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==

A '''moving object''' (like the Earth) has momentum. '''[https://www.quora.com/If-light-does-not-have-mass-then-how-does-it-have-momentum-1 Momentum]''' is the '''mass''' (size) of the object multiplied by the '''velocity''' (speed) of the moving object. So the Earth has a '''very high momentum''' because the Earth has a '''large mass''' (size) and is moving at a '''high velocity''' (speed) around the Sun. However, the momentum referenced in this comic is the angular momentum of the Earth spinning on its axis, which creates the days and nights. A moving object has to keep moving '''at the same velocity''' for its momentum to stay the same. The momentum of a moving object can increase, decrease, or stop via the force of another object. '''Force''' is the transfer of momentum from one object to another.

[[Megan]] attempts to slow down the Earth's angular momentum, and spins counter-clockwise to force her momentum onto the Earth, so that she can have more time with the one she loves. 

The Earth has a massively high momentum, and the momentum that she produces is minuscule relative to the Earth's. And the few nanoseconds gained by spinning, while being with Cueball, is effectively offset by the seconds spent spinning.

Slowing down the rate of time in the universe directly slows down the velocity of life, so there would be no change in the total duration of life. And as the text implies, this isn't even possible: ''While not being able to reverse time, enjoy your night time. Sunrise always comes too early.'' 

Her attempt of surmounting the seemingly impossible is grand; culturally, we value this kind of high romanticism.

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.

Technical notes: Angular momentum [https://www.quora.com/What-is-angular-momentum-in-laymans-terms depends on the axis used for measuring angular momentum].

Apparently, the time Megan is stopping is “[https://www.reddit.com/r/theydidthemath/comments/5ccbzs/request_this_xkcd_angular_momentum_by_what_small/ less than 1/20th of the time light takes to cross the diameter of a hydrogen atom]”

A considerably larger (but still minuscule) effect could be achieved by Megan (and/or Cueball and/or the bed) [https://www.reddit.com/r/theydidthemath/comments/4mdihu/request_if_every_single_person_in_the_world_did/d3uvmk3/ moving even a few meters closer to the equator]. This would also have the advantage of not interfering with any other activities Megan and Cueball might want to undertake in their time together.

==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 [[:Category:Footer comics|six footer comics]] linked at the bottom part of the {{xkcd}} website.
*This comic is available as a signed print in the [https://store.xkcd.com/products/signed-prints xkcd store].
*The {{w|Wired (magazine)}} [https://www.wired.com/2014/04/can-you-slow-down-a-day-using-angular-momentum/ calculated] how much time [[Megan]] slowed down. 

{{comic discussion}}
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