Recent comments in /f/askscience

dukesdj t1_j5pdaql wrote

Reply to comment by CrustalTrudger in What are the forces on Earth’s Inner Core that change its speed? by BayRunner

Given the arrival of another very similar question in this subreddit I suspect you are correct that this paper (or more likely the press release I assume it got) has caused some confusion. I can imagine that this particular sentence "This globally consistent pattern suggests that inner-core rotation has recently paused." which is in the abstract has been misunderstood by a nonzero number of people!

edit to add... when I initially answered the question there was no context text showing just a title. Not sure if the context was added later or this is a weird bug of reddit.

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0sted t1_j5pd9q2 wrote

Reply to Why does hot air cool? by AspGuy25

Reflectivity. The metal housing is reflecting the cooler temperatures behind the thermal camera and including it in the imaging.

Relatable similar occurance: I was working on an offshore oil platform once using a thermal gun to try to identify a leaking valve and found out pretty quickly that the polished steel gasket between the valve and pipe would reflect the temperature of open sky. I thought I found a leak when the gun registered a chilly 32F but was actually at like 100F on contact.

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flight_recorder t1_j5pb01t wrote

Reply to If I had two cups of water, one normal size and one as big as a swimming pool and stirred them both with proportionally sized spoons, would the larger pool of water keep spiraling longer than the smaller? by r3volc

That depends on how much velocity you give the water. If it’s spiralling at a similar rate then the outside water of the pool will have a higher velocity than the outside of the cup, that higher velocity means a massively larger amount of energy which will take a LOT longer to dissipate

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SXTY82 t1_j5p84u4 wrote

Reply to comment by Appaulingly in Why does hot air cool? by AspGuy25

yes. Also the reflectivity will affect non-touch thermal measurements. I use them at work now and then and anything that is silver colored, even non-shiny metals, I have to paint black to get an accurate reading from them.

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StunningScientist267 t1_j5p44uw wrote

Reply to comment by [deleted] in Why does hot air cool? by AspGuy25

Much like a flame of a fire or heat from an oven, as particles accelerate w heat they expand. This expansion makes them eventually condense back down due to temperature loss over distance. Hence why we get rain systems over mountains. If you want it to rain, build something big. Move mountains. Just ask permission first.

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shlepky t1_j5p2k9q wrote

Reply to comment by aspheric_cow in Why does hot air cool? by AspGuy25

Infrared thermometers usually have to be calibrated. When you get them, they measure radiation as if the surface they're measuring has emissivity ratio of 1 (black body radiation - which means all of the bodies heat is radiated out). If you know what the actual temperature is, you iteratively change the emissivity until you get the correct measurement. When you measure a different surface, you'll have to repeat the same process though. Cc: /u/AspGuy25

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CrustalTrudger t1_j5oyp4q wrote

Reply to comment by dukesdj in What are the forces on Earth’s Inner Core that change its speed? by BayRunner

I assume this question originated from buzz (and general misunderstanding) around the newly published Yang & Song, 2023 paper. Many are misinterpreting the suggestion made in this paper that there is a slowing or reversal of differential rotation of the inner core to mean instead mean a slowing or reversal of absolute rotation of the inner core. The competition between the EM and gravitational torques are front and center in this paper, so it's an important clarification to make.

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wazoheat t1_j5oxpe7 wrote

Reply to comment by FootballImpossible38 in What are the forces on Earth’s Inner Core that change its speed? by BayRunner

The core is not stopping or reversing it's course. That would be impossible due to being a violation of conservation of momentum.

The study that has been making it's rounds in the media suggests that the core has slightly changed it's rotational velocity relative to the surface, so that it is now spinning slightly slower compared to the surface rather than slightly faster as has been previously noted. They also show evidence that this may be a cycle that reverses every few decades. This is unrelated to the magnetic dynamo of the earth and it's roughly 100,000-year cycles.

The media coverage on this study is probably the worst I have ever seen. It's a very simple concept to explain, but if you explain it correctly it's boring, so I have to imagine that the journalists involved are being wilfully mislead, writing willfully misleading articles, or some combination of both.

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