Tuesday, February 17, 2009

Atmosphere and Centrifugal Force

Roland wrote:
Thanks for the Mars answer. That's exactly what I was looking for. On that one: from my years of experience half-watching the Science Channel, I learned that we still have an atmosphere because of the magnetosphere deflecting solar winds that would otherwise strip it away. Is that entirely erroneous, or how do the lack of geological replenishment and the lack of magnetic protection compare in the care and feeding of an atmosphere?
Well, that too is important, but only to an extent. The magnetosphere shields us from charged particles - such as energetic protons and electrons emitted in solar flares - but can't do anything about the uncharged ones like energetic photons. Sputtering will certainly happen faster without a magnetosphere, but extreme UV can still get in and do its worst.

Roland then wrote:
And, continual resupply: this means the molten hooey down there contains lots of N and about a fifth that much O, or what?
Well, sort of. The nitrogen that's emitted is largely in the form of various nitrous oxide compounds...but eventually gets to N2 in one way or another, as that's a really low energy state for N to occupy. Oxygen, on the other hand, also gets emitted via a much larger supply of CO2, (as well as SO2) but there's a lot of extra sinks for the oxygen to go to, such as carbonates, silicate rocks, iron oxide, and such. O2 only gets into that form through plants, and is actually quite a high-energy state...left to its own devices with no photosynthesis, O2 would pretty quickly disappear from the atmosphere.

Roland continued:
There are really centrifugal force deniers? Do they think that Wonder Woman's lasso has magical levitation properties in addition to its magical truth-extraction properties? What do they think is happening, you know, in a centrifuge? Have they ever been on a Tilt-O-Whirl? The mind boggles, and it's making me queasy just recalling how much I concretely, viscerally accept that that there is such a thing as centrifugal force. (You really shouldn't have mentioned the taffee right before I was going to have to mention the Tilt-O-Whirl.)
Hmm, I recall in high school physics that we learned "there's really no such thing as centrifugal force, it's just inertia and centripetal force." In college physics, I then learned that depending on your coordinate system (e.g. a turning car), there really is centrifugal force. It's all summed up rather nicely in this xkcd.

Roland concluded with:
Are there really people who think the moon *is bigger* on the horizon? Or do you just mean those who think the moon appears bigger because of atmospheric lensing? Because one is just insane and the other is just the kind of clever idea your high school science teacher would be wrong about. (I think the moon appears bigger because of my brain and seeing it near the horizon and other large-looking things without other scale reference. It seems likely I got both this and the atmosphere idea from people like high school teachers.)
I just mean the atmospheric lensing hypothesis, which is absolutely not true. The moon appearing larger is entirely psychological...as you stated, you don't realize how large an angular size the moon actually subtends until you see something like a distant building next to it. The moon is actually slightly smaller on the horizon (but only in the vertical direction) due to a steady gradation in atmospheric refraction.

But your statement, "just the kind of clever idea your high school science teacher would be wrong about," is, in general, precisely the kind of thing I'm railing against.


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