DAL59

Serious Scientific Answers to Absurd Hypothetical questions

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You can throw stuff by hand and get noticeable reaction thrust.

Say you throw a baseball at (since you're not a pitcher for MLB) 30 m/s.  The ball masses around .175 kg.  That gives an impulse of (30 * 1.75) = 5.25 kg*m/s -- which, assuming 100 kg of thrower plus EVA suit, would impart a velocity of about .05 m/s.  Not much velocity; that's about two inches per second in American units.  Still, it's not nothing.  Of course, the kind of overhand baseball throw that lets you get this kind of velocity would also put you into an uncontrollable tumble...

So, when you were out on the hull doing an emergency repair (hence why you'd be out there at all without either a maneuvering unit or a tether), you did remember to take your trusty sidearm (because what space libertarian would go anywhere without a gun? -- L. Neil Smith is smiling, somewhere in Colorado).  In a holster on the outside of your suit.  Better yet, it's been proofed for space conditions -- vacuum, which will evaporate the lubricants from the mechanism, and potentially cryogenic temperatures if it's been left in shadow for a few hours.  The grip and trigger guard have been modified to allow you to use the gun with space suit gloves.

You pull the gun, hold it in front of your belly (where your center of mass is), aimed directly away from your body, and pull the trigger.  Since you don't like wimpy guns, it's a 10 mm Auto (the most powerful semi-auto pistol that's both easily available and for which factory ammunition is readily found), kicking a 210 grain (13.6 g) bullet out the muzzle at 1600 ft/s (488 m/s).  We'll ignore the rocket effect of the gas from the cartridge -- it'll surely increase the impulse, but there's no convenient way to estimate it.  We get a bit over 6.6 kg*m/s from the bullet alone, possibly as much as that again from the gas -- so, at least as much, possibly as much as double the effect of throwing a baseball, in a much more controllable package (which, conveniently, has a magazine of perhaps a dozen or more cartridges available for immediate use and is easily reloaded with a spare magazine).

Better hope you brought several magazines -- if you're receding from the hull at a perceptible rate, you'll go through at least one just trying to stop...

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On 17/11/2017 at 10:03 PM, DAL59 said:

Could a sufficiently powerful magnet attract the iron in your blood?  

Hey, look, a video: 

 

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If the Earth, it's magnetic field and it's atmosphere were compressed into a flat disk, say, 10m high and was stabilized (by ultrahandwavium) in that configuration;
Could life exist and what effect would there be at different radii on the disk? 
Would this change the shape of Earth's gravity well and stability in solar orbit?
How would this effect spaceflight?

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3 hours ago, James Kerman said:

If the Earth, it's magnetic field and it's atmosphere were compressed into a flat disk, say, 10m high and was stabilized (by ultrahandwavium) in that configuration;
Could life exist and what effect would there be at different radii on the disk? 
Would this change the shape of Earth's gravity well and stability in solar orbit?
How would this effect spaceflight?

Morning :-)

I fear this one cannot be answered in a serious scientific way since it includes ignoring physics in many ways. The answer is left to imagination.

We are still trying to fully understand the current configuration ....

 

Edited by Green Baron
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Just for funsies:(

Gravitational force at the surface of the Earth (in 'disk' configuration):

GMm/r^2

M = 5.972 × 1024 kg

Now then, the average density of the Earth remains unchanged at 5.51 g/cm³ or 5.51 x 10-9 kg/m3 (because I said so)

Assuming the disk is a smooth disk with h = 10m, that makes Vdisk = 2 πhRdisk = 3.29 m3, so Rdisk = 5.237 x 1014 m2

G = 6.67408 × 10-11 m3 kg-1 s-2

so F (on a mass at the 'rim' of the Earth) = m*(1.45m/s2)

 

Or 1.45m/s2) is our new 'g'

To be continued when I get home/feel like it

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On 11/24/2017 at 11:23 PM, James Kerman said:

If the Earth, it's magnetic field and it's atmosphere were compressed into a flat disk, say, 10m high and was stabilized (by ultrahandwavium) in that configuration;
Could life exist and what effect would there be at different radii on the disk? 
Would this change the shape of Earth's gravity well and stability in solar orbit?
How would this effect spaceflight?

There was a novel by Stephen Baxter, Raft, which (incidental to the plot) explored some of the physics of gravity on a flat plate (the plate was the disassembled hull of a starship, after it had fallen through a wormhole into a universe where the gravitational constant was something like ten billion times what it is in ours -- stars were ten miles across, and when they died, a matter of some decades, left behind a ball of porous iron with 3 G at the surface).

Bottom line, gravity points inward to the barycenter of the plate.  The further you get toward the edge, the "steeper" the plate's surface gets, and at the very edge, you could stand (in greatly reduced gravity, since you're now much more than 4000 miles from the center, assuming mass and density are also preserved) with your body parallel to the "ground" of the upper and lower surfaces.  The titular raft of Baxter's novel had an apparent slope of around 45 degrees near the edge, but a wider plate could still get significantly steeper.

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On 11/24/2017 at 11:23 PM, James Kerman said:

If the Earth, it's magnetic field and it's atmosphere were compressed into a flat disk, say, 10m high and was stabilized (by ultrahandwavium) in that configuration;
How would this effect spaceflight?

If you're close enough to the center of the disk to encounter gravity normal (perpendicular) to the surface, you're bound to find a surprise as you fly away.  The gravitational force of a sphere falls away as 1/r2 from the center of the sphere; the gravitational force from an infinite disk (and the disk is "close enough" to infinite to act pretty infinite before you put some appreciable distance between you and it(*)) falls off as 1/r.  In other words, you'd find it harder to get away from a disc than to get away from the surface of a sphere.  I can do the math if you're interested.

---

(*) This is a pretty common trick in physics.  Sometimes, the math is easier if you pretend a surface is infinite.  The electric field of a capacitor can usually be modeled by an infinitely-large plate where the charges on it are distributed uniformly; the math is much easier, and the results you get are "close enough" to real life.

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What if 10% of CO2 atoms were replaced with Sulfur Hexaflourine (SF6) - most potent and nontoxic greenhouse gas?

This is done on Venus, Earth and Mars, I know they all get hotter, but by how much?

Universe Sandbox or Space Engine doesn't simulate atmospheric composition impact on temperature yet....

 

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5 hours ago, raxo2222 said:

What if 10% of CO2 atoms were replaced with Sulfur Hexaflourine (SF6) - most potent and nontoxic greenhouse gas?

This is done on Venus, Earth and Mars, I know they all get hotter, but by how much?

Universe Sandbox or Space Engine doesn't simulate atmospheric composition impact on temperature yet....

 

Fortunately, SF6 is also one of, if not the densest gas known.  Since gas density (at a set pressure and temperature) is proportional to molecular weight, with a molecular weight of 32+(19x6) = 146, SF6 is more than three times as dense as CO2 (MW 44). 

On Venus, you'd get an atmosphere that shrinks significantly, as the denser gas will compress the bottom a lot more than CO2 can.  Atmospheric pressure (in an atmosphere that's almost entirely CO2) will approximately triple, going from 90 bar to 270-ish bar.  Can't tell you what it would do to the temperature -- the atmosphere would be less deep, but the gas would block more of the long-wave infrared.  If I had to guess, I'd say it might get hotter, but couldn't guess by how much.

On Earth, with only a fraction of 1% of the atmosphere affected, you might actually get a net cooling, because of the density increase relative to CO2.  The gas would tend to sink to ground/sea level much more strongly than is the case now, and if it did so strongly enough to even partially differentiate (which CO2 can do in very sheltered locations when the concentration is high), the net greenhouse effect would be reduced, due to significant areas (highlands and mountains) rising above the bulk of the greenhouse gas.

On Mars, the atmosphere would shrink as it did on Venus -- but without 270 bar resisting, the effect would be much more pronounced.  The atmosphere would wind up concentrated in the Valles Marinaris, Hellas basin, and other deep depressions.  Most of Mars would get colder, rather than warmer, as it would be exposed to vacuum instead of slightly protected as it is now.

Edit: woops, I read that as all the CO2 becoming SF6.  With only 10% changed, you'd get some atmosphere shrinkage on Venus and Mars, and some pressure increase, but not as much.  Earth might not notice -- the net replacement would amount to less than .1% of the atmosphere, or less than the anthropogenic increase in CO2 over the past two centuries.

Edited by Zeiss Ikon
Misread question
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7 hours ago, Nikolai said:

I can do the math if you're interested.

I was just interested in the general effects but thank you.  My imagination had me thinking that you would be walking on the walls at some radii and you would be spun off nearing the rim and so I thought it might be easier getting to orbit than a sphere.  Very interesting about the center.

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If 1% of raindrops from now on were equal volume raindrops of osmium(they magically get turned into osmium when they start falling), what would happen?  

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4 minutes ago, DAL59 said:

If 1% of raindrops from now on were equal volume raindrops of osmium(they magically get turned into osmium when they start falling), what would happen?  

We would all die. Crystalline osmium is relatively inert at room temperature, but it becomes pyrophoric (spontaneously ignites in contact with air) when heated or powdered; either way osmium will eventually oxidise, producing osmium tetroxide which is highly volatile and very toxic. It is also soluble in water, meaning that even if you sheltered yourself from the rain, you'd eventually drink it.

Also, raindrops would probably hurt: each Os drop would be 22 times heavier, solid and much faster due to the increased density.

Finally, assuming Earth's water cycle remains constant (it won't) and all water is readily available for rain (it isn't), you'd be producing roughly 1017 kg of Os (over 10,000 times the world annual iron production) consuming about 5*1015 kg of water (0.0004% of the total mass of the oceans) the first year, decaying exponentially onwards (because you have less water to change to Os). Half of Earth's water would have decayed to Os after about 200,000 years.

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7 hours ago, Gaarst said:

Also, raindrops would probably hurt: each Os drop would be 22 times heavier, solid and much faster due to the increased density.

Actually, depending on cloud height, raindrops might be immediately lethal.  If the rain was water with 1% Os suspended in each drop, the impact wouldn't do significant harm, but if 1% of the drops were solid osmium, they'd have a terminal velocity close to the speed of sound (a round drop couldn't fall supersonic, at least at low altitudes) -- the rain would be like getting hit with the fringe of a charge of birdshot at 25 yards or so.  Unlikely to kill, as demonstrated by Dick Cheney a few years ago, but getting caught in a shower could result in an ER visit to get the osmium drops picked out of your scalp and shoulders, plus possible eye injuries (looking up at what's hitting you is a reflex) -- and if your luck is bad that day, you could die directly from a raindrop wound.  Going outdoors during the rainy season would entail wearing light armor and at least a hard hat and safety glasses, if you have more sense than a teen boy.

Interesting gunshot fact: most times, unless a bullet is in a location where slight movement could be fatal, they aren't removed; the surgery to pull a bullet out is likely to do more harm than leaving the bullet where it is.  The body will encyst the lead and if it doesn't rub on a bone or similar the lead won't dissolve -- hence the bullet can remain, harmless, for decades.  That would not be the case if you were using osmium shot -- its toxicity is much higher than that of lead.  In fact, cost aside, use of osmium shot would be a Federal crime in the United States, where it's illegal to use poisoned bullets or ammunition.

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Could we possibly make a nuclear grenade? Aka a nuke that can fit inside your hand, can be thrown like a grenade, and having the "mushroom cloud" explosion the size of grenade blast, and still leaves radiation in a relatively small area compared to tac nukes

Edited by ARS

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14 minutes ago, kerbiloid said:

Highly tabloidal, possible derivative of an April 1st PopMech article.

The radioactive decay issue should have been too obvious to even start going.

47 minutes ago, ARS said:

and having the "mushroom cloud" explosion the size of grenade blast, and still leaves radiation in a relatively small area compared to tac nukes

No, this part is the most impossible one. The smaller the nuke/thermonuke, the higher the radiation/blast ratio; that includes both fallout (larger bombs are more efficient at reacting their fuel) and the neutron emission - micronukes like the Davy Crockett are inherently neutron bombs.

So, no, it’d be decidedly unsafe to throw.

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13 minutes ago, DDE said:

Highly tabloidal, possible derivative of an April 1st PopMech article.

?
This (californium) theme was discussed since 1960s at least.

Edited by kerbiloid

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1 hour ago, ARS said:

Could we possibly make a nuclear grenade? Aka a nuke that can fit inside your hand, can be thrown like a grenade, and having the "mushroom cloud" explosion the size of grenade blast, and still leaves radiation in a relatively small area compared to tac nukes

 

47 minutes ago, DDE said:

No, this part is the most impossible one. The smaller the nuke/thermonuke, the higher the radiation/blast ratio; that includes both fallout (larger bombs are more efficient at reacting their fuel) and the neutron emission - micronukes like the Davy Crockett are inherently neutron bombs.

So, no, it’d be decidedly unsafe to throw.

It is possible.

You'd need the 'grenade' to be shaped like a teardrop.
The teardrop is filled with an chemical propellant with a high density and specific energy. It would produce a sharp shockwave.
The conical tail of the teardrop is a wave shaping device. It bends the shockwave by using bubbles to alter the density of the medium the shock wave travels through. This focuses the shockwave down to a point. It is a shaped charge that is potentially powerful enough to detonate a fusion fuel. 

icS8M2r.png
At bulbous end is the fission fuel. Fission has a minimum critical mass- for uranium, it is 52kg, for californium, it is 2.73kg. However, if the fission fuel is compressed by the aforementioned shockwave, and surrounded by a neutron reflector, then the minimum mass can be significantly reduced.

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On Titan, could you build a plane that ran off of tanks of compressed air and intaked methane from the atmosphere?  

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7 hours ago, MatterBeam said:

It is possible.

You'd need the 'grenade' to be shaped like a teardrop.
The teardrop is filled with an chemical propellant with a high density and specific energy. It would produce a sharp shockwave.
The conical tail of the teardrop is a wave shaping device. It bends the shockwave by using bubbles to alter the density of the medium the shock wave travels through. This focuses the shockwave down to a point. It is a shaped charge that is potentially powerful enough to detonate a fusion fuel. 

At bulbous end is the fission fuel. Fission has a minimum critical mass- for uranium, it is 52kg, for californium, it is 2.73kg. However, if the fission fuel is compressed by the aforementioned shockwave, and surrounded by a neutron reflector, then the minimum mass can be significantly reduced.

I've always wondered if it's possible to create a nuclear railgun shell that doesn't require a chemical implosion assembly.

8 hours ago, kerbiloid said:

This (californium) theme was discussed since 1960s at least.

I don't doubt californium exists, I just doubt this was ever went into such an advanced stage.

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3 hours ago, DAL59 said:

On Titan, could you build a plane that ran off of tanks of compressed air and intaked methane from the atmosphere?  

Absolutely, though it would make more sense to store tanks of nitrous oxide, which is  can be warmed and midly pressurized to be a liquid on Titan.  Lower pressure = lighter tank, and liquid = denser fuel, both of which improve overall performance.  Even better, N2O has a much higher fraction of usable oxygen (by mass) than air, even at the same density.

You'll have some fun dealing with temperature swings, though -- Titan's surface temperature is low enough that impure methane falls as rain and stands in lakes and "seas" (albeit at higher than standard pressure).   Combustion, however, would be at a similar temperature to what we're used to, so instead of a jet turbine's combustion section running at ~800 C in a -10 C environment (jet cruising altitude), you've got ~800 C combustion chamber in a -200 C environment.

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11 hours ago, MatterBeam said:

You'd need the 'grenade' to be shaped like a teardrop.

The teardrop is filled with an chemical propellant with a high density and specific energy. It would produce a sharp shockwave.
The conical tail of the teardrop is a wave shaping device. It bends the shockwave by using bubbles to alter the density of the medium the shock wave travels through. This focuses the shockwave down to a point. It is a shaped charge that is potentially powerful enough to detonate a fusion fuel. 

icS8M2r.png
 

Hmm.  I wonder if anyone has done any work on 3D printing in octanol?  That would allow precisely placing the focusing cavities ("bubbles").  I also wonder how big this would need to be to ignite a fusion core big enough to be "worth the effort" -- i.e. significantly more powerful than the initiating explosion?

Edited by Zeiss Ikon

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10 hours ago, Zeiss Ikon said:

Hmm.  I wonder if anyone has done any work on 3D printing in octanol?  That would allow precisely placing the focusing cavities ("bubbles").

DELET THIS

You’re giving Rocket Man ideas!

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On 29.11.2017 at 1:07 PM, DDE said:

No, this part is the most impossible one. The smaller the nuke/thermonuke, the higher the radiation/blast ratio; that includes both fallout (larger bombs are more efficient at reacting their fuel) and the neutron emission - micronukes like the Davy Crockett are inherently neutron bombs.

So, no, it’d be decidedly unsafe to throw.

A bit off topic but some explosions who are not nuclear give an mushroom cloud. Either because its an large air burst like huge fuel air bombs, during the first gulf war the US used fuel air bombs, mostly against mine fields and some soldiers reported it as nuclear explosions. Yes it was probably in the 50 ton tnt size. 

You can also get it other ways, remember in the army we dug an hole in an bog, put around 100 kg of explosives in it before filling it. 
It generated an picture perfect mushroom cloud, it even generated fallout with bog water many hundreds of meter downrange, raining down on one soldier who was left as guard. Think this cheated a bit blast was directed upward, and it included some ton of bog, as this slowed down it started to spread out. 
You would not get it from an normal airburst. 

 

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On 29.11.2017 at 2:14 PM, MatterBeam said:

 

It is possible.

You'd need the 'grenade' to be shaped like a teardrop.
The teardrop is filled with an chemical propellant with a high density and specific energy. It would produce a sharp shockwave.
The conical tail of the teardrop is a wave shaping device. It bends the shockwave by using bubbles to alter the density of the medium the shock wave travels through. This focuses the shockwave down to a point. It is a shaped charge that is potentially powerful enough to detonate a fusion fuel. 

icS8M2r.png
At bulbous end is the fission fuel. Fission has a minimum critical mass- for uranium, it is 52kg, for californium, it is 2.73kg. However, if the fission fuel is compressed by the aforementioned shockwave, and surrounded by a neutron reflector, then the minimum mass can be significantly reduced.

This don't look powerful enough to set of fusion but should work for fission. It has been a lot of work with making fusion work without the fission primer as in fusion power :)
Laser compression or z-pinch work but is not break even in energy. 
Modern US nukes uses an similar design but shaped like an american football and has two fuses, its smaller and way safer as both fuses has to trigger at once for the bomb to work.

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