Fat people in zero gravity

[Enraged Slith]

I'm curious, what would an incredibly fluffy fat person look like in zero gravity? Would they become perfectly rotund or would they jiggle around in space like a giant jello mold?

 

I know there are quite a few physics experts here, so fess up; the people demand answers.

[Student of Trinity]

Zero gravity is just like falling. Well, except for air resistance, but that only becomes noticeable after you've been falling far enough to pick up a lot of speed, and at that point, you're in trouble. If you want to know what it feels like to turn off gravity, just jump from a high diving board. If you want to know what someone else looks like in zero gravity, sit at a pool with a high tower, and watch people jump.

 

(In fact, when people say that being in space makes you weightless, what they really mean is that being in orbit around the earth makes you weightless. It's not because there's no gravity at that altitude. If there were really no gravity up there, the space shuttle would just go sailing off in a straight line toward the stars and not come back. It's being in orbit that makes you weightless, because orbit is falling. It's just falling while moving forward fast enough that the curvature of the Earth is sinking away beneath you as fast as you're falling down, so you never hit the ground. Orbit is falling forever.)

[Alorael at Large]

Do people jiggle more in space? Probably a bit, because gravity isn't there to pull things down if they bounce up. But not a lot more, because quite a bit of what keeps us from jiggling is us: our connective tissues, our muscle, or skin, everything that holds us together.

 

Would fat people be rounder? That, of course, depends on the fat. Sagging bellies would sag less without something tugging them down, but you have to have quite a lot of fat around your midsection for it to go down and not just out.

 

—Alorael, who thinks one of the biggest differences would have nothing to do with fat. Without gravity pulling it down, a lot of fluid in your body would end up in strange places, probably especially noticeably in your face.

[Necris Omega]

Well the lack of gravity does promote muscle dystrophy, so while a person in space may not necessarily be jigglier, they will overtime become squishier.

[Alorael at Large]

Muscular atrophy. Dystrophy refers to genetic disorders that lead to progressive loss of muscle function.

 

—Alorael, who doesn't think anyone would volunteer for space flight with muscular dystrophy as the consequence.

[Pyrrhus]

You have to remember that they are FAT. Would nasa hurt the weight limit by putting a team of Fat people? I think not.

[Actaeon]

Surely even a three or four hundred pound man would be negligible in comparison with a two thousand ton shuttle (or the Russian equivalent).

[Alorael at Large]

NASA would be unlikely to send anyone up who didn't meet stringent fitness criteria because it's a cautious agency. As far as feasibility goes, weight wouldn't make much difference.

 

—Alorael, who imagines that the burgeoning space tourism industry will start getting more people with more weight into less gravity. Surely someone will bring a camera. Just keep your eyes on YouTube.

[waterplant]

Internal space may become an issue with oversized bodies passing through connecting portals and working in the confined workspace of a capsule. Also, larger bodies, according to Ernest Shackleton, require considerably more food to sustain themselves.

[Enraged Slith]

If we can send a person into space, then we can send an obese person into space. Then, someday, we can send every obese person into space.

[Actaeon]

Well, if "we" means the United States, we actually cannot currently send anyone into space.

[A less presumptuous name.]

I'm surprised no one has mentioned Wall-E yet.

[keira]

Ship in deep space lists to the side. Fat people start sliding.

 

In other words, a movie that should not be permitted to exist.

[Student of Trinity]

Meh, they had artificial gravity. Just smile and nod.

[Alorael at Large]

If humans were to invent strong AI, I think we'd try to pile on a lot of human traits. It would make us feel a lot less uncomfortable about our inevitable steel overlords.

 

—Alorael, who would just be happy if the ship in deep space didn't start listing because all the fat people were over on one side.

[Necris Omega]

... maybe staffing a ship with fat people means they have to waste less energy on any sort of artificial gravity system?

[Lilith]

Originally Posted By: Necris Omega

... maybe staffing a ship with fat people means they have to waste less energy on any sort of artificial gravity system?

that's not how gravity works

[Dintiradan]

Soylent Gravity!

[keira]

speaking of fat people, overflow leftovers had to go into the fridge in my room. I have half a ham and an entire 7/8 3/4 of a pumpkin pie now.

[waterplant]

fat floats doesn't it?

[Trenton.]

No, but bowling balls, and rusty anchors, and jets, and elephants, and wieghts float.

[Erebus the Black]

1Kg propelled to space ~= 20,000$ in fuel costs (including the cost of the extra fuel weight required to propel the extra fuel for the 1Kg).

Fuel cost of propelling a fat man to space: ~20,000 * ~200 = 4,000,000

to top that you need extra gear in the worth of a few 10^7$ just to keep him alive through all stages of travel (departure, travel & return).

[A less presumptuous name.]

Erasmus - just how fat are we talking? 200 kg is 441 lb.

[Actaeon]

I don't think I know anyone that heavy.

[Dantius]

Originally Posted By: waterplant

fat floats doesn't it?

In what? Helium floats in air, fat floats in water, and pretty much everything floats in mercury...

[keira]

Fat is less dense than water, so yeah fat floats. If you're ever in a cruiseship with deficient amounts of lifeboats, just run to the buffet line and grab the biggest one you can find.

[Aran]

Originally Posted By: Student of Trinity

It's just falling while moving forward fast enough that the curvature of the Earth is sinking away beneath you as fast as you're falling down, so you never hit the ground. Orbit is falling forever.)

Or, in the words of DNA, "throwing oneself at the ground and missing".

[Alorael at Large]

Everything is less dense than 0 gravity!

 

—Alorael, who knows a guy whose BMI puts him in the solidly overweight and nearly obese category. He's a bodybuilder, and it's all muscle. The guy can't swim because he has trouble with buoyancy.

[Student of Trinity]

Originally Posted By: Lilith

Originally Posted By: Necris Omega

... maybe staffing a ship with fat people means they have to waste less energy on any sort of artificial gravity system?

that's not how gravity works

Well, people do generate gravity, and so a big enough crew could generate as much gravity as you want. But they might not be effective as a crew if they were all clumped together in the hold.

[Harehunter]

I knew a guy in my reserve unit who was like that; had to do a weight/displacement test to pass his physical every year.

 

On a lighter note, a lead zeppelin will fly; but it's not very durable or practical. You have to press the lead so thin, it would be little more than foil.

[Dintiradan]

I remember doing something like that in one high school science class. How big does a hollowed-out steel cube containing a vacuum have to be to float in air? I think we assumed 1cm thick walls, and that the steel wouldn't have to be otherwise enforced.

[Erebus the Black]

Originally Posted By: Master1

Erasmus - just how fat are we talking? 200 kg is 441 lb.

I have an uncle who weighed more before he had his stomach stapled, so I'm not impressed.

[Harehunter]

I don't believe that it is possible. The requirement of strength in the container walls to resist the implosive force of 1 atmosphere of pressure means that the mass (or weight) of the container would always exceed the mass of the air displaced, thus having a negative buoyancy. The larger you made the container, in an effort to increase the displacement, the more steel you would have to have to A) contain the added volume, and to strengthen the already too heavy walls.

 

Nice thought, though. Anti-gravity anyone?

[Lilith]

Originally Posted By: Harehunter

I don't believe that it is possible. The requirement of strength in the container walls to resist the implosive force of 1 atmosphere of pressure means that the mass (or weight) of the container would always exceed the mass of the air displaced, thus having a negative buoyancy. The larger you made the container, in an effort to increase the displacement, the more steel you would have to have to A) contain the added volume, and to strengthen the already too heavy walls.

Actually, the square-cube law would seem to imply that it's possible: the total force on the big steel balloon from air pressure will be proportional to its surface area, which is proportional to the square of its length, but the buoyancy of the balloon will be proportional to its volume, which is proportional to the cube of its length. That means the buoyancy should increase faster than the amount of steel you need.

[Harehunter]

I thought of that, but as the size of the container increases, it presents a less and less curved surface to that 1 atmosphere of pressure, making it more likely to be crushed, and thereby lose it's displacement. In order to prevent that, more steel would have to be added to the thickness of the wall to resist that crushing force. I do know from my engineering courses that with piping, if you have a 3" pipe with 1/2" walls with a material strength of 1000psi and a safety factor of 1.5, it can operate at 300psi safely with a bursting pressure of 500 psi. Increase the diameter of the pipe to 6", leaving all other variables constant, and you can only operate safely at 100psi with a bursting pressure of only 200psi.

Engineers calcs.

 

In order to bring the 6" pipe to the same spec as the 3" pipe you would have to *double* the wall thickness of the 6" pipe to 1".

[Alorael at Large]

The original question explicitly assumes an infinitely strong material with the density of steel.

 

I'm also not an engineer, but I don't understand your claim. For one thing, the "balloon" here is cubic. It doesn't present any curved surfaces. The force at all points on the balloon is 1 atmosphere, which inch-thick steel can withstand without breaking. The real difficulty is the non-infinite stiffness of steel, and that's beyond my physics/engineering acumen.

 

—Alorael, who would find this much more tractable with a hydrogen-filled steel balloon.

[Harehunter]

When you turn the sphere into a cube, you bring in another factor, hydrodynamics. It gets pretty complicated, but essentially it boils down to this: A sphere is an object that presents the most uniform force distribution against all points of its surface than any other object. With a cube, you get the greatest force factor in the corners, a little less along the edges, and progressively less force as you move towards the center of the face. To prevent an implosion with this type of structure, you would need to add reinforcing struts to apply force against the faces, meaning more mass of materials, increasing your weight, without an increase of volume.

 

Filling the space with helium is more feasible because you decrease the density of material in the contained volume, but you can equalize the pressure, allowing you to use thinner walls, less mass, and therefore achieve buoyancy.

 

As for finding an infinitely strong material, I suppose that is possible...

 

at the heart of a neutron star...

 

where the gravity is even greater, therefore requiring an infinitely large displacement to establish a positive buoyancy...

 

I've think I've such gone over the event-horizon..........

[Randomizer]

Originally Posted By: Better living through shaping!

—Alorael, who would find this much more tractable with a hydrogen-filled steel balloon.

Hindenberg? Oh, the humanity.

Zepplins didn't use steel to save weight.

[Lilith]

there actually isn't very much difference in buoyancy between using hydrogen, helium and vacuum, since they're all a lot closer to the density of each other than they are to the density of air. the main reason helium wasn't used very much in early zeppelins is that it's expensive

[Erebus the Black]

Originally Posted By: Lilith

there actually isn't very much difference in buoyancy between using hydrogen, helium and vacuum, since they're all a lot closer to the density of each other than they are to the density of air. the main reason helium wasn't used very much in early zeppelins is that it's expensive

A. Pure vacuum is probably even more expensive.
B. Hare's assertion was that Helium would provide pressure to the inside of the cube which vacuum would not, hence removing the destructive pressure factor.

[Lilith]

Originally Posted By: Erasmus

Originally Posted By: Lilith

there actually isn't very much difference in buoyancy between using hydrogen, helium and vacuum, since they're all a lot closer to the density of each other than they are to the density of air. the main reason helium wasn't used very much in early zeppelins is that it's expensive

A. Pure vacuum is probably even more expensive.
B. Hare's assertion was that Helium would provide pressure to the inside of the cube which vacuum would not, hence removing the destructive pressure factor.

i know all that, i was just mentioning a thing that people might find interesting

[Student of Trinity]

What you really want is a tiny bit of really hot hydrogen inside the steel balloon, to supply exactly one atmosphere of pressure, with negligible weight. Then your balloon skin can be pretty flimsy.

 

What actually lifts the balloon is not the total air pressure, but the pressure gradient. Even in a tiny little kid's balloon, the air pressure at the bottom of the balloon is just a tiny bit greater than the air pressure at the top of the balloon. It would not be easy to measure such a tiny difference, but it is definitely there, because otherwise all the air in the slab of volume between the balloon's top and bottom would fall down. Air has weight, after all. The only thing that keeps any given layer of air from falling is that the air beneath it pushes up a bit harder than the air above it presses down.

 

In fact the pressure difference, properly integrated over the balloon's surface and blah blah blah and all, has to provide exactly one simple amount of total force: the weight of that volume of air, at the ambient density. Because that's why the air around the balloon isn't falling.

 

So with equalized total pressure from a very low-density filling, what a balloon skin really has to support is just the stress of its own weight, and that of its payload. A modest thickness of steel can probably manage that okay. Heck, you could use plastic wrap inside a thin steel mesh.

 

Heat-resistant plastic wrap, so the hot filling doesn't make it melt.

 

I guess you could do the same thing with hot vacuum. That is, black body radiation at high enough temperature would supply one atmosphere of pressure. How hot would it have to be? Lemme see. Pressure is basically energy density, so we've got to make an energy density of temperature and the speed of light, and I guess Planck's constant, since thermodynamics is really quantum mechanics laying low. So something like (k_B T)^4/(\hbar c)^3, to be one atmosphere, which is about 100,000 Pa. So something like 100,000 degrees Celsius, that ballpark. Pretty hot. Might need to find something better than electrician's tape for the balloon skin.

 

Interestingly, the Casimir force on a sphere is positive, opposite to that between two parallel planes. So a really small balloon could be supported by vacuum pressure even at absolute zero. I'm not sure how helpful this is.

[Alorael at Large]

Originally Posted By: Harehunter

With a cube, you get the greatest force factor in the corners, a little less along the edges, and progressively less force as you move towards the center of the face. To prevent an implosion with this type of structure, you would need to add reinforcing struts to apply force against the faces, meaning more mass of materials, increasing your weight, without an increase of volume.

I know nothing about fluid dynamics, and I'm confused. I agree about reinforcing, which was still deliberately removed as a concern in the original problem. I don't understand the beginning of what you said. Is force factor force tolerance? I can see there being more force on corners and edges, or at least the sum of more than one force vector from pressure against different faces, but why would there be less pressure on the center of a face than on any other part of the edge?

—Alorael, who doesn't think the Hindenburg just avoided metal for weight. He also somehow suspects that surrounding hydrogen with metal would be a bad idea, which was part of the thinking behind the original rigid airship materials. And he's surprised to hear that vacuums are expensive. He'd guess that a reasonable approximation thereof shouldn't be too bad. Are pumps much more expensive than the fossil fuels needed to produce hydrogen? Production by electrolysis seems like it would almost certainly be less energy efficient.

[Niemand]

Quote:

I can see there being more force on corners and edges, or at least the sum of more than one force vector from pressure against different faces, but why would there be less pressure on the center of a face than on any other part of the edge?

Surely the point is that the force is the same, but the centers of the faces are weaker and will collapse under a smaller force?

Quote:

Alorael, who doesn't think the Hindenburg just avoided metal for weight. He also somehow suspects that surrounding hydrogen with metal would be a bad idea, which was part of the thinking behind the original rigid airship materials.

Zeppelins did use metal skeletons, for exactly the same reason that most modern airplanes are metal: you want a good strength-to-weight ratio for your structure. I think that sparks jumping to or from the frame was a concern, and has been suggested as the cause of the Hindenburg disaster. I'm not sure if you're suggesting that there would be chemical implications, but the hydrogen wasn't directly in contact with the metal, since it was in bags made of Goldbeater's skin. (Perhaps that was part of what you were getting at though. )

Originally Posted By: SoT

I guess you could do the same thing with hot vacuum. . .

I love this idea, and all the more because of its total impracticality. It's a sort of stellar balloon, supported against the air by radiation pressure just as stars are against gravity.

[Alorael at Large]

You're agreeing with what I've said, but it seems like the opposite of what Harenhunter said about forces. Or maybe I've misunderstood.

 

Zeppelins are basically rigid structures built around balloons.The structure can be arbitrarily dense as long as the balloons provide enough lift to counter it. The balloons themselves weren't metal, probably for a combination of reasons. The practicality of having large, thin metal sacks is one. The risk of putting the hydrogen in contact with metal is probably another, which was what I was saying.

 

—Alorael, who is of course well aware that brass and wood, preferably with a dark stain, are the high standard for all airships and other steampunk accoutrements. But, alas, in the early 20th century there was less concern for such aesthetic niceties.

[Lilith]

Originally Posted By: Everything is Impossible

He also somehow suspects that surrounding hydrogen with metal would be a bad idea, which was part of the thinking behind the original rigid airship materials.

your suspicion is correct for what it's worth, although i don't know if it has anything to do with the composition of airships. hydrogen atoms are small enough that they can intercalate themselves into the spaces between metal atoms, causing defects in the metal's structure and making it brittle. it's called hydrogen embrittlement and it's a serious problem when you want to store hydrogen

[Harehunter]

I just lost a few more hairs on the top of my nearly bald pate. Yes, according to fluid dynamics, there is an equal pressure applied at every point of the surface of the container. The problem with the cube buckling under pressure has less to do with fluid dynamics, and more to do with Structural Engineering.

 

The ability of practically any material to resist compressive forces better than they can resist shearing or bending forces is at the crux of this problem. The mathematics is nothing less than applied differential calculus, but to make a long story short, an arch is a structural shape that translates all forces applied against it into a compression axis. When you apply the concept of the arch to 2 dimensions you get a dome, and in 3 dimensions you get a sphere.

 

In the case of a cube you are creating a structure that presents six planes at right angles to the force applied to it, leaving it up to the tensile strength of the material to resist the force applied to it. The differential calculus of continuum mechanics can be used to calculate the effect of mechanical stresses on materials, but it is so complicated that most engineers just use data from empirical measurements more than the math.

 

Note, I said continuum mechanics, not fluid dynamics, nor even fluid mechanics. That similarity of terms tripped me up too. They have their place in this problem, but by themselves they don't answer the problem at hand.

 

You can still build a cube that will have the same uniform load-bearing capacity across of its surfaces by simply thickening the material gradually as you approach the center of the plane, sort of a lensatic increase rather than angular.

 

You guys are fun to discourse with. You challenge me intellectually. And Lilith, you gave me an intellectual thrill to think of hydrogen embrittlement. That tweaks my memories to when I was a chemistry major in college.

[Karoka]

At this rate, I'll end up getting a major in science as a sophomore.

[Dantius]

Originally Posted By: Harehunter

snip

Oooooor you could just assume infinite structural strength with the density of steel like Dinti said, and then use a trivial amount of basic math to solve a cubic and get "a side length 369.815 m", since I highly doubt a high-schooler is expected to be well-versed in solid mechanics or tensor calculus or stress analysis or any sort of structural principles beyond maybe Hooke's law.

[Harehunter]

It's that teensy little thing in your assumption that bothers me:

Where would you be able to find a material of infinite structural strength? In order for it to have infinite tensile strength, it would have to have an infinite density, yielding an infinite mass, thereby requiring an infinite displacement in order to achieve the buoyancy to escape that infinitely strong gravity well.

 

Essayons, Karoka