed satisfied, the immediate dangers of {{w|United Airlines Flight 173|UFIT}} and {{w|Controlled flight into terrain|CFIT}} are proportionately reduced (insofar as any pilot's {{w|Loss of control (aeronautics)|current circumstances}} allow) and yet leave time to be able to coordinate properly with any {{w|Separation (aeronautics)|other hazards}}.

[[Randall]] humorously "extends" this standard list with other ''-ate'' checklist items that pilots could do if they're not too busy aviating, navigating and communicating. These extra tasks go from somewhat hilarious to physically impossible or dangerous, see the [[#Table of extended priority items|table]] below for explanations. These actions {{w|Sterile flight deck rule|should generally not be taken}}, as they could distract the pilot and prevent them from reaching the cabin in case of an emergency, or simply vaporize everyone inside — including the plane itself.

The title text adds another ''-ate'' to the check list with Celebrate. It refers to airspace with stricter entry requirements overhead of large airports. In the US, the {{w|Airspace_class_(United_States)|airspace class}} over, for instance an airport, starts with a small circle over the airport and then becomes wider in one or two steps at higher altitudes. When depicted graphically, this looks like an [https://en.wikipedia.org/wiki/Airspace_class_(United_States)#/media/File:Airspace_classes_(United_States).png inverted tiered cake], as opposed to a [https://3brothersbakery.com/product/wedding-white-chandelier-tier/ regular tiered cake]. Randall suggests that after having congratulated yourself for flying a plane, you could then celebrate by serving the passengers cakes in this inverted shape. It would, however, be unsuitable for a plane to serve cakes that are smaller at the bottom than at the top because of turbulence.

===Table of extended priority items===
{| class="wikitable"
! Checklist item
! Description
! Explanation
|-
| Decorate || Make the cockpit fancy || {{w|Interior design}} of aircraft cockpits is usually starkly utilitarian and could conceivably benefit from enhancements if they aren't distracting.
|-
| Accelerate || See how fast you can go || While pilots are often keenly interested in the extents of their aircraft flight capabilities, maximum speed is inefficient in jet aircraft, and probably best explored in modern flight simulators than passenger flights.
|-
| Roller skate || Zoom down the aisle || Passengers would probably not appreciate this,{{cn}} although fellow crew members might be amused.
|-
| Exfoliate || Scrub away dead skin || {{w|Emery board}}s and {{w|pumice}} are used to prevent flaking and the development of {{w|callus}}es but dermatologists caution exfoliation is very often unnecessary and can have unwanted consequences.
|-
| Sublimate || Turn directly into a vapor || To the contrary, one of the most important duties of aircraft pilots is to prevent passengers and crew from vaporizing.
|-
| Pollinate || Fly low to stir up pollen || Low-flying helicopters can assist in plant {{w|pollination}},[https://www.sciencedirect.com/science/article/abs/pii/S037842901931175X] and are offered as a [http://www.flyingmair.com/ag-services/corn-pollination/ commercial service by helicopter pilots.] However, this is not normally done by (commercial) planes and would likely be both dangerous{{cn}} and ineffective.{{Actual citation needed}}
|-
| Congratulate || You're doing a good job flying a plane! || Self-esteem is an important component of mental health, and encouragement can help build it.
|-
| Celebrate (title text) || Serve passengers tiered cakes shaped like the airspace class diagram || See discussion of the title text above.
|}

==Transcript==
:[A list with ten numbered points are shown. Above the list is a large header. Below this is a divided line with a section header written in a smaller than standard font. The three first numbered points are below this. Then follows another divided line with section header written in smaller font and below this the next seven numbered points. All ten points have two lines of text. A line with a normal sized font and below each of these a description in a smaller light gray font.]
::<big>Pilot Priority List</big>
:-----------Standard section-----------
:1. Aviate
::Maintain control of the aircraft
:2. Navigate
::Figure out where you're going
:3. Communicate
::Stay in touch with ATC and others
:-----------Extended section-----------
:4. Decorate
::Make the cockpit fancy
:5. Accelerate
::See how fast you can go
:6. Roller skate
::Zoom down the aisle
:7. Exfoliate
::Scrub away dead skin
:8. Sublimate
::Turn directly to a vapor
:9. Pollinate
::Fly low to stir up pollen
:10. Congratulate
::You're doing a good job flying a plane!

{{comic discussion}}

[[Category:Food]]

2345: Wish on a Shooting Star

2020-08-13T05:58:30Z

172.69.33.129:

{{comic
| number = 2345
| date = August 12, 2020
| title = Wish on a Shooting Star
| image = wish_on_a_shooting_star.png
| titletext = Congratulations to whoever wished for revenge on a forest near the Tunguska River, a 1980 Chevy Malibu in Peekskill NY, Alabama resident Ann Hodges, every building in Chelyabinsk with glass windows, and the non-avian dinosaurs.
}}

==Explanation==
{{incomplete|Created by a NON-AVIAN DINOSAUR HATER. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
It is a common practice to make a wish when one sees a shooting star, in hopes that the wish comes true. This comic consists of a [[:Category:Venn diagrams|Venn diagram]] showing what things are commonly wished for upon seeing a shooting star, and what things the shooting star may cause. Shooting stars, as they are actually meteors, can only cause changes to physical phenomena, such as radio noise or the appearance of the sky as they burn up in the upper atmosphere. The only thing that is shared between the potential wish side of the diagram and the shooting star caused side is revenge. This would occur when a shooting star actually hits the planet, becoming a meteorite. This is frequently highly destructive, given the high speed of falling meteors. As such, it would be possible for the meteorite to hit something that someone for some reason or another wished revenge upon. However, given the massive surface area of the planet, the likelihood that someone's revenge would be "granted" by a meteorite would be very low. The title text makes fun of this by detailing several incidents where a meteorite landed and caused damage.

List of things that were damaged by meteors (from title text):
* On June 30, 1908 ({{w|Gregorian Calendar}}, Russia still used Julian and was recorded there as June 17), an {{w|airburst}} caused by the {{w|Tunguska Event|breakup of a 100-meter falling meteorite or comet}} with the energy of some 30 megatons of {{w|TNT}} flattened some 80 million trees over 830 square miles of land in central {{w|Siberia}} near the {{w|Podkamennaya Tunguska|Tunguska River}}. Due to the remoteness of the area, no people were confirmed dead in the incident.
* On October 9, 1992, a meteorite {{w|Peekskill meteorite|damaged a 1980 Malibu in Peekskill, NY}}.
* On November 30, 1954, a {{w|Sylacauga (meteorite)|fragment of a meteorite}} passed through the roof of a house and struck a woman named Ann Hodges. She survived.
* On February 15, 2013, a meteorite {{w|Chelyabinsk meteor|exploded in an airburst}} over Chelyabinsk, Russia, creating a shockwave that shattered windows in the area.
* The {{w|Cretaceous–Paleogene extinction event|extinction of the dinosaurs}} around 65 million years ago is believed to be caused by an {{w|Alvarez hypothesis|impact of a comet or asteroid}}. Randall mentions "non-avian" dinosaurs, as birds are descendants of dinosaurs, though they are not commonly thought of as dinosaurs.

Meteorites were most recently mentioned in [[2328: Space Basketball]].

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[A Venn diagram is shown:]

:[The left circle is labeled "Things people wish for" and contains:]
:Love
:Money
:Fame
:Health
:Power
:Luck
:Success

:[The right circle is labeled "Things shooting stars can cause" and contains:]
:Radio noise
:Dust and ionized gas in the upper atmosphere
:Infrasound
:Cool lights in the sky

:[The only item in the overlapping section is:]
:Revenge

{{comic discussion}}
[[Category:Astronomy]]
[[Category:Venn diagrams]]
[[Category:Comics featuring real people]]

2321: Low-Background Metal

2020-06-18T05:42:26Z

172.69.33.129: /* Explanation */ (A less destructive approach would be to simply drop metal into the water, without sinking any ships.)

{{comic
| number = 2321
| date = June 17, 2020
| title = Low-Background Metal
| image = low_background_metal.png
| titletext = The only effect on the history books were a few confusing accounts of something called 'Greek fire.'
}}

==Explanation==
{{incomplete|Created by a TIME TRAVELER. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
In this comic, a team including [[Megan]] and [[Black Hat]] have invented {{w|time travel}}. Time travel is a common trope in science fiction, and such a discovery would be likely to change the world as we know it. However, Megan and Black Hat's machine requires the use of "low-background" metal, which is in short supply.

Megan explains that, while delicate equipment is often shielded from radiation by lead, metal produced in modern times is contaminated by {{w|nuclear fallout}} in the atmosphere, which means that the shielding itself has enough radioactivity to interfere with highly delicate equipment. In order to shield this equipment, "low-background metal" is salvaged from sunken Roman ships. This metal, primarily lead, was used as ballast in the ships. The Roman lead was produced before atmospheric nuclear tests occurred and therefore did not have {{w|radionuclides}} in the air used in its manufacture. Because it has spent many centuries continually underwater, it is both shielded from radioactive particles, and has had time for natural radioactivity to fade.

The number of shipwrecks of that age that can be found and successfully salvaged for metal is quite small, which puts this material in short supply. Megan mentions that they have only enough for a single trip. The team realizes (apparently at [[Black Hat]]'s suggestion), that a solution is to use their single trip to take modern military hardware back to the era of the {{w|Roman Empire}} and use it to sink multiple ships. This would both provide for many more shipwrecks to salvage, and give the team a good idea of where those wrecks were, when they returned to modern times. They could also specifically target ships that were in waters that are well-suited for salvage operations. (A less destructive approach would be to simply drop metal into the water, without sinking any ships, eliminating the need to bring back modern military hardware.)

Megan is most likely referring to {{w|low-background steel}}, used in real life as shielding for highly sensitive particle detectors in physics and medicine. Low-background steel is in actuality salvaged from ships sunk before 1945 (the {{w|Trinity (nuclear test)|Trinity nuclear test}}), however, the ships used typically date back to World War I or World War II, and not the Roman Empire.

The title text refers to {{w|Greek fire}}, which was an incendiary weapon invented and employed by the Byzantine empire. It was a flammable liquid, famously said to burn on water, that was used in naval combat to set fire to enemy ships. As it was a closely-guarded military secret, many of the details have been lost to time, and modern chemists have only been able to develop educated guesses of what it ''probably'' was. Randall proposes a rather outlandish alternative hypothesis: that all records of Greek fire were actually in reference to the modern weapons used by the time travelers.

This is the second time a single-use time machine is available. The first occurrence was [[1063: Kill Hitler]].

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Megan, Black Hat and Cueball stand around a time machine on a table.]
:Megan: Our time machine works.
:Megan: But we're almost out of low-background metal.
:Cueball: What's that?

:[Close-up on Megan.]
:Megan: Modern metal is contaminated by fallout from nuclear testing, and lead also has natural radioactivity that fades over time.
:Megan: To shield sensitive equipment, physicists use lead from sunken Roman ships.
:Megan: But shipwreck lead is hard to find.

:[Zoomed back out to the group. Megan is facing Black Hat, who has his hand on his chin.]

:Black Hat: How much do we have?
:Megan: Enough for one trip through time.
:Black Hat: ''Hmmm...''

:[The scene changes to the group having traveled through time. They are in a helicopter, with Megan piloting, Cueball as a passenger, and Black Hat firing a flamethrower at a Roman ship. The sailors on the ship are alarmed and attempting to escape. Two already-burning ships can also be seen, with one almost completely sunk.]
:Flamethrower: FWOOOSH

{{comic discussion}}

[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Time travel]]

Talk:2321: Low-Background Metal

2020-06-18T04:50:44Z

172.69.33.129: Links

I can't help but notice that the basic premise of this comic is very much like the reason for going back to 1970 in ''Avengers: Endgame'', when they needed more Pym particles for time travel. I wonder if Randall re-watched it again recently? — [[User:KarMann|KarMann]] ([[User talk:KarMann|talk]]) 17:10, 17 June 2020 (UTC)

== Drawing ==

There's one leg of the time-machine missing from the 3rd panel. (or is it the side of a base?) --[[Special:Contributions/162.158.155.126|162.158.155.126]] 19:57, 17 June 2020 (UTC)

== Mined lead ==

Pb-210 (half-life 20.4 years) is a decay product of radon, and thus accumulates everywhere that is exposed to the atmosphere or where radon seeps from the ground. I suspect it could be a contaminant in lead from some lead mines, but wasn't able to find any references [[User:ShadwellNH|ShadwellNH]] ([[User talk:ShadwellNH|talk]]) 20:00, 17 June 2020 (UTC) Paul

== One use only? ==

The way I understand it, the time machine is one-use unless you find other Low-Background Metal. If you find it, you can make more trips. It would appear that the trip is successful.
--[[Special:Contributions/188.114.103.129|188.114.103.129]] 01:31, 18 June 2020 (UTC)

== Real life use of this lead? ==

Does anyone know whether there is any truth whatsoever to scientists using lead from sunken ships to shield delicate equipment? Obviously not time machines, but there are some pieces of equipment that might be sensitive to radiation.

Also, would lead that was in the ocean actually be safer from nuclear fallout than lead that was underground and mined after the nuclear testing ended? [[Special:Contributions/108.162.216.172|108.162.216.172]] 03:31, 18 June 2020 (UTC)
: Yes. At least it is done with steel. [https://hackaday.com/2017/03/27/low-background-steel-so-hot-right-now/][https://www.good.is/articles/the-search-for-low-background-steel][https://www.stainless-steel-world.net/mobile/webarticles/joanne-mcintyre/disappearing-warships-scavengers-raid-war-graves-for-low-background-steel.html] [[Special:Contributions/172.69.33.129|172.69.33.129]] 04:50, 18 June 2020 (UTC)