What-if 0064: "Rising Steadily"

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davidstarlingm
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Re: What-if 0064: "Rising Steadily"

Postby davidstarlingm » Wed Sep 25, 2013 2:13 pm UTC

rmsgrey wrote:Using the calculator on this site, a naked human with 2 square meters of skin radiating as a black-body at a temperature of 34 Celsius against a background of 3K radiates at around 1kW - so, treating the human body as mostly water, with a specific heat capacity of around 4 kJ/K/kg, and a typical body mass of around 60kg, it would take about 4 minutes to lose enough heat energy to reduce the average body temperature by 1K - call it 5 minutes to account for rounding errors.

Of course, that's ignoring the body's natural heat production - spot research turns up a basal metabolic rate of 90W, which can be supplemented by additional heat generation, but on its own is enough to make it "about 5 minutes" rather than "less than 5 minutes". To get it up to an hour, you'd need to be producing over 90% of the heat being radiated (call it 900W or ten times the basic rate).

Of course, the other factor is the body's ability to conserve core heat at the expense of extremities, which I'm not even going to guess at.

My prior calculation had assumed a non-naked human with less than one square meter of exposed skin; in this scenario, the body's metabolism accounts for large fraction of the radiative heat loss. I think it was around seven hours for the first two degrees, give or take three hours.

gmalivuk wrote:Well, since 1K isn't enough to freeze to death, but 5 minutes is enough to asphyxiate, I doubt too much additional precision would really be that useful.

And if you're stupid enough to hold your breath, bad things happen.

Durandal_1707 wrote:Wait, if the Death Zone is above "all but the highest mountains", then that means the very highest mountains go into it.

So how do people manage to climb Everest and not die of asphyxiation?

Acccclimatization. Or oxygen tanks.

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Re: What-if 0064: "Rising Steadily"

Postby Sandor » Wed Sep 25, 2013 2:28 pm UTC

davidstarlingm wrote:
Durandal_1707 wrote:Wait, if the Death Zone is above "all but the highest mountains", then that means the very highest mountains go into it.

So how do people manage to climb Everest and not die of asphyxiation?

Acccclimatization. Or oxygen tanks.

There's a documentary about this - Doctors in the Death Zone (see YouTube). A bunch of doctors climb Everest, to see what exactly happens to the human body as it acclimatizes to being almost 8km up. There are some surprisingly large physiological changes (vastly expanded blood vessels, etc.). Even with many weeks/months of acclimatization you still only have a limited time within the death zone for the final ascent and descent (if you're doing it without oxygen).

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Re: What-if 0064: "Rising Steadily"

Postby Whizbang » Wed Sep 25, 2013 3:28 pm UTC

What if this "Take off" was perfectly timed (and placed) so that "up" was tangental to the orbit of the center of the Earth? So, in fact, she is slowing her orbital velocity relative to the sun (am I terming that right? I don't science very well.) such that she seperates from the Earth at 1f/s, but is still traveling in the same orbital path as the earth, only slightly slower (and the invisible, infinite energy rocket is always pushing tangental to the Earth's orbit, thereby decelerating her, rather than pushing her farther out). This would, I believe, solve the light-speed horizontal speed issue. The Earth would spin beneath her, of course, which causes an issue someone mentioned before, namely running into stuff as the Earth spins around while she is close to the gorund. Assuming she didn't run into anything, what would happen? Would her orbital path change very much (ie move toward or away from the sun)? If so, would she move far enough away to avoid the Earth colliding with her as it catches up with her going the other way? How long before the Earth laps/smashes into her?

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Re: What-if 0064: "Rising Steadily"

Postby david.windsor » Wed Sep 25, 2013 4:15 pm UTC

Ok, all this talk of how cold is it at 2km up, I'm almost totaly certain she is rising through the International Standard Atmosphere if so, it is still 2.004ºC at 2km She would not hit the freezing level until 2.309km
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Re: What-if 0064: "Rising Steadily"

Postby speising » Wed Sep 25, 2013 9:11 pm UTC

http://mvl.mit.edu/EVA/biosuit/index.html

the biosuit is a space suit which is not airtight. it only uses mechanical pressure to keep its wearers bits in. evidently its designers do not consider heating neccessary.

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Re: What-if 0064: "Rising Steadily"

Postby DanD » Wed Sep 25, 2013 9:31 pm UTC

speising wrote:http://mvl.mit.edu/EVA/biosuit/index.html

the biosuit is a space suit which is not airtight. it only uses mechanical pressure to keep its wearers bits in. evidently its designers do not consider heating neccessary.



They appear to be primarily focusing on non-terrestrial planetary surfaces. It's also not clear from the limited information if temperature regulation of the gas inside the suit (torso and helmet are airtight, limbs include gas filled tubes) is intended to be implemented if necessary.

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Re: What-if 0064: "Rising Steadily"

Postby Klear » Wed Sep 25, 2013 10:15 pm UTC

speising wrote:http://mvl.mit.edu/EVA/biosuit/index.html

the biosuit is a space suit which is not airtight. it only uses mechanical pressure to keep its wearers bits in. evidently its designers do not consider heating neccessary.


I've been wondering about feasibility of this, ever since I read that vacuum is a lot less hostile that I always though. By that I mean, yeah, it's pretty hostile, but not on the level of immediate explosion, freezing, and boiling at the same time.

It appears that as long as you don't hold your breath, your respiratory system won't get too damaged (though you'll obviously start to suffocate, parts of your body will begin to swell (but having tight clothing is enough to prevent it) and the low pressure won't make your blood boil, since if it began to boil, it would only serve to increase the pressure, thus stabilizing you. The 0 K temperature doesn't really affect you that much since there is nowhere for your heat to go (I think I remember reading that you'd feel a little chilly from moisture on your skin evaporating... or something).

Turns out you can probably remain conscious in vacuum for a little over 10 seconds and then have more than a minute to survive without irreversible damage...

(Of course, feel free to point out any and all inaccuracies I've just made. I don't feel like re-reasearching this right now.)

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Re: What-if 0064: "Rising Steadily"

Postby kiochi » Wed Sep 25, 2013 10:38 pm UTC

As you approach the Death Zone, your blood oxygen content would plummet. Your veins are supposed to bring low-oxygen blood back to your lungs to be refilled with oxygen. But in the Death Zone, there's so little oxygen in the air that your veins lose oxygen to the air instead of gaining it.[10]


This seems to be clearly false. The article cited has no sources but contains the following

(Note that the partial pressure of oxygen in alveolar air at 25,000 feet is 14% of 281.8 mm Hg or 39.5 mm Hg -- slightly less than that normally found in venous blood returning from the tissues. Which way do you think the oxygen will diffuse at altitudes above 25,000 feet?)


Which is perhaps where RM got his "fact" from. In fact, people have spent long periods in the Death Zone, including a sherpa who spent 21 hours on the summit of everest (8850m). (I can't post a link because it is getting flagged as spam, but google "Babu Chirri Sherpa".) If your veins were only losing blood to the air around (and never gaining) then this would be impossible. Indeed, that scenario would be worse than not breathing, which results in death in a matter of minutes.

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Re: What-if 0064: "Rising Steadily"

Postby speising » Wed Sep 25, 2013 11:38 pm UTC

of course...
The Hitchhiker's Guide to the Galaxy wrote: that if you hold a lungful of air you can survive in the total vacuum of space for about thirty seconds. However, it does go on to say that what with space being the mind-boggling size it is the chances of getting picked up by another ship within those thirty seconds are two to the power of two hundred and seventy-six thousand, seven hundred and nine to one against.

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Re: What-if 0064: "Rising Steadily"

Postby gmalivuk » Thu Sep 26, 2013 12:06 am UTC

Whizbang wrote:What if this "Take off" was perfectly timed (and placed) so that "up" was tangental to the orbit of the center of the Earth? So, in fact, she is slowing her orbital velocity relative to the sun (am I terming that right? I don't science very well.) such that she seperates from the Earth at 1f/s, but is still traveling in the same orbital path as the earth, only slightly slower (and the invisible, infinite energy rocket is always pushing tangental to the Earth's orbit, thereby decelerating her, rather than pushing her farther out). This would, I believe, solve the light-speed horizontal speed issue. The Earth would spin beneath her, of course, which causes an issue someone mentioned before, namely running into stuff as the Earth spins around while she is close to the gorund. Assuming she didn't run into anything, what would happen? Would her orbital path change very much (ie move toward or away from the sun)? If so, would she move far enough away to avoid the Earth colliding with her as it catches up with her going the other way? How long before the Earth laps/smashes into her?
If she slows down relative to the Sun, and the rocket exactly counters the effects from Earth but nothing else, then her orbit would fall a bit toward the Sun because it wouldn't be quite fast enough to stay at the same distance.

Slowing by 1fps in Earth's orbit around the sun is about a 10ppm change in velocity, which translates to a similar change in kinetic energy, or about a 20ppm change in specific orbital energy, and thus in semimajor axis. If Earth were in a circular orbit at exactly 150 million km from the center of the Sun, this translates to 3000km, or about half Earth's radius.

In other words, she wouldn't be out of the way when Earth came back around, but it would only hit her at the previously stipulated one foot per second, so the main problem would still be running into things on the surface as it rushes by at 1000mph.
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Re: What-if 0064: "Rising Steadily"

Postby Mistake_not » Thu Sep 26, 2013 5:58 am UTC

I'm sure there is something obvious about basic mechanics that I'm not understanding but I'd appreciate if someone could explain how an object travelling at 1 foot per second achieves escape velocity?
Thanks!

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Re: What-if 0064: "Rising Steadily"

Postby dalcde » Thu Sep 26, 2013 8:52 am UTC

Mistake_not wrote:I'm sure there is something obvious about basic mechanics that I'm not understanding but I'd appreciate if someone could explain how an object travelling at 1 foot per second achieves escape velocity?
Thanks!


It doesn't.

You don't need to reach escape velocity to escape.
On the other hand, reaching escape veloctiy does not gaurantee escape.

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Re: What-if 0064: "Rising Steadily"

Postby gmalivuk » Thu Sep 26, 2013 12:11 pm UTC

Also, it would eventually reach escape velocity, because escape velocity decreases with distance, so there's eventually a point where it is 1 foot per second.
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Re: What-if 0064: "Rising Steadily"

Postby mathmannix » Thu Sep 26, 2013 1:48 pm UTC

Not a physicist, but my understanding is escape velocity is the initial speed necessary to escape gravity without using any further propulsion. But we are assuming that Megan climbs with a constant net velocity of 1 foot per second, not just that she was initially thrown vertically at that speed, which would cause her to quickly return to earth.

Basically, a wizard did it.
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Re: What-if 0064: "Rising Steadily"

Postby davidstarlingm » Thu Sep 26, 2013 4:15 pm UTC

Technically, the accurate term would be "escape speed", because as long as you're up to that speed, you will escape regardless of what direction you're headed in. Unless, of course, you're headed in a direction which intersects the surface of the planet, in which case you're screwed.

Earth's escape velocity drops to one foot per second around 9e15 meters away, or roughly 20% beyond the outer radius of the hypothesized Oort cloud. Of course, Earth's sphere of gravitational influence is only 1.5e9 meters, much less than a millionth of this distance.

With a ballistic trajectory, escape velocity is reached over a relatively short distance with a very rapid engine burn, and then you "coast" the rest of the way. Once you're "coasting", you're in free fall, but you're moving away from Earth too fast for Earth's gravity to ever "catch" you. Megan, on the other hand, will still be pulled down by gravity just as much as if she were simply in an elevator.

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Re: What-if 0064: "Rising Steadily"

Postby SteveMB » Fri Sep 27, 2013 3:48 pm UTC

FrobozzWizard wrote:River Tam has let me down with her calm assurance that we'd freeze to death before asphyxiating!


The explanation is clear enough:

If you were nude, you'd probably succumb to hypothermia somewhere around the five hour mark, before your oxygen ran out.


Obviously, River's statement was contingent upon the implicit assumption that everybody would be getting naked. I'm afraid she let you down far worse than you thought.

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Re: What-if 0064: "Rising Steadily"

Postby gmalivuk » Fri Sep 27, 2013 4:30 pm UTC

No, becauae she wasn't talking about rising at 1 ft/s.
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Re: What-if 0064: "Rising Steadily"

Postby zaphodbeebledoc » Wed Oct 02, 2013 3:18 pm UTC

After reaching the Death Zone watch out for targeted lightening bolts and a super-fast silver fighting Robot. Also if someone offers you immortality, don't accept!
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Re: What-if 0064: "Rising Steadily"

Postby gladiolas » Fri Jan 09, 2015 10:19 pm UTC

How much fat and muscle you have, and how they're distributed on your body, would affect how fast you lose heat.


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