explain xkcd - User contributions [en]

300: Facebook

2022-05-04T20:36:53Z

141.101.105.27: Undo revision 242146 by Ex Kay Cee Dee (talk)

{{comic
| number = 300
| date = August 8, 2007
| title = Facebook
| image = facebook.png
| titletext = 'Here, I'll put my number in your cell pho -- wait, why is it already here?'
}}

==Explanation==
This comic approaches how {{w|Social network}}s have changed the ways of human interaction. With everyone placing their personal interests on their {{w|Facebook}} profile pages, it has become fairly easy to gather a lot of information about people. In the comic, [[Cueball]] uses this information to his advantage: He ascertained [[Megan|Megan's]] musical preferences beforehand in order to create the illusion of their sharing mutual interests. Megan is led to believe that he is {{w|soulmate|like-minded}}, thus making it easier for Cueball to persuade her into having sex with him. Here the comic takes at the fact that many people use Facebook as a hunting ground for sexual contacts.

Apparently, Megan did not only mention her favorite bands in her profile, but also her preferred {{w|sex position}}. This can be read as a sideswipe at what intimate details some people are willing to share on the internet. Although mentioning sexual preferences is hyperbolic here.

Megan's taste in both fields can be regarded as outside the mainstream. {{w|Regina Spektor}} and {{w|The Polyphonic Spree}} are representatives of the {{w|indie pop}} genre. The [http://www.menshealth.com/sex-position-playbook/wheelbarrow-standing ''Wheelbarrow''] ({{w|NSFW}}) features the man standing behind the woman and holding her legs, while she props up in a wheelbarrow-like position. The retrograde variant has the woman facing upwards. Unusual sex positions are also mentioned in comics [[414: Mistranslations]] and [[487: Numerical Sex Positions]].

The title text suggests that Cueball did not stop at reading Megan's interests on her Facebook profile, but also obtained her phone number and placed it in his phone. It is implied that some of the "mildly sleazy" uses of Facebook can border on the verge of {{w|stalking}}. When Megan discovers the number, she may realise this and stay clear of Cueball...

==Transcript==
:Mildly sleazy uses of Facebook, part 14:
:Looking up someone's profile before introducing yourself so you know which of your favorite bands to mention
:Cueball: Favorite bands? Hmm...
:Cueball: Maybe Regina Spektor or the Polyphonic Spree.
:Megan: Whoa, those are two of my favorites, too!
:Megan: Clearly, we should have sex.
:Cueball: Okay! My favorite position is the retrograde wheelbarrow.
:[Megan raises arms.]
:Megan: Ohmygod, mine too!

{{comic discussion}}

[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Sex]]
[[Category:Social networking]]

2614: 2

2022-05-03T08:21:10Z

141.101.105.27: Undo revision 232231 by 162.158.107.84 (talk)

{{comic
| number = 2614
| date = May 2, 2022
| title = 2
| image = 2.png
| titletext = It's like sigma summation notation, except instead of summing the argument over all values of i, you 2 the argument over all values of 2.
}}

==Explanation==
{{incomplete|Created by 2 squared - Please change this comment when editing this page. The titletext needs to be worked in there, but I think I got everything else in some sort of order, pending general improvements. Do NOT delete this tag too soon.}}

This demonstrates the different ways in which the number 2 can be typeset in various scientific fields.

The dotted box represents any character (presumably a letter or bigram of letters). All the other notation consists only of the digit 2, in various fashions with occasional additional punctuation, and labelled as to what the 'purpose' might normally be of any particular element(s) as indicated, with respect to the general term, in the following fashions:
;Regular Math
:Precedes the term. "2x" indicates two times the value of ''x'' in normal {{w|algebra|algebraic}} use that should be familiar for many people.
;Physics
:A preceding superscript. "2H" would indicate the particular {{w|isotope}} of Hydrogen with the atomic weight of two, i.e. deuterium, which is most often encountered when working with the atomic level of matter where the total number of neutrons and protons in the atom is important.
;Chemical Physics
:A preceding subscript, "2He" indicates the atomic number of an atom, which is the number of protons it contains, and thus a guide to the number of electrons its unionised form usually has and hence meaningful in its potential chemical interactions with other atoms. This should be invariant for any particular named element, but is usually given simultaneously with the presuperscripted mass number where it can be indicative of the applicable nuclear physics.
;Regular Math or Footnotes
:A trailing superscript is typical of a {{w|Exponentiation|power value}}, in this case "x²" would be ''x'' multiplied by a second copy of itself, and a fairly typical mathematical standard.
:Additionally, superscripted numbers are one common way to mark words in a line of text in a way to refer to a {{w|Note (typography)|footnote}}, typically placed at the bottom of the page, with additional information that would not be appropriate or easily comprehendable to edit into the main text itself. The ambiguity between footnotes and exponents was used in [[1184: Circumference Formula]]
;Chemistry
:A trailing subscript is used in chemistry to indicate a multiple of the element (or group of elements, in brackets) in a {{w|chemical formula}}. "H2O" indicates two hydrogen atoms bond with a single oxygen atom in a molecule of water.
;Matrices!
:Extending the trailing subscript with a comma-separated value usually indicates a multidimensional array (e.g. establishing a 2-by-2 square of numbers, or this particular position in such an array), which is in the realms of {{w|Matrix (mathematics)|matrix mathematics}}. This is a little bit beyond 'everyday algebra' for many people, as seemingly indicated by the exclamation of the mere mention of matrices!
;The Physicists Are At It Again
:This label encompases a mark that turns the prior comma into a semicolon, as part of the trailing subscript. This is a common notation for the {{w|Covariant derivative}} of a tensor field, which is commonly used in the mathematics of general relativity.
;Either High School Math Function or Incomprehensible Group Theory
:The number 2 in parentheses that follow a term would normally be the argument to a {{w|Function (mathematics)|function}}, e.g. "f(2)", which means that you should take the value (in this case 2) and find the result if manipulated by the predefined function ''f''. It is generally taught as part of algebraic mathematics already described, i.e. at {{w|Secondary school|High School}}.
:In {{w|group theory}}, however, the number 2 in parentheses could indicate a cyclic subgroup or ideal generated by two or a special case of cycle notation for elements of symmetry groups used to mean an element that keeps 2 fixed. This may be somewhat beyond high-school level.
;Oh no. Whatever this is, it's cursed.
:A symbol centered underneath another symbol is normally reserved for doing summations, where the big symbol is Σ, or some other operation applied to a sequence of numbers.
:It does not make sense to have a single number there, as indicated in the alt text. As with [[2529: Unsolved Math Problems|other things]] in Randall's comic universe, the explanation for this particular anomaly is that it is 'Cursed'.

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

[An apparently scientific expression:]

[normal text:] 2 [superscript behind the box:] 2 [subscript behind the box:] 2 [an empty box with a dotted outline] [superscript:] 2 [subscript:] 2;2 [normal text:] (2) [smaller and beneath the last 2:] 2

;[Captions above the numbers]
:[with an arrow pointing to the first 2:] Regular Math
:[with an arrow pointing to the behind superscript 2:] Physics
:[with an arrow pointing to the regular superscript 2:] Regular math or footnotes
:[with an arrow pointing to (2):] Either high school math functions or incomprehensible group theory

;[Captions below the numbers]
:[with an arrow pointing to the behind subscript 2:] Chemical Physics
:[with an arrow pointing to the regular subscript 2:] Chemistry
:[with an arrow pointing to a grey circle around ";2":] The physicists are at it again
:[with an arrow pointing to a smaller grey circle inside the other circle that leaves out the dot of the semicolon:] Matrices!
:[with an arrow pointing to the 2 below the 2:] Oh no. Whatever this is, it's cursed.

{{comic discussion}}
[[Category:Math]]
[[Category:Physics]]
[[Category:Chemistry]]

2509: Useful Geometry Formulas

2021-08-31T13:00:24Z

141.101.105.27: /* Explanation */ (I want to use "db.sinθ" notation for clarity, but it looks wrong(er), so trying this way.) The d*b rhomboid is the d*b 'rectangle' ''times sinθ'', I think, in all cases, including as rhomboid prism face and factored into volume. Ok?

{{comic
| number = 2509
| date = August 30, 2021
| title = Useful Geometry Formulas
| image = useful_geometry_formulas.png
| titletext = Geometry textbooks always try to trick you by adding decorative stripes and dotted lines.
}}

==Explanation==
{{incomplete|Created by a DECEITFUL TEXTBOOK ILLUSTRATOR. Explain the formulas for each of the areas, and also the correct formula for the 3D object they seems to represent. Do NOT delete this tag too soon.}}
This comic showcases area formulae for four two-dimensional geometric shapes which each have extra dotted and/or solid lines making them look like illustrations for 3-dimensional objects - the first, a simple equation for a circle, the second an equation for a triangle with an elliptical base, the third an equation for a rectangle with an elliptical base and top, and the fourth a hexagon consisting of two opposing right angled corners and two parallel diagonal lines connecting their sides. In each case, only the outlines of each shape have any practical meaning.

Such illustrations are commonly found in geometry textbooks, which need to depict three-dimensional figures on a two-dimensional page. They use slanted lines to indicate edges receding into the distance, and dashed lines to indicate an edge occluded by nearer parts of the solid. The joke is that the formulae given here are for the area of each two-dimensional shape as drawn, not for the surface area or volume of the illustrated 3D object (as would be shown in the geometry textbook). And that the textbooks just add the "decorative" stripes and dotted lines within a 2D shape to trick the reader, as stated in the title text.

The illustrations depict the following plane or solid figures, depending on the interpretation.

Top left.&emsp;A circle (illustrating a sphere) with radius r. The equation for the area of a circle is A = πr2 as is given below the figure. The surface area of a sphere is 4πr2 , which is what we would have expected from the figure. The volume of a sphere is 4/3 πr3.

Top right.&emsp;An isosceles triangle of height h combined with a semi-ellipse with semiaxes a and b (illustrating a right elliptic cone). The area of the triangle is bh, and the area of the semi-ellipse is π/2 ab. he equation for this area is A = 1/2 πab + bh as is given below the figure. However, if this was in a text book then a=b even if drawn like this, thus the cone has a circular base, in the 3D drawing. Such a "normal" cone has an area A = πb^2 + πbl. (a=b). That cones volume would be πr^2*h/3. Taking the 3D drawing literal with a≠b then the lateral surface area of a right elliptic cone is 2a√(b2 + h2) ∫01 √(a²h²(t²-1) - b²(a²+h²t²)/a²(t²-1)(b²+h²)) dt. The volume is π/3 abh.

Bottom left.&emsp;A rectangle of width d and height h between two semi-ellipses of semi-minor axis r (illustrating a right elliptic cylinder). The area of the rectangle is dh and the area of the two half-ellipses equals the area of one full ellipse, π/2 dr. The equation for this area is A = d(πr/2 + h) as is given below the figure. For a 3D representation the cylinder has circular base so d = 2r, (not elliptical as indicated in the 2D drawing). Such a cylinder has a surface area of 2πr^2 + πdh. The volume of such a cylinder is πr^2h. Taking the 3D drawing literal with d≠2r then the lateral surface area of the right elliptic cylinder is 4h ∫01 √(1 - t²(1-4r²/d²)/1 - t²) dt. The volume is π/2 rdh.

Bottom right.&emsp;A convex hexagon with three pairs of parallel sides and two right angles at opposite vertices (illustrating a rectangular prism). The area of the rectangle representing the front face of the prism is bh. The area of the upper parallelogram is db sin θ. The area of the right parallelogram is dh cos θ. The equation for this area is A = bh + d(b sinθ + h cosθ) as is given below the figure. The surface area of the prism would be 2bh + 2db sinθ + 2dh. The volume is bdh sinθ.

In the history of the development of computer-generated 3D graphics, calculations of the apparent visual area taken up by the projection of a volume may have been useful in occlusion-like optimizations, where each drawn pixel may be passed through many fragment shaders.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Four figures in two rows of two, each depicts a two-dimensional representation of a three-dimensional object, with solid lines in front and dotted lines behind. Each figure has some labeled dimensions represented with arrows and a formula underneath indicating its area. Above the four figures is a header:]
:Useful geometry formulas

:[Top left; a 'sphere', or a circle with a concentrict half-dotted ellipse sharing its major axis, with the shared semi-major radius labeled 'r']
:A = πr²

:[Top right; a 'cone', or a triangle with the base replaced by a half-dotted ellipse. The triangular/conic height is 'h'. The ellipse in place of the base has semi-minor axis 'a' and major axis 'b']
:A = 1/2 πab + bh

:[Bottom left; a 'cylinder', or a pair of ellipses connected by verticals. The vertical side/edge is shon as height 'h'. The ellipses have semi-minor axis r, in the lower half-dotted ellipse, and major axis d, across the upper ellipse]
:A = d(πr/2 + h)

:[Bottom right; a 'rhomboid-based prism', or a semi-regular hexagon with identical pairs of vertical, horizontal and diagonal sides, plus three more congruent pairs (one of each dotted) all linking inwards from their own vertex to meet at one of two complimentary points within. The representative horizontal line is marked 'b', a vertical is 'h', a diagonal as 'd'. Between the base horizontal and the lower internal diagonal is a non-'rightangled' angle 'θ']
:A = bh + d(b sinθ + h cosθ)

{{comic discussion}}

[[Category:Math]]

Talk:2507: USV-C

2021-08-25T17:57:46Z

141.101.105.27:

I just did my first edit! It'll definitely get changed, but I guess this is good enough for a start

[[Special:Contributions/162.158.89.204|162.158.89.204]] 16:30, 25 August 2021 (UTC)

that's not as absurd as it sounds. there are optical usb cables which work by converting the usb signals to and from light signals.[[Special:Contributions/162.158.92.83|162.158.92.83]] 16:48, 25 August 2021 (UTC)

I bet this is going to be an xkcd that gets recreated in real life.

[[Special:Contributions/108.162.215.87|108.162.215.87]] 17:01, 25 August 2021 (UTC)

There are ultraviolet LED lamps that are powered at 5V with an USB connector. xkcd in real life it's already done.
[[Special:Contributions/141.101.105.27|141.101.105.27]] 17:57, 25 August 2021 (UTC)

2504: Fissile Raspberry Isotopes

2021-08-19T05:48:47Z

141.101.105.27: Raspberry pie meson, not blackberry.

{{comic
| number = 2504
| date = August 18, 2021
| title = Fissile Raspberry Isotopes
| image = fissile_raspberry_isotopes_2x.png
| imagesize = 559x290px
| titletext = Grandma's shelf-stable blackberry pie meson recipe was a huge seller until her farm was shut down by a joint FDA/NRC investigation.
}}

==Explanation==
{{incomplete|Created by a NUCLEAR FARM INVESTIGATOR. Do NOT delete this tag too soon.}}

The comic is a joking analogy to {{w|nuclear chain reactions}}, in which the {{w|nuclear fission|fission}} (splitting in two) of one {{w|atomic nucleus}} releases {{w|neutrons}}, which then strike other nuclei and cause them in turn to fission, releasing more neutrons. This chain reaction releases a great deal of energy and is what makes possible both {{w|nuclear power}} and {{w|nuclear bombs}}. A {{w|fissile isotope}}, such as {{w|uranium-235}}, is one that is sufficiently large and unstable to undergo such a chain reaction. Here [[Ponytail]]'s raspberries are shown undergoing a similar fission-driven chain reaction, though of course in real life raspberries don't do that.{{citation needed}} As an {{w|aggregate fruit}}, raspberries resemble common depictions of atomic nuclei, with each ovary corresponding to a nucleon (proton or neutron), which is probably why they are the subject of the comic. Perhaps these raspberries are byproducts of the experiments depicted in [[1949: Fruit Collider]].

This comic is also a pun on "pi mesons" or {{w|pions}}, subatomic particles that transmit the {{w|strong nuclear force}}. This transmission happens most importantly in the atomic nucleus and is responsible for keeping the nucleus intact, i.e., preventing it from undergoing fission despite the strong repulsive {{w|electromagnetic force}} present from all the positively-charged {{w|protons}}. The faith in the pie recipe being able to impede the danger seems to be toned much like a typical resigned commentary on someone's consistently and relentlessly awful cooking, perhaps over-processed until what is always naively intended to be a fruity treat turns out to be a dense, stodgy, even glue-like filling and/or pastry that acts to {{w|Neutron moderator|mitigate}} any budding {{w|Aggregate fruit|'berry'}} chain-reaction.

The title text refers to the {{w|Food and Drug Administration}} (FDA) and the {{w|Nuclear Regulatory Commission}} (NRC). The FDA is responsible for the regulation and inspection of food in the U.S., and the NRC for the regulation and inspection of nuclear facilities and materials. A hypothetical "raspberry pie meson" might well run afoul of both, being both nuclear and therefore subject to NRC regulations and permitting requirements, and unhealthy to eat and thus violating FDA rules.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
[Ponytail and Cueball are standing in a field, looking at a farm.]

Ponytail: I reckon it'll be a good harvest.

Ponytail: So long as we don't get too many fissile raspberry isotopes.

Cueball: Too many ''Whats''?

[A picture of a raspberry splitting into smaller parts is shown below some text]

Text: If a raspberry breaks in half, it releases fragments which can cause more splits. Within seconds you've lost the whole crop.

[Ponytail and Cueball face each other to discuss this]

Ponytail: Luckily the berries are bound by fresh raspberry pie mesons.

Cueball: I hope they hold.

Ponytail: It's my grandma's recipe. They'll hold.

{{comic discussion}}