#angular momentum

[n0rtist]

Mers Chrimbo Everyone!

[dreaminginthedeepsouth]

[thank you xkcd]

[sleepy-bebby]

Source 🚲

[elkement]

Poinsot's Pixel Spaceship

Physics of the force-free gyroscope:

The energy ellipsoid intersects the angular momentum sphere!

(Series, work in progress)

[yesterdays-xkcd]

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?)

Angular Momentum [Explained]

Transcript Under the Cut

[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

[whats-in-a-sentence]

Move mass closer to something's spin axis and, if angular momentum is conserved, and will spin faster; move it farther out and things will slow down. It is an underappreciated side benefit of scientific progress that figure skating, originally developed on a frozen fen near Cambridge as a way of demonstrating this phenomenon, has gone on to become a very popular sport.*

* This is not true.

"The Moon: A History for the Future" - Oliver Morton

[startswithabang]

Did We Just Find The Largest Rotating ‘Thing’ In The Universe?

"Why are they rotating, however? Is it something that can truly be explained by tidal torques and nothing else? The early evidence points to “yes,” as the presence of large masses near the filaments — what cosmologists identify as “haloes” — seems to intensify the rotation. As the authors note, “the more massive the haloes that sit at either end of the filaments, the more rotation is detected,” consistent with gravitational torques inducing these motions. Nevertheless, more study is needed, as temperature and other physics may also play a role.

The big breakthrough is that we’ve finally detected rotation on these unprecedentedly large scales. If all goes well, we’ll not only figure out why, but we’ll be able to predict how quickly each filament that we see ought to be spinning, and for what reason. Until we can predict how every structure in the Universe forms, behaves, and evolves, theoretical astrophysicists will never run out of work to do."

We know that on small scales, everything rotates. We know that on the scale of the entire observable Universe, there's no rotation to be seen. Well, what are the largest structures, then, that do rotate? Galaxies? Galaxy clusters? Something even bigger? Yes, something bigger!

The cosmic filaments that connect galaxy clusters, spanning 100+ million light-years, really do rotate! Here's what we know, and here's what we think is going down.

[therealuniverse]

BLACK WIDOW PULSAR TURNS OUT TO BE FASTEST PULSAR DISCOVERED About 18 years ago astronomers came across a strong source of gamma-rays in the Centaurus constellation which they have now confirmed to be a pulsar, PSR J1311-3430. What makes this discovery different is that until now pulsars have only been found using pulsed radio emissions whereas this one was the first to be found using its gamma radiation pulse. Interestingly enough this pulsar is also a member of a superfast moving binary system.

A team of scientists lead by Dr. Holger Pletsch(Max Planck Institute) collected data using NASA's Fermi satellite which is designed to find gamma radiation pulses. After a 4 year data collection period they were able to clearly identify a gamma pulse signal. Their calculations found that this is the fastest pulsar discovered so far, spinning at a staggering 390 times per second. This means a single rotation would take this pulsar roughly 2.5 milliseconds to complete. However, PSR J1311-3430 didn't get to this blistering speed on its own. What has now become a highly dense stellar core is the pulsar's companion star. The picture to the left is an artist’s rendition of the binary system. At eight times more massive than Jupiter yet a little over half the size, this stellar core has around 30 times the density of our sun. The companion stellar core, which was once a star, was slowly stripped of its material over time and absorbed by the pulsar. As a result PSR J1311-3430 accelerated to its current rotational speed. The companion being stripped of its stellar material also resulted in the two objects moving closer together and they are now orbiting their center of mass in about 93 minutes. The two objects are just under 1.5 times the distance of the moon from the Earth and the pulsar's orbit speed is around 13,000 km/h where the stellar core companion's orbit speed is just under 3 million km/h. "At present, the remaining stellar core, which presumably consists mainly of helium, is heated by the radiation from the pulsar and literally evaporated," said Holger Pletsch. What this means is that eventually the stellar core will be completely absorbed by the pulsar, hence the term black widow, and the pulsar will spend the rest of its life tumbling through space on its own. -TAZ Image Credit: SDO/AIA, AEI Source: https://science.sciencemag.org/content/338/6112/1314