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| − | ''Welcome to the | + | __NOTOC__{{DISPLAYTITLE:explain xkcd}} |
| + | <center> | ||
| + | <font size=5px>''Welcome to the '''explain [[xkcd]]''' wiki!''</font><br> | ||
| + | <span style="font size:210%;">We have an explanation for all [[List of all comics (full)|'''{{#expr:{{PAGESINCAT:All comics|R}}}}''' xkcd comics]], and only {{PAGESINCAT:Incomplete explanations|R}} ({{#expr: {{PAGESINCAT:Incomplete explanations|R}} / {{LATESTCOMIC}} * 100 round 1}}%) are incomplete. [[:Category:Incomplete explanations|Help us finish them!]]</span><!-- Note: the -1 in the calculation above has been removed (it was there to discount "comic" 404, but we've categorized it to be a comic and so has Randall.) --> | ||
| + | </center> | ||
| + | <!-- Go to this explanation button --><span style="position: absolute; right:0; padding-top:1.4em; font-size: 100%;"><span class="no-link-underline">[[{{LATESTCOMIC}}| </span>'''Go to this explanation''']]</span> | ||
| − | + | =Latest comic= | |
| + | <div style="border:1px solid grey; background:#f6f6f6; padding:1.5em;"> | ||
| + | {{:{{LATESTCOMIC}}}} | ||
| + | ---- | ||
| − | == | + | <span style="position: absolute; left:0; padding-top:1.35em; font-size: 105%;"><span class="no-link-underline"> [[File:new topic.png|21x21px|link={{LATESTCOMIC}}#Discussion]][[{{LATESTCOMIC}}#Discussion| </span>'''View comic discussion''']]</span><br><br></div> |
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| − | + | == New here? == | |
| − | + | <div style="float:right; margin: 0 0 1em 1em">{{Special:ContributionScores/10/7/nosort,notools}}<div style="font-size:0.85em; width:28em; font-style:italic">[[Special:ContributionScores|Lots of people]] contribute to make this wiki a success. Many of the recent contributors above have [{{fullurl:Special:Contributions|contribs=newbie}} just joined]. You can do it too! Create your account [[Special:UserLogin/signup|here]].</div></div> | |
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| − | + | You can read a brief introduction about this wiki at [[explain xkcd]]. Feel free to [[Special:UserLogin/signup|create an account]] and contribute to the wiki! We need explanations for xkcd [[:Category:Incomplete explanations|comics]], [[:Category:Characters|characters]], [[What If? chapters|''What If?'' articles]], and [[:Category:xkcd|everything in between]]. If it is referenced in an [[xkcd]] comic, it should be here. | |
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| − | + | * If you're new to wiki editing, see the [[explain xkcd:Editor FAQ]] for a specific guidance to this wiki and the more general help on [[mw:Help:Editing pages|how to edit wiki pages]]. There's also a handy {{w|Help:Cheatsheet|wikicode cheatsheet}}. | |
| − | + | * Discussion about the wiki itself happens at the [[explain xkcd:Community portal|Community portal]]. | |
| − | + | * You can browse the comics from the [[List of all comics (full)|list of all comics]] or by navigating the category tree at [[:Category:Comics]]. | |
| − | + | * The incomplete explanations are listed [[:Category:Incomplete explanations|here]]. Feel free to help out by expanding them! | |
| − | + | == Rules == | |
| − | + | Don't be a jerk! | |
| − | + | There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic. | |
| − | + | If you want to talk about a specific comic, use its discussion page. | |
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| − | + | Please only submit material directly related to xkcd and, of course, only submit material that can legally be posted and freely edited. Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked. | |
| − | If you | + | If you need assistance from an [[explain xkcd:Administrators|admin]], post a message to the [[explain xkcd:Community portal/Admin requests|Admin requests]] board. |
| − | + | [[Category:Root category]] | |
| − | [[ | ||
Latest revision as of 19:52, 31 July 2025
Welcome to the explain xkcd wiki!
We have an explanation for all 3190 xkcd comics, and only 55 (1.7%) are incomplete. Help us finish them!
Latest comic
| Jumping Frog Radius |
 Title text: Earth's r_jf is approximately 1.5 light-days, leading to general relativity's successful prediction that all the frogs in the Solar System should be found collected on the surface of the Earth. |
Explanation
The Schwarzchild radius is essentially the size of a black hole -- the maximum distance from the center where gravity is so strong that light can't escape.
The comic suggests a more useful radius of large gravitational bodies. The "Jumping Frog radius" is the size of a planet so that its gravity keeps a champion jumping frog from being able to achieve escape velocity.
The title text points out that the rjf of the Earth is about 1.5 light days, which is about 3 times the distance to Pluto. Since Earth's surface is much smaller than this[citation needed], no frogs will be able to escape, so they'll all collect here on Earth. As far as we know, all the frogs in the Solar System are on Earth, so the data apparently matches the theory.
The Schwartzchild radius is part of a solution to Einstein's field equations. It is usually calculated as the following:
r_{jf} = (2*G*M)/(c^2),
where G is the gravitational constant, M is the mass of the object, and c is the speed of light.
Instead of the 299,792,458 m/s speed of light, this comic uses a much smaller value of 4.5 m/s. It is possible that Randall got that value from this paper, which on page 179 puts an upper limit on the maximum velocity of adult Australian rocket frogs at 4.52 m/s.[1] This much smaller denominator increases the calculated radius from the 9 mm Schwartzchild radius to almost 4*10^13 m, or just over 1.5 light-days. As Pluto is never more than about 0.3 light-days away from Earth, we can safely say that any frogs in the Solar System should be found on the surface of Earth, despite there likely not being a real frog prediction in general relativity.[citation needed]
Transcript
- [The panel shows a formula and a drawing to its right.]
- rjf = 2GM/(4.5 m/s)2
- [A small planet with the radius marked as rjf and a frog jumping on the surface. The frog jumps about as high as the planet's radius, saying "ribbit" in midair and "plop" as it lands.]
- [Caption below the panel:]
- More practically useful than the Schwartzchild radius, the Jumping Frog Radius is the radius at which an object's gravitational pull is so strong that even a champion jumping frog can't escape.
View comic discussionNew here?
Last 7 days (Top 10) |
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You can read a brief introduction about this wiki at explain xkcd. Feel free to create an account and contribute to the wiki! We need explanations for xkcd comics, characters, What If? articles, and everything in between. If it is referenced in an xkcd comic, it should be here.
- If you're new to wiki editing, see the explain xkcd:Editor FAQ for a specific guidance to this wiki and the more general help on how to edit wiki pages. There's also a handy wikicode cheatsheet.
- Discussion about the wiki itself happens at the Community portal.
- You can browse the comics from the list of all comics or by navigating the category tree at Category:Comics.
- The incomplete explanations are listed here. Feel free to help out by expanding them!
Rules
Don't be a jerk!
There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic.
If you want to talk about a specific comic, use its discussion page.
Please only submit material directly related to xkcd and, of course, only submit material that can legally be posted and freely edited. Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked.
If you need assistance from an admin, post a message to the Admin requests board.- ↑ R. James & R. Wilson, "Explosive Jumping: Extreme Morphological and Physiological Specializations of Australian Rocket Frogs (Litoria nasuta)", Physiological and Biochemical Zoology, 81 (March/April 2008): 176-185.
