Editing 162: Angular Momentum

{{comic
| number    = 162
| date      = September 25, 2006
| title     = Angular Momentum
| image     = angular_momentum.jpg
| titletext = With reasonable assumptions about latitude and body shape, how much time might she gain them? Note: whatever the answer, sunrise always comes too soon. (Also, is it worth it if she throws up?)
}}

==Explanation==
Every moving object, including the Earth, possesses {{w|momentum}}. The Earth has a very high momentum due to its large mass and high speed as it orbits the Sun. However, the comic refers specifically to the Earth's angular momentum generated by its rotation on its axis, which creates the day/night cycle. This momentum can change (increase, decrease, or halt) through the application of force from another object, which acts as the transfer of momentum from one object to another.

[[Megan]] is attempting to slow down the Earth's angular momentum by spinning counterclockwise (a.k.a. {{wiktionary|anticlockwise}}) and force her momentum onto the Earth, so she can have more time to spend with [[Cueball]]. The momentum she produces is minuscule relative to the Earth's. The attosecond she's gaining by spinning while being with Cueball is nothing compared with the seconds spent spinning. A Reddit user [https://www.reddit.com/r/theydidthemath/comments/5ccbzs/comment/d9vskah calculated] that the time Megan is gaining by spinning is less than 1/20th of the time light takes to cross the diameter of an atom. Megan could gain a considerably larger (but still minuscule) amount of time [https://www.reddit.com/r/theydidthemath/comments/4mdihu/request_if_every_single_person_in_the_world_did/d3uvmk3/ by walking to the equator]. Later, in [[442: xkcd Loves the Discovery Channel]], the same kind of spinning Megan is used in the first frame to tell that xkcd loves momentum.  {{w|Wired (magazine)|Wired}} [https://www.wired.com/2014/04/can-you-slow-down-a-day-using-angular-momentum/ calculated] how much time Megan slowed down. This comic is referenced at the end of the ''[[what if? (blog)|what if?]]'' article ''{{what if|42|Longest Sunset}}''.

The title text also jokes that the amount of time Megan is gaining from spinning might also not be worth her risk of vomiting due to the dizziness.

==Transcript==
:[Cueball sits sideways on a bed under an open window in the corner of a room. He is looking at Megan, who is spinning fast, indicated with two large circles indicating where her arms that are spread far out rotate, as well as two smaller circles around her knees and feet. The bed sheets are clearly messed up, as if someone has used it for activities other than sleeping. It is night and dark gray outside the window, and inside the room everything is also gray but lighter. Behind the spoken text, the background is white, but fades to the darker gray at the edges. There is also different gray shading in different parts of the room.]
:Cueball: What are you doing?
:Megan: Spinning counterclockwise
:Megan: Each turn robs the planet of angular momentum
:Megan: Slowing its spin the tiniest bit
:Megan: Lengthening the night, pushing back the dawn
:Megan: Giving me a little more time here
:Megan: With you

==Trivia==
* This is one of the six [[Footer comics|footer comics]] featured in the bottom segment of [https://xkcd.com xkcd.com].
* This comic used to be [https://web.archive.org/web/20220125023401/https://store.xkcd.com/products/signed-prints available as a signed print] in the xkcd store before it was [[Store|shut down]].

{{comic discussion}}

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