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Nicolas
2006-Jul-24, 10:05 AM
I had some questions on moving around in a spacecraft. So zero G, but inside an atmosphere.

Is it possible to swim in the atmosphere as you do underwater? (slower I guess, but anyway :))

If you swing your arms backwards, does your body move forward as a reaction to this backwards impulse? (so disregarding pushing yourself against the atmosphere as in the swimming question). Could you move yourself over large distances this way, or would the time integrated impulse of your movements be zero anyway, no matter how violently you swing your arms backwards and gently put them back to front?

And when floating in a horizontal way, can you roll over your longest axis (like turning in bed) just by twisting your body?

I'm a bit stuck on action/reaction things within a single body. Must be the holidays :).

Tog
2006-Jul-24, 10:27 AM
Totally guessing here:

I would think that swimming wouldn't work, as the density of air is so much less than water, there wouldn't be the resistance to use to "push off" for swimming to work.

I also think that swinging both arms back might move your body forward due to that 'every action has an equal and opposite reaction' thing, but that the two may balance each other out.

On the other hand, I can swivel my chair by rapidly twisting my arms in the air in front of me.

What would concenr me in 0g is sneezing. I have some pretty good ones sometimes. I'd hate to end up in some sort of rapid spin with no way to stop.;)

Nicolas
2006-Jul-24, 10:42 AM
Thinking about it (and doing some testing :)) I think that you can move yourself around by swinging your arms. I can turn on a turning chair by swinging my arm sideways. I think that the pushing against the atmosphere would be really small compared to the impulse* reaction force.

So swimming would be possible, but not in the first place due to the atmosphere but due to impulse*. With the right arm movements, I think you could propell yourself forward with your arms using impulse*, though I still have some doubts about the time integrated impulse possibly being zero.

Does anyone know whether you indeed can travel distances using impulse* or does the time integration indeed add up to zero, so you don't really move long distances?

*oh btw what I call "impulse" is called "momentum" in English IIRC. mass*velocity.

trinitree88
2006-Jul-24, 10:44 AM
I had some questions on moving around in a spacecraft. So zero G, but inside an atmosphere.

Is it possible to swim in the atmosphere as you do underwater? (slower I guess, but anyway :))

If you swing your arms backwards, does your body move forward as a reaction to this backwards impulse? (so disregarding pushing yourself against the atmosphere as in the swimming question). Could you move yourself over large distances this way, or would the time integrated impulse of your movements be zero anyway, no matter how violently you swing your arms backwards and gently put them back to front?

And when floating in a horizontal way, can you roll over your longest axis (like turning in bed) just by twisting your body?

I'm a bit stuck on action/reaction things within a single body. Must be the holidays :).

nicholas. I think the swimming will work. Air is less dense than water, by ~ a factor of 1000. But even a low density will make some net propulsion....witness birds, insects, doing it in your yard. For fluid flow, the thing is Reynolds numbers....sometimes they model airflow around buildings with a cross-section in a liquid stream table, where they can adjust the rate, and see the turbulence better..(aircraft wings were studied this way, too).
The trick in bird, insects flying is that the forward sweep needs to have a less-drag-profile, usually by folding the wing a bit....and it's kind of a figure 8 motion...forward and up, followed by backward and down. Slo-mo films of them helped in the design of micro-aerial-vehicles for the military. A webbed glove would help in the cabin of a space craft....like swimming flippers. Of course conservation of momentum would still hold....the splashing of the air against the back cabin wall would result in the ship going backwards, as you went forwards.
You could also use little jet thrusters, or a can of compressed air...like the EVA suits do.
There is another way, too...but I'm not saying without a sitdown with NASA.:shifty: Pete.

Ronald Brak
2006-Jul-24, 10:47 AM
I would think that swimming wouldn't work, as the density of air is so much less than water, there wouldn't be the resistance to use to "push off" for swimming to work.

Air is about 1,300 times less dense than water, so swimming in air, despite being even being done in old novels by Arthur C. Clarke, wouldn't be very effective.

And throwing your arms back will move your head and torso forwards but only relative to each other. You won't move anywhere do to the old equal and opposite reactions thingy.

You can twist your body, but you can't roll over without pushing on anything.

A good sneeze could propel you backwards at about 0.0002 meters per second.

grant hutchison
2006-Jul-24, 10:53 AM
You can't shift your centre of gravity unless you push on something, so you're stuck in one place unless the swimming thing works, or you have something you can throw.
You can rotate your body around your centre of gravity by moving your arms. Windmill your arms in one direction, and your body goes the other way until you stop windmilling, because your angular momentum must stay equal to zero. It's also possible to rotate your body on its long axis by lifting your arms out to right angles with your body, rotating one forward and one back, then bringing them back to your sides and repeating the manoeuvre. The "front and back" rotary movement turns your body in the opposite direction, and you can accumulate those rotations until you're facing in the opposite direction: there's old film of Skylab astronauts doing this.

Grant Hutchison

Ronald Brak
2006-Jul-24, 11:03 AM
Oh yeah, I think I remember that footage. I could think of what people did in old novels but I never stopped to consider what people had actually done in space.

Just being my usual efficent self.

astromark
2006-Jul-24, 11:21 AM
All that a sneeze will do is mess up the inside of your helmet. . . or annoy the other occupants of the ISS as the floating debris wonders about. I would sagest the small cans of compressed air would be all you need., and a hankie.

gwiz
2006-Jul-24, 11:57 AM
The "front and back" rotary movement turns your body in the opposite direction, and you can accumulate those rotations until you're facing in the opposite direction: there's old film of Skylab astronauts doing this.
Which is a similar technique to that used by a cat to land on its feet when dropped.

trinitree88
2006-Jul-24, 11:11 PM
[QUOTE=Ronald Brak]Air is about 1,300 times less dense than water, so swimming in air, despite being even being done in old novels by Arthur C. Clarke, wouldn't be very effective.

snippet: Ronald Brak. Perhaps you could then explain how a bird flies 40mph. Pete.

Jens
2006-Jul-25, 03:39 AM
I think the problem with swimming in 0G is the shape of our hands and the lightness of the medium. I think it could be done, but it would probably only be effective if you used some kind of tool. Just think about it: you can splash water easily using your hands, but to move air around you have to use something like a fan (like flippers, really). So if you used something like a foldable fan (like the ones they have in China and Japan) you could probably propel yourself.

Ronald Brak
2006-Jul-25, 04:00 AM
snippet: Ronald Brak. Perhaps you could then explain how a bird flies 40mph. Pete.

It has wings. Plus huge breast muscels and highly efficent lungs and a high metabolism.

Human arm muscles are puny compared to bird wing muscles. Even our leg muscels are puny in comparison. If you had some artificial flippers/wings it would make it easier to move, but a human will still have a really lousy power to weight ratio compared to a bird.

A pedal powered fan might be the way to go as that would enable you to efficently use your largest muscles to power yourself. Of course, stability would be a problem.

Tog
2006-Jul-25, 06:01 AM
I think the torque from a pedal powered fan wold cause you to "wheelie" over backwards. You'd also need to have the blades collapse or rotate once they started moving in the direction of travel. Otherwise they wouldn't give a push in any one direction.

I think something that simulated bird wings would be the best bet. A light weight frame (mylar and carbon fiber) could be built to transfer a small motion such as rotating the lower arms from palms down to palms in and back to flap the wings. Maybe with the addition of a flywheel like on those toy cars you run along the floor a few times, then release. It might take a while to get it going, but it would use mainly the biceps/triceps for power and little else.

Van Rijn
2006-Jul-25, 06:15 AM
It has wings. Plus huge breast muscels and highly efficent lungs and a high metabolism.

Human arm muscles are puny compared to bird wing muscles. Even our leg muscels are puny in comparison. If you had some artificial flippers/wings it would make it easier to move, but a human will still have a really lousy power to weight ratio compared to a bird.


Sure, but the question is what you want to accomplish. If in microgravity instead of lunar gravity then lift isn't an issue, only propulsion and attitude control. And unless this is a very large space, you probably don't want to go very fast (dangerous!). I could see oversized fins for hands and feet for flight at moderate speed.

WaxRubiks
2006-Jul-25, 06:17 AM
didn't the people in the ArturCCLarke(3065?)novel have some sort of wing or membrane under their arms?

Ronald Brak
2006-Jul-25, 06:23 AM
A human with stuff to help them swim through air could get somewhere, but without anything to help a human isn't going to get far. You can sit on an inflatable raft in a pool and move by waving a big fan, but just waving your hands isn't going to get you anywhere in a hurry.

Ronald Brak
2006-Jul-25, 06:27 AM
didn't the people in the ArturCCLarke(3065?)novel have some sort of wing or membrane under their arms?

I'm thinking of the kids' stuff he wrote maybe 50 years ago. Apparently the characters could manage some movement by waving their hands and so on but it wasn't much. I think local air currents would have more effect upon your movement, but I don't think he says that wasn't what was propelling them.

WaxRubiks
2006-Jul-25, 07:25 AM
You can sit on an inflatable raft in a pool and move by waving a big fan, but just waving your hands isn't going to get you anywhere in a hurry.

but in a pool of water you'll have a high resistance to movement from the water, in space there would just be air resistance which wouldn't be much at low speeds.

Ronald Brak
2006-Jul-25, 07:41 AM
but in a pool of water you'll have a high resistance to movement from the water, in space there would just be air resistance which wouldn't be much at low speeds.

The friction of the water shouldn't make a large difference. You'll get a higher top speed in weightlessness but it still won't be much just using your hands. Right now I'm trying to get a screwed up piece of tissue paper that weighs maybe one and a half grams to move across my desk by flapping my hand at it and I can't manage a great deal of speed.

astromark
2006-Jul-25, 07:56 AM
There has been some recent news of this very subject from NASA. Not actually asking about how to move in a 0 gravity environment. I will get to that shortly. Your question Nicolas is a good one. Yes some movement is possible by twisting or other contortions of your body but, this might be changes to your orientation not real movement. As stated by others to actually move you need to move some mass or create thrust. I would like to mention at this point that this is all a little pointless as when inside your pressurized space craft ( ISS ) you can simply push off your surroundings. Out side of this environment and in a pressurized space suit you need to have some thruster power in order to move your center of G. Or you are in deep trouble.
The NASA item was regarding the effect of gravity on the human body. Reproduction would not be impossible but, without straps or the odd bungee cord nearly impossible. Mind boggling is it not ? The real problem is with the way the human mind develops. Learning to walk in a 0 G world could be tricky. What is your view ?.

Ronald Brak
2006-Jul-25, 08:05 AM
...Reproduction would not be impossible but, without straps or the odd bungee cord nearly impossible...

There goes space tourism.

mugaliens
2006-Jul-29, 03:36 PM
I had some questions on moving around in a spacecraft. So zero G, but inside an atmosphere.

Is it possible to swim in the atmosphere as you do underwater? (slower I guess, but anyway :))

Much slower, but yes, as skylab astronauts demonstrated.


And when floating in a horizontal way, can you roll over your longest axis (like turning in bed) just by twisting your body?

Yes.

afterburner
2006-Jul-29, 04:04 PM
Is it possible to use controlled vibrations of the air that fills the cabin? IOW, produce some kind of ultrasonic vibration that would slowly "shuffle" you in the preferred direction? Simlar to how objects move on a vibrating piece of paper?

If the above is an impossibility, then maybe...

Hook the astronauts up with a metal object (glove, belt, metal containing suit? anything really), and have electromagnets all throughout the craft, which the astronauts would be able to activate with some kind of remote control. This would push/pull them in a desired direction. With our advance technology, we could plug their brain in, and have them control it by though. :think:

But then again, flippers/wings/electric motors would also do the job.